Lake Maurepas Research Articles

Podcast: The battle for Lake Maurepas

Carbon capture and sequestration is the process of trapping carbon dioxide emitted by industrial processes and depositing it beneath Earth’s surface. Spurred on by tax credits offered by recent federal legislation, companies are racing to implement the technology in geologically suitable locations. However, the community around Lake Maurepas, Louisiana, has resisted efforts by Air Products and Chemicals to green-light such a project under the lake. In this episode of Stereo Chemistry , C&EN reporters Rick Mullin and Craig Bettenhausen discuss the community’s fears about the implementation of carbon capture and sequestration around Lake Maurepas and the response from Air Products. This conversation is part of C&EN Uncovered, a podcast project in which reporters take listeners behind the scenes of their cover stories. Mullin’s cover story about the battle for Lake Maurepas appeared in the April 3, 2023, issue of C&EN. Listen at cenm.ag/uncovered-lakemaurepas .

Podcast: Lake Maurepas is a battleground for climate change mitigation

Podcast: Lake Maurepas is a battleground for climate change mitigation

Enhancing Flood Hazard Assessments in Coastal Louisiana Through Coupled Hydrologic and Surge Processes

Traditional coastal flood hazard studies do not typically account for rainfall-runoff processes in quantifying flood hazard and related cascading risks. This study addresses the potential impacts of antecedent rainfall-runoff, tropical cyclone (TC)-driven rainfall, and TC-driven surge on total water levels and its influence in delineating a coastal flood transition zone for two distinct coastal basins in southeastern Louisiana (Barataria and Lake Maurepas watersheds). Rainfall-runoff from antecedent and TC-driven rainfall along with storm surge was simulated using a new rain-on-mesh module incorporated into the ADCIRC code. Antecedent rainfall conditions were obtained for 21 landfalling TC events spanning 1948–2008 via rain stations. A parametric, TC-driven, rainfall model was used for precipitation associated with the TC. Twelve synthetic storms of varying meteorological intensity (low, medium, and high) and total rainfall were utilized for each watershed and provided model forcing for coastal inundation simulations. First, it was found that antecedent rainfall (pre-TC landfall) is influential up to 3 days pre-landfall. Second, results show that antecedent and TC-driven rainfall increase simulated peak water levels within each basin, with antecedent rainfall dominating inundation across the basin's upper portions. Third, the delineated flood zones of coastal, transition, and hydrologic show stark differences between the two basins.

Modeling current and future freshwater inflow needs of a subtropical estuary to manage and maintain forested wetland ecological conditions

Riverine input is essential for the sustainability of the estuaries, wetlands, and swamps into which they flow. An existing coastal ecosystem model was used with forested wetland and fish habitat indicators to evaluate current environmental conditions as well as future restoration projects via 50-year simulations of riverine flow with sea level rise and subsidence. The objective of this study was to utilize the Integrated Compartment Model developed for the Louisiana Coastal Protection and Restoration Authority’s 2017 Coastal Master Plan to understand how alternations of riverine flow from existing rivers and future restoration projects may influence the spatial and temporal distribution of wetland habitats and suitability of fish habitats. The model was applied to the Lake Maurepas ecosystem where the Amite River flows into the lake and supports vital fisheries for surrounding communities, as well as a unique and valuable recreational resource. Additionally, the Amite River nourishes the marshes and swamps around Lake Maurepas that are essential for storm surge protection for the broader region. Modeling results suggest that the major contributing factor to the freshwater conditions to the Lake Maurepas area is the challenge of relative sea level rise − the combination of rising seas and subsidence. Fresh forested areas comprised of bald cypress (Taxodium distichum) and tupelo gum (Nyssa aquatica) in Maurepas Swamp decrease significantly under all future climate and relative sea level rise simulations except when future restoration projects are utilized. An estimated ∼1000km2 of fresh forested wetland could be maintained over a 50-year period when considering certain restoration projects that increase freshwater flow and under climate change-related rainfall patterns, sea level rise and subsidence. However, modeled results indicate that more than 100% of the current riverine flows into the Maurepas Swamp region are still not sufficient to fully counteract the impacts of the assumed future sea level rise scenario and maintain the current forested wetlands surrounding Lake Maurepas. The higher salinities and more estuarine open water areas provide additional habitat in the future that will likely be more suitable for spotted seatrout (Cynoscion nebulosus), and adult bay anchovy (Anchoa mitchilli) than largemouth bass (Micropterus salmoides). Modeled future conditions of this ecosystem can inform restoration agencies and organizations by helping to prioritize and plan for future decades by incorporating critical factors such as sea level rise, subsidence and precipitation patterns, including the possible need to plan and prepare for changes in the fish communities and consider how that might influence the well-being of local communities.

