How do people influence the quality of lakes?

How do people influence the quality of lakes?

Tue May 23 16:16:35 CEST 2017

Scientists have reviewed the ecological status of lakes across Europe. A total of 556 lakes in 10 European countries were analysed in more than three-year research by hydrobiologists from the Biology Centre of the CAS along with their foreign colleagues. They have found that fish communities in the lakes are affected by many stressors that human activity has caused, e.g., water pollution by sewage substances or coastal modifications. In order to evaluate the level of the influence of each of the lakes and compare them across the continent, scientists created a common database and a new benchmarking tool, the total anthropogenic pressure intensity index – TAPI.

One of the most important stressors that has an impact on the ecological quality of Europe’s lakes is the excessive supply of nutrients, which is caused mainly by intensive agricultural production and sewage waters from settlements. Other stressors that heavily burden a lake include changes in the hydromorphological parameters, such as coastal modifications or fluctuations of the water level, and the intensity of the usage of lakes, especially recreational. “In our study, we investigated how fish stocks are affected by these major stressors. The combination of stressors has always had a stronger impact on fish indicators than when we tested the stressors individually,” says Petr Blabolil, research employee of the Institute of Hydrobiology of the Biology Centre of the CAS.

Precisely this combination of stressors has been used by scientists to produce the total anthropogenic pressure intensity index – TAPI. This has become a suitable alternative for biological indexes that are often difficult to compare at the international level. This makes it possible to evaluate the intensity of stressors on individual lakes and to unify environmental quality across the continent.

The results of the analyses from the examined European lakes were not very pleasing however. “Unfortunately, the ecological status of fish stocks in EU countries is often worse than we would wish and what is required by the Water Framework Directive,” assessed Jan Kubečka, Director of the Institute of Hydrobiology of the Biology Centre of the CAS. The lakes in Germany and Estonia are probably the best, with Denmark, Lithuania, the Netherlands and the Czech Republic on the opposite side of the scale. These are the consequences of the activities of society; in countries with a high population density, lakes are under greater pressure caused by stressors than in less populated ones. The second aspect is the behaviour of people; In some countries, water is perceived as a key ancestral heritage, which must be cared for in order to serve our descendants as well. In this point, the Czechs still have reserves.

In the Czech Republic, scientists conducted analyses at 23 artificial lakes, more precisely dam reservoirs, from all parts of the country. The best evaluations were given to the reservoirs in the former military area Brdy (today the protected landscape area of the same name) as well as the Šumava reservoir Nýrsko and Fláje in the Ore Mountains. Quality fish communities are also formed in the so-called mine lakes in Northwest Bohemia, which were created by flooding of surface brown-coal mines. Perhaps the most investigated Czech reservoir is the Roman dam in the České Budějovice district, which supplies the drinking water of South Bohemia. The hydrobiologists of České Budějovice have constantly monitored this dam for more than forty years already. During this time, there have been a number of historical events, including changes in fish tracking. Already since 1999, a single monitoring of the networks corresponding to the European standard has been introduced, and the evaluation of these data has shown progressive improvements in ecological quality.

Prepared by: Biology Centre of the CAS
Photo: Biology Centre of the CAS