Environmental Health - Toxic Substances
U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 3 of 3--Subsurface Contamination From Point Sources, Water-Resources Investigations Report 99-4018C
Stable Isotope Composition of Dissolved O2 Undergoing Respiration in a Ground-Water Contamination Gradient.
By Kinga Révész, John-Karl Böhlke, Richard L. Smith, and Tadashi Yoshinari.
Dissolved oxygen is a key ground-water constituent, controlling both the geochemistry and microbiology of an aquifer. Two methods were developed to analyze isotopes of dissolved O2: the traditional method, which uses dual inlet mass spectrometry for analyzing CO2 previously converted from O2 , and a newly developed method, which uses continuous flow isotope-ratio mass spectrometry for analyzing directly the isotopes of dissolved O2 . The major differences between the two methods are in the sample size and sample handling in the field and laboratory. Isotope analyses of dissolved O2 were used to document the occurrence of microbial respiration near the boundary of an anoxic ground-water plume consisting of treated wastewater at the Massachusetts Military Reservation on Cape Cod. The upper boundary of the plume was a mixing zone between contaminated, anoxic plume water and uncontaminated, oxic local recharge water. Concentrations of dissolved oxygen decreased downward near the top of the plume and were inversely correlated with 18O. Apparent oxygen isotope fractionation factors (e) were -1 to -10 per mil (‰) in the absence of a dilution correction, whereas values as low as -20 ‰ were obtained by adjusting for the effects of dilution.