Regional policies needed to tackle eutrophication in Europe`s seas
Eutrophication is a serious problem in some European seas, but each sea responds differently to excessive nutrient input from human activities. For this reason, a recent study recommends that policies to address eutrophication of marine waters should be tailored to each regional sea.
Marine waters that are enriched with excessive nutrients, particularly nitrogen and phosphorus, can experience enhanced growth of phytoplankton (algae), increased cloudiness of the water and a decreased supply of oxygen in benthic (seabed) environments from decaying phytoplankton.
However, the relationship between nutrient loading of coastal seas from human activity, such as agricultural practices, and reduced water quality from eutrophication is not simple. Regional seas are affected by many influences and as such respond differently to nutrient enrichment. The structures of the seas, feedback mechanisms, as well as other factors, including overfishing and a changing climate, all interact to create regionally specific responses to nutrient loading.
Monitoring and comparing the eutrophic state of Europe's seas is further complicated by the different indicators and assessment methods used across the continent. However, from 2012, the Marine Strategy Framework Directive1 requires all Member States to monitor eutrophication in their seas using consistent indicators and similar methods of collecting data.
As part of the EU ELME project2, researchers investigated the ecological states of four seas in Europe affected by eutrophication: the coastal North Sea, the Baltic Proper (one basin within the Baltic Sea), the Northern Adriatic Sea and the northwest shelf of the Black Sea. Three issues were identified that would have an impact on the development and implementation of eutrophication policy:
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The extent of eutrophication. The Baltic Sea exhibits the most severe signs of eutrophication, requiring urgent policy action. In the coastal North Sea, although nutrient loads are decreasing, levels are still high enough to promote phytoplankton growth, aided by favourable climatic conditions: further actions are required to reduce nutrient levels entering this sea. The Northern Adriatic appears to be recovering as a result of policies to abate nutrient loads, and although improvements have been seen in the Black Sea, this has mainly been due to the post-Soviet decline in the economy.
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Evidence of ecosystem recovery. For example, despite 20 years of nutrient abatement measures and the degeneration of communist economies, improving the eutrophication state of the Baltic Sea has been hampered by a natural feedback system which makes sedimentary nutrients available to fuel phytoplankton blooms. This could make it difficult to sustain public support for policies to reduce nutrients loads when results might not be apparent for at least 10 years.
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Other pressures on marine ecosystems. Marine ecosystems are subject to a wide range of natural and anthropogenic pressures. Separating the effects of eutrophication from those of climate shifts and overfishing is not always possible. It is hoped that monitoring programmes under the Marine Strategy Directive will help separate effects and so help policy-makers prioritise their actions.
Monitoring programmes should continue to supply long-term data to support predictive models. These are crucial for the management and control of eutrophication in marine waters. A suite of eutrophication indicators, such as suggested in the Marine Strategy Directive, together with specific information on the ecosystem features of European seas, are needed to collectively capture the variability of responses to nutrient loading across the region.
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