In 1987-1989 the species composition of phytoplankton, its abundance a
nd chlorophyll concentrations were studied in the irrigation reservoir
s Petrova Ves and Prietrz (West Slovakia). Resevoirs were utilized not
only for irrigation but also for production of stocking and marketabl
e carps as well as in two-year cycles. The phytoplankton community of
both reservoirs is very similar in species composition and development
dynamics and is considered to be a typical pond community. A total of
270 algal taxa were identified, of which 14 were observed in Slovakia
for the first time. In Petrova Ves we recorded 221 taxa and in Prietr
z 178. Chlorophytes and diatoms represented the largest proportion in
both reservoirs. The chlorophyll a content reached maximum concentrati
on during spring and autumn. Generally higher values of chlorophyll as
well as in the mean summer concentration of chlorophyll were measured
in Petrova Ves, where remarkable differences were monitored during gr
owth season. The abundance of phytoplankton and content of chlorophyll
in both reservoirs of the study were lower in years of fish stocking
than in the year of harvesting marketable fish. The phytoplankton comm
unity of Prietrz was more stable, cell concentrations and chlorophyll
content were lower here, without any remarkable differences during the
year of study.