A wetland to improve agricultural subsurface drainage water quality

The effectiveness of wetlands to cleanse event-driven agricultural drainage water in east-central Illinois was studied. A wetland was constructed at the outlet of a subsurface-drained agricultural field in a corn-soybean rotation. Hydrology data from the wetland inlet and outlet, including precipitation and evapotranspiration data, were used to develop a water budget for the system. Water quality data were collected from the wetland inlet, outlet, and the pond section of the wetland and analyzed for nitrate-nitrogen (NO₃-N), orthophosphate (PO₄-P), and nine common Midwestern herbicides: trifluralin, atrazine, alachlor, metolachlor, ethalfluralin, butylate, clomazone, cyanazine, and pendimethalin. Constituent mass loads were calculated at the inlet and outlet, and both concentration and mass load data sets were statistically analyzed. Results indicated variable performance based primarily on seasonal processes and individual chemical constituent. Overall, NO₃-N mass load assimilation was approximately 174 kg (32.9%) over the course of the Study, although assimilation rates were seasonally dependent. PO₄-P and herbicide concentration and mass load assimilation were not significant.