Stream Dissolved Organic Carbon Concentrations Research Articles

Sources and sinks of dissolved organic carbon in a forested swamp catchment

Concentrations of dissolved organic carbon (DOC) were measured in precipitation, throughfall, stemflow, and soil, peat and stream water in a 50 ha catchment with a central 5 ha swamp at Mont St. Hilaire, Quebec. DOC concentrations in precipitation were low (2.0 mg L−1), but increased in passage through the tree canopies as throughfall (9.1–14.6 mg L−1) and stemflow (23.1–30.1 mg L−1). For the period July 1–November 15, 1987, 0.5 g DOC m−2 was imported as precipitation, and forest canopies contributed a further 1.4–1.7 g m−2 2 to the soil surface. DOC concentrations were higher (46.0 and 67.6 mg L−1) in upland soil organic horizons, but decreased with depth because subsoil mineral horizons acted as a major sink of DOC. A laboratory experiment using leaf leachate revealed that subsoil horizons were able to adsorb DOC, with equilibrium DOC concentrations ranging from 3 to 19 mg L−1. Soil organic carbon appeared to be an important determinant of equilibrium DOC concentrations. The swamp was a major source of DOC, with an overall average DOC concentration of 58.6 mg L−1 and showed strong spatial and temporal variations related to hydrologic and thermal regimes. During base flow periods, stream DOC concentrations were small (< 3 mg L−1), dominated by water fed from springs draining upland soils. During high flows, stream DOC concentrations increased through the contribution of DOC-rich water originating in the swamp. Sources, sinks and transport of DOC are thus a function of a complex set of inter-related biotic and abiotic process.

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 &lt; 1% wetland revealed DOC concentrations in streams averaging 3.5–7.2 mg∙L−1 with significant (r2 = 0.28–0.66, P &lt; 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 &lt; 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) 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. These results indicate that stream DOC concentrations may be predicted from easily-obtained catchment variables, such as percent wetland.

Influence of soil clay content on dissolved organic matter in stream waters

Dissolved organic carbon (DOC) is of major importance for freshwater ecology and water treatment, particularly in Australia. Work comparing two small catchments, one yielding water with high DOC concentrations (Lawless) and the other yielding water with low DOC concentrations (Retreat Valley), is described. Differences between stream DOC concentrations in the two catchments were related to differences between the properties of the catchment soils. The Retreat Valley soils had higher C contents than the Lawless soils, but the C was less soluble, resulting in lower DOC concentrations in soil core leachates. The lower solubility of C in the Retreat Valley soils was the result of a higher clay content and hence a higher surface area for adsorption reactions. The Retreat Valley soils had a higher adsorption capacity for organic matter than did the Lawless soils. The clay contents of soils was found to be an important factor influencing stream DOC concentrations throughout the Mt Lofty Ranges, and the prediction of DOC concentrations in streams on a broad scale is discussed.

Stocks: Credibility?

Dissolved organic carbon (DOC) concentrations in south-western Nova Scotia streams, sampled at weekly to biweekly intervals, varied across streams from about 3 to 40 mg L−1, being highest mid-summer to fall, and lowest during winter to spring. A 3-parameter model (DOC-3) was proposed to project daily stream DOC concentrations and fluxes from modelled estimates for daily soil temperature and moisture, year-round, and in relation to basin size and wetness. The parameters of this model refer to (i) a basin-specific DOC release parameter “kDOC”, related to the wet- and open-water area percentages per basin, (ii) the lag time “τ” between DOC production and subsequent stream DOC emergence, related to the catchment area above the stream sampling location; and (iii) the activation energy “Ea”, to deal with the temperature effect on DOC production. This model was calibrated with the 1988–2006 DOC concentration data from three streams (Pine Marten, Moosepit Brook, and the Mersey River sampled at or near Kejimkujik National Park, or KNP), and was used to interpret the biweekly 1999–2003 DOC concentrations data (stream, ground and lake water, soil lysimeters) of the Pockwock–Bowater Watershed Project near Halifax, Nova Scotia. The data and the model revealed that the DOC concentrations within the streams were not correlated to the DOC concentrations within the soil- and groundwater, but were predictable based on (i) the hydrologically inferred weather-induced changes in soil moisture and temperature next to each stream, and (ii) the topographically inferred basin area and wet- and open-water area percentages associated with each stream (R2 = 0.53; RMSE = 3.5 mg L−1). Model-predicted fluxes accounted 74% of the hydrometrically determined DOC exports at KNP.