DOLOMITE MINERAL WEATHERING CONTRIBUTIONS TO THE BICARBONATE FLUX FROM HEADWATER STREAMS IN THE DANUBE RIVER BASIN

Calcite and dolomite solubility in open weathering environments is proportional to pCO₂, inversely proportional to temperature, and dolomite solubility is progressively greater than calcite below 25^oC.  Continent-scale weathering budgets reveal the significance of the Northern Hemisphere (NH) to globally integrated riverine fluxes of Ca²⁺, Mg²⁺ and HCO₃^-. We present results of a hydrogeochemical study of carbonate mineral equilibria and weathering fluxes for headwater streams in Slovenia within the Danube River Basin. Surface water geochemistry and discharge were determined to examine the contribution of calcite and dolomite weathering to the geochemical fluctuations of the Sava River and its tributaries. The bedrock in Slovenia is primarily composed of Mesozoic carbonates (limestone and dolomite) and siliclastic sediments. The alpine regions have thin soils (<30 cm) and the more gentle slopes of the dinaric karst region develop deeper soils (0 to >70 cm). The geochemistry of the Sava River watershed is dominated by carbonate mineral dissolution. The Mg²⁺/Ca²⁺ mole ratio (average 0.4) indicates that the HCO₃^- concentration of the Sava River watershed results from slightly higher proportions of dolomite to calcite weathering, however an individual catchment's lithology also exerts local control on the mole ratio.  The ability of both calcite and dolomite dissolution to keep pace with increased discharge indicates that carbonate weathering is limited only by water flux, pCO₂, and temperature dependent solubility in temperate zone carbonate-bearing watersheds. Carbonate weathering intensity is a parameter that normalizes river runoff and HCO₃^- to catchment area (meq HCO₃^-km^-2s^-1) and is used to gauge the effects of climate, land use, and soil thickness on organic-inorganic carbon processing rates. Carbonate weathering intensity in the Slovenian catchments exceeds the world average by factors of between 2 to 20.  The weathering intensity of dolomite in Slovenian catchments, estimated from riverine Mg²⁺ fluxes, exceeds the world average by factors between 2 to 15. The global flux of carbonate-related weathering products appears heavily skewed in favor of carbonate-bearing environments at higher latitudes with relatively low mean annual temperatures and high runoff values.