some uses of channel bed sediment concentration data determine the spatial distribution of trace...
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Some Uses of Channel Bed Sediment Concentration Data
• Determine the spatial distribution of trace metals– Identify point and non-point sources of pollution– Assessment of the rates and patterns of contaminant dispersal
• First approximation of potential ecological and human health effects (and regional water quality surveys)
• Monitoring of potential impacts of waste waters from industrial or municipal sites
• Geochemical exploration (surveys)
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Downstream Trends in Channel Bed
• Where point sources are present the concentrations generally decline from the point of input.
From Salomons& Forstner, 1984
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Concentrations 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, 2003. Quality assessment of bed sediments of the Po River (Italy). Water Research, 37:501-518. (from 2 of 8 graphs from figure 3, page 507)
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Downstream Trends in Channel Bed
• Where point sources are present the concentrations generally decline from the point of input.
From Salomons& Forstner, 1984
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Characteristics of channel deposits (adapted from Knighton 1998; Church and Jones 1982; Hoey 1992)
Scale Characteristic
Transitory deposits Micro-forms Meso-forms
Bedload temporarily at rest
Coherent 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 ribs
Alluvial bars Macro-forms
Mega-forms
From 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 zones
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Braided Island Braided Anastomosing
Meandering Braided
Meandering
Meandering
Laterally Inactive Channels Laterally Active Channels
Straight-Island Form
Straight-Ridge Form
Sinuous-Stable
Braided
AnabranchingRivers
Meandering
Single-ChannelRivers
Single-ChannelRivers
AnabranchingRivers
(B)
(A) Bedload Mixed Load Suspended LoadStraight Straight Straight
Figure from Huggett, J.R., 2003. Fundamental of Geomorphology, Routledge Fundamentals in Physical Geography, Routledge, London, fig. 7.7, p. 185.
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Ele
vatio
n
Distance Downstream
Riffle
Riffle
Riffle
Pool
Pool
Mean Water Surface Slope
Point Bars Pools
Riffle
Point BarPoint Bar
Point Bar
Point Bar
Point Bar
Pools
Riffle
(A)
(B)
(C)
Meandering Channel
Straight Channel
Longitudinal Profile
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From Markham, A.J. and Thorne, C.R., 1992. 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. 433-456, New York, Jonh Wiley and Sons, Ldt., figure 22.2, p. 436.
Secondary Flow Directions
Point Bar
Super ElevatedWater Surface
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From Thompson, A., 1986. Secondary Flows and the Pool-Riffle, Earth Surface Processes and Landforms, 11:631-641., Figure 4, p. 636.
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Reading, H.G., 1978. Sedimentary Environments and Facies, Blackwell Publications,New York, Fig. 3.26, page 34. Company may have been purchased by Elsevier?
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Figure 20. Laremie River, Wyoming (photo by J.R. Balsley); obtained from USGS Photo Library
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Knighton, D., 1998. Fluvial Form and Processes: A New Perspective, Arnold, London.Fig. 5.23, p. 233.
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Grain-Size & Compositional Variations
• Ladd et al. 1998– Examined 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
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•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)
Density-Dependent Variations
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Guilbert, J.M. and Park, C.F., Jr., 1986. The Geology of Ore Deposits. New York, W.H. Freemand and Company, figures 16-1, p. 746 and 16-4b p.749.
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Bateman, A.M., 1950. Economic mineral deposits, 2nd edition. New York, Wiley and Sons.
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Reservoir
0
1
1B2
2B
3 4
5
67
7B
7C 7D9 10
11
1213 14
15
16 1718
Gagingstation
GagingStation
MineralCanyon
Dayton
CarsonCity
VirginiaCity
TableMtn.
Canyon
(Brunswick)
FortChurchill
395
0
0 1 2 3 4
1 2 3 4 5 Miles
Km
95
Six Mile
Canyon Fan
Gold Canyon
Six M
ile Canyon
Fork
Reno Fallon
CarsonCity
Carson River
Watershed Boundary
Carson Lake
Carson Playa Stillwater
WildlifeRefuge
Lahontan Reservoir
LakePyramid
SIERRA NEVADA
NevadaCalifornia
ForkE
ast
Truckee R
.
Car
son
R.
Tru
ckee
R
.Wes
tF
ork
C
arso
n R. .
