U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2011–1094

Prepared in cooperation with Louisiana Coastal Areas Science and Technology Program and 

in collaboration with Louisiana State University, the Louisiana Governor’s Office of Coastal 

Protection and Restoration, and the University of Louisiana at Lafayette

Geomorphic and Ecological Effects of Hurricanes Katrina 

and Rita on Coastal Louisiana Marsh Communities

Geomorphic and Ecological Effects of 

Hurricanes Katrina and Rita on Coastal 

Louisiana Marsh Communities

By Sarai C. Piazza, Gregory D. Steyer, Kari F. Cretini, Charles E. Sasser, 

Jenneke M. Visser, Guerry O. Holm, Jr., Leigh Anne Sharp, D. Elaine Evers, and 

John R. Meriwether

Prepared in cooperation with Louisiana Coastal Areas Science and 

Technology Program and in collaboration with Louisiana State University, 

the Louisiana Governor’s Office of Coastal Protection and Restoration, and 

the University of Louisiana at Lafayette

Open-File Report 2011–1094

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

This and other USGS information products are available at http://store.usgs.gov/

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U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Piazza, S.C., Steyer, G.D., Cretini, K.F., Sasser, C.E., Visser, J.M., Holm, G.O., Jr., Sharp, L.A., Evers, D.E., and 

Meriwether, J.R., 2011, Geomorphic and ecological effects of Hurricanes Katrina and Rita on coastal Louisiana 

marsh communities: U. S. Geological Survey Open-File Report 2011-1094, 126 p.
iii

Acknowledgments

We wish to recognize the financial support of the Louisiana Coastal Area Science & 

Technology Program in accomplishing this research. 

We would like to thank all of the landowners who provided permission to access their 

properties to conduct this assessment, especially the Louisiana Department of Wildlife and 

Fisheries, Apache Corporation, Delacroix Corporation, Jeanerette Lumber, Louisiana Land 

and Exploration Company, and Miami Corporation. A tremendous amount of field, laboratory, 

and analytical assistance was provided by personnel from many agencies and affiliations. Five 

Rivers Services, LLC, staff includes Jason Byrd and Brad Griffin, and U.S. Army Engineer 

Research and Development Center staff includes Glen Suir. Louisiana State University 

personnel includes Azure Bevington, Thomas Blanchard, Dan Bond, Edward Castaneda-Moya, 

Jay Gore, Manoch Kongchum, Brian Milan, Alaina Owens, Eric Peterson, and Daniel Sasser. 

Louisiana Governor’s Office of Coastal Protection and Restoration (OCPR) personnel includes 

Brady Carter, Mike Miller, Tommy McGinnis, Mark Mouledous, John Troutman, and Dona 

Weifenbach. University of Louisiana at Lafayette personnel includes Katherine Zaunbrecher 

and Matt Williams. We would also like to thank Brian Perez of CH2M Hill. 

Evamaria Koch (University of Maryland Center for Marine Science) and Michael Beck 

(OCPR) reviewed the document and provided useful comments. 

This project could not have been completed without the field efforts, sample processing, 

data entry, and input of U.S. Geological Survey personnel including Gregg Snedden, Jeff 

Broussard, Brady Couvillion, Ada Diz, Jessica Goodwin, Arianne Logwood, Alison Martin, 

and Elin Sandy.
iv

Contents

Acknowledgments........................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................2

Materials and Methods.................................................................................................................................4

Study Area..............................................................................................................................................4

Methods..................................................................................................................................................8

Vegetation .....................................................................................................................................8

Hydrology ......................................................................................................................................8

Porewater in Soil ........................................................................................................................9

Sediment Deposition and Condition .........................................................................................9

Bulk Density and Organic Matter..............................................................................................9

Sediment Elevation, Accretion, and 

Shallow Subsidence ....................................................................................................10

Statistical Analyses............................................................................................................................10

Vegetation and Porewater Salinity .........................................................................................10

Soils .........................................................................................................................................10

Results and Discussion...............................................................................................................................10

Recovery After Hurricanes Katrina and Rita..................................................................................10

Summary of All Vegetation Types ...........................................................................................10

Fresh Marsh Sites......................................................................................................................14

Brackish/Intermediate Marsh Sites .......................................................................................35

Saline Marsh Sites ....................................................................................................................39

Case Studies........................................................................................................................................44

Case Study 1: CRMS0605-H and CRMS1277-H .....................................................................44

Overall Site Description...................................................................................................44

Salinity Before and After the Storms.............................................................................44

Plant Biomass Before and After the Storms ................................................................44

Plant Community Change After the Storms..................................................................49

Discussion..........................................................................................................................56

Case Study 2: CRMS0135..........................................................................................................58

Overall Site Description...................................................................................................58

Surface-Water and Porewater Salinities .....................................................................61

Vegetation Cover...............................................................................................................61

Aboveground and Belowground Biomass....................................................................64

Sediment Characterization, Accretion, and Elevation................................................67

Summary of the Classification of Impacts....................................................................67

Case Study 3: CRMS0672-H......................................................................................................67

Overall Site Description...................................................................................................67

Surface-Water and Porewater Salinity.........................................................................72

Vegetation Cover...............................................................................................................72

Aboveground and Belowground Biomass....................................................................75

Sediment Characterization, Accretion, and Elevation................................................77

Summary of the Classification of Impacts....................................................................80
v

Case Study 4: CRMS0326-H......................................................................................................80

Overall Site Description...................................................................................................80

Surface-Water and Porewater Salinity.........................................................................80

Vegetation Cover...............................................................................................................82

Aboveground and Belowground Biomass....................................................................82

Sediment Characterization, Accretion, and Elevation................................................85

Summary of the Classification of Impacts....................................................................88

Case Study 5: CRMS0164-H......................................................................................................88

Overall Site Description...................................................................................................88

Historical Datasets ..................................................................................................88

Monitoring Program for the Louisiana Offshore Oil Port .................................91

Marsh Stability .........................................................................................................91

Surface-Water and Porewater Salinity.........................................................................91

Vegetation Cover...............................................................................................................91

Aboveground and Belowground Biomass....................................................................91

Sediment Characterization, Accretion, and Elevation................................................95

Summary of the Classification of Impacts....................................................................95

Soil Process Rates of Wetlands in the Chenier and Deltaic Plains of Louisiana............98

Results and Discussion....................................................................................................98

Accretion Rates Between the Chenier and Deltaic Plains...............................98

Contribution of Organic and Mineral Fractions to Soil Accretion ...................99

Organic, Mineral, and Nutrient Content in Relation to 

Accumulation Rates.................................................................................100

Overall Conclusions...................................................................................................................................100

References Cited........................................................................................................................................105

Appendix 1. Hydrographs for study sites within the Coastwide Reference Monitoring 

System (CRMS).............................................................................................................................111

Appendix 2. Site elevation and accretion at study sites within the Coastwide 

Reference Monitoring System (CRMS) ....................................................................................118

Figures

1. The interconnected influences of hurricane storm surge on marsh dynamics.................3

2. Thirty intensive site locations within coastal Louisiana ........................................................5

3. Coastal Louisiana divided into nine hydrologic basins ..........................................................7

4. Mean values of porewater salinity for fresh, brackish/intermediate, and 

saline marsh types by season .................................................................................................12

5. Total live vegetation cover for fresh, brackish/intermediate, and saline 

marsh types by season .............................................................................................................13

6. Percentages of disturbance and nondisturbance taxa present in live 

vegetation cover of fresh, brackish/intermediate, and saline vegetation 

types by season ..........................................................................................................................14

7. Live aboveground biomass in fresh, brackish/intermediate, and saline 

marsh types by season .............................................................................................................15

8. Total belowground biomass in fresh, brackish/intermediate, and saline marsh 

types by season .........................................................................................................................16
vi

9. Mean values of porewater salinity for fresh, brackish/intermediate, and saline 

marshes by type of hurricane influence and year ................................................................16

10. Porewater salinity at the end of the growing season in 2006 and in 2007 at 

study sites within fresh, brackish/intermediate, and saline marshes ...............................17

11. Total live cover of emergent vegetation at fresh, brackish/intermediate, 

and saline marsh sites at the end of the growing season in 2006 and in 2007 ................24

12. Cover by disturbance taxa (black bars) relative to nondisturbance taxa in 

emergent vegetation at fresh marsh sites at the end of the growing season 

in 2006 and in 2007 ......................................................................................................................25

13. Percentages of biomass composed of disturbance versus nondisturbance 

species at fresh marsh sites in 2006 and 2007.......................................................................27

14. Species composition of biomass harvested at sites CRMS0128 and 

CRMS0128-H by season.............................................................................................................28

15. Species composition of biomass harvested at sites CRMS0605 and 

CRMS0605-H by season.............................................................................................................29

16. Live aboveground biomass is displayed for each habitat type by level of 

hurricane influence and year ...................................................................................................30

17. Total and live aboveground biomass at fresh marsh sites where historical 

data were available....................................................................................................................32

18. Peak aboveground biomass at the end of growing seasons in 2006 and 

2007 for each habitat type by hurricane influence and year...............................................33

19. Total aboveground biomass at the end of growing seasons in 2006 and 

2007 at fresh, brackish/intermediate, and saline marsh sites.............................................34

20. Total belowground biomass at the end of growing seasons in 2006 and 

2007 at fresh, brackish/intermediate, and saline marsh sites.............................................36

21. Mean values of belowground biomass for each marsh type by hurricane 

influence and year......................................................................................................................37

22. Total and live belowground biomass at fresh marsh sites at the end of 

growing seasons.........................................................................................................................38

23. Cover of disturbance taxa relative to nondisturbance taxa in emergent 

vegetation at brackish/intermediate marsh sites at the end of growing 

season in 2006 and 2007 ............................................................................................................40

24. Percentages of biomass in disturbance versus non-disturbance species at 

brackish/intermediate marsh sites for 2006 and 2007 ..........................................................41

25. Species composition of biomass harvested at sites CRMS0135 and 

CRMS0135-H by season.............................................................................................................42

26. Percentages of biomass from disturbance and nondisturbance species in 

2006 and 2007 for each marsh type by hurricane influence................................................43

27. Locations of Coastwide Reference Monitoring System (CRMS) sites 0605-H, 

0605, 1277-H, and 1277 sites within the Lake Misere and Mermentau River 

watershed ....................................................................................................................................45

28. Continuous and discrete samples of porewater salinity taken from 30 cm 

deep at Coastwide Reference Monitoring System (CRMS) site 0605-H from 

2005 to 2007..................................................................................................................................46

29. The plant community at Coastwide Reference Monitoring System (CRMS) 

site 0605-H before and after Hurricane Rita...........................................................................47

30. Aboveground live, dead, and total biomass at the end of growing seasons at 

Coastwide Reference Monitoring System (CRMS) site 0605-H before Hurricanes 

Katrina and Rita and two years thereafter.............................................................................48

31. Live belowground biomass for Coastwide Reference Monitoring System 

(CRMS) site 0605-H at the end of growing seasons before Hurricane Rita and 

two years thereafter...................................................................................................................49
vii

32. Live aboveground biomass at Coastwide Reference Monitoring System 

(CRMS) sites 1277-H and 0605-H..............................................................................................50

33. Live aboveground biomass at Coastwide Reference Monitoring System 

(CRMS) sites 0605-H and 0268-H..............................................................................................51

34. Live belowground biomass at Coastwide Reference Monitoring System 

(CRMS) sites 0605-H and 1277-H..............................................................................................52

35. Live belowground biomass at Coastwide Reference Monitoring System 

(CRMS) sites 0605-H and 0268-H..............................................................................................53

36. Live aboveground biomass and species composition by season two 

years after Hurricane Rita.........................................................................................................54

37. Characteristics of initial plant recolonization by clonal, patch-forming 

species prior to the seedbank release of annual species at Coastwide 

Reference Monitoring System (CRMS) site 0605-H..............................................................55

38. A description of plant community change at Coastwide Reference 

Monitoring System (CRMS) site 0605-H following Hurricane Rita .....................................57

39. Vegetation in marshes north of Lake Misere, near Coastwide 

Reference Monitoring System (CRMS) site 0605-H..............................................................58

40. Timeline of vegetation community changes and relative plant biomass before 

and after Hurricane Rita ............................................................................................................59

41. Location of Coastwide Reference Monitoring System (CRMS) sites 0135-H 

and 0135 within middle Breton Sound basin ..........................................................................60

42. Coastwide Reference Monitoring System (CRMS) site 0135 on May 4, 2006, 

after Hurricanes Katrina and Rita ............................................................................................61

43. Mean values of daily surface-water salinity and discrete porewater salinity 

at 30 cm deep from April 2006 to November 2007 at site Coastwide Reference 

Monitoring System (CRMS) site 0135 ......................................................................................62

44. Seasonal species composition of total live vegetation cover at Coastwide 

Reference Monitoring System (CRMS) site 0135 ..................................................................62

45. Coastwide Reference Monitoring System (CRMS) site 0135 after Hurricanes 

Katrina and Rita...........................................................................................................................63

46. Seasonal coverage of disturbance taxa relative to nondisturbance taxa at 

Coastwide Reference Monitoring System (CRMS) site 0135 ..............................................64

47. Total and live aboveground biomass at a historically sampled site near Lake 

Cuatro Caballo and at Coastwide Reference Monitoring System (CRMS) site................65

48. Live and dead aboveground biomass by season at Coastwide Reference 

Monitoring System (CRMS) site 0135 ......................................................................................65

49. Species composition of live aboveground biomass by season at Coastwide 

Reference Monitoring System (CRMS) site 0135 ..................................................................66

50. Seasonal aboveground biomass of disturbance and nondisturbance taxa at 

Coastwide Reference Monitoring System (CRMS) site 0135 ..............................................66

51. Seasonal above and belowground biomass at Coastwide Reference 

Monitoring System (CRMS) site 0135. .....................................................................................68

52. Seasonal belowground biomass of dead and live components at Coastwide 

Reference Monitoring System (CRMS) site 0135 ..................................................................68

53. Bulk density and caesium-137 profiles at Coastwide Reference Monitoring 

System (CRMS) site 0135...........................................................................................................69

54. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference 

Monitoring System (CRMS) site 0135 ......................................................................................70

55. Location of Coastwide Reference Monitoring System (CRMS) sites 0672-H 

and 0672 within lower Calcasieu/Sabine basin .....................................................................71

56. Seasonal discrete porewater salinity at Coastwide Reference Monitoring 

System (CRMS) site 0672-H.......................................................................................................73
viii

57. Average daily surface-water salinity from a sampling station within the CS20 

project of the Coastal Wetlands Planning, Protection and Restoration Act 

(CWPPRA) from January 2005 to July 2007 ............................................................................73

58. Seasonal species composition of total live vegetation cover at Coastwide 

Reference Monitoring System (CRMS) site 0672-H..............................................................74

59. Live vegetation cover of disturbance taxa relative to nondisturbance taxa by 

season at Coastwide Reference Monitoring System (CRMS) site 0672-H........................74

60. Live and dead aboveground biomass by season at Coastwide Reference 

Monitoring System (CRMS) site 0672-H..................................................................................75

61. Species composition of live aboveground biomass by season at Coastwide 

Reference Monitoring System (CRMS) site 0672-H..............................................................76

62. Total aboveground and belowground biomass by season at Coastwide 

Reference Monitoring System (CRMS) site 0672-H..............................................................76

63. Live and dead components of total belowground biomass by season at 

Coastwide Reference Monitoring System (CRMS) site 0672-H..........................................77

64. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference 

Monitoring System (CRMS) site 0672-H..................................................................................78

65. Short term accretion rates at Coastwide Reference Monitoring System 

(CRMS) site 0672-H and elevation and accretion change at CRMS0672 ..........................79

66. Location of Coastwide Reference Monitoring System (CRMS) sites 0326-H 

and 0326 within lower Terrebonne basin................................................................................81

67. Discrete porewater salinity measured by season at 30 cm deep at Coastwide 

Reference Monitoring System (CRMS) site 0326-H..............................................................82

68. Mean values of daily surface-water salinity and discrete porewater salinity 

measured at 30 cm deep from April 2006 to November 2007 at Coastwide 

Reference Monitoring System (CRMS) site 0326 ..................................................................83

69. Species composition (all Spartina alterniflora) of total live vegetation cover 

by season at Coastwide Reference Monitoring System (CRMS) site 0326-H ................83

70. Seasonal cover of nondisturbance taxa at Coastwide Reference Monitoring 

System (CRMS) site 0326-H.......................................................................................................84

71. Live and dead aboveground biomass by season at Coastwide Reference 

Monitoring System (CRMS) site 0326-H..................................................................................84

72. Total and live aboveground biomass measured at the end of growing 

seasons at Coastwide Reference Monitoring System (CRMS) site 0326-H......................85

73. Total aboveground and belowground biomass by season at Coastwide 

Reference Monitoring System (CRMS) site 0326-H..............................................................86

74. Live and dead components of total belowground biomass by season at 

Coastwide Reference Monitoring System (CRMS) site 0326-H..........................................86

75. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference 

Monitoring System (CRMS) site 0326-H..................................................................................87

76. Bulk density and caesium-137 profiles at Coastwide Reference Monitoring 

System (CRMS) site 0326-H.......................................................................................................89

77. Rate of elevation change at Coastwide Reference Monitoring System (CRMS) 

site 0362-H....................................................................................................................................89

78. Location of Coastwide Reference Monitoring System (CRMS) sites 0164-H 

and 0164 within lower Barataria basin ...................................................................................90

79. Discrete porewater salinity measured at 30 cm deep by season at Coastwide 

Reference Monitoring System (CRMS) site 0164-H..............................................................92

80. Species composition (all Spartina alterniflora) of total live vegetation cover 

by season at Coastwide Reference Monitoring System (CRMS) site 0164-H ..................92
ix

81. Species composition (all Spartina alterniflora) of seasonal live aboveground 

biomass at site Coastwide Reference Monitoring System (CRMS) site 0164-H..............93

82. Total and live aboveground biomass at the end of growing seasons at saline 

marsh sites with availability of historical data acquired before Hurricanes 

Katrina and Rita...........................................................................................................................94

83. Aboveground biomass at the end of growing seasons as measured during 

various studies conducted in the vicinity of Coastwide Reference Monitoring 

System (CRMS) site 0164-H.......................................................................................................94

84. Live and dead belowground biomass by season at Coastwide Reference 

Monitoring System (CRMS) site 0164-H..................................................................................95

85. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference 

Monitoring System (CRMS) site 0164-H..................................................................................96

86. Mean values of bulk density by various depth intervals at Coastwide 

Reference Monitoring System (CRMS) site 0164-H..............................................................97

87. Feldspar marker horizon and short-term accretion on July 10, 2008, at 

Coastwide Reference Monitoring System (CRMS) site 0164-H..........................................97

88. Carbon and nitrogen content in sediment and their ratios from the upper 

20 cm of soil across different marsh types, with combined values from the 

Louisiana chenier and deltaic plains.....................................................................................101

89. The distribution of carbon and nitrogen accumulation in sediment across 

different marsh types, with combined values from the Louisiana chenier and 

deltaic plains .............................................................................................................................102

Tables

1. Intensive study site locations, associated marsh types, hurricane influence 

area, region, and sampling event details .................................................................................6

2. Porewater salinity by marsh type. Minimum, mean, and maximum values 

by season and for the entire study period are presented ...................................................11

3. Observed taxa characterized as disturbance because of their typical 

presence in marshes that have been recently disturbed by physical or 

biological forces .........................................................................................................................15

4. Results of analysis of variance testing for porewater salinity at the end of 

growing seasons in fresh, brackish/intermediate, and saline marsh types ....................17

5. Site-specific summaries of soils, porewater salinity, and vegetation data......................18

6. Results of analysis of variance testing for aboveground biomass from 

nondisturbance species in fresh and brackish/intermediate marsh types .....................26

7. Results of analysis of variance testing for live aboveground biomass at the 

end of growing seasons in fresh, brackish/intermediate, and saline 

marsh types ................................................................................................................................30

8. Comparisons of aboveground and belowground biomass among different 

marsh types before and after Hurricanes Katrina and Rita.................................................31

9. Results of analysis of variance testing for peak aboveground biomass in 

fresh, brackish/intermediate, and saline marsh types ........................................................33

10. Results of analysis of variance testing for total belowground biomass at 

the end of growing seasons in fresh, brackish/intermediate, and saline 

marsh types .................................................................................................................................37

11. Changes in clonal expansion of ten monospecific patches of three species 

observed at CRMS0605-H on February 28 and May 9, 2007 ................................................56
x

12. Summary of mean values for long-term (since 1963) rates of soil accretion 

and organic/mineral accumulation in herbaceous marshes of the chenier 

and deltaic plains of Louisiana.................................................................................................98

13. Mean values for long-term rates of soil accretion in three marsh types 

in the deltaic and chenier plains of Louisiana .......................................................................99

14. Regression relationships between long-term rates of vertical accretion and 

accumulation of organic and mineral matter for three marsh types across 

Louisiana at research sites from the Coastwide Reference Monitoring System 

paired with sites that were historically sampled by Holm, 2006 ........................................99

15. Mean values of organic, mineral, nitrogen, and carbon density in the upper 

20 cm of soil in three marsh types .........................................................................................100

16. Mean values of accumulation rates of organic, mineral, nitrogen, and 

carbon fractions in soil from three marsh types in the deltaic and chenier 

plains of Louisiana....................................................................................................................102

17. Comparison of study parameters for fresh, brackish/intermediate, and 

saline marsh types and sample year ....................................................................................103

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

Area

square meter (m2) 10.76 square foot (ft2) 

Volume

cubic centimeter (cm3) 0.06102 cubic inch (in3) 

cubic meter (m3) 35.31 cubic foot (ft3)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Radioactivity

becquerel per liter (Bq/L) 27.027 picocurie per liter (pCi/L) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Vertical coordinate information is referenced to the insert datum name (and abbreviation) here, 

for instance, “North American Vertical Datum of 1988 (NAVD 88)”

Horizontal coordinate information is referenced to the insert datum name (and abbreviation) 

here, for instance, “North American Datum of 1983 (NAD 83)”
Geomorphic and Ecological Effects of Hurricanes Katrina 

and Rita on Coastal Louisiana Marsh Communities

By Sarai C. Piazza1, Gregory D. Steyer1, Kari F. Cretini1, Charles E. Sasser2, Jenneke M. Visser3, 

Guerry O. Holm, Jr. 2, Leigh Anne Sharp4, Elaine Evers2, and John R. Meriwether5

1

 U.S. Geological Survey, National Wetlands Research Center, Lafayette, Louisiana

2

 Louisiana State University, Department of Oceanography and Coastal Sciences

3

 University of Louisiana at Lafayette, Department of Renewable Resources

4

 Louisiana Governor’s Office of Coastal Protection and Restoration

5

 University of Louisiana at Lafayette, Department of Physics

Abstract

Hurricanes Katrina and Rita made landfall in 2005, 

subjecting the coastal marsh communities of Louisiana to 

various degrees of exposure. We collected data after the 

storms at 30 sites within fresh (12), brackish/intermediate 

(12), and saline (6) marshes to document the effects of 

saltwater storm surge and sedimentation on marsh community 

dynamics. The 30 sites were comprised of 15 pairs. Most 

pairs contained one site where data collection occurred 

historically (that is, prestorms) and one Coastwide Reference 

Monitoring System site. Data were collected from spring 

2006 to fall 2007 on vegetative species composition, 

percentage of vegetation cover, aboveground and belowground 

biomass, and canopy reflectance, along with discrete 

porewater salinity, hourly surface-water salinity, and water 

level. Where available, historical data acquired before 

Hurricanes Katrina and Rita were used to compare conditions 

and changes in ecological trajectories before and after the 

hurricanes. Sites experiencing direct and indirect hurricane 

influences (referred to in this report as levels of influence) 

were also identified, and the effects of hurricane influence 

were tested on vegetation and porewater data. Within fresh 

marshes, porewater salinity was greater in directly impacted 

areas, and this heightened salinity was reflected in decreased 

aboveground and belowground biomass and increased cover 

of disturbance species in the directly impacted sites. At the 

brackish/intermediate marsh sites, vegetation variables and 

porewater salinity were similar in directly and indirectly 

impacted areas, but porewater salinity was higher than 

expected throughout the study. Interestingly, directly impacted 

saline marsh sites had lower porewater salinity than indirectly 

impacted sites, but aboveground biomass was greater at the 

directly impacted sites.

Because of the variable and site-specific nature of 

hurricane influences, we present case studies to help define 

postdisturbance baseline conditions in fresh, brackish/

intermediate, and saline marshes. In fresh marshes, the 

mechanism of hurricane influence varied across the landscape. 

In the western region, saltwater storm surge inundated 

freshwater marshes and remained for weeks, effectively 

causing damage that reset the vegetation community. This 

is in contrast to the direct physical disturbance of the storm 

surge in the eastern region, which flipped and relocated 

marsh mats, thereby stressing the vegetation communities 

and providing an opportunity for disturbance species to 

colonize. In the brackish/intermediate marsh, disturbance 

species took advantage of the opportunity provided by shifting 

species composition caused by physical and saltwater-induced 

perturbations, although this shift is likely to be short lived. 

Saline marsh sites were not negatively impacted to a severe 

degree by the hurricanes. Species composition of vegetation 

in saline marshes was not affected, and sediment deposition 

appeared to increase vegetative productivity. 

The coastal landscape of Louisiana is experiencing high 

rates of land loss resulting from natural and anthropogenic 

causes and is experiencing subsidence rates greater than 

10.0 millimeters per year (mm yr-1); therefore, it is important 

to understand how hurricanes influence sedimentation and soil 

properties. We document long-term vertical accretion rates and 

accumulation rates of organic matter, bulk density, carbon and 

nitrogen. Analyses using caesium-137 to calculate long-term 

vertical accretion rates suggest that accretion under impounded 

conditions is less than in nonimpounded conditions in the 

brackish marsh of the chenier plain. Our data also support 
2 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

previous studies indicating that accumulation rates of organic 

matter explain much of the variability associated with vertical 

accretion in brackish/intermediate and saline marshes. In 

fresh marshes, more of the variability associated with vertical 

accretion was explained by mineral accumulation than in the 

other marsh types. The marsh types in this study span a wide 

distribution of nutrient accumulation rates but exhibit similar 

upper limits of carbon (200 grams per square meter per year 

[g m-2 yr-1]) and nitrogen (10–14 g m-2 yr-1) accumulation. 

Information regarding site-specific soil properties is provided 

through soil profiles, and short-term elevation change and 

accretion are also reported for sites where historical data 

collection occurred.

This study provides new ecological baseline conditions 

following Hurricanes Katrina and Rita and an assessment 

of site-specific hurricane impacts, recovery, and potential 

changes in ecological trajectories. Paired with the ongoing 

data collection through the Coastwide Reference Monitoring 

System program, this study should provide useful information 

for resource managers and modelers that can be used for 

comparisons of conditions occurring after future landscapescale disturbances.

Introduction 

The coastal wetlands of Louisiana have sustained 

the highest rate of wetland loss in the United States, with 

approximately 2,976 km2 of wetlands converting to open 

water from 1956 to 2004 (Barras, 2006). Many factors, both 

natural and human-induced, have been linked to land loss, 

including altered hydrology, saltwater intrusion, wave erosion, 

and high relative sea level rise (RSLR) (Boesch and others, 

1994). Stone and others (1997) identified hurricanes as a 

primary force controlling the transgressive evolution of the 

barrier islands of Louisiana. Recent evidence also suggests 

the importance of hurricanes in altering coastal wetland 

landscapes (Guntenspergen and others, 1995; Barras, 2006, 

2007; Steyer, 2008). Since Hurricane Andrew in 1992, there 

have been two major (3 category 3) storms, Hurricanes Katrina 

and Rita, to strike Louisiana and significantly influence 

barrier islands and interior coastal wetlands. Four additional 

hurricanes (< category 3), Georges (1998), Lili (2002), Gustav 

(2008), and Ike (2008), made landfall in Louisiana or near the 

Louisiana border with Texas or Mississippi, subjecting coastal 

marshes to storm surge and hurricane-force winds. The net 

wetland loss associated with Hurricanes Katrina and Rita 

(2005) alone was estimated at 562 km2 (Barras, 2006). Based 

on a 105-year dataset, Louisiana has hurricane return periods 

of 7 years in the eastern coastal zone, 10 years in central, and 

15 years in western (Keim and others, 2007). Since 1995, an 

increase in storm intensity and frequency has been observed 

for the north-central Gulf of Mexico coast (Keim and others, 

2007), including Louisiana. 

Increased storm intensity and frequency could produce 

more major hurricanes, such as Hurricanes Katrina and Rita, 

which have the potential to dramatically influence Louisiana’s 

coastal wetlands. Hurricane Katrina made landfall in 

eastern coastal Louisiana near Empire on August 29, 2005. 

Approximately one month later, Hurricane Rita struck western 

Louisiana near Johnsons Bayou on September 24, 2005. 

Assuming a constant annual loss rate (~ 62 square kilometers 

per year [km2 yr-1]) from 1956 to 2004, Hurricanes Katrina 

and Rita produced 9 year’s worth of wetland loss in one 

month. Storm surge depths were greatest in eastern Louisiana 

marshes from Hurricane Katrina (> 4.5 m), while Hurricane 

Rita produced storm surge depths greater than 3 m in western 

Louisiana marshes. Both hurricanes produced winds greater 

than 161 kilometers per hour (km hr-1) in the vicinities where 

they made landfall, and tropical storm-force winds influenced 

the entire coastal landscape of Louisiana.

Hurricanes and related storm surges cause a wide range 

of impacts to coastal wetland systems (fig. 1). While severe 

habitat damage and mortality of vegetation caused by high 

winds and storm surge are not uncommon (Doyle and others, 

1995; Guntenspergen and others, 1995; Cahoon, 2003; Barras, 

2006; Barras, 2007), hurricanes produce beneficial subsidies 

of sediments to coastal wetlands, which affect their long-term 

sustainability (Cahoon and others, 1995; Nyman and others, 

1995; Cahoon, 2003). Hurricanes and tropical storms can 

transport sediments from the inner shelf into coastal bays 

and marsh ecosystems within the northern Gulf of Mexico 

(Nyman and others, 1995; Perez and others, 2000; Walker and 

Hammack, 2000; Goni and others, 2006; Turner and others, 

2006). Hurricanes often produce spatially complex patterns 

of wetland damage and benefits that vary with landscape 

attributes (geology, shoreline orientation, and management) 

and unique storm characteristics (intensity, duration, and path).

Storm-related damage to coastal wetlands is generally 

biological (for example, salt or inundation stress to vegetation) 

or physical (for example, organic mat upheaval or mineral 

erosion) in nature. Salinity and flooding pulses to coastal 

marsh ecosystems can result in significant alteration of 

vegetation communities (Chabreck and Palmisano, 1973; 

Meeder, 1987; Doyle and others, 1995; Steyer and others, 

2007). Because plant associations are well established 

along estuarine salinity gradients (Odum and Hoover, 1988; 

Latham and others, 1994; Mitsch and Gosselink, 2000), 

episodic events that disrupt these gradients can cause 

plant death, decrease plant production, lead to changes in 

species distributions, and promote invasions of nonnative 

or opportunistic plant species (Ewel, 1986). Disturbances 

that alter salinity regimes provide opportunities for scientists 

to directly evaluate vegetation salt tolerance and indirectly 

evaluate competitive ability of marsh vegetation, two factors 

that have been suggested to be inversely related (Barbour, 

1978; LaPeyre and others, 2001; Crain and others, 2004). 

In addition to episodic disturbances, sea level rise has 

the potential to influence vegetation communities. Louisiana 
Introduction 3

Hurricane storm surge

Marsh elevation Land:Water

ratio

Hydroperiod

Vegetation

Salinity

Erosion

Sedimentation

Nutrients

Soil properties

coastal marshes are particularly susceptible to sea level rise 

because of their naturally minimal slope and high subsidence 

rates. Global sea level rise is estimated to be between 1.0 

and 2.4 mm yr-1 (Douglas and Peltier, 2002). As global sea 

level increases, greater areas of the Louisiana coastal zone 

will be inundated with saline waters, potentially exposing 

vegetation that is not adapted to saline conditions. This issue 

is compounded by subsidence rates greater than 10 mm yr-1

in some areas of the Louisiana coastal zone. Relative sea 

level rise accounts for global sea level rise and local 

subsidence thus it can be much greater than rates of global 

sea level rise. For Grand Isle, La., estimates of RSLR are 

approximately 9.85 mm yr-1. With RSLR estimates of nearly 

1 cm per year, coastal wetland communities of Louisiana 

will experience not only increased inundation and saltwater 

intrusion but will be more vulnerable to storm surges and 

erosion from future hurricanes.

