Trends and Causes of Historical Wetland 

Loss, Sabine National Wildlife Refuge, 

Southwest Louisiana

By Julie C. Bernier, Robert A. Morton, and Kyle W. Kelso

Open File Report 2011–1169

U.S. Department of the Interior

U.S. Geological Survey

SABINE NATIONAL WILDLIFE REFUGE, 2008

SABINE NATIONAL WILDLIFE REFUGE, 1955
Cover: Aerial photographs from 1955 and 2008 illustrate the extent of wetland loss in Sabine National Wildlife 

Refuge in the western chenier plain, Cameron Parish, Louisiana. Scale 1:150,000.
Trends and Causes of Historical Wetland 

Loss, Sabine National Wildlife Refuge, 

Southwest Louisiana

By Julie C. Bernier, Robert A. Morton, and Kyle W. Kelso

Open File Report 2011–1169

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

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Suggested citation:

Bernier, J.C., Morton, R.A., Kelso, K.W., 2011, Trends and Causes of Historical Wetland 

Loss, Sabine National Wildlife Refuge, Southwest Louisiana, U.S. Geological Survey, 

Open File Report 2011-1169, 36p., plus app.
 v

Contents

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

Introduction.....................................................................................................................................................1

Geological Setting and Depositional History of the Chenier Plain ...............................................1

Field and Laboratory Methods.....................................................................................................................2

Coring Operations.................................................................................................................................2

Core Deformation.........................................................................................................................3

Water-Level Measurements and Elevation Corrections..............................................................10

Wetlands of the Sabine National Wildlife Refuge..................................................................................11

Historical Land- and Water-Area Changes ....................................................................................11

Sabine National Wildlife Refuge Management Unit 1.........................................................12

Sabine National Wildlife Refuge Management Unit 3.........................................................13

Sabine National Wildlife Refuge Management Unit 5.........................................................13

Summary – Historical Wetland Losses at Sabine National Wildlife Refuge....................15

Historical Changes in Wetland-Vegetation Types.........................................................................16

Effects of Climate and Marsh Management on Wetlands...........................................................18

Sedimentary Facies.....................................................................................................................................19

Historical Subsidence and Erosion of SNWR Marshes ........................................................................21

Sabine National Wildlife Refuge Management Unit 1..................................................................22

Study Area 1................................................................................................................................22

Study Area 2................................................................................................................................23

Sabine National Wildlife Refuge Management Unit 5..................................................................24

Study Area 3................................................................................................................................24

Study Area 4................................................................................................................................25

Sabine National Wildlife Refuge Management Unit 3..................................................................26

Study Area 5................................................................................................................................26

Historical Land-Surface Subsidence ......................................................................................................27

Subsurface Fluid Withdrawal ....................................................................................................................28

Discussion and Conclusions......................................................................................................................30

Acknowledgments.......................................................................................................................................34

References....................................................................................................................................................34
vi 

Figures

Figure 1. Regional map of the Calcasieu-Sabine hydrologic basin in southwestern Louisiana 

showing locations of coring sites in Sabine National Wildlife Refuge (SNWR) relative 

to SNWR management units and nearby hydrologic gages .................................................2

Figure 2. Regional map of the Calcasieu-Sabine hydrologic basin in southwestern Louisiana 

showing locations of coring sites, oil-and-gas fields, Pleistocene sediments, and areas 

of historical wetland loss from 1932 to 2006.............................................................................3

Figure 3. Water levels recorded at (A) Coastwide Reference Monitoring System (CRMS) site 

#0641 on June 4-8, 2008, (B) Louisiana Office of Coastal Protection and Restoration 

(OCPR) coastal monitoring station #CS02-05 on June 4-8, 2008, (C) CRMS site #0660 on 

June 7-12, 2008, and (D) CRMS site #0694 on August 5-10, 2010 ........................................11

Figure 4. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 1 showing locations of coring sites and historical land-loss trends between 1932 and 2006 ..................13

Figure 5. Locations of sediment cores at Sabine National Wildlife Refuge (SNWR) Management 

Unit 1 superimposed on pre- and post-land-loss aerial photographs taken in (A) 1955, 

(B) 1965, (C) 1978, and (D) 2008 .................................................................................................14

Figure 6. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 3 showing locations of coring sites and historical land-loss trends between 1932 and 2006 ..................15

Figure 7. Locations of sediment cores at Sabine National Wildlife Refuge (SNWR) Management 

Unit 3 superimposed on pre- and post-land-loss aerial photographs taken in (A) 1955, 

(B) 1965, (C) 1978, and (D) 2008 .................................................................................................16

Figure 8. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 5 showing locations of coring sites, Pleistocene sediments, and historical land-loss trends between 

1932 and 2006...............................................................................................................................17

Figure 9. Locations of sediment cores and Pleistocene sediments at Sabine National Wildlife 

Refuge (SNWR) Management Unit 5 superimposed on pre- and post-land-loss aerial 

photographs taken in (A) 1955, (B) 1965, (C) 1978, and (D) 2008..........................................18

Figure 10. Linear-regression trend for mean annual water levels at Calcasieu Pass recorded at 

the U.S. Army Corps of Engineers Cameron tide gage (USACE #73650) from 

1942 to 2005..................................................................................................................................19

Figure 11. Conceptual diagram showing the geometric derivation of the reference stratigraphic 

section used to estimate the subsidence and erosion components contributing to the 

total one-dimensional accommodation space at an open-water core site......................19

Figure 12. Locations of sediment cores and sediment-surface profiles collected at Sabine 

National Wildlife Refuge study area 1.....................................................................................20

Figure 13. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB1-09 to SB1-01 illustrating the magnitude of subsidence and 

wetland erosion at study area 1...............................................................................................20

Figure 14. Locations of sediment cores and sediment-surface profiles collected at Sabine 

National Wildlife Refuge study area 2.....................................................................................21

Figure 15. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB1-18 to SB1-20 illustrating the magnitude of subsidence and 

wetland erosion (in centimeters) at study area 2..................................................................22

Figure 16. Combined bathymetric profile and stratigraphic cross section for marsh and open-water 
 vii

core sites SB1-13 to SB1-16 illustrating the magnitude of subsidence and wetland erosion 

(in centimeters) at study area 2 ..................................................................................................23

Figure 17. Locations of sediment cores and sediment-surface profiles collected at Sabine 

National Wildlife Refuge study area 3.....................................................................................24

Figure 18. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB5-08 to SB5-012 illustrating the magnitude of subsidence and 

wetland erosion at study area 3...............................................................................................25

Figure 19. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB5-01 to SB5-07 illustrating the magnitude of subsidence and wetland erosion at study area 3......................................................................................................26

Figure 20. Locations of sediment cores and sediment-surface profiles collected at Sabine 

National Wildlife Refuge study area 4.....................................................................................27

Figure 21. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB5-24 to SB5-36 illustrating the magnitude of subsidence and wetland erosion at study area 4......................................................................................................28

Figure 22. Combined bathymetric profile and stratigraphic cross section for (A) marsh and openwater core sites SB5-32 to SB5-30 and (B) core sites SB5-35 to SB5-40 illustrating the 

magnitude of subsidence and wetland erosion at study area 4.........................................29

Figure 23. Locations of sediment cores and sediment-surface profiles collected at Sabine 

National Wildlife Refuge study area 5.....................................................................................30

Figure 24. Combined bathymetric profile and stratigraphic cross section for marsh and openwater core sites SB3-01 to SB3-06 illustrating the magnitude of subsidence and wetland erosion at study area 5......................................................................................................31

Figure 25. Annual fluid production through 2009 from oil-and-gas fields surrounding the Sabine 

National Wildlife Refuge. (A) Black Bayou complex, (B) East and West Hackberry complex, (C) Cameron Meadows complex, and (D) Mud Lake and Second Bayou 

complex ........................................................................................................................................32

Figures continued
viii 

Tables

Table 1. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at Sabine National Wildlife Refuge..................................................... 4-10

Table 2. Types and sources of imagery used to investigate land-water changes in the Sabine 

National Wildlife Refuge and surrounding areas..................................................................12

Table 3. Discovery year, number of wells drilled, and cumulative volumes of fluids produced 

through 2009 from oil-and-gas field complexes surrounding the Sabine National Wildlife Refuge wetlands...................................................................................................................32

Table 4. Comparison and ranges of parameters at wetland-loss sites in the chenier and delta 

plains.............................................................................................................................................33
 ix

Area

square kilometer (km2) 247.1 acre

Vertical coordinate informaton is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate informaton is referenced to the North American Datum of 1983 (NAD 83).

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Conversion Factors

By Julie C. Bernier, Robert A. Morton, and Kyle W. Kelso

Abstract

Prior U.S. Geological Survey studies (Open-File Reports 

2005-1216 and 2009-1158) examined historical land- and 

water-area changes and estimated magnitudes of land 

subsidence and erosion at 10 wetland sites in the Mississippi 

River delta plain. The present study extends that work by 

analyzing interior wetland loss and relative magnitudes of 

subsidence and erosion at five additional wetland sites in 

Sabine National Wildlife Refuge (SNWR) in the western 

chenier plain. The study sites were selected because their 

geologic setting differed from that of the delta plain; also, 

although the refuge marshes had been managed partly to 

minimize wetland loss, interior wetland losses there were 

extensive. Historical aerial photography, datum-corrected 

marsh elevations and water depths, and sediment cores were 

integrated to evaluate historical land- and water-area changes 

at SNWR.

The thickness of the uppermost Holocene sediments 

(peat and organic-rich mud) and the elevation of stratigraphic 

contacts were compared at marsh and open-water sites across 

areas of formerly continuous marsh to estimate magnitudes 

of recent elevation loss caused by vertical erosion and 

subsidence. Results of these analyses indicate that erosion 

greatly exceeded subsidence at most of the core sites, 

although both processes have contributed to historical wetland 

loss. Comparison of these results with results of our prior 

studies indicates that magnitudes of subsidence and total 

accommodation space that formed in the western chenier plain 

were less than those in the delta plain. Compared with the 

delta plain, where subsidence generally exceeded erosion and 

peat thicknesses were so great that peat was preserved even 

where erosion was greater than subsidence, the SNWR peats 

are thin and were absent (eroded) at most open-water sites. 

Although historical subsidence rates in the chenier plain are 

substantially lower than most of the same rates in the delta 

plain, the temporal and spatial trends of rapid wetland loss, 

highest rates of land-surface subsidence, and high rates of 

oil-and-gas production are similar, indicating that historical 

wetland loss was likely initiated by similar processes (deepsubsurface subsidence) in both regions. 

Introduction

Wetland loss in coastal Louisiana has been such an 

important environmental and economic issue that decades of 

scientific research have been dedicated to the topic since the 

trend was first recognized in the late 1960s (National Research 

Council, 2006). In support of that effort, the U.S. Geological 

Survey (USGS) has been conducting research directed toward 

a better understanding of the physical processes and human 

activities that contribute to wetland loss and the timing of that 

loss. Recent USGS efforts have concentrated on hotspot areas 

of the Mississippi delta plain, where high rates of interior 

wetland loss were difficult to explain when only surficial 

processes and wetland ecology were considered. Prior USGS 

studies that examined interior wetland loss in the delta region 

demonstrated close temporal and spatial correlations between 

wetland loss, delta-plain subsidence, and deep-subsurface 

hydrocarbon production (Morton and others, 2003; 2005; 

2006; 2009a; Morton and Bernier, 2010). 

To complement the extensive wetland-loss research 

conducted in the delta plain, fieldwork completed in 2008 

and 2010 was designed to investigate the temporal and spatial 

distribution of wetland loss in the western chenier plain, which 

has a different geological setting and depositional style than 

the delta plain, using the same techniques and general data 

sources that were used in the delta plain. The Sabine National 

Wildlife Refuge (SNWR) in the Calcasieu-Sabine hydrologic 

basin (figs. 1 and 2) was selected for study because interior 

wetland loss there had been extensive, the refuge marshes had 

been managed partly to minimize wetland loss, and study sites 

were accessible by airboat without concern for land-ownership 

issues.

Geological Setting and Depositional History of 

the Chenier Plain

The modern Mississippi River and delta overlie a deep 

incised valley that was excavated during the last Pleistocene 

fall and lowstand in sea level. The valley was subsequently 

backfilled when sea level rose during the late Pleistocene 

and Holocene (Kolb and Van Lopik, 1958). Within the 

valley fill, the Holocene sedimentary section is more than 

60 meters (m) thick (Roberts, 1997). The extant delta plain 

was constructed by sediment transported through a series of 

distributary channels that deposited overlapping delta lobes 

(Frazier, 1967). In general, the direction of sediment supply 

was perpendicular or at a high angle to the gulf shoreline. 

This depositional style left remnant active and abandoned 

distributary channels and promoted the development of lakes 

(areas of incomplete filling) and a network of tidal channels in 

the wetlands. 

