A doctoral dissertation completed at the University of Jyväskylä (Finland) investigated the effects of increased sulfate concentrations on various aquatic species in boreal freshwater and northern coastal Baltic Sea. The study is especially unique because the effects of enhanced sulphate concentration on Baltic Sea species were previously unknown. New information provides scientific evidence for deriving safe sulfate concentrations in natural waters to regulate sulfate discharges and protect aquatic life.
Sulfate is a natural major ion that is generally considered as benign, but an enhanced sulphate concentrations can be harmful to aquatic life. Anthropogenic activities, such as agriculture, forestry and mining, have caused an alarming rise in sulfate concentrations in rivers, lakes and the sea. Recently, prolific industrial and mining activities in Finland have increased the potential to discharge high sulfate loads to aquatic ecosystems. Thus, research was needed to examine the effects of increased sulphate concentrations on various freshwater and brackish water species.
Determining safe sulfate concentrations in natural waters provides information to decision-making
In her doctoral dissertation, Xiaoxuan Hu examined experimentally how sensitive various aquatic species were to enhanced sulfate concentrations and conducted a multi-species modeling (Species Sensitivity Distribution) to derive predicted no effect concentrations for sulfate in boreal freshwater and in the coastal Baltic Sea brackish systems. Test species included altogether 15 freshwater and 13 brackish water species, e.g. European whitefish, freshwater pearl mussel, common water moss and water louse.
- Given the rising sulfate discharges from anthropogenic sources, scientific data on harmful effects of increased sulphate concentrations to aquatic life were urgently needed. Our research provided such scientific evidence, which would be needed in the development of safe threshold concentrations for sulfate in aquatic ecosystems, comments the Doctoral Researcher Xiaoxuan Hu from the University of Jyväskylä.
In Finland, freshwater is generally soft, where aquatic life tends to be more sensitive to increased sulfate than that in hard water. Thus, sulfate concentration regulations for Finnish soft waters are particularly important for protecting the aquatic ecosystems. Previously, it was not known how sensitive Baltic Sea brackish water species were to increased sulfate concentrations.
Data supports sulfate regulations in the Baltic Sea
This is the first time that sulfate toxicity to multiple brackish species was examined, and the findings would help the authorities sulfate-containing wastewater loads in northern coastal Baltic Sea areas. The research was conducted in close collaboration with the Finnish Environment Institute (SYKE).
- The most sensitive Baltic Sea species tested were the common water moss and the European whitefish, whose distributions are limited to the less saline part of the coastal Baltic Sea. Given the natural increasing salinity and background sulfate concentrations southward in the Baltic Sea, sulfate limits set by the authorities may need to vary depending on the location of the target areas to be protected, say Hu.
Xiaoxuan Hu graduated in 2022 as Master of Science from the Department of Biology and Environmental Science in the University of Jyväskylä. She started her PhD studies in 2023. The supervisors of the doctoral thesis are professor Juha Karjalainen and professor Katja Räsänen. Funding came from the University of Jyväskylä and industry collaborators.
Xiaoxuan Hu will defend her doctoral dissertation “Sulfate sensitivity of boreal freshwater and coastal Baltic Sea biota: an ecotoxicological risk assessment across multiple taxa” on Friday 10.10.2025 at 12 o’clock in Ylistönrinne auditorium YAA303. The opponent is research professor Laura Uusitalo (Natural Resources Institute Finland, LUKE) and custos professor Juha Karjalainen (University of Jyväskylä). The dissertation language is English.
Live streaming of the public examination can be found on Moniviestin: https://r.jyu.fi/dissertation-hu-101025
The dissertation “Sulfate sensitivity of boreal freshwater and coastal Baltic Sea biota: an ecotoxicological risk assessment across multiple taxa” is available in the JYX publication archive: https://urn.fi/URN:ISBN:978-952-86-0984-1