Export of DOC from forested catchments on the Precambrian Shield of Central Ontario: clues from 13C and 14C

• Published in: Biogeochemistry 1997, Vol.36 (1), p.43-65
• Main Authors: Schiff, S.L, Aravena, R, Trumbore, S.E, Hinton, M.J, Elgood, R, Dillon, P.J
• Format: Article
• Language: English
• Subjects: Carbon; Carbon isotopes; Catchments; Decomposition; Dissolved organic carbon; Forest floor; Forest watersheds; Forested watersheds; forestry; Groundwater; Harps; Lakes; limnology; Organic matter; Photochemicals; Precambrian; Radiocarbon; soil chemistry; Soil columns; Soil horizons; soil physics; soil science; Soils; Streams; Surface water; Watersheds; Wetlands
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1023/a:1005744131385

Export of dissolved organic carbon (DOC) from forested catchments is governed by competing processes of production, decomposition, sorption and flushing. To examine the sources of DOC, carbon isotopes (14C and 13C) were analyzed in DOC from surface waters, groundwaters and soils in a small forested catchment on the Canadian Shield in central Ontario. A significant fraction (greater than 50%) of DOC in major inflows to the lake is composed of carbon incorporated into organic matter, solubilized and flushed into the stream within the last 40 years. In contrast, 14C in groundwater DOC was old indicating extensive recycling of forest floor derived organic carbon in the soil column before elution to groundwater in the lower B and C soil horizons. A small upland basin had a wide range in 14C from old groundwater values at baseflow under dry basin conditions to relatively modern values during high flow or wetter antecedent conditions. Wetlands export mainly recently fixed carbon with little seasonal range. DOC in streams entering the small lake may be composed of two pools; an older recalcitrant pool delivered by groundwater and a young labile pool derived from recent organic matter. The relative proportion of these two pools changes seasonally due the changes in the water flowpaths and organic carbon dynamics. Although changes in local climate (temperature and/or precipitation) may alter the relative proportions of the old and young pools, the older pool is likely to be more refractory to sedimentation and decomposition in the lake setting. Delivery of older pool DOC from the catchment and susceptibility of this older pool to photochemical decomposition may consequently be important in governing the minimum DOC concentration limit in lakes.