Trends and Causes of Historical Wetland Loss, Sabine 

National Wildlife Refuge, Southwest Louisiana
2 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Figure 1. Regional map of the Calcasieu-Sabine hydrologic basin in southwestern Louisiana showing locations of coring sites in 

Sabine National Wildlife Refuge (SNWR) relative to SNWR management units and nearby hydrologic gages. Landsat 5 Thematic 

Mapper (TM) image acquired December 13, 2006; RGB visual display uses bands 4 (near-infrared), 5 (mid-infrared), and 3 (visible red). 

Abbreviations: CRMS, Coastwide Reference Monitoring System; OCPR, Louisiana Office of Coastal Protection and Restoration; NOAA,

National Oceanic and Atmospheric Administration; USACE, U.S. Army Corps of Engineers.

0 10 KILOMETERS

0 10 MILES

Unit 1

Unit 3

Unit 5

CRMS #0641

OCPR #CS02-05

NOAA #8770590

(Sabine Pass, TX)

USACE #73650

(Cameron, LA)

CRM6 #0694

CRMS #0660

93° 50' 93° 40' 93° 30' 93° 20'

30° 0'

29° 50'

29° 40'

GULF OF MEXICO

SABINE LAKE CALCASIEU LAKE

LOUISIANA

GULF OF MEXICO

EXPLANATION

Core location Tide gage SNWR refuge boundary SNWR Management Unit boundary Calcasieu-Sabine basin

In contrast to the geologic setting of the delta plain, the 

chenier plain consists of a thin wedge of Holocene sediments 

overlying stiff over-compacted Pleistocene sediments that 

were subaerially exposed during the late Pleistocene sea-level 

lowstand. Sabine and Calcasieu Lakes are unfilled remnants of 

incised valleys excavated by the Sabine-Neches and Calcasieu 

Rivers, respectively, during the same lowstand. Cores taken by 

Gould and McFarlan (1959) show that below the chenier-plain 

surface, muddy sediments above the Pleistocene-Holocene 

unconformity range in thickness from less than a meter to 

about 6 m, with thickness generally increasing toward the Gulf 

of Mexico. 

The chenier plain was constructed by progradation of 

the gulf shoreline as the coastal plain advanced seaward with 

the addition of broad mudflats and intervening narrow, sandy 

beach ridges (cheniers). Radiocarbon dates from the beach 

ridges indicate that progradation of the chenier plain began 

about 3,000 years ago (Gould and McFarlan, 1959; Penland 

and Suter, 1989; McBride and others, 2007). In general, the 

direction of sediment supply for the chenier plain was parallel 

to the gulf shoreline because sediment transport by coastalplain rivers is trapped in Sabine and Calcasieu Lakes. As a 

result of the alongshore processes of sediment progradation 

and aggradation, only a few tidal channels were constructed 

within the chenier-plain wetlands, and vast continuous 

meadows of dense wetland grasses were the natural setting 

before they were altered by human activities.

Field and Laboratory Methods

Coring Operations

Both push cores and vibracores were used to determine 

the thickness and characteristics of shallow sediments beneath 

the chenier plain at SNWR using the methods described in 

Morton and others (2009a; 2009b). The push cores and vibracores are designated ‘p’ and ‘v,’ respectively, after the core 

number (table 1; appendix A). The ‘p’ and ‘v’ designations 

are not used when referring to a specific core site rather than 

to individual cores. A Russian peat corer (Jowsey, 1966) was 
 3

Figure 2. Regional map of the Calcasieu-Sabine hydrologic basin in southwestern Louisiana showing locations of coring sites, oil-andgas fields, Pleistocene sediments (Heinrich and others, 2002; Henirich, 2005a), and areas of historical wetland loss from 1932 to 2006. 

0 10 KILOMETERS

0 10 MILES

SECOND BAYOU

HACKBERRY, WEST

HACKBERRY, EAST

MUD LAKE, EAST

BLACK BAYOU

BLACK BAYOU, SOUTH

CAMERON MEADOWS

Unit 5 Unit 1

Unit 3

93° 50' 93° 40' 93° 30' 93° 20'

30° 0'

29° 50'

29° 40'

GULF OF MEXICO

SABINE LAKE CALCASIEU LAKE

LOUISIANA

GULF OF MEXICO

EXPLANATION

Core location

SNWR refuge boundary

State boundary

Oil-and-gas field

1932-2006 land loss

Pleistocene outcrop

Land

SNWR Management Unit boundary Water

used to collect sediment cores in 50-centimeter (cm) intervals 

at each of the emergent-marsh, marsh-edge, and open-water 

coring sites. If the organic-clastic contact was not recovered in 

the first 50-cm coring interval, the push corer was inserted into 

the same hole left by extraction of the previous core in order 

to limit resistance against the coring device and to ensure 

recovery of the correct depth interval. Each 50-cm core section was transferred into pre-cut, semi-cylindrical PVC pipe. 

The cores were then encased in plastic wrap, sealed to retain 

moisture, and labeled according to core number, core interval, 

and orientation.

Vibracores were collected only at the emergent-marsh 

sites in SNWR Management Units 1 and 5. The vibracoring 

technique was illustrated and described by Lanesky and others 

(1979). Compared to push cores, vibracores provide deeper, 

continuous penetration, which can reveal stratigraphy below 

the organic-rich sediments that occur near the surface. After 

extraction, each continuous core length was capped, sealed, 

and labeled with the core number and orientation.

Twenty-three vibracores and 95 push cores were located 

with a portable Global Positioning System (GPS) receiver at 

the five study sites. Cores taken along transects across areas of 

historic wetland loss provided close stratigraphic correlation 

between the present emergent-marsh sediments and adjacent open-water sediments, where emergent marsh formerly 

existed. 

The cores were transported to the USGS St. Petersburg 

Coastal and Marine Science Center in Florida. Each vibracore 

was cut into 1-m sections and split lengthwise. The push cores 

and one-half of each vibracore were cleaned, photographed, 

and described in detail. The second half of each split vibracore 

was immediately sealed for future sampling. All core sections were then placed in containers and stored onsite. The 

core descriptions and photographs (appendix A) were used 

to identify the predominant sedimentary facies and to select 

stratigraphic contacts that were correlated between cores and 

used to estimate magnitudes of wetland subsidence and erosion (table 1).

Core Deformation

The peat sections recovered in the push cores typically 

are thicker than those recovered by the vibracores at the same 

Field and Laboratory Methods
4 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Table 1. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at Sabine 

National Wildlife Refuge.

[A detailed derivation of the reference stratigraphic section for each study area is given in appendix B. The specific reference stratigraphic thicknesses 

and contact elevations at each core site are a function of the adjacent emergent-marsh stratigraphy and distance along the transect. Positive marsh-minuswater (m-w) adjusted depth-difference values indicate erosion, and negative m-w depth-difference values indicate sediment accumulation; m-w adjusted 

elevation-difference values represent estimated subsidence. Cores are arranged in the same order that they are shown on the stratigraphic cross sections 

(figs. 13, 15, 16, 18, 19, 21, 22, and 24). cm, centimeters]

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Study area 1: transect SB1-09 to SB1-01 (fig. 13)

reference section at SB1-10 marsh 50 17 33 31 19

SB1-10p marsh edge 13 10 3 20 -7

difference (m-w) 37 7 30 11 26

reference section at SB1-27 marsh 46 31 15

SB1-27p water 4 12 -8

difference (m-w) 42 19 23

reference section at SB1-26 marsh 39 31 8

SB1-26p water 3 14 -11

difference (m-w) 36 17 19

reference section at SB1-08 marsh 31 23 8 31 0

SB1-08p marsh edge 18 12 6 22 -4

difference (m-w) 13 11 2 9 4

reference section at SB1-25 marsh 32 33 -1

SB1-25p water 5 10 -5

difference (m-w) 27 23 4

reference section at SB1-06 marsh 33 27 6 35 -2

SB1-06p marsh edge 17 9 8 17 0

difference (m-w) 16 18 -2 18 -2

reference section at SB1-24 marsh 36 37 -1

SB1-24p water 3 10 -7

difference (m-w) 33 27 6

reference section at SB1-04 marsh 45 43 2

SB1-04p1 marsh edge 8 14 -6

difference (m-w) 37 29 8

reference section at SB1-23 marsh 42 42 0

SB1-23p water 0 10 -10

difference (m-w) 42 32 10

reference section at SB1-22 marsh 39 40 -1

SB1-22p1 water 2 17 -15

difference (m-w) 37 23 14
 5

reference section at SB1-02 marsh 36 26 10 39 -3

SB1-02p marsh edge 14 17 -3 28 -14

difference (m-w) 22 9 13 11 11

Study area 2: transect SB1-18 to SB1-20 (fig. 15)

reference section at SB1-19 marsh 48 32 16 40 8

SB1-19p marsh edge 14 20 -6 28 -14

difference (m-w) 34 12 22 12 22

reference section at SB1-34 marsh 47 37 10

SB1-34p water -3 14 -17

difference (m-w) 50 23 27

reference section at SB1-35 marsh 47 35 12

SB1-35p2 water -6 19 -23

difference (m-w) 53 16 35

reference section at SB1-37 marsh 46 29 17

SB1-37p water 2 11 -9

difference (m-w) 44 18 26

reference section at SB1-21 marsh 46 20 26 25 21

SB1-21p marsh edge 16 7 9 11 5

difference (m-w) 30 13 17 14 16

Study area 2: transect SB1-13 to SB1-16 (fig. 16)

SB1-13p marsh interior 71 63 8

SB1-11p marsh 55 52 3

difference 16 11 5

reference section at SB1-12 marsh 55 52 3 64 -9

SB1-12p marsh edge 26 27 -1 43 -17

difference (m-w) 29 25 4 21 8

reference section at SB1-28 marsh 54 47 7 59 -5

SB1-28p water 3 20 -17 32 -29

difference (m-w) 51 27 24 27 24

reference section at SB1-29 marsh 52 51 1

SB1-29p water -1 13 -14

difference (m-w) 53 38 15

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

Field and Laboratory Methods
6 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

reference section at SB1-30 marsh 49 43 6

SB1-30p water -2 16 -18

difference (m-w) 51 27 24

reference section at SB1-31 marsh 43 32 11

SB1-31p water -5 17 -22

difference (m-w) 48 15 33

reference section at SB1-15 marsh 37 28 9

SB1-15p2 marsh edge 12 4 8

difference (m-w) 25 24 1

reference section at SB1-32 marsh 36 19 17 27 9

SB1-32p water 5 5 0 12 -7

difference 31 14 17 15 16

reference section at SB1-33 marsh 33 25 8

SB1-33p water -1 9 -10

difference (m-w) 34 16 18

reference section at SB1-17 marsh 30 23 7

SB1-17p marsh edge 8 9 -1

difference (m-w) 22 14 8

Study area 3: transect SB5-01 to SB5-07 (fig. 19)

reference section at SB5-02 marsh 40 58 -18 67 -27

SB5-02p marsh edge -9 13 -22 21 -30

difference (m-w) 49 45 4 46 3

reference section at SB5-14 marsh 39 58 -19 67 -28

SB5-14p water -26 11 -37 20 -46

difference (m-w) 65 47 18 47 18

reference section at SB5-15 marsh 36 57 -21 67 -31

SB5-15p water -28 5 -33 13 -41

difference (m-w) 64 52 12 54 10

reference section at SB5-16 marsh 34 57 -23 68 -34

SB5-16p water -22 8 -30 17 -39

difference (m-w) 56 49 7 51 5

reference section at SB5-17 marsh 32 57 -25 68 -36

SB5-17p water -16 14 -30 22 -38

difference (m-w) 48 43 5 46 2

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)
 7

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

reference section at SB5-04 marsh 30 57 -27 68 -38

SB5-04p marsh edge -9 20 -29 29 -38

difference (m-w) 39 37 2 39 0

reference section at SB5-18 marsh 36 70 -34 78 -42

SB5-18p water -8 31 -39 38 -46

difference (m-w) 44 39 5 40 4

reference section at SB5-06 marsh 38 83 -45

SB5-06p1 marsh edge 14 62 -48

difference (m-w) 24 21 3

SB5-05p marsh 38 75 -37 83 -45

SB5-07p marsh interior 44 80 -36 94 -50

difference (m-w) -6 -5 -1 -11 5

Study area 3: transect SB5-08 to SB5-12 (fig. 18)

