07 Jul 2014

Water quality targets for European lakes: defining the threshold for ecological shifts

Water quality targets for European lakes: defining the threshold for ecological shifts

© EU G.Free

A recent JRC co-authored paper provides ecological water quality targets for lakes in Europe. The study provides an ecology-based definition for the "good" status of lake waters, based on criteria including the low probability of occurrence of cyanobacteria (blue-green algae) blooms, the low probability of a significant decline in macrophytes (aquatic plants that provide oxygen, cover and food for fish), and clear water. Since eutrophication is the most important pressure and one of the main causes of the less than ‘good’ ecological status of 44% of European lakes, the scientists established target values for chlorophyll a, which is a metric widely used to measure the impact of eutrophication in lakes. To determine these values for the two most common lake types in lowland Central Europe, they collected data from more than 400 lakes (some of which were sampled over several years) from nine Central European countries. They defined the ‘good-moderate’ status boundaries of chlorophyll a for moderately deep lakes (mean depth 3-15 m) and for shallow lakes (mean depth below 3 m) in Central Europe, based on ecological concepts and evaluation of risks of human impact. They recommend that this approach could be more widely used for other water body types and for biomonitoring schemes in other types of ecosystems.

Mainly caused by the presence in the water of substances such as nitrates and phosphates from fertilisers or sewage, eutrophication has severe consequences on the environment and water supply. Its effects include a great increase of phytoplankton in response to increased levels of nutrients and a depletion of oxygen in the water, causing a reduction in specific fish and other animals or an increase in population that negatively affects other species.

 

Background

The European Water Framework Directive commits European Union Member States to achieve "good ecological status" for all waters by 2015. The definition of ‘good status’ is therefore a critical step to establishing river basin management plans while avoiding possible variations of interpretation.

Human impact on lakes degrades their ecological status. Eutrophication is the enrichment of an ecosystem with chemical nutrients – such as nitrogen and phosphorus – through fertilizers or sewage, which drives excessive growth of algae. It is one of the main causes of impairment of freshwater ecosystems and the main culprit for the ecological deterioration of 44% of European lakes. The effects of eutrophication include a great increase of phytoplankton in response to increased levels of nutrients and a depletion of oxygen in the water, causing a reduction in certain fish and other animals or an increase in population that negatively affects other species.

JRC Institutes