During the latest decades, there have been indications that the limiting nutrient are changeable in the Bothnian Sea. The current national regulations for wastewater treatment plants which have coastland towards the Gulf of Bothnia have no regulations regarding nitrogen purification, as these basins traditionally has been seen to have phosphorus-limited conditions. The aim of this study was to investigate how the temporal change of phosphorus and nitrogen has developed during the years 1991-2021 in the Bothnian Sea and if there were any differences between coastal and offshore stations. The ultimate goal was to give an overview of the nutrient situation and develop a guideline whether the current regulations for wastewater treatment plants are sufficient. Three coastal and two offshore stations were studied at the depth 0-10 m by investigating data from national monitoring programs, using trend analysis and comparison of means. The result showed that phosphorus is increasing in all the sampling stations. Consequently, the limited nutrient has evolved towards being more nitrogen-limited. The nitrogen load has instead been larger at the coastal compared to the offshore stations, especially for locations affected by river inlets. However, the conclusion according to this study is that the current regulations are sufficiently. This is due to the more recent shift towards nitrogen-limited conditions at the stations affected by river inlets and the high contribution with phosphorus-rich water from the Baltic Proper, as at the same time wastewater treatment plants is not the greatest contributor to the nitrogen load in the Bothnian Sea.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:umu-196752 |
| Date | January 2022 |
| Creators | Johansson, Nadja |
| Publisher | Umeå universitet, Institutionen för ekologi, miljö och geovetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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