The Geochemistry and Evolution of Natural Organic Solutes in Groundwater

This paper describes the organic carbon cycle of the recharge environment of a shallow, sandy aquifer, with an emphasis on the origin, flux and geochemical evolution of dissolved organic carbon using liquid chromatography, carbon isotopes and GC-MS techniques. The two components of DOC investigated are hydrophobic acids and C1-C10 hydrophilic compounds. The 14C activity of these components of the DOC was measured using TAMS. 14C analyses of DOC components may provide an additional tool for groundwater dating. The initial 14C activity of DOC in a recharge zone, however, depends mainly on the residence times and cycling of DOC sources in the recharge environment. Using 14C DOC to estimate groundwater residence times between sampling points along a flow path compares well with residence times estimated on the basis of hydraulic parameters and 14C DIC under closed system conditions.