COMPARISON OF CHEMICAL WEATHERING OF LIMESTONE AND DOLOMITE EVALUATED IN MODELING AND DIRECT IN-SITU MEASUREMENTS

The results presented in this article focus on quantitative analysis of the chemical denudation using numerical models and measured in in-situ measurements of buried capsules. This research has been conducted in the drainage basin of the Bialy Potok, located in the West Tatra Mountains, Poland. The experimental field area is mainly composed of dolomites and limestones, with quartz sandstones and small amounts of illite and plagioclase feldspars. Surface waters and groundwater are weakly alkaline and their total dissolved solids (TDS) between 200 and 300 mg/L. Values of the oxidizing-reducing potential (300-400 mV) indicate oxidizing conditions in the aquifer. This range of Eh values accompanied with pH ranging from 7,5 to 8,1, is characteristic for groundwater in the active chemical transfer zone in carbonate rocks regolith. Calcium, magnesium and bicarbonate ions dominate in surface waters and groundwater. Capsules were disc-shaped, 5 cm in diameter and 2 cm high, and weigh about 100 g. These capsules were accurately weighted before and after exposure to weathering processes. Weathering processes have been also evaluated in thin sections made of native rocks, which were also buried and subsequently recovered. Quantitative analysis was conducted based on dissolved amount of the rock in the native rock capsules that were placed both in the aquifers and on the ground surface. Changes in chemical composition of the weathered capsules have observed in SEM and their elemental chemical composition was determined using EDAX SEM chemical analyzer. Observed denudation in the field rock capsules is consistent with the results of the numerical modeling. Based on the capsule evaluation, it was observed that rock specimen placed on the ground surface and in direct contact with atmospheric precipitation, underwent more intense weathering than the specimen buried in the aquifer. It agrees with the modeling analysis results, indicating much greater mineral dissolution in atmospheric precipitation water than in water infiltrating through the vadose zone.