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.