Peter C. Van Metre, B.J. Mahler, and Edward Callender

Analysis of sediment cores from Elephant Butte Reservoir, New Mexico, provides a method for investigating historical trends in water quality in the upper Rio Grande. Dating using ¹³⁷Cs abundance is combined with core lithology and reservoir history to interpret the sedimentary record. Sediments at the coring site date only from about 1957, due to removal by erosion of sediment deposited from 1915, when the reservoir was built, to the drought in the 1950s. Polychlorinated biphenyls (pCBs) and total DDT (=p, p' - DDT + p, p' - DDE + p, p' - DDD) are present at low concentrations in the sediment core. Concentrations peak at 5.0 and 11.3 g/kg, respectively, in sediment deposited in about 1970-72, then decrease in sediments deposited after that date. This decrease correlates closely with National bans on the uses of those chemicals. The chemical signature of the reservoir sediments supports the hypothesis that sediment from the Rio Grand is diluted by sediment from the Rio Puerco. The sediment signature of the Rio Puerco also is reflected in uranium-thorium activity ratios greater than unity in recent reservoir sediments, indicating the release of drainage waters into the Rio Puerco from uranium mines.

International Journal of Sediment Research. Vol. 13, No. 4, Dec. 1998. 1-11.

Barbara J. Mahler
U.S. Geological Survey
8027 Exchange Drive
Austin, TX 78754

Edward Callender
U.S. Geological Survey
432 National Center
Reston, VA 20192