Climate-induced shifts in food webs of Arctic/alpine lakes (Master)

This master project links to the FORMAS-funded ARCWEB project that aims at understanding climate-driven biodiversity and food web changes in Swedish Arctic/alpine lakes.

Using an experimental approach, the project will address (1) how changes in water N/P ratio affect the taxonomic and biochemical composition of benthic algal biofilms and(2) how this affects the transfer of nutrients and energy to grazers at higher trophic levels, as well as their growth.

Why is this project important?

Arctic freshwaters are under increasing stress, as warming of Arctic regions is twice as high as the global average. As a consequence of this, Swedish Arctic/alpine lakes have undergone major decline in nutrient concentrations since the mid-1990s. Phosphorus (P) concentrations have declined by up to 50%, while nitrogen (N) concentrations are low and slowly declining. The underlying climate-induced processes that govern these changes include the increase in terrestrial vegetation, the trapping of nutrients in soils, and low and declining atmospheric N-deposition. Changes in these processes impact on the growth and assemblage composition of algae, which form the base of aquatic food webs.

Primary production in Arctic/alpine lakes is predominated by benthic (bottom-living) algae, with assemblages dominated by diatoms, cyanobacteria, and green algae. Due to high water transparency in these lakes, photosynthesis can occur at depths >20 m. Benthic algal assemblages are highly sensitive to environmental shifts in ambient nutrient concentrations. Such shifts will have both quantitative (biomass) and qualitative (taxonomic/biochemical) impacts on algal assemblages, and strong repercussions on higher trophic levels.

We hypothesize that the ongoing oligotrophication of Arctic/alpine lakes will favor cyanobacteria over diatoms and green algae (see figure). As cyanobacteria lack highly unsaturated fatty acids that are vital for the growth and reproduction of invertebrate grazers, we expect that such a shift will result in lower growth and reproduction of invertebrates (and ultimately fish).

Project details

The hypotheses outlined above will be tested in a laboratory experiment in which we will grow algal assemblages on tiles under different nutrient conditions (see figure). We expect that this will give assemblages with a gradual shift from diatoms to cyanobacteria. We will then introduce invertebrate grazers into the experimental units and measure their growth and development.

You will be working in a research group with senior researchers and a postdoc. You will learn to handle experimental units, do measurements on the alga and grazers, and prepare samples for stable isotope and/or fatty acid analysis. We expect that the results from this project will be of sufficiently high quality that they can be published in a high-ranked scientific journal (with you as a co-author).

Facts

• Main subject area: Biology or Environmental Science
• Level: Advanced (Master)
• Length: 30 credits/20 weeks
• Language for written report: English.
• Location: Department of Aquatic Sciences and Assessment, Ultuna
• Start date: Tbd