TEMPORAL AND SPATIAL DYNAMICS OF NITRITE ACCUMULATION IN THE RIVER-LAHN

Both the inorganic nitrogen pool and environmental factors controlling the spatial and temporal variability of nitrite concentration were mo nitored in the River Lahn at two sites with different sediment composi tion (coarse gravel/fine gravel and fine sediments). The field studies were conducted both in the free flowing and the interstitial water. A ccumulation of nitrite in the River Lahn occurred in correlation to wa ter temperatures over a range of 13 degrees C during the warmer season and coincided with high concentrations of ammonium. An annual as well as daily variations of the concentrations could be determined with th e highest data in the summer and lower values at the beginning of the colder season. Maxima were measured from May until July 1993, especial ly in the hours around noon, sometimes in ecotoxicologically critical concentrations (greater than or equal to 0.3 mg NO(2)(-)Nl(-1)). A spa tial variability depending on the depth of the interstitial strata (8- 28 cm) was only found at a muddy study site. Here the concentration of nitrite was four to sixfold of that in the free flowing water. At the other study-site consisting of coarse gravel, no accumulation of nitr ite could be detected. In order too assess the importance of abiotic f actors, e.g. temperature, on the nitrification process, laboratory exp eriments were also conducted. Nitrifying biofilms of a defined substra te from the River Lahn were used as a model for patterns and processes in the river-bed. The results indicate a critical temperature domain (16-22 degrees C) in which the activity of Nitrobacter seems to be mor e inhibited than the nitritation by Nitrosomonas, resulting in a trans ient build-up of nitrite. (C) 1998 Elsevier Science Ltd. All rights re served.