Quantifying Restoration Impacts of Wetland Ecosystem Health and Carbon Export
USGS is investigating the impact of restoration on Louisiana's coastal wetlands' carbon dynamics.
The Science Issue and Relevance: The Deepwater Horizon (DWH) oil spill settlement in 2016 provides the Natural Resource Damage Assessment (NRDA) Trustees (Trustees) up to US 8.8 billion USD, distributed over 15 years, to restore natural resources and services injured by the spill. Given the unprecedented temporal, spatial, and funding scales associated with the DWH oil spill restoration effort, the Trustees recognized the need for robust Monitoring and Adaptive Management (MAM) to support restoration planning and implementation. As such, one of the programmatic goals is to “Provide for Monitoring, Adaptive Management, and Administrative Oversight to Support Restoration Implementation” to ensure that the portfolio of restoration projects provides long-term benefits to natural resources and services injured by the spill. This framework allows the Trustees to evaluate restoration effectiveness, address potential uncertainties related to restoration planning and implementation, and provide feedback to inform future restoration decisions. The Louisiana Trustee Implementation Group (LA TIG) MAM Strategy (LA TIG, 2021) has identified a need to “Quantify wetland net ecosystem carbon balance at pre-spill/post-spill time scales and basin/sub-basin spatial scales, including export to nearshore Gulf of Mexico…and within the next 5 years, targeted numerical modeling based upon available/collected data to calculate carbon capture of flora, fauna, and soils, associated with restoration.”
Net ecosystem carbon balance (NECB) is the sum of carbon entering the ecosystem minus the carbon leaving the ecosystem (Figure 1). NECB measures three primary carbon fluxes: 1) vertical gas flux, 2) lateral aquatic flux, and 3) changes to soil carbon storage, to determine whether the ecosystem is a net sink (carbon sequestration) or a net source (carbon export) of carbon. Because NECB is an integrative measure of ecosystem productivity, it serves as a strong indicator of ecosystem health. Generally, negative NECB represents a degrading system, where the majority of energy is leaving the system (carbon export). In contrast, positive NECB represents a healthy system, where energy is being stored (carbon sequestration). For coastal marshes, negative NECB is associated with increased vulnerability and a greater risk of conversion to open water. Therefore, a primary goal of restoration is to create marshes with a positive NECB that are more resilient and have high rates of carbon sequestration. To address the fundamental objective to “Maximize the combined benefits of the various Restoration Types and approaches across the overall restoration portfolio,” we are conducting targeted data collection and model development to estimate NECB in both a freshwater marsh and a saltwater marsh ecosystem, which will provide a baseline for comprehensive assessments of restoration activities in coastal Louisiana.
Methodology for Addressing the Issue: To assess the impact of restoration on coastal wetland NECB, we have developed an assessment tool using a modeling framework composed of integrated sub-models of landscape change and carbon dynamics, where changes in land cover (pre-spill/post-spill time scales) dictate changes in carbon stocks and fluxes (Figure 2) to project historic and future estimates of NECB with uncertainty estimates. Developed by the USGS over the past decade, the Land Use CArbon Simulator (LUCAS) model has assessed management activities in terrestrial ecosystems at multiple scales (Daniel et al., 2018; Sleeter et al., 2022), and the wetland model has been developed and validated using in-situ field data collected over the last decade in 24 sites across the Mississippi River Deltaic Plain (Holm et al., 2016; Baustian et al., 2017; 2021; Krauss et al., 2016; Stagg et al., 2017; 2018; Cadigan et al., 2022; Schoolmaster et al., 2022). Leveraging over a decade of USGS data collection and research from 24 sites in the region, this proposed activity would build off the existing model to expand to all coastal wetlands of Louisiana, and incorporate improved estimates of NECB, including export from vegetated wetlands to adjacent estuarine waters. Accurately assessing NECB requires quantifying the lateral flux component, and there are currently only two other coastal sites in the United States that use this approach in a comprehensive way. Using this approach, we will provide spatially explicit assessments of NECB for all coastal wetlands in Louisiana, at 30-meter resolution, allowing Trustees to see where and how restoration activities impact NECB. Spatially explicit assessments with uncertainty are critical to informing ecosystem restoration and conservation performance within the context of NRDA.
Built upon our existing LUCAS model, our framework will allow models of restoration and carbon dynamics to continually adapt and improve as new data become available and as understanding evolves over time. For example, results from the Louisiana Coastal Master Plan (Coastal Protection and Restoration Authority of Louisiana, 2023) will directly inform the LUCAS land cover change sub-model, providing high resolution wetland class maps that will improve historic and future scenarios of land cover change and NECB. The framework and information produced will allow decision makers involved in the design and implementation of Louisiana’s restoration portfolios to assess and compare alternative model projections for local accuracy and relevance, thus building confidence over time in their forecasts.
Future Steps: The assessment tool can be used by NRDA decision makers to identify the historic impacts of previous land management activities and future benefits (or losses) of planned activities to coastal wetland carbon sequestration. The results from this activity will provide spatially explicit NECB estimates for two major wetland habitats, and quantify export from the vegetated wetlands to adjacent open waters. The scenario-based modeling framework will allow users to define specific restoration scenarios (for example, Mississippi River diversion) and generate projections that quantify the impact of those activities on NECB. Because the model output, NECB, is an integrative metric of ecosystem resilience, it provides data on both the sustainability of habitat in the face of stressors (such as sea-level rise and hurricanes), as well as the amount of carbon available to support wetland and aquatic food webs in the estuary complex.