Direct, physical damage from a hurricane usually takes 

the form of upheaval and redistribution of organic surface 

layers or extensive lateral compression of the marsh surface 

(that is, accordion-like folding and stacking of the marsh mat) 

(Guntenspergen and others, 1995). These organic surface 

layers can be up to 1.0 m thick (Evers and others, 2007), and 

their removal often results in landscape conversion of marsh 

to open water. Given the high rates of geological subsidence 

and sea level rise that Louisiana wetlands experience, the 

rate of landscape recovery from open water to marsh is slow 

and uncertain. The slow and uncertain pace of recovery 

is due to the slow and uncertain process by which coastal 

wetlands maintain an equilibrium elevation with sea level 

for their long-term stability. This equilibrium elevation 

is maintained through interactions among tidal flooding, 

sediment deposition, and plant production that compensate 

for the combined effects of local subsidence and eustatic sea 

level rise (Morris and others, 2002). In marsh areas that are 

sediment poor, are undergoing high subsidence, or have low 

productivity, an accretion and elevation deficit can exist that 

over time may result in a conversion to open water (DeLaune 

and others, 1983; Baumann and others, 1984; Nyman and 

others, 1993; Cahoon, 2003). 

High-energy events such as hurricanes provide a 

significant pulse of mineral sediments that can contribute to 

elevation gain and help offset RSLR (Rejmanek and others, 

1988; Day and others, 1995; Reed, 2002; Turner and others, 

2006). Storm surges can account for extensive transport of 

sediments from the coastal inner shelf and bays to interior 

wetlands (Cahoon and others, 1995; Turner and others, 2006). 

This subsidy of sediments can increase wetland elevation 

and enhance plant nutrition. Mineral sedimentation plays 

an important role in marsh accretion by supplying nutrients 

that can promote plant production (Broome and others, 1975; 

DeLaune and others, 1981; Bricker-Urso and others, 1989; 

Nyman and others, 1990; DeLaune and others, 1992; Nyman 

and others, 1993). Given the volumetric characteristics 

Figure 1. The interconnected influences of hurricane storm surge on marsh dynamics.
4 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

of organic matter, its accumulation from aboveground and 

belowground production contributes more significantly to 

long-term vertical accretion of soil than to mineral fractions 

(McCaffrey and Thomson, 1980; Hatton and others, 1983; 

Nyman and others, 1993; Turner and others, 2001; Turner 

and others, 2004); however, both are critical in sediment-poor 

environments (Steyer, 2008). 

Hurricanes can simultaneously influence both surface 

and subsurface soil processes, creating unpredictable changes 

to soil elevation when focusing on sediment deposition and 

erosion only (Cahoon, 2006). Aboveground and belowground 

production can also be impacted by hurricanes through 

flooding and the introduction of saltwater. When marshes 

experience storm-related plant mortality, organic matter 

decomposition can negatively influence marsh elevation. 

These impacts could offset potential benefits accrued through 

mineral introduction. The influence of subsurface processes 

on soil elevation (for example, sediment compaction, soil 

shrinkage, poststorm peat decomposition, soil swelling) can 

be a major difference between high frequency, low 

magnitude events and low frequency, high magnitude 

events (Cahoon, 2006). 

Disturbance magnitude and characteristics of the 

impacted ecosystem determine the time required for ecosystem 

structure or function to return to predisturbance form or rate 

(DeAngelis, 1980). Vogt and others (1997) suggest that an 

ecosystem is resilient if its recovery periods are shorter than 

the recurrence interval of disturbance events. Very few studies 

of hurricane impacts have tracked development and recovery 

of vegetation communities beyond one growing season after 

the disturbance, limiting opportunities for the evaluation of 

ecosystem resiliency.

With respect to plant communities, a general gradient of 

decreasing subsidy from mineral sediment and increasing salt 

stress associated with storm surge is typically observed with 

increasing distance inland. Saline marshes experience damage 

from physical erosion, but because of their proximity to the 

coastline, they receive sediments from the inner continental 

shelf that move inshore with tropical disturbances. Saline 

marsh vegetation is better adapted than fresh marsh vegetation 

to the high salinity waters associated with hurricanes and the 

physical energy associated with storm surge. Fresh marshes 

experience more biological damage than saline marshes 

because they are highly organic environments where salinity 

impairs plant health and, in turn, alters the balance of organic 

matter that helps sustain elevation.

Previous research on hurricane impacts in coastal 

Louisiana has focused on physical disturbance of the marsh 

substrate (Morgan and others, 1958; Chamberlain, 1959; 

Guntenspergen and others, 1995; Barras, 2006; Barras, 

2007) and sediment distribution (Baumann and others, 1984; 

Rejmanek and others, 1988; Cahoon and others, 1995; Nyman 

and others, 1995; Cahoon, 2003; Turner and others, 2006). 

Fewer studies have investigated the effects of salinity intrusion 

and flooding on coastal marsh vegetation (Ensminger and 

Nichols, 1957; Chabreck and Palmisano, 1973; Meeder, 1987; 

Jackson and others, 1995). Many of the prior investigations 

reported general observations, and other studies focused on 

small geographic areas or specific vegetation species 

of interest. There are relatively few studies (Cahoon and 

others, 1995; Guntenspergen and others, 1995; Jackson and 

others, 1995) that assess both physical and biological effects 

of hurricanes across broad geographic regions and 

vegetation communities. 

Hurricane-induced saltwater intrusion and flooding 

provide an ideal opportunity to assess how wetland plant 

communities and species respond to a variety of stressors and 

subsidies following severe disturbance. Because the entire 

coast of Louisiana was influenced by Hurricanes Katrina 

and Rita, a coastwide assessment of impacts and recovery 

within fresh, brackish/intermediate, and saline marshes was 

designed by using field-based and remotely sensed data. Our 

objective was to document the effect of saltwater storm surge 

and sedimentation from Hurricanes Katrina and Rita on marsh 

community dynamics in coastal Louisiana. Specifically, 

we document new ecological baseline conditions following 

the two major hurricanes and assess site-specific hurricane 

impacts, recovery, and potential changes in ecological 

trajectories. Documenting new baseline conditions is 

important because catastrophic storms such as Katrina and 

Rita create a range of effects, from marginal impacts to a total 

resetting of the system, such that one static baseline condition 

may not equally apply to all community types. 

Materials and Methods

Study Area

Thirty sites located within fresh (12), brackish/

intermediate (12), and saline (6) marsh communities across 

coastal Louisiana were selected for this study (fig. 2, table 1) 

on the influences of Hurricanes Katrina and Rita on coastal 

marshes. The sites provide detailed data on soils, vegetation, 

and porewater within different marsh communities. Site 

locations generally fall along north-south gradients within 

eastern, central, and western regions of the coast, which has 

been categorized into nine hydrologic basins by the Louisiana 

Coastal Wetlands Planning, Protection and Restoration Act 

Program (n.d.; fig. 3). 

The parameters for determining whether a site or region 

was directly or indirectly influenced by the 2005 hurricanes 

were consistent with Steyer and others (2010). Direct 

influence was determined by evaluating areas exposed to 

at least two of the three following factors: hurricane force 

winds, storm surge greater than 2 m (Ebersole and others, 

2007; McGee and others, 2007), and physical disturbance. 

Indirectly influenced areas experienced flooding from 0.0 

to 1.2 m and tropical storm-force winds (Doyle and others, 

2007). The eastern region includes an area directly influenced 
Materials and Methods 5 Figure 2. Thirty intensive site locations within coastal Louisiana. Sites with “H” designations were historically sampled by various research projects, and sites without “H” designations are within the Coastwide Reference Monitoring System (CRMS). Vegetation types are defined in Chabreck and Linscombe, 2001; hydrologic basins are defined by the Louisiana Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) Program (n.d.). 
6 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

by Hurricane Katrina. Study sites located in this area of 

direct influence are within the Breton Sound hydrologic basin. 

The western region includes the area directly influenced by 

Hurricane Rita (Mermentau and Calcasieu/Sabine basins), and 

the central region, less influenced, was indirectly exposed to 

hurricane conditions. 

Among the 30 study sites, pairs of sites were established 

along the north-south gradients (that is, 30 sites total 

comprised of 15 pairs). A typical pair consisted of one 

historical research or monitoring site and one site included 

in the Coastwide Reference Monitoring System (CRMS) 

(Steyer and others, 2003). Historical sites were sampled 

before Hurricanes Katrina and Rita as part of various research 

projects, and we used data from historical samplings of 

those sites to evaluate posthurricane effects and changes in 

ecological trajectories. In this study, we tried to build upon 

the historical research by sampling the same variables at 

or nearby the original sampling sites. The historical sites 

(containing an “-H” in the site name) were paired with CRMS 

sites to assess long-term recovery because CRMS monitoring 

Table 1. Intensive study site locations, associated marsh types, hurricane influence area, region, and sampling event details. 

[ ID, identification; UTM, Universal Transverse Mercator; CRMS, Coastwide Reference Monitoring System; H, historically sampled sites]

Site ID Marsh type

2005

hurricane influence Region UTM Y UTM XMissed sampling event

CRMS0128 Fresh Direct Eastern 3304046.44 794926.32 Summer 2007

CRMS0128-H Fresh Direct Eastern 3304476.93 796648.25 Summer 2006

CRMS0135 Brackish/Intermediate Direct Eastern 3288445.77 813508.42 None

CRMS0135-H Brackish/Intermediate Direct Eastern 3290676.79 817515.16 None

CRMS0147 Saline Direct Eastern 3286564.23 828709.78 None

CRMS0147-H Saline Direct Eastern 3278155.79 828063.93 None

CRMS0164 Saline Indirect Central 3232787.60 775200.39 None

CRMS0164-H Saline Indirect Central 3236233.93 780828.40 None

CRMS0219 Fresh Indirect Central 3300396.61 759143.07 None

CRMS0219-H Fresh Indirect Central 3301502.44 758598.21 None

CRMS0268 Fresh Indirect Central 3298721.54 731669.82 None

CRMS0268-H Fresh Indirect Central 3296809.99 729760.19 None

CRMS0294 Fresh Indirect Central 3256189.48 698975.97 None

CRMS0294-H Fresh Indirect Central 3259134.40 698168.19 None

CRMS0312 Brackish/Intermediate Indirect Central 3266791.38 753464.56 Spring 2006

CRMS0312-H Brackish/Intermediate Indirect Central 3265434.05 755785.15 Spring 2006

CRMS0326 Saline Indirect Central 3239849.80 687109.59 None

CRMS0326-H Saline Indirect Central 3238431.55 685120.68 None

CRMS0605 Fresh Direct Western 3303357.00 508034.00 None

CRMS0605-H Fresh Direct Western 3306980.33 514030.15 None

CRMS0610 Brackish/Intermediate Direct Western 3275262.00 535288.00 None

CRMS0610-H Brackish/Intermediate Direct Western 3276220.94 537281.07 None

CRMS0651 Brackish/Intermediate Direct Western 3314723.06 450738.12 None

CRMS0651-H Brackish/Intermediate Direct Western 3312912.00 449408.00 None

CRMS0669 Brackish/Intermediate Direct Western 3305990.69 429573.82 None

CRMS0672 Brackish/Intermediate Direct Western 3300211.00 459731.00 None

CRMS0672-H Brackish/Intermediate Direct Western 3300398.00 460480.00 None

CRMS1277 Fresh Direct Western 3299450.66 550313.63 None

CRMS1277-H Fresh Direct Western 3302219.98 549282.01 None

CRMS2156 Brackish/Intermediate Direct Western 3305166.74 432586.58 None
Materials and Methods 7Figure 3. Coastal Louisiana divided into nine hydrologic basins as defined by the Louisiana Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) Program (n.d.).
8 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

stations have a 20-year funded life, and sampling at these 

locations will continue beyond the scope of our study.

Classifications of marsh vegetation were determined 

for the sites according to the Chabreck and Linscombe 2001 

aerial survey. Fresh marsh sites were typically dominated 

by Panicum hemitomon (maidencane) and/or Sagittaria 

lancifolia (bulltongue). Although brackish and intermediate 

habitat types are distinct classes in the classification system 

of Chabreck and Linscombe (2001), we combined these sites 

into a brackish/intermediate vegetation type. This decision 

was based on the presence of Spartina patens (marshhay 

cordgrass) as a dominant species at the majority of brackish 

and intermediate sites within this study. Saline marsh sites 

were dominated by Spartina alterniflora (smooth cordgrass).

Methods

Data from seven sampling periods are included in this 

report. Sampling occurred quarterly from spring 2006 to fall 

2007 (that is, spring [Apr. and May] 2006 and 2007; summer 

[July and Aug.] 2006 and 2007; fall [Sept. and Oct.] 2006 and 

2007; winter [Jan. and Feb.] 2007). Occasionally throughout 

the study period, some sites could not be sampled because of 

access issues (for example, low water or conflicts with hunting 

seasons) or logistical problems (table 1).

Vegetation

Percentage of vegetation cover, species composition, and 

height of the dominant plants within a 2- by 2-m (4-m2) plot 

were determined by using a modified Braun-Blanquet method 

described in Steyer and others (1995). This method only 

counts emergent vegetation that is rooted in the plot; therefore, 

floating aquatic vegetation is not reflected in percentage of 

cover values. Percentage of cover values can be greater than 

100 percent because of multiple layers/canopies of vegetation 

within one plot. 

Aboveground plant biomass was sampled by harvesting 

plant material from replicate 0.25-m2 quadrats in three 

randomly selected locations within each study site. All 

standing live and dead stems were clipped within 1 cm of the 

sediment surface. Clipped stems and litter were placed in 

bags and returned to the laboratory. The plant material was 

not washed but was separated into live and dead components 

according to the presence (live) or absence (dead) of green 

pigment on the stems. Live material was separated by species, 

and stems were counted to determine stem density (stems m-2). 

All sorted material was oven dried at 65 °C to a constant 

weight and weighed to the nearest 0.5 g. 

Following removal of aboveground material from each 

of the three clip plots, belowground biomass was sampled via 

10-cm (4-inch) diameter cores made of aluminum or polyvinyl 

chloride (PVC). The cores were taken to a maximum depth 

of 40 cm or the entire mat thickness if the mat was less than 

40 cm. Cores were sliced in the field or transported to the 

laboratory intact, divided into 8-cm sections, and washed in 

2.0-mm mesh sieves stacked within 0.5-mm mesh sieves to 

remove soil particles and prevent loss of fine root material. 

Live roots and rhizomes were separated from the remaining 

matrix of dead roots and other organic material. Dead roots 

and rhizomes were separated into coarse and fine components. 

All belowground material (that is, live, dead coarse, and dead 

fine) was dried at 65 °C to a constant weight and weighed to 

the nearest 0.5 g.

Remotely sensed data of canopy reflectance were 

used to investigate the normalized difference vegetation 

index (NDVI) to detect live, green plant canopies in marsh 

communities. Steyer (2008) includes a complete explanation 

and methods for using NDVI to evaluate anomalies, as well as 

significant and persistent damage to Louisiana coastal marsh 

communities following Hurricanes Katrina and Rita. In brief, 

MODerate Resolution Imaging Spectroradiometer (commonly 

referred to as MODIS) imagery was collected monthly from 

February 2000 to March 2005. For each month, NDVI values 

were averaged to generate baseline NDVI values. These 

monthly baseline conditions were compared to composites for 

the end of the growing season immediately after Hurricanes 

Katrina and Rita and one growing season thereafter (fall 2005 

and fall 2006) in order to evaluate index values occurring 

after the hurricanes. Scores that departed from average NDVI 

values were calculated for September and October 2005 and 

2006 for individual pixels where study sites were located. In 

this study, departure from average scores ranged from -1.14 

to 0.25. Sites experiencing departure from average scores on 

the low end of the range (-1.14) experienced significant loss 

of vegetation (and likely conversion to open water), while 

sites with departures from average closer to 0.25 showed a 

higher density of vigorous vegetation beyond the baseline 

average. Sites with no variation between the monthly baseline 

average and the sampling date would receive a departure from 

average score of zero. Although the NDVI can be used to 

estimate aboveground biomass and productivity, we measured 

aboveground biomass directly for this study and used NDVI 

as a secondary tool to evaluate marsh condition and recovery 

after Hurricanes Katrina and Rita. The NDVI can be a 

useful tool to evaluate vegetative vigor but does not give 

any indication of species composition or vegetative 

community change.

Hydrology

Water level and salinity were measured hourly by using 

an YSI model 6920 multiparameter continuous hydrologic 

recorder or equivalent instrument at CRMS stations. 

Continuous hydrologic recorders were only established at one 

of the paired sites because of the proximity and hydrologic 

similarity of the sites to each other. The basic recorder 

measured water level through a pressure transducer by using 

a cable that was vented to the atmosphere. The recorders 
Materials and Methods 9

were surveyed to the North American Vertical Datum of 1988 

(NAVD 88), and water levels to datum were used to calculate 

depth, duration, and frequency of marsh inundation. The 

instrument specifications and procedures for field deployment, 

servicing, data processing, and quality assurance are described 

in Steyer and others (1995). See appendix 1 for hydrographs 

of water level (ft, NAVD 88) and salinity at selected CRMS 

study sites with available data from April 1, 2006, to 

November 1, 2007. 

Porewater in Soil 

Samples of porewater were collected from soil at 30-cm 

depth with a sipper probe to aid in extracting interstitial water 

(McKee and others, 1988). Porewater salinity was measured 

in the field with a portable, hand-held instrument (YSI 63). 

Procedures for fieldwork and quality assessment and control 

are described in Folse and West (2005).

Sediment Deposition and Condition

Sedimentation was determined from the distribution of 

caesium (caesium-137, 30-yr half life) in the sediment profile 

(DeLaune and others, 1978). Two cores were obtained at each 

station by twisting a 10-cm-diameter, thin-walled aluminum or 

PVC cylinder to a maximum depth of 50 cm. Core collection 

for analyzing caesium-137 occurred during sampling period 

of fall 2006 (Sept. and Oct.) at all sites. Compaction was 

minimized by using large, thin-walled cores. The cores 

were sectioned in the field into 2-cm increments, following 

procedures outlined in Folse and West (2005). In the 

laboratory, the specific activity of caesium-137 in each section 

was determined by using gamma ray spectroscopy with 

high-purity germanium detectors. The 662-kiloelectronvolt 

(keV) gamma emission from caesium-137 was measured for 

a minimum of 11 hours. The gamma spectrometers were 

calibrated for energy and efficiency by using a referencemixed gamma ray source traceable to the National Institute 

of Standards and Technology. The specific activity (A) was 

calculated by using the following equation:

, C A

EBmt = (1)

where 

C is the integrated counts of caesium-137, 

t is the counting time, 

m is the sample mass, 

B is the branching ratio (0.85 for 

 caesium-137), and 

E is the detection efficiency at 662 keV.

The depth profile of caesium-137 was determined by 

plotting the specific activity for each section. The centroid of 

a peak was determined by calculating a weighted average of 

the three points that define the peak. The depth of the peak 

was calculated by using the following equation: 

3

1

3

1

,

i i

i

i

i

y A

d

A

=

=

=

∑

∑

(2)

where 

d is the depth of the peak, 

y is the depth of the section, and 

A is specific caesium-137 activity.

Long-term accretion rates (centimeters per year [cm yr-1]) 

were calculated by dividing the depth of the caesium-137 peak 

by the number of years since 1963. In 1963, caesium-137 was 

deposited from atmospheric fallout providing a marker horizon 

in sediment cores that can be reliably identified. This analysis 

and interpretation resulted in 49 datable cores from a total of 

60 cores taken. Of the 30 total sites, 20 had two datable cores, 

9 had one datable core, and only 1 did not have a datable core. 

After gamma counting, the samples were transferred to the 

Wetland Biogeochemistry Institute, Analytical Services Lab at 

Louisiana State University (Baton Rouge, La.) for carbon and 

nitrogen analyses. 

A mean accretion rate was calculated for each site 

when two datable cores were available (n = 20 sites); 

otherwise, only one estimate of accretion was available for 

the remaining sites (n = 9). We calculated the mean (n = 2) 

content of carbon, nitrogen, and mineral and organic matter 

(see below) for each depth interval (2 cm); these means were 

used to calculate accumulation. The sum of the bulk soil and 

nutrient constituents above the level of the 1963 layer was 

then divided by the appropriate age factor (difference in 

years, date of collection minus 1963) to estimate a yearly 

rate of accumulation. 

Bulk Density and Organic Matter

Bulk density and percentage of organic matter were 

determined from the same cores (n = 60) used for caesium-137 

analysis. Core sections were dried at 60 °C and ground 

through a 2-mm mesh sieve. The material remaining on 

the sieve (mostly plant material) was then ground through 

a Wiley mill with 0.6 mm mesh. Bulk density (grams per 

cubic centimeter [g cm-3]) was determined by dividing the 

dry weight of the core section by the section volume. Organic 

matter content was determined by using the loss-on-ignition 

method (Dean, 1974). A subsample of 1 g was removed from 

each section for combustion at 550 oC for 2 hours.
10 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Sediment Elevation, Accretion, and 

Shallow Subsidence

Rod-surface elevation tables (RSET) were deployed at 

each CRMS station (16 total) and one historically sampled 

station (CRMS0326-H) to estimate elevation changes in marsh 

surface. The RSET is a removable instrument that was placed 

on permanently installed benchmarks driven into the substrate 

to refusal (10–18 m depth). The RSET was placed in the exact 

same location at each recording interval and measured changes 

in the distance between the marsh sediment surface and the 

instrument itself. Measurements were taken three times (that 

is, spring 2007, winter 2008, and fall 2008) following the 

procedures described in Cahoon and others (2002a, b). The 

sediment elevation and accretion data collected in winter and 

fall 2008 are included in this report but this is the only data 

type for which 2008 data are reported. Sediment elevation and 

accretion must be sampled over longer periods of time (that 

is, usually a 6-month minimum interval between readings), so 

data collection occurred over a longer timescale for these data 

types than the vegetation, water, and soil parameters. 

Three artificial marker horizons were established at each 

CRMS station and at a subset of historically sampled stations 

by using a feldspar marker technique (Knaus and Cahoon, 

1990). A 1-cm layer of white feldspar clay was placed on the 

marsh surface in three 0.25-m2 plots during either the spring 

2006 or summer 2006 sampling period. Frozen marsh cores 

were extracted from each feldspar plot at the time of RSET 

readings, and the depth of sediment deposited over the marker 

horizon was measured to the nearest millimeter to determine 

the accretion rate. 

By using the above two techniques in combination, 

estimates of shallow subsidence were calculated by subtracting 

measurements of elevation change from measurements of 

accretion (Cahoon and others, 1995). Two gages were used 

to provide estimates of RSLR in coastal Louisiana. The 

Grand Isle, La., gage (National Oceanic and Atmospheric 

Administration 8761724) was used for all sites in the eastern 

and central study areas, and the Sabine Pass, Tex., gage 

(National Oceanic and Atmospheric Administration 8770570) 

was used for the western region. Site elevation change 

(cm yr-1) was then compared to the projected RSLR estimates 

for each site for which we had sufficient data.

Statistical Analyses

All statistical analyses were performed by using SAS 

software (SAS Institute, Inc., 1989), and an alpha of 0.05 was 

used to indicate significance. Data were tested for normality 

by examining model residuals and homogeneity of variance to 

satisfy the assumptions of the statistical analyses performed. 

Subsequent [log10 (x+1)] transformation was performed on 

porewater salinity data to improve normality.

Vegetation and Porewater Salinity

Site-specific comparisons of total and live aboveground 

biomass before and after Hurricanes Katrina and Rita were 

performed with analysis of variance (ANOVA). Pearson 

correlation was used to evaluate the potential relationships 

between total cover of live vegetation; live aboveground 

biomass; and porewater salinity among all vegetation types. 

Porewater salinity data acquired after the hurricanes were 

tested with ANOVA for site-specific, seasonal variation.

Aboveground and belowground biomass, porewater 

salinity, and total cover of live vegetation were analyzed with 

ANOVA to test for differences among vegetation type, season, 

and vegetation type-by-season interactions. In addition, the 

influence of hurricanes (that is, direct or indirect), year, and 

the interaction of hurricane influence by year was investigated 

for porewater salinity and belowground biomass at the end of 

growing seasons by using ANOVA.

Aboveground biomass data were subsetted into biomass 

and peak biomass at the end of growing seasons and were 

analyzed with ANOVA to test for differences among the level 

of hurricane influence, year, and the interaction of these two 

factors. To estimate values of biomass at the end of growing 

seasons, the biomass data were subsetted to include only those 

data that were harvested during the fall (Sept. and Oct.) of 

2006 and 2007. Peak biomass was determined by the highest 

average biomass harvested at each site during each year. 

The highest biomass generally occurred either in summer 

or fall harvests. Percentages of aboveground biomass that 

were contributed by disturbance and nondisturbance species 

were also determined and averaged for each of three seasons 

(spring, summer, and fall). 

Soils

Data on bulk density from two sites that were historically 

sampled were analyzed with t-tests to evaluate differences 

in values from before and after Hurricanes Katrina and Rita. 

Simple linear regression was used to examine relationships 

between long-term rates of vertical accretion and accumulation 

of organic and mineral matter within vegetation types.

Results and Discussion

Recovery After Hurricanes Katrina and Rita

Summary of All Vegetation Types

Within all vegetation types, porewater salinities were 

typically greatest in the spring and summer of 2006 and 

generally decreased throughout the study (table 2). In a 
Results and Discussion 11

characterization of the Louisiana coastal marshes from 

August 1968, Chabreck (1972) reported mean porewater 

salinity of 1.5 (± 1.2) in fresh marshes, 5.7 (± 3.2) in brackish/

intermediate marshes, and 15.9 (± 3.1) in saline. In this 

study, seasonal porewater salinities were greater than those 

documented by Chabreck, averaging 2.2 (± 0.2) in fresh, 

10.4 (± 0.3) in brackish/intermediate, and 18.6 (± 0.5) in saline 

marshes. The only exception was fresh marsh in fall 2007, 

when mean porewater salinity was 1.2 (± 0.4). Porewater 

salinity differed significantly by vegetation type (p < 0.0001) 

(fig. 4), with greatest salinity in saline marsh, followed by 

brackish/intermediate, and fresh marshes. 

Salinity plays a major role in the regulation of plantcommunity dynamics because individual plant species have 

different tolerances and adaptations to deal with the osmotic 

and toxic effects of salt (Mitsch and Gosselink, 2000). 

Salinity tolerances of plant species determine vegetation zones 

in coastal wetlands (Gosselink, 1984), and changes in salinity 

affect community composition and species survival. Shifts 

in salinity cause the expansion of some plant species and the 

retreat of others, thus leading to shifts in community types 

along a salinity gradient. For example, increases in salinity 

above 2.0 can cause fresh marshes to shift to intermediate, and 

decreases in salinity below 2.0 can cause intermediate marshes 

to shift to fresh (Visser and others, 2003). Salinity levels 

above the optimal range of an individual species can lead to 

decreases in function (that is, productivity and reproduction) 

or death of that species. 

Hurricanes Katrina and Rita inundated all marsh types 

with high-salinity storm surge. In western Louisiana, 

the marsh remained flooded with saline water for several 

weeks, exposing fresh and brackish/intermediate vegetation 

to conditions near or above their salinity thresholds. In 

addition to the site-specific surface-water salinities reported 

in appendix 1, we measured seasonal porewater salinity 

at each station. Porewater salinity is often higher than the 

Table 2. Porewater salinity by marsh type. Minimum, mean (with standard errors), and maximum values by season and for the entire 

study period are presented. 

[SE; standard error]

Mash type Season Minimum Mean (SE) Maximum

Fresh Spring 2006 0.2 2.9 (0.6) 10.2

Summer 2006 0.3 3.3 (0.6) 10.8

Fall 2006 0.2 2.7 (0.6) 10.1

Winter 2007 0.1 2.0 (0.4) 8.5

Spring 2007 0.0 2.3 (0.5) 11.7

Summer 2007 0.1 1.5 (0.4) 9.5

Fall 2007 0.0 1.2 (0.4) 8.8

Study 0.0 2.2 (0.2) 11.7

Brackish/Intermediate Spring 2006 6.4 11.3 (0.6) 19.0

Summer 2006 4.5 11.1 (0.7) 18.6

Fall 2006 4.4 12.2 (1.0) 23.7

Winter 2007 4.9 11.4 (0.8) 21.3

Spring 2007 1.4 10.0 (0.9) 19.2

Summer 2007 1.8 7.9 (0.7) 15.9

Fall 2007 0.1 9.5 (1.1) 20.7

Study 0.1 10.4 (0.3) 23.7

Saline Spring 2006 12.4 21.3 (1.7) 30.7

Summer 2006 16.9 22.5 (1.3) 29.6

Fall 2006 12.4 21.3 (1.7) 30.7

Winter 2007 13.2 18.0 (0.7) 22.4

Spring 2007 5.4 16.9 (1.3) 22.7

Summer 2007 9.7 17.6 (1.1) 25.4

Fall 2007 0.0 15.8 (2.0) 26.4

Study 0.0 18.6 (0.5) 30.7
12 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

surface-water salinity at a site (Penfound and Hathaway, 1938; 

Hackney and Cruz, 1978; Alexander and Dunton, 2002) and, 

thus, is a better indicator of the root-zone environment than 

is surface-water salinity. If precipitation or other sources 

of freshwater are available after storm-surge inundation, 

porewater salinity tends to decline as it diffuses into the 

overlying surface water; however, if a freshwater source 

is not available, porewater salinity tends to increase from 

evapotranspiration. Alexander and Dunton (2002) showed 

that porewater and tidal-creek salinities in an estuarine marsh 

decreased as cumulative precipitation increased but that 

freshwater inflow from a river was more effective at flushing 

salt from soils than precipitation events alone. Timing of 

precipitation events also affects site salinity. For example, 

in the same estuarine marsh studied by Alexander and 

Dunton (2002), Dunton and others (2001) saw significant 

decreases in surface-water salinity and subsequent shifts in 

community composition in the summer of the second year of 

the study, which were attributed to large (that is, double the 

50-yr average) amounts of precipitation that fell early in the 

growing season of the second year. The timing of the large 

precipitation event led to the decrease in salinity because total 

rainfall in the first year of the study was similar to year two, 

but year one lacked the abundant rainfall early in the growing 

season that occurred in year two, thus leading to higher 

salinity in year one compared to year two. From fall 2005 

(when Hurricanes Katrina and Rita made landfall) to July 

2006, the coastal zone of Louisiana received less rainfall than 

the 30-yr mean (1971–2000, National Climatic Data Center) 

for this region, indicating that porewater salinities likely 

remained high because of the lack of available precipitation 

for flushing.

For this study, we examined fresh marshes dominated 

by Panicum hemitomon, brackish/intermediate marshes 

dominated by Spartina patens, and saline marshes dominated 

by Spartina alterniflora. Surface-water salinity tolerances 

for these species are available from field and greenhouse 

studies. Hester and others (2001) reported that a salinity 

of 4.0 significantly depressed both plant photosynthetic 

response and biomass in P. hemitomon. Prolonged exposure 

to even relatively low salinity levels was detrimental to this 

species. The hydrographs in appendix 1 show that surfacewater salinity at fresh marsh sites was generally 1.0 or less 

during the majority of the study; however, seasonal porewater 

salinities from 1.2 to 3.3 were observed, with seasonal 

maximum porewater salinities greater than 8.0 (table 2), 

thereby exposing P. hemitomon to salinities outside the ideal 

range. 

