Dynamics of the nitrogen transformation in a shallow stream and possible interventions.
This paper presents the assessment of the efficiency of the main biological nitrogen transformation processes in a shallow well-oxygenated river and conditions under which they are active and stabilise. The process dynamics was studied with the help of mathematical modelling of 2 years on-line data series measured in a reach of the Toess River, Switzerland. The algal nitrogen uptake was very stable and unaffected by most but frequent flood events. Daylight photosynthetic nitrogen uptake stabilised at 6 mgN mstreambed(-2) h(-1) (15 degrees C), dark uptake on storage products at rates of 0.5-2.5 mgN mstreambed(-2) h(-1). Nitrogen uptake by heterotrophic bacteria in the hyporheic zone was relatively constant at a level of 1.5-3.5 mgN mstreambed(-2) h(-1). Streambed nitrification could establish only during periods with average an daily concentration of at least 0.3 g(NH4-N) m(-3) in river water for several weeks. The maximum nitrification rate was 35 mgN mstreambed(-2) h(-1) for 3 g(NH4-N) m(-3). The effects of reduced nitrification in the WWTP and of river banks shading on a sudden ammonium peak were simulated. A river reach endangered by ammonium spills should be kept open to sun to favour ammonium uptake by algae. In-stream nitrification reduces ammonium peaks efficiently but leads to toxic nitrite concentrations.
Kabelkova-Jancarkova
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Czech Technical University in Prague, Faculty of Civil Engineering, Laboratory of Ecological Risks in Urban Drainage, Thákurova 7, 166 29 Praha 6, Czech Republic. kabelkova@lermo.cz
D001420:Bacteria, Aerobic / Q000378:metabolism; D056890:Eukaryota / Q000378:metabolism; D008962:Models, Theoretical; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D010100:Oxygen / Q000378:metabolism; D045483:Rivers / Q000382:microbiology; D013557:Switzerland; D014874:Water Pollutants, Chemical / Q000378:metabolism*
D014874:Water Pollutants, Chemical; D009584:Nitrogen; D010100:Oxygen