Nitrite and the two stages of nitrification in nitrogen polluted Onondaga Lake, New York

Nitrite (NO2-) concentrations in the upper waters of N polluted Onondaga La ke, New York, are documented for the April through October interval for a 1 0-yr (1989-1998) period. Inputs of NO2- from a domestic waste treatment fac ility (METRO) and tributaries (4) to the lake are quantified for four of th e gears (1991-1994). The NO2- concentrations measured in Onondaga Lake (e.g ., annual maxima in the range 200-1000 mg N m(-3)) are some of the highest reported for lakes and rivers in the literature. These levels represent sev ere violations of toxicity standards. Annual average concentrations in the METRO effluent ranged from 412 to 1097 mg N m(-3). The METRO load represent ed >90% of the total external NO2- load to the lake. A mechanistic mass bal ance model for NO2- and NO3- is developed and applied for the lake to ident ify occurrences, and quantify the rates, of the first and second stages of nitrification. Nitrite is found to behave in a nearly conservative manner i n the upper waters of the lake over the April to July interval. The progres sive increases in concentrations over this interval have been largely in re sponse to inputs from METRO. Major deviations from conservative behavior oc curred for NO2- in most years over the July to October interval as a result of the irregular operation of the two stages of the nitrification process. This has been manifested as large and abrupt changes in NO2- concentration in the July to October interval, Potential factors responsible for the obs erved dynamics in nitrification and the NO2- pool are considered.