An investigation on phytoplankton composition and bacterial load relationship in a drinking water resource: Büyükçekmece Dam Lake (Istanbul, Türkiye)

ABSTRACT Bacterial and phytoplankton communities, which are important components of lakes, are affected by both abiotic and biotic factors, especially each other. The relationship between phytoplankton communities and the bacteriological load was investigated in Büyükçekmece Dam Lake and selected 8 influent streams. In accordance with this purpose, water samples were collected seasonally from 9 sampling stations. The phytoplankton composition of Büyükçekmece Dam Lake and its streams constitutes 63 taxa belonging to Bacillariophyta, Charophyta, Chlorophyta, Cryptophyta, Cyanobacteria, Euglenozoa, Miozoa and Ochrophyta divisions. Minimum and maximum load of total heterotrophic aerobic bacteria, total and fecal coliforms were determined as 1 × 102 – 1,330 × 102, 1 × 102 – 378 × 102 and 9 × 102 – 551 × 102 CFU/mL, respectively. Especially Karasu and Çekmece streams’ bacteriological load was found above the acceptable amounts in terms of bacteriologic pollution. The maximum nutrient concentrations were measured in parallel to the stations where the bacteriological load was detected at the highest density. The maximum bacteriological load was determined at Çekmece Stream (st. 6) which is passing through the agricultural areas and has a low flow. Also, the water bloom-forming cyanobacterium Aphanizomenon flos-aquae Ralfs ex Bornet et Flahault was recorded as dominant. The lake basin, which shows mesotrophic characteristics according to physicochemical variables, has been defined as close to eutrophy since it has high nutrient salt and chlorophyll-a concentrations. Büyükçekmece Lake is the second largest drinking water source and the most affected reservoir by anthropogenic pollution in Istanbul. The water quality of the lake is affected negatively by the discharges from domestic, industrial wastewaters, and also inputs from agricultural areas. Continuing limnological studies on phytoplanktonic and bacterio-logic organisms, which are accepted bioindicators in waters, have a vital role in monitoring and protecting the water of Büyükçekmece Dam Lake and its feeding streams.