Diversity of phytoplankton and trophic status in the Gaga Lake, Turkey

The phytoplankton composition of Gaga Lake was studied monthly for one year, from February 2005 to January 2006. A total of 99 algal taxa which have into 7 taxonomic groups were determined. The range of taxonomic groups from the most rich in species to less species, were Chlorophyta (35 taxa), Ochrophyta (22 taxa), Charophyta (16 taxa), Cyanobacteria (14), Myzozoa (5), Euglenozoa (5), and Heterokontophyta (2) respectively. Green algae were dominant in out of the total species number. Ceratium hirundinella that belongs to Dinophyceae, and Dinobryon divergens and D. sertularia that belong to Chrysophyceae were the dominant taxon through in the study. Ecological status of the Gaga Lake was mesotrophic, according to both planktonic algae composition and the phytoplankton compound quotient (PCQ=3.78). As a result of dominant genus scores (4.43), the lake has a mesotrophic character according to trophic level. In addition, the water quality of Lake Gaga is moderate. When OECD criterias are compared, the lake is oligotrophic according to chlorophyll-a and Secchi depth. It has also mesotrophic feature as to total phosphorus values. The results of Carlson's Trophic State Index (TSI) show an change from oligotrophy to mesotrophy in the Gaga Lake. The trophic level of the Gaga Lake is oligotrophic (<40) according to TSIChl-a and TSISD values, mesotrophic according to TSITP value (40-50).