Agriculture and Water Quality in the Canadian Great Lakes Basin: I. Representative Agricultural Watersheds

Abstract

AbstractThe 1972 U.S.‐Canada Great Lakes Water Quality Agreement established the Pollution from Land Use Activities Reference Group (PLUARG). To meet the objectives of the Pilot Watershed Studies of PLUARG, an approach was developed tbat would allow the quantification of the agricultural component of Great Lakes drainage basin pollution loads. A primary separation of agricultural regions was based on an index of the soil's potential to transfer pollutants to surface and ground water. Agricultural watersheds representative of major soils‐crops‐livestock combinations were monitored and studied. Selection and preliminary monitoring processes led to 11 sites being monitored for 2 years.The areas of the 11 study watersheds ranged from 20 to 79 km2, of which 22–89% was cultivated, and 0–99% tile‐drained. Row‐cropped laud, which occupied 10–66% of the watershed areas, was strongly correlated with tile‐drained area and fertilizer use. Mean surface‐soil clay contents ranged from 7 to 36%. Livestock densities were negligible in some watersheds, but were up to 0.77 animal units ha−1 in others. Mean precipitation and stream discharge during the study period were approximately 9 and 26% higher, respectively, than expected from long‐term means. The proportion of annual precipitation occurring in the January–April period averaged 32%, while approximately 65% of the stream discharge was measured during these 4 months.Intensive flow‐related stream sampling and chemical analyses revealed that the watersheds yielded a wide range of nutrient, sediment, and pesticide loadings to Great Lakes tributaries. The subsequent papers in this series discuss these results and their significance to water quality in the Great Lakes Basin.