Water quality and nutrient limitation in an area of the Danube River and an adjoining oxbow lake (1299 r. km): Algal bioassay

The purpose of this study was to evaluate the effect of nutrient limitation on the growth of freshwater green alga Chlorella kessleri using algal bioassay in a shallow oxbow lake of the Danube River (1299 r. km). The TN/TP ratio in oxbow lake water samples suggests that phyto-plankton growth, in general, depended on the availability of N rather than P. The nutrient enrichment experiments in tile drainage water samples show no limitation by either N or P. In the Danube River water samples, nitrogen is the most limiting nutrient for the growth of C. kessleri, while P is also important in some cases. The addition of N, either singly or in combination with P, to the water samples from the oxbow lake caused a significant increase of C. kessleri growth rate only during the inundation period. Trophic conditions in the oxbow lake ranged from meso-eutrophic (during high Danube water levels) to hypertrophic (during periods of low water level) indicating the influence of two main water sources. There is an increasing awareness of the need to assess nutrient enrichment using algal bioassaysand ambient concentrations as a part of integrative water quality assessment.