Benthic microbial respiration in Appalachian Mountain, Piedmont, and Coastal Plains streams of the eastern U.S.A.

1. Benthic microbial respiration was measured in 214 streams in the Appalachian Mountain, Piedmont, and Coastal Plains regions of the eastern United States in summer 1997 and 1998. 2. Respiration was measured as both O₂ consumption in sealed microcosms and as dehydrogenase activity (DHA) of the sediments contained within the microcosms. 3. Benthic microbial respiration in streams of the eastern U.S., as O₂ consumption, was 0.37 ± 0.03 mg O₂ m^-2 day^-1. Respiration as DHA averaged 1.21 ± 0.08 mg O₂ m^-2 day^-1. 4. No significant differences in O₂ consumption or DHA were found among geographical provinces or stream size classes, nor among catchment basins for O₂ consumption, but DHA was significantly higher in the other Atlantic (non-Chesapeake Bay) catchment basins. 5. Canonical correlation analyses generated two environmental axes. The stronger canonical axis (W₁) represented a chemical disturbance gradient that was negatively correlated with signatures of anthropogenic impacts (ANC, Cl^-, pH, SO₄²), and positively correlated with riparian canopy cover and stream water dissolved organic carbon concentration (DOC). A weaker canonical axis (W₂) was postively correlated with pH, riparian zone agriculture, and stream depth, and negatively correlated with DOC and elevation of the stream. Oxygen consumption was significantly correlated with W₂ whereas DHA was significantly correlated with W₁. 6. The strengths of the correlations of DHA with environmental variables, particularly those that are proven indicators of catchment disturbances and with the canonical axis, suggest that DHA is a more responsive measure of benthic microbial activity than is O₂ consumption.