Variations in <i>Melosira islandica</i> valve morphology in Lake Ontario sediments related to eutrophication and silica depletion1

Abstract

Different types of valves are found in Melosira islandica populations preserved in Lake Ontario sediments. Three morphotypes were distinguished, the more coarsely structured of which are most abundant in assemblages deposited before 1840. Finely structured forms become more abundant upcore, reaching maximum abundance ca. 1962. These changes appear to be related to increased phosphorus loading and consequent silica depletion in Lake Ontario waters.