Decision Support for Managers Restoring Texas Coastal Marshes with Beneficial Use of Dredged Material
USGS researchers will define the range of elevation targets supporting optimal plant performance and oil strength by identifying the lower and upper thresholds of marsh conversion, and characterize ecosystem development of restored marshes over time to identify the lifetime and sustainability of restored marsh during sea-level rise. This work addresses priority science needs to improve restoration outcomes in coastal Texas marshes restored with beneficial use of dredge material.
The Science Issue and Relevance: Ecological thresholds represent critical conditions that often define transitions between ecosystem types, such as vegetated marsh and open water. Knowledge of lower and upper thresholds is critical for practitioners to guide placement of dredge materials or sediments for optimal plant production. To determine the longevity of these restored marshes, it is necessary to understand how ecosystem function changes over time and within the context of future climate conditions. Identifying time to submergence of restored systems will provide restoration planners with important information to support adaptive management, including re-application of dredge material. Identifying elevation thresholds and time to submergence is critical to inform restoration efforts and build resilience of coastal marshes in a changing climate.
Methodology for Addressing the Issue: The study will be conducted on the Texas Chenier Plain coast in Spartina patens (also known as saltmeadow cordgrass) marshes located within the McFaddin National Wildlife Refuge and J.D. Murphree State Wildlife Management Area. These areas contain long-term and active study sites where beneficial use of dredge material has restored large areas of S. patens marshes. The landscape includes natural and restored marshes of varying elevation and age that we will use to address the following two objectives.
1: “How high?” We will define the range of elevation targets supporting optimal plant performance and soil strength by identifying the lower elevation threshold controlling conversion to open water, and the upper elevation threshold controlling conversion to bare ground/salt flat. Newly collected and existing data on plant community and soil strength along an elevation gradient will be used in nonlinear data analyses to quantify elevation thresholds.
2: “How long?” We will characterize ecosystem development of restored marshes over time to identify the lifetime and sustainability of restored marsh during sea-level rise. Plant community, soil strength, and elevation measurements will be collected within each age class. Linear regression analyses will be used to characterize the relationships between time and vegetation and soil variables. These analyses will be used along with natural reference marsh elevations to calculate the time it takes for the restored marsh to reach equivalence with the natural marshes. The future elevation of the marsh will be determined by a model developed using an U.S. Army Corps of Engineers (USACE) program and compared to local projections of sea-level rise to calculate time to submergence of restored marshes.
Future Steps: Our work addresses priority science needs to improve restoration outcomes in coastal Texas marshes restored with beneficial use of dredge material. This work will support marsh restoration management to enhance numerous ecosystem services, including providing critical habitat for species of concern, such as the Whooping Crane and the Mottled Duck. It will also help inform efforts to increase coastal wetland resilience and restoration in the face of climate change and extreme weather events. The results from this project will be immediately relevant to ongoing restoration efforts planned by the co-Principal Investigators and primary stakeholders Todd Merendino with Ducks Unlimited (DU), Michael Rezsutek with Texas Parks & Wildlife Department (TPWD), and Jena Moon with the U.S. Fish and Wildlife Service (USFWS), along with their respective organizations, who seek approaches to reduce coastal wetland loss and preserve the societal benefits provided by coastal wetlands for current and future generations. In recent years, DU have been working with partners to develop a Texas Beneficial Use of Dredge Material Master Plan, which prioritizes coastal marsh sites for restoration via sediment additions. The results of this project will provide decision support tools for natural resource decision makers. Adding sediment layers of dredge material to coastal wetlands results in immediate gains in marsh elevation and works towards meeting the USACE priority goal of using 70% of dredge material via beneficial use by 2030.
USGS researchers will define the range of elevation targets supporting optimal plant performance and oil strength by identifying the lower and upper thresholds of marsh conversion, and characterize ecosystem development of restored marshes over time to identify the lifetime and sustainability of restored marsh during sea-level rise. This work addresses priority science needs to improve restoration outcomes in coastal Texas marshes restored with beneficial use of dredge material.
The Science Issue and Relevance: Ecological thresholds represent critical conditions that often define transitions between ecosystem types, such as vegetated marsh and open water. Knowledge of lower and upper thresholds is critical for practitioners to guide placement of dredge materials or sediments for optimal plant production. To determine the longevity of these restored marshes, it is necessary to understand how ecosystem function changes over time and within the context of future climate conditions. Identifying time to submergence of restored systems will provide restoration planners with important information to support adaptive management, including re-application of dredge material. Identifying elevation thresholds and time to submergence is critical to inform restoration efforts and build resilience of coastal marshes in a changing climate.
Methodology for Addressing the Issue: The study will be conducted on the Texas Chenier Plain coast in Spartina patens (also known as saltmeadow cordgrass) marshes located within the McFaddin National Wildlife Refuge and J.D. Murphree State Wildlife Management Area. These areas contain long-term and active study sites where beneficial use of dredge material has restored large areas of S. patens marshes. The landscape includes natural and restored marshes of varying elevation and age that we will use to address the following two objectives.
1: “How high?” We will define the range of elevation targets supporting optimal plant performance and soil strength by identifying the lower elevation threshold controlling conversion to open water, and the upper elevation threshold controlling conversion to bare ground/salt flat. Newly collected and existing data on plant community and soil strength along an elevation gradient will be used in nonlinear data analyses to quantify elevation thresholds.
2: “How long?” We will characterize ecosystem development of restored marshes over time to identify the lifetime and sustainability of restored marsh during sea-level rise. Plant community, soil strength, and elevation measurements will be collected within each age class. Linear regression analyses will be used to characterize the relationships between time and vegetation and soil variables. These analyses will be used along with natural reference marsh elevations to calculate the time it takes for the restored marsh to reach equivalence with the natural marshes. The future elevation of the marsh will be determined by a model developed using an U.S. Army Corps of Engineers (USACE) program and compared to local projections of sea-level rise to calculate time to submergence of restored marshes.
Future Steps: Our work addresses priority science needs to improve restoration outcomes in coastal Texas marshes restored with beneficial use of dredge material. This work will support marsh restoration management to enhance numerous ecosystem services, including providing critical habitat for species of concern, such as the Whooping Crane and the Mottled Duck. It will also help inform efforts to increase coastal wetland resilience and restoration in the face of climate change and extreme weather events. The results from this project will be immediately relevant to ongoing restoration efforts planned by the co-Principal Investigators and primary stakeholders Todd Merendino with Ducks Unlimited (DU), Michael Rezsutek with Texas Parks & Wildlife Department (TPWD), and Jena Moon with the U.S. Fish and Wildlife Service (USFWS), along with their respective organizations, who seek approaches to reduce coastal wetland loss and preserve the societal benefits provided by coastal wetlands for current and future generations. In recent years, DU have been working with partners to develop a Texas Beneficial Use of Dredge Material Master Plan, which prioritizes coastal marsh sites for restoration via sediment additions. The results of this project will provide decision support tools for natural resource decision makers. Adding sediment layers of dredge material to coastal wetlands results in immediate gains in marsh elevation and works towards meeting the USACE priority goal of using 70% of dredge material via beneficial use by 2030.