Project Details
Projekt
Littoral and pelagic Methane sources: a thorough cross-examination of methane production, oxidation and transport in lakes (LiMeth)
Applicant
Karla Martinez-Cruz, Ph.D.
Subject Area
Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 517753859
Lakes are recognized as one of the main contributors of atmospheric methane (CH4). CH4 emissions from lakes occur via ebullition and diffusive transport of CH4 across the water-atmosphere interface. The latter depends on the CH4 oversaturation in the surface water. During stratified conditions, CH4 concentrations in the oxic epilimnion can be larger than in the oxic hypolimnion.This enrichment of CH4 in the epilimnion is not yet fully understood and commonly referred to as the “methane paradox” because: (i) vertical diffusion of CH4 cannot fuel this enrichment, as the CH4 concentration is lower in profundal water layers than within the epilimnion, and (ii) CH4 production (methanogenesis) is usually not expected to occur in oxic environments. Therefore, there are two main hypotheses around the methane paradox suggesting that the main source of the enriched CH4 in the oxic layers is either (i) lateral transport of CH4 from highly productive littoral zones or (ii) methanogenesis that occurs in the oxic water of the epilimnion. Despite the effort undertaken during the past years to elucidate the main source(s) and pathways of the enriched CH4 in the epilimnion of lakes, both hypotheses are still lacking strong support by experimental evidence. For the proposed project, we will conduct detailed field and laboratory measurements for testing the two hypotheses. Spatial distributions of CH4 concentration, CH4 fluxes, oxic CH4 production and oxidation rates will be used to quantify the puzzling CH4 source(s) in the epilimnion. Transects of vertical profiles of dissolved CH4 will support the estimation of CH4 transport within the littoral zone and from the littoral to the pelagic zone. The collection of thorough data required for these analyses will be achieved by the application of a high-sensitive measuring system allowing rapid assessment of spatially well-resolved distributions of dissolved CH4. The CH4 fluxes and CH4 production and oxidation rates will be assessed with the flux chamber method and respiration assays, respectively. In addition, stable isotope analysis and molecular biological tools will be used to identify the main biochemical pathways and actors. The research will be conducted in Lower Lake Constance and in Lake Überlingen, a basin of Upper Lake Constance. The two lakes have similar water chemistry but differ in their CH4 concentration, which will allow a comparative assessment of the CH4 dynamics. Overall, this project seeks to unveil the “methane paradox” by not only revealing the main CH4 source(s) of the oversaturated epilimnion, but also by closing the mass balance of CH4 in lakes with similar characteristics.
DFG Programme
Research Grants
