Carbon cycling and stable isotope evolution in neutral mine drainage

Scope and method of study. Dissolved inorganic carbon and stable carbon isotopes evolution in contaminated surface and groundwater was investigated by laboratory and field experiments.;The laboratory experiment was conducted by progressively acidifying natural and artificial water samples to determine shifts in delta13C DIC and carbon isotope fractionation during DIC transformation and to model carbon isotope evolution during progressive acidification.;The field experiments were conducted in three carbonate rich tailings piles found in the St Francois County, SE Missouri, where lead mining resulting in the disposal of tailings material in several tailings piles, to investigate how acid production and neutralization affects DIC generation and CO 2(g) production in the vadose zone and how these reactions affect the carbonate evolution of groundwater and surface discharge from the tailings pile.;Findings and conclusions. The results of this study show that: Carbon isotope values in conjunction with concentrations of DIC species (CO2(aq), HCO3-, and CO 32-) can be used to provide evidence for the effects of acidification on DIC in surface waters.;In natural and anthropogenic settings where sulfuric acid production by metal sulfides and neutralization by carbonates occur, the carbonate evolution of shallow groundwater is not described by the classical model ascribed to soil zone CO2(g);Groundwater discharged from carbonate rich mine tailings excess CO 2(aq) that is loss to atmosphere. The CO2(g) that is loss is initially high and decreases with downstream. The CO2(g) loss results in kinetic isotopic enrichment of DIC and the magnitude of delta13CDIC shifts depends on the initial concentration of excess CO2(aq) in the water discharged to the surface and the amount of CO2(g) that is lost from the water.