Algal responses to nutrient additions in water of Nature Park Kopacki Rit (Croatia) by Miniaturized Algal Growth Bioassay

The algal growth potential (AGP) in original water samples from Nature Park Kopacki Rit and the Danube, as well as the influence on the AGP due to adding nitrates (final concentration of 0,180; 0,360; 0,723 g 1 -1 ) and phosphates (final concentration of 0,028; 0,056; 0,169 g I -1 ) was investigated by miniaturized bioassay method. According to the classification for waters of Middle Europe, during March and April 2001 the waters of Kopacki Rit belonged to meso-mesoeutrophic waters, and in January 2001 to oligotrophic. During the period of investigation, the Danube River belonged to the meso-mesoeutrophic waters. On the basis of AGP results, toxic substances were equally present at all sites, except at Lake Sakadas. In all three concentrations the nitrates stimulated the growth of Chlorella kessleri. Samples from the Danube and Hulovo Channel from January 2001 were exceptions. In April 2001 phosphates inhibited the growth of alga Chlorella kessleri, mainly through samples from the bottom. During the whole investigated period, nitrates control the eutrophication in Kopacki Rit.