Sources of Nitrite in Streams of an Intensively Cropped Watershed

Abstract

The sources of high in-stream nitrite (NO 2 2 ) concentrations were investigated in two major streams located in an intensively cropped watershed in Quebec, Canada. Nitrogen retention was determined to evaluate the dynamics in relation to nitrogen transport along both stream branches during summer-low-water and fall-recharge regimes. In the first stream branch, NO 2 2 and ammonium (NH 4 + ) showed removal patterns during summer-low-water and fall-recharge periods, whereas, in the second branch, NO 2 2 and NH 4 + exports occurred during both hydrologic regimes. The study also demonstrated that seepage water is a source of NO 2 2 instream, which varies within the watershed stream branches and with the hydrologic regime. The results highlighted a significant reductive microbial activity in seepage water from either denitrification or dissimilatory nitrate reduction to ammonium (DNRA), leading to nitrate (NO 3 2 ) consumption. Differences in groundwater NO 3 2 concentrations feeding each stream branch may have significantly influenced NH 4 + and NO 2 2 concentrations found in seepage water, which potentially resulted in quantitatively significant NO 2 2 formation. Water Environ. Res., 82, 622 (2010).

Phosphorus Fluxes at the Sediment-Water Interface in a Temperate Region Agricultural Catchment

“…They are characterized by steep slopes, unstable banks, and a water surface well below the bank level, even during flood events (Corriveau et al 2010a). The channel widths of the two streams vary from 0.5 to 2 m, and the water depths are about 15 to 35 cm during summer low water levels.…”

“…A seepage meter to collect sediment pore water directly beneath the sediment-water interface was installed near the pipe in each sampling site, following the methods described by Corriveau et al (2010a) (Fig. 2).…”

“…1). The piezometers were built using 5.0-cm diameter PVC tubes, screened and sand packed at the water table to sample groundwater from the water table (Corriveau et al 2010a). Samples from piezometers were collected in 2 L HDPE bottles, after a 10 L purge with an inertial pump.…”

“…Br14 was mainly supplied by the regional aquifer where anoxic conditions prevailed, while Br15 was mainly connected to the surficial aquifer which was characterized by high dissolved oxygen concentrations (Corriveau et al 2010a). Thus, we expected that sediment P could be released to the pore water and then flow upward to streams with the groundwater or the mix of groundwater and stream water passing across the sediment-water interface during low flow period in Br14.…”

“…The two branches were fed by a mix of groundwater with contrasting chemistry due to in situ heterogeneous hydrogeologic conditions (Corriveau et al 2010a). Br14 was mainly supplied by the regional aquifer where anoxic conditions prevail, while Br15 was mainly connected to the surficial aquifer which was characterized by high dissolved oxygen concentrations (Corriveau et al 2010a). This contrast in redox status of aquifer systems had partly explained the significant differences of NO 2 − concentration in the seepage water collected in the two branches.…”