TRACING THE MOVEMENT OF PEDOGENIC CARBONATES WITHIN IRRIGATED AND NON-IRRIGATED SOILS IN THE WESTERN SNAKE RIVER PLAIN, IDAHO, USING PRESSURIZED CALCIMETRY

Soil carbon is the 3^rd largest reservoir within the global carbon cycle and exists as both inorganic (SIC) and organic (SOC) carbon. Secondary accumulation of calcium carbonate (CaCO₃), known as pedogenic carbonate, is a function of time, seasonal wetting and drying intervals, as well as anthropogenic influences (e.g. agriculture). Pedogenic carbonates comprise the majority of the Western Snake River Plain (WSRP).

Secondary SIC occurs in a variety of forms ranging from precipitates within pore spaces to indurated plates several meters thick. These precipitates form calcic to petrocalcic layers, referred to as K-horizons. When stable, K-horizons are considered a long-term carbon sink, but certain agricultural land-use processes (e.g. tillage, irrigation and soil amendments) can destabilize these reservoirs resulting in pedogenic instability and dissolution. Dissolved SIC that is not reprecipitated can potentially bolster atmospheric CO₂ levels by escaping back into the atmosphere, becoming a significant source of further greenhouse gas accumulation.

Previous and ongoing analysis, using pressurized calcimetry, will provide a comparative baseline for determining how much SIC is sequestered at depth, and how agricultural processes have positively or adversely affected the carbon reservoir over time. Preliminary results within the WSRP estimated SIC levels between 32MT ha^-1 and 57MT ha^-1 for non-irrigated soils developed on the Gowen River Terrace within Boise, Idaho (K-Ar age of 0.527 +/- 0.210 Ma (Othberg, 1994)). Pending results of the Mountain Home, Idaho, sites will investigate differences between non-irrigated prairie lands to that of adjacent, irrigated, agricultural fields to determine if movements or changes in volume of SIC have occurred at depth. Although there have been numerous studies aimed at quantifying agricultural influences of SOC, there have been relatively few that have investigated the same effects on SIC. With a better understanding of these interactions between agricultural land-use practices and the calcareous soils of the WSRP, preservation of the carbon reservoir and its effects on atmospheric CO₂ can be better mitigated.