Effects of declining sulfur deposition on methane cycling in lakes

As a result of coordinated political action to mitigate acidification, eutrophication and climate change, northern surface waters are experiencing an unprecedented drop in sulfate concentrations.

This may have unforeseen consequences for the microbial communities of lakes and the biogeochemical processes they mediate.

One area of concern is the unknown impacts of sulfate shortage on ecosystem-scale methanogenesis, methane oxidation and coupled atmospheric emissions of this potent greenhouse gas.

We will assess if known competition for resources between sulfate reducing bacteria and methanogenic archaea will shift over time in favor of methanogens as the current decline in sulfate concentrations proceed.

We will also study the impacts of this chemical shift on the efficiency of the biological methane filter that is mediated by the methane oxidizing bacteria and archaea in water and sediment.

Finally, we will quantify and model the net effects of this ongoing chemical regime shift on ecosystem-scale methane emissions.

The research will be based on a combination of field observations across lakes with contrasting sulfate concentrations and experimental sediment microcosm incubations where sulfate levels are manipulated.

Responses and shifts in microbial communities will be followed with molecular methods and this will be combined with tracer experiments and chemical analysis of methane and sulfur cycling in both lakes and experimental incubations.