Sulfate uptake by microplankton communities in western Lake St. Clair1

The uptake of sulfate by microplankton communities in western Lake St. Clair was studied during 1972 and 1973 using ‘%-SOe. Sulfate uptake rates were generally highest at the juncture where the lake and Clinton River cutoff channel meet and gradually decreased in nearshore water south of the cutoff channel and in the offshore waters. Phosphorus and dissolved organic carbon showed these same patterns, indicating that the Clinton River effluent is probably the major contributing polluter of western Lake St. Clair. Examination of the uptake of organic sulfur indicated that sulfate is probably the only significant source of sulfur for biomass production in natural aerobic microplankton communities. Measurements of sulfate uptake may provide a good estimate of total microbial production. I have suggested that a realistic estimate of total (photosynthetic and heterotrophic) production by microbial plankton (microplankton) communities may be provided by the measurement of sulfate uptake rates ( Monheimer 1974). Lake St. Clair has been the field location for studying microplankton sulfate uptake. This paper providcs information both to support this proposed new production measurement method and to add significantly to the sparse literature on Lake St. Clair. The idea of using sulfate uptake as a measure of total microplankton production is quite straightforward. Sulfur is an elemcnt essential to all life, and, while it might seem that organic sulfur could satisfy the sulfur requirements of microplankton for biomass production, certain forms of soluble organic sulfur such as cysteine and methionine must certainly be ( re ) incorporated into biomass by planktonic microbcs. But, the literature concerning the sulfur cycle indicates that sulfur enters into the biomass largely in the form of sulfates (Butlin 1953; Kuznetsov 1968; ZoBell 1963). Since no biological process other than biomass production converts sulfate sulfur 1 Contribution No. 323 of the Department of Biology, Wayne State University. This work was supported in part by the Office of Water Resources Research, U. S. Department of Interior, project A-OBO-MICH, and in part by the Wayne State University Center for Urban Studies. ’ Present address: State Science Scrvicc, New York State Education Department, Albany, New York 12234. from a soluble to a particulate (filterable) form under aerobic conditions, the accumulation of particulate sulfur from dissolved sulfate, excluding that from any physical processes indicated by abiotic controls, should be a measure of biomass production. Lake St. Clair is an integral component of the Laurcntian Great Lakes through which the water flows from Lake Huron to Lake Erie ( Fig. 1) , As a section of the international boundary between the United States and Canada, the lake has considerable political and socioeconomic significance to the Detroit-Windsor metropolitan arca. Little information, however, has been published about it. Much of the literature available is old (Marsh 1895; Pieters 1895; Reighard 1894), while relevant contemporary information about Lake St. Clair must be extrapolated from studies of adjacent waters (Beeton 1965, 1966; Int. Jt. Comm. 1918, 1951, 1968; Int. Lake Erie Pollution Bd. 1969; Vaughan and Harlow 1965). Hiltuncn ( 1971) surveyed the bcnthic fauna of the western basin and Leach (1972) and Winner et al. (1970) studied planktonic primary production in the Ontario waters of Lake St, Clair, but virtually no other data of biological concern have been published. Therefore, the sampling stations for studying microplankton sulfate uptake were established in western Lake St. Clair so as to provide maximum information about the lake. This paper summarizes those data. I wish to thank the Detroit Boat Club for LIMNOLOGY AND OCEANOGRAPIIY 183 MARC11 1975, V. 20( 2)