Hydrology and water budget analysis of the East Joyce wetlands: Past history and prospects for the future

The East Joyce Wetlands (EJW) bordering northwest Lake Pontchartrain have a long history of human induced changes, such as leveeing of the Mississippi River that eliminated almost all riverine input to the area and segmentation of the east and west Joyce wetlands by the construction of a railroad, U.S. highway 51, and Interstate 55. Dredged drainage canals and associated spoil banks channel upland runoff around the wetlands. The deep canal associated with I-55 causes both rapid short-circuiting of freshwater runoff to Lake Maurepas and saltwater intrusion from Lake Pontchartrain. Increasing soil salinity has caused wide-spread loss of forested wetlands in the areas. Recently, the discharge of secondarily treated municipal effluent into the northeastern EJW as part of the Hammond wetland assimilation project has focused attention on the area (i.e., Bodker et al., 2015). In response, we carried out a number of studies at the Hammond Assimilation Wetlands (HAW) detailed in Shaffer et al. (2015), as well as a series of hydrological measurements and modeling detailed here. These data show that drainage under the railroad was minimal and most flow through the wetlands was to the southeast. Water levels in the HAW were highly variable prior to the beginning of effluent discharge in 2006, with relatively high mean water levels that did not increase substantially from 2007 through summer 2009 despite the addition of municipal effluent. Following effluent addition, surface water levels lacked the variability of the pre-discharge period and mean water levels were about 20cm higher from late 2009 until 2014 due to high rainfall in 2009, 2012, and 2013 and high effluent inflow due to significant infiltration into the city collection system. Historical net watershed inputs averaged 2.69cmyr−1 if this volume of water were spread over the 4km2 area immediately south of the effluent distribution system, compared to 0.38cmyr−1 for the effluent and 0.13cmyr−1 for direct precipitation. Salinity records from five sites in the EJW showed a gradient of increasing salinity from north to south and strong seasonality, averaging 1.9–2.1 PSU near the lake to 0.4–0.6 PSU in the northwestern EJW. Peak salinities were 4.6–5.1 PSU near the lake and 1.8 PSU in northwestern EJW. There was also a significant decrease in salinity over time. Salinity was lower beginning in 2010 coinciding with the closure of the Mississippi River Gulf Outlet, high precipitation in the fall and winter of 2009, and in 2012 and 2013, and continuing operation of the assimilation system. Proposed plans to alternate effluent discharge between east and west Joyce wetlands should increase surface water depth variability as seen prior to effluent discharge and minimize salinity intrusion in both areas.

Mercury concentrations in oligohaline wetland vegetation and associated soil biogeochemistry

Concentrations of mercury were determined in above- and below-ground tissues of dominant plant species, as well as soils, in the wetlands of Lake Maurepas, Louisiana. Indicators of wetland soil biogeochemical status, such as soil redox potential, pore-water nutrient concentrations, and pore-water total sulfides, were also determined. Total mercury concentrations in plant tissues were within the typical range for vegetation not exposed to mercury contamination. Similarly, total mercury concentrations in soils were typical of uncontaminated wetlands within this geographic region. Soil methyl mercury levels in this study are slightly lower than those reported in other studies of nearby wetlands. This may reflect the less extensive geographic sampling in this study, or the low water levels in the Lake Maurepas system immediately prior to and during this study, which would have altered soil biogeochemical status. This is corroborated by measurements of soil redox potential and soil pore-water nitrogen and sulfur constituents conducted during this study that suggest minimal sulfate reduction was occurring in surficial soils. This study indicates that the wetlands surrounding Lake Maurepas are typical of many uncontaminated oligohaline wetlands in the southeastern U.S. in regard to mercury concentrations.

Changing nutrient levels in Lake Maurepas following human population shifts in response to Hurricane Katrina

Following Hurricane Katrina in August 2005, as many as 57% of residents in some parishes in the Lower Lake Pontchartrain Basin were displaced from their homes. Concurrently, the population in the Upper Lake Pontchartrain Basin, which drains into Lake Maurepas, increased by 62,000 residents, leading to increased residential and urban land use. These changes led to significant increases in phosphate and silicate concentrations in Lake Maurepas that are likely caused by non-point source pollution through erosion from new construction sites, fertilisation of new lawns and stress to existing wastewater treatment facilities. Average phosphate concentrations at three sites in Lake Maurepas increased by 76–205% and silicate levels increased by 60–83% compared with data collected in 2003 prior to the hurricane. Discharge-weighted averages increased even more dramatically, with phosphate and silicate concentrations increasing up to 161 and 394%, respectively. Discharge-weighted silicate and phosphate concentrations were 2.5 and 3.4 times greater than in 2003, respectively. Discharge-weighted silicate levels were 3.9 times greater than similar measurements from 1963. These large increases in nutrient and discharge-weighted nutrient concentrations are indicative of increased human population in the Upper Lake Pontchartrain Basin following Hurricane Katrina.

