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Spatial variability of sediment methane production and methanogen communities within a eutrophic reservoir: importance of organic matter source and quantity
Citation:
Berberich, M., J. Beaulieu, T. Hamilton, S. Waldo, AND I. Buffam. Spatial variability of sediment methane production and methanogen communities within a eutrophic reservoir: importance of organic matter source and quantity. LIMNOLOGY AND OCEANOGRAPHY. American Society of Limnology and Oceanography, Lawrence, KS, 65(5):1-23, (2020). https://doi.org/10.1002/lno.11392
Impact/Purpose:
Freshwater reservoirs are an important source of the greenhouse gas methane (CH4). Efforts to mitigate these emissions require an understanding of the factors that control the rate of CH4 production in these systems. Laboratory studies have shown that CH4 production rates can be stimulated by additions of carbon derived from algae, but field studies suggest that carbon derived from the watershed (i.e. soil erosion) is more important. Resolving the relative importance of these two carbon sources is important because controlling watershed derived carbon would require different management interventions than controlling algal derived carbon. We use a suite of geochemical measurements to resolve the relative importance of these carbon sources in a eutrophic reservoir in Ohio, USA. We found that both sources of carbon were important and that mitigation efforts need to address both watershed and algal derived carbon.
Description:
Freshwater reservoirs are an important source of the greenhouse gas methane (CH4) to the atmosphere, but global emission estimates are poorly constrained (13.3 – 52.5 Tg C yr-1), partially due to extreme spatial variability in emission rates within and among reservoirs. Spatial heterogeneity in the availability of organic matter (OM) for biological CH4 production by methanogenic archaea may be an important contributor to this variation. To investigate this, we measured sediment CH4 potential production rates, OM source and quantity, and methanogen community composition at fifteen sites within a eutrophic reservoir in Ohio, USA. CH4 production rates were highest in the shallow riverine inlet zone of the reservoir, even when rates were normalized to OM quantity, indicating that OM was more readily utilized by methanogens in the riverine zone than in the transitional or lacustrine zones. Sediment stable isotopes and C:N indicated a greater proportion of terrestrial OM in the bulk sediment of this zone. Methanogens were present at all sites, but the riverine zone contained a higher relative abundance of methanogens capable of acetoclastic and methylotrophic methanogenesis, likely reflecting differences in decomposition processes or OM quality. While we found that methane production rates were negatively correlated with autochthonous carbon in bulk sediment OM, production rates were positively correlated with indicators of autochthonous carbon in the porewater dissolved OM. It is likely that both dissolved and bulk OM affect CH4 production rates, and that both terrestrial and aquatic OM sources are important in the riverine methane production hotspot.
URLs/Downloads:
DOI: Spatial variability of sediment methane production and methanogen communities within a eutrophic reservoir: importance of organic matter source and quantity
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