Kneebone, P. E. California Institute of Technology, penelope@cco.caltech.edu
Hering, J. G. California Institute of Technology, jhering@cco.caltech.edu

 
REDOX CYCLING OF ARSENIC IN LAKE CROWLEY, CA: IMPLICATIONS FOR WATER QUALITY IN THE LOS ANGELES AQUEDUCT
 
Elevated arsenic concentrations in Lake Crowley derive from geothermal springs in Hot Creek, an indirect tributary. We monitored arsenic concentration and speciation in the water column of Lake Crowley under stratified conditions. Total arsenic was relatively constant; no depletion observed in the eutrophic epilimnion and no increase in the bottom waters. In contrast, manganese and phosphorous concentrations increased strongly with depth below the oxycline. Arsenic speciation studies showed oxidation states consistent with redox conditions with no evidence for the presence of methylated species. These results suggest that uptake and transformation of arsenic by phytoplankton are not important in Lake Crowley despite high productivity. This may be a consequence of the elevated phosphorus concentrations, also of geothermal origin, in Lake Crowley and its tributaries. Preliminary results suggest that arsenic is not cycled to any significant extent between the sediments of Lake Crowley and the overlying water column. Since the geothermal input of arsenic is relatively localized, treatment near the source may be a feasible strategy to meet new drinking water standards for arsenic. Our results indicate that, if external loading of arsenic to Lake Crowley were removed, the sediments would not become a significant source of arsenic to the water column.
 
Day: Wednesday, Feb. 3
Time: 03:30 - 03:45pm
Location: Sweeney Center
 
Code: SS28WE0330S