reference section at SB5-09 marsh 35 42 -7

SB5-09p marsh edge -4 14 -18

difference (m-w) 39 28 11

reference section at SB5-23 marsh 35 36 -1 46 -11

SB5-23p water -15 4 -19 15 -30

difference (m-w) 50 32 18 31 19

reference section at SB5-22 marsh 35 45 -10

SB5-22p water -23 7 -30

difference (m-w) 58 38 20

reference section at SB5-21 marsh 36 52 -16 62 -26

SB5-21p water -27 4 -31 15 -42

difference (m-w) 63 48 15 47 16

reference section at SB5-20 marsh 37 57 -20 67 -30

SB5-20p water -18 8 -26 17 -35

difference (m-w) 55 49 6 50 5

reference section at SB5-11 marsh 37 57 -20 67 -30

SB5-11p marsh edge -20 19 -39 29 -49

difference (m-w) 57 38 19 38 19

reference section at SB5-19 marsh 38 67 -29

SB5-19p water -7 20 -27

difference (m-w) 45 47 -2

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Field and Laboratory Methods
8 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

reference section at SB5-13 marsh 39 56 -17 67 -28

SB5-13p marsh edge 11 34 -23 50 -39

difference (m-w) 28 22 6 17 11

Study area 4: transect SB5-24 to SB5-36 (fig. 21)

reference section at SB5-25 marsh 47 65 -18 78 -31

SB5-25p marsh edge -16 10 -26 21 -37

difference (m-w) 63 55 8 57 6

reference section at SB5-50 marsh 46 77 -31

SB5-50p water -21 14 -35

difference (m-w) 67 63 4

reference section at SB5-49 marsh 44 75 -31

SB5-49p water -19 18 -37

difference (m-w) 63 57 6

reference section at SB5-27 marsh 42 60 -18 73 -31

SB5-27p marsh edge -16 7 -23 20 -36

difference (m-w) 58 53 5 53 5

reference section at SB5-46 marsh 41 61 -20 73 -32

SB5-46p2 water -26 3 -29 15 -41

difference (m-w) 67 58 9 58 9

reference section at SB5-45 marsh 40 62 -22

SB5-45p water -14 10 -24

difference (m-w) 54 52 2

reference section at SB5-44 marsh 38 63 -25 74 -36

SB5-44p water -4 17 -21 27 -31

difference (m-w) 42 46 -4 47 -5

reference section at SB5-29 marsh 38 64 -26 74 -36

SB5-29p marsh edge 22 50 -28 60 -38

difference (m-w) 16 14 2 14 2

reference section at SB5-43 marsh 40 63 -23

SB5-43p3 water -21 10 -31

difference (m-w) 61 53 8

reference section at SB5-42 marsh 42 63 -21 74 -32

SB5-42p water -21 10 -31 19 -40

difference (m-w) 63 53 10 55 8

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)
 9

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

reference section at SB5-40 marsh 44 63 -19 74 -30

SB5-40p2 water -23 7 -30 16 -39

difference (m-w) 67 56 11 58 9

reference section at SB5-39 marsh 47 64 -17 75 -28

SB5-39p water -20 9 -29 21 -41

difference (m-w) 67 55 12 54 13

reference section at SB5-38 marsh 49 74 -25

SB5-38p water -26 10 -36

difference (m-w) 75 64 11

reference section at SB5-37 marsh 51 64 -13 75 -24

SB5-37p marsh edge -8 5 -13 17 -25

difference (m-w) 59 59 0 28 1

Study area 4: transect SB5-32 to SB5-30 (fig. 22A)

reference section at SB5-33 marsh 40 60 -20 71 -31

SB5-33p4 marsh edge 13 2 11 16 -3

difference (m-w) 27 58 -31 55 -28

reference section at SB5-47 marsh 41 72 -31

SB5-47p water -22 8 -30

difference (m-w) 63 64 -1

reference section at SB5-31 marsh 55 74 -19

SB5-31p3 marsh edge 9 32 -23

difference (m-w) 46 42 4

Study area 4: transect SB5-34 to SB5-40 (fig. 22B)

reference section at SB5-40 marsh 44 63 -19

SB5-35p3 marsh edge -8 10 -18

difference (m-w) 52 53 -1

reference section at SB5-40 marsh 44 63 -19

SB5-41p3 water -24 5 -29

difference (m-w) 68 58 10

Study area 5: transect SB3-01 to SB3-06 (fig. 23)

reference section at SB3-02 marsh 54 101 -47 115 -61

SB3-02p marsh edge 9 40 -31 59 -50

difference (m-w) 45 61 -16 56 -11

reference section at SB3-03 marsh 44 87 -43 102 -58

SB3-03p water -44 34 -78 51 -95

difference (m-w) 88 53 35 51 37

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Field and Laboratory Methods
10 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

1

Contact at base of unit 1 is indistinct.

2

Located at intersection of transects.

3

Contact at base of unit 2 is indistinct. 

4

Excluded from figure 22A (see appendix B).

reference section at SB3-05 marsh 35 74 -39 90 -55

SB3-05p marsh edge 4 81 -77 96 -92

difference (m-w) 31 -7 38 -6 37

reference section at SB3-08 marsh 37 71 -34 88 -51

SB3-08p water -28 32 -60 43 -71

difference (m-w) 65 39 26 45 20

reference section at SB3-07 marsh 42 66 -24 84 -42

SB3-07p marsh edge -2 52 -54 63 -65

difference (m-w) 44 14 30 19 25

Table 1 continued. Adjusted depths (thickness) and NAVD88 elevations for stratigraphic contacts correlated between cores at 

Sabine National Wildlife Refuge.

Base unit 1 Base unit 2

Core ID Core location

Core 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

Contact 

depth 

(cm)

Contact 

elevation 

(cm)

core site. The peat-thickness discrepancies are caused partly 

by the two different coring techniques. Vibracoring tends to 

compact saturated sediments, making them seem thinner than 

they actually are; as a result, at most vibracoring sites the 

core barrel penetrates deeper than the length of sediment that 

is recovered (Morton and White, 1997; Morton and others, 

2009b). In contrast, the push corer (Jowsey, 1966) is designed 

to minimize sediment compaction and core shortening by 

cutting through the sediment after the corer is inserted to the 

desired sampling depth.

Compaction is estimated in the field by measuring how 

far the surface of the sediment in the core barrel is below the 

actual sediment surface. There are no standard quantitative 

definitions for the magnitudes of compaction. For the purposes of this report, core compaction (appendix A) is reported 

relative to total penetration and is defined as minor (0-10%), 

moderate (11-20%), or major (>20%) after Morton and others 

(2009a). Major compaction may preclude using the stratigraphic data for quantitative analysis, depending on which 

stratigraphic intervals are shortened.

Water-Level Measurements and Elevation 

Corrections

The water depth at each coring site and at points along 

transects between core locations was measured with a 

graduated rod, while the geographic coordinates and time of 

each depth measurement were obtained simultaneously with 

a handheld GPS receiver. Water depths and marsh elevations 

measured in the field (table 1) can be compared only if they 

are corrected for any local conditions (tidal stage, wind 

set-up) that would influence the water-level data. Water-level 

fluctuations at the coring sites during field operations were 

assumed to be comparable to those recorded at nearby tide 

gages (fig. 3 and Morton and others, 2009b). 

As part of the Coastwide Reference Monitoring 

System (CRMS; Steyer and others, 2003), the USGS, in 

cooperation with the Louisiana Office of Coastal Protection 

and Restoration (OCPR; formerly Louisiana Department of 

Natural Resources), operates a network of hydrologic gages 

located throughout the coastal wetlands of south Louisiana. 

OCPR also operates an independent network of hydrologic 

gages at monitoring stations located in coastal waters 

throughout south Louisiana. Electronic water-level data for 

nearby CRMS and OCPR gages were downloaded from the 

OCPR website (http://coastal.louisiana.gov/) and used to 

correct primary water depths and relative marsh elevations 

for the dates and times of data collection (fig. 3) to the North 

American Vertical Datum of 1988 (NAVD 88). Water depths 

measured in SNWR Management Unit 1 were corrected using 

data from CRMS site #0641, located about 4.5 kilometers 

(km) south of study area 2, and OCPR coastal monitoring 

station #CS02-05, located about 2 km north of study area 1. 

Water depths measured in Management Unit 5 were corrected 

using data from CRMS site #0660, located between study 

areas 3 and 4 about 1.5 km northeast of study area 4, and 

water depths measured in Management Unit 3 were corrected 

using data from CRMS site #0694, located about 3.5 km 

southeast of study area 5 (fig. 1).
 11

A

30

35

40

45

50

55

60

WATER LEVEL,

IN CENTIMETERS ABOVE NAVD88

0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00

6/4/2008 6/5/2008 6/6/2008 6/7/2008 6/8/2008

CRMS #0641

B

30

35

40

45

50

55

60

WATER LEVEL,

IN CENTIMETERS ABOVE NAVD88

0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00

6/4/2008 6/5/2008 6/6/2008 6/7/2008 6/8/2008

OCPR #CS02-05

C

30

35

40

45

50

55

60

WATER LEVEL,

IN CENTIMETERS ABOVE NAVD88

0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00

6/7/2008 6/8/2008 6/9/2008 6/10/2008 6/11/2008 6/12/2008

CRMS #0660

D

30

35

40

45

50

55

60

WATER LEVEL,

IN CENTIMETERS ABOVE NAVD88

0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00 12:00 0:00

8/5/2010 8/6/2010 8/7/2010 8/8/2010 8/9/2010 8/10/2010

CRMS #0694

Figure 3. Water levels recorded at (A) Coastwide Reference Monitoring System (CRMS) site #0641 on June 4-8, 2008, (B) Louisiana 

Office of Coastal Protection and Restoration (OCPR) coastal monitoring station #CS02-05 on June 4-8, 2008, (C) CRMS site #0660 on 

June 7-12, 2008, and (D) CRMS site #0694 on August 5-10, 2010. Phases of the tides during field operations are highlighted (in gray). 

Gage locations are shown on figure 1.

Wetlands of the Sabine National 

Wildlife Refuge

Historical Land- and Water-Area Changes

 SNWR is the largest coastal-marsh refuge and wetland-management site on the gulf coast (Louisiana Coastal 

Wetlands Conservation and Restoration Task Force, 2002), 

encompassing about 125,000 acres (about 500 km2) of coastal 

wetlands between Sabine and Calcasieu Lakes on the Louisiana chenier plain in Cameron Parish (fig. 1). The refuge 

was established in 1937 and is managed by the U.S. Fish and 

Wildlife Service (FWS) primarily to maintain, restore, and 

perpetuate habitat for migratory waterfowl (U.S. Fish and 

Wildlife Service, 2007). SNWR is divided into several marshmanagement units (fig. 1), and water levels and salinities 

are intensely managed and monitored through four Coastal 

Wetlands Planning, Protection, and Restoration Act (CWPPRA) projects and 22 CRMS sites on refuge lands. Around the 

coring transects, control structures within canals and bayous 

at the eastern boundary of SNWR Management Unit 1 and the 

western boundary of Management Unit 5 are designed to limit 

the inflow of saline waters from Calcasieu and Sabine Lakes, 

respectively, to the interior marshes (Miller, 2003; Clark and 

Mazourek, 2004), and levees and rock dikes around Management Unit 3 prevent higher salinity waters from entering this 

hydrologically isolated freshwater impoundment (Sharp, 

2003). In addition, prescribed burning is commonly used in 

the SNWR wetlands to control the growth of non-native plant 

species (U.S. Fish and Wildlife Service, 2007). 

The SNWR wetlands occupy a broad, shore-parallel, 

topographically low area that formed between the 

topographically higher beach ridges along the gulf shoreline 

to the south and Pleistocene upland areas to the north (figs. 1 

and 2). This large wetland area initially supported trapping, 

hunting, and fishing by native inhabitants (U.S. Fish and 

Wildlife Service, 2007). In the 1920s, the area was used 

primarily for oil-and-gas exploration, with fur trapping as a 

secondary economic resource. After the muskrat population 

Wetlands of the Sabine National Wildlife Refuge
12 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Year Type Imagery Source

1933 Black and white Edgar Tobin Aerial Surveys

1955-1956 Black and white Edgar Tobin Aerial Surveys

1965 Black and white Edgar Tobin Aerial Surveys

1969 Black and white U.S. Army Corps of Engineers

1975 Black and white U.S. Geological Survey

1978 Color-infrared National Aeronautics and Space Administration

1981, 1983 Color-infrared U.S. Geological Survey (NHAP)

1985 Color-infrared National Aeronautics and Space Administration

1989 Color-infrared U.S. Department of Agriculture (NAPP)

1998 Color-infrared Louisiana Oil Spill Coordinator's Office (DOQQ)

2000 Black and white Louisiana Department of Natural Resources

2004 Color-infrared U.S. Geological Survey (DOQQ)

2005 Color-infrared U.S. Geological Survey (DOQQ)

2007 Color U.S. Department of Agriculture (NAIP)

2008 Color-infrared U.S. Geological Survey (DOQQ)

Table 2. Types and sources of imagery used to investigate land-water changes in the Sabine National Wildlife Refuge and 

surrounding areas.

