Quantifying Pedogenic Carbon Content Within the Boise River Terraces Using Pressurized Calcimetry

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 \u27caliche\u27 layers in soils formed on many of the Boise River terraces. The larger goals of this project are to quantify inorganic carbon sequestered within the Boise River terraces, and investigate rates of carbonate dissolution due to irrigation. This portion of the project focuses on developing methods for measuring inorganic carbon content in soils using pressurized calcimetry. Samples are acidified 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, and variations in carbon content for terraces of different ages

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

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

Understanding the Active Carbon Budget: A Study of Soil Inorganic Carbon in Southwestern Idaho

Soil inorganic carbon (SIC) represents the third largest carbon pool within the active carbon cycle; however, there is much contention on whether fluxes into this pool are inextricably linked to the storage of atmospheric CO2. This study is investigating the total amount of carbon storage and whether or not this pool is being disturbed by irrigation practices. We collected soil samples along terraces of the Boise River and along irrigated and adjacent undisturbed transects near Mountain Home (MH). We analyzed samples for their inorganic carbon content using pressurized calcimetry. Results show SIC storage as CaCO3 is significant, with an undisturbed storage density of 187 t/ha carbon (1 m depth). In undisturbed transects (~ 1.5 m), average SIC is 2.2 wt. % compared to 1.5 wt. % in irrigated profiles. SIC in irrigated soils may be lower than in undisturbed profiles; however, peak carbonate amounts are deeper in irrigated transects. This could imply that in irrigated profiles, there is a downward movement of SIC due to the leaching of carbonates from increased water percolation during irrigation. A smaller peak in SIC at ~ 0.5 m in both irrigated and non-irrigated profiles may be CaCO3 precipitation associated with the rooting zone