Coupling between Primary Terrestrial Succession and the Trophic Development of Lakes at Glacier Bay, Alaska |
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| Authors: | D R Engstrom S C Fritz |
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| Institution: | (1) St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix, MN 55047, USA;(2) Department of Geosciences and School of Biological Sciences, University of Nebraska, 214 Bessey Hall, Lincoln, 68588-0340, NE, USA |
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| Abstract: | The natural eutrophication of lakes is still an accepted concept in limnology, arising as it does 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 this idea, and suggest more variable trends in lake trophic development which are under local (catchment-level)
control. Here we use sediment cores from several lakes in Glacier Bay National Park to examine the relationship between successional
changes in catchment vegetation and trends in water-column nitrogen (a limiting nutrient) and lake primary production. Terrestrial
succession at Glacier Bay follows several different pathways, with older sites in the lower bay being colonized directly by
spruce (Picea) and by-passing a prolonged alder (Alnus) stage that characterizes younger upper-bay sites. Sediment cores from three sites spanning this successional gradient demonstrate
that the variability in nitrogen trends among lakes is a consequence of the establishment and duration of N-fixing alder in
the lake catchment. In the lower-bay lakes, diatom-inferred nitrogen concentrations rise and then fall in concert with the
transient appearance of alder in the catchment, while in the upper bay, high nitrogen concentrations are sustained by the
continuous dominance of alder. Diatom accumulation, a proxy for whole-lake biological productivity, increases steadily at
all three sites during the first century following lake formation, but declines in more recent times at the lower-bay sites
in apparent response to the disappearance of alder and decreasing lake-water nitrogen. These results demonstrate a tight biogeochemical
coupling between terrestrial succession and lake trophic change during the early developmental history of Glacier Bay lakes. |
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| Keywords: | Diatom accumulation Glacier Bay Lake ontogeny Nitrogen Primary production Primary succession |
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