Contrasting the geochemistry of suspended particulate matter and depositedsediments within an estuary

The geochemistry, as defined by amounts of easily reducible Mn (ERMn; Mn ox ides), reducible Fe (RFe; Fe oxides), organic matter (% loss on ignition), total metal (Cu, Pb and Zn) and metals associated with the ERMn, RFe and or ganic matter components of deposited sediments (DS) and suspended particula te matter (SPM) were contrasted over a 1-year period (two-way ANOVA with se diment type and month as the two factors) within the Fraser River Estuary, BC, Canada. The geochemistry of SPM as compared to DS was distinctly differ ent. The geochemistry of SPM displayed a marked seasonality. By contrast, s easonal differences in the geochemistry of DS were much less pronounced ove r the 12-month sampling period. Concentrations of organic matter and RFe in SPM were significantly greater (two-way ANOVA; P < 0.05) in winter months maximums of 23% and 53 g kg(-1) respectively) as compared to the rest of th e year (maximums of 9.3% and 11 g kg(-1), respectively). Concentrations of organic matter in DS did not change over the 12-month period; however, RFe in DS was significantly greater in winter months (7.3 g kg(-1)) as compared to summer months (2.3 g kg(-1)). Easily reducible Mn in both SPM: and DS w as highly variable throughout the year with no apparent seasonal dependence . Total concentrations of Cu, Pb and Zn and their partitioning among the 3 sediment components (i.e. ERMn, RFe and organic matter) were also month-dep endent (two-way ANOVA, P < 0.05); metal concentrations in SPM were up to 17 times greater than DS with a higher proportion of these metals associated with the easily reducible component (oxides of Mn and amorphous forms of Fe oxides) during winter as compared to summer months. Trace metal concentrat ions and partitioning in DS showed the same seasonal trends, although not t o the same degree as occurred for SPM, throughout the 4 seasons of study. S easonal changes in the partitioning of metals in addition to greater propor tions of the metal occurring in an easily reducible form in SPM relative to DS has potentially important implications for sediment ingesting organisms capable of filter-feeding on both SPM and DS. Specifically, metal bioavail ability to sediment ingesting organisms from SPM may be seasonally dependen t with periods of greatest exposure occurring during winter months, as comp ared to DS where no seasonal dependence occurs. To identify main vectors of metal exposure to sediment ingesting organisms, both the type off sediment and when they are feeding on the particular type of sediment need to be de termined. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.