Nitrogen Fixation in the Sediment of Shallow Lake Balaton, a Reservoir and Fishponds

Abstract

AbstractFor the in situ measurement of nitrogen fixation in lake sediments, we developed a method which assures the rapid saturation with acetylene of the whole enzyme pool in the sediment and maintains near intact physical, chemical and biological environment at the water‐sediment interface. On the basis of seasonal measurements, the annual nitrogen fixation in the sediment was estimated in four types of shallow water ecosystem: the Keszthely Basin, Lake Balaton: 4.7 g N m−2; Körös backwater reservoir: 6.5 g N m−2; a polycultural fishpond: 0.49 g N m−2; and a liquid manure oxidation fishpond: 0.61 g N m−2. The amount of nitrogen fixed in the sediment of the Keszthely Basin was close to the fixation in the water column, while that fixed in the sediment of Körös backwater reservoir was considerably greater.A multiple regression analysis was made on the basis of synoptic studies on the vertical distribution of nitrogen fixation in the sediment, the pH, Eh, and concentrations of organic N, NH4‐N, NO3‐N, and NO2‐N in the interstitial water. The results indicate that nitrogen fixation is related to the dep, the NH4‐N concentration, and the redox potential. The vertical distribution of nitrogen fixation cannot be explained in every case by the densities and distributional patterns of the Azotobacter and Clostridium populations. No correlation was observed between nitrogen fixation and total organic‐C in lake sediment. A surprisingly close correlation was found between plankton primary production and the sedimentary nitrogen fixation in these lakes (r = 0.85, y = 4.5 X0.85). Short‐term (4 h) in vitro studies revealed a glucose mediated increase of nitrogen fixation, but there was no NH4‐N inhibition detected during this short incubation period.