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Predicting a temperature-oxygen critical habitat squeeze for endangered pacific salmon and sculpin in a small, coastal monomictic lake

University of British Columbia

Cultus Lake, British Columbia is critical freshwater lake habitat for two species-at-risk, the Cultus Lake Sockeye Salmon (Oncorhynchus nerka, Cultus population) and Cultus Lake Pygmy Sculpin (Coastrange Sculpin, Cottus aleuticus, Cultus population). This lake ecosystem is degrading and threatened by epilimnetic warming and decreasing hypolimnetic dissolved oxygen concentrations, largely the result of the effects and interactions of ongoing lake eutrophication and climate change. Exploration of lake modeling and monitoring data (2009-2018) revealed a correlation between Cultus Lake, BC hypolimnetic temperatures and the volume of hypoxic (<6 mg L-₁) deep water lake habitat (r₂ = 0.73). As oxygen and water temperatures are important constraints on fish growth and survival, the temperature-hypoxic volume relationship was coupled to the predictive outputs from a 1-D hydrodynamic model (GLM) that estimates lake thermal structure, modeling lake temperature and oxygen conditions to 2100 CE under two climate change scenarios (RCP4.5, moderate emissions scenario; and RCP8.5, extreme emissions scenario). The findings substantiate the intensification of a temperature-oxygen squeeze in Cultus Lake under climate change, and permit estimation of generalized future critical habitat restrictions for endemic species at risk. Model simulation results forecasted to 2100 CE, predict a significant future temperature-oxygen habitat squeeze, resulting from the encroachment of surface waters of deleterious temperatures (>17ºC; -25% of lake volume currently; -30% (-34%) under RCP4.5 (RCP8.5) by 2100), and hypoxic hypolimnetic waters (< 6mg/L DO; -20% of lake volume currently; -41% (-58%) under RCP4.5 (RCP8.5). With warming temperatures, the predicted temperature-oxygen squeeze (and volumetric optimal habitat loss) is likely to progressively intensify through time, reducing suitable oxythermic habitat conditions for stenothermic, hypoxia-intolerant fish species in Cultus Lake. If nutrient loading to Cultus Lake remains unabated, our model predicts the likely elimination of optimal critical habitat for both the Cultus Lake Sockeye Salmon and Cultus Pygmy Sculpin, with intensified warming and/or nutrient loading likely to significantly advance such exclusion. Reducing the known nutrient loadings to Cultus Lake is essential in order to lower lake primary productivity and associated seasonal hypolimnetic oxygen deficits, particularly before significant internal loading of nutrients from sediment stores enhances and more permanently reinforces the eutrophied lake state.

Text

2020-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/75789

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/