Transcript Distribution and dynamics of suspended particles in the

Biogeochemical Cycling of Cu Associated
with Particulate Matter in Lake Superior
Jaebong Jeong
Environmental Engineering
Michigan Technological University
1
KITES Project (Keweenaw Interdisciplinary Transport Experiment in Superior)
Keweenaw Current
Thermal Bar
Courtesy of Judy Budd, MTU
2
(NOAA CoastWatch L. Superior Surface Temperature Imagery)
My project: Cu cycling associated with particles (SP and mine tailings).
47.75
Eagle Harbor
Freda and Redridge
47.50
Latitude
Copper Harbor
Gay
Houghton
Portage Canal
& Torch Lake
Ontonagon
Keweenaw Peninsula
89.5
89.0
88.5
Longitude
47.25
47.00
46.75
88.0
87.5
3
Gay, MI
4
Courtesy of Dave Bolgrien, EPA
Freda Old Smelter Site
5
Freda Stamp Sands
6
 Copper (Cu)
 Copper is a trace metal essential to healthy life of
plants and animals (micro-nutrient).
 The elevated copper concentrations have toxic effects
on animal and plant communities.
 Particulate matter (PM)
 Particles play an important role in regulating trace
metals (sink and source terms).
 It is important to understand copper cycling associated with
particles in this area.
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Objectives
 Characterize the source sediments (Freda Stamp
Sands, Ontonagon sediments, Wisconsin red clay).
 Investigate transport of suspended particles and
sediments redistribution.
 Investigate the spatio-temporal patterns of dissolved Cu.
 Identify the factors controlling biogeochemical cycling of
Cu.
8
Intensive Shipboard Sampling (1998~2000)
9
The RV Laurentian (U of Michigan)
Methodology
 Sediment and Suspended Particles
Total Suspended Particles (TSP): GFF filters
Particle Size of Sediments: Sieve & Particle Counter
Mineralogical Composition: XRD
Chemical Composition: Chemical Extractions & ICP and AAS
Organic Carbon and Nitrogen of Suspended Particles: TOCA
 Water
Dissolved Cu: Ultraclean Technique (Teflon)
Cu analysis: Atomic Absorption Spectrophotometer (AAS)
Cations and Anions: Ion Chromatography
Alkalinity: PC-TitrateTM Autotitrator
CTD data: Conductivity, Temperature, Chlorophyll a, &
Transmissivity
10
Major Sampling Sites
Wisconsin
red clay
CH Transect
EH Transect
Eagle Harbor
HN Transect
Copper Harbor
Surface Sediment
sampling Sites
FR Transect
Core Sediment
(MCA2)
Redridge
Freda
ON Transect
Ontonagon
Freda
stamp sands
Ontonagon River
sediments
11
Depth Profile of Cu in the Core Sediment
0.0
1.0
2.0
3.0
4.0
Depth (cm)
0
MCA2-Surf
5
10
[Cu]Tot
(mmol/g sediment)
MCA2-Cu
Mean Mass Diameter
(mm)
15
20
MCA2-BG
 The background level of Cu is 0.1 mmol/g Sediment.
 The Core Sediment shows the maximum Cu concentration at
2.5~3cm depth and slightly high Cu in the surface.
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Longshore Transport ?
Or
Dissolution and Precipitation?
Or
Algae Uptake & Sink?
MCA2
Copper Harbor
Eagle Harbor
Redridge
Freda
Original dumping site
of stamp sands
Ontonagon
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Characterization of Sediments
Freda stamp sands
Ontonagon clay
Wisconsin red clay
1400
illite 3
1200
Smectite
Intensity
1000
Chlorite 1
Chlorite 2
Chlorite 4
illite 1
800
Chlorite 3
Albite
illite 2
600
400
200
0
2
6
10
14
18
22
26
30
2 Theta
 Glycerol-treated X-ray diffraction patterns of clay-size particles of the
three source materials.
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Mineralogical Composition
Illite
30
70
40
60
50
Freda SS
IChlorite
IIllite +IChlorite
60
MCA2-Surf
IIllite
50
IIllite +ISme ctite
Freda 020
MCA2-Cu
Freda 001
40
Onto Clay
Freda 070
70
WI Red Clay
80
Chlorite
0
10
20
30
MCA2-BG
40
30
50
20
Smectite
ISme ctite
ISme ctite +IChlorite
 Ternary phase diagram (Illite-Smectite-Chlorite system) of clay minerals
 Three sediment source materials (triangle) and near Freda lake
sediments (circle) including a core sediment.
