EFFECTS OF CARBON AND NITRATE ON DENITRIFICATION IN BOTTOM SEDIMENTS OF AN EFFLUENT-DOMINATED RIVER

Nitrogen and carbon limitation of denitrification in the bed sediments of an effluent-dominated stream were investigated by quantifying the effects of nitrate and glucose additions on the rate of sediment N2O p roduction. Bed sediment samples were collected from a 30-km stretch of the South Platte River where up to 95% of the base flow discharge con sists of effluent from a water treatment plant in Denver, Colorado. Th e rate of denitrification in upstream sediment samples incubated under in situ nitrate and carbon conditions was primarily limited by nitrat e supply. The stimulatory effect of nitrate additions on the rate of b ed sediment denitrification decreased with increasing distance downstr eam of the treatment plant. Approximately 35 km downstream of the trea tment plant, denitrification in the bed sediment samples was carbon li mited. The observed decreases in the concentration of total inorganic nitrogen (as NH4 + NO3) dissolved in the river and the organic carbon content of the bed sediments with increasing distance downstream of th e treatment plant suggest that bed sediment denitrification is a signi ficant sink for nitrogen in this stretch of the river.