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Methane (CH4), a very potent green house gas, is generated in
seabed sediments. Because of high deposition of organic matter,
continental margins, estuaries, harbors and river deltas are
hotspots for methane production. The amount of CH4 produced in
the sediments depends on the amount and quality of organic
carbon buried in the sediment. In marine sediments, where sulfate
concentrations are high most of the buried organic carbon is
degraded by anaerobic sulfate reduction. As sulfate becomes
consumed further down in the sediment, carbon mineralization is
taken over by methanogenesis. In the absence of oxidants the
produced CH4 accumulates and may move upwards through the
sediment via diffusion or as gas phase through cracks in the
sediment. Accumulation of shallow gas in continental shelves is a
widespread phenomenon and is usually found in rapidly
accumulating and thick sediments. Investigations in Aarhus Bay and
other areas showed that gas only accumulated where the organic-
rich Holocene mud exceeded 4-5 m in thickness. However, until
today, it is unclear how and why the CH4 is accumulating in areas
with thick Holocene mud layers, but not in layers < 4-5 m thick.

In a second project I am investigating the effect of salinity and the
origin and quality of organic carbon on CH4 fluxes in the sediment
of the Gdansk Bay.

Both these projects are embedded in the EU founded project
BALTIC GAS.

2004 - 2008

PhD Project

The aim of this dissertation was to assess the effects of simulated
global warming and N enrichment on biogeochemical processes
involved in the carbon cycle and on microbial communities in a
freshwater wetland. Global warming and sustained N deposition
were simulated in a mesocosm field experiment by raising average
water temperature to a target of 4 ºC above ambient and
periodically fertilizing mesocosms with a solution of Ca(NO3)2 to a
target concentration 5 times above ambient. The responses
measured included methane (CH4) emission (ebullition and diffusive
flux), litter decomposition, and a range of parameters
characterizing litter-associated microbial communities. We
performed the experiments in a highly productive littoral stand of
common reed, Phragmites australis, in Central Switzerland, located
on the eastern shore of Lake Hallwil.

1. Experimentally simulated global warming and nitrogen
enrichment effects on methane emissions in a marsh (more
details....)

2. Experimentally simulated global warming and nitrogen
enrichment effects on microbial litter decomposers in a marsh
(more details....)

3. Responses of litter decomposition and associated microbial
activity to simulated global warming and nitrogen enrichment:
disentangling direct environmental and litter quality effects (more
details....)