EUTROPHICATION IN THE KRKA ESTUARY

Changes in longitudinal distribution of eutrophication parameters in b rackish and marine layers of a stratified karstic estuary have been in vestigated from December 1988 until October 1989 on a gradient between a pristine and a moderately polluted area. In the estuary, only marin e phytoplankton blooms were found to develop. Near the head of the est uary, blooms develop below the halocline. Marine phytoplankton is fed by nutrients released from the decay of sinking freshwater phytoplankt on. Phytoplankon growth is P-limited. Hypoxia near the bottom follows the decay of occassionally large quantities of allochtonous freshwater and autochthonous marine phytoplankton. In the lower estuary, blooms have been observed to develop in the brackish layer above the haloclin e due to high salinity in the layer and the existence of a local anthr opogenic nutrient input.