Relation of baseflow to row crop intensity in Iowa

Increasing baseflow and baseflow percentage over the second half of the 20th century in Iowa has contributed to increasing nitrate-nitrogen concentrations measured in Iowa rivers because nitrate is primarily delivered to streams as baseflow and tile drainage. The relation of baseflow and baseflow percentage to row crop land use was evaluated for 11 Iowa rivers and their watersheds for their period of streamflow record (58-73 years period). Results indicated increasing baseflow in Iowa's rivers is significantly related to increasing row crop intensity. A 13-52% increase in row crop percentage in many Iowa watersheds has contributed to an increase of 33-135 mm increase in baseflow and 7-31% increase in baseflow percentage. Limited historical water quality data from two larger Iowa rivers (Cedar and Raccoon rivers) suggest that increasing row crop land use over the 20th century has produced more baseflow and contributed to increasing nitrate concentrations in Iowa's rivers.