Variability of benthic methane-derived carbon along seasonal, biological, and sedimentary gradients in a polymictic lake

Abstract

The spatial and seasonal variations of methane-derived carbon contributions to Chironomus plumosus larvae and oligochaetes biomass at four stations in a polymictic, eutrophic lake were examined to determine which factors (CH4 and/or dissolved oxygen) affect the methane-derived carbon contributions, and quantify impacts of benthic methane-derived carbon on the lake food web. Methane-derived carbon contributions were estimated by a two-source mixing model using δ13C values of monthly particulate organic matter (−29.5 to −20.8‰) and methane-oxidizing bacteria (−85.7‰). Large spatial and seasonal variability of methane-derived carbon contributions to C. plumosus and oligochaetes within the lake (0–38% and 0–32%, respectively) were observed, where contributions varied spatially along a gradient of sediment CH4 concentration, but not dissolved oxygen. The results suggest that for both C. plumosus and oligochaetes, spatial variabilities of the methane-derived carbon contributions are regulated by CH4. Seasonal variability of methane-derived carbon contributions to C. plumosus revealed increases in summer and autumn following increases in CH4. Methane-derived biomass (methane-derived carbon% × biomass) of C. plumosus were also higher in summer and autumn, suggesting transfer of methane-derived carbon to higher trophic organisms may be larger during those seasons, and limited in winter and spring. Although oligochaetes did not show seasonal variability of methane-derived carbon contributions, they provided a consistent source of methane-derived biomass to higher trophic levels throughout the year. Our study demonstrates that two major macroinvertebrates complementarily contribute to fueling methane-derived carbon cycling through trophic transfer in a polymictic lake.