Community electron transport of procaryotes in euryoxic estuarine sediment

Rates of both tetrazolium and oxygen reduction were obtained seasonally from the top 8 cm of euryoxic estuarine sediment in southeastern New England, USA, over an in situ temperature range of 0 to 20 'C. Anoxic tetrazolium reduction was highest i n the 3 to 5 cm layers at 15 O C (up to 860 n m o l 2 e c m 3 h l ) . Changes in the chemistry of deeper pore-waters (20 to 60 cm) occurring over 90 d indicated that metabolic rates (ca 42 nmol 2 e c m 3 h ' ) were about an order of magnitude lower than those in the surface sediments. Parallel simultaneous estimates of 0; reduction (reduced sediment preincubated in Os-saturated ambient waters 10 mM NaN3) averaged 4 times greater than tetrazolium reduction. The postulated occurrence of a mixed metabolic community consisting of facultatively anaerobic heterotrophs and chemolithotrophs agrees with the field data. The community is spread out vertically through watery sediment of a quiescent, highly depositional cove. Soft-bodied infauna may help maintain the Eh potential at ca -200 mV from 1 to 60 cm; the sediment is not sufficiently cohesive to be strongly poised,