Sea level rise and nutrient cycling in coastal wetlands

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This article is part of the Fall 2014 issue of the Earth Science Matters Newsletter. 

 

dead trees along the Savannah River

Coastal wetlands and swamps are vulnerable to increased salinity from sea level rise. Trees that dominated this site are dying and being replaced by brackish marsh.

(Credit: Ken Krauss, USGS. Public domain.)

Sea level rise and land use changes are causing salt water to encroach into many formerly freshwater tidal wetlands along the US coast. In many areas, this process, known as salinification, is converting freshwater-forested wetlands to low-salinity marshes with distinctively different plant and animal communities. 

While species shifts along salinity gradients have been well-documented, other less well-known impacts may also be important. For example, salinification-induced changes in cycling of nutrients such as phosphorous and nitrogen can affect primary productivity in terrestrial habitats. They can also fuel excessive nutrient build-up (eutrophication) in adjacent aquatic habitats, altering water quality and triggering algal blooms. 

In a new paper by USGS research scientists and university colleagues, changes in soil nitrogen and phosphorus cycling were measured in response to salinification of tidal freshwater-forested wetlands and their subsequent conversion to more saline marshes in South Carolina and Georgia. Salinification was found to increase the rates with which these key soil nutrients changed chemically. These increases in soil nutrient availability likely lead to nutrient export to estuaries and fueled the migration of marsh plants into salt-stressed tidal forests. The findings from this research advance our understanding of coastal wetland response to sea level rise. These data are critical to improve our capabilities to model and forecast impacts of future climate and sea level scenarios.

The paper, published in Biogeochemistry, is available at https://pubs.er.usgs.gov/publication/70046072.

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