One tale of two dryland ecosystems: How does irrigation modify inorganic carbon dynamics in drylands

Authors: JIN, LIXIN - University Of Texas - El Paso; PIERCE, JENNIFER - University Of Texas - El Paso; MURILLO, CARMEL - University Of Texas - El Paso; Bjorneberg, David - Dave; GUTIERREZ-JURADO, HUGO-ALBERTO - University Of Texas - El Paso

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/20/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Pedogenic carbonates accumulate in drylands, and they represent a large global soil inorganic carbon (SIC) stock. With growing demand for food, fuel and fiber, these marginal lands are converted to agricultural fields. Irrigation promotes water-soil interaction in otherwise water-limited ecosystems, and thus modifies the stability of pedogenic carbonates. We compared two managed dryland sites, in Tornillo, Texas and in Kimberly, Idaho, and investigated how irrigation water chemistry and intensity, soil texture, crop types, and climate conditions have combined to govern the relative proportion of productive (transpiration) and non-productive (transpiration) water, soil pCO2, and thus the saturation indexes of soil water with respect to calcite, leading to either dissolution or accelerated accumulation of this SIC. At the pecan orchard at Texas, the irrigation water is mainly from the Rio Grande river that is high in total dissolved solids (TDS). With finer soil texture, and high evaporative loss in the hot and dry summer, soil water is supersaturated with respect to calcite, promoting the formation of pedogenic carbonate, even releasing abiotic CO2. At the Idaho site, soils are developed on loess deposits, and have accumulated pedogenic carbonate naturally. The Snake River is used for irrigation and it is relatively low in TDS, dissolving existing calcite in irrigated fields, especially under high soil pCO2 conditions from soil respiration. Looking into future scenarios, two systems might move in a similar direction. In American Southwest along the Rio Grande Valley, when river water becomes less available during drought, more salty deep groundwater is used, leading to even faster pedogenic carbonate accumulation rates. The hotter and dryer summer will evaporate more water, limiting salt leaching, and thus precipitating more calcite. At Idaho, soil water might be more concentrated if evaporation is elevated in the hot summer, and approach the saturation, and even become oversaturated with respect to calcite. This work summarized our Dryland Critical Zone project, and showed sensitivity of pedogenic carbonate dynamics to climate change and human activities. More importantly it highlighted how this SIC reservoir is disturbed and more active in the C exchange with atmosphere and hydrosphere at human scales.