Conserving and Restoring Critical Habitats

The Mississippi barrier islands are dynamic coastal landforms that protect the Mississippi mainland coast against wave impacts from the Gulf of Mexico. This barrier island chain reduces storm surge energy from tropical cyclones and winter storms mitigating potential shoreline erosion and salt-water intrusion. However, in the last century these islands have experienced major land loss from hurricanes, relative sea-level rise, and decreases in sediment supply due to channel dredging. In 2009, the U.S. Army Corp of Engineers (USACE), in conjunction with other Federal and State agencies, developed the Mississippi Coastal Improvements Program (MsCIP) with the goal of restoring the Mississippi barrier islands to mitigate damage from future storm surges. In December 2020, the USACE completed the barrier island restoration project through direct sand placement on Cat and Ship Islands as well as replenishing sand in the littoral transport zone. The USACE, in collaboration with the U.S. Geological Survey, developed the MsCIP long-term monitoring and adaptive management program (MAMP) to incorporate a science-based approach into this large-scale restoration effort. The MsCIP MAMP includes identification of risk and uncertainties, performance measures, in situ and remote sensing-based monitoring, structured decision making, and potential adaptive management actions. All elements will be used to evaluate restoration efficacy on the Mississippi barrier islands and provide information necessary to improve future project design and coastal resource management. This presentation will provide an overview of the MsCIP MAMP restoration of the islands, highlighting baseline conditions and discussing preliminary post-construction monitoring and results.

The Nature Conservancy in Alabama (TNC) first made their mark in Mississippi Sound when they constructed three types of reefs along 1.5 miles of southeast Coffee Island in 2009 using NOAA American Recovery and Reinvestment Act funds. Fifteen years later, TNC is a permanent resident in this waterbody through its tireless efforts to implement projects to restore shorelines and habitats, while solidifying relationships with the local communities who thrive on these waters. Through Coffee Island breakwater construction, long-term monitoring across projects, and large-scale shoreline restoration at Lightning Point, our efforts have remained steady in Mississippi Sound. Managing multiple relationships from federal to state to local stakeholders and leveraging our partners' plans and initiatives has helped bridge gaps and find connections between diverse projects. This presentation will provide an example of working in a waterbody with multiple stakeholders and how to balance the needs and wants of each entity to sustain the health and quality of the waterbody and its habitats. The lessons learned from TNC's journey from the first, small-scale project at Coffee Island to multiple interconnecting projects happening today focused on improving Mississippi Sound's economic and ecosystem resilience for future generations can be applied to other waterbodies across the nation.

Indigenous peoples residing on coasts rely heavily on coastal wetlands for their livelihoods and protection from storms. However, the stability of coastal wetlands is threatened by sea-level rise (SLR), as well as other natural and anthropogenic factors. Their loss would result in the disappearance of critical ecosystem services, leading to significant ecological and economical consequences. This study aims to predict the impact of SLR on the coastal wetland landscape adjacent to the Point-au-Chien Indian Tribe (PACIT) in southeastern Louisiana. The goal is to help the Indigenous community restore and conserve these key ecosystems to better adapt to SLR. Specifically, we modeled how belowground biomass responded to inundation and salinity, two key abiotic factors associated with SLR. Belowground biomass plays a crucial role in stabilizing sediments, mitigating erosion, and contributing to the accretion of wetland platforms through the accumulation of organic matter. However, it can reduce as salinity and inundation levels rise, in conjunction with SLR. We implemented multi-level Bayesian models to predict depth-specific live belowground biomass in peak growing season synthesizing data across multiple spatial scales, including site-scale elevation (as a proxy for inundation) and depth-scale soil porewater salinity. We then applied the model to a future SLR scenario, where the salinity maximum, represented by the mean high-water level, moves inland. The results showed negative response of belowground biomass to elevated inundation and salinity that will contribute to coastal wetland loss. The findings will be further assimilated into a landscape model to predict coastal wetland change and disseminated to the PACIT to facilitate the tribe's decision making in costal wetland restoration.   

Coastal wetland ecosystems provide a multitude of crucial environmental functions including water quality improvement, flood mitigation, shore stabilization, and recharging groundwater reservoirs. However, sea level rise (SLR) has threatened the stability of coastal wetlands as it can lead to lowered productivity and plant death with increasing inundation and salinity. This study aims to predict landscape change of coastal wetlands neighboring the Pointe-au-Chien Indian Tribe (PACIT) under SLR to provide insights on suitable locations of potential living shorelines to protect and restore them. Particularly, we focus on evaluating below ground biomass in the peak growing season in response to inundation.


Aboveground and belowground vegetation samples were taken from five sites at PACIT in September 2023. Each site has two elevational transects with three subsites at each transect. At each subsite, 15 x 15 cm quadrats were used to sample aboveground biomass and soil cores, 12.7 cm in diameter were used to sample belowground biomass from the surface down to 30 cm (root zone). In the lab, aboveground biomass was separated into live and dead based on color. Sediments were separated into 5-cm depth and then belowground biomass were separated into live and dead based on buoyancy, color, and turgidity, before being dried. We evaluated the vertical profiles of dry live biomass through its response to inundation using mixed-effects models. We found decreasing live below-ground biomass with depth in general with maximum biomass in 5-10 cm depth and 52.27% of biomass in the first 10 cm. We did not find significant relation between belowground biomass and inundation; however, the aboveground biomass showed a quadratic function with a peak mass biomass at a certain elevation. These findings help better understand how SLR affects the health of coastal wetland ecosystems and can facilitate decision making in wetland restoration efforts.

Coastal marshes provide essential ecological functions, but they are susceptible to a variety of stressors. Sea level rise (SLR) threatens coastal marshes as total marsh extent will decrease if marshes are unable to maintain elevation with the rate of SLR. Since 2012, Surface Elevation Tables and marker horizon plots have been used to measure marsh elevation and accretion, respectively, at the Grand Bay National Estuarine Research Reserve (GNDNERR). Measurements have been taken quarterly (2012 – 2016) and biannually (2017 – present) at five sites along a coastal transition transect extending from open water to upland slash pine (Pinus elliottii) forests. Elevation change rates ranged from 1.12 mm/year (95% CI: -0.07 – 2.31) to 6.79 mm/year (95% CI: 5.13 – 8.44). Accretion rates ranged from 0.44 mm/year (95% CI: 0.26 – 0.61) to 4.05 mm/year (95% CI: 3.40 – 4.70). The highest elevation change and accretion rates were seen at the two southernmost, low elevation marsh sites. Elevation change rates were lowest at a high elevation marsh site and accretion rates were lowest at the highest elevation site located in a slash pine forest. Only the two southernmost, low elevation sites have elevation change rates greater than the long-term SLR rate (4.39 mm/year; 95% CI: 3.83 – 4.94), while all sites are below the 19-year SLR rate (10.86mm/year; 95% CI: 8.62 – 13.11). The Grand Bay estuary is a retrograding delta with no major freshwater inflow and limited sediment delivery possibly hindering the ability of higher elevation marshes at GNDNERR to keep pace with the future rate of SLR. Facilitating marsh migration through prescribed fire could preserve total marsh extent; however, quantification of baseline marsh migration rates, ideally with and without fire restoration, needs to be conducted to optimize conservation efforts.