PARENT SESSION
PT8 - Chemistry & Toxicity of Sediments
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P664) Recent History of Anthropogenic Trace Metals in Two Southern California Borderland Basins.

Nilsen, Elena^*,1, Delaney, Margaret¹, ¹ University of California, Santa Cruz, Santa Cruz, Ca, USA

ABSTRACT- Sediment cores from Santa Barbara and Santa Monica Basins were analyzed for organic carbon, barium (Ba) and several other redox-sensitive trace metals to track the effects of petroleum exploration and production activities and wastewater treatment emissions on the geochemistry of these basins through recent decades. Offshore oil drilling results in marine discharges, some of which have been shown to have detrimental effects on benthic communities. Ba is commonly used as an additive for drill mud and is buried in close proximity to the discharge site due to its high density. Ba has low bioavailability and toxicity, but its persistence in the environment makes it a sensitive tracer for introduction of drill mud to benthic environments over time. Anthropogenic metals have been used previously to track geochemical effects of discharges on Santa Monica Basin sediments from adjacent wastewater treatment facilities. Multi-cores (~35 cm in length) were collected from the Santa Barbara and Santa Monica Basins (approximate sedimentation rates are 2.5 mm yr^-1 and 0.6 mm yr^-1, respectively) in November 2001. Approximate age ranges/resolutions are 140 yrs/4-yr for Santa Barbara Basin and 600 yrs/17-yr for Santa Monica Basin. Ba in Santa Barbara Basin sediments increases from near background levels before ~1960 to nearly three times that in ~1970. Ba concentrations then decrease gradually until ~1985, after which they again increase. Organic carbon measurements suggest that observed changes in barium burial are not linked to sewage inputs or biological production in the overlying water column. These results indicate that after a decline since the 1970′s, deposition of drilling discharges has again increased in the Santa Barbara Basin over the last decade. A high correlation of organic carbon, Ba, Mn and U in Santa Monica Basin sediments is consistent with association of trace metals with sewage-derived organic particulates in this basin.

Key words: anthropogenic metals, sediment geochemistry, barium, California