Agriculture and Water Quality in the Canadian Great Lakes Basin: II. Fluvial Sediments

Unit‐area yields of suspended sediments discharged from 11 small (<6,000 ha) agricultural watersheds in southern Ontario ranged from <100 to 1,000 kg ha −1 year −1 in a 2‐year study. Estimated bank erosion contributed between 0 and 30% of the suspended sediment, while estimated cropland sheet and rill erosion contributed 70–100%. Regression analyses relating 14 watershed characteristics to unit‐area yields showed that percent clay of the surface soil and percent row crop were the most significant ( R 2 = 0.64) factors in estimating suspended sediment yields. Detailed studies in the agricultural watersheds were used to generate and test three independent methods for the prediction of suspended sediment yields from cropland. The agricultural contribution to suspended sediment were predicted for the Grand and Saugeen river basins and for the over 300 subbasins of the Canadian Great Lakes Basin. It was estimated that agricultural land‐use activities contribute over 650 × 10 3 t of suspended sediment to the Great Lakes annually.