QUANTITATIVE EVALUATION OF KARST LANDSCAPE/AQUIFER SYSTEM DYNAMICS USING CARBON AS A TRACER

Inorganic and organic carbon exist in a wide variety of solid, aqueous, and gas phases within karst landscape/aquifer systems. Quantitative relationships coupling equilibrium chemistry, reaction kinetics, and other properties of carbon in natural and anthropogenically influenced waters make it possible to derive mathematical models that reveal fine detail about the behavior and partitioning of carbon within karst systems, and to use such models to better understand the impact of these processes on the global carbon cycle at human-influenced timescales.

Here we report on mass balance arguments that allow partitioning of the inorganic carbon leaving karst systems resulting from atmospheric, biological (summed among soil, vadose and phreatic zones), and carbonate mineral sources. Examination of elementary reactions of the calcite-dolomite/water/carbon dioxide system allows further theoretical partitioning of the proportions of carbon leaving such systems resulting from interactions between carbonate minerals and carbonic acid, protons, and water, respectively. In addition to providing information on the internal dynamics of karst systems, with these methods we are quantitatively evaluating the carbonate mineral weathering atmospheric carbon sink over the ten or so percent of the Earth's land surface over which carbonate minerals are exposed.

Much dissolved organic matter is fluorescent. We also use evolving methods by which organic carbon fluxes through karst systems can be measured with fluorescence, calibrated with total organic carbon (TOC) analysis. Analysis of three-dimensional excitation emission matrix (EEM) fluorescence of organic carbon bearing waters can discriminate between various natural and anthropogenic carbon sources. Naturally derived humic and fulvic-like acid fluorescence can be differentiated from anthropogenically derived organic matter (sewage, farm wastes) that are typically rich in tryptophan and tyrosine fluorescent proteins. Fluorescence EEM analyses can therefore source different fractions of the organic carbon budget.