[DOQQ, Digital Orthophoto Quarter Quadrangle; NAPP, National Aerial Photography Program; NAIP, National Agriculture Imagery 

Program; NHAP, National High Altitude Photography]

declined in the late 1920s and early 1930s, the land surface 

was sold to the Federal Government (U.S. Fish and Wildlife 

Service, 2007). 

The temporal baseline for quantifying historical land- and 

water-area changes in the western chenier plain, including 

SNWR, is 1932-34, which represents the dates of the earliest 

available aerial photographs and topographic maps. Britsch 

and Dunbar (1996) and Barras and others (2008) presented 

maps depicting historical wetland losses of the chenier plain 

for successive decadal periods. The land-water changes 

displayed on the published maps were supplemented for 

this study by visually examining aerial photographs from 

1933, 1955-56, 1965, 1969, 1975, 1978, 1981, 1985, 1989, 

1998, 2000, 2004, 2005, 2007, and 2008 (table 2). One of the 

difficulties associated with establishing the timing of land-area 

change is distinguishing between apparent land loss associated 

with anomalous high-water conditions such as seasonal 

flooding or land-management operations and permanent 

conversion of land to water. Compared with black-and-white 

photography, color and color-infrared images provide greater 

contrasts and tonal differences that facilitate making the land 

and water distinctions.

Sabine National Wildlife Refuge Management Unit 1

SNWR Management Unit 1 (figs. 1 and 4) occupies the 

northeast corner of the refuge. Both the 1933 and 1955-56 

images show mostly continuous wetland vegetation around 

the Unit 1 core transects and northward-flowing dendritic 

channels with a parallel zone of wet marsh (the marsh surface 

is submerged but still visible; Morton and others, 2005; 

Bernier and others, 2006) between the transects (fig. 5A). By 

1965, marshes around the transects were fragmented by small 

water bodies (fig. 5B). Wetland loss consisted of orthogonalelongate ponds and amorphous ponds, which were possibly 

the result of Hurricane Carla (Morton and Barras, in press). 

On both sides of Northline Canal in the northwest quadrant 

of Unit 1, expanses of wet marsh in the 1965 photography 

indicate the onset of widespread wetland loss at the 

Pleistocene-Holocene contact north of SNWR (fig. 2). There 

were sharp land-water contacts east of the Unit 1 transects and 

at the West Hackberry oil-and-gas field, indicating possible 

fault activation.

Water levels on the 1969 and 1975 images appeared to be 

high, and marshes around the transects were generally broken 

and flooded. In 1978 (fig. 5C), the marshes around study area 

2 were in the wet-marsh stage, whereas marshes around study 

area 1 were broken. Little land loss occurred around the coring 

transects after 1978, although the 1998 images show continued 

water-body enlargement and deepening across Northline Canal 

along the northern Unit 1/SNWR boundary. After 1998, there 

was little additional land-water change except for a dense 

network of northwest-southeast oriented braided channels 

and orthogonal-elongate ponds with peripheral drainage east 

of Beach Canal (fig. 5D) that were eroded by the 5- to 6-m 

wind-driven surge of Hurricane Rita (Barras, 2006). Beginning 

in 2005, marsh-restoration terraces were constructed in 
 13

0 2 KILOMETERS

0 2 MILES

93° 30' 93° 25'

29° 55'

STUDY AREA 2 STUDY AREA 1 

NORTHLINE CANAL

BEACH CANAL

EXPLANATION

Management Unit 1 boundary

1932-1956 land loss

1956-1978 land loss

1978-1990 land loss

1990-2004 land loss

Core location 2004-2006 land loss

Figure 4. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 1 showing locations of coring sites and historical landloss trends between 1932 and 2006. Wetland-loss trends from Barras and others (2008) and John Barras (USGS, written commun., 

2008); USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source imagery acquired November 18-19, 2008; display uses band 4 

(near-infrared).

large water bodies north of Northline Canal. By 2007, some 

water bodies had enlarged and coalesced, and some marshrestoration terraces had been constructed in the large openwater body formed by subsidence around the Hackberry field.

Sabine National Wildlife Refuge Management Unit 3

SNWR Management Unit 3 (figs. 1 and 6) occupies the 

north-central part of the refuge. The 1933 and 1955-1956 

images show that narrow canals and levees impounded what 

is now Unit 3, and the wetland vegetation was continuous, 

except for a cluster of permanent water bodies in the 

southeastern quadrant known as Five Lakes (fig. 7A). The 

vegetated surface had a mottled appearance and there were 

a few small ponds. The natural marsh drainage was not well 

developed except for a northward-flowing dendritic channel 

in the northwest corner of Unit 3 and a southwest-flowing 

channel (Old North Bayou) draining Five Lakes. Small ponds 

and areas of greater marsh wetness were concentrated in the 

northern half and southeastern quadrant of the impoundment. 

By 1965, there was extensive wetland loss covering 

most of the southeastern quadrant of Unit 3. There was 

also extensive flooding of broken, fragmented marsh in the 

northwestern quadrant, and a band of wetland loss near and 

parallel to the northwestern levee (fig. 7B). In 1978, the 

extensive wetland loss covering most of the southeastern 

quadrant of the impoundment persisted (fig. 7C). Little 

permanent land loss occurred in Unit 3 after 1978, although 

the extent of drowned marsh in the northwestern quadrant has 

fluctuated since 1998. Storm surge associated with Hurricanes 

Rita and Ike in 2005 and 2008, respectively, flooded the 

emergent marshes in the southern half of Unit 3 (fig. 7D). 

Sabine National Wildlife Refuge Management Unit 5

SNWR Management Unit 5 (figs. 1 and 8) borders the 

eastern shoreline of Sabine Lake in the northwest part of the 

Wetlands of the Sabine National Wildlife Refuge
14 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

NORTHLINE CANAL

BEACH CANAL

D 2008

NORTHLINE CANAL

BEACH CANAL

C 1978

NORTHLINE CANAL

BEACH CANAL

B 1965

NORTHLINE CANAL

BEACH CANAL

A 1955

0 4 KILOMETERS

0 4 MILES

EXPLANATION N

Core location Management Unit 1 boundary

Figure 5. Locations of sediment cores at Sabine National Wildlife Refuge (SNWR) Management Unit 1 superimposed on pre- and 

post-land-loss aerial photographs taken in (A) 1955, (B) 1965, (C) 1978, and (D) 2008. Image sources are (A) Edgar Tobin Aerial 

Surveys controlled aerial mosaics, source imagery acquired October 1955; (B) Edgar Tobin Aerial Surveys black-and-white aerial 

photography, source imagery acquired January 27, 1965; (C) National Aeronautics and Space Administration (NASA) color-infrared 

aerial photography, source imagery acquired October 10, 1978; and (D) USGS Digital Orthophoto Quarter Quadrangles (DOQQ), source 

imagery acquired November 18-19, 2008; RGB visual display uses bands 4 (near-infrared), 3 (red), and 2 (green).

refuge. In 1933 and 1955-56, the marsh vegetation in Unit 

5 was continuous except for Greens Lake and associated 

channels (fig. 9A). The vegetated surface had a mottled 

appearance, indicating greater moisture around small ponds. 

Short dendritic channels drained into Greens Lake, and Greens 

Bayou flowed from Greens Lake into Black Bayou, but there 

was no other natural integrated surface-channel network. 

Marsh drainage was not well developed south of Greens 

Lake. Because water levels were slightly higher in 1965, 

small ponds, drainage channels, and tracks of geophysical 

surveys crossing the marsh were prominent. A few orthogonalelongate ponds with marginal incised drainage formed west 

and northwest of study area 4. However, the marshes around 

the transects and Greens Lake were still unbroken (fig. 9B). 

Water levels also were high on the 1969 image and 

marshes were generally flooded, accentuating the slightly 

higher elevations of levees along the streams. Marshes south 

and east of Greens Lake were still unbroken, but marshes near 

the transects were broken and flooded. Britsch and Dunbar 

(1996) showed most of the land loss around Greens Lake 

occurring prior to 1974, with some additional loss occurring 

between 1974 and 1983. Using different source datasets, 

Barras and others (2008) showed the greatest amount of 

land loss in the same area occurring between 1978 and 1990 
 15

Figure 6. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 3 showing locations of coring sites and historical landloss trends between 1932 and 2006. Wetland-loss trends from Barras and others (2008) and John Barras (USGS, written commun., 

2008); USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source imagery acquired November 18-19, 2008; display uses band 4 

(near-infrared).

0 2 KILOMETERS

0 2 MILES

93° 35'

29° 55'

STUDY AREA 5 

EXPLANATION

Management Unit 3 boundary

1932-1956 land loss

1956-1978 land loss

1978-1990 land loss

1990-2004 land loss

Core location 2004-2006 land loss

(fig. 8). Visual examination of the 1970s and 1980s images 

showed that water levels were higher in 1975 than in 1978, 

when the outlines of Greens Lake and associated peripheral 

drainage channels were still visible but the surrounding 

marshes, including those surrounding the transects, were 

mostly inundated (fig. 9C). Between 1981 and 1989, most 

of the remaining areas of wet marsh became permanently 

submerged. By 1998, there was extensive permanent 

wetland loss with large water bodies occupying formerly 

continuous marsh. The largest area of continuous open water 

(approximately 13 km2) encompassed the former Greens Lake. 

After 1998, there was little land-water change. Historic land 

losses were less extensive north and northwest of Greens Lake, 

where the Pleistocene Prairie Formation crops out (fig. 8; 

Heinrich, 2005a).

Between 2004 and 2008, about 200,000 linear feet (about 

61,000 m) of vegetated terraces were constructed in the water 

body surrounding the former Greens Lake as part of efforts 

to restore the emergent wetlands. In 2008, abundant narrow 

orthogonal-elongate ponds with peripheral drainage formed 

south of study area 4 as a result of marsh erosion by Hurricane 

Ike (fig. 9D).

Summary – Historical Wetland Losses at Sabine 

National Wildlife Refuge

Most of the wetland losses in the western chenier plain, 

including losses around coring transects in SNWR (fig. 2), 

occurred between 1956-58 and 1974 (Britsch and Dunbar, 

1996). Wetland loss during that period coincides with a rapid 

rise in relative sea level recorded at the U.S. Army Corps 

of Engineers (USACE) Cameron tide gage (fig. 10). Some 

of the wetland loss within SNWR Management Unit 3 was 

associated with intentional impoundment in the 1950s to 

create a freshwater area for wildlife habitat with an emphasis 

on migratory waterfowl (U.S. Fish and Wildlife Service, 

2007). Additional wetland losses in the western part of Unit 

3 and around Greens Lake occurred between 1974 and 1983 

Wetlands of the Sabine National Wildlife Refuge
16 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

C 1978 D 2008

A 1955 B 1965

0 4 KILOMETERS

0 4 MILES

N

FIVE LAKES

EXPLANATION

Core location Management Unit 3 boundary

Figure 7. Locations of sediment cores at Sabine National Wildlife Refuge (SNWR) Management Unit 3 superimposed on pre- and 

post-land-loss aerial photographs taken in (A) 1955, (B) 1965, (C) 1978, and (D) 2008. Image sources are (A) Edgar Tobin Aerial 

Surveys controlled aerial mosaics, source imagery acquired October 1955; (B) Edgar Tobin Aerial Surveys black-and-white aerial 

photography, source imagery acquired January 27, 1965; (C) National Aeronautics and Space Administration (NASA) color-infrared 

aerial photography, source imagery acquired October 10, 1978; and (D) USGS Digital Orthophoto Quarter Quadrangles (DOQQ), 

source imagery acquired November 18-19, 2008; RGB visual display uses bands 4 (near-infrared), 3 (red), and 2 (green).

(Britsch and Dunbar, 1996). Wetland losses since 1983 

were associated primarily with storm impacts (for example, 

Hurricane Rita in 2005 and Hurricane Ike in 2008).

Heinrich (2005b) mapped several short fault traces 

visible on aerial photographs around the West Hackberry 

and Cameron Meadows oil-and-gas fields (fig. 2). Recent 

movement along these fault traces have locally influenced the 

historical land-water changes by increasing land subsidence 

and wetland losses on the downthrown side of the faults. 

The difference in elevation between the topographically 

lower Holocene coastal-plain marshes (typically <0.55 m) 

and the higher Pleistocene upland surfaces (typically >1 m) 

helps explain some of the wetland-loss patterns. For example, 

subsidence around the West Hackberry oil-and-gas field 

caused submergence of the low wetland areas, but the slightly 

higher Pleistocene exposures on the southeast side of the field 

did not lose enough elevation to cause permanent inundation 

and land loss (fig. 2).