Spartina patens has a greater tolerance for salinity than 

P. hemitomon. In a greenhouse study, La Peyre and others 

(2001) found that growth did not decrease with increasing 

salinity treatments from 0.0 to 8.0. Ewing and others (1995) 

Figure 4. Mean values (see standard error bars) of porewater salinity for fresh, brackish/intermediate, and saline marsh types 

by season. 
Results and Discussion 13

found that live aboveground biomass of S. patens was greater 

in salinity treatments of 0.0 and 7.0 than in treatments of 14.0, 

21.0, and 28.0. In a field experiment, Chabreck and Palmisano 

(1973) reported that a salt pulse up to 6.7 had no effect on 

S. patens total cover. In all seasons throughout our study, 

mean porewater salinity in brackish/intermediate marshes was 

close to or greater than 8.0, though maximum values in each 

season exceeded 15.0, which is at the high end of the range for 

brackish/intermediate marshes (table 2). 

In saline marshes, mean porewater salinity was greater 

than 15.8 in all seasons, with all values well within the 

tolerance range of S. alterniflora, the dominant species within 

these marshes. The storm surge did not increase surface or 

porewater salinities beyond the ideal range for saline marshes.

Total cover of live vegetation showed seasonal trends 

among all vegetation types, with lowest mean values for 

cover occurring in winter 2007 or in the first sampling after 

the hurricanes (fig. 5). In the first growing season after the 

hurricanes, saline marsh sites exhibited the greatest live cover 

followed by fresh and brackish/intermediate sites. Throughout 

the second growing season after the hurricanes, live cover 

was greater at brackish/intermediate marsh sites than at fresh 

marsh sites, a reverse from 2006. When averaged throughout 

the study period, live cover in saline marsh sites was 

80.4 (± 2.8) percent; in brackish/intermediate marsh sites, it 

was 66.9 (± 3.1) percent; and in fresh marsh sites, it was 

60.0 (± 4.1) percent. Analysis of variance indicated that mean 

values of live total cover differed significantly according to the 

interaction of vegetation type and season (p = 0.0075). 

Disturbance vegetation species occurred in fresh and 

brackish/intermediate marsh sites during all seasons, but 

no disturbance taxa were observed in saline marsh (fig. 6). 

Disturbance taxa are those that are found in marshes that have 

been recently disturbed by physical (for example, wind shear 

stress) or biological (for example, heavy grazing) forces. 

Taxa were assigned to the disturbance group based on the 

extensive experience of Drs. Sasser and Visser with disturbed 

and undisturbed marshes in coastal Louisiana (table 3). In 

2006, cover of disturbance taxa relative to nondisturbance 

taxa was greater in brackish/intermediate marsh than in fresh 

marsh; however, disturbance taxa at brackish/intermediate 

sites decreased in the 2007 growing season (fig. 6). The 

opposite trend occurred in fresh marsh, with greater relative 

cover of disturbance species occurring in 2007 versus 2006. 

In both vegetation types, relative cover of disturbance taxa did 

not exceed 30 percent in either of the growing seasons after 

Hurricanes Katrina and Rita. The persistence of disturbance 

species in fresh and brackish/intermediate marshes two full 

growing seasons after the hurricanes is consistent with 

patterns observed by Guntenspergen and others (1995) after 

Hurricane Andrew. 

Figure 5. Total live vegetation cover (see standard error bars) for fresh, brackish/intermediate, and saline marsh types by season. 
14 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

During the first growing season after Hurricanes 

Katrina and Rita, live aboveground biomass was greatest at 

saline marsh sites, followed by brackish/intermediate and 

fresh marsh sites (fig. 7); however, in the second growing 

season after the hurricanes, brackish/intermediate marsh 

sites produced greater live aboveground biomass than 

saline sites, followed by fresh sites. This is different from 

what was observed in the data on live vegetation cover, 

according to which saline marsh sites produced the most 

live vegetation cover in the second growing season after the 

hurricanes, followed by fresh and brackish/intermediate marsh 

sites. The difference between the trends observed in live 

vegetation cover and live aboveground biomass emphasize the 

importance of looking at both variables together and may be 

explained by the fact that aboveground biomass is a parameter 

that is more sensitive to species composition and stem density 

than are estimates of vegetation cover. Typical of seasonal 

trends, live aboveground biomass was generally lowest in the 

winter and greatest in the summer or at the end of the growing 

season (fall). The greatest change in live aboveground 

biomass was observed in brackish/intermediate sites, with 

totals ranging from 108.0 (± 222.6) grams of dry weight per 

square meter (g dry weight m-2) in spring 2006 to 1,321.1 

(± 740.9) g dry weight m-2 in fall 2007. Analysis of variance 

indicated that the mean value of live aboveground biomass 

differed significantly among the interactions of vegetation type 

and season (p = 0.0133).

When all vegetation types were combined, Pearson 

correlation showed a significant positive relationship between 

total cover of live vegetation and live aboveground biomass 

(r = 0.56, p < 0.0001). Generally, as live vegetation cover 

increased, live aboveground biomass increased. This was 

not surprising because both variables are measures of live 

vegetation; however, these variables did not show the same 

Brackish/Intermediate marsh

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

20

40

60

80

100

Fresh marsh

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Disturbance and nondisturbance taxa, by percent

0

20

40

60

80

100

Saline marsh

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

20

40

60

80

100

Season Season

trends when the data were separated by vegetation type. 

Total cover of live vegetation was negatively correlated with 

porewater salinity within brackish/intermediate marsh sites 

(r = - 0.4492, p < 0.0001) and fresh marsh sites (r = - 0.32197, 

p = 0.003) but was not significantly correlated at saline marsh 

sites. This correlation supports our general understanding 

of salinity tolerances specific to marsh types, with fresh 

and brackish/intermediate marshes being less tolerant of 

increases in salinity than saline marshes (for example, McKee 

and Mendelssohn, 1989; Howard and Mendelssohn, 1999; 

Spalding and Hester, 2007).

Total belowground biomass showed seasonal trends, with 

greatest values in winter 2007 within all vegetation types 

(fig. 8). Saline habitats produced greater belowground 

biomass than brackish/intermediate and fresh habitats 

throughout the entire study period. Belowground biomass 

differed significantly among vegetation types (p < 0.0001) 

and seasons (p = 0.0009) but not by the interaction of 

vegetation and season (p = 0.5830). Belowground biomass 

was significantly greater in winter 2007 than in all other 

seasons except spring 2006. The general seasonal patterns of 

belowground biomass were the inverse of patterns observed in 

live aboveground biomass.

Fresh Marsh Sites

Porewater salinity ranged from 0.0 to 11.7 at fresh 

marsh study sites. The overall study mean for fresh marsh 

sites was 2.2 (± 0.2), which is greater than the 1.46 (± 1.20) 

reported by Chabreck (1972) (table 2). The mean value 

for porewater salinity at the end of the growing season 

was significantly greater in 2006 (2.6 ± 0.5) than in 2007 

(1.1 ± 0.3) (fig. 9). Sites within the directly influenced 

hurricane area also experienced significantly greater porewater 

Figure 6. Percentages of disturbance (black bars) and nondisturbance (gray bars) taxa present in live vegetation cover of fresh, 

brackish/intermediate, and saline vegetation types by season. 
Results and Discussion 15

Table 3. Observed taxa characterized as disturbance because 

of their typical presence in marshes that have been recently 

disturbed by physical or biological forces.

Disturbance taxa—Continued

Aeschynomene indica

Alternanthera philoxeroides

Amaranthus australis

Andropogon spp.

Centella erecta

Cirsium horridulum

Cyperus erythrorhizos

Cyperus spp.

Cyperus odoratus

Echinochloa spp.

Echinochloa crus-galli

Echinochloa walteri

Eupatorium capillifolium

Disturbance taxa—Continued

Leptochloa fusca ssp. fascicularis

Mikania scandens

Panicum dichotomiflorum

Pluchea camphorata

Pluchea odorata

Ranunculus spp.

Rorippa palustris ssp. fernaldiana

Salix nigra

Sesbania drummondii

Sesbania herbacea

Sesbania spp.

Symphyotrichum spp.

Symphyotrichum subulatum

Symphyotrichum tenuifolium

Vigna luteola

Figure 7. Live aboveground biomass (see standard error bars) in fresh, brackish/intermediate, and saline marsh types by season. 
16 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Marsh type by hurricane influence

Fresh direct

Fresh indirect

Brackish/Intermediate direct

Brackish/Intermediate indirect

Saline direct

Saline indirect

Porewater salinity

0

5

10

15

20

25

30

2006

2007

Figure 8. Total 

belowground biomass 

(see standard error 

bars) in fresh, brackish/

intermediate, and saline 

marsh types by season. 

Figure 9. Mean values 

of porewater salinity 

(see standard error 

bars) for fresh, brackish/

intermediate, and saline 

marshes by type of 

hurricane influence (direct 

or indirect) and year. 
Results and Discussion 17

Table 4. Results of analysis of variance testing for porewater 

salinity at the end of growing seasons in fresh, brackish/

intermediate, and saline marsh types. 

[Hurricane influence is defined as direct or indirect. P-values less than 0.05 

indicate significant differences. n, number; p, p-value]

Marsh type Factor p

Fresh marsh (n=69) Hurricane influence 0.0088

Year 0.0082

Hurricane influence by year 0.7590

Brackish/Intermediate 

marsh (n=69)

Hurricane influence 0.0996

Year 0.0618

Hurricane influence by year 0.9977

Saline marsh (n=35) Hurricane influence 0.0013

Year 0.0062

Hurricane influence by year 0.0438

Sites

CRMS0326

CRMS0326-H

CRMS0164

CRMS0164-H

CRMS0147

CRMS0147-H

Porewater salinity

0

5

10

15

20

25

30

35

CRMS0669 CRMS2156 CRMS0651 CRMS0651-H CRMS0672 CRMS0672-H CRMS0610 CRMS0610-H CRMS0312 CRMS0312-H CRMS0135 CRMS0135-H

Porewater salinity

0

5

10

15

20

25

30

35

CRMS0605

CRMS0605-H CRMS1277

CRMS1277-H CRMS0294

CRMS0294-H CRMS0268

CRMS0268-H CRMS0219

CRMS0219-H CRMS0128

CRMS0128-H

Porewater salinity

0

5

10

15

20

25

30

35

Fresh marsh

Saline marsh

Brackish/Intermediate marsh

W C E

W C E

C E

Figure 10. Porewater salinity at the end of the growing season 

in 2006 (black bars) and in 2007 (gray bars) at study sites within 

fresh, brackish/intermediate, and saline marshes. Sites with 

“H” designations were historically sampled by various research 

projects, and sites without “H” designations are within the 

Coastwide Reference Monitoring System (CRMS). Western (W), 

central (C), and eastern (E) regions of Louisiana are represented.

salinity (2.8 ± 0.6) as compared to the indirectly influenced 

area (0.8 ± 0.1), but the interaction of year and hurricane 

influence was not statistically significant (table 4). Of all the 

fresh marsh sites, porewater salinity at the end of growing 

seasons was greatest at CRMS0605 and CRMS0605-H in 

fall 2006 (fig. 10). Salinity at these sites was approximately 

9 in 2006, abnormally high for fresh marshes (Chabreck, 

1972). Porewater salinity remained high (8.5) at CRMS0605 

through the end of the growing season in 2007 but decreased 

at CRMS0605-H. At the remainder of the fresh marsh sites, 

porewater salinity was typical of fresh marshes in both years 

except at CRMS0294 in fall 2006 (3.7); however, salinity 

dropped at this site to 0.3 by fall 2007 (table 5). 

Across all fresh marsh sites, live vegetation cover at 

the end of growing seasons averaged 68.9 (± 7.7) percent in 

2006 and increased to 81.8 (± 9.4) percent in 2007. The live 

cover at the end of the growing season in 2006 was similar 

to measurements of fresh marsh cover acquired before the 

storms in 2003 and 2004 under the CWPPRA monitoring 

program (http://www.lacoast.gov). There were no statistical 

differences in total live cover at the end of growing seasons 

between years, across levels of hurricane influence, or among 

interactions of years and hurricane influence (p > 0.05). Live 

cover at most sites increased or remained equal between fall 

2006 and fall 2007 except at CRMS1277, CRMS1277-H, 

CRMS0219-H, and CRMS0128-H, where live cover 

decreased in the second growing season (fig. 11). Of the 

sites with less cover in fall 2007, the only site where cover 

decreased substantially was CRMS0128-H, where live cover 

decreased by 40 percent between fall 2006 and fall 2007, 

largely because of an increase in floating aquatics in the 

plot. Floating aquatics are not counted as live cover because 
18 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Table 5. Site-specific summaries of soils, porewater salinity, and vegetation cover data.

[Disturbance taxa indicated in bold text. Underlined porewater values are > 1 standard deviation, and bold porewater values are > 2 standard deviations from 

the specific mean values delineated for marsh types by Chabreck, 1972 (fresh = 1.4 ± 1.2, brackish/intermediate = 5.7 ± 3.15, saline = 15.8 ± 3.11). Indirect 

hurricane influence defined by < 2 m of storm surge at sites not located in Calcasieu/Sabine, Mermentau, or Breton Sound hydrologic basins. ID, identification; 

FEMA, Federal Emergency Management Agency; m, meter; GOM, Gulf of Mexico; km, kilometer; cm, centimeter; g cm-3, grams per cubic centimeter; 

STD, standard deviation; cm yr-1, centimeters per year; g m-2 yr-1, grams per square meter per year; g C m-2 yr-1, grams of carbon per square meter per year; 

min, minimum; max, maximum; g dry weight m-2, grams of dry weight per square meter; *, estimates from one core only; NA, not applicable]

Soil characteristics 

Marsh 

vegetation type

Site ID 

(from west to 

east within 

vegetation type)

2005 

hurricane 

influence

FEMA 

surge 

elevation 

(m)

Distance 

from GOM 

(km)

Mean depth 

of peak 137Cs 

(cm)

Bulk density 

since 1963 

(g cm-3) 

mean (std)

Accretion rate 

since 1963 

(cm yr-1) 

mean (std)

Fresh

CRMS0605 Direct 3.3 17 -34.1 0.173 (0.002) 0.79 (0.028) 

CRMS0605-H Direct 3.3 23 27.1* 0.049* 0.63* 

CRMS1277 Direct 2.4 29 -9.0* 0.039* 0.21* 

CRMS1277-H Direct 2.4 32 -26.9* 0.033* 0.63* 

CRMS0294 Indirect 1.8 23 -28.2 0.113 (0.003) 0.66 (0.028) 

CRMS0294-H Indirect 1.8 26 -30.9 0.207* 0.72 (0.070) 

CRMS0268 Indirect 1.8 86 -19.9 0.065 (0.004) 0.46 (0.035) 

CRMS0268-H Indirect 1.8 86 -13.6* 0.047* 0.32* 

CRMS0219 Indirect 1.2 70 -25.0 0.051* 0.58 (0.070) 

CRMS0219-H Indirect 1.2 71 -26.3 0.055 (0.007) 0.61 (0.098) 

CRMS0128 Direct 4.8 49 -26.9 0.133 (0.008) 0.63 (0.007) 

CRMS0128-H Direct 4.8 48 -23.6 0.174 (0.025) 0.55 (0.021) 

Brackish / 

Intermediate

CRMS0669 Direct 3.0 16 -17.9 0.088 (0.007) 0.42 (0.035) 

CRMS2156 Direct 3.0 14 -15.0* 0.096* 0.35* 

CRMS0651 Direct 2.7 21 -15.1 0.194 (0.049) 0.35 (0.070) 

CRMS0651-H Direct 2.7 20 -18.3* 0.142* 0.43* 

CRMS0672 Direct 3.0 7 -16.9 0.262 (0.021) 0.39 (0.007) 

CRMS0672-H Direct 3.0 7 -14.3 0.219 (0.022) 0.33 (0.035) 

CRMS0610 Direct 3.0 3 -35.0* 0.459* 0.81* 

CRMS0610-H Direct 3.0 4 -20.9 0.361 (0.016) 0.49* 

CRMS0312 Indirect 1.5 48 -24.7* 0.083* 0.57* 

CRMS0312-H Indirect 1.5 45 -36.5 0.089 (0.006) 0.85 (0.070) 

CRMS0135 Direct 5.1 25 -31.8 0.240 (0.027) 0.74 (0.042) 

CRMS0135-H Direct 5.1 23 none NA NA 

Saline

CRMS0326 Indirect 1.5 8 -30.0 0.377 0.7* 

CRMS0326-H Indirect 1.5 6 -20.9 0.288 (0.031) 0.46 (0.028) 

CRMS0164 Indirect 2.1 7 -28.6 0.146 (0.010) 0.67 (0.021) 

CRMS0164-H Indirect 2.1 7 -36.2 0.285 (0.013) 0.84 (0.042) 

CRMS0147 Direct 4.8 11 -17.2* 0.539* 0.4* 

CRMS0147-H Direct 4.8 8 -30.9 0.534 (0.042) 0.72 (0.000) 
Results and Discussion 19

Soil characteristics Porewater salinity

Carbon 

(g m-2 yr-1)

Nitrogen 

(g m-2 yr-1)

Mineral 

accumulation 

(g m-2 yr-1)

Organic 

accumulation 

(g C m-2 yr-1)

End-of-season 

2006 mean 

(std) 

End-of-season 

2007 mean 

(std) 

Overall 

study mean 

(std)

Overall 

study min

Overall 

study max

207 (13.3) 17.4 (2.7) 890 (112) 515 (37) 9.9 (0.2) 8.5 (0.3) 9.1 (1.2) 7.6 11.7

113 (18.0) 5.2 (1.1) 110 (27) 242 (40) 8.9 (0.3) 1.3 (0.1) 5.6 (3.4) 1.3 9.2

35 (7.3) 2.2 (0.4) 10 (3) 69 (13) 0.4 (0.2) 0.2 (0.0) 0.3 (0.2) 0.2 1.1

81 (11.0) 4.7 (1.0) 42 (8) 160 (25) 0.2 (0.0) 0.3 (0.0) 0.2 (0.0) 0.2 0.3

177 11.1 365 (35) 405 (28) 3.7 (0.7) 0.3 (0.3) 3.4 (2.0) 0 6.4

182 (25.4) 11.9 (1.1) 929 (148) 457 (50) NA 0.2 (0.3) 2.8 (2.3) 0 6.7

125 (15.7) 7.6 (0.8) 62 (10) 260 (29) 0.4 (0.1) 0.1 (0.0) 0.2 (0.2) 0 0.5

72 (5.9) 4.7 (0.9) 31 (3) 149 (18) 0.4 (0.0) 0.0 (0.0) 0.2 (0.2) 0 0.6

132 (12.4) 7.0 (1.2) 33 (6) 263 (41) 1.0 (0.1) 0.7 (0.1) 0.8 (0.4) 0.5 2.4

144 (25.1) 9.0 (1.3) 53 (16) 302 (48) 1.5 (0.0) 1.1 (0.1) 1.2 (0.2) 0.9 1.9

206 (16.2) 13.1 (1.5) 401 (97) 473 (19) 1.0 (0.2) 0.4 (0.1) 1.0 (0.5) 0.4 2.2

144 (13.8) 8.5 (1.1) 674 (93) 339 (26) 1.7 (0.2) 1.0 (0.2) 1.5 (0.4) 0.9 2.5

102 (7.9) 5.7 (0.6) 142 (12) 251 (15) 16.0 (0.3) 7.1 (3.2) 11.9 (4.6) 3.4 16.3

102 (5.7) 5.8 (0.4) 185 (69) 253 (20) 11.3 (0.2) 8.6 (0.6) 9.7 (1.7) 5.8 11.7

119 (18.1) 7.7 (1.4) 482 (94) 272 (36) 7.9 (2.2) 8.6 (0.3) 8.9 (1.6) 6.3 11.1

132 (12.5) 8.8 (0.9) 452 (72) 307 (31) 9.9 (0.6) 9.3 (0.7) 9.8 (1.3) 7.5 11.5

107 (9.8) 6.8 (0.7) 819 (214) 283 (20) NA 16.3 (0.5) 13.4 (2.7) 8.6 16.9

80 (5.3) 4.2 (0.5) 527 (94) 241 (17) 14.2 (2.0) 15.8 (1.6) 13.9 (2.3) 8.9 18.6

120 (20.4) 10.2 (1.1) 3,199 (307) 472 (33) 22.6 (1.0) 17.2 (1.9) 15.9 (3.6) 9.2 23.7

106 (10.4) 7.3 (0.7) 1,496 (135) 354 (21) 21.6 (0.3) 19.6 (1.0) 17.8 (4.2) 7.5 21.3

202 13.9 77 (16) 425 (64) 6.1 (0.6) 3.4 (0.1) 4.7 (1.2) 3.3 6.6

204 (20.0) 14.0 (1.4) 313 (78) 483 (45) 10.1 (0.6) 6.7 (0.3) 7.9 (1.6) 6 11.5

127 (23.9) 9.1 (4.5) 1,392 (514) 434 (51) 8.5 (0.7) 1.2 (0.4) 5.2 (2.8) 0.9 9.1

. . . . 5.5 (1.8) 0.1 (0.0) 3.6 (2.7) 0.1 7.6

183 (35.0) 9.6 (2.0) 2,059 (681) 420 (41) 15.9 (0.1) 11.3 (0.3) 14.0 (2.3) 11.1 18.6

154 (20.7) 7.1 (0.8) 1,052 (110) 354 (11) 18.7 (1.0) 18.5 (0.1) 18.3 (1.1) 15.9 19.7

132 (12.4) 9.6 (0.9) 598 (90) 390 (29) 29.6 (0.5) 21.2 (1.1) 24.0 (3.7) 19.5 30.1

203 (34.8) 11.9 (1.5) 1,911 (154) 540 (41) 30.0 (0.6) 24.6 (3.0) 25.4 (3.8) 19 30.7

104 (32.5) 5.9 (1.9) 1,439 (520) 275 (22) 12.8 (0.4) 0.0 (0.1) 9.8 (4.9) 0 14.6

122 (13.3) 8.7 (0.7) 3,471 (283) 509 (31) 20.5 (2.5) 18.9 (1.4) 18.4 (2.3) 13.5 22.3
20 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Vegetation data 

Total live cover (%) 

Marsh vegetation type

Site ID 

(from west 

to east within 

vegetation type)

2005 

hurricane 

influence1 End-of-season 2006

Dominant species 

end-of-season 

2006 (% cover) End-of-season 2007

Fresh

CRMS0605 Direct 55 Echinochloa spp. (20) 75 

CRMS0605-H Direct 8 Spartina patens (8) 80 

CRMS1277 Direct 75 Panicum hemitomon (70) 60 

CRMS1277-H Direct 95 Panicum hemitomon (95) 90 

CRMS0294 Indirect 75 Eleocharis spp. (55) 125 

CRMS0294-H Indirect 90 Typha sp. (35) 95 

CRMS0268 Indirect 100 Panicum hemitomon (70) 100 

CRMS0268-H Indirect 90 Panicum hemitomon (70) n/a 

CRMS0219 Indirect 60 Leersia oryzoides (35) 75

CRMS0219-H Indirect 80 Panicum hemitomon (45) 70 

CRMS0128 Direct 70 Ludwigia spp. (65) 120 

CRMS0128-H Direct 50 Polygonum spp. (25) 10 

Brackish / Intermediate

CRMS0669 Direct 20 Spartina patens (15) 75 

CRMS2156 Direct 60 Spartina patens & 

Iva frutescens (35) 90 

CRMS0651 Direct 80 Spartina patens (50) 95 

CRMS0651-H Direct 50 Spartina patens (25) 60 

CRMS0672 Direct 40 Distichlis spicata (20) 75 

CRMS0672-H Direct 20 Paspalum vaginatum (15) 105

CRMS0610 Direct 85 Distichlis spicata (50) 65 

CRMS0610-H Direct 70 Spartina patens (65) 95 

CRMS0312 Indirect 60 Spartina patens (60) 100 

CRMS0312-H Indirect 100 Spartina patens (95) 95 

CRMS0135 Direct 100 Echinochloa spp. (25) 120 

CRMS0135-H Direct 100 Spartina patens (80) 100 

Table 5. Site-specific summaries of soils, porewater salinity, and vegetation cover data.

[Disturbance taxa indicated in bold text. Underlined porewater values are > 1 standard deviation, and bold porewater values are > 2 standard deviations from 

the specific mean values delineated for marsh types by Chabreck, 1972 (fresh = 1.4 ± 1.2, brackish/intermediate = 5.7 ± 3.15, saline = 15.8 ± 3.11). Indirect 

hurricane influence defined by < 2 m of storm surge at sites not located in Calcasieu/Sabine, Mermentau, or Breton Sound hydrologic basins. ID, identification; 

FEMA, Federal Emergency Management Agency; m, meter; GOM, Gulf of Mexico; km, kilometer; cm, centimeter; g cm-3, grams per cubic centimeter; 

STD, standard deviation; cm yr-1, centimeters per year; g m-2 yr-1, grams per square meter per year; g C m-2 yr-1, grams of carbon per square meter per year; 

min, minimum; max, maximum; g dry weight m-2, grams of dry weight per square meter; *, estimates from one core only; NA, not applicable]—Continued
Results and Discussion 21

Vegetation data—Continued

Total live cover (%)

Total aboveground biomass 

(g dry weight m-2)

Total belowground biomass 

(g dry weight m-2)

Dominant 

species 

end-of-season 

2007 (% cover)

Overall 

study mean 

(std)

Overall study 

min

Overall study 

max

End-of-season 

2006 mean 

(std) 

End-of-season 

2007 mean 

(std) 

End-of-season 

2006 mean 

(std) 

End-of-season 

2007 mean 

(std) 

Pluchea camphorata (25) 48.3 (31.4) 0 77 248 (160) 959 (234) 3,494 (695) 4,114 (852)

Spartina patens (40) 35.8 (40.4) 1 80 102 (24) 707 (606) 3,800 (373) 5,209 (1,141)

Panicum hemitomon (50) 58.4 (24.9) 4 75 698 (214) 643 (206) 4,261 (807) 5218 (315)

Panicum hemitomon (85) 66.8 (36.1) 5 95 879 (59) 1,079 (300) 5,549 (711) 5,144 (590)

Typha sp. (80) 72.1 (28.2) 35 125 543 (207) 853 (437) 4,862 (1,331) 6,860 (1,392)

Typha sp. (60) 78.5 (27.0) 25 100 597 (163) 1,010 (366) 5,965 (4,412) 7,746 (1,544)

Panicum hemitomon (95) 80.0 (37.5) 5 120 1,822 (746) 1,998 (440) 5,589 (2,336) 8,405 (2,364)

n/a 80.5 (36.6) 8 110 1,102 (155) 920 (103) 5,699 (1,536) 9,080 (1,266)

Leersia oryzoides & 

Panicum 

hemitomon (30)

58.5 (24.4) 5 75 812 (250) 930 (225) 4,138 (1,500) 4,744 (655)

Panicum hemitomon (45) 77.5 (5.2) 5 85 1,052 (323) 1,010 (241) 7,657 (3,244) 5,483 (78)

Polygonum spp. (35) 61.0 (47.4) 3 120 761 (660) 628 (176) 5,682 (1,171) 4,719 (1,069)

Alternanthera 

philoxeroides (10) 27.1 (30.9) 3 80 1,009 (446) 430 (267) 6,212 (1,352) 3,619 (443)

Spartina patens (45) 41.4 (25.9) 10 75 218 (199) 870 (608) 6,281 (1,063) 4,607 (763)

Spartina patens (60) 72.1 (11.1) 65 90 1,369 (77) 2,934 (2,122) 5,796 (896) 5,459 (1,837)

Spartina patens (90) 79.5 (14.0) 55 95 2,568.00 

(1,258.70) 3,182 (1,056) 4,856 (1,305) 6,131 (3,985)

Spartina patens (35) 69.2 (17.6) 50 95 1,903 (411) 2214 (574) 4,425 (1,310) 4,049 (1,259)

Distichlis spicata (50) 49.2 (23.3) 10 75 1,980 (122) 1,347 (332) 4,148 (232) 5,248 (572)

Distichlis spicata & 

Paspalum 

vaginatum (45)

36.7 (38.2) 5 105 2,295 (1,280) 2,317 (463) 4,434 (1,291) 3,336 (1,212)

Spartina patens (50) 62.1 (18.4) 30 80 1,255 (365) 2,216 (494) 3,535 (616) 4,229 (525)

Spartina patens (95) 66 (25.3) 25 95 931 (436) 3,931 (1,318) 3,209 (592) 4,273 (1,360)

Spartina patens (85) 63.3 (27.5) 25 100 1,642 (1,331) 865 (202) 4,857 (428) 2,220 (1,007)

Spartina patens (70) 80.8 (19.3) 45 100 2,572 (306) 1,649 (959) 5,280 (1,772) 4,383 (1,248)

Spartina patens & 

Vigna luteola (35) 85 (36.6) 20 120 930 (198) 1,046 (359) NA 6,938 (459)

Spartina patens (80) 91.4 (14.9) 60 100 3,173 (641) 2,331 (1,166) NA 6,774 (1,653)
22 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Saline

CRMS0326 Indirect 65 Spartina patens (35) 85 

CRMS0326-H Indirect 85 Spartina alterniflora (85) 85 

CRMS0164 Indirect 95 Spartina alterniflora (80) 95 

CRMS0164-H Indirect 90 Spartina alterniflora (90) 95 

CRMS0147 Direct 85 Spartina alterniflora (85) 95 

CRMS0147-H Direct 90 Spartina alterniflora (90) 85 

Table 5. Site-specific summaries of soils, porewater salinity, and vegetation cover data.

[Disturbance taxa indicated in bold text. Underlined porewater values are > 1 standard deviation, and bold porewater values are > 2 standard deviations from 

the specific mean values delineated for marsh types by Chabreck, 1972 (fresh = 1.4 ± 1.2, brackish/intermediate = 5.7 ± 3.15, saline = 15.8 ± 3.11). Indirect 

hurricane influence defined by < 2 m of storm surge at sites not located in Calcasieu/Sabine, Mermentau, or Breton Sound hydrologic basins. ID, identification; 

FEMA, Federal Emergency Management Agency; m, meter; GOM, Gulf of Mexico; km, kilometer; cm, centimeter; g cm-3, grams per cubic centimeter; 

STD, standard deviation; cm yr-1, centimeters per year; g m-2 yr-1, grams per square meter per year; g C m-2 yr-1, grams of carbon per square meter per year; 

min, minimum; max, maximum; g dry weight m-2, grams of dry weight per square meter; *, estimates from one core only; NA, not applicable]—Continued

Vegetation data—Continued 

Total live cover (%) 

Marsh vegetation type

Site ID 

(from west to 

east within 

vegetation type)

2005 

hurricane influence1 End-of-season 2006

Dominant species 

end-of-season 

2006 (% cover) End-of-season 2007
Results and Discussion 23

Schoenoplectus 

americanus (80) 62.8 (27.5) 20 95 1,051 (187) 1,045 (56) 6,204 (667) 7,986 (783)

Spartina alterniflora (85) 76.4 (13.7) 50 85 957 (377) 607 (82) 8,002 (1,122) 6,077 (1,142)

Spartina alterniflora (95) 87.8 (12.1) 65 100 2,889 (1,096) 2,140 (597) 4,550 (442) 7,230 (1,412)

Spartina alterniflora (90) 86.4 (6.9) 75 95 1,870 (274) 1,638 (721) 5,685 (976) 7,489 (250)

Spartina alterniflora (95) 90.7 (10.1) 70 100 1,492 (362) 1,706 (313) NA 7,391 (2,032)

Spartina alterniflora (95) 80 (19.1) 50 95 1,970 (64) 1,620 (464) 7,580 (1,560) 9,778 (354)

Vegetation data

Total live cover (%)

Total aboveground biomass 

(g dry weight m-2)

Total belowground biomass 

(g dry weight m-2)

Dominant 

species 

end-of-season 

2007 (% cover)

Overall 

study mean 

(std)

Overall study 

min

Overall study 

max

End-of-season 

2006 mean 

(std) 

End-of-season 

2007 mean 

(std) 

End-of-season 

2006 mean 

(std) 

End-of-season 

2007 mean 

(std) 
24 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

they are not rooted, emergent vegetation within 

the permanent vegetation plot. The CRMS0605-H 

site showed the greatest change in cover between 

the end of the growing seasons of 2006 and 2007, 

with cover increasing by 72 percent. In fall 2006, 

CRMS0605-H was largely nonvegetated, and 

porewater salinity was approximately 8.5, while in 

fall 2007 live cover was estimated at 80 percent, 

with porewater salinity at 1.4 (see case study 1 for 

further discussion).

