Ground Water/surface Water Interactions

A baseflow survey of 41 tributary creeks investigated the tiansport of alrazine, nilrate-nitrom chloride and sulfate in two 5,000 ha Jasper County, Iowa watersbeds. The waterskds comprise a long-tam paired shldy to evaluate the effects of largesale conversion of row nop to prairie in Walnut creek watershed compared to highly agricultural Squaw creek watershed. Discharge and chemical concentrations measured at subwabmhed wtlets were used to asses chemical losses. Streamnow varied considerably among subwaterskis but was found to be SignifcanUy related w0.05) to the amount of alluvial soils present in drainage areas. Two methods were. used to estimaGe basenow from riparian conidors where discharge could not be directly measured: 1) a watershed flow budget; and 2) a regtwion equation related to the amount of alluvial soils present DitFuse groundwater discharge along major tributary corridors was found to be the mejor source of Streamnow and pollutant loading in both watersheds. Concentrations of atrazine (<0.05 to 0.24 @), nitrate (a.05 to 14 a) and chloride (6.2 to 34 mgL) varied but were highest in water draining pdominautly row crop atas. Baseflow from restored prairie subwatersbeds contained low concentrations of ag-pllutauts. M e restoration wncentrated in the riparian corridor of the Walnut Creek watefihed has produced a different pollutant-loading paaem compared to Squaw Creek. In Walnut creek watershed, nibate losses occurred priowily in k d v a t e r drainages dominated by row crop. Nitrate concentrations demased downsbeam as baseflow from restored prairie areas diluted stream nitrate concentrations. Nitrate concentrations in Squaw C m k incrpased dawnstream as basenow containing elevated nitrate concentrations discharged from riparian row crop areas. KEY TERMS: riparian corridor, prairie restoremion, nim-nitrogen, pes!i&b, basenow In Squaw Creek, no differenoes in nitrate losses were observed among subwatersheds.