Wilhelm Granéli

Wilhelm Granéli

Professor emeritus

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My research focus is on “brownification” (browning) of streams, lakes and coastal waters. Many fresh waters, but also brackish coastal waters, are more or less strongly brown colored by terrestrial humic matter, both in temperate and tropical climate zones. During the last few decades there has been a marked increase in this coloring of surface waters in northern Europe and North America. Since brownification causes a deterioration of the light climate and adds organic matter that is the substrate for bacteria, it is a process that has profound effects on aquatic ecosystems, including ecosystem services as recreation, fishing and drinking-water supply. In a multidisciplinary project we are trying to find the cause of brownification and its effect on aquatic ecosystems. We use paleolimnology to reconstruct past water color as well as catchment vegetation, for lakes in S Sweden. In field experiments the effects of acid deposition (SO4) on soil water color has been studied.

Through comparison of lakes in a color gradient and experimental studies we have investigated effects from brownification on lake thermal stratification, light climate and phytoplankton species composition and the balance between production and respiration.

I have also been studying freshwater crayfish ecology, especially population development and production of the introduced North American signal crayfish (Pacifastacus leniusculus). Populations show more or less dramatic fluctuations, but the underlying mechanism is still unknown. Temperature during critical phases in the life cycle may be an explanation. We have used modeling and long-term catch data to test this hypothesis.

Additional interest is the Baltic Sea: how should eutrophication be combated? Which nutrient should be reduced and can lake-type restoration approaches, e. g. mixing/aeration, chemical sediment treatment and fish manipulation be used?

Earlier in my limnological life I studied sediment respiration, e. g. effects of bioturbation and temperature, and the exchange of nutrients between sediment and water. I have also worked with reed, Phragmites australis, its ecology and possibilities to use reed as a biofuel.

I am examiner for the PhD-program in Limnology and Marine Ecology and serve as teacher on undergraduate courses in aquatic ecology.


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