Occurrence of high in-stream nitrite levels in a temperate region agricultural watershed

This study is the first to report nitrite occurrence and variability in surface water across an agricultural watershed in the province of Quebec, Canada. Nitrite (NO2-) concentrations were monitored across a 2.4 km2 watershed during 2 years. Water samples were collected at the outlet from April to November and in three contrasted stream branches (six stations) during three hydrological regimes (summer low water levels, fall recharge, and snowmelt). Our study clearly demonstrates that NO2- levels observed at the outlet are not representative of NO2- variability across the micro-watershed. Surface water collected in cropped areas presents high NO2- concentrations during summer low water levels, often exceeding guidelines for aquatic life, with NO2- means ranging from 0.022 to 0.107 mg N L-1 and maximum value reaching 0.156 mg N L-1. Furthermore, the two stream branches in cropped area have demonstrated significant differences in NO2- concentrations and other water quality parameters. The importance of groundwater discharge to streams in the micro-watershed Bras d'Henri may potentially generate different in-stream sources of NO2- and water quality parameters. However, further studies are essential to determine sources and processes related to in-stream NO2- peaks. © 2009 Springer Science+Business Media B.V.