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Nutrients and eutrophication in the Gulf of Bothnia

Research project Historically, phosphorus has been pointed out as the limiting nutrient in large parts of the Gulf of Bothnia. However, recent data indicate elevated phosphorus concentrations and increasing nitrogen limitation. This project addresses how the nutrient concentrations vary over time and space and how the phytoplankton composition changes with varying environmental conditions.

Head of project

Project overview

Project period:

2022-03-01 2024-02-29

Participating departments and units at Umeå University

Department of Ecology and Environmental Science, Umeå Marine Sciences Centre (UMF)

Research area

Marine science

External funding

Swedish Environmental Protection Agency

Project description

Assessment of the eutrophication status in the Gulf of Bothnia is difficult due to limited knowledge of the nutrient conditions and the phytoplankton responses to changes in the environment. Historically, phosphorus has been pointed out as the limiting nutrient in large parts of the Gulf of Bothnia. Recent data indicate elevated phosphorus concentrations, and that nitrogen limitation increases. Application of the present EU WFD system often provides contrasting status classification in the Gulf of Bothnia. Thus, there is a great need to investigate how the nutrient concentrations vary over time and space and how the phytoplankton composition changes with varying environmental conditions.

Within the project the nutrient dynamics and effects of anthropogenic activity on limiting nutrient and eutrophication in the Gulf of Bothnia are elucidated.

Specifically we address the following questions:

  • What nutrient is limiting primary production in the Gulf of Bothnia? – Spatial and temporal variation
  • How to best assess eutrophication in the Gulf of Bothnia?
  • How does reduction of nutrient load affect nutrient concentrations and stoichiometry in coastal areas?
  • How does nutrient exchange between the Baltic Proper and the Bothnian Sea, and between the Bothnian Sea and the Bothnian Bay affect the nutrient concentrations and stoichiometry?

Information in published reports and scientific papers is analyzed, and data from monitoring and recipient control programs (SRK) is compiled. We also include data from various research projects in the syntheses. The project is performed in close collaboration with Kustgrupp Nord, representing all County Administrative Boards along the Gulf of Bothnia. The results are usable in achieving efficient marine management.

Publications

Here we list the publications produced within the project.

Master thesis
Limiting substance in the Bothnian Sea: A changing marine system

Nadja Johansson

In her work, Nadja has investigated the nutrient situation on coastal and offshore stations in the Bothnian Sea during the period 1991-2021 with extra focus on the development of limiting substances for phytoplankton production. The results show that phosphorus has increased at all stations included in the study and that the environment has changed from phosphorus-limited to nitrogen-limited. Despite the changed situation, Nadja believes that current legislation is sufficient where nitrogen is not considered to need to be removed in water treatment plants in the Bothnian Sea. This is because the shift to a nitrogen-restricted environment is relatively recent and that the higher phosphorus levels are estimated to be due to the supply of phosphorus from the Baltic Proper. Furthermore, wastewater treatment plants contribute a relatively small part of the nitrogen concentrations to the coastal water, particularly in northern Sweden.

Link to the report in DIVA

External funding