A LABORATORY STUDY OF MINERAL WEATHERING AND INTER-STORM PERIODS IN SOILS

Chemical weathering is an important aspect of the rock cycle and aids in the removal of CO2 from the atmosphere. Weathering rates can be accelerated by being in the presence of a biologically active soil. However, deriving relationships from field soils to laboratory experiments can be difficult due to a disparity in weathering rates. This study was designed to test the effects of inter-storm periods on chemical weathering rates in soil. A series of soil columns were assembled representing the upper 10 cm (A horizon) of a soil. These experiments were conducted in three different soils, < 2 mm quartz sand, sandy loam forest soil from Santa Cruz, California, and sandy loam coastal soil from Monterey, California. Weathering rates were measured by the amount of mass loss in pure calcite (Iceland spar) and gypsum (selenite) crystals, buried in the soil columns. Rain storms were simulated by an automatic drip irrigation system. The pore water was then allowed to equilibrate with the crystals during the inter-storm periods of 1, 2, 3, and 5 days. Inter-storm periods may be responsible for increased weathering rates, since minerals and bedrock in soil are allowed to react with pore waters for longer periods than a single leaching event. Inter-storm periods have implications for increased chemical weathering in climates with seasonal drying times, such as California's mediterranean dry summer and wet winter.