Role of Nitrification in Contributing to Low Oxygen Conditions in an Urban Waterway

摘要

Rates of nitrification were measured with 15N tracer methods in the Providence River (R.I.) an urban river with high ammonia inputs. The rates found for fall and winter were lower than expected, 0.0099 - 0.0404 micromol liter 1d. Rates of nitrification calculated for ammonia-enriched Narragansett Bay mescosms were an order of magnitude higher at the same concentrations of ammonium ion as the river samples. Possible reasons for the low rates are: a lag period of little or low nitrification activity, delayed recovery of upper water nitrifiers from light inhibition, low concentrations of nitrifying bacteria or, most likely, a substance within the river is inhibiting nitrification. The measured nitrification rates indicate an annual nitrogenous oxygen demand to the river comparable to only about 1% of the annual carbonaceous oxygen demand of the river, suggesting that nitrification is not consuming a significant amount of oxygen in the Providence River.