Name
Seasonal temperature trend overrides the effect of discharge on dissolved organic matter in Boreal Plains streams
Description
Stream dissolved organic matter (DOM) has been the focus of substantial research due to its role in carbon cycling, aquatic ecosystem functioning and its effects on drinking water treatability. Studies conducted in different forested regions have found varying relationships between discharge and DOM, and we set out to test these relationships on the Boreal Plains. Our research site in northern Alberta is representative of most of the Boreal Plains ecozone, which occupies 8.5% of Canada’s land. It is characterized by low-relief terrain with an abundance of wetlands and lakes, thick overburden, and subhumid climate, all of which differentiate it from other forested regions, where most DOM studies have been conducted. We monitored DOC concentration and DOM optical properties (absorbance and fluorescence) in 15 streams over three years, and found both spatial and temporal differences in DOM. Spatial differences were explained by the presence of lakes and surficial geology, which in turn determined wetland distribution and groundwater contribution to streams. Seasonal changes were driven by a progressive increase in soil temperature, and were more important than the diluting or flushing effect of storm events. DOM in our streams was more photolabile than biolabile, and lability also changed seasonally. Our findings suggest that as climate becomes warmer, we may see a shift in stream DOM concentrations and composition in this region.