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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-284
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-284
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 29 Aug 2019

Submitted as: research article | 29 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Organic matter and sediment properties determine in-lake variability of sediment CO2 and CH4 production and emissions of a small and shallow lake

Leandra Stephanie Emilia Praetzel1, Nora Plenter2,3, Sabrina Schilling1, Marcel Schmiedeskamp1, Gabriele Broll2, and Klaus-Holger Knorr1 Leandra Stephanie Emilia Praetzel et al.
  • 1University of Münster, Institute of Landscape Ecology, Biogeochemistry and Ecohydrology Research Group, Germany
  • 2University of Osnabrück, Institute of Geography, Agroecology and Soil Research Group, Germany
  • 3University of Applied Sciences Osnabrück, Faculty of Agricultural Sciences and Landscape Architecture, Germany

Abstract. Inland waters are significant sources of CO2 and CH4 to the atmosphere, following recent studies this is particularly the case for small and shallow lakes. The spatial in-lake heterogeneity of CO2 and CH4 production processes and their drivers in the sediment yet remain poorly studied. We thus measured potential CO2 and CH4 production in sediment incubations from 12 sites within the small and shallow crater lake Windsborn in Germany as well as fluxes at the water-atmosphere interface at four sites. Production rates were highly variable and ranged from 7.2 and 38.5 µmol CO2 g C−1 d−1 and from 5.4 to 33.5 µmol CH4 g C−1 d−1. Fluxes lay between 4.5 and 26.9 mmol CO2 m−2 d−1 and between 0 and 9.8 mmol CH4 m−2 d−1. Both CO2 and CH4 production rates and CH4 fluxes were significantly negative (p < 0.05, rho < − 0.6) correlated with the prevalence of recalcitrant organic matter compounds in the sediment as identified by FTIR spectroscopy. The C / N ratio was significantly (p < 0.01, rho = − 0.88) correlated with CH4 fluxes, but neither with production rates nor CO2 fluxes. Inorganic (nitrate, sulfate, ferric iron) and organic (humic acids) electron acceptors together could explain differences in CH4 production rates (R2 = 0.22) whereas we did not find clear relationships between organic matter quality, methanogenic pathways (acetoclastic vs. hydrogenotrophic) and electron accepting capacity of the organic matter. Grain size distribution could sufficiently (p < 0.05, rho = ± 0.65) explain differences in CH4 fluxes. Surprisingly, sediment gas storage, potential production rates and water–atmosphere fluxes were decoupled from each other and did not show any correlations. Our results show that there exists a significant spatial variability of sediment gas production even within small lakes which can be explained by the origin and pre-processing, and therefore the degradability of the organic matter. We highlight that measuring production rates is not a suitable way to replace in-situ flux measurements as it neglects physical sediment properties and production and oxidation processes in the water column.

Leandra Stephanie Emilia Praetzel et al.
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Leandra Stephanie Emilia Praetzel et al.
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Short summary
Small lakes are important but variable sources of greenhouse gas emissions. We performed lab experiments to determine spatial patterns and drivers of CO2 and CH4 emission and sediment gas production within a lake. The observed high spatial variability of emissions and production could be explained by the degradability of the sediment organic matter. We did not see correlations between production and emissions and suggest on-site flux measurements as the most accurate way for determing emissions.
Small lakes are important but variable sources of greenhouse gas emissions. We performed lab...
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