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Selenium Stable Isotope Investigation into Selenium Biogeochemical Cycling in a Lacustrine Environment: Sweitzer Lake, Colorado
Author(s) -
Clark Scott K.,
Johnson Thomas M.
Publication year - 2010
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2009.0380
Subject(s) - biogeochemical cycle , environmental chemistry , phytoplankton , isotope , biogeochemistry , chemistry , isotope fractionation , selenium , stable isotope ratio , isotopes of nitrogen , selenate , isotopic signature , geology , fractionation , nutrient , nitrogen , physics , organic chemistry , quantum mechanics
We present a comprehensive set of Se concentration and isotope ratio data collected over a 3‐yr period from dissolved, sediment‐hosted, and organically bound Se in a Se‐contaminated lake and littoral wetland. Median isotope ratios of these various pools of Se spanned a narrow isotopic range (δ 80/76 Se SRM‐3149 = 1.14–2.40‰). Selenium (VI) reduction in the sediments is an important process in this system, but its isotopic impact is muted by the lack of direct contact between surface waters and reduction sites within sediments. This indicates that using Se isotope data as an indicator of microbial or abiotic Se oxyanion reduction is not effective in this or other similar systems. Isotopic data suggest that most Se(IV) in the lake originates from oxidation of organically bound Se rather than directly through Se(VI) reduction. Mobilization of Se(VI) from bedrock involves only a slight isotopic shift. Temporally constant isotopic differences observed in Se(VI) from two catchment areas suggest the potential for tracing Se(VI) from different source areas. Phytoplankton isotope ratios are close to those of the water, with a small depletion in heavy isotopes (0.56‰). Fish tissues nearly match the phytoplankton, being only slightly depleted in the heavier isotopes. This suggests the potential for Se isotopes as migration indicators. Volatile, presumably methylated Se was isotopically very close to median values for phytoplankton and macrophytes, indicating a lack of isotopic fractionation during methylation.