Drivers, magnitudes, and trends of microbial sulfate reduction (MSR) in freshwater systems

• Microbial sulfate reduction (MSR), which transforms sulfate into sulfide through the consumption of organic matter, plays an integral part in sulfur and carbon cycling. Yet, its magnitude beyond snap-shot conditions in specific surface water systems such as individual wetlands or lakes is with few exceptions unknown. We use stream water samples and a sulfur isotopic fractionation and mixing scheme to derive MSR at relatively large scales, both within and between five study areas located between southern Sweden and the Kola Peninsula, Russia. Results showed that the freshwater MSR ranged from 0 to 79% within the catchments and from 2 to 28% between the catchments, displaying a catchment-average value of 13%. The MSR-values showed differences between seasons, in particular in wetland/lake catchments where they were high during the spring flood, which is consistent with the mobilization of water that under low-flow winter periods can have developed anoxic conditions needed by the sulfate-reducing microorganisms (SRM). The combined abundance or deficiency of several landscape elements were found to indicate relatively well whether or not catchment-scale MSR would be high, such as the percentage of forest cover that can support MSR by the provision of organic matter to the SRM, and the areal percentage of lakes/wetlands providing longer hydrological residence times and the anoxic conditions needed by the SRM. This study, for the first time, shows compelling evidence in multiple catchments of MSR at levels around 10%, which is unaccounted for in global weathering budgets, implying for instance that the terrestrial pyrite oxidation may be underestimated.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Naturgeografi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Physical Geography (hsv//eng)

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