Proceedings of the 2022 Mississippi Water Resources Conference

Year: 2022 Authors: Feldpausch K., Wu W.

Wetlands are highly productive ecosystems that provide important ecosystem services. However,they have been threatened by extreme hydrological events, such as diversions of freshwater, droughts, and accelerated sea-level rise through change of inundation and salinity regimes. This study evaluated how diversions of freshwater, particularly Bonnet Carrè Spillway openings in 2019, affected vegetation productivity in salt marshes on the Mississippi Gulf Coast, US. The Bonnet Carrè Spillway was built to prevent and mitigate flooding in New Orleans. The frequency of its opening has increased over the last two decades, and 2019 was marked the first time in history that this spillway was opened in two consecutive years and twice in one year.

We first developed a model to link vegetation green biomass to spectral information of Landsat and Sentinel satellite images, and then applied the model to hindcast vegetation green biomass based on the historical images before and after the openings of the Bonnet Carrè Spillway to assess the openings' impact on vegetation. My study area is two estuarine systems that differ in their proximity to the Bonnet Carrè Spillway, elevation, salinity, nutrient levels, including Hancock County Marshes on the west, and Grand Bay National Estuarine Research Reserve on the east in Mississippi. We found marginal short-term impact. Future studies should focus on long-term impact of these extreme events on salt marshes. This study improves our understanding of vegetation and blue carbon dynamics in highly productive salt marsh ecosystems. It also informs the unexpected consequences of anthropogenic activities on valuable ecosystems.