A sediment record of recent nutrient loading and trophic state change in Lake Norrviken,Sweden |
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Authors: | Joyanto Routh Preetam Choudhary Philip A Meyers Bhishm Kumar |
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Institution: | (1) Department of Geology and Geochemistry, Stockholm University, 10691 Stockholm, Sweden;(2) Department of Earth Sciences, Indian Institute of Technology, Roorkee, 247667, India;(3) Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA;(4) National Institute of Hydrology, Roorkee, 247667, India |
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Abstract: | Human-induced perturbations in the Lake Norrviken catchment, Sweden, over the last 100+ years have left distinctive geochemical
imprints in the sediments. Disposal of sewage, industrial, and agricultural run-off into the lake since the end of the nineteenth
century changed the trophic status from eutrophic to hyper-eutrophic. The primary organic matter (OM) source in the lake is
in situ algal material. Total organic carbon (TOC) concentrations increased near the mid-section of a short sediment core
collected from the deepest part of the lake, reflecting elevated epilimnetic productivity and consequent hypolimnetic anoxia.
Accompanying shifts to lighter stable organic C and total N isotopic compositions suggest that cyanobacterial productivity
increased during this period. The distribution of pigments in the core indicates a shift in the phytoplankton community to
a cyanobacteria-dominated system. Moreover, pigments confirm that N2-fixing versus non-N2-fixing phytoplankton varied depending upon the external inputs of N and P. Conditions in the lake improved after sewage input
was diverted and the lake is currently mesotrophic. |
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