EGU22-2896, updated on 27 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Impacts of anthropogenic pressures on mountain lake underwater light conditions and diatom functional groups

Sanna Atti1, Marttiina Rantala1, Andrea Lami2, Carsten Meyer-Jacob3, Jan Weckström4, John Smol3, and Liisa Nevalainen1
Sanna Atti et al.
  • 1Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, University of Helsinki, Niemenkatu 73, 15140 Lahti, Finland (
  • 2Water Research Institute (CRN IRSA), Unit Verbania, Viale Tonolli 50, 28922 Verbania (VB), Italy
  • 3Paleoecological Environmental Assessment & Research Lab (PEARL), Queen’s University, Department of Biology 116 Barrie St., Kingston, Ontario K7L 3N6, Canada
  • 4Faculty of Biological and Environmental Sciences, Ecosystems and Environment Research Programme, Environmental Change Research Unit (ECRU) and Helsinki Institute of Sustainability Science (HELSUS), University of Helsinki, Viikinkaari 1, P.O. Box 65, 00014

Solar radiation fuels primary production and carbon uptake in aquatic environments, but shorter ultraviolet radiation (UVR) wavelengths may cause adverse effects and trigger photoprotective mechanisms in organisms inhabiting lakes. In sensitive mountain lakes, ice cover and dissolved organic matter (DOM) mainly control underwater light conditions. Climate warming and other anthropogenic pressures impact the length of the ice cover period and the concentration and composition of DOM. A prolonged growing season with increased light availability may change habitat availability and drive changes in the functional group distribution of phototrophic communities. However, the roles of changing habitats and possible adverse effects of UVR as drivers of micro-algae functional group distributions have not been separated, and lake studies have thus far mainly focused on species specific sensitivities.

This study focuses on changes in underwater light conditions and UVR exposure during the past ~200 years and the impacts on functional group distributions of diatom (Bacillariophyceae) communities in two mountain lakes with different altitude and catchment size. Dated short sediment cores from each lake were analysed for elemental composition and stable isotopes of carbon and nitrogen, as well as sediment-inferred lake water total organic carbon (TOC) and chlorophyll-a. Diatoms were analysed to the species level and further divided into eco-morphological groups to investigate parallel changes in diatom functional group distributions. Geochemical proxies were used to describe trends in lake water transparency and duration of ice cover period. In addition, changes in diatom functional group distributions were analysed from the main habitat in the shallow littoral zone to detect diatom functional groups tolerances to high UVR.

Anthropogenic pressure was identified as a likely driver of sediment-inferred lakewater TOC concentration changes within the past ~200 years, suggesting changes in light conditions and UVR. Diatom functional group distributions in the lake located at higher altitude with a smaller catchment showed an increase of planktic life-forms within the past ~100 year, which may be related to shortening of the ice cover period. Earlier studies have shown trade-offs between motility and photoprotective capacity, but in this study clear differences between occurrences of motile or non-motile functional groups in the shallow littoral zone were not found. Based on these results, further research with broader habitat sampling is needed to separate the roles of habitat availability and UVR, and their roles affecting the distribution of diatom functional groups.

How to cite: Atti, S., Rantala, M., Lami, A., Meyer-Jacob, C., Weckström, J., Smol, J., and Nevalainen, L.: Impacts of anthropogenic pressures on mountain lake underwater light conditions and diatom functional groups, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2896,, 2022.