Historical Changes in Wetland-Vegetation Types

Chabreck and others (2001) and Sasser and others 

(2008) presented a series of coastal-wetland maps depicting 

vegetation types of the marshes in coastal Louisiana at decadal 

intervals. The sequence of maps depicting habitat shifts shows 

that between 1949 and 2007 some assemblages of marsh 
 17

0 2 KILOMETERS

0 2 MILES

93° 45' 93° 40'

29° 55'

STUDY AREA 4 

STUDY AREA 3 

GREENS

LAKE

EXPLANATION

Core location

Management Unit 5 boundary

Pleistocene outcrop

1932-1956 land loss

1956-1978 land loss

1978-1990 land loss

1990-2004 land loss

2004-2006 land loss

Figure 8. Map of Sabine National Wildlife Refuge (SNWR) Management Unit 5 showing locations of coring sites, Pleistocene 

sediments (Heinrich, 2005a), and historical land-loss trends between 1932 and 2006. Wetland-loss trends from Barras and others 

(2008) and John Barras (USGS, written commun., 2008); USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source imagery 

acquired November 18-19, 2008; display uses band 4 (near-infrared).

plants at SNWR converted to fresh marsh, whereas other plant 

assemblages alternated between intermediate and brackish 

marsh as a result of both natural variations in climate and 

human activities. 

In 1949, before construction of the marsh-management 

impoundments, the marshes were classified as predominately 

intermediate, with some fresh marsh along the northern 

boundary of the refuge. By 1968, water-management 

practices had converted the Unit 3 impoundment to a fresh 

marsh, whereas the surrounding marshes in Unit 1 remained 

intermediate, and those of Unit 5 had converted to brackish 

except for those that remained intermediate around Greens 

Lake. The conversion of some marshes from intermediate to 

brackish may have been partly attributed to prolonged flooding 

after Hurricane Audrey in 1957 and (or) to droughts in 1956-

57 and 1964-68. In 1978, the impounded fresh marshes of 

Unit 3 were surrounded by intermediate and brackish marshes 

in both Units 1 and 5. The greater extent of brackish marshes 

was probably related to lower rainfall between 1970 and 1978. 

By 1988, intermediate marshes surrounding the impounded 

fresh marshes of Unit 3 had entirely converted to brackish 

marshes. However, by 1997, the same brackish marshes had 

reverted back to intermediate marshes at a time when there 

were no severe droughts or hurricane impacts in the chenier 

plain. In 2007, Unit 3 remained a fresh-marsh impoundment, 

Unit 5 remained an intermediate marsh, and Unit 1 displayed 

a gradient with intermediate marsh nearest to Unit 3 and 

brackish marsh to the east toward Calcasieu Lake (Sasser 

and others, 2008). The conversion of intermediate marsh to 

brackish marsh near Calcasieu Lake was likely related to 

increased salinities from the extensive saltwater flooding 

associated with Hurricane Rita in 2005 (Steyer and others, 

2010). Considering the temporal and spatial variability of the 

marsh-vegetation types, it is uncertain if they were caused 

Wetlands of the Sabine National Wildlife Refuge
18 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

C 1978 D 2008

GREENS

LAKE

B 1965

GREENS

LAKE

A 1955

0 4 KILOMETERS

0 4 MILES

EXPLANATION N

Core location

Management Unit 5 boundary

Pleistocene outcrop

Figure 9. Locations of sediment cores and Pleistocene sediments (Heinrich, 2005a) at Sabine National Wildlife Refuge (SNWR) 

Management Unit 5 superimposed on pre- and post-land-loss aerial photographs taken in (A) 1955, (B) 1965, (C) 1978, and (D) 2008. 

Image sources are (A) Edgar Tobin Aerial Surveys controlled aerial mosaics, source imagery acquired October 1955; (B) Edgar Tobin 

Aerial Surveys black-and-white aerial photography, source imagery acquired January 27, 1965; (C) National Aeronautics and Space 

Administration (NASA) color-infrared aerial photography, source imagery acquired October 10, 1978; and (D) USGS Digital Orthophoto 

Quarter Quadrangles (DOQQ), source imagery acquired November 18-19, 2008; RGB visual display uses bands 4 (near-infrared), 3 

(red), and 2 (green).

mainly by climatic cycles of greater and less rainfall, storm 

impacts, or a combination of natural processes and human 

activities.

Effects of Climate and Marsh Management on 

Wetlands

Historical wetland loss and habitat changes from fresh 

to intermediate or brackish marshes in the western chenier 

plain have been attributed largely to saltwater intrusion 

and a reduction in freshwater inflow (Louisiana Coastal 

Wetlands Conservation and Restoration Task Force, 2002; 

U.S. Fish and Wildlife Service, 2007). The saltwater intrusion 

and associated stresses on marsh vegetation resulted from 

deepening of the Calcasieu Ship Channel and Sabine-Neches 

Waterway and subsequent salinity increases in tidal waters 

that flowed through the natural channels of the marshes 

adjacent to Calcasieu and Sabine Lakes as well as through 

the many interconnected manmade canals that transect the 

marshes. Increased wetland salinities were also attributed to 

construction of the Gulf Intracoastal Waterway and associated 
 19

20

30

40

50

60

70

80

ANNUAL MEAN WATER LEVEL,

IN CENTIMETERS ABOVE MLG

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

USACE #73650

RSLR 4.1 mm/yr

accelerated hydrocarbon production

highest subsidence rates

greatest wetland loss

Marsh

core

Marsh

core

Open-water

core

Sediment - water interface

Elevation datum

Reference contact

Reference emergent-marsh surface

E

TW

S

A

TR

Peat Mud or clay

EXPLANATION

Figure 10. Linear-regression trend for mean annual water levels 

at Calcasieu Pass recorded at the U.S. Army Corps of Engineers 

Cameron tide gage (USACE #73650) from 1942 to 2005. Also 

shown are the overlapping periods of highest rates of wetland 

loss, land subsidence, and subsurface-fluid production. Gage 

location is shown on figure 1. Abbreviations: MLG, Mean Low 

Gulf; RSLR, relative sea-level rise; mm/yr, millimeters per year.

Figure 11. Conceptual diagram showing the geometric derivation of the reference stratigraphic section used to estimate the 

subsidence and erosion components contributing to the total 

one-dimensional accommodation space at an open-water core 

site (modified from Morton and others, 2009a). Abbreviations: A, 

accommodation space, E, erosion; S, subsidence, TR, reference 

stratigraphic thickness, TW, stratigraphic thickness in the openwater core.

Sedimentary Facies

banks of dredged material north of SNWR that impede the 

flow of freshwater that normally would flow southward into 

marshes of the refuge. Secondary factors that contributed to 

habitat changes and wetland loss in SNWR included surface 

discharge of produced formation water, the timing of stormrelated flooding by hurricanes Audrey and Carla, the 1956-57 

drought, and nutria herbivory (Louisiana Coastal Wetlands 

Conservation and Restoration Task Force, 2002).

Early in the 20th century, extensive networks of artificial 

channels, known as trainasse, were dug in the coastal wetlands 

to promote the fur-trapping industry (Davis, 1976). These 

were originally narrow, shallow ditches that allowed oneway passage of a small canoe-like boat. The trainasse were 

later enlarged naturally by water flow and also artificially 

by dredging. Still later in the 20th century, the network 

of channels within the marsh was greatly expanded to 

support oil-and-gas exploration and development. Despite 

conventional wisdom that wetland losses were related to canal 

dredging, Day and others (2000) found that there was no 

statistically significant relation between direct wetland losses 

associated with canal dredging and all other wetland losses in 

the Calcasieu-Sabine hydrologic basin.

Levees and other structures were placed in wetlands 

of the chenier plain in an attempt to manage the marshes by 

controlling salinity and water levels. The marsh-management 

structures and practices have not been entirely successful in 

accomplishing their intended goals, which were mitigation of 

salt-water intrusion and reduction or prevention of wetland 

loss (Cowan and others, 1988). For example, impoundments 

may contribute to wetland loss by reducing sediment and 

nutrient influx (Day and others, 1990; Reed, 1992; Boumans 

and Day, 1994; Cahoon, 1994; Reed and others 1997; Kuhn 

and others, 1999), and prolonging exposure to high-water 

events by increasing the residence time that marshes are 

flooded (Flynn and others, 1999).

Sedimentary Facies

Most of the cores collected at SNWR recovered a 

succession of unconsolidated sediments representing three or 

four general facies. The most common facies, from youngest 

to oldest, are (1) peat, (2) mud or clay, (3) interbedded lightand dark-gray clay, and (or) (4) mottled clay and silty clay. 

In most of the cores, contacts between facies are gradational. 

At the emergent-marsh sites, the youngest sediments consist 

of a mat of fibrous roots interspersed with water-saturated 

gray or brown mud associated with living Spartina sp. and 

Schoenoplectus sp. marsh-plant assemblages. The “live” 

roots and saturated mud indicate recent accumulation of both 

organic and clastic sediments. Below the most recent marsh 

deposits are brownish-black peat deposits with abundant root 

pieces that contain some dispersed mud. The abundance of 

visible root pieces typically decreases down-core.

The second sedimentary facies is an olive-gray mud or 

clay that typically contains root fragments and abundant root 

traces. The root traces and total organic content decrease with 

depth. The massive appearance of this facies is likely the 

result of extensive bioturbation. The deepest facies penetrated 

by most cores consists of mottled yellowish-orange to gray 

clay and silty clay. The oxidized nature of some of the facies 

4 sediments indicates that they are Pleistocene. Even though 

there is an unconformity present, the Pleistocene-Holocene 

contact is gradational in most cores. At study areas 4 and 5, 

facies 4 was penetrated only in the vibracores and a few push 

cores. At these study areas, and also in some cores near the 
20 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

EXPLANATION

Base of unit 1 Base of unit 2 Peat and

muddy peat Sediment-water interface Organic-rich mud Mud or clay Silty clay

SB1-09

SB1-10p

SB1-27p SB1-26p

SB1-08p

SB1-07p

SB1-25p

SB1-05

SB1-06p

SB1-24p

SB1-03v

SB1-04p

SB1-23p SB1-22p

SB1-02p

SB1-01p

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 250 500 750 1000 1250

DISTANCE, IN METERS

WEST NORTHEAST EAST

Figure 13. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB1-09 to SB1-01 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 1. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 12; vertical scale is greatly 

exaggerated.

N

0 300 METERS

0 300 YARDS

EXPLANATION

Core location Measured water depth

SB1-27

SB1-26

SB1-10

SB1-04

SB1-08 SB1-06

SB1-09

SB1-03 SB1-07 SB1-05

SB1-25 SB1-24 SB1-23 SB1-22

SB1-02

SB1-01

Figure 12. Locations of sediment cores and sediment-surface profiles collected at Sabine National Wildlife Refuge study area 1. 

USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source imagery acquired November 18-19, 2008; display uses band 4 (nearinfrared).
 21

Figure 14. Locations of sediment cores and sediment-surface 

profiles collected at Sabine National Wildlife Refuge study 

area 2. USGS Digital Orthophoto Quarter Quadrangle (DOQQ) 

source imagery acquired November 18-19, 2008; display uses 

band 4 (near-infrared).

N

0 300 METERS

0 300 YARDS

EXPLANATION

Core location

Measured water depth

SB1-19

SB1-13

SB1-34

SB1-33

SB1-32

SB1-31

SB1-30

SB1-29

SB1-28

SB1-21

SB1-17

SB1-12

SB1-18

SB1-20

SB1-11

SB1-14

SB1-15

SB1-16

SB1-35 SB1-37

SB1-36

center of the study area 3 open-water body, a relatively thick 

(≥50 cm) sequence of interbedded light- and dark-gray clay 

(facies 3) overlies the Pleistocene-Holocene contact below 

facies 2.

Historical Subsidence and Erosion of 

SNWR Marshes

Morton and others (2009b) described the methodology 

for estimating the magnitudes of subsidence and erosion of 

marsh sediments within interior coastal marshes (table 1). 

This method assumes that emergent-marsh elevations, marshsediment (peat) thicknesses, and stratigraphic positions of 

correlated markers are uniform over short horizontal distances 

(tens to hundreds of meters) and compares the elevations and 

vertical offsets of stratigraphic contacts correlated between 

adjacent cores. At SNWR, however, marsh elevations and 

marsh-peat thicknesses at each study site varied by as much as 

43 and 46 cm, respectively. As a result, estimated magnitudes 

of subsidence and erosion at each open-water core site may 

vary significantly depending on which adjacent marsh core is 

used as the reference stratigraphic section. 

We modified the methodology of Morton and others 

(2009b) and used a geometric solution to describe the 

reference stratigraphic section and account for natural 

variation in marsh-surface elevations and stratigraphic 

thicknesses between emergent-marsh sites along each 

transect. The geometric solution assumes that elevations of 

the marsh surface and shallow stratigraphic contacts vary 

linearly between adjacent marsh-core sites (fig. 11). Thus, 

the reference elevation of those contacts at each intervening 

marsh-edge or open-water core site can be determined by 

knowing the equation describing the change in elevation 

along the contact and the distance of each core site along 

the transect. A detailed derivation of the geometric solution 

for each study area is given in appendix B. The amount of 

erosion at an open-water core site is equal to the difference in 

marsh-sediment thickness between the open-water core and 

the reference stratigraphic section at that core site. Similarly, 

the amount of subsidence at an open-water core site is equal to 

the elevation difference of the correlated stratigraphic contact 

between the open-water core and the reference section at that 

core site. The estimates of subsidence and erosion at a core 

location equal the one-dimensional (vertical) accommodation 

space created by the land-to-water change, which is the 

difference between the reference marsh-surface elevation and 

the existing water depth at that core site. 

