A primer on sediment-trace element chemistry

Abstract

BioavailabilityIn general, refers to that portion of dissolved, biologically-, or sediment-associated chemical constituents that are readily accessible to biota either through physical contact or by ingestion; this is an operationally defined term. Bottom sediment, bed sediment, bed materialInterchangeable terms that refer to material that temporarily is stationary in the bottom of a water course. Dissolved load, dissolved constituentOperationally defined as that material that passes through a 0.45-fim (micrometer) filter. Geochemical factorsRefers to various physical and chemical characteristics which can affect a sediment's chemical concentration. Geochemical substrateRefers to the compounds or substances that are important in providing a sediment with the capacity to collect and retain trace elements.Isokinetic A term used to describe a type of suspended sediment sampling in which a whole water sample is collected such that no acceleration or deceleration is imparted to the mixture as it enters the sampling device.Operationally defined Refers to the quantitation of a physical or chemical constituent or property which is dependent on the method used for its determination.If the method is altered the measurement changes also; many of the physical and chemical determinations performed on sediment/solid samples fall into this category. SedimentParticles derived from rocks or biological materials that have been transported by a fluid, or solid material suspended in or settled from water. Suspended load, suspended constituentOperationally defined as that material that is retained by a 0.45-fim (micrometer) filter during the filtration of a whole water sample. Suspended sediment, seston, particulatesInterchangeable terms that refer to a material actively transported by a fluid.Total concentration Refers to the true concentration of a constituent in a sediment/ solid sample; geochemists further define total as >95 percent of the actual concentration in the material being analyzed.Certain analytical procedures, or digestion techniques can produce a measure of total concentration without the complete dissolution of a solid sample.Unless otherwise stated, concentrations in this Primer are totals. Total recoverable concentrationRefers to the concentration of a constituent in a sediment/solid sample that has been extracted with a reagent(s) that does not completely solubilize the constituent; in other words, this is an operationally defined concentration, the definition being dependent upon the extraction procedure. Trace element, trace metal, heavy metal, metalTerms that are used interchangeably throughout the sediment-chemical literature and this Primer.VI Table 1.4-1.Transport (in metric tons/day) of Trace Elements Associated with Suspended Sediment in Selected Rivers Element Susauehanna River 3/8/79 Discharge1 346,000 CFS Concentration2 Transport3 in mg/L in metric tons/day Sediment 406 344,200 Iron 12 10,200 Manganese 0.59 500 Zinc 0.07 59 Lead 0.018 15 Copper 0.015 13 Cobalt 0.010 8.5 Chromium 0.003 2.5 Nickel Arsenic Willamette River 1/16/80 189,000 CFS Concentration2 Transport in mg/L in metric tons/day 106 49,100 4.4 2,040 0.10 46 0.03 14 0.005 23 0.006 2.8 0.010 4.6 0.004 1.9 0.002 0.9 MississiDoi River 1/18/81 671,000 CFS 3 Concentration2 Transport3 in mg/L in metric tons/day 641 1,050,000 46 75,600 1.3 2,140 0.09 148 0.03 49 0.018 30 0.005 8.2 0.028 46 0.035 58 0.012 20 Discharge -in cubic feet per second Concentration -total recoverable, in milligrams per liter 3Sediment and chemical transport in metric tons per day, calculated from Porterfleld, 1972: (concentration, in milligrams per liter)(discharge, in cubic feet per second) 0.00245 'Discharge during the sampling operation remained constant at 1995 ft'/s (56.5mVs) with no change in stage 4.27 ft (130 m) 'Underlined data are significantly different from the others In the same column