Eutrophication and Hypoxia in Coastal Areas: A Global Assessment of the State of Knowledge

Eutrophication – the overenrichment of waters by nutrients – threatens and degrades many coastal ecosystems around the world. The two most acute symptoms of eutrophication are hypoxia (or oxygen depletion) and harmful algal blooms, which among other things can destroy aquatic life in affected areas.

Of the 415 areas around the world identified as experiencing some form of eutrophication, 169 are hypoxic and only 13 systems are classified as “systems in recovery.”

Mapping and research into the extent of eutrophication and its threats to human health and ecosystem services are improving, but there is still insufficient information in many regions of the world to establish the actual extent of eutrophication or identify the sources of nutrients. To develop effective policies to mitigate eutrophication, more information is required on the extent of eutrophication, the sources of nutrients, and the impact of eutrophication on ecosystems.

Recommendations

To improve knowledge of where eutrophication is occurring and its impacts, environmental agencies or coastal authorities worldwide need to proactively assess and monitor water quality, specifically those variables commonly linked to eutrophication such as nutrient levels and dissolved oxygen. In addition, internationally accepted methods and definitions for assessing and classifying eutrophic coastal waters—including proxies for eutrophication—need to be developed.

In Asia, Africa, and Latin America, environmental agencies or coastal authorities should:

1. Undertake systematic and routine assessments of coastal areas, particularly those exhibiting symptoms of eutrophication.
2. Develop transparent and public reporting procedures for tracking the occurrence of eutrophication and hypoxia, as well as monitoring their impact on ecosystem health.
3. Develop and adopt decision-support tools – such as nutrient budgets and water quality models – that can facilitate the development of appropriate local and regional responses to eutrophication.

In the United States, Europe, and Australia, environmental agencies or coastal authorities should:

1. Continue coastal zone assessments.
2. Ensure that eutrophication assessment methodologies are being consistently applied.
3. Enhance existing decision-support tools and develop tools for those areas where none currently exist.

Additional Links

This policy note is first in a series. Click below to read the other two:

• Eutrophication: Sources and Drivers of Nutrient Pollution
• Eutrophication: Policies, Action, and Strategies to Address Nutrient Pollution