Dissertation: The effects of sulfate on Finnish salmonid fish (Mäkinen)
Sulfate is a naturally present anion in aquatic environments formed by sulfur and oxygen. The natural background level of sulfate in Finnish surface waters is low, averaging only 4 mg/L. Mining operations, land usage and industry produce diffuse and point sources of sulfate pollution increasing the sulfate levels even hundreds of times higher than natural background.
Mikko Mäkinen experimentally examined in his doctoral dissertation the effects of short-term sulfate exposure on fertilization success and sperm motility in salmonids, as well as the effects of long-term exposure on embryonic development up to the juvenile stage. The salmonid species used in the research came from both freshwater and brackish water habitats. The sulfate concentrations used in the experiments corresponded to potentially elevated levels resulting from pollution that fish might encounter under natural conditions.
- The reproduction of freshwater-spawning whitefish species was clearly more sensitive to disturbance than that of Baltic Sea coastal and migratory whitefish, summarizes. Doctoral Researcher Mikko Mäkinen from the Ģֱ.
The most sensitive stage in development in terms of sulfate’s harmful effects was fertilization and early embryonic development. The most sensitive species in the study proved to be the freshwater-spawning vendace, for which the lowest calculated harmful concentration during long-term exposure was 335 mg/L. However, compared to other aquatic organisms, the fish tolerated sulfate relatively well.
Research provides new information to support water protection
For the first time, the doctoral research examined the sulfate tolerance of Finnish fish species and produced essential and highly timely background information for water protection needs. The results have been used in the preparation of species sensitivity distributions for both freshwater and brackish water organisms. Based on these distributions, safe threshold levels for sulfate emissions can be defined for aquatic life.
- The results presented in the thesis are important in regards of species conservation and have been used in creation of species sensitivity distributions for freshwater and brackish water environments. Based on the species sensitivity distributions limits for sulfate effluents can be derived which are protective for aquatic life, explains Mäkinen.
Mikko Mäkinen graduated 2020 as Master of Science from the Department of Biology and Environmental Science in Ģֱ and he started the PhD studies in 2021. Supervisor of the thesis was professor Juha Karjalainen and the funding for it was received from Ģֱ and from the collaborators in industry.
Mikko Mäkinen defends their doctoral dissertation "High sulfate concentration endangers reproduction and early development of salmonids” on Friday 29.8.2025 at 12 o’clock in Ylistönrinne auditorium YAA303. The opponent is professor Katja Anttila (University of Turku) and custos professor Juha Karjalainen (Ģֱ). The dissertation language is Finnish.
The dissertation “High sulfate concentration endangers reproduction and early development of salmonids” will be available in the JYX publication archive:
