0 1 2 3 4 KILOMETERS N

0 1 2 3 4 MILES

Condition classification of forested wetland

Project boundary—Total classified project area 

(about 16,583 hectares). White areas represent 

unclassified project area (for example, open water, 

canals, unclear habitat) (1,691 hectares)

EXPLANATION

Closed forest canopy—Undegraded, 4,991 hectares (30 percent)

Transitional forest—Intermediate, 9,672 hectares (58 percent)

Open canopy wetland—Degraded, 1,920 hectares (12 percent)

Project 

boundary

Lake

Pontchartrain

Lake

Maurepas

Mississippi

River

Project 

boundary

Prepared in cooperation with the Coastal Protection and Restoration Authority (CPRA) of Louisiana

Expectations of Maurepas Swamp Response to

a River Reintroduction, Louisiana

Introduction

Mississippi River reintroductions (freshwater diversions) into wetlands previously disconnected 

from the river have been implemented in southeastern Louisiana as a means to rehabilitate degraded and 

submerging wetlands. To date, all active Mississippi River reintroductions have targeted marsh habitat. 

However, a 57 cubic meter per second (2,000 cubic foot per second) river reintroduction is being designed 

and implemented by the Coastal Protection and Restoration Authority (CPRA) of Louisiana to rehabilitate 

a degraded and submerging swamp forest of approximately 16,583 hectares (40,977 acres) in the Maurepas 

Swamp; 30 percent of the project area is closed forest canopy, 58 percent is transitional forest, and 12 percent 

is open canopy wetland (severely degraded forest and open marsh) (Keim and others, 2010a; Krauss and others, 

2017) (fig. 1). The goal of this project is to reduce or minimize loss of swamp forest habitat in the project area 

through reintroduction of Mississippi River water. River reconnection has often been stated as the most critical 

step necessary to rehabilitate and preserve the integrity of the natural and cultural resources of the Maurepas 

Swamp ecosystem (Shaffer and others, 2016).

Figure 1. Condition classifications of forested wetlands in the Maurepas Swamp, 

Louisiana, project area (modified from Keim and others, 2010a; Krauss and others, 2017). 

“Open canopy wetland” represents severely degraded forest and open marsh.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3072

October 2018 Printed on recycled paper
Degradation of the Maurepas Swamp is representative of the degradation in many coastal 

Louisiana swamp forests. Because this is the first river reintroduction into swamp forest in Louisiana, 

expectations of successful rehabilitation of the Maurepas Swamp have been made relative to what 

scientists know about healthy swamp forests. The performance measures (PMs), developed by the U.S. 

Geological Survey (USGS) in cooperation with the CPRA and two universities (Krauss and others, 2017), 

will serve to adjust operation for optimum positive performance, and measurement and monitoring will inform 

the design of other river reintroductions targeting freshwater swamp forests in the future.

Expectations

Wetland restoration projects often have many expectations associated with improving habitat function. However, 

it is often most effective to track a small number of more easily assessed and specific responses in postrestoration 

monitoring. Expectations of habitat response can be expressed as PMs. Metrics associated with a PM can be tracked 

through scientific efforts over time and assigned numeric value relating to the PM. Implementation of current and future 

projects can then be altered adaptively to produce desired outcomes or left unchanged if PMs are being met. For the river 

reintroduction into the Maurepas Swamp, water flow can be managed adaptively and 

will be a primary means by which adjustments are made if required. 

Five PMs have been established (Krauss and others, 2017) to track swamp 

forest response to the Mississippi River reintroduction into Maurepas Swamp. 

These PMs are associated with restoring hydrology, reducing salinity, 

facilitating elevation gain, rehabilitating forest structural integrity, and 

facilitating nutrient uptake and retention.

Establishing a Hydrologic Regime Consistent With Swamp Forest 

Sustainability (PM1)

Reestablishing hydrological patterns that mimic the flooding 

conditions that existed before levees disconnected the Maurepas Swamp 

from the Mississippi River is an important goal. While not all aspects 

of hydrologic rehabilitation are attainable, reestablishing duration and 

frequency of flooding will serve as PM1. At any given location in the 

swamp, hydrologic connectivity with the Mississippi River should occur 

at intervals between twice annually and once per decade. Hydrologic 

management must allow for the potential for water drawdowns to simulate 

periodic winter and spring drought conditions in the Mississippi River 

watershed that are necessary for tree seedling germination and establishment 

every 3–13 years. Within the 3–13-year cycle, a dry winter may require a 

delay in the opening of the diversion structure in early spring. Such dry periods 

promote water drawdowns and expose soils to facilitate establishment of tree 

seedlings, as would have occurred naturally during dry periods. 

