Evaluating Dissolved Inorganic Carbon Cycling in a Forested Lake Watershed Using Carbon Isotopes

Abstract

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 C02, groundwater and stream DIC were characterized chemically and isotopically. Soil CO2 concentration profiles reflect both changes in production and in losses due to diffusion. S13C soil CO2 profiles (b13C values of -23%o in summer, slightly enriched during the fall and -25%o 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

Isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in Allegheny County, Pennsylvania, USA

“…The average C isotope signatures of the two contributing end members, soil CO 2 and carbonates, are very distinct. The average d 13 C of soil CO 2 in C3-plantdominated temperate areas like the study site is expected to be approximately À23‰ VPDB (Aravena et al, 1992). On the other hand, the d 13 C of most carbonate rocks is around 0 ± 2‰.…”

Conceptual model of recharge to southeastern Badain Jaran Desert groundwater and lakes from environmental tracers

“…Assuming that the sample with highest pmC value (W40) is representative of recharging waters and that calcite dissolution is negligible, then gaseous CO 2 in the unsaturated zone would have a value of ~18‰ δ 13 C. This value is between expected values for soil gas in soils hosting C 3 (-23‰) and C 4 vegetation (-12.5‰) (Aravena et al, 1992, Vogel, 1993, and a similar value has been found elsewhere in arid China (Zongyu et al, 2003). While C 3 plants comprise the vast majority worldwide (approximately 90%), C 4 plants are prominent in cold arid environments (Pyankov et al, 2000), and several C 4 -pathway shrubs including Haloxylon ammodendron have been documented as important species in the Alashan Plateau (Kürschner, 2004, Wang, 2007.…”

Sources and Transformation of Dissolved Organic Carbon in the Harp Lake Forested Catchment: The Role of Soils

“…From these measurements, we infer the major controls of DOC production and cycling in the Harp Lake catchment. The results presented here are part of a larger, ongoing study of the carbon cycle in soft-water lakes using carbon isotopes Aravena and Schiff, 1991;Aravena et al 1992). Harp Lake catchment is a small forested watershed located in the District of Muskoka, Ontario, Canada.…”