Ecological change in Arctic/alpine lakes – Food web effects of ongoing climate-change induced oligotrophication (ARCWEB)

Swedish Arctic/alpine lakes are undergoing drastic oligotrophication, i.e. declines in ambient nutrients (N and P) due to ongoing, climate-driven shifts in catchment processes including (1) nutrient accumulation through increases in tundra vegetation, a.k.a. “Greening of the Arctic”, (2) more efficient P and N trapping in soils, and (3) declines in atmospheric N deposition.

The concerted action of these large-scale changes has transformed northern lakes toward ultra-oligotrophic, more N-limited conditions and an increased predominance of N2-fixing cyanobacteria.

As cyanobacteria are a poor food source and potentially produce toxins, these changes in basal resources have expected, yet unknown, repercussions on invertebrate consumers and fish.We propose field and lab studies to quantify the depth distribution, cyanotoxin production, and trophic importance of cyanobacteria in mountain lakes across gradients in water nutrient concentrations and N:P ratios.

We will apply novel fatty acid-based models, compound-specific stable isotope analysis, and isotope mixing models to infer oligotrophication-induced changes in basal resources for invertebrates and fish, and the subsequent impacts on nutritional quality, growth, and trophic pathways of consumers.

ARCWEB will produce new knowledge on oligotrophication effects and develop tools (e.g. indicators of cyanobacteria dominance and food-web consequences) for assessing impacts of these effects on Arctic/alpine lakes.