Rv. Smith et al., FREE AMMONIA INHIBITION OF NITRIFICATION IN RIVER SEDIMENTS LEADING TO NITRITE ACCUMULATION, Journal of environmental quality, 26(4), 1997, pp. 1049-1055
Previous studies have reported that only 40% of nitrite (NO2-) in majo
r rivers in Northern Ireland originates from land drainage. The remain
der appears to originate from N transformations at the interface betwe
en sediment and water within river systems. Streams in two major river
catchments in Northern Ireland were monitored for the presence of NO2
-. Mean NO2- concentrations (which all exceeded 3.0 mu g N L-1 which i
s the European Community (EC) guide values for supporting salmonid fis
h) ranged from 3.8 to 84.5 mu g N L-1 in 14 streams in the Upper Bann
and 10.7 to 60.0 mu g N L-1 in 14 streams in the Colebrooke river syst
em. Evidence from multiple regression analysis suggested that NO2- acc
umulation in these streams was associated with the presence of free NH
3. Incubation and differential N-15 labeling of sediment extracts with
ammonium nitrate (NH4NO3) provided support for this hypothesis that s
howed that the mechanistic process involved in NO2- accumulation is ni
trification inhibition rather than denitrification. Free NH3 partially
inhibits NO2- oxidation by Nitrobacter, but does not inhibit the oxid
ation of ammonium (NH4+) by Nitrosomonas. Most of the NH4+ in streams
originates from pollution by agricultural effluents and must be curtai
led to prevent NO2- accumulation.