Potential effects of the invasive bivalve Corbicula fluminea on methane cycling processes in an urban stream

Lotic methane production, consumption, and flux depends on biogeochemical conditions that vary at fine scales within streams. The invasive bivalve, Corbicula fluminea, is known to affect stream biogeochemistry and may influence methane cycling via bioturbation and respiration. Response of methanogenesis rate, potential rate of methanotrophy, and net methane flux to Corbicula density was tested using intact sediment core incubations. Potential methanotrophy decreased and net methane flux increased with Corbicula density in sediment cores. However, the magnitude of this effect decreased at the highest Corbicula densities tested here. Response of sediment pore water methane concentration to Corbicula density was tested using in situ cage enclosures in a randomized block design over a 50 m stream reach. Block effect was the most significant predictor of in situ pore water methane concentration, and Corbicula density had a positive, marginally significant, interaction with the block effect, indicating that Corbicula’s effect on methane concentration varies with in situ conditions. Our study shows that Corbicula influences methane cycling processes in the laboratory, apparently via their impact on dissolved oxygen, but this effect depends on stream conditions in the field. Further study is needed to evaluate mechanisms of this relationship more fully.