Annual chemical loads and application amounts to the watershed are shown in Table 1. Atrazine and metolachlor show the largest loads in discharge. Amounts lost during 1994 were the smallest of any year sampled to date and if we assume similar application amounts to the previous years, then these losses would be less than 0.2 percent for atrazine and less than 0.1 percent for metolachlor. Nitrate-N loads from the watershed range from 40 to 150 percent of the total fertilizer applied. Nitrate-N Altrazine Alachlor Metribuzin Metolachlor Year Appl.
Little herbicide is found at any depth.
Unlike nitrate, no trend was found for herbicides except atrazine in either mean concentrations or frequency of detection. Atrazine was detected more frequently at depths of 0.9 to 1.5 m and at 1.5 to 3 m increments. Conclusions Walnut Creek has proven to be a valuable study site to integrate farming practices with observations of water quality in various parts of the hydrologic system. The tile drainage network across the landscape provides a sample of the herbicide and nitrate-nitrogen moving through the root zone. Tile drains are responsive to precipitation events and during events, herbicide concentrations increase and nitrate-nitrogen concentrations decrease.