RATES AND PROCESSES OF SOIL INORGANIC CARBON FORMATION IN NATURAL AND MANAGED COOL SEMI-ARID ECOSYSTEMS

Carbon stored in soils provides a natural way of carbon sequestration and therefore a potential climate change mitigation strategy. Some recent studies help quantify global SIC stocks but the rate of SIC accumulation, particularly in human-altered agroecosystems, is poorly constrained. Moreover, irrigation of drylands may render them a net C source.

This research will examine how much organic and inorganic carbon is sequestered in irrigated, pasture, and natural dryland soils and how agriculture impacts carbon stocks in drylands. This study is focused on two areas in southwestern Idaho; the Reynolds Creek Experimental Watershed (RCEW), which is primarily a native dryland sagebrush steppe ecosystem, and Kimberly Northwest Irrigation and Soils Research Laboratory (NWISRL), which transitioned from a native sagebrush ecosystem to agricultural lands with the advent of irrigation in the early 1900s. While precipitation (~240 mm/yr) is similar at both sites, ~900 mm of irrigation water from the Snake River is added annually to the Kimberly (85% of total water). The total soil carbon storage in non-irrigated and irrigated sites at RCEW and NWISRL is determined by measuring the SIC and SOC in these soils. Quaternary dating methods (Optically Stimulated Luminescence dating, U-series dating, and radiocarbon dating) date the deposition of loess parent material and the subsequent formation of pedogenic carbonates; combined with stratigraphic data, these dates can be used to constrain rates and conditions of Quaternary SIC formation. The comparison of SIC and primary control factors (ClORPT, Climate, Organic material, Relief, Parent Material, and Time) for SIC dissolution/precipitation dynamics are further changed by anthropogenic activities. Overall, this study will determine if native and managed sites act as a net source or sink of carbon due to changes in soil carbonates. In Kimberly, soil profiles developed in ~3 m of loess at both irrigated and non-irrigated sites contain evidence of buried A and Bk horizons; however, the distribution of SIC with depth at the irrigated site is more homogenous. Preliminary OSL ages indicate that loess parent material was deposited ~50-7 ka ago.

Keywords: Soil total carbon, irrigated and non-irrigated soils, paleosols, Quaternary dating