CLIMATIC FACTORS LIMITING LIMESTONE DISSOLUTION AT THE SOIL-BEDROCK INTERFACE

A small catchment in a limestone terrain in the Appalachian Valley and Ridge is characterized by a mantle of clay-rich regolith 0.5 m thick overlying black limestone with finely interbedded black shale. The catchment is covered with young hardwood forest. The area typically receives 1000 mm of precipitation per year, roughly evenly distributed throughout the year. Average monthly ambient air temperatures range from 1^oC in January to 24^oC in July. During the summer months, the soil becomes dry, with matric potentials near the soil-bedrock interface rarely exceeding -1.8 bars. Thus, the downward flux of water reaching the soil-bedrock interface is inferred to generally be very small during the summer months. Soil pore waters and shallow ground waters collected following relatively wet periods are typically close to saturation with respect to calcite. Thus, dissolution of calcite appears to be limited primarily by the flux of water reaching the soil-bedrock interface. This result is consistent with watershed-scale studies in temperate climates which suggest that denudation rates in limestone terrains are directly proportional to runoff. However, the flux of water through the soil-bedrock interface is minimal during the summer months when soil pCO₂ and reaction kinetics should reach a maximum. This indicates that limestone weathering and the resulting consumption of carbonic acid in temperate regions may potentially be very responsive to increases in precipitation during the summer months.