World Congress of Soil Science Logo 18th World Congress of Soil Science
July 9-15, 2006 - Philadelphia, Pennsylvania, USA
International Union of Soil Sciences

Friday, 14 July 2006
99-1

This presentation is part of 99: 1.2B Soil System Behavior in Time - Theater

Stable Isotope Geochemistry Used in Recent Pedological Studies: Carbon Cycle in Soils of Boreal Regions.

Ahmad Landi, University of Saskatchewan, 238 Willoughby Cres, Saskatoon, SK S7H 4W7, Canada

Information about the amount and rate of organic and inorganic carbon accumulation in soils is important for the estimation of global carbon pools and fluxes in terrestrial environments and establishment of past climatic conditions. Because of the complexity of processes involved in atmosphere-vegetation-soil-landscape relationships, Several attempts have been made to calculate the rate of Pedogenic Carbonate (PC) and Organic Carbon (OC) accumulation in soils. Stable isotope ratios of elements in both organic and inorganic components often record and integrate information related to the kind of processes and the environmental conditions that were involved in the formation of the components. The objective of this study was to determine the amount and accumulation rate of organic and inorganic carbonate in soils of the boreal grassland and forest regions of Saskatchewan, Canada. A southwest to northeast transect of about 500 km length across five different soil-climatic zones (Dry Brown, Brown, Dark Brown, Black, and Gray) in Saskatchewan, between 49o 13 N and 53o 63N latitude and 104o 92 W and 107o 66 W longitude, was included in this study. Three replicates from each soil zone, and three profiles from the Rego Black Chernozem soils (Mollisols), totally 18 profiles, were described in detail and sampled. The soils were sampled to 120-cm depth to ensure that calculations are based on a constant depth. This is also a depth at which PC accumulation is near zero. Bulk density was measured on replicate samples from each horizon. A Global Positioning System (GPS) was used to record the elevation, longitude, and latitude of the soils. The amount of organic C to a 1.2 m depth generally increases from an average of 9.1, 11.7, 14.9 and 21.0 kg C m-2 for Brown, Dark Brown, Black, and Rego Black Chernozem soils. Annual organic carbon accumulation rates in the soils studied are 0.57, 0.90, 1.18, 0.84, and 1.83 g C m-2 yr-1. Avarage rate was found to be 1.25 g C m-2 yr-1. The storage of pedogenic carbonate increases from 134 kg m-2 in semi-arid grassland (Brown soils) in the southwest to 165 kg m-2 in the northeast, under forest (Gray soils), within the time decreasing from 17,000 yr in the southwest to 11,500 yr in the northeast. The rate of pedogenic carbonate accumulation likewise increases from 8.3 to 14.3 g m-2 yr-1 in the same direction. The results show that the soils of the prairies and forests have sequestered 1.4 times more C in the form of pedogenic carbonates than as organic matter. The rate of pedogenic carbonate and organic matter accumulation increases with increasing annual precipitation. Keywords: carbon stable isotope, pedogenic carbonate, boreal region, rate of C accumulation, carbon stocks, soils of Saskatcewan.


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