Quantifying Pedogenic Carbon Content in the Boise River Terraces and Assigning Rates to Potential Irrigation Carbon Fluxes in Southwestern Idaho using Pressurized Calcimetry

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Student Presentation

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Jen Pierce


Soil carbon is the third largest carbon pool within the global carbon cycle; however, soil carbon amounts are not well quantified, and exchange rates of soil carbon are not well understood. Soil carbon can be divided into organic carbon and inorganic carbon, where inorganic carbon (pedogenic carbonate) is precipitated during soil formation and accumulates over time in semi-arid and arid environments. Calcic soils within the semiarid regions of the Boise Valley result from active pedogenic accumulation of secondary CaCO3 resulting in prominent petrocalcic (K) horizons and well-developed ‘caliche’ layers in soils formed on the Boise River terraces. There are two primary goals of this project: (1) to quantify inorganic carbon sequestered within the Boise River terraces and (2) investigate rates of carbonate dissolution due to irrigation in sites near Mountain Home, ID. For the second portion of the project we will take samples from irrigated and adjacent non-irrigated soils. Both portions of this project focus on developing methods for measuring inorganic carbon content in soils using pressurized calcimetry. This involves acidifying samples within a closed system to form CO2 under constant temperature, allowing time-pressure readings to delineate the levels of inorganic carbon present. Future work will reveal trends in carbon content with depth in individual soil profiles, variations in carbon content for terraces of different ages, whether there is a flux of carbon out of irrigated soils, and what the rate of this flux may be.

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