Zooplankton population seasonal variations in relation to nutrients. Case study of Lake Kastoria, Western Macedonia, Greece
In order to evaluate the trophic status of Lake Kastoria, seasonal pattern of nutrients, chlorophyll-a and zooplankton have been examined from January to December 2011. Lake Kastoria is a polymictic lake, characterized by both urban and agricultural activities. It has an area of 27.9 Km2 and is located in the northwestern part of Greece. Forests and semi-natural areas are characterized as dominant land use type (52%) in the lake's watershed (281 km2) followed by agriculture areas (39%). Urban land covers 2% of the lake's watershed. The lake's water retention time varies due to hydraulic adjustments of its outflow to Gioli torrent. Water samples were collected monthly from 5 sampling sites. The average of the measured values in all sampling sites, was estimated and the seasonal variation is demonstrated. The sequence of dominant zooplankton species groups in Lake Kastoria was Rotifera > Copepoda > Cladocera. Correlation between zooplankton species and nutrient level was established. The chlorophyll-a, an indicator of phytoplankton biomass, reached its maximum during the summer period. The values of total P and total N were also in high values in early spring and early autumn. Concerning chlorophyll-a and TSI indexes values, the trophic status of Lake Kastoria varied from eutrophic to hypertrophic depending on the season. The present study was to investigate the composition and abundance of species of zooplankton in the coastal zone of Lake Kastoria. The diversity of zooplanktonic organisms in lake ecosystem worldwide is a "key" factor of the biological and ecological status of the lake, as links the functioning of the ecosystem, the complexity of the food web and ecosystem stability. © 2017 PSP.