Reducing Saltwater Intrusion (PM2)

PM2 focuses on maintaining acceptable salinity 

concentrations throughout the Maurepas Swamp. The dominant 

forested wetland tree species in the Maurepas Swamp are 

Taxodium distichum (baldcypress) and Nyssa aquatica (water 

tupelo). Both species typically occur in freshwater habitats 

throughout their geographic range, but they differ slightly 

in the tolerances to salinity. Mean annual target porewater 

salinity for the Maurepas Swamp is less than 1.3 parts 

per thousand (ppt) for areas with higher concentrations 

of baldcypress but below 0.8 ppt for areas with higher 

concentrations of water tupelo. While pulses of salinity 

from storms or severe droughts may be difficult to manage, 

adaptive management of the diversion structure to increase 

freshwater flow through the structure to lower salinity may be 

possible when necessary. 
Increasing Rates of Soil Surface Elevation Gain (PM3)

PM3 focuses on maintaining wetland soil surface 

elevations over time and thus reducing swamp forest 

submergence. Wetlands forming in large deltas often have 

high rates of submergence of the soil surface because of 

settling and dewatering of recently deposited sediments, 

compaction of older buried soils, and geologic subsidence 

occurring far beneath overlying wetlands. If rivers are 

disconnected from the wetlands, as in the Maurepas Swamp, 

adequate sediment is not delivered, and surface elevation losses are 

unbalanced. Surface elevation of the Maurepas Swamp must build 

vertically at rates that match or exceed the combination of elevation 

loss plus sea-level rise (termed “relative sea-level rise”), or at least at 

higher rates than is currently happening. Wetlands of the Maurepas Swamp 

should have surface elevation gains of 8–9 millimeters per year, or higher, 

as a result of the river reintroduction in order to keep up reasonably well with 

relative sea-level rise, even though sediment delivery to the Maurepas Swamp 

may be modest. Additional sediment amendments may be 

needed in the future if sediment loading capacity from 

the freshwater reintroduction is too low.

Increasing Forest Structural Integrity (PM4)

PM4 is designed to target the visual and structural integrity of the 

Maurepas Swamp. The structure of swamp forests is measured by assessing 

individual tree diameters, individual tree heights, tree density, and 

understory distribution and abundance of herbaceous plants, tree seedlings, 

and tree saplings. These characteristics are fairly well defined for healthy 

swamp forests. Three metrics were developed for rating forest structural 

integrity: one targeting stand density, one targeting leaf area index, and 

one targeting species composition of overstory trees and herbaceous 

understory plants. Swamp forests in the Maurepas Swamp should realize 

increases in stand density index (SDI) (Keim and others, 2010b) of as 

much as 30–45 percent of maximum values for the stand type while 

maintaining an overstory leaf area index (LAI) of 2.0–2.9 square meters 

of leaf area per square meter of ground area or higher. Simultaneously, the 

Forested Floristic Quality Index (FFQI) (Wood and others, 2017) will be 

used. The FFQI is a technique used to evaluate habitat integrity on the basis 

of native species composition. These values should increase by approximately 

12 percent upon river reintroduction, although expected changes to understory 

vegetation may be more rapid than for overstory trees.

Facilitating Nutrient Uptake and Retention (PM5)

PM5 focuses on nutrients delivered from the river reintroduction into the 

Maurepas Swamp. The forested wetlands of the Maurepas Swamp have low 

nutrient concentrations because of the swamp’s long-term disconnection from 

the Mississippi River and stagnant water flows (Shaffer and others, 2016). 

Furthermore, waters of Lake Maurepas have low levels of dissolved 

inorganic nitrogen (N) (that is, nitrite, nitrate, and ammonium) that 

are far less than N concentrations in the Mississippi River (Lane and 

others, 2003). Assessing inputs of N in the form of nitrate, the most 

common form of N, into the Maurepas Swamp is critical because 

evidence suggests that swamp forests can benefit from more N but 

that excess N can cause soil loss or eutrophication in downstream 

water bodies. To maximize uptake of N and prevent negative 

consequences of excessive N, nitrate loading into the Maurepas 

Swamp from river water should be approximately 11.25 grams 

of N per square meter per year. This nitrate loading is 

significantly more N than the swamp forest receives currently, 

and modeling indicates that a large percentage of nitrate will 

be taken up by vegetation rapidly from diverted river water.
Summary and Acceptable Ranges

Along with each PM, acceptability ranges also were developed because of the broad range of variability associated with each 

expectation (table 1). These acceptability ranges were established by consulting statistical metrics within the scientific literature. 