In most cases, elevations of stratigraphic contacts from 

the push core collected at each emergent-marsh core site 

were used to define the local reference stratigraphic section. 

In some push cores, however, not all stratigraphic units were 

penetrated and (or) some stratigraphic contacts could not be 

resolved. In those cases, the vibracore collected at the same 

site was used to determine the elevations of some or all of 

the reference stratigraphic contacts. The linear decompaction 

method (Morton and others, 2009b) was used to adjust 

sediment-contact depths and elevations in those vibracores. 

Because imprecision may be introduced by gradational facies 

changes (up to ±1-2 cm) at the stratigraphic contacts and (or) 

by core compaction, results of the stratigraphic comparisons 

should be viewed as providing approximate magnitudes of 

subsidence and erosion (table 1) and as a way of determining 

the relative importance of the two processes in converting 

formerly emergent wetlands to open water. Whereas onedimensional accommodation measurements can be highly 

accurate because they only involve the difference between 

marsh elevations and water depths (Morton and others, 2010), 

subsidence and erosion estimates should not be viewed 

Historical Subsidence and Erosion of SNWR Marshes
22 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Figure 15. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB1-18 to SB1-20 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 2. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 14; vertical scale is greatly 

exaggerated.

EXPLANATION

Base of unit 1

Base of unit 2

Peat and

muddy peat

Organic-rich mud

Mud or clay

Silty clay

Muddy sand

Sediment-water interface

SB1-18

SB1-19p

SB1-34p SB1-35p SB1-36p SB1-37p

SB1-21p

SB1-20v

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 100 200 300 400 500

DISTANCE, IN METERS

WEST EAST

as absolute, highly accurate values. This is especially true 

at SNWR, where stratigraphic contacts in most cores are 

gradational and the basal peat-mud contact, which represents 

the establishment of the first extensive marsh and is the 

preferred contact to use for calculating subsidence and erosion 

at a core site (Morton and others, 2005; 2009a; 2009b), is not 

present in many of the open-water cores. As a result, in most 

cases, the base of the underlying organic-rich mud was used to 

estimate subsidence and erosion.

Sabine National Wildlife Refuge Management 

Unit 1

Study Area 1

The study area 1 (figs. 4 and 12) landscape in northcentral Management Unit 1 consists of highly fragmented 

wetlands. Five vibracores and 16 push cores were collected at 

16 sites along a transect that intersected small ponds separated 

by remnants of the formerly continuous emergent marsh. 

Marsh-surface elevations at five emergent-marsh sites range 

from 30 cm at SB1-07 to 50 cm at SB1-09 and average about 

39 cm. Elevations at the sediment-water interface along the 

study area 1 transect range from 18 to 0 cm and average about 

6 cm where the marsh surface previously existed (fig. 13). 

Compaction of the study area 1 vibracores was minor (2 cores) 

to moderate (3 cores). 

The generalized stratigraphic section at study area 1 

consists of four stratigraphic units: (1) peat and muddy peat, 

(2) organic-rich mud, (3) organic-poor clay and silty clay, and 

(4) mottled clay and silty clay (appendix A, cores SB1-07p 

and SB1-07v). Silty-to-sandy clasts and lenses are common 

in both stratigraphic units 2 and 3, and those units are sandy 

at marsh-core site SB1-09 on the western end of the study 

area 1 transect. In most cores, the contacts between adjacent 

stratigraphic units are gradational, including the contact 

between units 3 and 4, which represents the transition from 

Holocene to Pleistocene sediments. 

Peat thicknesses at the emergent-marsh sites (fig. 13) 

range from 16.5 cm at SB1-09 to 32 cm at SB1-03 and average 

about 25 cm. Reference elevations at the base of stratigraphic 

units 1 and 2 increase sharply to the west from marsh-core 
 23

EXPLANATION

Base of unit 1

Base of unit 2

Peat and

muddy peat

Organic-rich mud

Mud or clay

Silty clay

Muddy sand

Sediment-water interface

SB1-13p

SB1-11p

SB1-12p

SB1-28p SB1-29p SB1-30p SB1-35p SB1-31p

SB1-14v

SB1-15p

SB1-32p SB1-33p

SB1-17p

SB1-16p

0 250 500 750 1000 1250 1500

DISTANCE, IN METERS

-50

-25

0

25

50

75

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

SOUTH NORTH

Figure 16. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB1-13 to SB1-16 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 2. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 14; vertical scale is greatly 

exaggerated.

site SB1-07 toward SB1-09 (appendix B), where the marshsurface elevation is the highest and the peat thickness is 

thinnest of any of the study area 1 emergent-marsh sites. There 

is considerable relief on the Pleistocene-Holocene contact 

at the reference emergent-marsh sites, which decreases in 

elevation from west (-1 cm at SB1-09) to east (-19 cm at SB1-

01). The thickness of the Holocene sediments at the reference 

emergent-marsh sites ranges from about 40 cm at SB1-07 to 

about 55 cm at SB1-01 and SB1-03.

The accommodation space that formed at study area 1 

as a result of historic wetland loss ranged from 13 to 42 cm 

and averaged about 31 cm. The unit 1 peat was not present 

in any of the open-water cores or in marsh-edge core SB1-

04p (fig. 13; appendix A). Using the base of stratigraphic 

unit 2, erosion at the study area 1 core sites ranged from 9 

to 32 cm and averaged about 20 cm, whereas subsidence 

ranged from 0 to 26 cm and averaged about 11 cm (table 1). 

Erosion greatly exceeded subsidence at the open-water sites, 

except at SB1-26 and SB1-27, where erosion and subsidence 

were approximately equal. The predominance of one process 

over the other was more variable at the marsh-edge sites: 

erosion exceeded subsidence at SB1-08, SB1-06, and SB1-

04, subsidence exceeded erosion at SB1-10, and erosion and 

subsidence were approximately equal at SB1-02.

Study Area 2

Five vibracores and 21 push cores were collected at 21 

core sites in study area 2 (figs. 4 and 14), located about 2 km 

west of study area 1. The study area 2 cores were collected 

along two intersecting transects across an approximately 

1-km2 open-water body. Marsh-surface elevations at five 

emergent-marsh sites, which generally increase from north to 

south, range from 30 cm at SB1-16 to 71 cm at the interiormarsh site SB1-13 and average about 53 cm. Elevations at the 

sediment-water interface across study area 2 range from 26 to 

-6 cm and average about 1 cm (figs. 15 and 16). Compaction 

of the study area 2 vibracores was minor (4 cores) to moderate 

(1 core).

The generalized stratigraphic section at study area 2 

consists of four stratigraphic units: (1) peat and muddy peat, 

(2) organic-rich mud, (3) organic-poor clay and silty clay, and 

Historical Subsidence and Erosion of SNWR Marshes
24 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Figure 17. Locations of sediment cores and sediment-surface 

profiles collected at Sabine National Wildlife Refuge study area 

3. USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source 

imagery acquired November 18-19, 2008; display uses band 4 

(near-infrared).

N

0 300 METERS

0 300 YARDS

EXPLANATION

Core location

Measured water depth

Pleistocene outcrop

SB5-02

SB5-14

SB5-15

SB5-05

SB5-07

SB5-23

SB5-20

SB5-19

SB5-13

SB5-11

SB5-09

SB5-22

SB5-21

SB5-01

SB5-06

SB5-18 SB5-03

SB5-04 SB5-16 SB5-17

SB5-08

SB5-10

SB5-12

(4) mottled clay and silty clay (appendix A, cores SB1-11p 

and SB1-11v). Silty-to-sandy clasts and lenses are common 

in both stratigraphic units 2 and 3, or those units may be silty 

to sandy throughout. In most cores, the contacts between 

adjacent stratigraphic units are gradational.

Peat thicknesses at the study area 2 reference emergentmarsh sites (figs. 15 and 16) range from 13 cm at SB1-16 to 

52 cm at SB1-11 and average about 29 cm. Reference elevations along all stratigraphic contacts increase slightly to the 

east between SB1-18 and SB1-20 and decrease significantly 

south of this transect toward SB1-11 (appendix B). 

The accommodation space that formed at study area 2 as 

a result of historic wetland loss ranged from 22 to 53 cm and 

averaged about 40 cm. As at study area 1, the unit 1 peat was 

not present in most of the study area 2 open-water cores or 

in marsh-edge cores SB1-15p and SB1-17p (figs. 15 and 16; 

appendix A). Using the base of stratigraphic unit 2, erosion at 

the study area 2 core sites ranged from 12 to 38 cm and averaged about 20 cm, whereas subsidence ranged from 1 to 35 cm 

and averaged about 20 cm (table 1). Erosion was greater than 

or about equal to subsidence at most of the core sites, except 

at marsh-edge site SB1-19 and at sites SB1-31, SB1-35, and 

SB1-37 (near the center of the study area 2 open-water body), 

where subsidence was greater than erosion. Magnitudes of 

subsidence and erosion could not be estimated at SB1-36, 

which recovered only undifferentiated clay and silty clay (fig. 

15; appendix A). At a minimum, however, all of the unit 1 peat 

(about 25 cm) was eroded at this open-water site.

Sabine National Wildlife Refuge Management 

Unit 5

Study Area 3

Six vibracores and 23 push cores were collected at 23 

core sites in study area 3 (figs. 8 and 17), which is located 

north of and separated from Greens Lake by a resistant ridge 

of Pleistocene outcrop. Marsh-core site SB5-08 is located 

along this terrain, and core sites SB5-08, SB5-09, and SB5-23 

are located south of a former bayou through the study area 3 

wetlands. Marsh-surface elevations at six emergent-marsh sites 

range from 30 cm at SB5-03 to 44 cm at the interior-marsh site 

SB5-07 and average about 38 cm. Elevations at the sedimentwater interface across study area 3 range from 24 to -36 cm 

and average about -20 cm (figs. 18 and 19). With the exception 

of core SB5-05v, which underwent major compaction, 

compaction of the study area 3 vibracores was mostly minor (2 

cores) to moderate (3 cores).

The generalized stratigraphic section at study area 3 

consists of four or five stratigraphic units: (1) peat and muddy 

peat, (2) organic-rich mud, (3) organic-rich to organic-poor 

mud, (4) interbedded light- and dark-gray clay, and (5) 

mottled clay and silty clay. Silty-to-sandy clasts and lenses 

may occur in both stratigraphic units 1 and 2. Stratigraphic 

unit 4 underlies unit 3 between core sites SB5-10 and SB5-22 

near the center of the study area 3 open-water area (appendix 

A, core SB5-10v); elsewhere, stratigraphic unit 5 directly 

underlies unit 3 (appendix A, cores SB5-12p and SB5-12v). 

Unit 5 was penetrated below unit 4 only in vibracore SB5-10v. 

In most cores, the contacts between stratigraphic units are 

gradational. 

Peat thicknesses at the study area 3 reference emergentmarsh core sites (figs. 18 and 19) range from 32 cm at 

SB5-08 to 75.5 cm at SB5-05 and average about 56 cm. 

Reference elevations along the base of units 1 and 2 decrease 

slightly to the east between SB5-01 and SB5-05 and increase 

significantly south of this transect toward SB5-08 (appendix 

B).

The accommodation space that formed at study area 3 as 

a result of historic wetland loss ranged from 24 to 65 cm and 

averaged about 49 cm. At least some peat (stratigraphic unit 
 25

Figure 18. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB5-08 to SB5-12 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 3. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 17; vertical scale is greatly 

exaggerated.

SB5-08

SB5-09p

SB5-23p SB5-22p SB5-21p SB5-15p SB5-20p

SB5-11p

SB5-10v

SB5-19p

SB5-13p

SB5-12p

EXPLANATION

Base of unit 1 Base of unit 2 Peat and

muddy peat Sediment-water interface Organic-rich mud Mud or clay

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 250 500 750 1000 1250 1500

DISTANCE, IN METERS

SOUTH NORTH

1) was present at most of the study area 3 core sites (figs. 18 

and 19; appendix A), except for marsh-edge core SB5-09p 

and open-water core SB5-19p, where unit 1 was completely 

eroded. The estimated magnitudes of subsidence and erosion 

at each core (table 1) were similar regardless of which contact 

(base of unit 1 or base of unit 2) was used. Erosion at the study 

area 3 core sites ranged from 17 to 54 and averaged about 41 

cm, whereas subsidence ranged from 0 to 20 cm and averaged 

about 9 cm. Erosion greatly exceeded subsidence at all study 

area 3 core sites.

