An in-depth look at Iron in boreal streams

In boreal catchments, iron has a key role in biogeochemical and ecological contexts, and at the same time has many harmful impacts on aquatic organisms and ecosystems. Recent studies indicate that iron concentrations are increasing in boreal freshwaters, with the potential negative effects this can have on water ecology.

Finnish researchers have now explored the many aspects of iron in boreal waters, in a paper that will be published in 2022 in the journal Science of the Total Environment. The researchers have looked at this topic in a broad way, including perspectives of biogeochemistry, hydrology, ecology, and river basin management.

Jääli Stream in winter. The catchment is heavily drained, and the high iron contents are clearly visible. Photo: Markus Saari.

The authors express that land use management in boreal catchments should take into account the harmful effects of iron. Typical iron storage sites are peatlands, other wetlands and naturally moist areas, groundwater seepage areas and springs, stagnant water areas, and riparian zones, and the authors stress that activities in such areas are likely to contribute to higher levels of iron mobilization in downstream water bodies.

Based on their survey, they advice that water protection and management programs should aim to (i) prevent iron mobilization from soil layers by avoiding unnecessary land-use activities and minimizing soil disturbance in high-risk areas; (ii) disconnect iron-rich ground water discharge from directly reaching watercourses; and (iii) decrease transport of iron to watercourses by applying efficient water pollution control approaches. These approaches may require specific methods that should be given attention depending on catchment conditions.

Moreover, the researchers highlight the needs for additional research on boreal catchments. A key issue is to increase the understanding of the role of iron in the utilization of organic material in riverine food webs, which are typically highly heterotrophic. More knowledge is needed on the metabolic and behavioral resistance mechanisms that aquatic organisms, such as algae, invertebrates, and fish, have developed to counter the harmful impacts of iron in rivers with naturally high concentrations of both iron and organic matter.

Iron rich water is surfacing from a spring the catchment of River Kiiminkijoki. Photo: Markus Saari.

It is also emphasized that to fulfil the needs presented above, as well as to develop effective methods for decreasing the harmful impacts of iron in water management, the biogeochemical processes contributing to Fe transport from catchments via rivers to estuaries should be better understood.

Heikkinen, K., M. Saari, J. Heino, A.-K. Ronkanen, P. Kortelainen, S. Joensuu, A. Vilmi, S.-M. Karjalainen, S. Hellsten, M. Visuri, H. Marttila, 2022. Iron in boreal river catchments: Biogeochemical, ecological and management implications. Sci. Tot. Environ. 805 https://doi.org/10.1016/j.scitotenv.2021.150256

Feature photo: From Kalimenjoki, which is the main reach of the Jääli. In summer, the iron colours the stream water redish brown – or as the photographer says – it looks like your morning coffee! Photo: Markus Saari.