SUBMERGENT MACROPHYTES IN A COOLING POND IN ALBERTA, CANADA

The structure of the aquatic macrophyte community and factors leading to high plant production were examined in a 450 ha cooling pond on the prairie of southern Alberta, Canada, that receives thermal effluent f rom a coal-fired electrical generating station. Late-summer standing c rops, coverage and species composition were measured at intervals alon g ten transects perpendicular to the shore around the littoral zone of the pond. Physical and chemical features of the water column and sedi ments were measured concurrently to elucidate the factors controlling macrophyte growth. The cooling pond supported a simple but extraordina rily productive plant community dominated by species tolerant of high water temperatures and high concentrations of dissolved solids and alk alinity produced by evaporative concentration. Three of the seven domi nant species are uncommon or seldom abundant in other lakes of the reg ion but were apparently favoured here by high water temperatures, Stan ding crops of macrophytes at most points within the littoral zone were moderate (<100 g m(-2) dry mass), but were extremely high along the s heltered north and east shores (400-900 g m(-2)). The spatial distribu tion of species within the pond was evidently governed by (1) presence of suitable substratum, (2) light penetration, and (3) exposure to wa ve action. The situation in Sheerness cooling pond is comparable with that in other lakes receiving thermal effluent.