Mineral Weathering Trajectories of Granitic Parent Material Under Simulated Climate Change Regimes.

The climate of California is expected to change dramatically over the next 100 years depending on emission scenarios, population dynamics, and land use decisions. Changes in temperature and precipitation will likely affect processes that control the rate of mineral weathering at the soil-bedrock interface. A lab-based study was conducted to evaluate a Li-bearing granite for use in subsequent field-based mineral weathering experiments. The effects of rainfall intensity (80 mL vs. 160 mL of simulated rain per simulated month), temperature (4 deg. C vs. 20 deg. C), and plant residue (none vs. pine litter tea vs. oak litter) were simulated in the laboratory on 20-g samples of unconsolidated Li-bearing granite parent material. The timing of leaching events and quantity of simulated rain were based on a udic moisture regime, with either two or four equally-spaced rainfall events per simulated month, for a total of 3 simulated years; compressed into a time span of 3 actual months. Leachate collected after each rain event was analyzed for EC, pH, total inorganic carbon, total dissolved carbon, Li, Na and K. The Li-bearing granite material was analyzed by X-ray diffraction before and after the simulated 3 years of rainfall. Li loss ranged from 0.5 ug Li per gram of granite (no organic litter) to 2 ug Li per gram of granite (oak litter). Na loss ranged from 5 to ug Li per gram of granite (no organic litter) to 22 ug Li per gram of granite (oak litter). In leaching events performed at 20 deg., rates of cation loss appeared to vary exponentially with increased temperature, and linearly with increased simulated rainfall. Initial investigation of XRD patterns suggest that peak widths, heights, area, and shift near d-spacings of 1 nm may be able to be identified between treatments.