Boreal aquatic ecosystems with forested and peatland catchments naturally receive high loads of terrestrial organic matter. Moreover, catchment management of the carbon-rich soils, especially forestry operations and peat mining, may greatly add to the loading of organic humic matter into lakes. Bacteria and the microbial food chain of lakes are able to utilise the terrestrial organic carbon to some extent. Bacteria, however, are poor-quality food for the upper trophic levels. The organic matter loading also influences phytoplankton, which produce beneficial polyunsaturated fatty acids. All consumers in the food web, including humans, are dependent on these fatty acids.

On the other hand, organic matter loading often transports mercury into aquatic ecosystems, and in anoxic conditions it is easily methylated into the more toxic methyl-mercury. The approach of the TERLA consortium is multidisciplinary, combining expertise in forest sciences, limnology, biochemistry, ecotoxicology, public health and environmental law. The main objectives of the consortium are to examine 1) factors causing organic matter loading from the catchment, 2) impacts of terrestrial organic matter on lake food webs and 3) whether the food-web changes are reflected in the health condition of humans eating fish from these lakes. An important goal is also to 4) provide science-based knowledge for evaluating and improving the regulation on organic carbon loading. The multidisciplinary consortium has collected data from the same localities extending from catchment area to lakes and people fishing in these lakes. In addition, existing databases from previous studies have been applied.

In our part we have collected health information on humans eating fish from the studied lakes with low and high humic matter content. Some 70 persons participating in the study have been interviewed. Their blood samples have been analyzed for several variables including fatty acids, vitamin D and mercury. Intake of nutrients has been calculated from the FFQ data and fish eating diaries. Data analyses are going on. Final data will be compared with the epidemiological finding on these topics.

Terla is funded by the Academy of Finland.

More information: tomi-pekka.tuomainen at uef.fi, tarja.nurmi at uef.fi