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TECHNICAL REPORT
Wetlands and Aquatic Processes

Gas Dynamics in Eutrophic Lake Sediments Affected by Oxygen, Nitrate, and Sulfate

Department of Environmental Sciences, Univ. of Kuopio, Research and Development Unit of Environmental Health, P.O. Box 1627, FIN-70211 Kuopio, Finland

* Corresponding author (Anu.Liikanen{at}uku.fi)

Received for publication February 26, 2001. In many freshwater ecosystems, the contents of NO^-₃ and SO^2-₄ have increased, whereas O₂ has been depleted due to the increased acid and nutrient loads. These changes may affect carbon turnover and the dynamics of the major greenhouse gases CO₂, CH₄, and N₂O. We studied the effects of O₂, NO^-₃, and SO^2-₄ availability on carbon mineralization, and fluxes of CO₂, CH₄, and N₂O in the sediments of hyper-eutrophic Lake Kevätön, Finland. Undisturbed sediment cores from the deep (9 m) and shallow (4 m) profundal were incubated in a laboratory microcosm with oxic and anoxic water flows with NO^-₃ or SO^2-₄ concentrations of 0, 30, 100, 300, and 2000 µM. The carbon mineralization rate (i.e., the sum of released CO₂–C and CH₄–C) was not affected by the oxidants. However, the oxidants did change the pathways of carbon degradation and the release of CH₄. All of the oxidants depressed CH₄ fluxes in the shallow profundal sediments, which had low organic matter content. In the deep profundal sediments rich in organic matter, the CH₄ release was reduced by O₂ but was not affected by SO^2-₄ (the effect of NO^-₃ was not studied). There was an increase in N₂O release as the overlying water NO^-₃ concentration increased. Anoxia and highly elevated NO^-₃ concentrations, associated with eutrophication, increased drastically the global warming potential (GWP) of the sedimentary gases in contrast to the SO^2-₄ load, which had only minor effects on the GWP.

Abbreviations: GWP, global warming potential • MPP, methane production potential • RQ, respiratory quotient • SOC, sediment oxygen consumption

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