Greenhouse gas (GHG; CO2, CH4, N2O) emissions from running waters are supplied from instream processes (e.g., metabolism, weathering) and external sources (e.g., soils, groundwater). However, little information is known about the contribution of macroinvertebrates to lotic GHG emissions. To address this knowledge gap, we asked how the invasive filter-feeding and burrowing Asian clams (Corbicula spp.), whose population has exploded in North American streams, affect stream GHG cycling. We predicted that (1) clams directly emit CO2, CH4, and N2O, (2) direct CH4 and N2O emissions from clams are higher in agricultural streams, and (3) bioturbation from clams leads to higher total sediment to water gas fluxes. In urban streams in North Carolina (n=5) and agricultural streams in Georgia (n=4), we conducted field microcosm incubations using three treatments: clam vs. no clam, natural vs. sterile sediment, and light vs. dark treatments. For each treatment, net GHG production was calculated as the difference in GHG concentrations between the start and end of the incubations. We found that, regardless of light and sediment treatment, CO2 concentrations in clam treatments doubled, while stabilizing and even decreasing in control treatments. The concentrations of N2O generally increased in clam treatments from two to four times, except for two study sites where the concentrations decreased up to three times. Notably, the N2O concentration in clam treatment was higher in natural sediment than in sterilized sediment, implying an interactive effect between the Asian clams and the sediment microbial communities. Contrary to our initial prediction, CH4 concentration across all treatments declined, which could be due to clam bioturbation causing sediment oxygenation and CH4 oxidation. These results suggest that at high densities, the Asian clams can play a substantial role in affecting reach scale GHG flux. Our findings highlight the need for future studies and ultimately, for management of U.S. streams, to explicitly incorporate macroinvertebrates into models of lotic carbon cycling.