Study Area 4

Seven vibracores and 27 push cores were collected at 27 

core sites transecting open-water areas in study area 4 south 

of Greens Lake (figs. 8 and 20). Marsh-surface elevations at 

seven emergent-marsh sites range from 38 cm at SB5-28 to 

55 cm at SB5-30 and average about 44 cm. Elevations at the 

sediment-water interface across study area 4 range from 22 to 

-37 cm and average about -20 cm (figs. 21 and 22). Compaction of the study area 4 vibracores was minor (7 cores). 

The generalized stratigraphic section at study area 4 

consists of three stratigraphic units: (1) peat and muddy peat, 

(2) organic-rich mud, and (3) interbedded light- and darkgray clay (appendix A, cores SB5-24p, SB5-29p). A fourth 

unit consisting of massive clay and silty clay was penetrated 

only in the vibracores and push core SB5-46p (appendix A). 

In most cores, the contacts between stratigraphic units are 

gradational.

Peat thicknesses at the study area 4 emergent-marsh sites 

(figs. 21 and 22) range from 60 cm at SB5-32p to 74 cm at 

SB5-30 and average about 64 cm. Reference elevations along 

all stratigraphic contacts dip slightly toward SB5-28 near the 

center of study area 4 (appendix B).

The accommodation space that formed at study area 4 as 

a result of historic wetland loss ranged from 16 to 75 cm and 

averaged about 57 cm. At least some peat (stratigraphic unit 

1) was present at most of the study area 4 core sites (figs. 21 

and 22; appendix A), except for open-water cores SB5-38p, 

SB5-47p, SB5-48p, SB5-49p, and SB5-50p, where unit 1 was 

completely eroded. The estimated magnitudes of subsidence 

and erosion at each core (table 1) were similar regardless of 

which contact (base of unit 1 or base of unit 2) was used. 

Erosion at the study area 4 core sites ranged from 14 to 64 

and averaged about 52 cm, whereas subsidence ranged from 

0 to 13 cm and averaged about 5 cm. The contact between 

stratigraphic units 2 and 3 is indistinct in core SB5-48p (fig. 

22; appendix A); however, estimates of subsidence (3 cm) and 

erosion (65 cm) using a correlated unit 3 interbed are similar 

Historical Subsidence and Erosion of SNWR Marshes
26 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

SB5-01p

SB5-02p

SB5-14p SB5-15p SB5-16p SB5-17p

SB5-04p

SB5-03p

SB5-18p

SB5-06p

SB5-05p

SB5-07p

EXPLANATION

Base of unit 1 Base of unit 2 Silty clay Peat and

muddy peat Sediment-water interface Organic-rich mud Mud or clay

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 250 500 750 1000

DISTANCE, IN METERS

WEST EAST

Figure 19. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB5-01 to SB5-07 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 3. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 17; vertical scale is greatly 

exaggerated.

in magnitude to those numbers from nearby study area 4 openwater cores. Erosion greatly exceeded subsidence at all study 

area 4 sites. 

Sabine National Wildlife Refuge Management 

Unit 3

Study Area 5

Eight push cores were collected at study area 5 along a 

northwest-trending transect across the large open-water body 

in the southeastern quadrant of SNWR Management Unit 3 

(figs. 6 and 23). Core sites SB3-03 and SB3-04 are located 

near the south and north shorelines, respectively, of one of the 

historic Five Lakes (fig. 7A). Marsh-surface elevations at three 

emergent-marsh sites range from 35 cm at SB3-04 to 54 cm at 

SB3-01 and average about 44 cm. Elevations at the sedimentwater interface along the study area 5 transect range from 13 

to -45 cm and average about -16 cm (fig. 24).

The generalized stratigraphic section at study area 5 

consists of four stratigraphic units: (1) peat and muddy peat, 

(2) organic-rich mud, (3) interbedded light- and dark-gray 

clay, and (4) silty clay (appendix A, core SB3-07p). In most 

cores, the contact between stratigraphic units is gradational, 

except for the contact between stratigraphic units 2 and 3, 

which generally is sharp.

Peat thicknesses at the study area 5 emergent-marsh sites 

(fig. 24) range from 66 cm at SB3-06 to 101 cm at SB3-01 

and average about 80 cm. Marsh-surface elevations and peat 

thicknesses decrease slightly along transect from southeast 

to northwest, whereas reference elevations along the base 

of stratigraphic units 1 and 2 increase slightly in the same 

direction (appendix B).

The accommodation space that formed at study area 5 

as a result of historic wetland loss ranged from 31 to 88 cm 

and averaged about 55 cm. The unit 1 peat was present at 

all of the study area 5 core sites (fig. 24; appendix A). The 

estimated magnitudes of subsidence and erosion at each core 

(table 1) were similar regardless of which contact (base of unit 

1 or base of unit 2) was used. Erosion at the study area 5 core 

sites ranged from 0 to 61 and averaged about 32 cm, whereas 

subsidence ranged from 0 to 38 cm and averaged about 23 cm. 

Erosion exceeded subsidence at most of the core sites, except 

at marsh-edge sites SB3-05 and SB3-07, where subsidence 

exceeded erosion.
 27

N

0 600 METERS

0 600 YARDS

EXPLANATION

Core location Measured water depth

SB5-47

SB5-44

SB5-41

SB5-35

SB5-25

SB5-50

SB5-43 SB5-40 SB5-38

SB5-27 SB5-48

SB5-46

SB5-45

SB5-37

SB5-24 SB5-49 SB5-26

SB5-28

SB5-29

SB5-42 SB5-39 SB5-36

SB5-32

SB5-33

SB5-30

SB5-31

SB5-34

Figure 20. Locations of sediment cores and sediment-surface profiles collected at Sabine National Wildlife Refuge study area 4. USGS 

Digital Orthophoto Quarter Quadrangle (DOQQ) source imagery acquired November 18-19, 2008; display uses band 4 (near-infrared).

Historical Land-Surface Subsidence 

One process that can cause widespread, nearly 

simultaneous wetland loss is land-surface subsidence. This 

is especially true when the elevation of the land surface is 

near the water table, and only a few centimeters of elevation 

loss can result in more frequent or permanent inundation and 

conversion of wetlands to open water.

Only a few data sources provide land-surface subsidence 

measurements at point locations in the western chenier plain; 

however, most of the independent data indicate “background” 

subsidence rates of <6 millimeters per year (mm/yr). One of 

the first estimates of historical subsidence rates in the western 

chenier plain was <5 mm/yr, based on geodetic leveling data 

and tide-gage records (Hodahl and Morrison, 1974). Recent 

estimates of regional land subsidence near SNWR can be 

derived from the closest tide gages, which are at Sabine Pass 

at the mouth of Sabine Lake and Cameron at the mouth of 

Calcasieu Lake (fig. 1). The average global rise in sea level 

during the past century was 1.8 mm/yr (Douglas, 2001), 

and the average rate between 1993 and 2003 was 3.1 mm/yr 

(Intergovernmental Panel on Climate Change, 2007), so any 

relative rise in sea level greater than those values should be 

a measure of local subsidence rates. The National Oceanic 

and Atmospheric Administration (NOAA) tide-gage record 

at Sabine Pass shows an average relative rise in sea level 

of 5.7 mm/yr since the late 1950s (NOAA, 2010). Penland 

and Ramsey (1990) reported the same rate of relative sealevel rise for the U.S. Army Corps of Engineers tide gage at 

Cameron based on a record from 1942 to 1988. Extending 

the time series through 2005, the current limit of the record, 

yields a linear regression of 4.1 mm/yr (fig. 10). Inspection 

of the water-level trends at Cameron between 1942 and 2005 

indicates a rapid rise in relative sea level between 1954 and 

1975 but little increase in relative sea level since 1975.

Short-term subsidence rates in the chenier plain east of 

Calcasieu Lake were monitored near Sweet Lake as part of an 

investigation of potential environmental impacts associated 

with a U.S. Department of Energy geopressured-geothermal 

design well. Van Sickle and Groat (1981) reported a local 

subsidence rate of 4.2 mm/yr based on elevation measurements 

in the area between 1968 and 1980. Local subsidence rates in 

the western chenier plain also were investigated in conjunction 

with construction of the U.S. Department of Energy Strategic 

Petroleum Reserve at the West Hackberry salt dome. Bauer 

and Woodrum (2002) reported reductions in local land 

elevations of more than 60 cm between 1983 and 2001 at some 

benchmarks within the West Hackberry site. The induced 

subsidence, which was related to creep closure of the massive 

dissolution cavities, was initially rapid, but rates of subsidence 

declined toward the end of the monitoring period.

Shinkle and Dokka (2004) estimated rates of land 

subsidence at benchmarks located along Louisiana Highway 

27 (LA 27) that were surveyed in 1965 and 1982. Most of 

the reported rates of subsidence at benchmarks crossing the 

chenier plain between Hackberry and Holly Beach, including 

those within SNWR, were between 12 and 15 mm/yr. The 

reported rates of subsidence, which are substantially higher 

Historical Land-Surface Subsidence
28 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

SB5-24p

SB5-25p

SB5-50p SB5-49p

SB5-27p

SB5-26p

SB5-46p SB5-45p SB5-44p

SB5-29p

SB5-28p

SB5-43p SB5-42p SB5-40p SB5-39p SB5-38p

SB5-37p

SB5-36

EXPLANATION

Base of unit 1 Base of unit 2 Peat and

muddy peat Sediment-water interface Organic-rich mud Mud or clay

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750

DISTANCE, IN METERS

WEST SOUTHEAST EAST

Figure 21. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB5-24 to SB5-36 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 4. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 20; vertical scale is greatly 

exaggerated.

than estimates from other sources, could be an artifact of the 

methods used by Shinkle and Dokka (2004) or an accurate 

representation of movement at the benchmark locations 

between leveling surveys. The benchmark-releveling epoch 

(1965-1982) partly coincides with the period of highest rates 

of relative sea-level rise registered at the Cameron tide gage 

(fig. 10).

The historical subsidence rates in the western chenier 

plain are substantially lower than most of the historical 

subsidence rates in the delta plain (Shinkle and Dokka, 

2004), but they are similar to the most recent (post-1990) 

subsidence rates reported for the NOAA tide gage at Grand 

Isle and the National Geodetic Survey (NGS) Continuously 

Operating Reference Station (CORS) at Cocodrie (Morton 

and Bernier, 2010). Subsidence in the Mississippi delta plain 

was partly explained by compaction and dewatering of the 

thick underlying Holocene sediments (Roberts and others, 

1994). However, those processes are not significant in the 

chenier plain, where the Holocene section is thin (Gould and 

McFarlan, 1959). At the core transects, Holocene sediments 

generally are less than a meter thick (figs. 13, 15, 16, 18, 19, 

21, 22, and 24). Although the magnitude of subsidence around 

the core transects is not great (0 to 38 cm), it likely came from 

the deep subsurface and not from compaction of the nearsurface sediments because near-surface processes, such as 

storm-water loading and desiccation, can only account for less 

than 3 cm of elevation loss (Cahoon, 2006).

Subsurface Fluid Withdrawal

Areas of wetland loss in the SNWR are located between 

the Oligocene and lower Miocene producing trends of 

southwestern Louisiana. At least 107 wells have been drilled 

within the boundaries of the SNWR, and in 2007 there were 

four production facilities and 32 producing wells (U.S. Fish 

and Wildlife Service, 2007). However, the major hydrocarbonproducing fields are on the margins of the refuge, which 

overlies a deep structural low. The deep syncline formed 

in response to salt withdrawal and construction of the 

surrounding salt-cored uplifts and associated structural highs 

at the Black Bayou, West and East Hackberry, and Cameron 

Meadows oil-and-gas fields (fig. 2). Of the hydrocarbonproducing fields surrounding the SNWR, only the Mud LakeSecond Bayou complex lacks a shallow salt-piercement core. 

Oil-and-gas fields in the chenier plain near the SNWR 

generally are smaller and have produced less fluid than 
 29

EXPLANATION

Base of unit 1

Base of unit 2

Peat and

muddy peat

Organic-rich mud

Mud or clay

Sediment-water interface

B

SB5-34v

SB5-35p

SB5-41p SB5-40p

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 100 200 300 400

DISTANCE, IN METERS

SOUTH NORTH

A

SB5-32p

SB5-47p SB5-46p SB5-48p

SB5-31p

SB5-30

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 100 200 300 400 500

DISTANCE, IN METERS

SOUTHWEST NORTHEAST

Figure 22. Combined bathymetric profile and stratigraphic cross section for (A) marsh and open-water core sites SB5-32 to SB5-30 

and (B) core sites SB5-35 to SB5-40 illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 4. 

