Total Phosphorus Budget for Lake St. Clair: 1975–80

Abstract

As part of the U.S.-Canadian Upper Great Lakes Connecting Channels Study a total phosphorus budget was developed for Lake St. Clair. An unbiased ratio estimator technique was used to estimate annual loads and variances from monitored hydrologic areas. During the 1975–80 period, Lake Huron was the major source of phosphorus to Lake St. Clair, accounting for approximately 52% of the total annual load. Hydrologic area loads, which include diffuse and indirect point sources, contributed approximately 43% of the total annual load. The remaining 5% came from the atmosphere, shoreline erosion, and direct point sources. Of the hydrologic area loads, 85% could be attributed to diffuse sources. The Thames area contributed 58% of the total hydrologic area load, followed by the Sydenham (17%), the Clinton (9%), the Ruscom (7%), the Black (6%), the St. Clair (3%), and the Rouge (0.4%). Over the entire 6-year period examined, the lake's total input and output of phosphorus were nearly equal. It was concluded that there was no significant net source or sink of phosphorus in Lake St. Clair during the 1975–80 period.