Comparison of Phosphorus, Light Climate, and Photosynthesis between Two Culturally Eutrophied Bays: Green Bay, Lake Michigan, and the Bay of Quinte, Lake Ontario

Abstract

Trophic status, response to phosphorus control, and the underwater light climate were compared for the major bays of Lake Michigan (Green Bay) and Lake Ontario (Bay of Quinte). The Bay of Quinte has shown the greatest response to phosphorus controls, but conditions were not as eutrophic prior to controls as in Green Bay. There were distinct spatial gradients in trophic indicators (chlorophyll a and light extinction) as well as in background light extinction in both bays. Photosynthetic rates remain higher in Green Bay than in the Bay of Quinte, although this is more pronounced for daily photosynthesis per cubic metre at optimal light than for daily rates per square metre. Background light extinction reduced areal photosynthesis in Green Bay because of competition for light absorption between chlorophyll and suspended solids. Potential effects of remedial actions such as reduced phosphorus and suspended loading on phytoplankton photosynthesis were assessed. Lowering chlorophyll would cause a significant decline in areal photosynthesis rates but decreasing background light extinction could lead to higher rates.