DON-HYPO

The role of dissolved organic nitrogen (DON) on the development and extend of eutrophication-driven hypoxia and responses to global warming

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 Obiettivo del progetto (Objective)

'Coastal hypoxia is a mounting problem worldwide that has been recognised as a major threat to marine coastal biota. The decline in dissolved oxygen can affect ecosystems structure and functioning. Managerial efforts to prevent hypoxia and recover ecosystems that have already been affected by hypoxia are largely based on nutrient reduction plans. Most nutrient reduction plans are focused on the reduction of the inorganic fraction of the nutrient loadings, particularly in reductions of nitrate and phosphate inputs. However, the concentration of dissolved organic nitrogen (DON) frequently exceeds that of dissolved inorganic nitrogen (DIN) in both marine and freshwaters. Recent studies indicate that many components of the DON pool can play an active role in supplying, directly or indirectly, nitrogen nutrition to phytoplankton and bacteria and may affect community metabolic rates and species composition of the ambient microbial assemblage. Elucidate the role of DON in the development and extend of eutrophication-driven hypoxia is essential to set successful management strategies in order to reduce hypoxia development and recover ecosystems experiencing hypoxia at present, to better protect marine biodiversity. The main goal of this project is to evaluate the role of DON in planktonic and bacterial community metabolic rates, and on oxygen dynamics in the Baltic Sea, the largest coastal area suffering from eutrophication-driven hypoxia. The project also aims to evaluate the effects of global warming in the interaction between DON inputs, metabolic rates and oxygen dynamics. Predictions on effects of global warming and eutrophication in dissolved oxygen dynamics in near and far future are needed to elucidate the consequences of the lack of oxygen on biodiversity and ecosystems structure and functioning. The results of this project could help better protect marine ecosystems, preserve biodiversity and set successful management targets for coastal waters.'

Introduzione (Teaser)

Coastal hypoxia, whereby coastal waters experience a reduction in oxygen content, is a growing problem around the world. The decline in dissolved oxygen can threaten sea life and affect the structure and functioning of coastal ecosystems.

Descrizione progetto (Article)

Attempts to control hypoxia usually centre on reducing the level of inorganic nutrients, especially nitrate and phosphate, entering the marine environment. However, the concentration of dissolved organic nitrogen (DON) often exceeds that of dissolved inorganic nitrogen in both marine and freshwater.

The aim of the DON-HYPO project was to determine the role of DON in the metabolic rates of plankton and bacteria in the Baltic Sea. The Baltic is the largest coastal area to suffer from hypoxia due to eutrophication caused by excessive nutrients entering the mostly enclosed sea.

Researchers also determined the DON content of a coastal station in the Baltic Sea and analysed DON inputs from different sources. The sources included municipal wastewater treatment effluent, atmospheric deposition and three Swedish rivers representative of different land-use patterns.

Results supported the hypothesis that warming of the Baltic Sea through climate change will increase plankton respiration rates faster than plankton primary production. This may lead to a depletion in oxygen levels, further increasing hypoxia in the Baltic Sea.

In addition, DON inputs were found to work together with temperature to further increase respiration in response to global warming. It was also shown that nutrient reduction plans should also include the organ fraction of the nutrients, specifically DON, and take into account the synergistic effects of warming.

DON-HYPO will help to explain the effects of global warming and eutrophication on dissolved oxygen levels in the near and distant future on biodiversity and ecosystems. The project's results will therefore help to better protect marine ecosystems, conserve biodiversity and set successful management targets for coastal waters.

Results will be published in peer-reviewed scientific journals and press releases. The project will inform the public and policymakers about the importance of taking into account the organic fraction of nutrients when developing nutrient reduction plans. The plans will help to reduce eutrophication-driven hypoxia in coastal areas, particularly in the Baltic Sea.