We conducted comparisons of data from seven 

fresh marsh sites (CRMS0128, CRMS0128-H, 

CRMS0219-H, CRMS0294, CRMS0294-H, 

CRMS0605, and CRMS0605-H) where historical 

data acquired before Hurricanes Katrina and 

Rita were available. We found that the dominant 

vegetation species at fresh marsh sites differed 

among sites. Before the hurricanes, most fresh 

marsh sites were dominated by P. hemitomon, 

S. lancifolia, or occasionally, S. patens. At 

the end of the growing season in 2006, one 

site (CRMS0605) was dominated by multiple 

disturbance species, Echinochloa spp., while the 

other sites were dominated by species typical of 

fresh marshes (table 5). In the second growing 

season after the storms, dominant species differed 

from conditions documented before the storms at 

33 percent of sites. When a difference occurred 

between dominant species before and after the 

hurricanes, the change was not always towards a 

disturbance species, as was observed at CRMS0605 

and CRMS0128-H. Dominance at CRMS0219-H 

shifted from S. lancifolia before Hurricanes Katrina 

and Rita to P. hemitomon after the storms. At 

CRMS0605-H, dominance changed from 

P. hemitomon before the storms to S. patens after the 

storms (see case study 1 for additional information). 

At some sites (CRMS0294, CRMS0294-H, and 

CRMS0128), the differences between the end 

of the growing seasons of 2006 and 2007 were 

simply changes from one fresh marsh species to 

another (table 5). There was no consistent change 

in dominant species across fresh marsh sites (for 

example, change to intermediate or disturbance 

species), suggesting the importance of site-specific 

conditions. Temporary, site-specific changes 

caused by the degree of storm sediment deposition, 

salt exposure, erosion, and wrack deposition were 

characterized by Guntenspergen and others (1995) 

after Hurricane Andrew. They found that landscape 

structure before Hurricane Andrew and the path 

of the storm created a heterogeneous pattern of 

disturbance with various recovery rates.

Observations of live vegetation cover were 

grouped into percentages of relative cover among 

disturbance versus nondisturbance taxa. At the 

Sites

Fresh marsh

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Total live cover, by percent

0

20

40

60

80

100

120

140 W C E

Saline marsh

CRMS0326

CRMS0326-H

CRMS0164

CRMS0164-H

CRMS0147

CRMS0147-H

Total live cover, by percent

0

20

40

60

80

100

120

140

C E

Brackish/Intermediate marsh

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

Total live cover, by percent

0

20

40

60

80

100

120

140

W C E

Figure 11. Total live cover of emergent vegetation at fresh, 

brackish/intermediate, and saline marsh sites at the end of the 

growing season in 2006 (black bars) and in 2007 (gray bars). Sites 

with “H” designations were historically sampled by various 

research projects, and sites without “H” designations are within 

the Coastwide Reference Monitoring System (CRMS). Western (W), 

central (C), and eastern (E) regions of Louisiana are represented.
Results and Discussion 25

2006

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Cover, by percent

0

20

40

60

80

100

W C E

2007

Sites

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Cover, by percent

0

20

40

60

80

100

W C E

Figure 12. Cover by disturbance taxa (black bars) relative to 

nondisturbance taxa (gray bars) in emergent vegetation at fresh 

marsh sites at the end of the growing season in 2006 and in 2007. Sites 

with “H” designations were historically sampled by various research 

projects, and sites without “H” designations are within the Coastwide 

Reference Monitoring System (CRMS). Western (W), central (C), and 

eastern (E) regions of Louisiana are represented.

end of the growing season in 2006, disturbance 

taxa composed approximately 20 percent of the 

total cover at CRMS0128 and CRMS0128-H and 

greater than 65 percent at CRMS0605 (fig. 12). 

All three of these sites were within areas directly 

influenced by Hurricanes Rita (western region) and 

Katrina (eastern region) and experienced physical 

disturbance to the landscape because of hurricaneinduced marsh scouring, shearing, and eroding 

(Barras, 2006).

Other sites in the zone of direct influence did 

not show large percentages of disturbance taxa 

in fall 2006 (CRMS0605-H, CRMS1277, and 

CRMS1277-H), thereby illustrating the patchy 

nature of hurricane-related physical disturbance 

(Guntenspergen and others, 1995). The total 

cover of disturbance species increased in some 

sites in fall 2007 (fig. 12). Similar to 2006, there 

was substantial coverage by disturbance taxa at 

CRMS0605, CRMS0128, and CRMS0128-H in 

fall 2007, comprising greater than 40 percent of 

the total cover at these sites. The percentage of 

disturbance species also increased at CRMS0605-H, 

CRMS1277, and CRMS0294 in fall 2007. At 

CRMS0605-H, the increase in disturbance taxa from 

2006 to 2007 coincided with an increase in total 

cover from 8 to 80 percent.

The contribution of disturbance species to 

aboveground biomass was significantly greater in 

the sites directly impacted by Hurricanes Katrina 

and Rita, but this contribution did not differ 

significantly by year or among interactions of the 

variables levels of hurricane influence and year 

(table 6). As reflected in the vegetation cover 

values, the percentage of biomass composed of 

disturbance species was greater in the second year 

after the hurricanes than in the first year (fig. 13). 

This increase indicates that some of the biomass 

recovery in the second year was caused by a greater 

amount of biomass from disturbance species. 

The largest percentage of disturbance species in 

fresh marsh sites occurred at CRMS0128 and 

CRMS0128-H in upper Breton Sound, an area that 

was impacted by some of the highest storm surge 

(4.8 m, Federal Emergency Management Agency 

[FEMA], 2006) in the path of Hurricane Katrina. 

Species that typically dominate coastal fresh 

marshes of Louisiana, such as P. hemitomon, 

S. lancifolia, or Zizaniopsis miliacea (giant 

cutgrass), were not present at either of these sites 

(Visser and others, 1998). The CRMS0128-H site 

was dominated by S. patens in the spring of 2006, 

and this species remained an important component 

of the biomass into 2007 (fig. 14). CRMS0128 

was dominated by Ludwigia leptocarpa (anglestem 

primrose-willow) and Vigna luteola (hairypod 
26 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

cowpea) in 2006. Ludwigia leptocarpa is not considered a 

disturbance species because it generally occurs in undisturbed 

fresh and intermediate marshes, but V. luteola is considered 

a disturbance species. Neither of these species is typically 

dominant in fresh marsh. The CRMS0605 and CRMS0605-H 

sites, located west of Grand Lake, experienced storm surge 

from Hurricane Rita. At these sites, very little vegetation 

colonized in 2006 (fig. 15), and the species that did colonize 

(for example, S. patens, Distichlis spicata [seashore saltgrass], 

L. leptocarpa, Eleocharis parvula [dwarf spikesedge], 

Schoenoplectus robustus [sturdy bulrush], and Blutaparon 

vermiculare [silverhead]) are not considered disturbance 

species; however, most of these species do not occur in fresh 

marshes. In 2007, disturbance species were observed at 

CRMS0605 and CRMS0605-H, including Pluchea odorata

(sweetscent) and Amaranthus australis (southern amaranth).

Live aboveground biomass at the end of growing seasons 

at fresh marsh sites was significantly lower in the directly 

impacted sites (309 g dry weight m-2) than in the indirectly 

impacted sites (576 g dry weight m-2; table 7; fig. 16). At 

fresh marsh sites, live aboveground biomass at the end of the 

growing season 2 years after the hurricanes (in 2007, 543 g 

dry weight m-2) was not significantly greater than in the first 

growing season (in 2006, 343 g dry weight m-2) after the 

hurricanes. The interaction between year and hurricane impact 

was not statistically significant (table 7). Figure 16 shows 

that live aboveground biomass in fresh marsh at the end of 

growing seasons was lower in the first year after the hurricanes 

than in the second year, primarily because of the low level 

of fall biomass in the directly impacted plots. One year after 

the hurricanes, the average live biomass in the fall at directly 

impacted sites was greater than two standard deviations below 

the long-term (that is, 18-year) mean of values collected at 

three sites dominated by P. hemitomon (table 8). The low 

level of biomass occurring one growing season after the 

hurricanes has a 2.5 percent statistical probability of occurring 

normally because of interannual variation in fall biomass; 

however, it must be noted that not all study sites in fresh 

marsh were dominated by P. hemitomon prior to or after 

Hurricanes Katrina and Rita. Although the indirectly impacted 

sites had fall biomass that was below the long-term average, 

they were within one standard deviation and represent normal 

interannual variation in fall biomass. Two years after the 

hurricanes, fall biomass in the directly impacted sites was very 

similar to that in the indirectly impacted sites, and all sites had 

an average fall biomass within the range of normal interannual 

variation.

Of the sites with historical prestorm data, total 

aboveground biomass at the end of growing seasons after 

the hurricanes did not differ significantly from historically 

recorded values at any site except CRMS0605-H 

(p = 0.0005, fig. 17). Following the hurricanes of 2005, total 

and live aboveground biomass at CRMS0605-H decreased 

significantly from the values obtained at the end of the 

growing seasons in 2003 and 2004; however, the marked 

decrease in both live and total biomass in fall 2006 was not 

statistically different from the biomass measured in 2002. 

Total aboveground biomass ranged from 102.67 ± (13.92) g 

dry weight m-2 at CRMS0605-H to 1,102.00 ± (89.67) g dry 

weight m-2 at CRMS0268-H. Some sites did experience a 

substantial reduction in the live component of aboveground 

biomass after the storms (CRMS0294-H, CRMS0128-H), but 

these differences were not statistically significant. As was 

observed with species dominance, there was not a consistent 

response among fresh marsh sites in total or live aboveground 

biomass before and after the storms. Peak biomass at 

indirectly impacted fresh marsh sites (917 g dry weight m-2) 

was significantly greater than at the directly impacted sites 

(424 g dry weight m-2). There was no significant difference 

in peak biomass between years or a significant interaction 

between year and type of hurricane influence in the fresh 

marsh sites (table 9; fig. 18). The hurricanes had a significant 

negative impact on biomass in the fresh marshes within the 

directly influenced area that lasted for at least two growing 

seasons after the hurricanes. 

Estimates of aboveground and belowground biomass 

within specific vegetation types before and after Hurricanes 

Katrina and Rita are provided in table 8. According to 

estimates provided in the literature, live aboveground 

biomass at the end of the growing season in fall 2006 (first 

growing season after the storms) was lower than historical 

estimates but within the range of variability. In fall 2007, the 

mean value of live aboveground biomass increased and was 

within the range observed in other prestorm studies reported 

in the literature.

Total (live and dead) aboveground biomass at fresh 

marsh sites at the end of growing seasons ranged from 102.67 

to 1,998.80 g dry weight m-2 in 2006 and 2007. Mean values 

of total aboveground biomass among all fresh marsh sites 

averaged 802.50 (± 127.94) g dry weight m-2 in 2006 and 

increased to 904.06 (± 124.10) g dry weight m-2 in 2007. In 

both growing seasons, total aboveground biomass at the end 

of growing seasons was greater at CRMS0268 than at all other 

fresh marsh sites (fig. 19). Similar trends in total aboveground 

Table 6. Results of analysis of variance testing for aboveground 

biomass from nondisturbance species in fresh and brackish/

intermediate marsh types. 

[Hurricane influence is defined as direct or indirect. P-values less than 0.05 

indicate significant differences. n, number; p, p-value]

Marsh type Factor p

Fresh Marsh (n=70) Hurricane influence 0.0112

Year 0.1644

Hurricane influence by year 0.2089

Brackish/Intermediate 

Marsh (n=70)

Hurricane influence 0.3124

Year 0.7277

Hurricane influence by year 0.7801
Results and Discussion 27

2006

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

0

20

40

60

80

100

W C E

W C E

2007

Site

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Biomass of disturbance and nondisturbance species, by percent

0

20

40

60

80

100

Figure 13. Percentages 

of biomass composed of 

disturbance (black bars) 

versus nondisturbance (gray 

bars) species at fresh marsh 

sites in 2006 and 2007. Sites 

with “H” designations were 

historically sampled by 

various research projects, 

and sites without “H” 

designations are within 

the Coastwide Reference 

Monitoring System (CRMS). 

Western (W) and eastern (E) 

regions of Louisiana were 

affected by direct hurricane 

influence and the central (C) 

region by indirect influence.
28 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 14. Species composition of biomass harvested at Coastwide Reference Monitoring System sites 0128 and 0128-H by season.
Results and Discussion 29

Figure 15. Species composition of biomass harvested at sites CRMS0605 and CRMS0605-H by season. 
30 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Table 7. Results of analysis of variance testing for live aboveground biomass at the end of growing seasons in fresh, brackish/

intermediate, and saline marsh types. 

[Hurricane influence is defined as direct or indirect. P-values less than 0.05 indicate significant differences. n, number; p, p-value]

Marsh type Factor p

Fresh marsh (n=72) Hurricane influence 0.0099

Year 0.0739

Hurricane influence by year 0.4077

Brackish/Intermediate marsh (n=72) Hurricane influence 0.0917

Year 0.0586

Hurricane influence by year 0.3778

Saline marsh (n=36) Hurricane influence 0.0176

Year 0.3985

Hurricane influence by year 0.5037

Figure 16. Live aboveground biomass is displayed for each habitat type by level of hurricane influence and year. Mean values and 

standard errors are presented for the end of growing seasons in 2006 (black bars) and 2007 (gray bars).
Results and Discussion 31

Table 8. Comparisons of aboveground and belowground biomass among different marsh types before and after Hurricanes Katrina 

and Rita.

[Unit of measurement for biomass is grams of dry weight per square meter. NA, not available; La., Louisiana; Ga., Georgia; SE, Standard error. Numbers 

listed in the ""study"" column denote the following studies: (1) Visser and others, 1996; (2) Schubauer and Hopkinson, 1984; (3) Darby and Turner, 2008; 

(4) Turner and others, 2004; (5) Gross and others, 1991; (6) Swarzenski and others, 2008; (7) Hopkinson and others, 1978; (8) Moerschbaecher, 2008; 

(9) this study]

Marsh type Dominant vegetation

End-of-growingseason live 

aboveground 

biomass 

mean value (SE)

End-of-growingseason total 

belowground 

biomass 

mean value (SE) Location Study Notes

Fresh Panicum hemitomon 845 (285) NA La. 1 Prestorms

Panicum hemitomon 538 (31) NA La. 6 Prestorms, Barataria basin

Panicum hemitomon 504 (30) NA La. 6 Prestorms, Penchant basin

Panicum hemitomon, 

Typha sp., Leersia 

oryzoides

403 (78) 5,242 (341) La. 9 Poststorms, end of 

growing season 2006

Panicum hemitomon, 

Typha sp., Leersia 

oryzoides

570 (78) 5,862 (503) La. 9 Poststorms, end of 

growing season 2007

Brackish/

Intermediate Spartina patens 835 (374) NA La. 1 Prestorms

Spartina patens 2,400 NA La. 7 Prestorms, estimate 

from graph

Spartina patens 693 NA La. 8

Poststorms, end of 

growing season 2006, 

estimate from graph

Spartina patens 715 (124) 4,682 (300) La. 9 Poststorms, end of 

growing season 2006

Spartina patens 1,321 (213) 4,804 (399) La. 9 Poststorms, end of 

growing season 2007

Saline Spartina alterniflora 924 (307) NA La. 1 Prestorms

Spartina alterniflora 800 4,900 Ga. 2 Prestorms, estimate 

from graph

Spartina alterniflora NA 4,500 La. 3 Prestorms, estimate 

from graph

Spartina alterniflora 600 1,800 La. 4 Prestorms, estimate 

from graph

Spartina alterniflora 651 (89) NA Ga. 5

Prestorms, mean from 

June, July, Aug., Sept., 

Oct. and Mar.

Spartina alterniflora 1,042 (184) 6,404 (629) La. 9 Poststorms, end of 

growing season 2006

Spartina alterniflora 884 (149) 7,659 (496) La. 9 Poststorms, end of 

growing season 2007
32 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Year

Fall 2002

Fall 2003

Fall 2004

Fall 2006

Fall 2007

0

200

400

600

800

1,000

1,200

1,400

1,600

2,000

2,200

2,400

CRMS0605-H

A

AB

C

BC

BC

Fall 2002

Fall 2003

Fall 2004

Fall 2006

Fall 2007

Total and live aboveground biomass, 

in grams of dry weight per square meter

0

200

400

600

800

1,000

1,200

1,400

1,600

CRMS0268-H

Fall 1993 Fall 2006 Fall 2007

0

200

400

600

800

1,000

1,200

1,400

1,600

CRMS0219-H

Fall 1993 Fall 2006 Fall 2007

0

200

400

600

800

1,000

1,200

1,400

1,600

CRMS0294-H

Fall 1999 Fall 2006 Fall 2007

0

200

400

600

800

1,000

1,200

1,400

1,600

CRMS0128-H

Total and live aboveground biomass, 

in grams of dry weight per square meter

Total and live aboveground biomass,

 in grams of dry weight per square meter

Year

Year Year

Year

Figure 17. Total (white bars) and live (gray bars) aboveground biomass at fresh marsh sites for which historical data were compared 

with data from Coastwide Reference Monitoring System (CRMS) sites. Different letters indicate significant differences in total 

aboveground biomass (p < 0.05). Historical data are from Sasser and others, 1994; Holm, 2006; and Twilley and Nyman, 2000.
Results and Discussion 33

Table 9. Results of analysis of variance testing for peak aboveground biomass in fresh, brackish/intermediate, and saline marsh types. 

[Hurricane influence is defined as direct or indirect. P-values less than 0.05 indicate significant differences. n, number; p, p-value]

Marsh type Factor p

Fresh marsh (n=24) Hurricane influence 0.0005

Year 0.8001

Hurricane influence by year 0.7542

Brackish/Intermediate marsh (n=24) Hurricane influence 0.9781

Year 0.1849

Hurricane influence by year 0.2909

Saline marsh (n=12) Hurricane influence 0.1688

Year 0.9909

Hurricane influence by year 0.6659

Figure 18. Peak aboveground biomass at the end of growing seasons in 2006 and 2007 for each habitat type by hurricane influence 

(direct versus indirect) and year. Mean values and standard errors are presented for 2006 (black bars) and 2007 (gray bars).
34 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Total aboveground biomass, 

in grams of dry weight per square meter

0

1,000

2,000

3,000

4,000

5,000

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

Total aboveground biomass, 

in grams of dry weight per square meter

0

1,000

2,000

3,000

4,000

5,000

Sites

CRMS0326

CRMS0326-H

CRMS0164

CRMS0164-H

CRMS0147

CRMS0147-H

Total aboveground biomass, 

in grams of dry weight per square meter

0

1,000

2,000

3,000

4,000

5,000

Fresh marsh

Brackish/Intermediate marsh

Saline marsh

C E

W C E

W C E

Figure 19. Total aboveground biomass 

(see standard error bars) at the end 

of growing seasons in 2006 (black 

bars) and 2007 (gray bars) at fresh, 

brackish/intermediate, and saline 

marsh sites. Sites with “H” designations 

were historically sampled by various 

research projects, and sites without “H” 

designations are within the Coastwide 

Reference Monitoring System (CRMS). 

Western (W), central (C), and eastern (E) 

regions of Louisiana are represented.
Results and Discussion 35

biomass and total vegetation cover were observed at individual 

fresh marsh sites between fall 2006 and fall 2007, except at 

CRMS0128 where total biomass decreased in 2007 while 

cover increased. In 2006, CRMS0128 had multiple layers 

of aboveground biomass with a substantial amount of dead 

biomass, but by 2007 the aboveground dead biomass was 

much lower (about 33 percent) than in 2006.

Total belowground biomass at fresh marsh sites at the 

end of growing seasons ranged from 3,494.09 to 9,080.65 

g dry weight m-2 in 2006 and 2007 (fig. 20). In 2006, total 

belowground biomass at the end of the growing season 

averaged 5,242.75 (± 341.29) g dry weight m-2, while in 

2007 it increased slightly to 5,862.13 (± 503.87) g dry weight 

m-2. Belowground biomass at fresh marsh sites at the end of 

growing seasons differed significantly by hurricane influence, 

with directly influenced sites having less biomass 

(6,653.41 ± 433.44 g dry weight m-2) than indirectly 

influenced sites (8,250.26 ± 766.24 g dry weight m-2) 

(table 10, fig. 21). There was no significant difference in 

belowground biomass at the end of growing seasons by year 

or by the interaction of hurricane influence and year. Of all of 

the fresh marsh sites, CRMS0605 had the lowest amount of 

belowground biomass in 2006, which increased only slightly 

in 2007. Overall, the central region tended to have greater 

biomass in 2007 than the other regions; however, biomass 

at CRMS0219 and CRMS0219-H in 2007 was similar to 

the western and eastern regions. The decrease in fall-season 

belowground biomass between 2006 and 2007 at CRMS0128 

and CRMS0128-H is consistent with the decrease observed 

in aboveground biomass. These sites (CRMS0128 and 

CRMS0128-H) were subjected to storm surge greater than 4 

m from Hurricane Katrina and were located in an area where 

massive soil upheaval and erosion caused by this hurricane 

produced new open-water areas (Barras, 2006). The new 

open-water areas are exposed to increased inundation, which 

may explain the decrease in S. patens after Hurricanes Katrina 

and Rita. Increased inundation can reduce the productivity 

of S. patens (Burdick and Mendelssohn, 1987; Spalding and 

Hester, 2007) or may limit its reestablishment.

Belowground biomass at the end of growing seasons 

before and after the storms was compared at three fresh marsh 

study sites where available historical data exists for total and 

live belowground biomass (fig. 22). It is important to note 

that historical estimates of belowground biomass were from 

studies conducted with different methods than those presented 

in the current study. At CRMS0219-H and CRMS0294-H, 

historical measurements were made from 0- to 25-cm deep, 

while this study included measurements of the top 24 cm. At 

CRMS0268-H, the historical measurements were made from 

0- to 15-cm deep, and the current study included measurement 

of the top 16 cm. Because the depth profiles included in the 

previous studies were within 1 cm of our measurements, 

we decided to present the comparisons (fig. 22). After the 

hurricanes, live belowground biomass at the end of growing 

seasons at these sites ranged from 738 to 3,601 g dry weight 

m-2. The lowest and highest estimates of live belowground 

biomass after the storms occurred at CRMS0219-H, 

illustrating the site-specific, interannual variability that 

can occur with belowground biomass data. Live and total 

belowground biomass estimates from before and after the 

hurricanes were similar among all three study sites (p > 0.05). 

Although the mean value of live belowground biomass 

decreased between fall 2006 and fall 2007 at CRMS0219-H 

and CRMS0294-H, the differences were not statistically 

significant. Data from these sites indicated that belowground 

biomass was not significantly influenced by the hurricanes of 

2005. There was evidence, however, of localized losses in 

belowground biomass from CRMS0605-H (see case study 1).

Brackish/Intermediate Marsh Sites

Porewater salinity at the end of growing seasons 

generally decreased from 2006 to 2007 at all brackish/

intermediate marsh sites except CRMS0651 and 

CRMS0672-H, where salinity was slightly greater in 2007 

(fig. 10). There was no significant difference in mean values 

of porewater salinity at the end of growing seasons between 

2006 (12.1 ± 0.9) and 2007 (9.5 ± 1.0) or by hurricane 

influence or the interaction of year and hurricane influence 

(fig. 9, table 4). Changes in porewater salinity from 2006 to 

2007 varied by site, with the greatest difference occurring 

at CRMS0669 (that is, a decrease of 8.9 between 2006 

and 2007). Porewater salinities were typically greater in 

the western region as compared to the eastern and central; 

however, the majority of brackish/intermediate marsh sites 

were in the western region. The largest deviations from 

historical values of porewater salinity occurred in brackish/

intermediate marsh. At the end of the growing season in 2007, 

five brackish/intermediate marsh sites exhibited porewater 

salinities greater than one standard deviation above historical 

estimates (table 5).

The mean value of total cover by live vegetation was 

greater in fall 2007 (89.58 ± 5.05%) than in fall 2006 

(67.72 ± 8.82%) among all brackish/intermediate marsh sites 

but did not differ statistically (fig. 11). At sites monitored by 

CWPPRA in 2003 and 2004, live cover was 78.4 percent at 

all intermediate sites and 75.4 percent at all brackish marsh 

sites. Based on these historical CWPPRA data, live cover 

after Hurricanes Katrina and Rita was greater in the second 

growing season than before the hurricanes. At our study sites, 

the greatest difference between the vegetation cover at the 

end of growing seasons in 2006 and 2007 was observed at 

CRMS0672-H, where it increased by 85 percent. The only 

sites that decreased in live cover from 2006 were CRMS0610 

and CRMS0312-H. Overall, the largest differences between 

values estimated at the end of growing season occurred in the 

western region of Louisiana. These large differences could be 

attributed to the persistence of salinity stress during the 2006 

growing season and a subsequent decrease in salinity in 2007 

(appendix figs. 1-11 and 1-13) in the western sites. There 

were no statistical differences in total live cover at the end 

of growing season between years, hurricane influence, or the 

interaction of years and hurricane influence (p > 0.05).
36 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

W

W

C E

Fresh marsh

CRMS0605

CRMS0605-H

CRMS1277

CRMS1277-H

CRMS0294

CRMS0294-H

CRMS0268

CRMS0268-H

CRMS0219

CRMS0219-H

CRMS0128

CRMS0128-H

Total belowground biomass,

 in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000 W C E

W C E

Brackish/Intermediate marsh

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

Total belowground biomass,

 in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000

Saline marsh

Sites

CRMS0326

CRMS0326-H

CRMS0164

CRMS0164-H

CRMS0147

CRMS0147-H

Total belowground biomass,

 in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000

Figure 20. Total belowground biomass (see standard error bars) at the end of growing seasons in 2006 (black bars) and 2007 (gray 

bars) at fresh, brackish/intermediate, and saline marsh sites. Sites with “H” designations were historically sampled by various research 

projects, and sites without “H” designations are within the Coastwide Reference Monitoring System (CRMS). Western (W), central (C), 

and eastern (E) regions of Louisiana are represented.
Results and Discussion 37

Table 10. Results of analysis of variance testing for total belowground biomass at the end of growing seasons in fresh, brackish/

intermediate, and saline marsh types.

[Hurricane influence is defined as direct or indirect. P-values less than 0.05 indicate significant differences. Belowground biomass was the dependent variable 

for p-values. n, number; p, p-value]

Marsh type Factor p

Fresh marsh (n=72) Hurricane influence 0.0044

Year 0.2286

Hurricane influence by year 0.1326

Brackish/Intermediate marsh (n=66) Hurricane influence 0.3092

Year 0.3354

Hurricane influence by year 0.0866

Saline marsh (n=33) Hurricane influence 0.1511

Year 0.2773

Hurricane influence by year 0.9650

Marsh type by hurricane Influence

Fresh direct

Fresh indirect

Brack/Intermediate direct

Brack/Intermediate indirect

Saline direct

Saline indirect

Belowground biomass, 

in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000

Figure 21. Mean 

values of belowground 

biomass (see standard 

error bars) for each 

marsh type by hurricane 

influence (direct or 

indirect) and year. 

Values are for the end 

of growing seasons in 

2006 (black bars) and 

2007 (gray bars). 
38 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

CRMS0219-H

1993 2006 2007

0

2,000

4,000

6,000

8,000

10,000

CRMS0268-H

1993 2006 2007

Belowground biomass, in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

Fall 1993 Fall 2006 Fall 2007

0

2,000

4,000

6,000

8,000

10,000

CRMS0294-H Figure 22. Total (white bars) and live 

(gray bars) belowground biomass at 

fresh marsh sites at the end of growing 

seasons. Sites within the Coastwide 

Reference Monitoring System (CRMS) 

were selected based on availability of 

historically sampled data (sites with 

“H” designations) from Sasser and 

others, 1994. Historical measurements 

were taken at 0–25-cm depths at 

CRMS0219-H and CRMS0294-H, while 

our measurements at these sites in 

2006 and 2007 were made at 0–24-cm 

depths. At CRMS0268-H, historical 

measurements were made at 0–15 cm, 

while our measurements in 2006 and 

2007 were made at 0–16-cm depths.
Results and Discussion 39

In fall 2006, the relative cover of disturbance taxa relative 

to nondisturbance taxa was 10.12 percent, slightly greater than 

in fall 2007 at 8.95 percent. Although the mean value of cover 

by disturbance taxa relative to nondisturbance taxa was greater 

at the end of the growing season in 2006 than at the end of 

the growing season in 2007, there was an increase in the 

number of sites exhibiting disturbance taxa in 2007 (fig. 23). 

Sites with disturbance taxa occurred in both the directly and 

indirectly influenced areas. At the end of the growing season 

in both years, CRMS0135 had the greatest percentage of cover 

by disturbance taxa (that is, greater than 50 percent) when 

compared to all brackish/intermediate marsh sites (see case 

study 2 for additional information).

In brackish/intermediate marshes, we detected no 

significant impact of hurricanes or year on the percentage 

of disturbance taxa observed in live aboveground biomass 

(table 6). On average, 5 percent of the brackish/intermediate 

marsh biomass consisted of disturbance species; however, 

CRMS0135, a site in the center of the Breton Sound that 

received the full force of Hurricane Katrina, had much greater 

levels of disturbance species, with 70 percent of the biomass 

contributed by disturbance species in 2006 and 

40 percent in 2007 (fig. 24). The CRMS0135 site, which was 

an intermediate marsh site before Hurricane Katrina, was 

almost completely denuded of vegetation after the storm, 

with most of the biomass in the spring of 2006 consisting of 

A. australis (fig. 25). In contrast, the nearby site 

CRMS0135-H was not denuded, and most of the vegetation 

in the spring of 2006 consisted of S. patens. This dominance 

of S. patens is typical of brackish and some intermediate 

marshes. The difference between these two sites illustrates the 

patchiness of physical disturbance from a hurricane (Barras, 

2006), probably due to local wind eddies as well as the relative 

vigor of the site affected. In the fall of 2007, CRMS0135 was 

still dominated by species other than S. patens, the typical 

dominant species of intermediate/brackish marshes.

We detected no significant impact from the hurricanes 

related to live biomass at the end of growing seasons in the 

brackish/intermediate marsh (table 7). This lack of influence 

may be due to the experimental design, which has only two 

indirectly impacted sites that were less productive compared 

to other brackish/intermediate marsh sites (table 8). Overall, 

biomass was slightly greater in the second year after the storm 

(fig. 16); however, the difference between years was not 

statistically significant, probably because of the large variation 

in fall biomass among sites.

In the brackish/intermediate marsh, no significant 

differences were detected for peak biomass as a result of the 

variables hurricane impact, year, or the interaction of the 

two (table 9). Figure 18 shows that there was a great deal 

of variation in peak biomass, especially in the indirectly 

impacted sites. Because only two sites are classified as 

indirectly impacted, the uncertainty around the estimate is 

high, making it more difficult to detect statistical differences. 

In general, the directly impacted sites had lower peak biomass 

the first year after the storms than the indirectly impacted 

sites. In contrast, the peak biomass in the second year after 

the storms was greater in the directly impacted sites than in the 

indirectly impacted sites. 

Total (live and dead) aboveground biomass at the end of 

growing seasons ranged from 218.67 to 3,931.63 g dry weight 

m-2 in 2006 and 2007. The mean value of total aboveground 

biomass among all sites averaged 1,741.83 (± 244.68) g dry 

weight m-2 in 2006 and increased to 2,090.95 (± 273.11) 

g dry weight m-2 in 2007 (fig. 19). The greatest change 

between estimates at the end of growing seasons occurred 

at CRMS0610-H, where total biomass increased more than 

fourfold between the two growing seasons. Changes in total 

aboveground biomass at the end of growing seasons were 

inconsistent, with some sites having increased biomass at the 

end of the growing season in 2007 and some having decreased 

biomass. For example, the mean value of total biomass 

decreased between fall 2006 and fall 2007 at 5 of the 12 

brackish/intermediate marsh sites (fig. 19). 

