Land-Water Connectivity Drives Northern Lake Biogeochemistry

Background. In the lake-abundant Northwest Territories, Canada, permafrost thaw is threatening the stability of lake biogeochemistry and the role these lakes play in fragile and unique ecosystems. However, the high degree of landscape heterogeneity across the subarctic and arctic suggests that lakes may respond differently to permafrost thaw. Of particular interest is the varying ability to support microbial activity. High levels of microbial activity are tied to more humic organic matter and higher nutrient content and can result in the production of greenhouse gases.

Approach. In this work, we aim to explore how permafrost landforms relate to lake water biogeochemistry. In late summer 2023, we sampled 68 lakes spanning a latitudinal gradient of 10 degrees in the Northwest Territories for lake biogeochemistry. Multivariate regression trees were used to determine the most important landscape variables driving dissolved organic matter composition, physico-chemical properties, and trace metal concentrations. Principal component analyses were used to visually explore variation with lake groups determined by the multivariate regression trees. 

Results. Our results showed that landscape factors differently impact lake properties, with thermokarst formation and vegetation strongly influencing organic matter composition and physico-chemical properties yet exhibiting little influence over trace metal concentrations. Ground ice and permafrost zone did not seem to have a substantial impact on lake water relative to vegetation cover, thermokarst formation, and ecodistrict. The relationships between landscape features and lake biogeochemistry established with the multivariate regression trees were used to predict lakes with the potential for high rates of microbial activity. Further lake sampling will be required to confirm these predictions. Our study highlights the importance of incorporating landscape factors into studies on freshwater ecosystems and using a wide range of water biogeochemistry variables.