Baltic Sea Centre’s eutrophication model can provide knowledge about greenhouse gases – Stockholm University Baltic Sea Centre

The BALTSEM Model: Studying the Effects of Nutrient Inputs to the Baltic Sea

The BALTSEM model is a well-used tool for studying the effects of nutrient inputs to the Baltic Sea and has been used in the HELCOM Baltic Sea Action Plan. The modelling tool has now been further developed to include methane fluxes, which can provide important knowledge about the climate impact of the Baltic Sea.

Photo: Johan Bjurer/Mostphotos

Evaluating Methane Dynamics in the Baltic Sea

Emissions of methane from the Baltic Sea to the atmosphere can be significant and make the sea a net source of greenhouse gases. However, measurements of methane in the Baltic Sea region are still relatively few and limited to certain areas. Modelling can be an important tool to understand the large-scale fluxes and help to reduce the knowledge gaps, says researcher Erik Gustafsson, Stockholm University Baltic Sea Centre, who is the lead author of a new study on methane dynamics in the Baltic Sea.

The BALTSEM Model and its Development

The BALTSEM model was developed by researchers at the Baltic Sea Centre, among others, and has proved to be able to reproduce the nutrient dynamics in the Baltic Sea. The model has been used within the Baltic Sea co-operation HELCOM for calculations of how much the nutrient supply must be reduced in order to achieve the goal of a Baltic Sea unaffected by eutrophication, as well as in various research studies.

Oceanographer Erik Gustafsson, Stockholm University Baltic Sea centre. Photo: Niclas Björling

The New BALTSEM-CH4 Model

Erik Gustafsson and his colleagues in CoastClim, a collaboration between the Universities of Stockholm and Helsinki, have now developed the model to get a picture of the extent of methane fluxes between the Baltic Sea’s sediments, water, and air. The new BALTSEM-CH4 model includes methane of different flavors, known as isotopes. The composition of isotopes is affected by processes that take place when methane is formed and decomposed. The isotope composition therefore becomes a kind of fingerprint, which can provide a guide to how much different processes contribute to methane dynamics, explains Erik Gustafsson.

Methane Leaks from the Sediments

The model calculations show that the methane supply to the Baltic Sea is largely dominated by methane formed by decomposition processes in oxygen-free sediments and then leaking into the water above. The total amount of methane produced in the Baltic Sea each year is just over 120,000 tonnes, according to the modeling, which should be regarded as a first rough estimate. A small portion is also transported to the sea by the rivers. Most of the methane is oxidized in the water and converted to carbon dioxide and water. About 16,000 tonnes are released into the atmosphere, says Erik Gustafsson. Even if the emission to the atmosphere is small in relation to production, it can be significant for the climate, as methane is a powerful greenhouse gas. Calculated as carbon dioxide equivalents, the methane emissions amount to just under 450,000 tonnes in a 100-year perspective or just under 1.3 million tonnes in a 20-year perspective, according to the latest conversion table from the Intergovernmental Panel on Climate Change (IPCC). It is becoming increasingly urgent to reduce greenhouse gas emissions to limit global warming. It is therefore important to increase the knowledge about methane emissions, including those from natural environments, and to try to limit them, says Erik Gustafsson.

‘Hotspots’ Can Make Important Contributions

The BALTSEM-CH4 model includes the entire Baltic Sea, but due to the coarse resolution, the calculations are not fully representative of shallow areas near the coast, explains Erik Gustafsson. At the same time, these areas are probably the most important in terms of how much methane reaches the atmosphere. Emissions to the atmosphere are probably greater than these calculations indicate. In shallow coastal areas, methane concentrations have been measured at much higher levels than in the open Baltic Sea. It is not yet known how important such local ‘hotspots’ for methane formation are, compared to the low emissions from large areas.

The study is probably the first to include methane isotopes in a physical-biogeochemical model. The goal of the CoastClim researchers is now to conduct more measurements in different types of coastal areas and then develop the model further. This study is a first step to assess methane emissions from the Baltic Sea, but more studies from coastal areas are needed to get a more comprehensive picture, concludes Erik Gustafsson.

Read the publication in Geoscientific Model Development:

Methane dynamics in the Baltic Sea: investigating concentration, flux and isotopic composition patterns using the coupled physical-biogeochemical model BALTSEM-CH4 v1.0

Text: Lisa Bergqvist

SDGs, Targets, and Indicators

1. SDG 13: Climate Action

   • Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
   • Target 13.3: Improve education, awareness-raising, and human and institutional capacity on climate change mitigation, adaptation, impact reduction, and early warning.
   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.

   The article discusses the climate impact of methane emissions from the Baltic Sea. Methane is a powerful greenhouse gas, contributing to climate change. By studying methane dynamics in the Baltic Sea, researchers aim to increase knowledge about methane emissions and try to limit them, aligning with the goals of SDG 13.

2. SDG 14: Life Below Water

   • Target 14.1: By 2025, prevent and significantly reduce marine pollution of all kinds, particularly from land-based activities, including marine debris and nutrient pollution.
   • Target 14.7: By 2030, increase the economic benefits to small island developing states and least developed countries from the sustainable use of marine resources, including through sustainable management of fisheries, aquaculture, and tourism.

   The article mentions that the BALTSEM model has been used to study nutrient dynamics in the Baltic Sea. Nutrient pollution is a form of marine pollution that can lead to eutrophication. By understanding nutrient inputs and their effects on the Baltic Sea, researchers can contribute to the prevention and reduction of marine pollution, aligning with SDG 14.

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