Nitrogen (N) and phosphorus (P) levels in the base flow discharge of 10 small streams in south central and southwestern Wisconsin were measured in 1988-1989 and compared to historical data on the same streams. Nitrate concentrations had increased significantly in three streams, the Little Plover River in the north central Hardwood Forests Ecoregion and Cave Hollow and Mt. Vernon Creeks in the Driftless Area Ecoregion. Nitrate changes appear to be related to agricultural activities and fertilizer use in the watersheds. Highest nitrate levels have been found in the area south of the Wisconsin River where land use changes have occurred. Current P levels in the 10 streams were established, but trends could not be determined because of the unreliability of the historical data set.
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Mason et al. (1990) studied this question.