Quantification and regulation of carbon fluxes in Lake Windsborn (Eifel): do hot spots and hot moments of carbon cycling occur in shallow waters?
Final Report Abstract
This study has demonstrated the importance of including spatial and temporal patterns even for small and shallow lakes to determine representative estimates of CH4 and CO2 emissions. Moreover, despite the shallow water column of the lakes, the shallower shoreline areas behaved significantly differently from the center of the lake, which was only a few to tens of centimeters deeper, but had both higher CH4 and higher CO2 emissions overall due to the less wind sheltered location and increased accumulation of organic material. In small lakes, CH4 is apparently emitted mainly via ebullition, which was higher in the center of the lakes, but this was not due to the water depth but apparently related to the sediment physical and chemical properties. The quantity and quality of organic matter showed considerable spatial variability, with increasing quantity from shore to center but decreasing quality from shore to center. The quality of the solid organic matter controlled production and turnover rates. More specifically, a high proportion of recalcitrant constituents resulted in lower turnover. In addition to organic matter quality, porosity was an important control of ebullition. In addition to these spatial effects, important temporal effects occurred, especially during drying up events, but also seasonal and diel differences driven by temperature differences and biological activity due to irradiation. CH4 fluxes increased exponentially with temperature, both total emissions and ebullition. Due to the shallowness of the lakes, the entire lake is very sensitive to temperature changes as they affect the sediment more rapidly. Drying up shifted the anaerobic degradation via the CH4 pathway towards increased CO2 emission, which was in the following slowed down by the emergence of pioneer plants. Thus, it can be assumed that future temperatures will lead to increased emissions if a standing water column remains, but subsequent droughts will not lead to increased C emissions in small lakes due to the suppression of CH4 formation and the emergence of pioneer plants taking up C.
Publications
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(2020): Organic matter and sediment properties determine in-lake variability of sediment CO2 and CH4 production and emissions of a small and shallow lake, Biogeosciences, 17, 5057–5078
Praetzel, L. S. E., Plenter, N., Schilling, S., Schmiedeskamp, M., Broll, G., and Knorr, K.-H.
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(2021): Temperature and sediment properties drive spatiotemporal variability of methane ebullition in a small and shallow temperate lake, Limnol Oceanogr, 66: 2598-2610
Praetzel, L.S.E., Schmiedeskamp, M. and Knorr, K.-H.
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(2021): Whole-lake methane emissions from two temperate shallow lakes with fluctuating water levels: Relevance of spatiotemporal patterns, Limnol Oceanogr, 66: 2455-2469
Schmiedeskamp, M., Praetzel, L.S.E., Bastviken, D. and Knorr, K.-H.