Observed variations (standard deviations) associated with mean responses for each variable assessed from natural swamp forests 

were generally applied (Krauss and others, 2017).

Monitoring of all variables associated with each PM will be undertaken in cooperation with the CPRA and will be 

comprehensive enough to assess metrics associated with PMs adequately over time and to direct changes to the adaptive 

management protocol for the diversion structure. 

Table 1. Summary table of target values for performance measures (PMs) 1–5 and specific metrics detailing expectations of swamp forest 

response to a Mississippi River reintroduction into the Maurepas Swamp, Louisiana. 

PM Metric Target Low 

range

Lower 

OK?

High 

range

Higher 

OK?

Time 

frame 

(years)

1 River connectivity (year) 5.3 0.5 No 10 No 10–15

1 Low water event (year) 8 3 No 13 No 10–15

2 Baldcypress water salinity (parts

per thousand)

1.3 1 Yes 1.6 No 2–5

2 Water tupelo water salinity (parts per thousand) 0.8 0.5 Yes 1.1 No 2–5

3 Surface elevation gain (millimeters per year) 8–9 5 No 12 Yes 5–10

4 Stand density index (percent maximum) 45 30 No 60 Yes 1–5

4 Leaf area index (square meter per square meter) 2.9 2.0 No 3.8 Yes 1–5

4 Forested Floristic Quality Index (Wood and others, 2017)

(percent increase)

12.3 0 No 25.8 Yes 1–5

5 Nitrate loading (grams of nitrogen per square meter per year) 11.3 7.1 No 15.4 No 2–5

References Cited

Keim, R.F., Braud, D.H., Shaffer, G.P., and Chambers, J.L., 2010a, 

Mapping coastal wetland forests in coastal Louisiana: Baton Rouge, 

Louisiana Department of Environmental Quality, 21 p.

Keim, R.F., Dean, T.J., Chambers, J.L., and Conner, W.H., 2010b, 

Density relationships in baldcypress: Forest Science, v. 56, 

p. 336–343.

Krauss, K.W., Shaffer, G.P., Keim, R.F., Chambers, J.L., Wood, W.B., 

and Hartley, S.B., 2017, Performance measures for a Mississippi 

River reintroduction into the forested wetlands of Maurepas Swamp: 

U.S. Geological Survey Scientific Investigations Report 2017–5036, 

56 p., accessed September 28, 2018, at https://doi.org/10.3133/

sir20175036.

Lane, R.R., Mashriqui, H.S., Kemp, G.P., Day, J.W., Jr., Day, J.N., and 

Hamilton, A., 2003, Potential nitrate removal from a river diversion 

into a Mississippi Delta forested wetland: Ecological Engineering, 

v. 20, p. 237–249.

Shaffer, G.P., Day, J.W., Jr., Kandalepas, D., Wood, W.B., Hunter, R.G., 

Lane, R.R., and Hillmann, E.R., 2016, Decline of the Maurepas 

Swamp, Pontchartrain Basin, Louisiana, and approaches to 

restoration: Water, v. 8, article w8030101.

Wood, W.B., Shaffer, G.P., Visser, J.M., Krauss, K.W., Piazza, S.C., 

Sharp, L.A., and Cretini, K.F., 2017, Forested Floristic Quality 

Index—An assessment tool for forested wetland habitats using the 

quality and quantity of the woody vegetation present at Coastwide 

Reference Monitoring System (CRMS) vegetation monitoring 

stations: U.S. Geological Survey Open-File Report 2017–1002, 

15 p., accessed September 28, 2018, at https://doi.org/10.3133/

ofr20171002.

By Ken W. Krauss, Gary P. Shaffer, Richard F. Keim,

Jim L. Chambers, William B. Wood, and Stephen B. Hartley

For more information, contact

Director, Wetland and Aquatic Research Center

U.S. Geological Survey

700 Cajundome Blvd.

Lafayette, LA 70506

https://www.usgs.gov/centers/

wetland-and-aquatic-research-center-warc

This fact sheet is based on the following U.S. Geological

Survey report:

Krauss, K.W., Shaffer, G.P., Keim, R.F., Chambers, J.L., Wood, W.B., 

and Hartley, S.B., 2017, Performance measures for a Mississippi 

River reintroduction into the forested wetlands of Maurepas 

Swamp: U.S. Geological Survey Scientific Investigations Report 

2017–5036, 56 p., https://doi.org/10.3133/sir20175036.

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20183072