A comparison of electron transport system activity in stream and beaver pond sediments

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Abstract
Electron transport system (ETS) activity of sediments as an indication of microbial metabolic activity was measured at four beaver pond sites in central New York State. ETS activity, an indication of microbial biomass and respiration, was measured as the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to INT-formazan. Since INT can be reduced by both aerobes and anaerobes, the total microbial respiratory activity in the sediments was measured. The ETS activity increased from means of 11.1–65.0 μg O2∙g−1 dry weight∙h−1 at the free-flowing upstream reaches to means of 221.2–262.6 μg O2∙g−1 dry weight∙h−1 within the beaver ponds. ETS activity decreased with increased depth of sediment probably because of the loss of aerobic activity. When ETS activity was expressed on a per unit area basis (grams O2 per square metre per hour), the increase from upstream reaches to the ponds ranged from 13- to 35-fold. This difference increased to 460- to 2180-fold when the activity was expressed per unit length of stream (micrograms O2 per metre per hour). These data showed that beaver ponds greatly increased microbial activity along streams, likely resulting in changes in biogeochemical cycles controlled directly or indirectly by microorganisms.