Using enhanced wetlands for nitrogen removal in an agricultural watershed

Excerpt

Excess nitrogen (N) in temperate watersheds has been associated with an array of environmental problems, including polluted wells and surface water. The hypoxic zone in the Gulf of Mexico has created a particular focus on N loads in the Mississippi River Basin. Nitrogen sources include urban runoff; atmospheric deposition; point sources, such as waste-water treatment plants; and nonpoint sources, such as runoff from agricultural lands. Approximately two-thirds of the N load of the Mississippi River is from agriculture, underscoring the importance of balancing productive farming with water quality improvement (Goolsby and Battaglin 2000).

Wetland restoration has been identified as a strategy with the potential to reduce watershed N loads. Slowly moving water, high microbial activity, and long residence times can create low dissolved oxygen (O₂) conditions under which bacteria convert nitrate (NO₃) to N gas in shallow water wetlands (Kadlec and Knight 1996). This denitrification processs physically removes N in the form of inert N gas from the aquatic system (Hey et al. 2012). Forshay and Stanley (2005) documented rapid denitrification in wetland sloughs on the Wisconsin River floodplain, where NO₃ concentrations in floodwater captured by overbank flow into the sloughs decreased significantly over a few days.

This paper presents…