The interaction of regional and local drivers shapes summer ecosystem metabolism in lakes across Canada

Assessments of lake gross primary production (GPP) and respiration (R) and their balance (net ecosystem production, NEP) have been limited to specific watersheds and a limited number of lakes, often along narrow environmental gradients. This is because conventional approaches require either lengthy incubations or the deployment of monitoring equipment, none of which are feasible for large‐scale studies. Here we present a macroscale study of lake metabolism and explore the patterns and drivers of GPP, R, and NEP in lakes across Canada as part of the LakePulse network. We measured summertime water column metabolic rates in 742 lakes, using an oxygen isotopic (δ18O2) approach, which provide an integrative snapshot of mixed‐layer metabolism in stratified lakes, or whole‐lake metabolism in polymictic lakes. The lakes were distributed across the five major Canadian continental drainage basins, covering a wide range of in‐lake, land use, and climatic features. Gross primary production and R varied by four orders of magnitude across lakes and regions, driven by factors such as total phosphorus and nitrogen, dissolved organic carbon, and chlorophyll. Net ecosystem production had a weak but significant positive linear relationship with water column light and a negative relationship with colored dissolved organic matter. Our results reveal systematic differences in regional baseline GPP and R driven by landscape properties such as altitude, and that lake metabolism in some regions may be more sensitive to eutrophication and browning, mediated by regional hydrology, which is itself linked to climate.