CONTROLS ON DISSOLVED ORGANIC-CARBON CONCENTRATIONS IN STREAMS, SOUTHERN QUEBEC

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 4 catchments containing <1% wetland revealed DOC concentrations in streams averaging 3.5-7.2 mg.L-1 with significant positive relationships to discharge. In 4 catchments containing 15-69% wetland, average DOC concentrations in streams ranged from 14.5-40.0 mg.L-1; there was no significant relationship to discharge. DOC concentrations in streams draining the 42 catchments showed consistent relationships of varying strength 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 Uplands and Lowlands improved the predictive power of the regression model for the upland catchments. The poor relationships between DOC and percent wetland in the lowland catchments are attributed to the dry summer during sampling and extensive modification of land use, such as the drainage of wetlands and agriculture. -from Authors