Early Lake Ontogeny following Neoglacial Ice Recession at Glacier Bay, Alaska

This study explores the environmental forces controlling lake ontogeny at Glacier Bay as a model for early Holocene lake evolution in north temperate lakes worldwide. Long-term chemical and biological changes in lakes are investigated with two complementary research strategies: (1) limnological conditions are compared among 32 lakes of known age and in different stages of primary catchment succession and (2) sediment cores from these same lakes are analyzed stratigraphically for fossil diatoms to ascertain developmental trends in pH, alkalinity, algal composition, and trophic status at individual sites. Trends in water chemistry inferred from the chronosequence approach include a progressive loss of alkalinity and dilution of surface waters, an increase in apparent color from organic acids, and a decline in pH. Because of considerable scatter in the chronosequence data, these changes are not apparent until several hundred years after deglaciation. Preliminary observations of biotic trends include an apparent succession of higher aquatic plants mediated by alkalinity changes and a rapid diversification of the diatom flora associated with a proliferation of new growth substrates, particularly macrophytes. Several hypotheses concerning early postglacial landlwater interactions are supported by these results, including (a) the progressive leaching of catchment soils makes lakes more dilute and acidic over time, (b) peat growth and regional paludification impede internal soil drainage and groundwater recharge, causing dilution and eventual dystrophication of surface waters, and (c) hydrologic and geologic differences among sites act to control the rates and direction of limnological change.