The trophic development of lakes is a widely held concept in limnology, arising from the earliest efforts to classify lakes and place them in an evolutionary sequence. Recent studies of newly formed lakes at Glacier Bay, Alaska, only partially support the idea of a common pathway, and suggest more variable trends related to site-specific differences in terrestrial succession and hydrologic position. This presentation examines long-term lake trajectories at Glacier Bay through the dual lenses of chronosequence and paleoecology.
Results/Conclusions
Lakes are tightly coupled to their terrestrial catchments though hydrological linkage of biogeochemical cycles, yet the response of lakes to exogenous forces (climate change, human disturbance) is often highly individualistic, depending on factors such as landscape position, catchment size, lake morphometry, and geologic substrate. Is it possible then, to discern any coherent pattern among lakes over the long time-scales at which autogenic processes and landscape evolution occur? The two primary tools by which ecologists examine long-term change – chronosequences and sediment cores – each have their weaknesses, but in tandem can reveal both site-specific response and the overriding biogeochemical trajectory. The synergy of these two approaches is illustrated by recent studies from Glacier Bay, Alaska, where limnological change has been inferred from a chronosequence of modern lakes of different ages. Here successional patterns were modeled by a space for time substitution in the same way that terrestrial succession was described in the classic work of plant ecologists at Glacier Bay. Results provide strong evidence that long-term soil development and related hydrological changes cause alkalinity and pH to decrease, DOC to increase, and nitrogen levels to rise and then fall over time. These changes span time-scales ranging from a few centuries to several thousand years. However, a comparison of these general trends with the trajectories of individual lakes – as reconstructed from sediment cores – reveals site-specific differences, especially with respect to nutrient (nitrogen) concentrations. These differences are related to successional trends in catchment vegetation, which have been shown to vary substantially between sites in upper and lower Glacier Bay. In addition, differences in hydrologic setting, especially the relative importance of surface vs. groundwater flux, regulate the rate at which lakes lose base cations over time.
