Movement of Diffuse Source Pollutants in Small Agricultural Watersheds of the Great Lakes Basin

Abstract

Abstract A study was conducted to determine losses and distributions of nitrogen (N) and phosphorus (P) in runoff waters and sediments from heavily fertilized agricultural watesheds during both the growing and nongrowing seasons. The study was done on two small watersheds having well‐drained, fine, sandy loam soils. Runoff was measured continuously and sampled proportionately during 50–60 events over a 2‐year period. Ninety nine percent of the sediment loss over the period occurred during 11 months; 64–86% occurred during a single storm in April when no crop canopy was present. This event was associated with rainfall probabilities rising rapidly toward a primary annual peak for East Lansing, Mich. A second storm of equal magnitude in August was associated with a secondary annual peak in normal rainfall for this location. Both storms exceeded the 20‐year expectancy in erosion potential (erosion index = 68). Seventy to 95% of the N in runoff, and 90–98% of the P, were carried in sediments, except during winter months when up to 80% of the N and 33% of the P were in solution. Sediments were enriched, relative to soils, in total N, but not in extractable P.