Methane oxidation in the waters of a humic-rich boreal lake stimulated by photosynthesis, nitrite, Fe(III) and humics

Abstract. Small boreal lakes are known to contribute significantly global CH4 emissions. Lake Lovojärvi is a eutrophic lake in southern Finland with bottom water concentrations up 2 mM. However, the surface concentration, and thus diffusive emission potential, was low (< 0.5 µM). We studied biogeochemical processes involved removal by chemical profiling through incubation experiments. ?13C-CH4 of column revealed methane-oxidation hotspot just below oxycline zones oxidation within anoxic column. In experiments involving addition light and/or oxygen, rates hypolimnion were enhanced 3-fold, suggesting major role for photosynthetically fueled aerobic oxidation. observed distinct peak concentration at chlorophyll-a maximum, caused either situ production or other inputs such as lateral transport from littoral zone. dark 7 m depth, nitrite seemed be key electron acceptor oxidation, yet additions Fe(III), anthraquinone-2,6-disulfonate humic substances also stimulated Surprisingly, inhibit all depths. Overall, this study shows that can process humic, turbid lakes, thereby limiting emissions lakes. Yet, it highlights potential importance whole suite alternative acceptors, including humics, these freshwater environments absence oxygen.