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Extreme 13 C enrichments in a shallow hypereutrophic lake: Implications for carbon cycling
Author(s) -
Gu Binhe,
Schelske Claire L.,
Hodell David A.
Publication year - 2004
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2004.49.4.1152
Subject(s) - water column , environmental chemistry , dissolved organic carbon , pore water pressure , sediment , organic matter , methanogenesis , carbon cycle , chemistry , methane , geology , oceanography , ecology , geomorphology , ecosystem , organic chemistry , biology , geotechnical engineering
An analysis of stable carbon isotope (δ 13 C) ratios in Lake Apopka, Florida, reveals extreme 13 C enrichments of dissolved inorganic carbon (DIC) pools in the water column and sediment pore water of this shallow polymictic and hypereutrophic lake. The sediment pore water had high averageδ 13 C of DIC (26.4‰), DIC (8.37 mmol L− 1 ), and methane (CH 4 ) concentrations (1.23 mmol L− 1 ). The extreme 13 C enrichment in the sediment pore‐water DIC pool is attributed to methanogenesis, which produces 13 C‐rich carbon dioxide (CO 2 ) and 13 C‐poor CH 4 during the bacterial fermentation of organic matter. The δ 13 C in the water‐column DIC pool ranged from 5‰ to 13‰ with an average of 9.0‰. The flux‐weighted δ 13 C from the DIC due to external loading and sediment respiration was estimated as −12‰, whereas the δ 13 C from particulate organic carbon (POC) due to water‐column production was −13‰. The 13 C enrichment in the water column is attributed directly to the diffusion and advection of isotopically heavy DIC from the sediment and to the isotopic fractionation by phytoplankton photosynthesis and is attributed indirectly to the removal of isotopically light CH4 by ebullition and organic matter by sedimentation and outflow. Atmospheric invasion and sedimentation were the most important source and sink, respectively, in the carbon mass balance. CH 4 oxidation, atmospheric invasion, anaerobic respiration, and sedimentation are the important flux terms affecting the isotopic mass balance. A combination of shallow water depth, frequent wind mixing, anoxic sediments with high rates of methanogenesis, high phytoplankton productivity, and lack of external loading dominated by terrestrial carbon led to the 13 C enrichment of the water‐column DIC pool in Lake Apopka.