A Meta-analytical Comparison of Fish Assemblages from Multiple Estuarine Regions of Southeastern Louisiana Using a Taxonomic-Based Method

Abstract The estuarine ecosystems of southeastern Louisiana are threatened by numerous environmental impacts such as wetland loss, coastal development, and overharvesting of natural resources. If the relative health of different estuaries can be determined, then management efforts might be focused on those regions needing the most protection. Unfortunately, estuaries are by definition dynamic, precluding easy comparisons of relative environmental health. Meta-analyses can be used to overcome problems associated with this natural variability. Analyzing sizable ecological data sets that cover large spatial and temporal scales is helpful in assessing relative ecosystem health among different regions. To compare the health of four estuarine regions of southeastern Louisiana (the Barataria Basin, Lake Maurepas, Lake Pontchartrain, and the Biloxi Marsh and Chandeleur Islands region), we calculated taxonomic distinctness and variation in taxonomic distinctness for fishery-independent data collected from three ha...

Total and methyl mercury in wetland soils and sediments of Louisiana's Pontchartrain Basin (USA)

Accumulation of methylmercury (MeHg) in aquatic biota is a primary toxicological concern associated with Hg contamination in the environment. This study reports total mercury (THg) and MeHg measurements in 11 swamp and 24 marsh soils/sediments in wetlands surrounding Lake Pontchartrain and Lake Maurepas located in Louisiana's Pontchartrain Basin. The salinity level ranged from fresh, brackish to salt water. Average THg content in the swamp soils/sediments (112.3 μ g kg−1, n = 10) was significantly higher (P = 0.04) than in the marsh soils/sediments (56.5 μ g kg−1, n = 24). The THg content in the marsh soils/sediments tended to decrease with salinity increase, probably due to geographical locations of the sampling sites with less Hg input in more saline regions. Average MeHg content in the soils/sediments was 1.3 μ g kg−1 (n = 34), higher than reported values in the bottom sediments of Lake Maurepas (0.8 μ g kg−1, n = 27) and Lake Pontchartrain (0.6 μ g kg−1, n = 147). Average MeHg/THg ratio in the marsh soils/sediments (0.022) was considerably higher than in the swamp soils/sediments (0.012). Analysis of MeHg/THg ratio along the salinity gradient at the marsh soils/sediments show that the highest MeHg/THg ratio (up to 0.040, n = 5) was found at the fresh/brackish water sites, and the lowest (0.002, n = 1) at the salt water site. Results suggest that there was a greater potential for MeHg formation in wetland soils/sediments than in bottom sediments of adjacent lakes. Results suggest that wetland surrounding the lakes may be a potential source of MeHg to the aquatic food chain and significance is governed by area of the adjacent wetland.

Through droughts and hurricanes: Tree mortality, forest structure, and biomass production in a coastal swamp targeted for restoration in the Mississippi River Deltaic Plain

