Potential Denitrification Rates in an Agricultural Stream in Southern Illinois

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Abstract
The influences of stream temperature, nitrate concentration, dissolved oxygen concentration, and substrata composition on potential denitrification rate (PDR) were investigated over one year in Big Creek, an agricultural watershed in southern Illinois. PDR ranged from 0 to 106 μg N g AFDM−1 hr−1 with higher rates in the early spring and late summer. The greatest PDR's were measured in April 2000 and April 2001, which both coincided with newly established periphyton communities. PDR did not correlate as expected with seasonally variable, ambient stream conditions such as temperature, dissolved oxygen or nitrate concentration; however, significant relationships did exist between PDR and dissolved oxygen within seasons. The coarse sediments from the headwater section of Big Creek had a significantly higher PDR (13.1 μg N g AFDM−1 hr−1) than the fine sediments (5.2 μg N g AFDM−1 hr−1) from the lower channelized reach, which may have been a function of lower C:N organic matter in the headwater reach. Based on the PDR measured in this stream, denitrification was not a significant sink of the stream nitrogen load.