Sources and factors influencing the spatial distribution of heavy metals in a coastal lagoon adjacent to the San Quintin volcanic field, Baja California, Mexico

摘要

Heavy metals are introduced in aquatic environments by atmospheric deposition, weathering and erosion of the geological matrix or through anthropogenic sources (Molisani et al., 1999). In these environments, sediments act as an important reservoir for metals (Montouris et al., 2002). San Quintin Bay (SQB) is a Y-shaped coastal lagoon located in the northwest coast of Baja California (200 miles south of Mexico, USA border). Its western (WA) and eastern arms (EA) are known as Bahia San Quintin and Bahia Falsa, respectively. This coastal lagoon is an important ecosystem because it provides a refuge for many fish and invertebrates species, and it is also part of the Pacific fly-way. At present, the most important industrial activities in the WA are related to aquaculture and fisheries. This bay is exposed to potential pollution through industrial and recreation activities, fishing traffic and associated pollutants from agricultural run-off (Gutierrez-Galindo et al., 1996). Previous studies in the oyster aquaculture area of the bay have shown a contribution of the biodeposit formation to metals enrichments in surface sediments (Gutierrez-Galindo et al., 1991); however, no information has been published to date about the sources and factors influencing the spatial distribution of heavy metals such as Cd, Zn and Cu in this bay. In view of the increasing development of human activities in this area and the scientific interest in the past years, the present work discusses the earliest geo-chemical data available for this coastal lagoon. This baseline paper reports the concentration and distribution of selected heavy metals in San Quintin surficial sediments in order to: (1) identify the sources of these elements and factors affecting the spatial distribution of Cd, Zn, Cu, as well as Ni and Cr in sediments, and (2) establish an environmental baseline available with which to evaluate the extent of any change in sediment pollutant level that may occur as a result of the increasing urbanization and industrial activities. It exemplifies the complex interactions that may exist between geological, oceanographic and anthropogenic geochemical factors, influencing the assessment of coastal environmental contamination.