engleski

Algal bioassay procedure for assessing eutrophication of waters in Eastern Slavonija and Baranja

Excessive algal growth is a major pollution problem and is believed to be caused by large quantities of nutrients loaded into the aquatic environment. Therefore, investigations in this thesis were focused on the relationship between algal growth potential and the distribution of nitrogen and phosphorus in surface freshwaters. To achieve objectives of this thesis a responsive test was designed to assess quantitatively algal growth after nutrient additions in order to obtain a biologically relevant measure of nutrient deficiency. As a result, a bioassay method is introduced for the evaluation of trophic status and limiting nutrients in the investigated waters. Trophic conditions based on algal growth potential throughout the work were inversely related to trophic conditions based on phytoplankton chlorophyll-a concentrations. Thus, in defining the trophic state both parameters should be considered as complementary. In the Danube river floodplain system, the most significant factors that influenced nutrient dynamics were the location of floodplain water bodies regarding the river (spatial dimension) and hydrological connectivity between the river and its floodplain (temporal dimension) along with the retention time of floodwaters and nutrient uptake by biota. Based on low nitrogen to phosphorus ratios and the overall high phosphorus concentrations, nitrogen was the expected limiting nutrient for primary productivity in the investigated waters. However, nutrient enrichment results indicated that N/P ratio was not a reliable indicator of nutrient limitation. Watercourses of rural and agricultural catchment (the Biđ-Bosut) were badly damaged or at high risk of eutrophication and their nutrient contents were far above prescribed concentrations. Only moderate signs of distortion resulting from anthropogenic activities were observed in watercourses draining forested catchment (the river Spačva basin), while some watercourses draining agricultural watershed in the Baranja region showed even nutrient deficiency (primarily nitrogen). Nutrient loading from catchments with different land uses exhibited considerable uncertainties making temporal and spatial monitoring of water quality essential for predicting the effects of either nutrient increases or reductions. Moreover, systematic studies involving water quality assessment at catchment scale showed to be necessary for the development of integrated water quality management. Because financial cost and the type of nutrient reduction strategies vary considerably with the targeted nutrient, scientific foundations are needed for management decisions concerning eutrophication control.

Danube River; floodplain area; NaturePark Kopački rit; watershed in the Baranja region; Biđ-Bosut catchment; algal growth potential; Chlorella kessleri; eutrophication; nitrogen; phosphorus.

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