Browsing by Author "Tauru, Antti"

As an almost enclosed sea, the Baltic Sea is generally defined as eutrophic, as external nutrient loading has exceeded the natural processing capacity of the system during the last 50-100 years. Nutrients have also accumulated in the sediments of the Baltic Sea. The Baltic Sea is naturally sensitive to eutrophication due to the combination of very long residence times and stratification increasing deep sea anoxia. Research questions for this systematic review are: how much have the nutrient concentrations and the trophic state of the Baltic Sea changed from the Litorina stage to the end of the pre-industrial era compared with the industrial era – year 2000, how has the nutrient status of the Baltic Sea changed between the year 2000 and the 2020´s and how do the future (modelled) scenarios of eutrophication of the Baltic Sea compare to the present state? This systematic review followed the PRISMA process. To be included in this thesis, each article found in the search had to fulfil at least one inclusion criterion without any exclusion criteria. The aim of the criteria was to find all time-unlimited original studies and necessary review articles. The databases of my thesis are Helka, Helda, Scopus, Web of Science and Google Scholar. Moreover, I included in my thesis some relevant reports from HELCOM, Finnish Environment Institute, Natural Resources Institute Finland, and Ministry of the Environment. Overall, 89 articles qualified answering at least one research question. 66 articles answered one research question. 19 articles answered two research questions 1-2 and 2-3, but none discussed the combination 1 and 3. Four articles answered all research questions. Over the millennia, hypoxia and cyanobacteria blooms took place in many parts of the Baltic Sea. As the Litorina Sea stabilized, there was more oxygen in the deep basins whilst phosphate decreased in the surface waters. At the beginning of the industrial era, nitrogen and phosphorus loads started to rise significantly. When it comes to the future scenarios of the eutrophication of the Baltic Sea, the trophic state might generally 1) decrease, 2) improve somewhat, or 3) improve to a good status in most basins. A near-pristine Baltic Sea is not reached in any of the scenarios.