Highlighted contacts are the base of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 

20; vertical scale is greatly exaggerated.

Subsurface Fluid Withdrawal
30 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

N

0 600 METERS

0 600 YARDS

EXPLANATION

Core location

Measured water depth

SB3-08

SB3-06

SB3-05

SB3-03

SB3-01

SB3-07

SB3-04

SB3-02

Figure 23. Locations of sediment cores and sediment-surface 

profiles collected at Sabine National Wildlife Refuge study area 

5. USGS Digital Orthophoto Quarter Quadrangle (DOQQ) source 

imagery acquired November 18-19, 2008; display uses band 4 

(near-infrared).

fields in the Mississippi delta plain. An exception is the 

Hackberry complex, which was discovered in 1902 and has 

been producing since the 1920s. Together the West and East 

Hackberry fields have produced more than 231 million barrels 

(bbls) of oil, 213 billion cubic feet (Bcf) of gas, and 205 

million bbls of formation water from more than 1600 wells 

(table 3). Most of the fluid production was from Oligocene 

deep-water sandstone reservoirs around the north and west 

flanks of the structure (Spencer and others, 1994; New Orleans 

Geological Society, 1962a). 

 Other historically productive oil-and-gas fields 

surrounding the wetland-loss areas are Black Bayou, Cameron 

Meadows, and Mud Lake (table 3). Since their discovery in 

1927, the Black Bayou (New Orleans Geological Society, 

1962b), Black Bayou South, and Black Bayou Southeast 

fields have produced more than 60 million bbls of oil, 121 Bcf 

of gas, and 162 million bbls of formation water from more 

than 400 wells that penetrated both Miocene and Oligocene 

sandstone reservoirs. More than 300 wells penetrating 

Miocene sandstone reservoirs have produced 23 million bbls 

of oil, 167 Bcf of gas, and 97 million bbls of formation water 

from the Cameron Meadows and Cameron Meadows East field 

area, which was discovered in 1929 (New Orleans Geological 

Society, 1962c). The Mud Lake, Mud Lake East, and Second 

Bayou fields (Hoffman, 1970; Sloane, 1971) encompass 

primarily a gas-producing area that yielded 17 million bbls 

of oil, 1.1 trillion cubic feet of gas, and 41 million bbls of 

formation water from lower Miocene sandstone reservoirs 

penetrated by more than 200 wells.

The history of fluid withdrawal is slightly different for 

each of the oil-and-gas fields, but the general trend shows 

relatively low production rates from the time of discovery until 

the early 1960s, accelerated hydrocarbon production beginning 

in the 1960s and peaking about 1970, then rapidly declining 

production to rates below those of the pre-acceleration phase 

(fig. 25). For these same fields, water production was erratic 

and typically peaked after hydrocarbon production peaked, 

but high rates of water production were sustained through the 

1990s.

Approximately 30 shallow groundwater wells have been 

drilled within the SNWR. Most of the water wells were used 

for rig water in support of hydrocarbon exploration (Louisiana 

Department of Transportation and Development, 2010) and 

they are no longer producing groundwater. The total volume of 

water extracted from these wells was probably minor and local 

in its impact.

Discussion and Conclusions

Comparing wetland and wetland-loss parameters at 

SNWR Management Units 1, 3, and 5 (table 4) shows that 

the range of emergent-marsh elevations was similar except 

for the anomalously high interior-marsh elevation at core site 

SB1-13 in Unit 1 (71 cm). The magnitudes of subsidence were 

similar at all study areas, but peat thicknesses and the depths 

of erosion were generally greater in Units 3 and 5, so the 

accommodation space formed was also greater in those units. 

At most core sites in SNWR, magnitudes of subsidence were 

substantially less than those of erosion. The early wet-marsh 

stage of wetland loss at SNWR, which is evident on the 1960s 

and 1978 imagery, is a clear indicator that minor but rapid 

subsidence was the process that initiated fragmentation and 

conversion of the broad continuous marsh meadows to open 

water. However, erosion eventually exceeded subsidence in 

forming the accommodation space and excavating the former 

emergent-marsh surface to extant water depths. Vegetation in 

the emergent marsh and marsh remnants in SNWR Units 1 and 

5 is healthy and not adversely affected by prevailing salinities 

of the surrounding water bodies. The repeated surveys by 

Chabreck and others (1968; 2001), Sasser and others (2008), 

and Steyer and others (2010) show that marsh-vegetation 
 31

SB3-06p

SB3-07p

SB3-08p

SB3-05p

SB3-04p

SB3-03p

SB3-02p

SB3-01p

EXPLANATION

Base of unit 1 Base of unit 2 Peat and

muddy peat Sediment-water interface Organic-rich mud Mud or clay

-125

-100

-75

-50

-25

0

25

50

ELEVATION, IN CENTIMETERS RELATIVE TO NAVD88

0 250 500 750 1000 1250 1500 1750 2000 2250 2500

DISTANCE, IN METERS

SOUTHEAST NORTHWEST

Figure 24. Combined bathymetric profile and stratigraphic cross section for marsh and open-water core sites SB3-01 to SB3-06 

illustrating the magnitude of subsidence and wetland erosion (in centimeters) at study area 5. Highlighted contacts are the base 

of stratigraphic units 1 (in red; where present) and 2 (in green). Core locations are shown in figure 23; vertical scale is greatly 

exaggerated.

communities in the western chenier plain are adaptable to 

environmental stresses such as changing soil salinities and 

seasonal or episodic flooding events. Thus, increased salinities 

in some marshes associated with enlarging the deep-draft 

navigation channels that transverse Sabine and Calcasieu 

Lakes have contributed to changes in dominant vegetation type 

rather than causing widespread wetland loss.

The wetland and wetland-loss parameters at SNWR 

provide a basis for comparing attributes of land-water change 

in the western chenier plain with the same attributes in 

the delta plain (table 4) that were reported by Morton and 

others (2005; 2009a). Compared to the delta-plain cores, 

average emergent-marsh elevations were generally higher 

in the western chenier plain, where historical subsidence 

rates were lower. The organic-rich marsh sediments are 

generally thinner in the SNWR cores, probably as a result 

of lower natural subsidence rates and different sediment 

budget and hydrodynamic regimes that existed in the western 

chenier plain when the marshes were healthy and aggrading. 

In general, in SNWR, the peat facies was substantially 

thinner, the water depths were shallower, and magnitudes of 

subsidence and total accommodation were less than in the 

delta plain. In the delta plain, peat deposits were preserved 

at all the open-water core sites because subsidence generally 

exceeded erosion and the thickness of the peat deposits was so 

great that they were preserved even where erosion was greater 

than subsidence. However, at SNWR, peat deposits are absent 

at most open-water sites because erosion generally exceeded 

subsidence and the peat deposits generally were thin.

Analysis of disparate data from four independent sources 

shows that the highest rates of wetland loss, land subsidence, 

and subsurface fluid production in the western chenier plain 

all occurred between the mid-1950s and the early 1980s. 

Annual data showing continuous trends were available only 

for the relative rise in sea level at the Cameron tide gage 

and for production of oil, gas, and formation water at fields 

surrounding SNWR (figs. 10 and 23). Data for the other 

two parameters, wetland loss and local subsidence rates at 

benchmarks, were for discrete periods. Furthermore, for local 

subsidence rates, there was no information regarding rates 

before and after the leveling epochs that could be used to 

establish a trend. However, the geodetic land-subsidence rates 

were higher than indicated by other independent methods, 

such as the tide-gage records. 

 The temporal and spatial coincidence of rapid wetland 

loss, highest rates of land-surface subsidence, and high rates of 

Discussion and Conclusions
32 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

0

2

4

6

8

10

12

14

ANNUAL PRODUCED NATURAL GAS,

IN BILLIONS OF CUBIC FEET

ANNUAL PRODUCED FORMATION WATER,

IN MILLIONS OF BARRELS

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

0

1

2

3

4

5

6

7

ANNUAL PRODUCED OIL,

IN MILLIONS OF BARRELS

A

0

2

4

6

8

10

12

14

ANNUAL PRODUCED NATURAL GAS,

IN BILLIONS OF CUBIC FEET

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

0

2

4

6

8

10

12

14

ANNUAL PRODUCED OIL AND

ANNUAL PRODUCED FORMATION WATER,

IN MILLIONS OF BARRELS

B

0

2

4

6

8

10

ANNUAL PRODUCED NATURAL GAS,

IN BILLIONS OF CUBIC FEET

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

0

1

2

3

4

5

ANNUAL PRODUCED OIL AND

ANNUAL PRODUCED FORMATION WATER,

IN MILLIONS OF BARRELS

C

0

10

20

30

40

50

60

ANNUAL PRODUCED NATURAL GAS,

IN BILLIONS OF CUBIC FEET

1940 1950 1960 1970 1980 1990 2000 2010

YEAR

0.0

0.5

1.0

1.5

2.0

2.5

3.0

ANNUAL PRODUCED OIL AND

ANNUAL PRODUCED FORMATION WATER,

IN MILLIONS OF BARRELS

D

Oil Gas Water

EXPLANATION

Figure 25. Annual fluid production through 2009 from oil-and-gas fields surrounding the Sabine National Wildlife Refuge. (A) 

Black Bayou complex, (B) East and West Hackberry complex, (C) Cameron Meadows complex, and (D) Mud Lake and Second 

Bayou complex. Field locations are shown in figure 2. Data from Louisiana Department of Natural Resources and PI/Dwights PLUS 

database (HIS, Inc., 2009). 

Field Names Discovery 

Year Wells Cummulative Oil (bbls)

Cummulative Gas 

(mcf)

Cummulative Water 

(bbls)

East and West Hackberry 1902 1651 231,686,078 213,875,169 205,561,797

Black Bayou, Black Bayou South, and 

Black Bayou Southeast 1927 455 60,866,643 121,830,267 162,064,978

Cameron Meadows and Cameron 

 Meadows East 1929 316 23,394,287 167,330,703 97,523,750

Mud Lake, Mud Lake East, and Second 

Bayou 1945 210 17,153,742 1,197,043,997 41,403,354

Table 3. Discovery year, number of wells drilled, and cumulative volumes of fluids produced through 2009 from oil-and-gas field 

complexes surrounding the Sabine National Wildlife Refuge wetlands.

[Data from Louisiana Department of Natural Resources and PI/Dwights PLUS database (IHS, Inc., 2009). Field locations are shown in figure 2. Abbreviations: bbls, 

barrels; mcf, million cubic feet.]

oil-and-gas production in the western chenier plain is similar 

to those same trends in the delta plain, where long-term, largevolume subsurface fluid production was largely responsible for 

the land-surface subsidence that initiated widespread wetland 

loss (Morton and others, 2005; 2009a). Initial subsidence 

lowered the SNWR emergent marshes to a position where they 

were more susceptible to erosion by storm waves. Another 

major contributor to localized historical wetland loss in the 

western chenier plain was the impact of extreme hurricanes, 

such as those of Audrey in 1957 and Rita in 2008.
 33

Table 4. Comparison and ranges of parameters at wetland-loss sites in the chenier and delta plains.[Values (in centimeters) are from this report (highlighted in yellow) and Morton and others (2005, 2009a). SNWR, Sabine National Wildlife Refuge]

Parameter SNWR Unit 1 SNWR Unit 5 SNWR Unit 3 Bayou Perot1 Ironton Leeville Fourchon Caminada Bay St. Elaine Madison Bay DeLarge Pointe au Chien Bully Camp

Marsh elevation 30-71 30-55 35-54 31-51 23-31 26-48 35-42 21-40 49-50 17-30 32 32-39 28-49

Avg. elevation 46 41 44 41 28 33 40 32 49 28 35 42Peat thickness 13-52 32-75 66-101 320-365 99-203 103-200 89-119 103-131 96-105 168-198 110 99-103 93-103Subsidence 0-26 0-20 0-38 13-89 2-60 0-65 14-78 2-38 63-139 50-75 68 37-117 68-149Erosion 9-32 17-54 0-61 74-181 13-77 9-97 22-72 44-81 0 23-37 13 0-14 0-35Accommodation 13-42 24-75 31-88 62-202 35-95 61-122 39-111 47-104 56-85 70-138 88 73-101 57-184Avg. water depth 3 -20 -12 >100 -50 -55 -50 -40 -8 -73 -53 -48 deep2

1Eroded and enlarged channel.2Pit over sulfur mine >6 m.

Discussion and Conclusions
34 Trends and Causes of Historical Wetland Loss, Sabine National Wildlife Refuge, Southwest Louisiana

Acknowledgments

We thank Gary Hill and Gregg Snedden for operating 

the airboats and assisting with field operations, and the staff 

at Sabine National Wildlife Refuge for allowing access to the 

coring sites. We also thank John Barras for providing some of 

the historical images and Jennifer Miselis and Greg Steyer for 

conducting scientific and editorial reviews that improved the 

report.

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