Methane-Derived Carbon in the Benthic Food Web in Stream Impoundments

Methane gas (CH4) has been identified as an important alternative source of carbon and energy in some freshwater food webs. CH4 is oxidized by methane oxidizing bacteria (MOB), and subsequently utilized by chironomid larvae, which may exhibit low delta C-13 values. This has been shown for chironomid larvae collected from lakes, streams and backwater pools. However, the relationship between CH4 concentrations and delta C-13 values of chironomid larvae for in-stream impoundments is unknown. CH4 concentrations were measured in eleven in-stream impoundments located in the Queich River catchment area, South-western Germany. Furthermore, the delta C-13 values of two subfamilies of chironomid larvae (i.e. Chironomini and Tanypodinae) were determined and correlated with CH4 concentrations. Chironomini larvae had lower mean delta C-13 values (-29.2 to 225.5 parts per thousand), than Tanypodinae larvae (226.9 to 225.3 parts per thousand). No significant relationships were established between CH4 concentrations and delta C-13 values of chironomids (p. 0.05). Mean delta C-13 values of chironomid larvae (mean: 226.8 parts per thousand, range: 2 29.2 parts per thousand to 225.3 parts per thousand) were similar to those of sedimentary organic matter (SOM) (mean: 228.4 parts per thousand, range: -29.3 parts per thousand to 227.1 parts per thousand) and tree leaf litter (mean: 229.8 parts per thousand, range: 230.5 parts per thousand to 229.1 parts per thousand). We suggest that CH4 concentration has limited influence on the benthic food web in stream impoundments.