Lake Tahoe
Lahontan
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Eureka Mill, Brunswick Canyon
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0
2
4
6
8
10
12
Me
rc
ury
Co
nc
en
tra
tio
ns
(u
g/g
)
0 20 40 60 80 100
Distance Downstream from 395 (km)
Pool Riffle Point BarChannel
Hg Concentrations In Channel Bed
LahontonReservoir
GoldCanyon
SixmileCanyon
MineralCanyon
Carson City
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Variations Dependent on Time and Frequency of Inundation
• Examples– Queens Creek, Arizona– Rio Pilcomayo, Bolivia
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Graf, W.L., Clark, S.L., Kammerer, M.T., Lehman, T., Randall, K., Tempe, R., and Schroeder, A., 1991. Geomorphology of heavy metals in the sediments of Queen Creek, Arizona, USA. Catena, 18:567-582, figures 2, p. 572 and 6, p. 578.
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StudyArea
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“Modern Mine”
Pb & Zn ConcentrateBall Mill
Floatation Process
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Sampling Site RP-1~1.5 miles from Mills
Floatation Mill, Potosi
20 miles from Mills
You want me to live where?
Effluent
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20 miles from Mills
~60 miles from Mills
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Yikes!
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High-WaterChannel Deposits
Low-Water Channel Deposits
Rio Pilcomayo, southern Bolvia near Uyuni. Photo taken in July during the dry season.
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Implications 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 sites
• Reconnaissance level surveys and sample stratification by morphological units ?
• Sampling of specific units only?
– Composite sampling to minimize within unit variations
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Changes in Sediment Composition Can:
• Influence the spatial and temporal concentration patterns observed in aquatic systems
• Hinder 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.
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Types of Mathematical Manipulations Commonly Applied to Bulk Metal Data
After Horowitz, 1991
• Corrections for Grain-size differences
• Normalization to a single grain-size range
• Carbonate content corrections
• Recalculation of concentration data on a carbonate-free basis
• Normalization to a conservative elemental
• Use of multiple Normalizations
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Methods of Handling the Grain Size Effect
• Analysis of a specific grain-size fraction which is considered to be the chemical active phase– Does not provide for an understanding of the actual
concentrations that exist in the bulk sample– Inhibits the calculation of total trace metal transport rates
• Normalize 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 sample– Provides actual concentration found in bulk sample– Poorly documents the concentrations that would actually be
measured in the finer-grain size fractions
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Designation 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 fraction– It can be extracted from the bulk sample via sieving, a
process which does not alter trace metal chemistry
– It 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
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Grain Size Normalization
Normalized Concentration
= (DF *Bulk Metal Concentration)
Where,
DF = Dilution Factor
= 100/(100 - % of sediment > size range of Interest)
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Concentration vs. Quantity of Fine Sediment
Sizes Frequently Used
•2 μm
•16 μm
•62.5 μm
•63 μm
•70 μm
•125 μm
•200 μm
Data from deGroot et al., 1982
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Data from Horowitz and Elrik, 1988
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Differences between Measured and Normalized Values
• Selected chemical active phase (grain size fraction) may not contain all of the trace metals
• Differences in concentration are not solely due to grain size variations
• Data contain analytical errors associated with grain size or geochemical analyses
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Fractional Contributions of Selected Metals in Suspended Sediments
ConcentrationPercent Contribution
Constituent(mg/kg)
<63 μmfraction
>63 μmfraction
Total Sample
<63 μmfraction
>63 μmfraction
Arkansas River (sampled 5/11/87)a,b
Mn 1100 600 800 50 50
Cu 51 22 33 58 42
Zn 325 110 190 63 37
Pb 52 25 35 54 46
Cr 56 44 49 43 57
Ni 32 16 22 55 45
Co 15 11 12.5 45 55
Cowlitz River (sampled 4/20/87)a,c
Mn 650 670 660 40 60
Cu 63 33 46 57 43
Zn 62 68 59 42 58
Pb 12 10 10.8 45 55
Cr 35 19 25 56 44
Ni 25 16 19 53 47
Co 14 14 14 41 59
aThe 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 %.
(modified from Horowitz et al., 1990)
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Carbonate Correction
• 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.
Where,
DF = Dilution Factor
= 100/(100 - % of carbonate in sample)
Normalized Concentration (DF *Bulk Metal Concentration)=
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Conservative 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.
• Normalized value = (Concentration of Trace Metal) (Concentration of conservative element)
Note: this generates a ratio, not a concentration as did the previous procedures