CARBON SEQUESTRATION IN A COLD DESERT ECOSYSTEM: USE OF GEOCHEMICAL TECHNIQUES TO DETERMINE CALCIUM PROVENANCE AND SOIL CARBONATE FORMATION IN DRYLAND

About 90% of carbon in dryland soils is stored as soil inorganic carbon (SIC) which has a vital role in the global carbon, climate, and hydrological models. SIC accumulation in soils can lead to carbon sequestration, and it is a potential nature-based climate solution in dryland ecosystems. The role and provenance of calcium (Ca) in global carbon storage, however, is still understudied in cold deserts. Ca provenance and flux can determine whether or not SIC can be a sink for atmospheric CO2 and it is one of the controlling factors in the formation and accumulation of SIC. Improving the accuracy of climate and hydrological models, and the relative roles of parent material, weathering, and other critical zone processes in the control of SIC formation are possible through understanding the origin and flux of Ca.

Dust or loess is a well-known source of Ca, which can lead to the formation of SIC in arid and semi-arid areas. So too is irrigation water when applied in dryland agricultural sites. However, (1) the provenance of Ca is understudied in many native cold desert regions, and (2) the proportion of Ca added to the soil from dust, irrigation water, or the underlying parent material is not clear, which prevents accurate determination of net carbon storage as SIC in these ecosystems.

The goal of this study is to determine the provenance and amount of Ca from natural and anthropogenic sources using isotopic and mass balance techniques, and assess how these sources contribute to the formation of pedogenic carbonate in drylands. Dust samples have been collected seasonally since summer 2021 from installed dust traps in Reynolds Creek Experimental Watershed and agricultural lands at the USDA Northwest Irrigation and Soils Research Lab (NWIS at Kimberly) in southwestern Idaho. Sample processing has begun for analyses, which include organic and inorganic carbon, x-ray fluorescence (XRF) spectroscopy, coupled plasma-optical emission spectrometry (ICP-OES) for major ions, and strontium isotope ratio (87Sr/86Sr) with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) at the University of Texas at El Paso (UTEP).