Riparian Wetland Nitrate Retention is Influenced by both Floodwater Nitrate Concentration and Inundation Time

Abstract

Nitrate is the most common form of nitrogen pollution in agricultural rivers. Excess nitrogen can cause harmful algal blooms and low oxygen levels in aquatic environments. Riparian wetlands in agricultural watersheds can be very efficient at removing nutrients before they reach streams and restoring agricultural wetlands for improving water quality has become a major focus of the USDA Natural Resource Conservation Service Wetlands Reserve Program (WRP). Our objective was to gain more understanding of how nitrogen concentration in flood waters impacts nitrogen uptake rates across different restoration types implemented by the USDA to restore these agricultural wetlands in the WRP. We collected 60 soil cores across four restoration types in a west Tennessee wetland. Cores were incubated in a continuous flow-through setup for 48 hours at 24°C with synthetic lab water, with 5 individual water sources of differing nitrate concentrations (0.1, 0.5, 1.0, 5.0, 10.0 mg/L). Each restorative type had 15 cores total, split up into 3 cores per nitrogen concentration. Results show that nitrate uptake varied over time with soil generally releasing nitrate initially and retaining nitrate after 24 hours. As well as nitrate uptake rates increased with more nitrate availability in all habitats. Wetlands can potentially be a source of nitrate when they are initially flooded but become nitrate sinks with a longer water residence time.