A primer on trace metal-sediment chemistry
Antarctica A Keystone in a Changing World
PREFACE This Primer was originally developed as a companion volume to a short course on trace metal-sediment chemistry. The purpose of the course was to expose the participants to the basic principles and techniques that control and are used to elucidate trace metal sediment interactions. Participants were not expected to walk away from the course as experts in sediment chemistry; however, they were expected to have a good knowledge of the basic principles governing this complex subject. This
... lex subject. This Primer, organized in the same way as the instructional session, contains all the diagrams and tables used for the course, along with a descriptive text. It also includes a large list of selected references on the subject of trace metal-sediment chemistry. This list is by no means exhaustive. Many of the references were used in developing the material in the course and in the Primer. The other references are provided for information on techniques and methods, and as examples of how sediment chemistry can be used to deal with various types of environmental studies. Ill Abstract In most aquatic systems, concentrations of trace metals in suspended sediment and the top few centimeters of bottom sediment are far greater than concentrations of trace metals dissolved in the water column. Consequently, the distribution, transport, and availability of these constituents can not be intelligently evaluated, nor can their environmental impact be determined or predicted solely through the sampling and analysis of dissolved phases. This Primer is designed to acquaint the reader with the basic principles that govern the concentration and distribution of trace metals associated with bottom and suspended sediments. The sampling and analysis of suspended and bottom sediments are very important for monitoring studies, not only because trace metal concentrations associated with them are orders of magnitude higher than in the dissolved phase, but also because of several other factors. Riverine transport of trace metals is dominated by sediment. In addition, bottom sediments serve as a source for suspended sediment and can provide a historical record of chemical conditions. This record will help establish area baseline metal levels against which existing conditions can be compared. Many physical and chemical factors affect a sediment's capacity to collect and concentrate trace metals. The physical factors include grain size, surface area, surface charge, cation exchange capacity, composition, and so forth. Increases in metal concentrations are strongly correlated with decreasing grain size and increasing surface area, surface charge, cation exchange capacity, and increasing concentrations of iron and manganese oxides, organic matter, and clay minerals. Chemical factors are equally important, especially for differentiating between samples having similar bulk chemistries and for inferring or predicting environmental availability. Chemical factors entail phase associations (with such sedimentary components as interstitial water, sulfides, carbonates, and organic matter) and ways in which the metals are entrained by the sediments (such as adsorption, complexation, and within mineral lattices).