The Water Framework Directive was adopted to monitor water quality and achieve good ecological status and potential and to protect surface waters. It is one of the most important legal documents for the member states of the European Union in the area of water management. Under this directive, the assessment of the ecological status and potential of surface waters is based on biological quality elements (BQEs) such as phytoplankton, phytobenthos, macrophytes, macrozoobenthos and fish, as well as accompanying physico-chemical and hydromorphological components.
One of the main negative impacts on the ability to achieve good ecological status and potential in 60 % of European surface waters is nutrient overload. Excessive nutrient inputs impair the functioning of ecosystems and lead to accelerated eutrophication and a decline in biodiversity. First and foremost, the increased nutrient concentration in water promotes excessive growth of phytoplankton as primary producers, which is why phytoplankton organisms are good indicators of eutrophication in aquatic ecosystems.
Phytoplankton is an extremely diverse group of photosynthetic cyanobacteria and eukaryotic algae that are adapted to life in the water column. It is used as an indicator of water conditions in lakes and very large rivers. In the Republic of Croatia, it is monitored in 25 heavily modified and artificial lakes as well as in eight natural lakes and at five stations in the Drava and Danube rivers during a six-month growing season. Most of the phytoplankton samples are processed in the Main Water Laboratory of the Josip Juraj Strossmayer Water Institute.
The increasing influence of humans on the environment and the associated climate change make monitoring water quality more and more necessary. As classical microscopic analysis is time-consuming and requires a high level of expertise, making water monitoring expensive and limited in time and space, there is a need for new approaches such as environmental DNA analysis (genetic material extracted directly from the environment without isolating a specific organism).
In recent years, environmental DNA analysis has been intensively utilised and further developed as a new approach for monitoring biological quality components. As this approach represents a potential alternative to classical analysis, comparisons of phytoplankton communities using both methods are being carried out at the Josip Juraj Strossmayer Water Institute. The results of this research make an important contribution to the development of new methods for monitoring phytoplankton, both in the Republic of Croatia and at European level.
The research conducted at the Josip Juraj Strossmayer Water Institute shows that the classical method is much more reliable for assessing water status. However, for some other biological elements, such as phytobenthos, some European countries already officially apply environmental DNA analysis in water status assessment. In addition, it should be noted that phytoplankton in the Republic of Croatia indicates increasing eutrophication, especially in the water bodies of lakes and rivers in the Pannonian ecoregion.
