The Geochemistry of Heavy Metals in Mudflat of Salinas De San Pedro Lagoon, California
The Salinas de San Pedro, CA lagoon develops mainly into a mudflat habitat, which spreads in an enclosed coastal area containing freshwater as well as saltwater saturated sediments, resulting in a rich biodiversity. Many species depend on this fragile but yet threatened gradient-based habitat.
In this study, short sediment cores (up to 20 cm deep) from the Salinas de San Pedro seafloor were used to assess the recent pollutant deposition processes in response to extensive human activity. The cores consisted of alternating layers of clays and silts, with isolated sandy horizons. Analysis of the sediment cores for heavy metals (Ag, Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr, Ti, V, and Zn) was conducted with Inductively Coupled Plasma Optical Emission spectrometry (ICP-OES) for 20 sites showing enrichment for some of these metals.
In general, heavy metals appeared to be spread homogeneously throughout the lagoon, sometimes reaching higher levels in various sites, and most often mainly concentrated in fine grained sediments.
Heavy metal concentrations in surface sediments varied greatly for each metal, with concentration values (mg/g) ranging from 1.05-4.8 (Al); 0.003-0.011 (As); 0.001-0.005 (Cd); 0.02 to 0.82 (Cr); 0.085-0.47 (Cu); 5.98 - 14.22 (Fe); 0.06-0.19 (Mn); 0.03-0.67 (Ni); 0.05-0.38 (Pb); <0.008-0.069 (Se); 0.18-0.63 (Ti); 0.040-0.091 (V) and 0.149-0.336 (Zn). Arsenic, cadmium, chromium, copper, nickel, and zinc showed overall concentrations above the probable toxic effect level (PEL). The arsenic, cadmium and selenium retention in the sediments is highly variable and controlled by local processes resulting in a complex diversity of metal speciation. Assessment of the results using geo-accumulation index was correlated with the data on metal speciation. The geochemistry of these sediments is particular because of the association with the iron-rich clays. Iron was found in the highest concentration, acting as possible nutrient source for the lagoon. Enrichment factors (EFs>1) for these elements and their statistical association suggest anthropogenic inputs for most metals. The most likely sources for these element enrichment (especially As, Cr, Pb, Se, Ti, and Zn) are intensive industrial activities in the local harbor as well as the Tin, Copper and Lead based paint used intensively for boating activities during the last two decades.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California