Long-term Changes in del 13C in DOC-based Benthic Food Webs in Arctic Lakes

Arctic regions are rapidly warming, resulting in warmer summer lake temperatures and increased slumping of organic soils. In Lake NE-12, del 13C of primarily benthivorous lake trout has declined over eleven years. Two important lake trout prey, the caddisfly Grensia and the snail Lymnaea, also became more 13C-depleted. In Lake E-1, the deposit-feeding chironomid, Stictochironomus, also shifted toward lower del 13C, while filter-feeding Tanytarsini did not. Pelagic zooplankton did not show a trend toward 13C depletion overall, but were less consistent. Recent and concurrent studies have shown that DOC is an important resource for the benthic foodweb. Methanotrophy is part of the DOC-based foodweb. Our recent studies have shown that macrobenthos use some methanotroph production. Methane has very low del 13C, thus incorporation of a small amount of methane-based production has a large effect on del 13C. We suggest that climate-driven changes in the carbon pools available to microbes are resulting in increased importance of methanotrophs in macroinvertebrate diets, contributing to the observed long-term del 13C changes. Increased algal fractionation could also be important, but this mechanism has less support because zooplankton and filter-feeding chironomids did not show the same pattern, and previous studies have shown very limited benthic-pelagic coupling.