Evaluation of Dissolved Inorganic and Organic Carbon Concentrations (DIC, DOC) and Their Isotopic Compositions (δ 13C-DOC, δ 13C-DIC) in Water Resources of the Karde Catchment (North of Mashhad)

In this paper, the variations of dissolved inorganic and organic carbon (DIC, DOC) concentrations and their isotopic compositions (δ13C- DIC, δ13C- DOC) were evaluated in both surface and ground water resources in the Karde catchment area (with an area of about 547 Km2, located in the North of Mashhad). To identify the sources of the dissolved carbon (DIC and DOC), samples were collected in June 2011 from surface and ground water resources (river, dam’s lake, springs, wells, and Qanat) and from depths of 1, 5, 10, 15, and 20 meters of Karde dam lakeat a point located near the dam outlet. Field parameters (T, EC, and TDS) were measured during sampling. All measurements were performed in the G.G. Hatch Stable Isotope Laboratory at the University of Ottawa, Canada. The concentrations and isotopic compositions of DIC and DOC were determined using TCA and CF-IRMS instruments, respectively. Based on the results obt ained, the average values of DIC are 54.1 mg/l and 66.8 mg/l in the surface and ground water resources in the Karde catchment area, respectively; the average values of DOC are 2.2 mg/l and 0.45 mg/l; the average values of δ13C-DIC are -7‰ and -11 ‰; and the average values of δ13C-DOC are -31.6‰ and -29.5 ‰, respectively. In general, the concentrations of DIC, DOC, and their isotopic compositions (δ13C-DIC, δ13C-DOC) are different in the various water resources (surface and ground water) in the catchment and the major source of dissolved carbon in the catchment area is believed to be due to the lithology (limestone and dolomite carbonate rocks) and partly due to the vegetation (plants C3) in the region.