USGS is investigating the impact of restoration on Louisiana's coastal wetlands' carbon dynamics.
The Science Issue and Relevance: The Deepwater Horizon (DWH) oil spill settlement in 2016 provides the Natural Resource Damage Assessment (NRDA) Trustees (Trustees) up to US 8.8 billion USD, distributed over 15 years, to restore natural resources and services injured by the spill. Given the unprecedented temporal, spatial, and funding scales associated with the DWH oil spill restoration effort, the Trustees recognized the need for robust Monitoring and Adaptive Management (MAM) to support restoration planning and implementation. As such, one of the programmatic goals is to “Provide for Monitoring, Adaptive Management, and Administrative Oversight to Support Restoration Implementation” to ensure that the portfolio of restoration projects provides long-term benefits to natural resources and services injured by the spill. This framework allows the Trustees to evaluate restoration effectiveness, address potential uncertainties related to restoration planning and implementation, and provide feedback to inform future restoration decisions. The Louisiana Trustee Implementation Group (LA TIG) MAM Strategy (LA TIG, 2021) has identified a need to “Quantify wetland net ecosystem carbon balance at pre-spill/post-spill time scales and basin/sub-basin spatial scales, including export to nearshore Gulf of Mexico…and within the next 5 years, targeted numerical modeling based upon available/collected data to calculate carbon capture of flora, fauna, and soils, associated with restoration.”
Net ecosystem carbon balance (NECB) is the sum of carbon entering the ecosystem minus the carbon leaving the ecosystem (Figure 1). NECB measures three primary carbon fluxes: 1) vertical gas flux, 2) lateral aquatic flux, and 3) changes to soil carbon storage, to determine whether the ecosystem is a net sink (carbon sequestration) or a net source (carbon export) of carbon. Because NECB is an integrative measure of ecosystem productivity, it serves as a strong indicator of ecosystem health. Generally, negative NECB represents a degrading system, where the majority of energy is leaving the system (carbon export). In contrast, positive NECB represents a healthy system, where energy is being stored (carbon sequestration). For coastal marshes, negative NECB is associated with increased vulnerability and a greater risk of conversion to open water. Therefore, a primary goal of restoration is to create marshes with a positive NECB that are more resilient and have high rates of carbon sequestration. To address the fundamental objective to “Maximize the combined benefits of the various Restoration Types and approaches across the overall restoration portfolio,” we are conducting targeted data collection and model development to estimate NECB in both a freshwater marsh and a saltwater marsh ecosystem, which will provide a baseline for comprehensive assessments of restoration activities in coastal Louisiana.
Methodology for Addressing the Issue: To assess the impact of restoration on coastal wetland NECB, we have developed an assessment tool using a modeling framework composed of integrated sub-models of landscape change and carbon dynamics, where changes in land cover (pre-spill/post-spill time scales) dictate changes in carbon stocks and fluxes (Figure 2) to project historic and future estimates of NECB with uncertainty estimates. Developed by the USGS over the past decade, the Land Use CArbon Simulator (LUCAS) model has assessed management activities in terrestrial ecosystems at multiple scales (Daniel et al., 2018; Sleeter et al., 2022), and the wetland model has been developed and validated using in-situ field data collected over the last decade in 24 sites across the Mississippi River Deltaic Plain (Holm et al., 2016; Baustian et al., 2017; 2021; Krauss et al., 2016; Stagg et al., 2017; 2018; Cadigan et al., 2022; Schoolmaster et al., 2022). Leveraging over a decade of USGS data collection and research from 24 sites in the region, this proposed activity would build off the existing model to expand to all coastal wetlands of Louisiana, and incorporate improved estimates of NECB, including export from vegetated wetlands to adjacent estuarine waters. Accurately assessing NECB requires quantifying the lateral flux component, and there are currently only two other coastal sites in the United States that use this approach in a comprehensive way. Using this approach, we will provide spatially explicit assessments of NECB for all coastal wetlands in Louisiana, at 30-meter resolution, allowing Trustees to see where and how restoration activities impact NECB. Spatially explicit assessments with uncertainty are critical to informing ecosystem restoration and conservation performance within the context of NRDA.
Built upon our existing LUCAS model, our framework will allow models of restoration and carbon dynamics to continually adapt and improve as new data become available and as understanding evolves over time. For example, results from the Louisiana Coastal Master Plan (Coastal Protection and Restoration Authority of Louisiana, 2023) will directly inform the LUCAS land cover change sub-model, providing high resolution wetland class maps that will improve historic and future scenarios of land cover change and NECB. The framework and information produced will allow decision makers involved in the design and implementation of Louisiana’s restoration portfolios to assess and compare alternative model projections for local accuracy and relevance, thus building confidence over time in their forecasts.
Future Steps: The assessment tool can be used by NRDA decision makers to identify the historic impacts of previous land management activities and future benefits (or losses) of planned activities to coastal wetland carbon sequestration. The results from this activity will provide spatially explicit NECB estimates for two major wetland habitats, and quantify export from the vegetated wetlands to adjacent open waters. The scenario-based modeling framework will allow users to define specific restoration scenarios (for example, Mississippi River diversion) and generate projections that quantify the impact of those activities on NECB. Because the model output, NECB, is an integrative metric of ecosystem resilience, it provides data on both the sustainability of habitat in the face of stressors (such as sea-level rise and hurricanes), as well as the amount of carbon available to support wetland and aquatic food webs in the estuary complex.