Nutrient and Herbicide Movement in Streamflow from Two Midwestern Watersheds

Watersheds in different geographic areas offer many opportunities to study how differences in climate, crops, soils, and landscapes affect the off-site movement of runoff, sediment, nutrients, herbicides, and other environmental contaminants. The objective of this research was to compare differences in nitrate-nitrogen (NO3-N) and atrazine concentrations and discharges in streamflow from two watersheds in the Midwest for a 10-year period, 1992 through 2001. One watershed was the 7,280-ha Goodwater Creek watershed located in north-central Missouri, the other, the 5,130-ha Walnut Creek watershed in central Iowa. The Goodwater Creek watershed is located in the Central Claypan Major Land Resource Area (MLRA 113). Soils within this watershed are poorly drained because of a subsurface horizon 150 to 300 mm deep that has a clay content greater than 50%. The Walnut Creek watershed is located in the Central Iowa and Minnesota Till Prairies Major Land Resource Area (MLRA 103). Many of the soils within this watershed are tile drained to increase productivity. Over 80 % of the area within each watershed is cropped, but the fraction of corn cropping is higher in the Walnut Creek watershed. The drainage outlet of each watershed is instrumented with a concrete v-notch weir, water stage recorder, and refrigerated automatic pumping sampler. During low stages of streamflow, grab samples of baseflow were collected at the weir for chemical analyses. Mean annual precipitation values (1992-2001) for the Goodwater and Walnut Creek watersheds were 997 and 785 mm, with mean annual streamflow discharges of 392 and 223 mm, Alberts and Lerch are Soil Scientists, both at the U.S