Controls on dissolved organic carbon concentrations in streams, southern Québec

Dissolved organic carbon (DOC) concentrations were measured in streams draining 42 small (0.6–37.2 km2) catchments located in the Appalachian Uplands and St. Lawrence Lowlands. Weekly sampling from mid-April to late-November in four catchments containing < 1% wetland revealed DOC concentrations in streams averaging 3.5–7.2 mg∙L−1 with significant (r2 = 0.28–0.66, P < 0.01) positive relationships to discharge. In four catchments containing 15–69% wetland, average DOC concentrations in streams ranged from 14.5 to 40.0 mg∙L−1 and there was no significant relationship to discharge. Based on five sampling dates from May to November, DOC concentrations in streams draining the 42 catchments showed consistent relationships of varying strength (r2 = 0.26–0.67, P < 0.01) with the variable percent wetland in the catchment. Soil drainage rating, percent forest, mean catchment slope, and catchment area provided little improvement in the regression model. Separating the catchments into two regions (Uplands and Lowlands...