Water Resources Research Act Program

Details for Project ID 2020MS263B

Multi-scale Evaluation of the Impact of Hydrological Extremes on Coastal Wetland Vegetation

Institute: Mississippi
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $34,976 Total Non-Federal Funds: $70,126

Principal Investigators: Dr. Wei Wu

Abstract: Coastal wetlands are among the most productive ecosystems in the world and provide a wide variety of key ecosystem services. As they are sensitive to water levels, they are distributed within a narrow range in the intertidal zone. Hydrological extremes, which are predicted to occur more frequently under climate change, therefore affect coastal wetlands, including their vegetation productivity and green aboveground biomass and related ecological processes. As aboveground biomass traps mineral sediments in the water columns and contributes to accretion of salt marshes, dynamics of aboveground biomass is an important indicator for healthy status of coastal wetlands. Therefore, the critical water problem we will address is how hydrological extremes affect live aboveground biomass in salt marshes on the Mississippi Gulf Coast. Despite its importance, there exists limited research related to this problem in Mississippi. Furthermore, the knowledge of the response of Juncus roemerianus, a dominant salt marsh species east of Pearl River in the northern Gulf of Mexico, to hydrological extremes is scarce. In addition, there is an urgent need to understand the impact with uncertainties/variability accounted for. Through the proposed project, we aim to: 1) scale up the local live aboveground biomass to the Mississippi Gulf Coast with uncertainties accounted for, 2) evaluate the impact of hydrological extremes, including meteorologically driven events and anthropogenic activities such as drought, storms, and openings of Bonnet Carré spillways on live aboveground biomass in salt marshes, and 3) identify the optimum inundation depth and soil salinity for live aboveground biomass. We will test the following hypotheses: H1: Drought and flooding events reduced vegetation productivity in salt marshes in the short and long term. H2: The time it took for vegetation productivity to recovery depends on the type, intensity and duration of hydrological extreme events. H3: Anthropogenic activities such as openings of Bonnet Carré Spillway had longer-term impact on live above-ground biomass and it took longer for the biomass to recovery than meteorologically driven drought and flooding events. We will combine field survey, remote sensing techniques, and multi-scale modeling in Bayesian inference for the proposed research. We will conduct field surveys at Hancock County salt marshes, and the Grand Bay National Estuarine Research Reserve (NERR) salt marshes from west to east along the gradient of the largest to smallest impact from the historical Bonnet Carré Spillway openings. We will measure above-ground biomass (live and dead) in each season following the methods in Wu et al. (2017). In addition, we will measure or obtain related environmental factors including soil salinity, inundation level, elevation, air temperature, and precipitation/river discharge. In order to scale up the field measurements to the regional scale, we will develop multi-scale models that link the measured above-ground live biomass to vegetation indices derived from Landsat satellite images, and auxiliary environmental variables. We will explore different vegetation indices to predict green biomass. We will also explore whether the covariates have region-wide impact or spatial variant effect through model selection. The final model selected will be applied to unsampled marsh locations before, during, and after hydrological extreme events to evaluate the spatial and temporal patterns of live aboveground biomass and infer the impact of historical spillway openings, and drought and storm events. We will coproduce the research products with Mississippi Department of Marine Resources and Grand Bay National Estuarine Research Reserve. The project will generate empirical data and predictive models to improve the understanding of vegetation and blue carbon dynamics in highly productive salt marsh ecosystems. It will also advance the theory of ecological resilience. Furthermore, it will inform and facilitate the best practices of coastal restoration and conservation under climate change at the local and regional scales.