Oxygen depletion in aquatic ecosystems

As well as being detrimental to life in an aquatic ecosystem, increases in hypoxia also affect the wider environment. Under hypoxic conditions, substantial losses in biodiversity, ecosystem function, and services such as fisheries, aquaculture and tourism can occur and additional greenhouse gases may be released from the ocean seafloor.

The EU-funded HYPOX project took the first steps towards implementation of a global observation system for better understanding oxygen changes in aquatic systems. Researchers monitored oxygen depletion and associated processes in target areas, which differed in oxygen status and sensitivity to change. They included the deep Arctic Ocean, the semi-enclosed waters of the Black and Baltic Seas, fjords, and lagoons and land-locked lakes.

In order to maximise the knowledge generated by HYPOX, partners deployed a variety of reliable long-term sensors on different platforms for in situ monitoring of oxygen depletion and associated parameters. Targeted field campaigns were conducted to investigate the environmental impacts of hypoxia.

These impacts included the effect of hypoxia on the distribution of seafloor organisms as well as on biological and chemical processes involved in the large-scale cycling of elements. The consortium also adopted and refined numerical tools for predicting hypoxia and for separating natural variability from man-made changes.

Existing long-term monitoring data was also analysed to better understand the history of a water body's oxygenation status. Core samples were taken from the seabed of the Black Sea, as well as lagoons and lakes. These enabled scientists to examine the past, since a record of earlier biological and chemical conditions are preserved in the sediment.

Project results and modelling expertise will serve as a basis for accurate forecasts of oxygen depletion. This in turn will contribute to the planning of appropriately tailored climate change adaptation methods. Studies of previously eutrophied systems, such as the Swiss lakes, show how a reduction in nutrients from human activities can help alleviate the problem of oxygen depletion.

HYPOX has provided European policy and decision makers with the necessary knowledge of oxygen depletion in aquatic systems. This enables them to develop effective sustainable development strategies and negotiate internationally binding treaties.