| 14 Sep 2026
From sedimentary production to water-column accumulation: temperature and spatial controls on littoral methane
Abstract. Littoral sediments are important sources of methane (CH4) to lake water, but it remains unclear how strongly sedimentary CH4 production controls sediment-water fluxes and dissolved CH4 concentrations across seasons and spatially heterogeneous littoral zones. We measured sediment organic carbon, potential CH4 production, sediment-water CH4 fluxes, dissolved CH4 concentrations, and stable carbon isotopes of CH4 and CO2 at seven littoral sites in Upper Lake Constance (ULC) and Lower Lake Constance (LLC) over four seasons. Potential CH4 production, sediment-water CH4 fluxes, and dissolved CH4 concentrations were significantly related and showed similar temperature dependencies. Their apparent activation energies ranged from 0.81 to 1.11 eV and did not differ significantly. These results are consistent with a process chain from sedimentary production via sediment-water fluxes to dissolved CH4, although the shared temperature dependence of the three variables means that their relationships do not, by themselves, demonstrate causal propagation along this chain. Spatial patterns, however, became weaker along this process chain. Within ULC, differences in potential CH4 production were reflected in sediment-water fluxes but were no longer significant in dissolved CH4 concentrations. Between the two lakes, dissolved CH4 concentrations were significantly higher in LLC than in ULC, whereas potential CH4 production and sediment-water CH4 fluxes did not differ significantly. Potential CH4 production increased with sediment organic carbon, suggesting that substrate availability may have contributed to spatial differences in CH4 production. Carbon isotope patterns were consistent with a sedimentary, mainly acetoclastic CH4 source and indicated modification of part of the dissolved CH4 pool after release from the sediment. However, oxidation alone could not explain the isotopic contrast between the lakes, suggesting an additional influence of lateral mixing and hydrodynamic transport. Our results suggest that sedimentary CH4 production contributes to controlling littoral CH4 supply, whereas oxidation and physical transport can weaken or redistribute this signal in the water column.
Comments to “From sedimentary production to water-column accumulation: temperature and spatial controls on littoral methane” by Kiefer et al.
General comments
This study presents an extensive dataset on the potential production, transport, and concentration of methane (CH₄) in a connected two-lake system, with both spatial and seasonal resolution. The authors propose a plausible process chain linking sediment methane production, sediment-water CH₄ fluxes, and methane concentrations in the water column. This interpretation is supported by similarities in temperature dependencies and correlations among the measured variables. The statistical analyses are clearly presented and appropriately account for uncertainties in the observations. However, the interpretation remains somewhat inconclusive because three potentially important processes, namely the oxidation of CH4, the lateral exchange with pelagic waters and oxic methane production (OMP), were not quantified. Consequently, it is difficult to assess to what extent the observed methane concentrations and their spatial and temporal variability can be attributed to the proposed sediment-based process chain.
Specific comments
Technical corrections