The Influence of Copper, Lead and Iron on Stream Sediment Nitrification in Central Indiana Streams
Copper, lead, and iron have frequently been detected throughout Indiana freshwaters. Since microbial activity is a holistic measure of ecosystem function, changes in microbial activity in response to metal concentrations may indicate potential areas of concern. Metal concentrations in seven streams of the Upper White River watershed of central Indiana were measured during spring (May) and summer (August) in conjunction with measurement of sediment nitrification rates using the nitrapyrin-inhibition technique. Additionally, the influence of copper, lead, and iron on microbial nitrification was measured using in vitro mesocosms inoculated with stream sediment. Sediment metal concentrations ranged from 654–1,985 mg Fe/kg and 1.00–2.91 mg Cu/kg sediment. Dissolved metal concentrations ranged from below detection to 0.10 mg Fe /L and 0.01–0.02 mg Cu/L. Stream sediment nitrification rates were positively correlated to sediment copper concentrations. Metal concentrations of 127 mg/L may reduce stream sediment nitrification although stream physiochemical characteristics and history of metal exposure also influence microbial response. Further, stream sediment metal concentrations may affect nitrifying microbes more than dissolved metal concentrations.