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

Background of the ARCWEB-project

Swedish Arctic/alpine lakes are undergoing drastic oligotrophication, i.e. declines in ambient nutrients (nitrogen (N) and phosphorus (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 N and P trapping in soils, and
3. declines in atmospheric N deposition.

The concerted action of these large-scale changes has transformed the clear-water, nutrient-poor northern lakes toward ultra-oligotrophic, more N-limited conditions that affect the benthic algal communities, which predominate primary production and form the base of food webs in these lakes. The benthic algal communities are expected to shift toward an increased predominance of N2-fixing cyanobacteria upon oligotrophication. 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.  

The ARCWEB-project objectives

Objectives of ARCWEB are to:

• quantify the among-lake and depth-related differences in benthic algal assemblages and abundance of N₂-fixing and toxin-producing benthic cyanobacteria in Arctic/alpine lakes along gradients in lake nutrients and N:P ratios
• identify the tipping point at which benthic algae shift from diatoms-dominance to cyanobacteria-dominance upon oligotrophication
• assess the impacts of increasing cyanobacteria dominance on the nutritional quality of resource base and the trophic-transfer efficiency in benthic food-web pathways
• quantify the extent to which fish growth and trophic reliance on benthic prey are altered by increasing cyanobacteria dominance
• test whether lake water N:P ratios are adequate indicators for ecological changes of Arctic/alpine lakes upon oligotrophication

Implementation of ARCWEB

ARCWEB will use a combination of field and lab studies to quantify the depth distribution, cyanotoxin production, and trophic importance of cyanobacteria in Swedish Arctic/alpine lakes across gradients in water nutrient concentrations and N:P ratios. Novel fatty acid-based models, compound-specific stable isotope analysis, and isotope mixing models will be used to infer oligotrophication-induced changes in basal resources for invertebrates and fish, and the subsequent impacts on biochemical 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.

Participants from SLU

Danny CP Lau

Willem Goedkoop

Kerstin Holmgren

External partners

Ann-Kristin Bergström, Umeå University, Sweden

Kirsten Christoffersen, University of Copenhagen, Denmark

Martin Kainz, WasserCluster Lunz, Austria

Funder

ARCWEB is funded by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS).