Paper No. 12
Presentation Time: 11:05 AM
d18O OF PO4 AS A HYDROGEOLOGIC TRACER FOR NUTRIENT CONTAMINATION AND SUBSURFACE MICROBIAL ACTIVITY
We demonstrate the utility of phosphate oxygen isotope measurements for tracking anthropogenic phosphorus loadings with measurements on sewage treatment plant effluent, the Connecticut River, and an aquifer on Cape Cod. Microbial activity acts to equilibrate the oxygen isotope composition of PO4 with that of ambient water as a function of temperature. In surface and groundwater systems where dissolved PO4 loadings are high, the capacity of a microbial community to cycle an ambient dissolved PO4 reservoir may be exceeded. In such cases, disequilibrated oxygen isotope compositions for dissolved PO4 may prevail and provide a diagnostic source signal. A simple model is used to show how the approach of d18O values towards equilibrium along a flow path can constrain the rate of microbial phosphate cycling.