We quantified how microbial respiration is controlled by discharge and the supply of C, N, and P in a stream. We ran two rounds of experiments adding a conservative tracer, an indicator of aerobic respiration, and nutrient treatments: a) N, b) N+C, c) N+P, and d) C+N+P. Microbial respiration remained similar between rounds and across nutrient treatments. This suggests that complex interactions between hydrology, resource supply, and biological community drive in-stream respiration.