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Longshore & Cross-margin Transport
Source Materials
7.06 (mg/g)
1.5
Settling Particles & Sediments
In Lake Superior
Total [Cu] (mg/g)
Under water
1.0
Longshore
transport
Cross-margin
transport
Cu peak
Surface
Back
Ground
0.5
Settling Particles
0.0
Freda
Ontonagon River Wisconsin
Stamp Sands Sediments
red clay
Offshore @ the
HN transect
Core Sediments
 Concentrations of total Cu in the different particles.
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Sediment Trap Samples
Copper Harbor
Eagle Harbor
HN Transect
Freda
Ontonagon
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Cu Concentrations in Surface Sediments
Total Cu Concentrations
Grain Size of Sediments (mm)
1974
North Entry
Freda
Kraft (mg/kg)
Redridge
Bathymetry (m)
2000
Freda
North Entry
Redridge
Our Data (mg/g)
Freda
North Entry
Redridge
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Original
Dumping
Site
Dissolved Cu Concentrations ?
Contaminated Sediments
with High Cu
Normal Lake
Sediments
How the contaminated sediments in neashore contribute the
dissolved Cu concentrations in the water column?
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Spatial Variations of Dissolved Cu
[Cu]dis (ng/L)
1500
A
Nearshore
Offshore
1000
500
0
Freda
HN
ON
Transect
 Nearshore/offshore gradients in concentrations of dissolved Cu were
found due to the dissolution of Cu-rich tailings and river inputs.
 These values are low due to rapid mixing and dispersing.
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Nearshore/offshore gradients (HN Transect)
0.3
Surface Water
Pore Water
1000
0.2
500
0.1
0
0.0
0
5
10
15
20
[Cu]dis (m g/L)
[Cu]dis (ng/L)
1500
25
Distance (km)
What are the controlling factors for the gradients?
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The Vertical Profiles of Dissolved Cu
[Cu] (ng/L)
0
200
400
600
800 1000
0
0
2
Depth (m)
Depth (km)
50
3
4
6
800 1000
0
1
5
200
[Cu] (ng/L)
400 600
100
HN 010
ON 010
FR010
HN 210
ON 210
FR 100
150
Bruland, K. W., 1980
(North Pacific, Sept. 1977)
200
Our data
(L. Superior, Aug. 2000)
 Unlike Cu cycling in the Oceans, biological uptake and regeneration
seem not to be the major processes of Cu cycling in L. Superior.
22
Cu:C ratios in Settling Particles
1000
Our data
2000
Log Cu:C
Shafer and Armstrong
1990
100
Sigg
1987
Sunda and Susan
1995
10
1
Lake
Superior
Lake
Michigan
Lake
Constance
Algae
Cultures
North
Pacific
Redfield
Ratio
 High Cu:C ratios in suspended particles give strong evidence that dissolved
copper concentrations may be controlled by particles via sorption.
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DCM and BNL
0
HN210, 2000
20
40
60
80
100
0
20
Depth (m)
DCM
40
60
Transmissivity (%)
TSP (mg/L)*100
Fluorescence*1000
BNL
80
Temperature (oC)
100
HN 110, August 22, 1999
Deep chlorophyll maximum (DCM) and Benthic nepheloid layer (BNL) are cooccur during summer due to biological activity and resuspension of sediments.
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Particle Scavenging
0.0
0.2
0.4
0.6
0.8
1.0
0
@DCM
Depth (m)
50
100
TSP
(mg/L)
Transmissivity/100
(%)
Particulate
Cu (Fp, %)
@ BNL
150
ON 210, August2000
200
Particulate Cu fractions are closely related to particle resuspension in the BNL.
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Conclusions (Particle Transport)
 Copper tailings are distinguishable from other sediment sources and
usable as tracers for particle transport and sediment redistribution.
 The Keweenaw Current is responsible for the longshore transport of
fine particles, whereas wave action causes the lateral transport of the
coarse deposits along the shore.
 Bathymetry also plays an important role for movements of
resuspendable sediments.
 Some cross-margin transport occurs as evidenced by Cu-rich
particles in surface sediments and sediment traps in offshore stations.
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Conclusions (Cu Cycling)
 Continuous dissolution of Cu from the Cu-rich mine tailings causes
high Cu concentrations found in the nearshore zones.
 Tributaries containing high Cu concentrations contribute to spatial
variation in dissolved Cu in the Ontonagon area.
 Uniform depth profile and high Cu:C ratios in the settling particles
suggest that dissolved Cu is controlled by the suspended particles via
sorption rather than biological activity.
 Also, physical processes (i.e., the fast mixing of the entire water body
and transport by currents) appear to be significant factors regulating
the dissolved copper.
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Questions?
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