HR: 0800h
AN: H51E-0417    [Abstracts]
TI: Source and Fate of Sediments in the Bahia de Anasco, Puerto Rico
AU: * Webb, R M
EM: rmwebb@usgs.gov
AF: U.S. Geological Survey, Denver Federal Center Box 25046, MS413, Denver, CO 80225-0046 United States
AB: Sediments and wastewater mix in the insular marine waters of the Bah'{i}a de Añasco near Mayag{u}ez, Puerto Rico. Trace metal concentrations in fine sediments deposited in the bay were measured to assess potential impact of the ocean outfall on the biota and habitats that include coral reefs. A Q-mode factor analysis of elemental compositions identified three sediment sources and their relative proportions in 51 core and surficial samples collected from the bay and within the coral reefs: (1) sediments discharged by the R'{i}o Grande de Añasco; (2) calcareous skeletal remains; and (3) sediments discharged by the R'{i}o Guanajibo. The nickel and chromium derived from laterite deposits provide a unique fingerprint for sediments discharged from the R'{i}o Guanajibo. Naturally occurring concentrations of these elements exceed Probable Effect Limits (PEL's: 42 mg/kg for nickel and 160 mg/kg for chromium) in sediments deposited near the river mouth. The detection of mercury at 1 mg/kg in one sample from a core recovered near the wastewater outfall was the only indication of a possible outfall source in the data set. The temporal and spatial variations in source fractions proved useful in determining relative frequencies of historic floods and steady-state circulation patterns off the west coast of Puerto Rico.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
DE: 3002 Continental shelf and slope processes (4219)
DE: 4924 Geochemical tracers
SC: Hydrology [H]
MN: Fall Meeting 2005