Among all brackish/intermediate marsh sites, 

belowground biomass at the end of growing seasons averaged 

4,682.55 (± 300.28) g dry weight m-2 in 2006 and 4,804.32 

(± 399.36) g dry weight m-2 in 2007 (fig. 20). Sites within 

areas directly and indirectly influenced by the hurricanes 

had similar values in 2006 and 2007 (table 10, fig. 21). The 

largest within-site change was observed at CRMS0312, with 

biomass decreasing from 4,857.33 to 2,220.11 g dry weight 

m-2 between 2006 and 2007. At the site level, no consistent 

pattern in belowground biomass was observed between the 

two growing seasons.

Live aboveground biomass in brackish/intermediate 

marshes at the end of the growing season in fall 2007 was 

greater than prestorm literature values (table 8), suggesting 

that there was no negative influence from Hurricanes Katrina 

and Rita in these marsh types. Aboveground biomass 

estimates are, however, sensitive to dominant vegetation taxa 

and site-specific heterogeneity (for example, streamside versus 

interior marsh and impaired versus healthy marsh) and are 

highly variable across landscapes (Ellison and others, 1986). 

Furthermore, historical data collected before the hurricanes 

were limited, thus limiting comparisons of conditions before 

and after the storms. We caution, therefore, that broad 

conclusions regarding the influence of the hurricanes on 

aboveground biomass should not be drawn based on these 

limited data. 

Saline Marsh Sites

Porewater salinity at saline marsh sites at the end of 

growing seasons was significantly greater in 2006 (21.3 ± 1.6) 

than in 2007 (15.7 ± 1.9) (fig. 10, table 4). Interestingly, sites 

within the area of direct hurricane influence had significantly 

lower porewater salinity (12.4 ± 2.5) than those in areas of 

indirect influence (21.2 ± 1.2) (fig. 9). The interaction of 

variables year and hurricane influence was also statistically 

significant. This significance is likely due to the influence of 

freshwater from the Mississippi River upon salinity at the only 
40 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

2006

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

Cover, by percent

0

20

40

60

80

100

W C E

2007

Sites

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

Cover, by percent

0

20

40

60

80

100

W C E

Figure 23. Cover of disturbance 

(black bars) taxa relative to 

nondisturbance taxa (gray bars) in 

emergent vegetation at brackish/

intermediate marsh sites at the 

end of growing season in 2006 and 

2007. Sites with “H” designations 

were historically sampled by 

various research projects, and 

sites without “H” designations are 

within the Coastwide Reference 

Monitoring System (CRMS). 

Western (W), central (C), and 

eastern (E) regions of Louisiana 

are represented.
Results and Discussion 41

W C E

Biomass of disturbance and nondisturbance species, by percent

Site

2007

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

0

20

40

60

80

100

2006

CRMS0669

CRMS2156

CRMS0651

CRMS0651-H

CRMS0672

CRMS0672-H

CRMS0610

CRMS0610-H

CRMS0312

CRMS0312-H

CRMS0135

CRMS0135-H

0

20

40

60

80

100

W C E

Figure 24. Percentages of 

biomass in disturbance (black bars) 

versus nondisturbance (gray bars) 

species at brackish/intermediate 

marsh sites for 2006 and 2007. 

Sites with “H” designations were 

historically sampled by various 

research projects, and sites without 

“H” designations are within the 

Coastwide Reference Monitoring 

System (CRMS). Western (W) and 

eastern (E) regions of Louisiana 

were affected by direct hurricane 

influence and the central (C) region 

by indirect influence.
42 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 25. Species composition of biomass harvested at Coastwide Reference Monitoring System (CRMS) sites 0135 and 0135-H 

by season. 

pair of saline marsh sites directly affected by the hurricanes 

(CRMS0147 and CRMS0147-H) (Wiseman and others, 1990). 

Of the six saline marsh sites, porewater salinity was greatest 

at CRMS0164 and CRMS0164-H at the end of both growing 

seasons after the hurricanes. At CRMS0164-H, mean values 

for salinity at the end of the growing season in 2007 were 

greater than two standard deviations above the porewater 

salinity estimates for saline habitats observed by Chabreck 

(1972) (table 5). In fall 2007, porewater salinity at the 

remaining sites was typical of saline marsh habitats.

Total vegetation cover at the end of growing seasons 

was greater than 60 percent at all saline marsh sites in both 

2006 and 2007 (fig. 11). The lowest value for cover the end 

of a growing season was observed at CRMS0326 (65 percent) 

in fall 2006, but in fall 2007 all saline marsh sites had total 

cover greater than or equal to 85 percent. Little change was 

observed in total cover at saline marsh sites throughout the 

study period. (See the case studies section of this report for 

specific details related to CRMS0164-H and CRMS0326-H.) 

The total cover consistently comprised taxa typical of saline 
Results and Discussion 43

habitats. No disturbance taxa were observed at 

any of the saline marsh sites during any sampling 

period throughout the study (fig. 26).

In the saline marsh sites, live aboveground 

biomass at the end of growing seasons was 

significantly greater in the directly impacted sites 

(1,208 g dry weight m-2) (that is, eastern region) 

than in the indirectly impacted sites 

(841 g dry weight m-2; table 7; fig. 16). No 

significant difference among years was 

observed, and the interaction between variables 

of hurricane influence and year was also not 

significant. This lack of statistical difference is 

probably due to the small sample size. Biomass 

in the directly impacted sites was approximately 

one standard deviation above the long-term 

average for S. alterniflora sites in the Leeville 

area, located within the indirectly influenced 

area. This indicates that the hurricanes had a 

positive effect on saline marshes in terms of 

plant biomass, and this effect lasted for at least 

2 years after the storms; however, only two of 

the six saline marsh sites were in the zone of 

direct influence (eastern region). The positive 

effects on plant biomass may be explained by 

the deposit of sediments onto the saline marsh 

during the hurricanes (Turner and others, 2006).

Total aboveground biomass at the end of 

growing seasons ranged from 957.3 (± 377.7) to 

2,889.3 (± 1,096.1) g dry weight m-2, with the 

greatest values at CRMS0164 in fall 2006 and 

the lowest at CRMS0326-H in fall 2007 (fig. 19). 

In both growing seasons, CRMS0164 produced 

the greatest biomass. Sites in both the directly 

and indirectly influenced areas produced similar 

aboveground biomass, as was reflected in the 

peak biomass (fig. 18). 

Hurricanes Katrina and Rita did not 

influence site-specific species dominance or 

total aboveground biomass at the two study sites 

with available historical data (CRMS0164-H 

or CRMS0326-H). The dominant vegetation 

species was S. alterniflora before and after the 

storms at both sites, and there were no significant 

differences between prestorm and poststorm 

calculations of total aboveground biomass at the 

end of growing seasons. At both these saline 

marsh sites, the mean value of total aboveground 

biomass was greater at the end of the growing 

season in 2006 than in 2007, and the difference 

was not statistically significant. 

Belowground biomass at the end of 

growing seasons increased from 6,404.74 

(± 659.64) g dry weight m-2 in 2006 to 7,659.06 

(± 496.23) g dry weight m-2 in 2007 among 

all saline marsh sites (fig. 20). No significant 

differences occurred in belowground biomass by 

Fresh marsh

0

20

40

60

80

100

Brackish/Intermediate marsh

0

20

40

60

80

100

2006 2007 2006 2007

Direct Indirect

Saline marsh

0

20

40

60

80

100

Biomass of disturbance and nondisturbance species, by percent

Figure 26. Percentages of biomass from disturbance (black bars) and 

nondisturbance (gray bars) species in 2006 and 2007 for each marsh type by 

hurricane influence (direct or indirect).
44 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

variables of year, hurricane influence area, or the interaction of 

year and hurricane influence area (table 10, fig. 21). With the 

exception of CRMS0326-H, belowground biomass increased 

at all sites in the second growing season. Total belowground 

biomass at saline marsh sites at the end of growing seasons 

was greater after the storms than before, according to the 

published prestorm values (table 8). Although prestorm and 

poststorm estimates were all collected in marshes dominated 

by S. alterniflora, site-specific heterogeneity (for example, 

streamside versus interior marsh and impaired versus healthy 

marsh) may explain the variability between our study and 

previously published estimates.

Case Studies

This section includes a series of case studies for specific 

study sites. Site selection for case studies was based on 

habitat type, hurricane influence, and availability of historical 

data. We included CRMS0605-H and CRMS1277-H, which 

are located in fresh marsh habitats within the chenier plain 

(for definitions of the Louisiana chenier and deltaic plains, 

see Saucier, 1994). The CRMS0605-H site was directly 

influenced by Hurricane Rita and was exposed to a prolonged 

period of elevated salinities after the hurricanes, resulting in 

changes to the species composition of emergent vegetation. 

For both sites, there was availability of historical vegetation 

and salinity data. The CRMS1277-H site is located in 

proximity to the path of Hurricane Rita and was classified as 

being in the area of direct hurricane influence, but it was only 

marginally impaired by the storm because changes in species 

composition and elevations in salinity were not observed at 

the site. Within brackish/intermediate marshes, CRMS0135 

and CRMS0672-H are presented. Both sites were directly 

influenced by physical-biological disturbances associated with 

Hurricanes Katrina and Rita. Although no historical data were 

available from the exact location of these sites, hydrologic 

and vegetation data were available from sites located within 

proximity to these locations (paired sites). Saline marsh sites 

CRMS0326-H and CRMS0164-H were indirectly influenced 

by the hurricanes, and there were site-specific historical data 

for both sites, allowing for comparisons of data acquired 

before and after the hurricanes.

Case Study 1: CRMS0605-H and CRMS1277-H

Overall Site Description

The CRMS0605-H and CRMS1277-H sites are located 

in freshwater marshes near the Mermentau River and Grand 

Lake and have highly organic soils that are relatively isolated 

from freshwater exchange with the river and the lake 

(fig. 27). Instead, the semi-impounded hydrology of these 

marshes, which naturally arises from chenier confinement 

and a variable degree of artificial hydrologic management, 

is controlled by local rainfall (Gammill and others, 2001). 

Short-term, periodic introduction of the Mermentau River to 

the marshes south of Lake Misere and north of Little Chenier 

has been observed when canal plugs are removed for oil and 

gas exploration (G. Holm, oral commun.). Otherwise, these 

marshes are typically blackwater areas with limited connection 

to Grand Lake and the Gulf Intracoastal Waterway.

An interesting attribute of freshwater marshes in the 

chenier plain is their extensive plant coverage and the 

absence of significant areas of open water, save small 

potholes and narrow trenasses (Davis, 1976). Panicum 

hemitomon (maidencane) often forms uninterrupted, densely 

vegetated prairie. This species tolerates periodic fire and a 

broad range of water levels, but it has practically no tolerance 

for salt (Holm and Sasser, 2008). The largest, robust stands 

of maidencane occur in purely freshwater areas of the 

chenier plain.

Prior to Hurricanes Katrina and Rita, CRMS0605-H was 

a freshwater herbaceous marsh dominated by P. hemitomon, 

with interspersed patches of Morella cerifera (wax myrtle), 

Schoenoplectus tabernaemontani (softstem bullrush), and 

Phragmites australis (common reed) (Holm and others, 2003; 

Holm, 2006). Some of the marsh was buoyant (a 1.0-cm 

vertical adjustment of marsh water level corresponded to 

0.86-cm vertical adjustment of marsh mat), but there was high 

spatial variability because some areas were attached to a clay 

lens occurring at depth of 90 cm (Holm and others, 2003). 

The transition between attached and detached marsh was 

gradual, such that the mat was not separated or fragmented.

Salinity Before and After the Storms

Based on continuous water-level and salinity records 

from 2001 to early 2005, surface salinity never exceeded 

0.5; however, anecdotal evidence suggests that low-level salt 

exposure to this site occurred during the 1999–2000 drought. 

Before Hurricane Rita, from July to September 2005 surface 

salinity increased and reached 9.2 on September 13, 2005, 

when a point sample was collected (the gage record was 

not complete for this time period) (fig. 28). The surfacewater salinity increase was due to an opening of a water 

control structure on the Mermentau River above the Catfish 

Locks during an intense, localized drought in the summer 

of 2005. The introduction of saltwater to the marshes was a 

management measure to reduce noxious growth of submerged 

aquatic plants (R. Vincent, oral commun., 2005). Peak salinity 

associated with the Hurricane Rita is unknown. Two full years 

after the storms, salinity remained elevated (> 1.5) compared 

to the original background levels (< 0.5) at this site.

Plant Biomass Before and After the Storms

Before Hurricane Rita, the vegetation community at 

CRMS0605-H, which was dominated by P. hemitomon, had 

a total aboveground biomass of 1,340 g dry weight m-2 in 

2003 and 2,035 g dry weight m-2 in 2004. Live belowground 

biomass within the upper 15 cm (measured with in-growth 

cores) was 807 g dry weight m-2 in 2003 and 962 g dry weight 
Results and Discussion 45 Figure 27. Locations of Coastwide Reference Monitoring System (CRMS) sites 0605-H, 0605, 1277-H, and 1277 within the Lake Misere and Mermentau River watershed. Sites with “H” designations were historically sampled by various research projects, and sites without “H” designations are within the CRMS. There is limited exchange of the Mermentau River with the interior marshes of Lake Misere except when plugs are removed for episodic oil drilling activities. The interior Lake Misere marshes are isolated blackwater areas where rainfall largely determines the local hydrology.
46 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

m-2 in 2004. Complete mortality of the plant community had 

occurred throughout fall and winter 2005, such that by spring 

2006, a bare mat of peat was exposed with only some dead 

plant stubble remaining (fig. 29). By the end of the second 

growing season after Hurricanes Katrina and Rita 

(in fall 2007), live aboveground and belowground biomass 

were approximately one-half that before the storms 

(figs. 30 and 31).

The delayed colonization and poor plant growth 

following Hurricane Rita resulted in a potentially significant 

loss of organic matter to the soil. We used two other sites 

dominated by P. hemitomon to calculate the potential loss 

of organic matter to the soil, the premise being that these 

sites were comparable in dominant-species composition and 

provide an estimate of the potential loss in plant production 

that occurred at CRMS0605-H. We chose an adjacent site in 

the chenier plain that was within the region of direct hurricane 

influence, as defined by this study, but was only marginally 

impaired by Hurricane Rita (White Lake, CRMS1277-H), 

and a deltaic plain site (Lake Boeuf, CRMS0268-H) that was 

indirectly affected by Hurricane Rita in the central region of 

the study area. These two sites were selected based on our 

historical understanding of the stability of their communities 

(Holm, 2006). Comparisons of seasonal, live aboveground 

and belowground biomass among these sites were used to 

calculate potential organic matter deficits. The potential 

organic matter deficit was calculated by summing seasonal 

differences between the highly impacted site (CRMS0605-H) 

and the two other sites (CRMS0268-H and CRMS1277-H). 

We estimated a deficit of aboveground biomass at 

CRMS0605-H ranging between 2,091 and 2,915 g dry 

weight m-2 (figs. 32 and 33) and a belowground biomass deficit 

ranging between 3,385 and 8,814 g dry weight m-2 (figs. 34 

and 35). Given the long interval of minimal plant production, 

a cumulative deficit of live biomass over the 2 years of storm 

recovery was estimated to be between 5,400 and 11,700 g dry 

weight m-2.

A potential loss of live belowground biomass over this 

period (calculation based on 5,400 g dry weight m-2 = organic 

matter deficit; soil density = 0.1 g cm-3; 32-cm soil depth) 

Figure 28. Continuous and discrete samples of porewater salinity taken from 30 cm deep at Coastwide Reference Monitoring System 

(CRMS) site 0605-H from 2005 to 2007. Data from before August 2005 was collected with a continuous recorder that quit working; 

subsequent measurements are discrete. The first discrete measurement of elevated porewater salinity (9.2) was collected on 

September 13, 2005, approximately 11 days before Hurricane Rita made landfall. Prior to the storm, a local drought was developing, and 

the typically freshwater marshes of Lake Misere (see fig. 27) were exposed to high salinity because of the opening of a water control 

structure on the Mermentau River above Catfish Locks. 
Results and Discussion 47

A

B

C

Figure 29. The plant community at Coastwide 

Reference Monitoring System (CRMS) site 0605-H 

before and after Hurricane Rita. A, Before Hurricane 

Rita the site was dominated by Panicum hemitomon

(maidencane) which created a productive prairie that 

was mostly bouyant. Wax myrtle (Morella cerifera) 

and common reed (Phragmites australis) created 

moderate size patches. Clonal, salt intolerant species 

typically comprised the freshwater interior marsh 

community of the chenier plain (for definition, see 

Saucier, 1994). B, One year after Hurricane Rita there 

was extensive mortality of the marsh and limited plant 

recolonization due to a relatively high and lengthy 

residence of salt in the marsh peat. C, There was a 

potential loss of plant biomass over time. Limited 

plant recolonization resulted in a cumulative deficit 

of aboveground and belowground organic matter to 

the marsh over two years which is conservatively 

estimated at greater than 5,400 grams of dry weight 

per square meter.
48 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

2003-2004 2006 2007

Live biomass, in grams of 

dry weight per square meter

0

200

400

600

800

1,000

1,200

1,400

2003-2004 2006 2007

Dead biomass, in grams of 

dry weight per square meter

0

200

400

600

800

1,000

1,200

1,400

Year

2003-2004 2006 2007

Total biomass, in grams of 

dry weight per square meter

0

500

1,000

1,500

2,000

2,500

Figure 30. Aboveground live, dead, and total biomass (see standard error bars) at the end of growing seasons at Coastwide 

Reference Monitoring System (CRMS) site 0605-H before Hurricanes Katrina and Rita (mean values for 2003–4) and two years 

thereafter (in 2006 and 2007). There was complete mortality of the plant community at the study site vicinity shortly after the passage 

of Hurricanes Katrina and Rita from August to September 2005. Total biomass production by the end of 2007 was half that measured 

in 2003–4 before the storms.
Results and Discussion 49

Year

2003-2004 2006 2007

Live belowground biomass, 

in grams of dry weight per square meter

0

200

400

600

800

1,000

1,200

0-15 cm 0-32 cm

constitutes an 11 percent loss of soil mass, which corresponds 

to a vertical loss of soil elevation of approximately 3 cm. This 

potential decrease in soil elevation, if the mat looses buoyancy 

in the future, has immediate and longer term implications for 

vegetation community change.

Plant Community Change After the Storms

Prior to Hurricane Rita, CRMS0605-H had a relatively 

rich plant community with about 18 herbaceous species in 

the general site area (300-m radius) (Holm and others, 2003). 

The most common species were P. hemitomon, Thelypteris 

palustris (eastern marsh fern), and M. cerifera. There were 

also patchy, discrete stands of P. australis and Schoenoplectus 

californicus (California bulrush). A few small (< 0.25 m2) 

patches of S. patens were noted during the 2001–5 period; 

however, this species was never considered a significant 

component of the community. Based on harvest data over 

three years, P. hemitomon composed greater than 70 percent of 

the live biomass (Holm, 2006).

At the end of the first growing season after the storms, 

there was no plant recolonization of our pre-established 

harvest plots (fig. 36). This lack of recolonization was also 

reflected at the larger landscape level in the site-specific 

departure of -0.19 (± 0.05) from the average NDVI score, 

indicating that there was a decrease in vegetation vigor from 

the baseline condition. Also at the larger landscape level, 

however, the aforementioned sparse patches of S. patens were 

noticeably expanding. This was a rare opportunity to observe 

the guerrilla growth pattern of this species into a bare area 

with little competition. Clonal expansion advanced as long 

culms (>1.5 m) lodged on the water/soil surface, followed by 

adventitious root and ramet sprouting at culm nodes (fig. 37). 

At the end of this first growing season after Hurricanes Katrina 

and Rita, small patches of Typha domingensis (southern 

cattail) and Paspalum vaginatum (seashore paspalum) were 

also expanding. 

During winter 2007, we surveyed ten discrete patches 

of three species (S. patens, Typha spp., and P. vaginatum) to 

estimate clonal expansion rates. These patches were marked 

and their diameters measured along two right-angle transects 

during the February 2007 and May 2007 sampling periods. In 

most cases, the edge of the patch where culm bases met bare 

soil was fairly abrupt. By the 2007 summer sampling, edges 

of the patches had become sufficiently obscured by newly 

emerged seedlings, which precluded any further accurate 

measurements. Spartina patens and T. domingensis had 

similar rates of clonal expansion, such that within 70 days 

an increase of 10 m2 in area was observed, while Panicum 

vaginatum remained more compact and only increased by 3 m2 

during this same time period (table 11).

Figure 31. Live belowground biomass (see standard error bars) for Coastwide Reference Monitoring System (CRMS) site 0605-H at the 

end of growing seasons before Hurricane Rita (mean values for 2003–4) and two years thereafter (2006 and 2007). Prestorm data were 

based on the upper 15 cm of the soil, whereas poststorm data were based on the upper 32 cm.
50 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 32. Live aboveground biomass at Coastwide Reference Monitoring System (CRMS) sites 1277-H and 0605-H. The CRMS1277-H 

site was exposed to marginally direct effects from Hurricane Rita, and CRMS0605-H was exposed to direct effects. The upper panel 

shows the seasonal time course of live aboveground biomass, with standard errors. The lower panel shows the seasonal deficit of live 

aboveground biomass at CRMS0605-H compared to CRMS1277-H. Comparative recovery of aboveground biomass at CRMS0605-H took 

two full growing seasons.
Results and Discussion 51

Figure 33. Live aboveground biomass at Coastwide Reference Monitoring System (CRMS) sites 0605-H and 0268-H. The CRMS0605-H 

site was exposed to direct effects of Hurricane Rita, and CRMS0268-H was exposed to indirect effects. The upper panel shows 

the seasonal time course of live aboveground biomass, with standard errors. The lower panel shows the seasonal deficit of live 

aboveground biomass at CRMS0605-H compared to CRMS0268-H. Comparative recovery of the aboveground biomass at CRMS0605-H 

took two full growing seasons.
52 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 34. Live belowground biomass at Coastwide Reference Monitoring System (CRMS) sites 0605-H and 1277-H. The CRMS0605-H 

site was exposed to direct effects of Hurricane Rita, and CRMS1277-H was exposed to marginally direct effects. The upper panel 

shows the seasonal time course of live belowground biomass, with standard errors. The lower panel shows the seasonal deficit of live 

belowground biomass at CRMS0605-H compared to CRMS1277-H.
Results and Discussion 53

Figure 35. Live belowground biomass at Coastwide Reference Monitoring System (CRMS) sites 0605-H and 0268-H. The CRMS0605-H 

site was exposed to direct effects of Hurricane Rita, and CRMS0268-H was exposed to indirect effects. The upper panel shows 

the seasonal time course of live belowground biomass, with standard errors. The lower panel shows the seasonal deficit of live 

belowground biomass at CRMS0605-H compared to CRMS0268-H.
54 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 36. Live aboveground biomass and species composition by season two years after Hurricane Rita. The upper panel shows 

Coastwide Reference Monitoring System (CRMS) site 0605-H, and the lower panel shows CRMS1277-H. The CRMS1277-H site serves 

as a comparison of low-level, short-duration salinity exposure associated with Hurricane Rita. Before the storm, these sites were 

comparable in terms of plant dominance and biomass of Panicum hemitomon. 
Results and Discussion 55

A

B C

Figure 37. Characteristics of initial plant recolonization by clonal, patch-forming species prior to the seedbank release of annual 

species at Coastwide Reference Monitoring System (CRMS) site 0605-H. A, Early phase of marsh recolonization. The clonal species 

responsible for initial site recolonization consisted mostly of Spartina patens, Typha domingensis, and Paspalum vaginatum (photo is 

from early August 2006). B, Spartina patens. Given its salt tolerance, this species was capable of rapid expansion in bare areas. Unlike 

its characteristic tussock growth form, Spartina patens initiated a guerrilla growth pattern where culms lodged in open water, sprouted 

adventitious roots and daughter ramets at its nodes, and created self-sustaining plantlets over one meter away from the parent plant. C, 

Measuring clonal expansion rates. We followed the expansion rates of three different clonal species that formed discrete patches. In 

approximately 2 months, Spartina patens and Typha domingensis increased by an average of 10 m2 in coverage (table 11).
56 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

The summer of 2007 (23 months after Hurricane Rita) 

marked a threshold when visual landscape recovery was 

discernable (fig. 38). Widespread germination of the seed 

bank, in addition to an apparent exponential rate of clonal 

expansion, contributed to extensive plant coverage. The 

primary factors facilitating this rapid recolonization during 

the second growing season included (1) time since storm 

disturbance, which increased the likelihood of new seed 

recruitment/dispersal; (2) decreasing porewater salinity; 

(3) the onset of the growing season; and (4) subaerial 

emergence of peat mat as it became bouyant.

Discussion

In this case study, we documented the early stages of 

community succession following protracted salt exposure to 

a freshwater community. The widespread mortality of the 

plant community and its slow recovery serves as an extreme 

point in a continuum of storm impacts due to salt exposure. 

After 18 months of bare peat exposure, we found that neither 

community composition nor the standing stock of live 

biomass had returned to prestorm conditions. We observed a 

predictable shift to a more salt-tolerant assemblage. Predicting 

the trajectory of the future recovery for these wetland types 

is highly speculative. Nonetheless, it is worthwhile to 

discuss possible outcomes based on our knowledge of similar 

historical impacts.

After Hurricane Audrey in 1957, Valentine (1976) 

conducted a long-term, poststorm plant survey of marshes 

just north of Lake Misere, which is in the general vicinity 

of CRMS0605-H. His yearly surveys were done from 1958 

to 1967 and again in 1972 and 1974. Direct comparisons 

concerning the prestorm community in relation to poststorm 

community changes are not appropriate between this study and 

Valentine’s, because there was a lack of specific community 

information for his study area. We only know it was a 

freshwater marsh impacted by salt exposure. At the beginning 

of his survey in July 1958, one year after the storm, Valentine 

observed that, the marsh appeared devoid of vegetation, which 

translated into an open water/bare soil estimate of 86 percent 

across 5,900 m of transect lines. After 5 years, the open water/

bare soil coverage had dramatically decreased to 18 percent 

(fig. 39). Sagittaria lancifolia (bulltongue) was the species 

responsible for recolonization of Valentine’s study area. 

Interestingly, he never documented the presence of Typha spp. 

in his surveys. By the end of 1974, the community largely 

represented a freshwater, wet-prairie assemblage, including 

species capable of withstanding moderately deep flooding 

like Eleocharis quadrangulata (squarestem spikerush), 

Eleocharis equisetiodes (jointed spikerush), Pontederia 

cordata (pickerelweed), and two species within the family 

Nymphaeaceae.

Valentine largely attributed the demise of C. mariscus 

ssp. jamaicense (Jamaica sawgrass) in southwestern Louisiana 

to salt exposure from Hurricane Audrey (1957) and the 

subsequent 5 years of local drought. Within the past 10 years, 

Jamaica sawgrass has made a noticeable re-expansion in many 

of the freshwater areas of the chenier plain. To what degree 

the landscape loss of Jamaica sawgrass can be correlated with 

the saltwater impacts from Hurricane Audrey is uncertain. It 

is plausible, however, that major events like hurricanes can 

radically change a community, such that the possibility of 

its return to pre-event condition is unlikely or indefinitely 

extended (fig. 40). Major climate events such as tropical 

storms and local drought (Visser and others, 2002) may act as 

Table 11. Changes in clonal expansion of ten monospecific patches of three species observed at Coastwide Reference Monitoring 

System 0605-H on February 28 and May 9, 2007. The area was estimated by patch diameter on two right-angle axes. By summer 2007 

sampling, almost complete coalescence among patches had occurred, indicating an exponential expansion of both clonal growth and 

widespread seedbank germination. 

[m2, square meter; NA, not appicable]

Species

Feb. 28 area 

(m2)

May 9 area 

(m2)

Increase in

area (m2)

Increase in

area (%)

Mean increase 

(m2)

Mean increase 

(%)

Typha domingensis 3.3 16.0 12.7 378 NA NA

7.8 15.0 7.2 91 9.9 235

Spartina patens 6.5 18.5 12.0 184 NA NA

3.9 13.7 9.7 250 NA NA

1.9 9.5 7.6 411 NA NA

3.8 12.9 9.1 235 NA NA

10.2 21.2 11.0 107 NA NA

5.8 18.1 12.3 213 10.3 234

Paspalum vaginatum 4.5 8.1 3.6 82 NA NA

2.4 5.3 2.9 125 3.3 103
Results and Discussion 57

A

B

C

Figure 38. A description of plant community change 

at Coastwide Reference Monitoring System (CRMS) 

site 0605-H following Hurricane Rita. A, Sequence 

of community change. Beginning in the spring 2007, 

small patches of clonal species began the noticeable 

expansion across the bare peat surface (photo from 

early May 2007). B, Release of the seedbank. By 

summer 2007, an immense response of the seedbank 

was evident, such that most of the bare peat was 

colonized; at this time the peat mat had emerged 

from the water surface. Seedbank species included 

Echinochloa walteri, Cyperus spp., Eleocharis spp., 

Amaranthus spp., and Typha domingensis (photo from 

late June 2007). The delay in seedbank response was 

likely due to the combination of elevated salinity, mat 

submergence, and dispersal limitation. C, Community 

development. By spring 2008, seedbank annuals were 

replaced by Typha domingensis and Typha latifolia. At 

a landscape scale, the fresh to intermediate marsh 

community zones of the chenier plain (for definition, 

see Saucier, 1994) have been invaded by these 

two species, which has taken three years. These 

community types are subject to relatively rapid change 

and may be considered ephemeral alternate states. 

The possibility exists that such massive disturbances 

preclude a return to an original state.
58 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

the primary control on long-term wetland community change, 

while the type and intensity of hydrologic manipulation 

is likely the secondary control that determines the rates of 

community recovery during the intervening periods between 

episodic events. The CRMS0605-H site may serve as an 

important ongoing study site to understand how freshwater 

communities may recover over longer time periods and how 

resilient they are to future disturbance events.

Case Study 2: CRMS0135

Overall Site Description

The CRMS0135 site is located in middle Breton Sound 

approximately halfway between Oak River to the west 

and Bayou Terre Aux Boeufs to the east (N 29°41.193 ́, 

W89°45.628 ́, fig. 41). The site is south of Shell Lake and 

Figure 39. Vegetation in marshes north of Lake Misere (see fig. 27), near Coastwide Reference Monitoring System (CRMS) site 0605-

H, based on the research of Valentine (1976), who conducted plant surveys after Hurricane Audrey (1957). One year after Hurricane 

Audrey, Valentine noted that the marsh was devoid of vegetation. The return to a relatively stable plant assemblage occurred within 5–8 

years, when the perennial Sagittaria lancifolia became the dominant plant. Other species observed along the 5,900 m of transect plots 

exemplify a wet prairie community made up of floating-leaved aquatics (Nymphaeaceae), Eleocharis quadrangulata, and Eleocharis 

equisetoides.

north of Lake Fausan, on a relic of a natural bayou. The 

closest town, Delacroix Island, is approximately 8.8 km 

northwest of the site. The marsh in this area is fragmented, 

with an abundance of natural bayous and oil and gas canals 

traversing the area. The site is less than 0.3 km west of an 

oil and gas canal that runs directly from Lake Lery to Bay 

Gardene through Grand Point Bay. Water is freely exchanged, 

with no impoundments or weirs nearby. The CRMS0135 

site was classified as being in the direct area of impacts from 

Hurricanes Katrina and Rita because the eye of Hurricane 

Katrina passed approximately 14 km east of the site, and storm 

surge in the area was estimated at 5.2 m (Federal Emergency 

Management Agency, 2006). When sampling began in spring 

2006, there were visible signs of physical disturbance to the 

marsh surface. In some locations, wrack and multiple layers 

of vegetation and soil were stacked on top of each other, and 

in other locations the vegetation had been removed, leaving 

divots or holes in the marsh surface. In July 2005, prior to 
Results and Discussion 59

HighLow

2002 2003 2004 2005 2006 2007 2008 2009

s e biomas tiv la Re

Year (end of growing season)

ObservedPredicted

Stable freshwater

community

Rita

A

C

D

E

B

Figure 40. Timeline of vegetation community changes and relative plant biomass before and after Hurricane Rita. The year marks biomass at the end of the growing seasons (September). A, The prestorm vegetation community, dominated by Panicum hemitomon, had relatively stable amounts of live aboveground and belowground biomass (>2,500 grams of dry weight per square meter). B, After the storm, there was a period of 18 months during which there was a substantial loss of biomass to the soil because there was little vegetation biomass. C, By the end of the second growing season (2007), there was an extensive response of the seedbank with the establishment of disturbance species. D, Clonal expansion of Spartina patens, Typha latifolia, and Typha domingensis rapidly displaced the seedbank annuals and continued to be dominant species to fall 2008; 

their biomass production exceeded that of the earlier stable freshwater community. E, With the observed incremental decrease of salinity and assuming stabilization toward freshwater conditions, we can expect a transition from the salt-tolerant assemblage of Spartina patens and Typha spp. to another state. 
60 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 41. Location of Coastwide Reference Monitoring System (CRMS) sites 0135-H and 0135 within middle Breton Sound basin (see Coastal Wetlands Planning, Protection and Restoration Act [CWPPRA] Program [n.d.] for definition of the basin).
Results and Discussion 61

Hurricane Katrina, the site was dominated by S. patens and 

V. luteola (CRMS Preliminary Site Visit Report, unpub. data); 

however, in spring 2006, the dominant vegetation species was 

A. australis, an annual that colonizes disturbed areas (table 5). 

This site is part of the CRMS network; therefore, additional 

data beyond our samplings were incorporated into this 

report. The CRMS supplementary data (unpublished) include 

continuous hourly hydrographic data, discrete porewater data, 

vegetation survey data, and photo documentation acquired 

before the hurricanes. Estimates of aboveground biomass at 

the end of growing seasons in 2000 and 2001 were provided 

by Dr. John Day of Louisiana State University from a nearby 

study site (written commun.).

