Assessing the Factors That Alter Ecological Responses of Cold, Oligotrophic Lakes to Nutrient Subsidies

Arctic and alpine areas experience rapid environmental changes that are altering nutrient delivery to lakes. I review the current state of lake ecosystem subsidization research and summarize Arctic and alpine lake subsidies, their ecological importance, and ways they are changing. I identify current knowledge gaps in Arctic and alpine lake subsidization research and highlight the importance of Arctic and alpine lakes for ecosystem subsidy research. Meltwater from the Greenland Ice Sheet (GrIS) exports sediment and nutrients to lakes, but the ecological effects of this subsidy remain unclear. To assess the effects, four glacially fed (GF) lakes that receive GrIS meltwater were compared to snow and groundwater fed (SF) lakes. Total phosphorus (TP) was six times higher in GF lakes compared to SF lakes, but biological and chemical assays called into question its bioavailability. GF lakes had higher algal biomass, which may be due to moderately higher DIN in GF lakes compared to SF lakes. Increased nitrogen (N) deposition rates over the past century have affected North American and European alpine lakes by shifting nutrient limitation status and increasing algal biomass. I evaluated predictors of alpine and subalpine lake sensitivity across North American and European mountain ranges. North American lakes were more sensitive to N deposition than European lakes. Local-scale analyses revealed distinction of lake sensitivity controls, such as land cover, bedrock geology, maximum lake depth, and elevation. Altered Arctic lake thermal stratification may lead to hypolimnetic anoxia and sediment phosphorus release. To assess this, I investigated Greenland lakes that exhibit different stratification patterns. Among anoxia-susceptible lakes, morphometric and stratification strength metrics were not able to explain variation of anoxia. Cooler spring temperatures were associated with mid-summer lake anoxia. Increased TP concentration and algal biomass were associated with lake anoxia. My dissertation research summarizes how environmental change is altering lake nutrient subsidization and cycling in remote Arctic and alpine areas. It highlights ecological responses to those alterations. With accelerating rates of warming and increasing N deposition rates in Arctic and alpine areas, this research provides timely insights of how lakes located in cold, remote areas will change in the coming century