Coastal swamps are among the rapidly vanishing wetland habitats in Louisiana due to accelerated sea-level rise and hydrological alterations that alter the natural flooding regime. In particular, the swamp forests of Lake Maurepas, Louisiana, have degraded considerably, and research regarding their condition might suggest approaches for their restoration. We measured forest structure, species composition, tree mortality, annual aboveground net primary production (ANPP) of woody species, and aboveground biomass allocation to leaf litter and wood, and soil strength at forty study plots within the Lake Maurepas basin over 5 years to evaluate the current condition of this coastal forested wetland. Local measures of salinity and regional measures of flooding were used to predict ANPP and aboveground biomass allocation. The 5-year study period included an intense drought as well as years characterized by hurricane-induced flooding. The forty study plots could be divided into four distinct habitat clusters based on standing biomass, structural variables, and salinity. The majority of the plots were co-dominated by Taxodium distichum and Nyssa aquatica. Acer rubrum var. drummondii and Fraxinus pennsylvanica were common mid-story species throughout the western and southern parts of the study area, while Salix nigra, Morella cerifera, and Triadica sebiferum were more important at the more degraded plots in the eastern part of the basin. Annual mean soil salinity reached unprecedented level (2–5 psu) during the drought and cumulative tree mortality reached up to 85% in areas characterized by frequent saltwater intrusions. The ANPP was higher during the drought period in 2000–2001 than during subsequent years, and was dominated by T. distichum. At most sampling plots, litter production exceeded wood production annually. A negative correlation between aboveground biomass allocation to litter and flooding indicated that biomass allocation shifted from litter toward wood during wet years. Overall, the majority of the plots sampled produced less than 400 g m −2 yr −1 of aboveground biomass annually due to the interacting negative effects of saltwater intrusion and prolonged flooding with nutrient-poor water. Reintroduction of Mississippi River water to the Maurepas system has the potential to benefit these swamps greatly by restoring a greater flow of nutrients, sediments, and fresh water through the wetlands. The historically slow (i.e., multi-decadal) process of swamp deterioration was greatly sped by low salinity (i.e., 2–5 psu) saltwater intrusions during a drought in 1999–2000. The majority of the coastal swamps in the Pontchartrain Basin are deteriorating, and most of this swamp area will be lost to open water in the foreseeable future if no restoration action is taken.

Total Hg, methyl Hg and other toxic heavy metals in a northern Gulf of Mexico estuary: Louisiana Pontchartrain basin

Concentration of total Hg, methyl Hg, and other heavy metals were determined in sediment collected along a salinity gradient in a Louisiana Gulf Coast estuary. Surface sediment was collected at established coordinates (n = 292) along a salinity gradient covering Lake Maurepas, Lake Pontchartrain, Lake Borgne and the Chandeleur Sound located in the 12,170 km2 Pontchartrain basin estuary southeastern coastal Louisiana. Lake Maurepas sediment with lower salinity contained higher levels of methyl Hg (0.80 μ g/kg) than Lake Pontchartrain (0.55 μ g/kg). Lake Maurepas sediment also had higher levels of total Hg (98.0 μ g/kg) as compared to Lake Pontchartrain (67.0 μ g/kg). Average total Hg content of Lake Borgne and the Chandeleur Sound sediment was 24.0 μg/kg dry sediment and methyl Hg content averaged 0.21μ g/kg dry sediment. Methyl Hg content of sediment was positively correlated with total Hg, organic matter and clay content of sediment. Methyl Hg was inversely correlated with salinity, sediment Eh and sand content. Total Hg and methyl Hg decreased with increase in salinity in the order of Lake Maurepas > Lake Pontchartrain > Lake Borgne/ the Chandeleur Sound. Lake Maurepas containing several times higher amount of methyl Hg in sediment as compared to Lake Pontchartrain and Lake Borgne and the Chandeleur Sound is an area that could serve as potential source of mercury to the aquatic food chain. Methyl Hg content of sediment in the estuary could be predicted by the equation: Methyl Hg = 0.11670–0.0625 × Salinity + 0.05349 × O.M. + 0.00513 × Total Hg - 0.00250 × Clay. Concentrations of other toxic heavy metals (Pb, Cd, Ni, Cu and Zn) in sediment were not elevated and was statistically correlated with sediment texture and iron and aluminum content of sediment.

The Wetlands of Lakes Pontchartrain and Maurepas: Past, Present and Future

One of the largest wetlands along the Gulf Coast of North America (ca. 150 000 ha) occurs around the shorelines of Lake Pontchartrain and Lake Maurepas in southeastern Louisiana, just north and west of New Orleans. We provide an introduction to the environmental history of the marshes and swamps in the upper Lake Pontchartrain basin, a review of the existing vegetation patterns and their possible causes, and a discussion of restoration targets and priorities. The Mississippi River produced the St. Bernard Delta 3000–4000 years ago, trapping fresh water to produce both Lake Maurepas and Lake Pontchartrain (Frazier 1967). The natural vegetation of much of the region remains fresh or brackish marshes, mixed with swamps dominated by bald cypress ( Taxodium distichum ) and tupelo ( Nyssa aquatica ). Yearly flooding by the Mississippi River was once a major factor controlling vegetation patterns, but these processes have been greatly impaired by the construction of artificial levees for flood control. Humans also removed most of the cypress swamps in a pulse of logging between 1876 and 1956. Continued subsidence of the land, slowly rising sea levels, salinity pulses from hurricanes, and canals from the Gulf of Mexico, add further stress to these wetlands. Over the past century there has been a steady loss of wetland area, and a gradual conversion of fresh water to salt water vegetation types. Biotic processes are also important. An exotic species of mammal, nutria ( Myocastor coypus ), consumes both aboveground and belowground parts of wetland plants. Reforestation is strictly limited by the combination of salt pulses, competition, and nutria. Alligators are the top predator in this system, but their potential for reducing the impacts of nutria has received minimal attention from biologists. There are many potential future states for this ecosystem. In the extreme case of rising sea level and warmer climate, the area may become a salt and brackish embayment fringed with mangroves. The state closest to historical conditions would be large areas of bald cypress swamp. Two important priorities are to increase flow of freshwater into the system from multiple pulsed fresh water diversions, and to decrease saltwater intrusions by closing canals such as the Mississippi River Gulf Outlet.

