Sediment Transport Patterns in Todos Santos Bay, Baja California, Mexico, Inferred from Grain-Size Trends

Abstract

Contaminated sediments do not always remain in the same place in the environment. The mobility of sediments and the contaminants associated to them is a factor that complicates the evaluation of ecological risk, remediation potential and ultimately, the litigation process (e.g., Carriquiry & Sanchez, 1999; Sanchez et al., 2008). A rational decision in this regard must take into consideration the potential stability of contaminated sediments, its sources, transport and final destination (e.g., McLaren & Beveridge, 2006). A technique capable of providing that information in coastal sedimentary environments is the analysis of textural trends of sediments; an empirical method that is based on the relaive changes in the grain size distributrion of the sediments to determine the net direction of sediment transport (e.g., Sunamura & Horikawa, 1971; Mc Laren & Bowles, 1985; Gao & Collins, 1992, 1994; LeRoux, 2002; Poizot & Mear, 2008). Because many contaminants become adsorbed to the sedimentary particles, this information can help in evaluating the relationship between contaminant load and its sources, as well as providing an understanding about the behavior and destination of the contaminants in the sediments (e.g., Carriquiry & Sanchez, 1999; Sanchez et al., 2008). The original theory used to predict the direction of sediment transport based on the relative change in the particle size distribution was given by Sunamura & Horikawa (1971). Later on, McLaren & Bowles (1985) proposed a one-dimensional approach in which changes in the grain size distribution along a sequence of individual samples that were statistically analyzed by a Z-test could be used to determine the preferred transport direction. Gao & Collins (1991, 1992) and Gao (1996) proposed a two-dimensional model to determine the trend on the basis of vector analysis. A different approach based on analytic geometry and vector analysis to determine the direction of sediment transport was produced by LeRoux (1994) and LeRoux et al. (2002). A summary of all these techniques is provided by Poizot et al. (2008). In all the sediment transport models based on trend analysis of clastic material, there are considerations that limit the inferences made on the net direction of sediment transport. The