Evaluating How Hydrology Influences Nutrient Retention In Restored Floodplain Wetlands

Abstract

Floodplain wetlands are vital ecotones that mitigate nutrient pollution from the surrounding watershed. Despite their valuable role in maintaining healthy streams, floodplain wetlands have been historically drained or degraded by intense agricultural practices. The U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS) manages the Wetlands Reserve Program (WRP), which allows cropland to transition back to wetlands. A key WRP restoration practice reestablishes natural hydrology regimes and connectedness with the river, which in turn should improve nutrient retention. This study is evaluating the effectiveness of hydrology restoration at increasing soil nitrogen and phosphorus uptake in 40 WRP wetland easements across western Tennessee and Kentucky. Thirty soil cores were collected from each of nine restored wetlands during the summer of 2019 (year one) and incubated in a laboratory system for 32 hours. Preliminary data suggest that both standing water and easement age can regulate nutrient removal rates with shallow water areas retaining at least three times more nitrogen and phosphorus than dry forested and herbaceous vegetation areas during initial flooding. However, after 32 hours of inundation, removal rates decreased substantially in most habitat types. Additional analyses will relate maximum potential uptake rates to soil properties. This preliminary data shows that water permanence may be important in maximizing wetland function, but differences may be a function of individual site characteristics and time since restoration.