Proceedings of the 2019 Mississippi Water Resources Conference

Year: 2019 Authors: Taylor J.M., Lizotte R., Ochs C.

Denitrification (DNF) is a biologically-mediated mechanism that converts nitrate (NO₃-N) to di-nitrogen (N₂) gas and potentially removes excess N from intervening waterbodies distributed across the Mississippi Delta landscape. Despite its considerable influence on N cycling and potential mitigation potential as an ecosystem process, very little information is available on denitrification rates in Delta water bodies. We use two different approaches to measure DNF with data collected from two different Delta habitat types: a bayou within the Delta interior (Roundaway Lake), and historic river meander cutoff of the lower Mississippi River (Desoto Lake). Results indicate that significant DNF occurs within Delta lake habitats and rates are governed by organic matter and N availability. Sediment core incubations from Roundaway Lake indicate DNF rates increase with increasing N availability and were enhanced by crop organic matter transported from adjacent agricultural fields. Connectivity with the Mississippi River during spring flooding resulted in high N enrichment in Desoto Lake. After the river receded and separated from the lake, NO₃-N concentration decreased with corresponding increases in N₂ gas concentrations in the hypolimnion, indicating that denitrification can play a significant role in N removal within off channel habitats of the river. Information on factors that influence DNF in Delta waterbodies can improve models of N cycling and export within Delta watersheds as well as identify potential management strategies for enhancing DNF and N mitigation within the region.