Potential nitrate removal from a river diversion into a Mississippi delta forested wetland

The objectives of this study were: (1) to carry out a baseline study of water quality parameters in the Maurepas forested wetland in Louisiana, USA; and (2) to estimate potential nitrate uptake of a proposed Mississippi River diversion into the wetland. Water sampling trips were carried out monthly from April to October 2000. Average water quality parameter concentrations and ranges were: nitrate 0.008 mg-N l−1 (non-detectable (n.d)-0.143 mg-N l−1); ammonium 0.007 mg-N l−1 (n.d-0.048 mg-N l−1); total nitrogen 0.577 mg-N l−1 (0.193–1.285 mg-N l−1); phosphate 0.034 mg-P l−1 (n.d-0.369 mg-P l−1); total phosphorus 0.055 mg-P l−1 (0.022–0.424 mg-P l−1); total suspended sediment 16 mg l−1 (4–101 mg l−1), salinity 3‰ (0–12‰), and chlorophyll a 11 μg l−1 (1–31 μg l−1). A UNET hydrodynamic model was constructed to predict hydrologic patterns as diverted water flowed through the Maurepas swamp. The study area was divided into 53 storage cells based on topographical features that mostly consisted of natural bayous and degraded artificial levees. Nitrate loading was high in the initial cells and removal efficiencies were on the order of 40–70%. Loading in subsequent cells was much lower and simulated nitrate retention was greater than 90%. Since most nutrients will be retained in the swamp, the proposed diversion of Mississippi River water should not cause adverse water quality conditions or extreme or persistent algal blooms in the Lake Maurepas.

The Fish Fauna of Lake Maurepas, an Oligohaline Part of the Lake Pontchartrain Estuary

Lake Maurepas is a slightly saline body of water located at the upper end of the Lake Pontchartrain estuary. Of 67 fish species collected during 1983-84, 33 species (49%) are primarily freshwater, 6 (9%) are primarily marine, and 28 (42%) are estuarine or diadromous, commonly occurring in both freshwater and marine habitats. Major freshwater species (e.g. lctalurus furcatus, I. punctatus, and Aplodinotus grunniens) were present throughout the year, whereas most marine and estuarine species were seasonally present (e.g. Anchoa mitchilli, Brevoortia patronus, and Micropogonias undulatus), or were present during periods of higher (up to 2.5 o/oo) salinity (e.g. Cynoscion arenarius, Leiostomus xanthurus, and Pogonias cromis). Literature records indicate that larger percentages of marine species are present during years when salinities are higher (up to 8 o/oo).

Relict Eolian Dunes and the Age of the 'Prairie' Coastwise Terrace, Southeastern Louisiana

Five fluvial source-bordering eolian dune trends consisting of over 70 mounds and hills were recently recognized on the coastwise Prairie terrace surface in the Florida Parishes1 of southeastern Louisiana, north of Lake Maurepas and Lake Pontchartrain between the Co-mite and Tangipahoa Rivers. Oval plane outlines with dominantly near-parallel long axes characterize the dunes. Maximum dune length is 600 m, width 400 m, and height 10m. The dune sand is uniformly medium grained, mostly very well and well sorted and has predominantly near-symmetrical skewnesses; 2 to 13 percent of the 0.25 mm grains are rounded and well rounded. Surprisingly, no internal stratification is evident in the dunes, possibly due to reworking by biological activity during slow sand accumulation by westerly winds. The climate of dune formation was probably somewhat cooler and considerably drier than the present wet subtropical conditions. Until now the Prairie and other Pleistocene coastwise terrace deposits along the Gulf of Mexico were generally accepted as interglacial formations. New evidence suggests that the dunes, the Prairie terrace surface, and at least the upper section of the Prairie Formation in the study area, may be of Early Wisconsin (glacial) age. Later Wisconsin and Holocene ages are less likely, as the entrenched streams may not have provided adequate dune sand supply.