Presentation on theme: "Some Uses of Channel Bed Sediment Concentration Data"— Presentation transcript:
1Some Uses of Channel Bed Sediment Concentration Data Determine the spatial distribution of trace metalsIdentify point and non-point sources of pollutionAssessment of the rates and patterns of contaminant dispersalFirst approximation of potential ecological and human health effects (and regional water quality surveys)Monitoring of potential impacts of waste waters from industrial or municipal sitesGeochemical exploration (surveys)
2Downstream Trends in Channel Bed From Salomons& Forstner, 1984Where point sources are present the concentrations generally decline from the point of input.
3Concentrations of Cu and Ni in the <63 um fraction of channel bed sediments from the Po River, Italy. Samples were collected in the summer (grey bars) and winter (black bars). Acronyms along x-axis represent successive downstream sampling sites. Note minimal variations in concentration between seasons.Viganò, L., and 14 others, Quality assessment of bed sediments of the Po River (Italy). Water Research, 37: (from 2 of 8 graphs from figure 3, page 507)
4Downstream Trends in Channel Bed From Salomons& Forstner, 1984Where point sources are present the concentrations generally decline from the point of input.
5Bedload temporarily at rest ScaleCharacteristicTransitory depositsMicro-formsMeso-formsBedload temporarily at restCoherent structures such as ripples with λ ranging from 10-2 to 100 mFeatures with λ from 100 to 102 m; includes dunes, pebble clusters and transverse ribsAlluvial barsMacro-formsMega-formsFrom by lag deposition of coarse-grained sedimentStructures with λ from 101 to 103 m such as riffles, point bars, alternate bars, and mid-channel barsStructures with λ > 103 m such as sedimentation zonesCharacteristics of channel deposits (adapted from Knighton 1998; Church and Jones 1982; Hoey 1992)
6Figure from Huggett, J.R., Fundamental of Geomorphology, Routledge Fundamentals in Physical Geography, Routledge, London, fig. 7.7, p. 185.
8SecondaryFlow DirectionsPoint BarSuper ElevatedWater SurfaceFrom Markham, A.J. and Thorne, C.R., Geomorphology of gravel-bed river bends. In: P. Billi, R.D. Hey, C.R. Thorne, and P. Tacconi, (eds.), Dynamics of Gravel-bed Rivers, pp , New York, Jonh Wiley and Sons, Ldt., figure 22.2, p. 436.
9From Thompson, A., Secondary Flows and the Pool-Riffle, Earth Surface Processes and Landforms, 11: , Figure 4, p. 636.
10Reading, H.G., 1978. Sedimentary Environments and Facies, Blackwell Publications, New York, Fig. 3.26, page 34. Company may have been purchased by Elsevier?
11Figure 20. Laremie River, Wyoming (photo by J. R Figure 20. Laremie River, Wyoming (photo by J.R. Balsley); obtained from USGS Photo Library
12Knighton, D., 1998. Fluvial Form and Processes: A New Perspective, Arnold, London. Fig. 5.23, p. 233.
14Grain-Size & Compositional Variations Ladd et al. 1998Examined trace metal concentrations in 7 morphological units in Soda Butte Creek, Montana(lateral scour pools, eddy drop zones, glides, low gradient riffles, high gradient riffles, attached bars, and detached bars)Highest concentrations in eddy drop zones and attached lateral bars with largest amount of fine sediment
15Density-Dependent Variations Slingerland and Smith (1986) define a placer as “a deposit of residual or detrital mineral grains in which a valuable mineral has been concentrated by a mechanical agent,”A contaminant placer is defined here as a concentration of metal enriched particles by the hydraulic action of the river. Where they occur, trace metal concentrations will be locally elevated in comparison to other areas (Miller & Orbock Miller, 2007)
16Guilbert, J. M. and Park, C. F. , Jr. , 1986 Guilbert, J.M. and Park, C.F., Jr., The Geology of Ore Deposits. New York, W.H. Freemand and Company, figures 16-1, p. 746 and 16-4b p.749.
17Bateman, A. M. , 1950. Economic mineral deposits, 2nd edition Bateman, A.M., Economic mineral deposits, 2nd edition. New York, Wiley and Sons.
24Variations Dependent on Time and Frequency of Inundation ExamplesQueens Creek, ArizonaRio Pilcomayo, Bolivia
25Graf, W. L. , Clark, S. L. , Kammerer, M. T. , Lehman, T. , Randall, K Graf, W.L., Clark, S.L., Kammerer, M.T., Lehman, T., Randall, K., Tempe, R., and Schroeder, A., Geomorphology of heavy metals in the sediments of Queen Creek, Arizona, USA. Catena, 18: , figures 2, p. 572 and 6, p. 578.
