Trace Metals in Shallow Marine Sediments from the Ría de Vigo: Sources, Pollution, Speciation and Early Diagenesis

Abstract

The maintenance of the environmental quality of coastal environments requires a good knowledge on them, identifying their potential problems and considering the different anthropogenic activities that take place in these settings. A great proportion of the suspended material that arrives to these environments is incorporated to the bottom sediments. Sedimentation is favoured due to the abrupt changes that are produced in the physico-chemical parameters (pH, Eh, salinity, etc.) by the confluence of continental and marine waters. Their sediments constitute environmental archives, recording trace element inputs to the marine environment. Metal concentrations in these sediments usually surpass in several orders of magnitude those existing in the adjacent water column and in the interstitial waters (Tessier & Campbell, 1988). Their analysis allows covering different objectives, such as studying the spatial and temporal history of pollution of a particular place (Zwolsman et al., 1993), detecting pollutant sources (Dassenakis et al., 1996) and evaluating their potential effects to the organisms (Fichet et al., 1998). Sediments can act as a secondary source of pollution by resuspension or dissolution (early diagenesis) processes. Their study needs a multidisciplinary approach, taking into account the different physicochemical processes operating in the study area and considering the relationships between metal concentration, mineralogy, grain-size and metal sources. All these variables are reviewed in this chapter, showing examples of sediments from a shallow transitional environment: the Ria de Vigo (NW Spain).