The controls on phosphorus availability in a Boreal lake ecosystem since deglaciation |
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Authors: | Stephen A Norton Randall H Perry Jasmine E Saros Jr" target="_blank">George L JacobsonJr Ivan J Fernandez Ji?í Kopá?ek Tiffany A Wilson Michael D SanClements |
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Institution: | 1.Department of Earth Sciences,University of Maine,Orono,USA;2.School of Biology and Ecology,University of Maine,Orono,USA;3.Climate Change Institute,University of Maine,Orono,USA;4.Department of Plant, Soil, and Environmental Sciences,University of Maine,Orono,USA;5.Biology Centre ASCR,Institute of Hydrobiology,?eské Budějovice,Czech Republic;6.Institute of Arctic and Alpine Research,University of Colorado,Boulder,USA |
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Abstract: | The sediment record from a 5.3-m core from Sargent Mountain Pond, Maine USA indicates strong co-evolutionary relationships
among climate, vegetation, soil development, runoff chemistry, lake processes, diatom community, and water and sediment chemistry.
Early post-glacial time (16,600–12,500 Cal Yr BP) was dominated by deposition of mineral-rich sediment, low in organic matter
and secondary hydroxides of Al and Fe; pollen indicate tundra conditions; diatom taxa indicate pH between 7.5 and 8, and total
P concentrations of about 25 μg L−1, favoring higher productivity. Chemical weathering was rapid, with high alkalinity, pH, Ca, and P in runoff. As climate ameliorated,
about 12,500 Cal Yr BP, forest vegetation became established; soils would have developed vertical zonation, including organic
matter accumulation, and incipient podzolic horizons, with accumulating secondary hydroxides of Al and Fe that sequestered
P in the soils. Labile minerals (primarily apatite, Ca5(PO4)3(OH,F,Cl)) became depleted in the soil, further reducing the supply of P to the lake. Dissolved organic carbon (DOC) from
soil organic matter mobilized Al and Fe to the lake where Al(OH)3 (primarily) and Fe(OH)3 (minor) were precipitated. The sedimenting hydroxides adsorbed P from the water column, further reducing bioavailable P.
These long-term trends of moderating climate, and changing terrestrial biology, soils, and aquatic chemistry and phytoplankton
were interrupted by the 1,000-year long Younger Dryas cooling, which led to a temporary reversal of these processes, a period
that ended with the major onset of Holocene warming. The sequestration of P by soils would have strengthened because of long-term
soil acidification and pedogenesis. The lake was transformed from a more productive, high P, high pH, low DOC system into
an oligotrophic, relatively low P, acidic, humic lake over a period of 16,600 years, a natural trend that continues. In contrast
to many human-affected lakes that become increasingly eutrophic, many lakes become more oligotrophic during their history.
The precursors for that are: (1) absence of human land-use in watersheds, (2) bedrock lithology and soil with a paucity of
soluble Ca-rich minerals, and (3) vegetation that promotes the accumulation of soil organic matter, podzolization, and increased
export of metal-DOC complexes, particularly Al. |
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