Nitrate Removal in Surface-flow Constructed Wetlands Treating Dilute Agricultural Runoff in the Lower Yakima Basin, Washington

 

Situation: Increasing agricultural runoff with high concentrations of nitrate-N and other nutrients has led to eutrophication of surface waters. Constructed wetlands have been shown to effectively treat N-contaminated wastewaters, but documented, long-term studies of nitrate-N removal in constructed wetlands treating agricultural runoff is limited. 

 

Actions: The purpose of this study was to analyze four years of water quality data for a surface-flow constructed treatment wetland receiving irrigation return flows from agricultural fields in Yakima Basin, Washington. The constructed wetland consisted of a sedimentation basin followed by two surface-flow wetlands. The study specifically examined the effects of nitrate-N loading, temperature, and dissolved oxygen on nitrate-N removal. 

 

Take-home message: 

• The constructed treatment wetland was extremely effective in removing nitrate-N pollution.
• Concentration removal efficiencies in the treatment wetlands consistently exceeded 90% for nitrate-N and 60% for total N.
• The sedimentation basin removed nitrate-N and total N in the range of 20-30%.
• Nitrate removal rates were highly sensitive to temperature (removal rates where 2-4 times higher in warmer months).

 

For more information:

• Beutel, M.W., C.D. Newton, E.S. Brouillard, R.J. Watts. 2009. Nitrate removal in surface-flow constructed wetlands treating dilute agricultural runoff in the lower Yakima Basin, Washington. Ecological Engineering (35): 1538-1546.
• Email Marc W. Beutel at mbeutel@wsu.edu