31High-WaterChannel DepositsLow-WaterRio Pilcomayo, southern Bolvia near Uyuni. Photo taken in July during the dry season.
32Implications to Sampling Local variations – referred to as small scale or field variance (Birch et al. 2001)Can be on the order of 10 to 25 % relative standard deviation and may be significantly greater than analytical variation (error)May hinder ability to decipher differences in contaminant levels between sample sitesReconnaissance level surveys and sample stratification by morphological units ?Sampling of specific units only?Composite sampling to minimize within unit variations
33Changes in Sediment Composition Can: Influence the spatial and temporal concentration patterns observed in aquatic systemsHinder the determination of localized inputs of trace metals from either natural sources (e.g., ore bodies) or anthropogenic sources (e.g., mining operations or industrial complexes).Changes in grain-size have a particularly significant influence on metal concentrations.
34Types of Mathematical Manipulations Commonly Applied to Bulk Metal Data After Horowitz, 1991 Corrections for Grain-size differencesNormalization to a single grain-size rangeCarbonate content correctionsRecalculation of concentration data on a carbonate-free basisNormalization to a conservative elementalUse of multiple Normalizations
35Methods of Handling the Grain Size Effect Analysis of a specific grain-size fraction which is considered to be the chemical active phaseDoes not provide for an understanding of the actual concentrations that exist in the bulk sampleInhibits the calculation of total trace metal transport ratesNormalize the metal concentration data obtained for the bulk (< 2mm or sand) sized fraction using some form of mathematical equation and grain size data obtained from a separate sampleProvides actual concentration found in bulk samplePoorly documents the concentrations that would actually be measured in the finer-grain size fractions
36Designation of Chemical Active Sediment Phase Numerous size fractions have been used as the chemical active phase including <2 µm, <16 µm, <20 µm, <63 µm, <70 µm, <155 µm, <200 µm (Horowitz, 1991)Argument for using < 63 µm fractionIt can be extracted from the bulk sample via sieving, a process which does not alter trace metal chemistryIt is the particle size most commonly carried in suspension by rivers and streams and may therefore be the most readily distributed through the aquatic environment
37Grain Size Normalization NormalizedConcentration=(DF *Bulk Metal Concentration)Where,DF = Dilution Factor= 100/(100 - % of sediment > size range of Interest)
38Concentration vs. Quantity of Fine Sediment Sizes Frequently Used2 μm16 μm62.5 μm63 μm70 μm125 μm200 μmData from deGroot et al., 1982
40Differences between Measured and Normalized Values Selected chemical active phase (grain size fraction) may not contain all of the trace metalsDifferences in concentration are not solely due to grain size variationsData contain analytical errors associated with grain size or geochemical analyses
41Fractional Contributions of Selected Metals in Suspended Sediments ConcentrationPercent ContributionConstituent(mg/kg)<63 μmfraction>63 μmTotal SampleArkansas River (sampled 5/11/87)a,bMn110060080050Cu5122335842Zn3251101906337Pb5225355446Cr5644494357Ni32165545Co151112.5Cowlitz River (sampled 4/20/87)a,c6506706604060626859121010.81953471441aThe represents the mean of the initial and final composite samples obtained at these sampling sites. b<63 μm fraction equaled 37 %, >63 μm fraction equaled 63 %, c <63 μm fraction equaled 41 %, >63 μm equaled 59 %.Fractional Contributionsof Selected Metals inSuspended Sediments(modified from Horowitz et al., 1990)
42Carbonate Correction Normalized Concentration Assumes: Carbonate does not contain substantial quantities of trace metals and, thus, acts as a diluent. May not be true of Cd and Pb.Generally applied to streams in calcareous terrains, particularly those in areas with karst.NormalizedConcentration(DF *Bulk Metal Concentration)=Where,DF = Dilution Factor= 100/(100 - % of carbonate in sample)
43Conservative Element Corrections Assumes that some elements have had a uniform flux from crustal rocks. Thus, normalization to these elements provides a measure (or level) of dilution that has occurred.Elements most commonly used are Al, Ti, and to a lesser extent, Cs and Li.Normalizedvalue = (Concentration of Trace Metal)(Concentration of conservative element)Note: this generates a ratio, not a concentration as did the previousprocedures