Abstract
Dissolved inorganic carbon (DIC) is the main acid buffer in forested lake watersheds in Canada. We used carbon isotopes (13C, 14C) to evaluate the production and cycling of DIC in an acid-sensitive lake watershed of the Precambrian Shield. Soil CO2, groundwater and stream DIC were characterized chemically and isotopically. Soil CO2 concentration profiles reflect both changes in production and in losses due to diffusion. δ13C soil CO2 profiles (δ13C values of −23‰ in summer, slightly enriched during the fall and −25%‰ during the winter) are a reflection of the isotopic composition of the sources and changes in isotopic fractionation due to diffusion. Carbon isotopic composition (13C, 14C) of the groundwater and stream DIC clearly indicate that weathering of silicates by soil CO2 is the main source of DIC in these watersheds. 14C data show that, in addition to recent groundwater, an older groundwater component with depleted 14C activity is also present in the bedrock. The carbon isotope pattern in the groundwater also implies that, besides the main springtime recharge events, contributions to the groundwater may also occur during late winter/early spring.
Highlights
Growing concerns about the global carbon cycle and the natural and anthropogenic sources and sinks of carbon have fostered renewed research interest in the cycling of carbon in natural systems (e.g., Quay et al 1986; Hedges et al 1986; Cicerone & Oremland 1988)
Our approach involves the use of carbon isotopes, '3C and 14C, as tracers to evaluate sources and sinks of the main carbon pools; dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and solid organic carbon (SOC)
Soil CO2 concentration profiles collected from spring 1990 (May) to the end of winter 1991 (March) show three distinct patterns (Fig. 2): first, an increase in CO2 concentration that reaches a maximum (1.2%) at mid-summer; second, a decrease in CO2 concentration occurs between July and December, reaching a minimum concentration of 0.3%; we observed a slight increase from 0.3%-0.5% between December and March 1991
Summary
Growing concerns about the global carbon cycle and the natural and anthropogenic sources and sinks of carbon have fostered renewed research interest in the cycling of carbon in natural systems (e.g., Quay et al 1986; Hedges et al 1986; Cicerone & Oremland 1988). This paper constitutes part of an ongoing research project whose main objective is the evaluation of carbon cycling in Harp Lake, a forested watershed in the acid-sensitive region of the Precambrian Shield, southeastern Ontario, Canada (Schiff et al 1990; Aravena & Schiff 1990; Trumbore et a1.1992). We discuss here the sources of DIC in groundwater and streams of a forested watershed of the Precambrian Shield. DIC production and cycling are important in the acid neutralization capacity of these systems because DIC is the main acid buffer in these acid-sensitive lake watersheds
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
