Phytoplankton are microscopic biotic and photosynthesizing organisms and it has a key role in determining water quality. High nutritive value features of phytoplankton are important primary producers. Phytoplankton are distributed on wide habitat on earth and important organisms for the biosphere. However; phytoplankton have an essential ecological mission being food sources as well as being primary producers in surface water.
Phytoplankton or microalgae are free-living photosynthetic microorganisms in aquatic systems and are the primary producer of the limnetic zone. Phytoplankton communities dominate the surface water systems that cover 70% of the world’s surface area. As prokaryotic or eukaryotic, unicellular, colonial or filamentous free-living photosynthetic microorganisms in aquatic systems, phytoplankton play a key role in the organization and functioning of aquatic ecosystems and are most relevant bioindicators for the monitoring of nutrient enrichment.
Phytoplankton is one of the basic and key factors of a water ecosystem in the food web.
Dynamic features of lakes such as clarity, trophic status, zooplankton and fish production depend on phytoplankton. Freshwater communities are highly sensitive to environmental variables. Physicochemical factors strongly shape the all phytoplankton composition in the waters.
To improve the quality of ecosystems in water, it is necessary to know which environmental factors are affected. In particular, physical or chemical pollution seen, frequently seen in surface water sources; plays a primary role in the destruction of ecosystems, but physicochemical analyzes alone may not be sufficient to identify the adverse effects of pollution.
The ecological status of surface water following Annex V” is defined as “an expression quality of the water ecosystems structure classified associated with surface waters, in WFD. This classification system of the water ecological status should reflect the structure of the biological factors changes and response to human activity pressure. Phytoplankton are quite important bioindicators of the water ecology such as still waters, lakes, etc. Phytoplankton composition and dynamics act a key role in all lake ecosystem biodiversity. Phytoplanktons are considered good indicators of trophic conditions and water quality because they respond rapidly to environmental variables or water quality deterioration and the quantity and/or quality of phytoplankton dynamics should be considered water quality as well.
Appropriate environmental conditions and nutrients increment in the water causes the increase of phytoplankton biomass. It is very important to protect surface waters, which are very suitable for pollution. The cyanobacteria also provide an extraordinarily wide-ranging contribution to human affairs in everyday life.
Some cyanobacteria produce cyanotoxin and there have been many poisoning cases around the world caused by cyanotoxins in waters. Therefore, the beneficial aspects, as well as the harmful features of phytoplankton, should be considered. Based on increased environmental pollution and global climate change can be caused increased cyanobacteria population in surface waters. Thereby, health problems caused by cyano-toxins may increase.