EFFECT OF CHELATED TRACE-METALS ON PHOSPHORUS UPTAKE AND STORAGE IN NATURAL ASSEMBLAGES OF LAKE-MICHIGAN PHYTOPLANKTON

In experiments with natural phytoplankton assemblages from Lake Michigan, additions of chelated trace metals and orthophosphate increased phosphate uptake more than additions of orthophosphate alone. Enhanced phosphate uptake is attributed to the storage of polyphosphate by phytoplankton which can be triggered by high concentrations of trace metals. Similar effects were obtained with a surface phytoplankton assemblage collected in April and with a metalimnetic assemblage collected in September. Microscopic examination showed that polyphosphate formation was enhanced in populations of Melosira islandica and Scenedesmus opoliensis. These results and data from the literature suggest that polyphosphate storage may play an important role in the phytoplankton population dynamics of Lake Michigan, especially in bays and nearshore areas where tributary inputs of phosphorus and trace metals are high. If observed effects operate selectively at the population level, populations that accumulate and store phosphorus in nearshore areas of high phosphorus supply may have a competitive advantage over other populations in the nearshore or when transported to the offshore waters of this phosphorus-limited system. © 1990, International Association for Great Lakes Research. All rights reserved.