The CRMS0135 site was classified as brackish/

intermediate marsh habitat. In July 2005, the site had 

consolidated soils typical of that marsh type and fairly 

complete vegetation cover. When this study began in spring 

2006, the marsh was covered with multiple layers of wrack 

and storm-deposited material, and minimal live vegetation was 

present other than single-stemmed annuals (fig. 42). 

Surface-Water and Porewater Salinities

Surface-water salinity throughout the study was typical 

of brackish/intermediate marshes and ranged from 0.2 to 

13.9. Average surface-water salinity in the bayou adjacent to 

CRMS0135 was 2.82 (± 0.12) and was greatest from summer 

through fall 2006 and lowest from winter through summer 

2007 (fig. 43). The only time the marsh surface was flooded 

(2 cm) during the quarterly sampling visits was in spring 2007. 

Although continuous hydrographic data are available for the 

site, marsh elevation data are not currently available, so depth, 

duration, and frequency of marsh-surface flooding could not 

be included.

Porewater salinity ranged from 1.2 to 10.1 throughout 

the study, averaging 5.47 (± 0.55). In late October 2006, 

porewater salinity was elevated for this habitat type, 

measuring 10.1, which is greater than the mean value reported 

for brackish marsh salinity (8.2) by Chabreck (1972) and 

significantly greater than all other sampling periods 

(p < 0.0001). By spring 2007, porewater salinity decreased 

to ranges typically found in brackish/intermediate marshes. 

Elevated porewater salinity, in addition to hurricane-induced 

physical disturbance of the marsh, likely contributed to the 

changes in vegetation species composition at CRMS0135, 

which are described below.

Vegetation Cover

Live vegetation cover was lowest in spring 2006 and 

winter 2007 (fig. 44). In addition to the low cover (55 percent) 

in spring 2006, the species present were largely disturbance 

species, A. australis and V. luteola (fig. 44). Cover of these 

two species remained high through summer 2006, composing 

95 percent of the total live cover. Disturbance species 

continued to contribute substantially to the total live cover 

through fall 2007. The initial large contribution of 

A. australis to the total cover during the first growing season 

after Hurricanes Katrina and Rita was replaced with an 

increase in V. luteola in the second growing season after the 

hurricanes. By fall 2007, S. patens, the dominant species 

before the hurricanes, comprised 35 percent of the total cover, 

although 65 percent of the total cover remained composed of 

disturbance species.

Minimal live vegetation was observed at the site during 

construction of the CRMS project in early November 2005 

(fig. 45). Some of the dieback is assumed to be related to 

seasonal changes, but one would expect some living and 

standing dead vegetation to remain in early November in a 

typical growing season of marsh dominated by S. patens. 

We believe the lack of live vegetation was likely related 

to hurricane-induced physical disturbance and salt stress 

that remained 2 months after Hurricane Katrina (see fig. 43 

Figure 42. Coastwide Reference Monitoring System (CRMS) 

site 0135 on May 4, 2006, after Hurricanes Katrina and Rita. 

Multiple layers of wrack and storm deposited material, and 

single-stemmed annual vegetation colonized the area.
62 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Date

April 2006 

June 2006 

August 2006 

October 2006 

December 2006 

February 2007 

April 2007 

June 2007 

August 2007 

October 2007 

Salinity 

0

2

4

6

8

10

12

14

16

Figure 43. Mean 

values of daily surfacewater (solid line) 

salinity and discrete 

porewater (open 

circles) salinity at 30 cm 

deep from April 2006 

to November 2007 at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0135. 

Figure 44. Seasonal 

species composition 

of total live vegetation 

cover at Coastwide 

Reference Monitoring 

System (CRMS) site 0135.
Results and Discussion 63

A

B

Figure 45. Coastwide Reference Monitoring System (CRMS) site 0135 after Hurricanes Katrina and Rita. A, Photograph taken on 

October 25, 2005. B, Photograph taken on November 8, 2005, of the boardwalk and surrounding marsh.
64 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Cover, by percent

0

20

40

60

80

100

Season

Figure 46. Seasonal 

coverage of disturbance 

(black bars) taxa relative 

to nondisturbance (gray 

bars) taxa at Coastwide 

Reference Monitoring 

System (CRMS) site 0135.

for salinity data). By the initiation of our study in spring 

2006, live vegetation was present but was largely composed 

of disturbance species rather than S. patens (fig. 46). The 

presence of disturbance species continued throughout the 

study period.

Aboveground and Belowground Biomass

Before Hurricanes Katrina and Rita, measurements 

of biomass were collected approximately 5 km northeast 

of CRMS0135 at the end of growing seasons during fall 

2000 and 2001 (J. Day and others, unpub. data, 2007). The 

historical site (sampled by Day; N29.7006°, W89.7102°) is 

located in the marsh near the northwest corner of Lake Cuatro 

Caballo (locally known as Four Horse Lake; see fig. 41) and 

adjacent to the northern intersection of the twin pipeline canal 

and Four Horse Lake. The mean value of live biomass at the 

end of growing seasons was 981.6 (± 411.2) dry weight m-2 in 

2000 and 1,233.2 (± 150.1) g dry weight m-2 in 2001 (fig. 47). 

In fall 2006 live biomass at the end of the growing season was 

significantly lower at CRMS0135 than at the historical site 

before the hurricanes (p = 0.0117, fig. 47); however, in fall 

2007 live biomass was similar to fall 2000.

Throughout the course of this study, aboveground 

biomass followed seasonal trends, with decreased live 

biomass in winter and increased live biomass in summer and 

fall (fig. 48). Live aboveground biomass increased greatly 

from spring 2006 to summer 2006, but this increase was due 

to the presence of two disturbance species, A. australis and 

Echinochloa crus-galli (barnyard grass) (figs. 49 and 50). 

Both of these species are annuals, and A. australis can produce 

large amounts of biomass in one growing season (Wunderlin 

and Hansen, 2003). In the second growing season after 

the hurricanes, A. australis was not present, but two other 

disturbance species, V. luteola and Panicum dichotomiflorum 

(fall panic), were present, albeit in less quantity. The presence 

of S. patens in summer 2007 was the first sign that species 

composition was returning to conditions that existed before 

Hurricanes Katrina and Rita; however, it was not present in 

the sampled plots at the end of the growing season in 2007. 

Spartina patens was present at the site in fall 2007 but not in 

the plots sampled for aboveground biomass (fig. 44). Species 

composition was dynamic at this site and continued to change 

throughout the study period, partially because of the patchy 

distribution of species and the relatively small area harvested 

each period.
Results and Discussion 65

Fall 2000 Fall 2001 Fall 2006 Fall 2007

Aboveground biomass, 

in grams of dry weight per square meter

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

AB

A

B

AB

Season

Figure 47. Total 

(white bars) and 

live (gray bars) 

aboveground biomass 

at a historically sampled 

site near Lake Cuatro 

Caballo (see fig. 41) 

at the end of growing 

seasons in fall 2000 and 

2001 and at Coastwide 

Reference Monitoring 

System (CRMS) site 

0135 at the end of 

growing seasons in 

fall 2006 and 2007. 

No estimates of total 

biomass were available 

for fall 2000 and 2001. 

Differing letters indicate 

statistical differences 

for live biomass 

only (p = 0.0117).

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

500

1,000

1,500

2,000

2,500

3,000

Live and dead aboveground biomass,

 in grams of dry weight per square meter

Figure 48. Live (white 

bars) and dead (gray 

bars) aboveground 

biomass (see standard 

error bars) by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0135. 
66 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 49. Species 

composition of live 

aboveground biomass 

by season at Coastwide 

Reference Monitoring 

System (CRMS) site 0135. 

Season

2006 Spring

2006 Summer

2006 Fall

2007 Winter

2007 Spring

2007 Summer

2007 Fall

Biomass of disturbance and nondisturbance species,

 in grams of dry weight per square meter

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

Figure 50. Seasonal 

aboveground biomass 

of disturbance (black) 

and nondisturbance 

(gray) taxa at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0135. 
Results and Discussion 67

Total aboveground biomass ranged from 122.6 (± 32.5) 

to 1,835.3 (± 487.9) g dry weight m-2, while total belowground 

biomass ranged from 5,670.9 (± 1606.9) to 7,877.3 (± 1,328.5) 

g dry weight m-2 (fig. 51). Minimal changes in total 

belowground biomass were observed from spring 2006 to 

fall 2007, with the lack of significant change likely due to the 

dominance by annual species at this site. The expected trend 

of increased belowground biomass in spring, prior to 

an increase in aboveground biomass in summer, and 

subsequent decrease in belowground biomass found by 

Darby and Turner (2008) was not observed at this site. 

However, as is typical of Louisiana’s coastal marsh systems, 

the belowground component to vegetation biomass was far 

greater than the aboveground component (Gross and others, 

1991; Darby and Turner, 2008). Live belowground biomass 

was greatest in winter 2007 but did not account for more than 

20 percent of the total belowground biomass throughout the 

study period (fig. 52).

Sediment Characterization, Accretion, and Elevation

The average bulk density taken from two cores at 

CRMS0135 was 0.25 (± 0.02) g dry weight cm-3 from 0 to 

48 cm deep (fig. 53). In the bulk density profile, a strong 

mineral signal was present between -26 and -32 cm, depending 

on the core. In addition, the bulk density profile in core two 

shows a mineral signal peaking between -2 and -4 cm. The 

same signal is present in two archived cores taken for the 

CRMS project at the same site location (fig. 54). Because 

of its location in the profile (that is, in surface sediment) 

and the proximity with which Katrina passed in relation to 

CRMS0135, it is possible that this mineral sediment was 

deposited by Hurricane Katrina. 

Two cores analyzed for caesium-137 showed clear 

peaks of caesium activity at approximately 31 cm deep 

(fig. 54). This depth is assumed to correspond to the 1963 

level. The strong mineral signal between 26 and 32 cm deep 

occurs above (after) the 1963 level; therefore, it is probably 

from the passage of Hurricane Betsy in 1965. Betsy was a 

category 4 hurricane that passed approximately 71 km west of 

CRMS0135 and produced marsh scouring in Breton Sound 

(J. Barras, personal commun., 2007). 

Accretion since 1963 was calculated as 0.72 cm yr-1, 

which is within the range (from 0.59 to 0.95 cm yr-1) reported 

for brackish/intermediate marshes in Louisiana (Hatton, 1983; 

Smith and others, 1983; Chmura and Kosters, 1994; Nyman 

and others, 2006). 

From our limited data (three sampling periods over 

3 years) on elevation and short-term accretion, we estimated 

elevation change at 0.19 cm yr-1 and vertical accretion at 0.49 

cm yr-1 (appendix fig. 2-1). It appears that the site-specific 

vertical accretion is not fully contributing to elevation change; 

therefore, shallow subsidence is 0.30 cm yr-1. With estimates 

of RSLR at 0.92 cm yr-1 in this area, these data suggest 

that this site is not building sufficient elevation to prevent 

increased tidal elevation and stress related to RSLR. Care 

should be taken when interpreting these data because estimates 

of elevation change and shallow subsidence improve over 

longer time periods (Cahoon and others, 2002b), and 

data from one site cannot be generalized for the region. The 

bulk density profile (fig. 53, core 2) does reflect a mineral 

pulse indicative of sediment recently incorporated into the 

site, likely from Hurricane Katrina. Hurricane-induced 

subsidies have been shown to contribute to substantial 

elevation change and can be beneficial to the sustainability 

of coastal systems (Cahoon, 2003; Nyman and others, 1995; 

Turner and others, 2006).

Summary of the Classification of Impacts

Vegetation cover and species composition data, paired 

with observational findings, indicate that the hurricaneinduced impacts at this site were largely caused by physical 

disturbance of the marsh surface, likely from a combination 

of wind and storm surge. Physical disruption to the marsh 

surface was obvious from the divots, marsh balls, lack of 

live vegetation, and irregularity of the marsh surface (beyond 

typical surface heterogeneity) when sampling began. As 

the study progressed, the abundance of disturbance species 

that colonized the site provided further evidence of a marsh 

directly influenced by the storms. The porewater salinity was 

within the normal range anticipated for brackish/intermediate 

marshes, and there was not a shift in species composition to 

more salt-tolerant species. Both observations offer further 

support for the occurrence of physical disturbance rather than 

salinity-induced impacts. In the fall of 2005, the site-specific 

departure from average was -0.55 (± 0.04) from the NDVI 

value, indicating that there was a major decrease in vegetation 

vigor from the baseline condition. This departure from 

average was validated by the lack of live vegetation present in 

fall 2005 when the CRMS site was constructed. By fall 2006, 

the departure from average NDVI score increased to -0.16 

(± 0.08), indicating that plant vigor at the site did improve in 

the first growing season after Hurricanes Katrina and Rita, 

as was reflected in our aboveground biomass estimates, but 

remained below the baseline average.

Case Study 3: CRMS0672-H

Overall Site Description

The CRMS0672-H site (N29.83343o, W93.4091o) is 

located within the East Mud Lake Marsh Management project 

area (CWPPRA project CS-20), located in the Calcasieu/

Sabine basin in Cameron Parish, La. (Castellanos and others, 

2007) (fig. 55). The hydrology in this 3,222-ha project area is 

influenced by the fact that the project area is isolated by levees 

and roads. The project area is divided into Conservation 

Treatment Units (CTU). CRMS0672-H is located within 

CTU-2 and is actively managed by using variable crest 

culverts with flapgates, gated culverts, and variable-crest 
68 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 51. Seasonal 

above and belowground 

biomass at Coastwide 

Reference Monitoring 

System (CRMS) site 

0135. Total belowground 

biomass is represented 

by gray bars and total 

aboveground biomass 

by hatched bars.

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

Total aboveground and belowground biomass, 

in grams of dry weight per square meter

Season

Figure 52. Seasonal 

belowground biomass 

(see standard error 

bars) of dead (black) 

and live (gray) 

components at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0135. 

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Live and dead belowground biomass,

 in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000
Results and Discussion 69

0 20 40 60 80

Depth, in centimeters

-10-15-20-25-30-35-40-45-50

-5

0

Bulk density, in grams per cubic centimeter

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

0 20 40 60 80

-10-15-20-25-30-35-40-45-50

-5

0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Core 1 Core 2

Caesium-137 activity, in becquerels per kilogram

EXPLANATION

137Cs activity Bulk density

Figure 53. Bulk density and caesium-137 profiles at Coastwide Reference Monitoring System (CRMS) site 0135. Measurements were obtained from two cores taken at 0–50 cm deep. Peak caesium-137 activity of core 1 occurred at a depth of 33.1 cm, and peak caesium-137 activity of core 2 occurred at a depth of 30.5 cm. 
70 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 54. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference Monitoring System (CRMS) site 0135. Cores 1 and 2 are data collected for this study. Archived cores 1 and 2 are from a previous CRMS project sampling.
Results and Discussion 71 Figure 55. Location of Coastwide Reference Monitoring System (CRMS) sites 0672-H and 0672 within lower Calcasieu/Sabine basin (see Coastal Wetlands Planning, Protection and Restoration Act [CWPPRA] Program [n.d.] for definition of the basin). Both CRMS sites are located within the boundary of CWPPRA project CS-20 (East Mud Lake Marsh Management).
72 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

box structures. East Mud Lake Marsh Management project 

construction was completed in April 1996. The manipulation 

of water-control structures is designed to alleviate prolonged 

flooding of the marsh resulting from impoundment and to 

better control the rapid movement of high-salinity water (that 

is, >15) into the CWPPRA CS-20 project area via West Cove 

Bay, Oyster Bayou, and Mud Bayou. The Calcasieu Ship 

Channel, a navigation channel 15-m deep by 122-m wide and 

located 1.6 km east of the project area, is the primary source 

of high-salinity water.

In surveys conducted by Chabreck and Linscombe 

in 1968, 1978, 1988, 1997, and 2001, the habitat at 

CRMS0675-H was classified as brackish marsh, supporting 

flora and fauna typically adapted to surface salinities ranging 

from 5 to 18 (Chabreck, 1970). Marsh loss in this area has 

been minimal since 1978, and land change analyses from 

1994 to 2000 suggest increases in marsh within the entire 

CTU-2 (Castellanos, 2005). The site is located on Creole 

soils (Natural Resource Conservation Service, n.d.), a poorly 

drained mineral soil that has a fluid, mucky surface layer and 

underlying material of clay, sand, and loam. 

The dominant vegetation species at this site historically 

has been S. patens and D. spicata. Vegetation cover data 

from this site (CWPPRA station CS20-40) are available from 

1995, 1997, 1999, 2003, 2005, and 2006 (Louisiana Office of 

Coastal Protection and Restoration, 2010) and were used to 

evaluate changes in vegetation communities after Hurricanes 

Katrina and Rita. Additionally, we used historical surfacewater salinity data from a nearby CWPPRA station (CS20-03) 

to investigate salinity effects on vegetation. CRMS0672-H 

was classified as brackish/intermediate for the purposes of this 

study and was within the area directly impacted by Hurricane 

Rita, which passed within 37 km of the site. The study area 

received 1.8–2.4 m of storm surge (Coastal Emergency Risks 

Assessment, 2008).

Surface-Water and Porewater Salinity

There was very little surface water at CRMS0672-H 

during the study period, and the marsh surface was dry and 

cracked at the spring 2006 sampling. The seasonal mean 

values of porewater salinity ranged from 10.7 (± 1.0) in 

2007 to 16.3 (± 1.3) in 2006 and were significantly greater in 

summer 2006 and fall 2007 than in summer 2007 (p = 0.014, 

fig. 56). The salinity values are within the range of variability 

found in brackish marsh (Chabreck, 1970). Continuous data 

on surface-water salinity from station CS20-03 show that 

salinities remained above 20 from February through July 

2006, during which time drought conditions were prevalent 

(fig. 57). Damage to the salinity gage from Hurricane Rita 

prohibited measurements from September 2005 until February 

2006. Salinity conditions in 2007 were lower and appear to be 

associated with a return to normal precipitation patterns. The 

salinity patterns poststorms are on the high end of the typical 

brackish marsh salinity range; however, they are not as high 

as during the 1999–2000 drought, when mean value for daily 

salinity exceeded 20 for much of the period from August 

1999 to December 2000, peaking at 39 at station CS20-03 

(Castellanos, 2005). 

Vegetation Cover

The initial sampling of CRMS0672-H in spring 2006 

indicated that 95 percent of the cover was dead vegetation, 

primarily S. patens, with only 5 percent live cover comprising 

S. patens and D. spicata (fig. 58). Distichlis spicata was 

the dominant plant species throughout the study and tended 

to increase in cover from spring 2006 to fall 2007, whereas 

S. patens showed little recovery until spring 2007. The 

disturbance species, A. australis, comprised only 5 percent 

cover in summer 2006, but it accounted for 33 percent of 

the total cover at the site (figs. 58 and 59), and it was very 

abundant outside our sampling area in all seasons in 2006. 

During fall 2006 and fall 2007, Paspalum vaginatum was also 

codominant but did not occur in sample plots during other 

sampling times of the year. This species has been prevalent 

during low-water conditions in the study area and occurs along 

marsh-water interfaces (Castellanos, 2005). Overall, live 

cover values increased only slightly (from 5 to 20 percent) 

throughout 2006, but during 2007 the site fully recovered, 

with 100 percent cover by fall 2007.

The influence of the hurricanes at this site was very 

apparent from observations in spring 2006 because there was 

near complete dieback of S. patens within and outside this 

site and minimal live vegetation cover. The four vegetation 

surveys conducted at this site before the hurricanes (that is, 

as part of the CS-20 project in 1995, 1997, 1999, and 2003) 

reported cover values between 40 and 100 percent, with 

dominant species of S. patens and D. spicata (Louisiana Office 

of Coastal Protection and Restoration, 2010). Interestingly, 

the survey in July 1997 after the 2006 drought revealed 

a pattern similar to that observed in our study, in which 

S. patens almost completely died back and A. australis

composed the total live cover (40 percent), but by the July 

1999 survey S. patens was the dominant species again. It 

appears that after a large disturbance event, whether hurricane 

or drought, dominant perennials in this brackish marsh are 

initially set back during the first growing season after the 

event, and disturbance species become opportunistic. If 

stressful conditions do not persist, the dominant perennials 

can outcompete the disturbance species and reestablish typical 

values of vegetation cover. 
Results and Discussion 73

Season

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Porewater salinity 

0

2

4

6

8

10

12

14

16

18

20

22

24

Date

March 01, 2005 

July 01, 2005 

November 01, 2005 

March 01, 2006 

July 01, 2006 

November 01, 2006 

March 01, 2007 

July 01, 2007 

Salinity 

0

5

10

15

20

25

30

35

Figure 56. Seasonal 

discrete porewater 

salinity (see standard 

error bars) at Coastwide 

Reference Monitoring 

System (CRMS) site 

0672-H, sampled at a 

depth of 30 cm.

Figure 57. Average 

daily surface-water 

salinity from a sampling 

station (CS20-03) within 

the CS20 project of 

the Coastal Wetlands 

Planning, Protection 

and Restoration Act 

(CWPPRA) from January 

2005 to July 2007.
74 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 58. Seasonal 

species composition of 

total live vegetation cover 

at Coastwide Reference 

Monitoring System (CRMS) 

site 0672-H.

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Live vegetation cover, by percent

0

20

40

60

80

100

Season

Figure 59. Live vegetation 

cover of disturbance (black bars) 

taxa relative to nondisturbance 

(gray bars) taxa by season at 

Coastwide Reference Monitoring 

System (CRMS) site 0672-H.
Results and Discussion 75

Aboveground and Belowground Biomass

The pattern of live aboveground biomass was similar 

to that of vegetation cover (percent). Very low levels of 

live aboveground biomass were observed in spring 2006 

(255.33 ± 19.22 g dry weight m-2), then trended higher 

through the end of the study, with peak values of 1,927.02 

(± 276.96) g dry weight m-2 in fall 2007 (fig. 60). The live 

aboveground biomass in fall 2007 was nearly twice that of 

fall 2006. The species that comprised the live aboveground 

biomass were the same as those found in the 4-m2 plot used to 

measure vegetation cover; however, there was a much greater 

abundance of Paspalum vaginatum, which was dominant 

from fall 2006 until fall 2007 (fig. 61). The amount of dead 

aboveground biomass was very high from spring 2006 to 

spring 2007, with values exceeding 1,250 g dry weight m-2

(fig. 60). The dead aboveground biomass decreased during 

the 2007 growing season as the amount of live aboveground 

biomass increased. Observations from summer and fall 2007 

suggest that the large reduction in dead aboveground biomass 

is due to decomposition and incorporation of dead material 

in the soil substrate. White and others (1978) found that 24 

percent of dead plant material from D. spicata and 36 percent 

from S. patens remained in litter bags after one year.

The mean value for total belowground biomass was 

greater during the growing season in 2006 than in 2007 but 

not significantly (fig. 62). The pool of dead biomass was 

significantly larger than the pool of live biomass (fig. 63). The 

live biomass was only a small component of the total during 

the study, with contributions of 7 percent in fall 2006 and 

6 percent in winter 2007. Although live biomass did occur 

throughout the entire 32-cm core depth, the largest amount of 

live root and rhizome biomass was found in the upper 16 cm 

of the substrate, 6 cm deeper than Gross and others (1991) 

observed for S. alterniflora.

It is difficult to estimate the effects of Hurricane Rita 

on the basis of the biomass measured in this study alone 

because no prestorm data were available. Although the range 

of reported aboveground biomass estimates from Louisiana 

brackish marshes varies greatly over time and space, live 

biomass at this study site at the end of the growing season 

in fall 2007 (1,927 g dry weight m-2) was at the high end of 

the reported range. Louisiana Offshore Oil Port (LOOP) 

monitoring data from 1979 to 1997 indicated that aboveground 

biomass (that is, S. patens) in brackish marsh ranged from 

441 to 1,750 g dry weight m-2 (Visser and others, 1996).

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

500

1,000

1,500

2,000

2,500

3,000

Live and dead aboveground biomass,

 in grams of dry weight per square meter

Figure 60. Live (white 

bars) and dead (gray 

bars) aboveground 

biomass (see standard 

error bars) by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0672-H.
76 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 61. Species 

composition of 

live aboveground 

biomass by season 

at Coastwide 

Reference 

Monitoring System 

(CRMS) 

site 0672-H. 

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

Total aboveground and belowground biomass,

 in grams of dry weight per square meter

Season

Figure 62. Total 

aboveground (hatched 

bars) and belowground 

(gray bars) biomass 

(see standard error 

bars) by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0672-H.
Results and Discussion 77

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Total belowground biomass, by percent

0

20

40

60

80

100

Season

Figure 63. Live (white 

bars) and dead (gray 

bars) components of 

total belowground 

biomass by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0672-H. 

Sediment Characterization, Accretion, and Elevation

The bulk density, percentage of nitrogen, and percentage 

of carbon profiles are presented in figure 64. Average bulk 

density was 0.54 (± 0.05) g cm-3 throughout the entire 

profile. The caesium-137 peak occurred at -14.3 cm depth 

(table 5), which is assumed to correspond to the 1963 level. 

The mean value of bulk density above the 1963 level was 

0.22 (± 0.02) g cm-3, but bulk density is noticeably greater 

within the top 4 cm of the core. The high bulk density in the 

surface portion of the core is potentially due to a subsidy of 

mineral sediments brought in by Hurricanes Katrina and Rita 

(Steyer, 2008). Low-water conditions at the time of sampling 

exposed sediments that had accumulated on the dead plants, 

facilitating observations that sediments had been recently 

redistributed and deposited. The carbon and nitrogen contents 

of the soils were low compared to nonimpounded soils in the 

region (Steyer, 2008). The depth profiles reflect that carbon 

and nitrogen contents are positively related to the amount of 

organic matter, which is consistent with the findings of Craft 

and others (1993).

The calculated accretion rate since 1963 was 0.33 

(± 0.03) cm yr-1. This rate is below the range of typical 

accretion rates observed in brackish/intermediate marshes in 

Louisiana; however, we know that this site is hydrologically 

impounded and that impoundments can influence accretion 

(Foret, 2001; Phillips, 2002; Steyer, 2008). In Rockefeller 

State Wildlife Refuge and Game Preserve, Foret (2001) 

described average caesium-137 accretion rates of 0.50 (± 0.04) 

cm yr-1 in open reference sites, compared to 0.36 (± 0.04) 

cm yr-1 in manipulated sites (that is, mixed and impounded). 

Phillips (2002) also reported lower caesium-137 accretion 

rates in impounded marsh (0.19 ± 0.06 cm yr-1) compared 

to semi-impounded (that is, mixed) and open reference sites 

(0.31 ± 0.09 cm yr-1) in Rockefeller State Wildlife Refuge and 

Game Preserve. Within the Sabine basin, the only historical 

accretion rates for marshes dominated by S. patens are from 

feldspar plots in the CWPPRA CS-20 project area, where 

impounded sites CRMS0672 and CRMS0672-H are located. 

The CWPPRA CS-20 project averaged 0.40 cm yr-1 accretion 

from 1997 to 2003 and over 3.0 cm yr-1 from 2003 to 2006, 

accounting for deposition from Hurricane Rita (Castellanos 

and others, 2007). The short-term accretion rates from 

CRMS0672-H (1.11 cm yr-1) and CRMS0672 (0.67 cm yr-1) 

measured for the current study in 2007 and 2008 (fig. 65) are 

greater than the rates recorded before Hurricanes Katrina and 

Rita. Large organic accumulations may be contributing to 

these greater accretion rates, as suggested by the high values 

of live biomass measured in fall 2007.
78 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 64. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference Monitoring System (CRMS) site 0672-H. 
Results and Discussion 79

Figure 65. Short-term accretion 

rates at Coastwide Reference 

Monitoring System (CRMS) site 

0672-H and elevation and accretion 

change at CRMS0672. Estimates 

of site-specific elevation change, 

vertical accretion, and shallow 

subsidence (cm yr-1) are provided. 

A, There were no data on elevation 

change or shallow subsidence for 

CRMS0672-H. The rate of accretion 

(y = - 0.1924 + 0.0031X; r2 = 0.46) 

was 1.11 centimeters per year (cm 

yr-1). B, At CRMS0672 the shallow 

subsidence was -0.49 cm yr-1, and 

the relative sea level rise (RSLR) 

estimate was 0.57 cm yr-1. The 

rate of accretion (y = -0.3523 + 

0.0018X; r2 = 0.44) was 0.67 cm yr-1. 

The rate of elevation change (y = 

-2.9544 + 0.0032X; r2 = 0.01) was 

1.16 cm yr-1. Elevation change at 

CRMS0672 is projected to be 0.59 

cm yr-1 greater than RSLR.
80 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Vertical accretion is not necessarily equivalent to 

elevation gain (Cahoon, 2003). The accretion rate of 

3.0-cm yr-1 from 2003 to 2006 was reported to result in 

2.1 cm yr-1 of elevation gain, suggesting sediment compaction 

of underlying soils from the combined weight of storm 

surge and mineral deposition associated with Hurricane Rita 

(Castellanos and others, 2007). The 2007 to 2008 elevation 

change of 1.16 cm yr-1 at CRMS0672 (fig. 65) might be related 

to rebound from hurricane-induced compaction, changes in 

subsurface-water storage, or increases in root growth 

(Cahoon, 2003). Assuming a rate of 0.34 to 0.57 cm yr-1 in 

RSLR in the Calcasieu/Sabine basin from two long-term tide 

gage stations (Penland and Ramsey, 1990), it appears that 

impounded sites CRMS0672-H and CRMS0672 are currently 

maintaining sufficient elevation to keep pace with projected 

estimates of RSLR.

Summary of the Classification of Impacts

Although we did not sample vegetation on the ground 

in fall 2005, the departure from the average NDVI value 

(-0.19) at the end of the growing season in 2005 indicates 

that the plant vigor was below the baseline average. Such 

a decrease in vigor is expected following a hurricane, 

and ground observations of very little live vegetation and 

decreased aboveground biomass into spring 2006 illustrate the 

stressed nature of the vegetation. By fall 2006 the departure 

from the average NDVI score increased to -0.02 indicating 

improvement of the vegetative vigor in the first growing 

season after Hurricanes Katrina and Rita. Normalized 

difference vegetation index values provide an indication of 

plant vigor but cannot discriminate among species. In this 

case, the improved plant vigor can be attributed to an increase 

in coverage by disturbance species after the end of the first 

growing season.

