title: Laboratory investigations of weathering of soils from Mammoth Mountain, CA, a naturally CO2-impacted field site.
abstract: The potential impacts of CO2 leakage from a natural subsurface reservoir on soil and water quality were studied. Field measurements of soil pore CO2 concentrations and visual inspection of plants at Mammoth Mountain, CA, allowed the demarcation of tree-kill and non-tree-kill zones, with CO2 concentrations >100,000 ppm and ∼ 1,000 ppm, respectively. Soils collected from six sites along a transect stretching from the center of the tree-kill zone to an equidistant point into the non-tree-kill zone were analyzed for surface area and organic carbon content. Batch and column leaching tests were conducted to determine the extent of weathering induced by the presence of CO2 in the aqueous solution. Soils deep into the tree-kill area exhibited significantly higher surface areas (10.67 m(2)/g vs 2.53 m(2)/g) and lower organic carbon content (9,550 mg/kg vs 35,550 mg/kg). Batch results indicated that lower pH values (∼ 2) released higher concentrations of Mg, Si, Fe, and As, while, for soils in the tree-kill zone, longer-term batch results indicated higher releases at the higher pH of 5.5. Column experiments were used to compare the effects of pH adjusted using HCl vs CO2. For pore volumes (PV) < 100, CO2 enhanced trace element release. For 100 < PV < 10,000 concentrations of elements in the two systems were equivalent and steady. At PV > 10,000, after a drop in pH in the CO2 system, larger amounts of Fe and As were released, suggesting a CO2-induced dissolution of Fe-silicates/clays and/or reductive dissolution of Fe(3+) that releases Fe-bound arsenic. The specific role of pore water-dissolved CO2 on the release of trace elements is hitherto unknown. However, interactions of pore-water CO2 and the minerals in the Mammoth Mountain soils can cause the release of environmental pollutants.
authors.affiliation: Department of Civil Engineering, ‡Department of Geosciences and Environment, and §Department of Technology, California State University, Los Angeles , 5151 State University Drive, Los Angeles, California 90032, United States.
authors.forename: Helen
authors.initials: H
authors.lastname: Sanchez
authors.forename: Gustavo
authors.initials: G
authors.lastname: Menezes
authors.forename: Andre
authors.initials: A
authors.lastname: Ellis
authors.forename: Claudia
authors.initials: C
authors.lastname: Espinosa-Villegas
authors.forename: Crist
authors.initials: C
authors.lastname: Khachikian
mesh_terms: D000538:Aluminum Silicates; D000818:Animals; D001151:Arsenic / Q000032:analysis; D002140:California; D002244:Carbon / Q000032:analysis; D002245:Carbon Dioxide; D000077215:Clay; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D008670:Metals / Q000032:analysis; D008903:Minerals / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry; D012987:Soil / Q000737:chemistry*; D012996:Solutions; D014197:Trees; D014867:Water / Q000737:chemistry; D060753:Water Quality; D014887:Weather
chemical_list: D000538:Aluminum Silicates; D008670:Metals; D008903:Minerals; D017640:Silicates; D012987:Soil; D012996:Solutions; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon; D007501:Iron; D001151:Arsenic; D000077215:Clay