FACTORS AFFECTING NITROGEN LOSS IN EXPERIMENTAL WETLANDS WITH DIFFERENT HYDROLOGIC LOADS

Constructed or restored wetlands have great potential for reducing non point source contamination of surface and ground waters by agricultura l chemical contaminants. The work reported here combines field and exp erimental studies of factors affecting nitrogen loss in the Des Plaine s River Experimental Wetlands, northeastern Illinois, USA. These wetla nds receive approximately 5-36 cm/week of pumped river water with sign ificant but seasonally variable loads of nitrate and organic nitrogen. On an annual basis, the wetlands removed 78-95% of the nitrate and 54 -75% of the total nitrogen received. At the low hydrologic loading rat e, organic nitrogen exports approximately equalled imports. However at the higher hydrologic loading rate, the wetlands exported 22-33% more organic nitrogen than received. Seasonal variation in nitrate and org anic nitrogen loads had significant effects on the effectiveness of th e wetlands as sinks for total nitrogen. The wetlands were nitrogen sin ks during periods of high nitrate loading and nitrogen sources during periods of low nitrate loading. Experimental studies demonstrated the effects of nitrate concentration, temperature, and location on rates o f nitrate loss. Results suggest that nitrate loading rates might influ ence not only nitrate loss rates but also loss rate coefficients.