From the soil bulk-density profiles and the data on 

accretion and elevation change, it appears that this area 

(including CRMS0672) received a subsidy of mineral 

sediment from the hurricanes. The increase in soil bulkdensity affected the upper 4 cm of the soil horizon and 

represented an approximate doubling of bulk density 

compared to the underlying soil. Given the proximity of this 

area to the path of Hurricane Rita, this storm likely contributed 

more mineral sediment to the area via storm surge than did 

Hurricane Katrina. 

Storm impacts at CRMS0672-H and in the immediate 

vicinity were mixed. While the initial salinity pulse associated 

with the storm surge negatively influenced short-term plant 

productivity, there was some degree of enhanced sediment 

deposition to the marsh surface that may provide long-term 

benefits. Future data collections through the CRMS program 

may help clarify the storm-associated impacts, especially as 

they relate to the sediment record.

Case Study 4: CRMS0326-H

Overall Site Description

The CRMS0326-H site is located on Old Oyster Bayou 

(N29°15.673 ́, W91°05.685 ́) in lower Terrebonne basin 

approximately 5.9 km north of the Gulf of Mexico (fig. 66; 

see Louisiana Coastal Wetlands Planning, Protection and 

Restoration Act Program [n.d.] for definition of the basin). 

Old Oyster Bayou is a navigable waterway connecting Old 

Oyster Bayou Lake to the east with Fourleague Bay to the 

west. Water is exchanged freely between Fourleague Bay 

(approximately 2.3 km west of the site) and the gulf through 

Oyster Bayou. No weirs or impoundments restrict water 

movement or tides from the gulf to CRMS0326-H. Old 

Oyster Bayou is approximately 14 km from the mouth of the 

Atchafalaya River. Historically, the site has been a healthy 

S. alterniflora marsh, likely because of its proximity to 

sediments, nutrients, and water from the Atchafalaya River. 

This site was characterized as being in the indirect area of 

hurricane impacts from Hurricanes Katrina and Rita.

The CRMS0326-H site was classified as saline marsh 

habitat with surface salinities typical of Louisiana saline 

marshes (8–29). The marsh surface was stable enough to walk 

upon, with sediment input available from the Atchafalaya 

River. Historically and throughout our study period, the 

dominant vegetation species at the site was S. alterniflora. 

The CRMS0326-H site was used in previous studies 

conducted by scientists at the U.S. Geological Survey National 

Wetlands Research Center with surface elevation table (SET) 

measurements dating back to 1992. For comparisons before 

Hurricanes Katrina and Rita, we present historical data 

on aboveground biomass at the end of growing seasons in 

2001 and 2002, collected as part of a brown marsh study by 

scientists at the National Wetlands Research Center. 

Surface-Water and Porewater Salinity

Measurements of surface-water and porewater salinity 

were taken quarterly from spring 2006 to fall 2007. Surface 

water was only present on the marsh surface in spring, 

summer, and fall 2007. During these three seasons, surfacewater depth averaged 4 cm, and salinity ranged from 8.1 to 

18.3, with a mean salinity value of 13.2 (± 4.28). Throughout 

the remainder of the study, the marsh was not inundated at 

the sampling times. Discrete porewater salinity did not vary 

greatly throughout the study period, ranging from 15.9 to 19.7 

(mean = 18.3 ± 1.1) (fig. 67).

In order to report data collected more frequently than the 

quarterly sampling intervals of this study, CRMS0326 was 

paired with CRMS0326-H. The CRMS0326 site is located 

2.5 km north of CRMS0326-H in a similar saline marsh and 
Results and Discussion 81 Figure 66. Location of Coastwide Reference Monitoring System (CRMS) sites 0326-H and 0326 within lower Terrebonne basin (see Coastal Wetlands Planning, Protection and Restoration Act [CWPPRA] Program [n.d.] for definition of the basin).
82 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Porewater salinity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

Figure 67. Discrete 

porewater salinity 

measured by season 

at 30 cm deep at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326-H.

provided continuous hourly salinity data. At CRMS0326, 

surface-water salinity averaged 9.37 (± 3.84) from April 2006 

to October 2007 (fig. 68). Throughout the same time period, 

discrete porewater salinity at CRMS0326 ranged from 

10.4 to 18.2 (mean = 13.68 ± 2.51), less than at CRMS0326-H 

(mean = 18.35 ± 1.08). The greatest porewater salinity at 

CRMS0326 was observed in summer 2006.

Surface-water and porewater salinities at CRMS0326-H 

and CRMS0326 were typical of saline marsh environments. 

Surface-water salinities tended to decrease slightly throughout 

the study period, with seasonal increases in summer 2007 

and fall 2006 and 2007. Porewater salinity at CRMS0326 

was similar to that observed in saline marsh environments by 

Chabreck in 1972 (15.87 ± 3.11) (fig. 68). After Hurricanes 

Katrina and Rita, it appears that surface-water and porewater 

salinities have not been stressors to vegetation at CRMS0326 

and CRMS0326-H because salinities have remained within 

typical ranges found in saline marsh habitats.

Vegetation Cover

Monospecific stands of S. alterniflora were present at 

this site from spring 2006 through fall 2007 (fig. 69). Live 

vegetation cover averaged 76.4 (± 13.8) percent throughout 

the study period. Seasonal trends were observed, with the 

minimum cover (50 percent) occurring in winter 2007, when 

live cover is expected to be the lowest. The vegetation did 

not appear to be influenced by the hurricanes during the 

initial sampling period (spring 2006), and neither salt stress 

nor disturbance species were present throughout the study 

period (fig. 70). 

Aboveground and Belowground Biomass

Live aboveground biomass ranged from 168.0 to 626.7 g 

dry weight m-2 (fig. 71). The peak value of live aboveground 

biomass occurred in fall 2006, while the lowest value occurred 

in winter 2007. The dead component of aboveground biomass 

tended to show trends that were the inverse of those of the live 

component; as live biomass increased dead biomass decreased. 

The peak value of dead aboveground biomass occurred in 

winter 2007 (778.7 ± 50.3 g dry weight m-2). The live and 

dead aboveground biomass components were within published 

ranges for marshes dominated by S. alterniflora (Kaswadji 

and others, 1990; Visser and others, 2006; Darby and Turner, 

2008). A marked decrease in biomass indicative of hurricaneinduced stress was not evident after Hurricanes Katrina and 

Rita. As was observed with vegetation cover, the live and 
Results and Discussion 83

Date

April 2006 

June 2006 

August 2006 

October 2006 

December 2006 

February 2007 

April 2007 

June 2007 

August 2007 

October 2007 

Salinity 

0

5

10

15

20

25

Figure 68. Mean 

values of daily 

surface-water salinity 

(solid line) and 

discrete porewater 

salinity (open circles) 

measured at 30 cm 

deep from April 2006 

to November 2007 at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326. 

Figure 69. Species 

composition (all 

Spartina alterniflora) 

of total live vegetation 

cover by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326-H. 
84 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

500

1,000

1,500

2,000

2,500

3,000

Live and dead aboveground biomass,

 in grams of dry weight per square meter

Figure 71. Live (white 

bars) and dead (gray 

bars) aboveground 

biomass (see standard 

error bars) by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326-H.

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Relative cover, by percent

0

20

40

60

80

100

Season

Figure 70. Seasonal 

cover of nondisturbance 

taxa at Coastwide 

Reference Monitoring 

System (CRMS) site 

0326-H. There was no 

presence of disturbance 

taxa throughout the 

study period.
Results and Discussion 85

Fall 2001 Fall 2002 Fall 2006 Fall 2007

Total and live aboveground biomass,

 in grams of dry weight per square meter

0

500

1,000

1,500

2,000

2,500

Season

Figure 72. Total (white 

bars) and live (gray 

bars) aboveground 

biomass (see standard 

error bars) measured 

at the end of growing 

seasons at Coastwide 

Reference Monitoring 

System (CRMS) 

site 0326-H.

dead components of aboveground biomass remained similar 

to historically observed conditions (fig. 72), with no 

significant difference between total aboveground biomass 

(p = 0.211) before and after the storms. Hurricanes 

Katrina and Rita did not influence species dominance at 

the site because no vegetation taxa common to disturbance 

environments colonized the site (fig. 70). The stand remained 

monospecific to S. alterniflora throughout the study period and 

did not appear to be negatively influenced by the hurricanes.

Total and live aboveground biomass at the end of 

growing seasons was greater in fall 2006 than in fall 2001, 

2002, and 2007 (fig. 72). Total aboveground biomass at the 

end of growing seasons ranged from 607.4 to 957.3 g dry 

weight m-2, while live aboveground biomass at the end of 

growing seasons ranged from 356.4 to 626.7 g dry weight m-2. 

As with total vegetation cover, total aboveground biomass 

at the end of growing seasons did not vary greatly 

throughout the study period; however, it was lower in fall 

2007 (mean = 607.4 ± 82.0 g dry weight m-2) than in any 

other season. 

Total aboveground biomass ranged from 607 (± 82) 

to 1,157 (± 79) g dry weight m-2, while the amount of 

total belowground biomass was approximately eight times 

greater, ranging from 6,077 (± 1,142) to 9,114 (± 570) g dry 

weight m-2 (fig. 73). Both aboveground and belowground 

biomass estimates were similar to those reported by Darby 

and Turner (2008) from a similar marsh dominated by S. 

alterniflora within Terrebonne basin. Little seasonal variation 

occurred in total aboveground and belowground biomass 

throughout the study. Dead roots and rhizomes composed the 

majority of the belowground biomass for all seasons (fig. 74). 

Live belowground biomass was greatest in fall 2006 but never 

exceeded 25 percent of the total belowground biomass. There 

were discernable trends in the seasonal abundance, with 

live belowground biomass being greatest between fall 2006 

and spring 2007. After the hurricanes, live belowground 

biomass was greater overall in the second growing season 

than in the first.

Sediment Characterization, Accretion, and Elevation

Mean values of soil bulk-density averaged 0.30 

(± 0.04) g cm-3 from 0 to 48 cm in depth (fig. 75). These 

values are similar to other estimates of soil bulk-density for 

saline marshes dominated by S. alterniflora in Louisiana, 

which range from 0.23 to 0.30 g cm-3 (Hatton and others, 

1983; DeLaune and others, 1990; Nyman and others, 

1993). Carbon accumulation was estimated at 154 (± 20.7) 

g C m-2 yr-1, and nitrogen accumulation was 7.1 (± 0.8) 

g N m-2 yr-1 (table 5). The mean value for depth of the peak 
86 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Total belowground biomass, by percent

0

20

40

60

80

100

Season

Figure 74. Live (white 

bars) and dead (gray 

bars) components of 

total belowground 

biomass by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326-H. 

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

Total aboveground and belowground biomass, 

in grams of dry weight per square meter

Season

Figure 73. Total 

aboveground 

(hatched bars) and 

belowground (gray 

bars) biomass (see 

standard error 

bars) by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0326-H.
Results and Discussion 87Figure 75. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference Monitoring System (CRMS) site 0326-H. 
88 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

level of caesium-137 activity for two cores taken in fall 2006 

was 20.9 cm (fig. 76). By these estimates, the accretion rate 

since 1963 has been 0.46 cm yr-1, which is lower than rates 

published for other saline marshes in Louisiana, which range 

from 0.59 to 1.10 cm yr-1 (Hatton and others, 1983; DeLaune 

and others, 1990; Nyman and others, 1993; Chmura and 

Kosters, 1994; Nyman and others, 2006). 

Soil bulk-density since 1963 was calculated at 0.29 

(± 0.03) g cm-3, similar to the soil bulk-density estimate 

before 1963. The depth of the 1963 layer at this site was 

approximately 7 to 15 cm shallower than at the other saline 

marsh study sites in this study except at a site in lower 

Breton Sound (peak depth of caesium-137 activity = 17.2 cm 

at CRMS0147), where only one core was processed for 

caesium activity. 

No short-term estimate of vertical accretion was possible 

because of poor sampling conditions. The feldspar marker 

horizon was only located during one sampling period in one 

feldspar plot; therefore, we could not analyze the feldspar 

data at this site. Site-specific processes dictate elevation 

and accretion changes, so it is not appropriate to assume that 

the rates calculated from the paired site (CRMS0326 over 

2.5 km north) are identical to CRMS0326-H; however, the 

data from nine CRMS study sites are available in appendix 2. 

The CRMS0326-H site is much closer to the gulf and on a 

major bayou, thereby receiving greater tidal inundation and 

suspended sediment than CRMS0326, which is located within 

an area of solid marsh separated by small bayous and marsh 

ponds. The long-term accretion rate calculated from the 

caesium-137 analysis of one core was 0.70 cm yr-1, which is 

within the range of other Louisiana saline marshes (Hatton 

and others, 1983; DeLaune, 1990; Nyman and others, 1993; 

Chmura and Kosters, 1994; Nyman and others, 2006; Smith 

and others, 1983).

The short-term elevation change rate at CRMS0326-H 

(measured by RSET) was calculated at 0.23 cm yr-1 during 

this study (fig. 77). With current estimates of RSLR, the site 

elevation change is 0.69 cm yr-1, less than what would be 

required to keep pace with RSLR. The limited data from this 

study suggest that the site is not building sufficient elevation to 

prevent increased inundation and stress from longer frequency 

and duration of flooding associated with RSLR. Rates of 

short-term elevation change alone are not conclusive of a 

failure to compensate for projected sea level rise, unless they 

are interpreted with respect to the elevation of the site within 

the tidal frame.

Summary of the Classification of Impacts

The CRMS0326-H site did not appear to be negatively 

impacted by either Hurricanes Katrina or Rita. This lack of 

influence from the hurricanes was expected because the site 

is located greater than 140 km from the path of Hurricane 

Katrina and 280 km from that of Hurricane Rita. The storm 

surges at the site were estimated to be less than 1.5 m, and 

because no impoundments exist in the area, the storm surge 

flushed in and out of the marsh quickly. The mechanical 

destruction of vegetation and the marsh surface that was 

observed at other sites was not present at CRMS0326-H. The 

site experienced mean values of porewater salinity greater than 

the mean value observed by Chabreck (1970) but within the 

range of historically observed values. The species at this site 

are adapted to fluctuations in salinity such as those observed 

during this study.

In fall 2005, immediately after Hurricanes Katrina and 

Rita, the departure from the average NDVI value was -0.21, 

indicating some decrease in plant vigor from the baseline 

average. At the end of the second growing season after the 

storms, the departure from the average NDVI value increased 

to -0.07, thereby indicating that the plant community had 

recovered somewhat but not to the baseline average. Our 

study does not include data on aboveground biomass or live 

cover from fall 2005 to validate the change in NDVI values; 

however, seasonal photography does illustrate the vegetative 

vigor in fall 2006. The monospecific stand of S. alterniflora

appeared healthy throughout the study period.

Case Study 5: CRMS0164-H

Overall Site Description

The CRMS0164-H site is located in the saline marshes 

in southwestern Barataria basin (fig. 78; see Louisiana Coastal 

Wetlands Planning, Protection and Restoration Act Program 

[n.d.] for definition of the basin) in an area classified as 

being indirectly impacted by Hurricanes Katrina and Rita 

in 2005. Marshes in this general region of the coast are 

typically dominated by S. alterniflora with D. spicata, Juncus 

roemerianus (needlegrass rush), and, recently, Avicennia 

germinans (L.) L (black mangrove). The area includes 

numerous small ponds and shallow lakes within the marshes. 

The CRMS0164-H site is located near a small lake (locally 

known as Airplane Lake) in the marsh adjacent to Bayou 

Ferblanc, near larger water bodies Lake Palourde and Bay 

Macoin. These water bodies are part of the increasingly 

open estuarine system connected to Caminada Bay. There 

is no direct connection from CRMS0164-H to a navigation 

canal, although the Southwestern Louisiana Canal is located 

several kilometers north of the Airplane Lake area and is a 

major waterway connecting Bayou Lafourche at Leeville 

to Caminada Bay and Barataria Bay. The Southwestern 

Louisiana Canal further connects into Timbalier Bay to the 

west, providing a pathway for higher salinity waters from the 

bay to enter the marshes.

Historical Datasets

The CRMS0164-H site is an area with high historical data 

collection value. Several earlier studies included this general 

area for field research, dating back to the earliest studies by the 

Center for Wetland Resources at Louisiana State University. 
Results and Discussion 89

Core 1 Core 2

0 20 40 60 80

Depth, in centimeters

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Bulk density, in grams per cubic centimeter

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Caesium-137 activity, in becquerels per kilogram

0 20 40 60 80

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Core 1 Core 2

EXPLANATION

137Cs activity 

Bulk density

Figure 76. Bulk density and caesium-137 profiles at Coastwide Reference Monitoring System (CRMS) site 0326-H. Measurements 

were obtained from two cores taken at 0–50 cm deep. Peak caesium-137 activity for core 1 occurred at a depth of 19.1 cm, and peak 

caesium-137 activity for core 2 occurred at a depth of 22.7 cm. 

Date

January 2007 

May 2007 

September 2007 

January 2008 

May 2008 

September 2008 

January 2009 

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Elevation change, in centimeters

Figure 77. Rate of elevation 

change at Coastwide 

Reference Monitoring 

System (CRMS) site 0362-H. 

There were no data on 

vertical accretion or shallow 

subsidence at CRMS0362-H. 

The rate of elevation change 

(y = -2.1234 + 0.0006X; 

r

2

 = 0.12) was 0.23 

centimeters per year (cm 

yr-1), and the relative sea 

level rise (RSLR) was 

0.92 cm yr-1. Elevation 

change at CRMS0362-H is 

projected to be 0.69 cm yr-1

less than RSLR. 
90 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 78. Location of Coastwide Reference Monitoring System (CRMS) sites 0164-H and 0164 within lower Barataria basin (see Louisiana Coastal Wetlands Planning, Protection and Restoration Act Program [n.d.] for definition of the basin). 
Results and Discussion 91

Several graduate students used data collected in this area to 

determine primary production values in saline marshes (Kirby 

and Gosselink, 1976; Kaswadji, 1982; Kaswadji and others, 

1990). Historical field studies also include the LOOP baseline 

study for the original environmental impact work (Sasser and 

others, 1978). The baseline environmental impact study was 

followed by a long-term environmental monitoring program 

(that is, nearly 20 years) following construction of LOOP. The 

long term monitoring program (hereafter termed the LOOP 

study) included this site as a reference area.

Monitoring Program for the Louisiana Offshore Oil Port 

The LOOP study included measurements of impacts from 

the LOOP and was conducted from 1978 through 1995, during 

which time vegetation biomass was harvested from 0.25-m2

plots at the end of growing seasons (usually in September) at 

the CRMS0164-H site. At each site, the first plot on a transect 

was randomly selected. Subsequent plots were determined 

by orienting the transect perpendicular to the adjacent bayou 

and sampling at 20-m intervals. If a plot was located in open 

water, the location was changed to the nearest vegetated area 

along the transect line. Biomass measurements for the LOOP 

study followed the same procedures as used in this study. The 

dominant plant species was S. alterniflora, with S. patens and 

D. spicata occasionally present. Another aspect of the LOOP 

study included two graduate theses that involved mapping 

wetlands and vegetation change within the southwestern 

Barataria basin (Dozier, 1983; Evers, 1991). The authors of 

both theses used a grid cell size of 0.25 ha. As reported in 

Dozier (1983), the wetland classification included a series of 

classes that combined both percentage and configuration of 

the water bodies within the marsh. Vegetation in the area was 

classified by Dozier (1983) for 1945, 1956, 1965, and 1980, 

by Evers and others (1992) for 1985, and by Visser and others 

(1996) for 1989 and 1995. The vegetation categories were 

based on dominant species to define marsh types for 1983 and 

1995 (Evers and others, 1992).

In addition to the LOOP study, the Environmental 

Monitoring and Assessment Program (EMAP) funded by the 

Environmental Protection Agency included one site (BH3) that 

is in proximity (approximately 1 km) to site CRMS0164-H. 

Aboveground and belowground sampling methods were the 

same as outlined above. The site was originally sampled in 

1991 (Swenson and Turner, 1994) and then resampled in 1993 

(Turner and others, 1998). Six replicates were taken in the fall 

each year and the study focused on aboveground vegetation, 

belowground components, and salinity. Aboveground 

vegetation indices measured included live, standing dead, and 

dead biomass; percentage of vegetation cover; and stem count, 

length and diameter. Soil properties included percentage of 

organic content, bulk density, and soil reduction. Surfacewater and soil salinities were also measured. 

Marsh Stability

Land loss rates in the area have been relatively low 

since the 1950s. The saline marshes in the Airplane Lake area 

have been relatively stable, although in a relatively degraded 

condition (Evers, 1991). Sasser and others (1986) classified 

site CRMS0164-H as solid marsh in both 1945 and 1956, 

signifying that there was less than 10 percent open water 

within the marsh area. By 1969, the marsh area was classified 

as having 10–25 percent open water within the marsh. In 

1980 and 1985, enough breakup had occurred within the 

marsh to account for 25–40 percent open water (Evers and 

others, 1992). From 1989 through 1995, CRMS0164-H was 

classified as degraded, with 40–60 percent open water, because 

of typical processes of marsh degredation (for example, 

subsidence and oil and gas activities) that commonly occur in 

Louisiana marshes.

Surface-Water and Porewater Salinity

Surface salinity was not collected at site CRMS0164-H 

because it was paired with site CRMS0164 that had a surface 

salinity recorder. Historical surface salinities were, however, 

available from EMAP for site BH3, which is located near the 

area of Airplane Lake. Mean values for surface-water salinity 

at site BH3 were 17.4 in 1991 and 15.2 in 1993 (Swenson and 

Turner, 1994; Turner and others, 1998). 

Seasonal porewater salinities were significantly higher in 

the summer and fall of 2006 than in the same seasons in 2007 

(p < 0.0001, fig. 79). Porewater salinities from the EMAP 

site averaged 17.7 in 1991 and 17.1 in 1993 (Swenson and 

Turner, 1994; Turner and others, 1998), which were lower 

than the values (>20) obtained in the current study for site 

CRMS0164-H; however, all of the values reported here are 

within the typical salinity range of saline marsh. 

Vegetation Cover

Throughout our study, the CRMS0164-H site always 

had greater than 80 percent vegetation cover and showed no 

observable difference before and after Hurricanes Katrina and 

Rita. Spartina alterniflora was the only species consistently 

found during every sampling within the plot used to measure 

vegetation cover (fig. 80); however, A. germinans was present 

in the general vicinity in summer 2007. Spartina alterniflora

is a typical saline marsh species; therefore, no disturbance 

species were indicated by the vegetation cover data. Cover 

values at the end of growing seasons averaged 90 percent in 

2006 and 95 percent in 2007. 

Aboveground and Belowground Biomass

As in the vegetation cover data, S. alterniflora was the 

only species consistently present in the aboveground biomass 

data throughout the period of our study (fig. 81). Live 

aboveground biomass was greatest at the end of the growing 

season in 2006 (averaging 1,283 ± 49 g dry weight m-2) and 

2007 (averaging 1,128 ± 240 g dry weight m-2). These values 

are slightly greater but similar to those reported for other 

marshes dominated by S. alterniflora (Visser and others, 1996; 

Darby and Turner, 2008). Total (live and dead) 

aboveground biomass ranged from 1,051 (± 163) to 2,284 
92 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 80. Species 

composition (all Spartina 

alterniflora) of total live 

vegetation cover by season 

at Coastwide Reference 

Monitoring System (CRMS) 

site 0164-H.

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Porewater salinity

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

Figure 79. Discrete 

porewater salinity 

(see standard error 

bars) measured at 30 

cm deep by season at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0164-H.
Results and Discussion 93

Figure 81. Species 

composition (all 

Spartina alterniflora) 

of seasonal live 

aboveground biomass 

(see standard error 

bars) at Coastwide 

Reference Monitoring 

System (CRMS) 

site 0164-H.

(± 544) g dry weight m-2, peaking in spring 2007 because the 

greatest amount of dead biomass was collected in that season. 

Avicennia germinans was also found in at least one sampling 

period in biomass plots (accounting for < 10 percent of the 

biomass in spring 2007).

Total aboveground biomass was 1,870 (± 158) g dry 

weight m-2 at the end of the growing season in 2006 and 1,638 

(± 416) g dry weight m-2 at the end of the growing season 

in 2007 (fig. 82). A comparison between total aboveground 

biomass at the end of growing seasons in 1994 and 1995 

and at the end of growing seasons after Hurricanes Katrina 

and Rita showed no statistical difference (p = 0.0544). 

Comparable data were also obtained for this site for 1970 

(Kirby and Gosselink, 1976), from 1978 through 1995 (Visser 

and other, 1996), for 1980 (Kaswadji and others, 1990), and 

from a nearby site for 1991 (Swenson and Turner, 1994) and 

1993 (Turner and others, 1998). A comparison plot of these 

data (fig. 83) shows that all of the data within each of four 

datasets are within the range of the LOOP study data. 

Visser and others (2006) included the LOOP study data 

as part of a database they compiled to test quantile regression 

as a tool to best explain interannual variation. They found that 

maximum biomass correlated positively with optimal nitrogen 

levels in surface water. They also concluded that the flooding 

index they employed was a poor predictor of S. alterniflora

biomass, possibly because of the lack of elevation data at each 

plot sampled. 

Slocum and others (2005) studied the effects of sediment 

addition to saline marshes and found a positive relationship 

between percentage of vegetation cover, canopy height, 

and aboveground biomass of S. alterniflora for the 2 years 

following a slurry enrichment program that added up to 30 cm 

of sediment onto the marsh surface. The trend weakened with 

passage of time. 

Total belowground biomass ranged from 5,685 (± 976) 

to 8,127 (± 1,208) g dry weight m-2 throughout the study 

period (fig. 84). These values are similar to those reported 

by Darby and Turner (2008). The dead component of 

belowground biomass was greater than the live component in 

every sampling period and was highly variable. The amount 

of variability in the data on dead belowground biomass is 

typical of these types of measurements. Both total and live 

belowground biomass peaked in the winter 2007 samples. 
94 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

1970 1980 1990 2000 2010

Aboveground biomass, 

in grams of dry weight per square meter

0

500

1,000

1,500

2,000

2,500

Year

LOOP

EMAP

Kaswadji and others, 1990

Kirby and Gosselink, 1976

The current study

Figure 83. Aboveground 

biomass at the end of 

growing seasons as 

measured during various 

studies conducted in 

the vicinity of Coastwide 

Reference Monitoring 

System (CRMS) site 

0164-H. Data from the 

Environmental Monitoring 

and Assessment Program 

(EMAP) were found in 

Swenson and Turner 

(1994) and Turner and 

others (1998). Data from 

the Louisiana Offshore Oil 

Port (LOOP) 

annual report can be 

found in Sasser and 

others, 1978.

Fall 1994 Fall 1995 Fall 2006 Fall 2007

Total and live aboveground biomass,

 in grams of dry weight per square meter

0

500

1,000

1,500

2,000

2,500

Season

Figure 82. Total (white 

bars) and live (gray 

bars) aboveground 

biomass (see standard 

error bars) at the end 

of growing seasons at 

saline marsh sites with 

availability of historical 

data acquired before 

Hurricanes Katrina and 

Rita (historical data from 

Visser and others, 2006).
Results and Discussion 95

Season

Spring 2006

Summer 2006

Fall 2006

Winter 2007

Spring 2007

Summer 2007

Fall 2007

Dead and live belowground biomass,

 in grams of dry weight per square meter

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

Figure 84. Live (white bars) and dead (gray bars) belowground biomass (see standard error bars) by season at Coastwide Reference 

Monitoring System (CRMS) site 0164-H. 

Sediment Characterization, Accretion, and Elevation

Sediment bulk densities averaged 0.29 g cm-3 when 

computed above the 1963 horizon (36.2 cm depth, figs. 85 

and 86, table 5). Above the 1963 horizon, bulk density is 

highest at the 2- to 4-cm depth (0.36 g cm-3), decreasing 

with depth to 34 cm. Turner and others (2006) found the 

average bulk density in the newly deposited material after 

Hurricane Katrina to be 0.37 g cm-3. A noticeable decrease 

in bulk density is found at the 16-cm depth, with bulk density 

averaging 0.32 g cm-3 for the 0 to 14-cm depth and 0.24 g cm-3

in the 16- to 32-cm depth. The highest bulk density was found 

at 36 cm in both replicate cores (fig. 85). 

The caesium-137 analysis indicated that the accretion rate 

since 1963 averaged 0.84 cm yr-1 (individual core estimates 

of 0.87 cm yr-1 and 0.81 cm yr-1), which is a higher rate than 

the rate of 0.66 cm yr-1 found at its paired site, CRMS0164. 

Samples taken in 1993 at a nearby site by Swenson and 

Turner (1994) had an average accretion rate of 0.88 cm yr-1. 

After Hurricanes Katrina and Rita, Turner and others (2006) 

found accretion rates greater than 3 cm within the vicinity 

of this site. No elevation data were collected at this site 

because it was selected for its historical data and thus lacked 

an established RSET; however, feldspar data were collected. 

The short-term accretion rate was estimated at 2.69 cm yr-1, 

which was the highest calculated accretion rate from all the 

study sites but was based on excellent feldspar coring (fig. 87). 

Note that this accretion was not due to the 2005 hurricanes, 

as the feldspar marker horizon was established after the 

hurricanes. Without the site-specific elevation data, it is not 

possible to predict how this accretion influenced overall soil 

elevation (see appendix 2 for elevation and accretion change 

information from the paired site CRMS0164).

Summary of the Classification of Impacts

The data obtained from the Airplane Lake area indicated 

little or no observable effects from the 2005 hurricanes on 

vegetative productivity. This site was approximately 50 

km west of the track of Hurricane Katrina. The study site 

was then inundated with a 1.2–1.5-m (4–5-ft) storm surge 

during Hurricane Rita (Federal Emergency Management 
96 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 85. Depth profiles of bulk density, nitrogen, and carbon at Coastwide Reference Monitoring System (CRMS) site 0164-H. 
Results and Discussion 97

Bulk density, in grams per cubic centimeter

0.0 0.1 0.2 0.3 0.4 0.5

Depth interval, in centimeters

0-15

15-30

30-36

0-36

Figure 86. Mean 

values of bulk density by 

various depth intervals 

at Coastwide Reference 

Monitoring System 

(CRMS) site 0164-H. 

Figure 87. Feldspar 

marker horizon 

(deployed July 13, 2006) 

and short-term accretion 

on July 10, 2008, at 

Coastwide Reference 

Monitoring System 

(CRMS) site 0164-H.
98 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Agency, 2006). Mineral sedimentation was greatest at 

this site compared to all other sites according to the shortterm accretion data. The greater mineral content and the 

nonbuoyancy of the vegetated mat of saline marsh allowed 

the storm surge to submerge the marsh, rather than uplifting it 

and subjecting it to the full force of wind waves at the surface, 

as occurred in the buoyant (fresh and intermediate) organic 

marshes that were in the path of Hurricanes Katrina and Rita.

Soil Process Rates of Wetlands in the Chenier 

and Deltaic Plains of Louisiana

We analyzed new soil accretion estimates from 30 sites 

across fresh, brackish/intermediate, and saline marshes of the 

chenier and deltaic plains of Louisiana. We investigated basic 

relationships of mineral and organic matter contribution to 

wetland soil development and provided estimates of nitrogen 

and carbon accumulation (burial) rates among these different 

marsh types. These new data build on existing information 

about saline and brackish marshes, but also fill knowledge 

gaps about freshwater areas.

General methods for the soils analysis and calculations 

exist in the methods section of this document. Data were 

summarized for general trends among marsh types (fresh, 

brackish/intermediate, and saline) and also divided among 

geological provinces (deltaic and chenier plains). Similar 

to the vegetation analyses, we combined the data from 

intermediate and brackish marshes dominated by S. patens

to increase replication. Six hydrologically impounded 

sites in brackish marsh of the chenier plain were identified 

and separated from nonimpounded sites when examining 

vertical accretion rates. Otherwise, impounded sites were not 

distinguished in regression relationships for understanding 

the basic effects of mineral/organic contributions to vertical 

accretion of soil. To judge the relative strength of inference 

pertaining to an estimate, the number of sites with datable 

cores within a given marsh type and geologic province 

is provided in table 12. Site-specific information for all 

estimates of vertical accretion of soil and associated 

mineral/organic and nutrient accumulation rates are 

presented in table 5.

