Occurrence of Nitrite in the Lough Neagh River System

Abstract

The Lough Neagh catchment area covers about one‐third of the land area of Northern Ireland. This report documents NO2− concentrations in the major rivers entering Lough Neagh, which are frequently in the range of 100 to 150 μg N L−1 and exceed the European Community (EC) water quality guide values. The contribution of land drainage to NO2− loads carried by these rivers was estimated to be about 40%. The remaining 60% of NO2− appears to originate from N transformations at the sediment‐water interface of the river system. The available evidence suggests that NH+4 originating from agricultural pollution provides the N substrate for nitrification by Nitrosomonas to NO2−. What is anomalous is why this NO2− is not further oxidized rapidly to NO−3 by Nitrobacter. A possible mechanism is that the Nitrobacter is retarded by the presence of free ammonia concentrations that can be predicted to be present in the range of 65 to 76 μg N L−1.

Partial nitrification—operational parameters and microorganisms involved

“…A measuring campaign in the Lough Neagh river system (Northern-Ireland) demonstrated that minimum nitrite concentrations (0-19 lg N l -1 ) were normally observed during winter months, while maximum concentrations (90-235 lg N l -1 ) occurred during summer months (Smith et al 1995). Knowles et al (1965) determined that the ammonia and nitrite oxidation rates increase 2.6 and 1.8 times respectively per 10°C in a physiologically relevant temperature range.…”

Origin, causes and effects of increased nitrite concentrations in aquatic environments

“…In the river Lahn (Germany) maximum nitrite concentrations were measured from May until July (mid spring-mid summer) (Von Der Wiesche & Wetzel 1998). A measuring campaign in the Lough Neagh river system (Northern-Ireland) demonstrated that minimum nitrite concentrations (0-19 µg N L −1 ) were normally observed during winter months, while maximum concentrations (90-235 µg N L −1 ) occurred during summer months (Smith et al 1995). An increase in temperature from 20 to 30 • C in a compartmented (anoxic-oxic) labscale activated sludge installation resulted in a simultaneous decrease in suspended solids concentration and a temporary nitrite accumulation (from 0 to 6 mg N L −1 ) which stabilised after a few days at 0.5 mg N L −1 (Philips, unpublished observations).…”

Toxic effects of nitrite on freshwater organisms: a review

“…In the summer, however, nitrite concentrations can increase to levels ranging from tenths up to 1 mg L −1 in surface waters mainly in those across agricultural watersheds (Smith et al . ; von der Wiesche & Wetzel ; Corriveau et al . ).…”

“…The reason is that in oxic environments, they are subject to nitrification and quickly transformed into nitrates, whereas in anoxic environments, they undergo mainly denitrification to gaseous end products, elemental nitrogen (N 2 ) or nitrous oxide (N 2 O), or other biochemical reductions (Philips et al 2002;Pitter 2009). In the summer, however, nitrite concentrations can increase to levels ranging from tenths up to 1 mg L À1 NO À 2 in surface waters mainly in those across agricultural watersheds (Smith et al 1995;von der Wiesche & Wetzel 1998;Corriveau et al 2010). In wastewater, nitrite concentrations may exceed the level of 1 mg L À1 .…”