Results and Discussion

Accretion Rates Between the Chenier and Deltaic Plains

Long-term accretion rates for freshwater marshes 

were 0.57 (± 0.13) cm yr-1 for the deltaic plain and 0.57 

(± 0.25) cm yr-1 for the chenier plain (table 13). Accretion 

rates in nonimpounded brackish marshes were 0.72 (± 0.14) 

cm yr-1 for the deltaic plain and 0.65 (± 0.23) cm yr-1 for the 

chenier plain. Under impounded conditions, accretion was 

appreciably lower than under nonimpounded conditions 

(0.38 ± 0.04 cm yr-1). Accretion in saline marshes of the 

deltaic plain was 0.64 (± 0.16) cm yr-1; there were no cores 

from saline marshes in the chenier plain. 

The estimated mean value of accretion in freshwater 

marshes (0.57 cm yr-1) was below the range (0.72–1.02 

cm yr-1) of means reported by others (tables 12 and 13). There 

is good agreement, however, among data from this study 

on accretion in brackish marsh (0.65 and 0.72 cm yr-1, both 

geological provinces) and the range of other estimates of the 

Table 12. Summary of mean values for long-term (since 1963) rates of soil accretion and organic/mineral accumulation in 

herbaceous marshes of the chenier and deltaic plains of Louisiana (for definitions, see Saucier [1994]). 

[Mean values are provided with a standard error of plus or minus 1 unit. Numbers listed in the “study” column denote the following studies: (1) Nyman and 

others, 2006; (2) Holm, 2006; (3) Sasser and others, 2002; (4) DeLaune and Pezeshki, 2003; (5) Turner and others, 2001. No., number; cm yr-1, centimeters 

per year; g m-2 yr-1, grams per square meter per year]

Marsh type No. of cores Accretion 

(cm yr-1)

Organic 

(g m-2 yr-1)

Mineral

 (g m-2 yr-1)

Study Notes

Fresh 2 0.83 456 461 1 deltaic; stable

1 0.72 617 85 1 deltaic; stable

1 0.88 563 61 2 deltaic; floating marsh

1 1.02 488 621 1 chenier; stable

Brackish 12 0.96 (0.32) 542 (217) 724 (326) 1 deltaic; deteriorating

10 0.88 (0.14) 604 (83) 1,270 (255) 1 deltaic; stable

2 0.72 (0.07) 349 (66) 523 (405) 3 deltaic; deteriorating

3 0.65 (0.18) 315 (85) 178 (51) 4 deltaic; freshwater diversion

Saline 10 0.98 (0.36) 618 (261) 1,970 (941) 1 deltaic; deteriorating

12 0.59 (0.14) 424 (82) 1,928 (898) 1 deltaic; stable

52 0.66 (0.21) 492 (190) 1,354 (899) 5 deltaic
Results and Discussion 99

Table 13. Mean values for long-term rates of soil accretion in three marsh types in the deltaic and chenier plains of Louisiana (for 

definitions, see Saucier [1994]). Accretion rates were determined by calculating the depth of peak activity of caesium-137, which 

marked the year 1963. Cores were collected during the spring or summer of 2006, after the passages of Hurricanes Rita and Katrina.

[Mean values are provided with a standard error of plus or minus 1 unit. no., number; cm yr-1, centimeters per year; NA, not available]

Deltaic plain Chenier plain

Marsh type Sites/Cores (no.) "Accretion (cm yr-1)" Sites/Cores (no.) "Accretion (cm yr-1)"

Fresh 8/15 0.57 (0.13) 4/5 0.57 (0.25)

Brackish/Intermediate

 Natural 4/5 0.72 (0.14) 2/3 0.65 (0.23)

 Impounded NA NA 6/10 0.38 (0.04)

Saline 6/10 0.64 (0.16) NA NA

mean (0.65–0.96 cm yr-1). A notable pattern is evident, with 

higher rates of accretion in nonimpounded versus impounded 

brackish marshes in the chenier plain (tables 12 and 13). 

Saline marshes in the deltaic plain have remarkably consistent 

patterns of vertical accretion: 0.66 ± 0.21 cm yr-1 (52 cores, 

Turner and others, 2001); 0.59 ± 0.14 (12 cores, Nyman and 

others, 2006); and 0.64 ± 0.16 cm yr-1 (6 sites/10 cores, the 

current study) (tables 12 and 13).

Contribution of Organic and Mineral Fractions to Soil Accretion

For saline and brackish/intermediate marshes in 

Louisiana, there is agreement that rates of organic matter 

accumulation explain much of the variability associated with 

vertical accretion rates of marsh (Turner and others, 2001; 

Nyman and others, 2006). Data from our study support 

this strong relationship, such that 1.6 to 2.0 mm yr-1 (salt 

and brackish, respectively) of vertical accretion increase is 

associated with every 100 g dry weight m-2 yr-1 increase in 

organic matter accumulation (table 14). There has been a poor 

understanding of accumulation and accretion rates of mineral 

and organic matter in freshwater marshes because of limited 

data from these areas. While the general principle also holds 

for freshwater marshes that organic matter accumulation 

explains most of the variability in marsh vertical accretion, 

it also appears that 37 percent of the variability in vertical 

Table 14. Regression relationships between long-term rates of vertical accretion and accumulation of organic and mineral matter 

for three marsh types across Louisiana at research sites from the Coastwide Reference Monitoring System paired with sites that 

were historically sampled by Holm, 2006. 

[r2, coefficient of determination; mm yr-1, millimeters per year; g m-2 yr-1, grams per square meter per year; g m-2, grams per square meter]

Variable 

Slope Intercept r

2 Dependent Independent

Accretion Mineral

Fresh 0.381 0.48 0.37

Brackish 0.111 0.43 0.26

Saline 0.071 0.52 0.18

Accretion Organic

Fresh 0.91 0.28 0.64

Brackish 2.01 -0.16 0.92

Saline 1.61 -0.007 0.88

Organic Mineral

Fresh 32.52 205 0.66

Brackish 5.02 302 0.24

Saline 6.02 309 0.37

1

 Slope = mm yr-1 vertical accretion /100 g m-2 yr-1 of mineral or organic matter.

2

 Slope = g m-2 organic matter /100 g m-2 yr-1 mineral matter.
100 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

accretion can be explained by mineral matter accumulation in 

freshwater areas, compared to lower values for brackish (26 

percent) and salt (18 percent) (table 14). Moreover, 66 percent 

of the variance in organic accumulation rates can be explained 

by mineral accumulation rates for freshwater marshes, 24 

percent for brackish marshes, and 37 percent for saline 

marshes. For illustration purposes in freshwater marshes, an 

increase of 100 g dry weight m-2 yr-1 of mineral matter results 

in a concomitant increase of approximately 33 g dry weight 

m-2 yr-1 of organic matter accumulation. In contrast to the 

rates applicable to freshwater marshes, in saline marshes an 

increase of 100 g dry weight m-2 yr-1 of mineral matter results 

in an increase of 6.0 g dry weight m-2 yr-1 of organic matter 

accumulation (table 14). These relationships suggest that 

freshwater marshes may react more positively (that is, with 

increased organic matter accumulation) than saline marshes, 

given an equivalent amount of mineral sedimentation.

Organic, Mineral, and Nutrient Content in Relation to 

Accumulation Rates

Across marsh types, mean values of organic matter 

content in sediment from within the upper 20 cm is 

comparable to 0.051 g cm-3 for fresh marsh, 0.068 g cm-3 for 

brackish marsh, and 0.065 g cm-3 for saline marsh (table 15). 

There are appreciable differences in mineral density, with 

0.042 g cm-3 for fresh marsh, 0.150 g cm-3 for brackish marsh, 

and 0.300 g cm-3 for saline marshes (table 15). Nitrogen 

and carbon densities of these different marsh types mirror 

differences in organic content (table 15). All marsh types have 

carbon to nitrogen ratios below 20 (fig. 88), a threshold above 

which nitrogen immobilization is possible (Enriquez and 

others, 1993).

All three marsh types are capable of accumulating up 

to 200 g C m-2 yr-1 (fig. 89 and table 5). The upper limit on 

the mean value for nitrogen accumulation for all marsh types 

appears to be between 10 and 14 g m-2 yr-1. Mean values 

of organic matter accumulation tended to be lower in the 

chenier plain than in the deltaic plain for both freshwater and 

brackish marshes; however, variability within these estimates 

was high (table 16). All of the estimates of accumulation in 

mineral matter (across marsh types and basins) exhibited high 

Table 15. Mean values of organic, mineral, nitrogen, and carbon density in the upper 20 cm of soil in three marsh types. Values for 

the deltaic and chenier plains of Louisiana (for definitions, see Saucier [1994]) are combined. Cores were collected at research sites 

from the Coastwide Reference Monitoring System paired with sites that were historically sampled by Holm, 2006. 

[Mean values are provided with a standard error of plus or minus 1 unit. g cm-3, grams per cubic centimeter; mg cm-3, milligrams per cubic centimeter]

Density

Marsh type Organic (g cm-3) Mineral (g cm-3) Nitrogen (mg cm-3) Carbon (mg cm-3)

Fresh 0.051 (0.001) 0.042 (0.003) 1.78 (0.04) 29.5 (0.7)

Brackish 0.068 (0.001) 0.150 (0.010) 2.31 (0.09) 36.6 (1.5)

Saline 0.065 (0.001) 0.300 (0.016) 1.72 (0.10) 29.1 (1.6)

variability, which may reflect spatial heterogeneity of mineral 

sedimentation associated with Hurricanes Katrina and Rita. 

For example, Turner and others (2001) showed high variability 

in mineral sedimentation (1,354 ± 899 g m-2 yr-1) for Louisiana 

saline marshes. 

In our study, average rates of mineral sedimentation were 

approximately 1,800 g dry weight m-2 yr-1 for saline marsh, 

600 g cm-3 for brackish marsh, and 300 g dry weight m-2 yr-1

for fresh marshes of the deltaic plain (table 16). Since our 

sites were not under active river influence, these estimates do 

not represent upper limits of mineral sedimentation. Estimates 

of soil-building processes in active deltaic areas are lacking 

for coastal Louisiana.

Overall Conclusions

The influence of Hurricanes Katrina and Rita on coastal 

marsh communities was highly variable and site-specific. This 

study attempts to identify hurricane impacts by using new data 

collected across a broad landscape, with sites being subjected 

to various degrees of hurricane exposure. Documenting a new 

ecological baseline of coastal marshes is not straightforward, 

requiring adequate information to describe the spatially 

and temporally variable habitats that make up this dynamic 

ecosystem—an environment that is ever-changing, even under 

“normal” (nonstorm) conditions. Subsidence, sea level rise, 

erosion, sedimentation, and grazing are some of the processes 

that are always at work influencing the attributes of the 

system. Catastrophic storms such as Hurricanes Katrina and 

Rita create a range of effects, from marginal impacts to a total 

resetting of the system, such that one static baseline condition 

for the entire ecosystem is not totally appropriate. It may be 

more useful to think of coastal marshes as exhibiting dynamic 

baselines. Our overall assessment of changes resulting 

from Hurricanes Katrina and Rita contributes information 

relative to a new ecological baseline of the Louisiana coastal 

marshes. Generally, we found that fresh marshes experienced 

more negative effects from the hurricanes than did brackish/

intermediate and saline marshes. 
Overall Conclusions 101

Nitrogen,

 miligrams per cubic centimeter

0

1

2

3

Carbon, 

 miligrams per cubic centimeter

0

10

20

30

40

Marsh types

Fresh marsh

Brackish/Intermediate marsh

Saline marsh

Carbon to nitrogen ratio

0

5

10

15

20

25

Nitrogen immobilization

Figure 88. Carbon and nitrogen content in sediment (see standard 

error bars) and their ratios from the upper 20 cm of soil across different 

marsh types, with combined values from the Louisiana chenier and 

deltaic plains (for definitions, see Saucier [1994]). Carbon-to-nitrogen 

ratios above 20 are conducive to nitrogen immobilization.

Freshwater sites within areas directly influenced 

by Hurricanes Katrina (western region) and Rita 

(eastern region) shared the following characteristics 

when compared with indirectly influenced areas: 

(1) significantly higher porewater salinities at the 

end of seasons; (2) significantly lower values of 

live aboveground biomass at the end of seasons; 

(3) significantly lower values of peak biomass; (4) 

significantly greater contribution of disturbance 

species; and (5) significantly lower values of 

belowground biomass (table 17). All freshwater 

sites within the directly influenced area were not 

affected similarly. Specific location, dominant 

vegetation before Hurricanes Katrina and Rita, and 

surrounding hydrologic conditions likely influenced 

recovery from the storms. Two full growing seasons 

after Hurricanes Katrina and Rita, all freshwater 

sites had average values of aboveground biomass 

that were within the typical ranges; however, some 

sites exhibited shifts in dominant species towards 

disturbance or more salt-tolerant species. The longterm implications of changes in species composition 

cannot be determined with data from only two 

growing seasons because vegetation at many of the 

sites continues to undergo changes. At locations 

where site-specific data acquired before Hurricanes 

Katrina and Rita were available for comparison, the 

data indicate that these hurricanes had little effect on 

aboveground and belowground biomass. 

Brackish/intermediate marsh sites experienced 

the largest deviations from historical data on 

porewater salinity; however, directly and indirectly 

influenced sites had statistically similar porewater 

salinities at the end of growing seasons. Among 

the brackish/intermediate marsh sites, there was 

no statistically significant influence from hurricane 

impacts on the following marsh characteristics: 

(1) live biomass at the end of growing seasons; (2) 

percentage of disturbance taxa; (3) peak values of 

aboveground biomass; or (4) belowground biomass 

at the end of growing seasons (table 17). It should be 

noted, however, that our study included only 2 of 10 

sites in the zone of indirect influence. A few of the 

brackish/intermediate marsh sites that we studied did 

experience large changes in species composition after 

Hurricanes Katrina and Rita.

Saline marsh sites fared well after Hurricanes 

Katrina and Rita. A comparison of direct versus 

indirect hurricane influence showed that the directly 

impacted sites (2 of the 6) had significantly greater 

values of aboveground biomass at the end of 

growing season than did indirectly influenced sites, 

indicating that the hurricanes had a positive effect 

on plant biomass (table 17). Species composition 

remained consistent (S. alterniflora) at most sites, no 

disturbance taxa were observed, and live vegetation 
102 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Table 16. Mean values of accumulation rates of organic, mineral, nitrogen, and carbon fractions in soil from three marsh types in the 

deltaic and chenier plains of Louisiana (for definitions, see Saucier [1994]). Measurements were obtained from sites in the Coastwide 

Reference Monitoring System that were paired with sites that were historically sampled by Holm, 2006. The number of sites and cores 

used for calculations follow those in table 13. 

 [Mean values are provided with a standard error of plus or minus 1 unit. g m-2 yr-1, grams per square meter per year] 

Accumulation (g m-2 yr-1)

Marsh type Region Organic Mineral Nitrogen Carbon

Fresh Deltaic 331 (110) 319 (340) 9.1 (2.8) 148 (41)

Chenier 246 (192) 263 (420) 7.4 (6.8) 109 (73)

Brackish Deltaic 447 (31) 594 (701) 12.3 (2.8) 177 (44)

Chenier 304 (77) 913 (1,017) 7.1 (1.9) 109 (16)

Saline Deltaic 415 (98) 1,755 (1,000) 8.8 (2.1) 150 (38)

Figure 89. The distribution of carbon and nitrogen accumulation in sediment across different marsh types, with combined values 

from the Louisiana chenier and deltaic plains (for definitions, see Saucier [1994].) Marsh types span a wide distribution of nutrient 

accumulation rates and exhibit similar upper limits of carbon (200 grams per square meter per year [g m-2 yr-1]) and nitrogen 

(10–14 g m-2 yr-1) accumulation.
Overall Conclusions 103

Table 17. Comparison of study parameters for fresh, brackish/intermediate, and saline marsh types and sample year. 

[Definitions: cm yr-1, centimeters per year] 

Fresh Brackish/Intermediate Saline

Porewater salinity 2006 > 2007; 

direct impact > indirect 

impact; decreasing during 

study; overall 0.7 > 1968 

estimate

2006 slightly > 2007 though not 

significant; no difference 

between direct and indirect 

impact; decreasing during 

study; overall 4.7 > 1968 

estimate

2006 > 2007; 

direct < indirect impact;

decreasing during study; 

overall 2.7 > 1968 estimate

Total percent cover End of growing season 

2007 > 2006

End of growing season 

2007 > 2006

End of growing season 

2007 > 2006

Live aboveground biomass End of growing season 

2007 > 2006; direct 

impact < indirect impact

End of growing season 

2007 > 2006; greatest 

quantity increase during 

study of all habitat type; 

no difference between 

direct vs. indirect impact

End of growing season 

2006 > 2007; direct > indirect 

impact

Total belowground biomass No difference between end of 

growing season 2006 and 

2007; direct impact < indirect 

impact; decrease from historic 

condition and potential 

biomass deficit

No difference between end of 

growing season 2006 and 2007 

or direct vs. indirect impact 

Greatest quantity among all 

habitats throughout study;

no difference end of growing 

season 2006 vs. 2007 or direct 

vs. indirect impact

Cover of disturbance taxa 2007 > 2006; 

direct impact > indirect 

impact; present throughout 

entire study

2006 > 2007 but not significant; 

present throughout entire 

study; number of sites with 

disturbance taxa in 

2007 > 2006

none present

Long-term accretion rates Deltaic plain 0.57 ± 0.13 cm 

yr-1; chenier plain 0.57 ± 0.25 

cm yr-1; below the range in 

literature

Deltaic plain (unimpounded) 

0.72 ± 0.14 cm yr-1, chenier 

plain (unimpounded) 

0.65 ± 0.23 cm yr-1; within 

range of literature; chenier 

plain unimpounded sites with 

higher accretion rates than 

impounded sites

Deltaic plain 0.64 ± 0.16 cm 

yr-1; consistent with literature

Organic accumulation rates Chenier plain < deltaic plain Chenier plain < deltaic plain Estimate in deltaic plain only

Mineral accumulation rates Highly variable across coast but 

chenier plain < deltaic plain in 

fresh marshes

Highly variable across coast but 

chenier plain > deltaic plain in 

brackish/intermediate marshes

Much greater in saline marsh 

than fresh and brackish/

intermediate

Nitrogen accumulation rates Chenier plain < deltaic plain Chenier plain < deltaic plain Estimate in deltaic plain only

Carbon accumulation rates Chenier plain < deltaic plain Chenier plain < deltaic plain Estimate in deltaic plain only
104 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

cover remained above 60 percent throughout the period of 

our study. Values of belowground biomass were also similar 

among all sites. Although saline marsh sites were closest to 

the coast and therefore most exposed to hurricane effects, the 

dominant vegetation is better adapted to salinity surges, and 

the storm surge was not impounded on these sites for any 

appreciable amount of time. Some sites may have received a 

sediment subsidy associated with the storms.

Our analysis of long-term rates of vertical accretion in 

the brackish marsh of the chenier plain suggests that accretion 

under impounded conditions is less than under nonimpounded 

conditions. Our data also support the results of previous 

studies that found rates of organic matter accumulation explain 

much of the variability associated with vertical accretion in 

brackish/intermediate and saline marshes. In fresh marshes, 

more of the variability associated with vertical accretion 

can be explained by mineral accumulation than in the other 

marsh types. All marsh types span a wide distribution of rates 

of nutrient accumulation but exhibit similar upper limits of 

carbon (200 g C m-2 yr-1) and nitrogen (10–14 g N m-2 yr-1) 

accumulation.

Our study provides extensive information that will 

help define baseline conditions in multiple marsh types 

after Hurricanes Katrina and Rita, not only for salinity and 

vegetation variables, but also for soil characteristics and 

accumulation rates. Paired with the data that will continue to 

be collected through the CRMS program, the current study 

provides information for resource managers and scientists 

that can be used for comparisons of environmental conditions 

following future landscape-scale disturbances and to support 

development of ecological models of landscape response.

In this study, we documented severe damage to marshes 

by Hurricanes Katrina and Rita, but the mechanism of 

damage was variable across the landscape. For example, in 

the chenier plain, saltwater surged into freshwater marshes 

and stayed much too long, effectively causing damage that 

reset the vegetation community, even though the physical 

damage to these marshes was not overwhelming. The future 

of these marshes is uncertain. Will freshening conditions 

over time facilitate the vegetation community to return to 

highly productive freshwater species that were present before 

the storm, or has the saltwater influence caused a shift to 

dominance by more salt-tolerant species? Figure 40 provides 

an appropriate conceptual representation of the new ecological 

baseline for this condition. Impacts to the deltaic coastal 

wetlands in the eastern area were different from those in the 

west, with the freshwater marshes heavily damaged physically 

(marsh mats ripped, flipped, and relocated) by strong winds 

and the churning currents associated with high storm surge. 

The future of these marshes is also uncertain; however, 

because the saltwater surge was not impounded in this area, as 

it was in the chenier plain, an eventual recovery is likely, given 

a continuation of freshwater conditions. Saline marshes were 

not severely impacted by the hurricanes. Species composition 

of the vegetation in saline marshes was not affected, and 

sediment deposition in saline marshes actually seems to 

have increased vegetative productivity. In the brackish/

intermediate marshes, disturbance species took advantage of 

the opportunity provided by physical and saltwater-induced 

perturbations. The observed shifts in species composition to 

include disturbance species is a significant baseline change, 

although probably temporary. 

Further development of conceptual models for specific 

marsh types would support a better understanding of the 

factors that control how they function during average, 

nonstorm periods, as well as how storms and other stresssors 

might affect and change them. Some emphasis should be 

placed on understanding the differences in storm effects 

that are possible on managed versus nonmanaged areas (for 

example, differences in impounded versus nonimpounded 

wetlands). Data from this study suggest differences in 

response at managed versus nonmanaged areas, but more work 

will be necessary to verify and determine the implications. An 

important consideration is that management activities in the 

coastal landscape (for example, impoundments and canals) 

appear to have magnified the effect of stressors influencing 

the marshes. It is possible that some management actions 

may pre-establish how the coastal landscape responds to 

events such as catastrophic storms. This potential for dramatic 

human influence calls for a much better understanding of 

the implications of our management actions. For example, 

what are the implications of building impoundments in the 

coastal landscape to the overall productivity of the vegetation 

community occupying the marsh landscape? What are the 

physiological implications of impoundments and resulting 

hydrologic changes to productivity of belowground vegetation 

and its related soil composition, structure, and strength? Soil 

strength may be a robust indicator of vegetative productivity 

and marsh health, and studies to determine these relationships 

will be valuable to our ability to evaluate marsh conditions 

over a large landscape. 

Understanding the variable effects of large storms on an 

expansive and complex ecosystem of coastal marshes such as 

the Mississippi River deltaic wetlands requires landscapescale studies to provide a proper evaluation of the impacts. 

The landscape configuration of the coastal wetlands of the 

gulf coast reflects influences, at any given time, from current 

and previous forces exerted on the ecosystem, including 

storms, subsidence, erosion, and active sedimentation 

processes. Large hurricanes such as Katrina and Rita 

influence vast areas of the coast. Most previous evaluations 

of hurricane impacts have focused on the immediate areas 

of visible physical impact; however, the scientific community 

is now recognizing—supported by the more extensive 

network of data collection stations available through CRMS—

that high water levels and associated saltwater surge are 

influences that occur across very large areas. These effects 

could go virtually unreported without extensive efforts 

to collect data at the landscape scale in order to facilitate 

evaluation of coastwide impacts from episodic events, as well 

as other potential stressors. 
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Appendix 1. Hydrographs for study sites within the Coastwide Reference Monitoring System (CRMS) 111

Appendix 1. Hydrographs for study sites within the Coastwide Reference 

Monitoring System (CRMS)

Figure 1–1. Water level, with marsh elevation (red line), and surface salinity at site 0135 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

5

10

15

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4 A.

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

10

20

30

Salinity

B.

Figure 1–2. Water level, with marsh elevation (red line), and surface salinity at site 0147 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
112 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

20

40

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

1

2

3 A.

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0.5

1

1.5

Salinity

B.

Figure 1–3. Water level, with marsh elevation (red line), and surface salinity at site 0164 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.

Figure 1–4. Water level, with marsh elevation (red line), and surface salinity at site 0219 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
Appendix 1. Hydrographs for study sites within the Coastwide Reference Monitoring System (CRMS) 113

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4

A.

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

0.5

1

1.5

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

1

2

3

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

5

10

15

Salinity

B.

Figure 1–5. Water level, with marsh elevation (red line), and surface salinity at site 0268 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.

Figure 1–6. Water level, with marsh elevation (red line), and surface salinity at site 0294 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
114 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

10

20

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

-2

0

2

4

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

10

20

30

Salinity

B.

Figure 1–7. Water level, with marsh elevation (red line), and surface salinity at site 0312 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.

Figure 1–8. Water level, with marsh elevation (red line), and surface salinity at site 0326 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
Appendix 1. Hydrographs for study sites within the Coastwide Reference Monitoring System (CRMS) 115

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

1

2

3

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

10

20

30

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

1

2

3

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

5

10

Salinity

B.

Figure 1–9. Unadjusted water level and raw surface salinity at site 0610 of the Coastwide Reference Monitoring System (CRMS) from 

April 1, 2006, to November 1, 2007. No adjusted water level or salinity data were available; therefore, the data presented should be used 

for trend purposes only, not exact water-level or salinity values. A, Unadjusted water level. B, Raw surface salinity.

Figure 1–10. Water level, with marsh elevation (red line), and raw surface salinity at site 0651 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. No adjusted salinity data were available; therefore, the data presented should 

be used for trend purposes only, not exact salinity values. A, Water level. B, Raw surface salinity.
116 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

1

1.5

2

2.5

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

10

20

30

Salinity

B.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

1

2

3

4

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

5

10

15

20

Salinity

B.

Figure 1–11. Water level, with marsh elevation (red line), and surface salinity at site 0669 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.

Figure 1–12. Water level, with marsh elevation (red line), and surface salinity at site 0672 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
Appendix 1. Hydrographs for study sites within the Coastwide Reference Monitoring System (CRMS) 117

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0.5

1

1.5

2

Water level, in feet 

above or below 

North American 

Vertical Datum of 1988

A.

Apr 06 July 06 Oct 06 Jan 07 Apr 07 July 07 Oct 07

0

5

10

15

Salinity

B.

Figure 1–13. Water level, with marsh elevation (red line), and surface salinity at site 2156 of the Coastwide Reference Monitoring 

System (CRMS) from April 1, 2006, to November 1, 2007. A, Water level. B, Surface salinity.
118 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Appendix 2. Site elevation and accretion at study sites within the Coastwide 

Reference Monitoring System (CRMS)

Figure 2–1. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0135 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -1.0072 + 0.0005X; r2 = 0.02) was 0.19 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 0.5679 + 0.0013X; r2 = 0.21) was 0.49 cm yr-1. The rate of shallow subsidence was 0.30 cm yr-1, and the 

relative sea level rise (RSLR) was 0.92 cm yr-1. Elevation change at CRMS0135 is projected to be 0.73 cm yr-1 less than RSLR. Trend lines 

represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by subtracting 

the rate of vertical accretion from the rate of elevation change.
Appendix 2. Site elevation and accretion at study sites within the Coastwide Reference Monitoring System (CRMS) 119

Figure 2–2. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0147 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -2.2311 + 0.0029X; r2 = 0.09) was 1.05 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 0.8746 + 0.0028X; r2 = 0.62) was 1.01 cm yr-1. The rate of shallow subsidence was -0.04 cm yr-1, and 

the relative sea level rise (RSLR) was 0.92 cm yr-1. Elevation change at CRMS0147 is projected to exceed the RSLR by 0.13 cm yr-1. 

Trend lines represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by 

subtracting the rate of vertical accretion from the rate of elevation change.
120 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 2–3. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0164 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -0.6910+ 0.0026X; r2 = 0.07) was 0.96 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 1.0274 + 0.0013X; r2 = 0.50) was 0.49 cm yr-1. The rate of shallow subsidence was -0.47 cm yr-1, and 

the relative sea level rise (RSLR) was 0.92 cm yr-1. Elevation change at CRMS0164 is projected to exceed the RSLR by 0.04 cm yr-1. 

Trend lines represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by 

subtracting the rate of vertical accretion from the rate of elevation change.
Appendix 2. Site elevation and accretion at study sites within the Coastwide Reference Monitoring System (CRMS) 121

Figure 2–4. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0326 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -0.9312 - 0.0010X; r2 = 0.08) was -0.39 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 0.7184 + 0.0010X; r2 = 0.25) was 0.37 cm yr-1. The rate of shallow subsidence was 0.76 cm yr-1, and the 

relative sea level rise (RSLR) was 0.92 cm yr-1. Elevation change at CRMS0326 is projected to be 1.31 cm yr-1 less than RSLR. Trend lines 

represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by subtracting 

the rate of vertical accretion from the rate of elevation change.
122 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 2–5. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0605 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -1.1953 - 0.0008X; r2 = 0.004) was -2.94 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = -0.4420 + 0.0071X; r2 = 0.54) was 2.56 cm yr-1. The rate of shallow subsidence was 5.51 cm yr-1, and the 

relative sea level rise (RSLR) was 0.57 cm yr-1. Elevation change at CRMS0605 is projected to be 3.51 cm yr-1 less than RSLR. Trend lines 

represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by subtracting 

the rate of vertical accretion from the rate of elevation change.
Appendix 2. Site elevation and accretion at study sites within the Coastwide Reference Monitoring System (CRMS) 123

Figure 2–6. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0610 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = 1.6651 - 0.0072X; r2 = 0.24) was -2.59 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 0.1248 + 0.0031X; r2 = 0.62) was 1.12 cm yr-1. The rate of shallow subsidence was 3.71 cm yr-1, and the 

relative sea level rise (RSLR) was 0.57 cm yr-1. Elevation change at CRMS0610 is projected to be 3.16 cm yr-1 less than RSLR. Trend lines 

represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by subtracting 

the rate of vertical accretion from the rate of elevation change.
124 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 2–7. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0651 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -0.5780 - 0.0004X; r2 = 0.009) was -0.15 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 0.1077 + 0.0007X; r2 = 0.19) was 0.25 cm yr-1. The rate of shallow subsidence was 0.40 cm yr-1, and the 

relative sea level rise (RSLR) was 0.57 cm yr-1. Elevation change at CRMS0651 is projected to be 0.72 cm yr-1 less than RSLR. Trend lines 

represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by subtracting 

the rate of vertical accretion from the rate of elevation change.
Appendix 2. Site elevation and accretion at study sites within the Coastwide Reference Monitoring System (CRMS) 125

Figure 2–8. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 0672 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -2.9544 + 0.0032X; r2 = 0.01) was 1.16 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = -0.3523 + 0.0018X; r2 = 0.44) was 0.67 cm yr-1. The rate of shallow subsidence was -0.49 cm yr-1, and 

the relative sea level rise (RSLR) was 0.57 cm yr-1. Elevation change at CRMS0672 is projected to exceed the RSLR by 0.59 cm yr-1. 

Trend lines represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by 

subtracting the rate of vertical accretion from the rate of elevation change.
126 Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities

Figure 2–9. Changes in elevation and vertical accretion at Coastwide Reference Monitoring System (CRMS) site 2156 from January 

1, 2007, to January 1, 2009. The rate of elevation change (y = -2.6014+ 0.0018X; r2 = 0.04) was 0.68 centimeters per year (cm yr-1), and 

the rate of vertical accretion (y = 4.5957 - 0.0044X; r2 = 0.68) was-1.59 cm yr-1. The rate of shallow subsidence was -2.27 cm yr-1, and 

the relative sea level rise (RSLR) was 0.57 cm yr-1. Elevation change at CRMS2156 is projected to exceed the RSLR by 0.11 cm yr-1. 

Trend lines represent a best-fit linear regression from data collected in three sampling periods. Shallow subsidence is calculated by 

subtracting the rate of vertical accretion from the rate of elevation change.
Piazza and others—Geomorphic and Ecological Effects of Hurricanes Katrina and Rita on Coastal Louisiana Marsh Communities—OFR 2011–1094