1

Biogeochemical Cycling of Cu Associated with Particulate Matter in Lake Superior

Jaebong Jeong

Environmental Engineering

Michigan Technological University

2Courtesy of Judy Budd, MTU

KITES Project (Keweenaw Interdisciplinary Transport Experiment in Superior)

Nearshore

Offshore

Keweenaw Current

Cross-margin transport

Thermal Bar

(NOAA CoastWatch L. Superior Surface Temperature Imagery)

1 3

46.75

47.00

47.25

47.50

47.75

87.588.088.589.089.5

Longitude

Latit

ude

Houghton

Keweenaw Peninsula

Ontonagon

Eagle Harbor

Copper Harbor

My project: Cu cycling associated with particles (SP and mine tailings).

Freda and Redridge

Portage Canal & Torch Lake

Gay

4

Gay, MI

Courtesy of Dave Bolgrien, EPA

5Freda Old Smelter Site

6Freda Stamp Sands

7

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.

8

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.

9

Intensive Shipboard Sampling (1998~2000)

The RV Laurentian (U of Michigan)

10

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

Methodology

11

ON Transect

CH TransectEH Transect

HN Transect

FR Transect

RedridgeFreda

Ontonagon

Eagle HarborCopper Harbor

Major Sampling Sites

Ontonagon Riversediments

Fredastamp sands

Wisconsinred clay

Surface Sediment sampling Sites

Core Sediment(MCA2)

12

Depth Profile of Cu in the Core Sediment

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.

0

5

10

15

20

0.0 1.0 2.0 3.0 4.0

Dep

th (c

m)

[Cu]Tot

(mmol/g sediment)

Mean Mass Diameter

(m)

MCA2-Cu

MCA2-BG

MCA2-Surf

13

Ontonagon

Eagle HarborCopper Harbor

Longshore Transport ?

Or

Dissolution and Precipitation?

Or

Algae Uptake & Sink?

MCA2

Redridge

Freda Original dumping site of stamp sands

14

Characterization of Sediments

Glycerol-treated X-ray diffraction patterns of clay-size particles of the three source materials.

0

200

400

600

800

1000

1200

1400

2 6 10 14 18 22 26 30

2 Theta

Inte

ns

ity

Freda stamp sandsOntonagon clayWisconsin red clay

Chlorite 1 Chlorite 2

Chlorite 3

Chlorite 4

Smectite

illite 1

illite 2

illite 3

Albite

15

0 10 20 30 40 5020

30

40

50

60

7030

40

50

60

70

80

Freda 001

Freda SSMCA2-Cu

Freda 020

WI Red Clay MCA2-BG

Freda 070

Onto Clay

MCA2-Surf IChlorite

IIllite+IChlorite

Illite

ISmectite+IChlorite

ISmectite

Smectite

IIllite

Chlorite

IIllite+ISmectite

0 10 20 30 40 5020

30

40

50

60

7030

40

50

60

70

80

Freda 001

Freda SSMCA2-Cu

Freda 020

WI Red Clay MCA2-BG

Freda 070

Onto Clay

MCA2-Surf IChlorite

IIllite+IChlorite

Illite

ISmectite+IChlorite

ISmectite

Smectite

IIllite

Chlorite

IIllite+ISmectite

Mineralogical Composition

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.

16

0.0

0.5

1.0

1.5

Longshore & Cross-margin Transport

Longshoretransport

7.06 (mg/g)

Under water

Back Ground

Cu peakSurface

Freda

Stamp SandsOntonagon River

Sediments

Settling Particles

Offshore @ the HN transect

Core SedimentsWisconsin

red clay

Concentrations of total Cu in the different particles.

Cross-margin

transport

Source Materials Settling Particles & Sediments

In Lake Superior

Tot

al [

Cu

] (m

g/g)

17

HN Transect

Freda

Ontonagon

Eagle HarborCopper Harbor

Sediment Trap Samples

Cross-margin Transport

18

Cu Concentrations in Surface Sediments

North Entry

FredaRedridge

Grain Size of Sediments (m)

Freda

North EntryRedridge

Bathymetry (m)

RedridgeFreda

North Entry

Total Cu Concentrations

2000

1974

Kraft (mg/kg)

Our Data (mg/g)

19

How the contaminated sediments in neashore contribute the dissolved Cu concentrations in the water column?

Contaminated Sediments with High Cu Normal Lake

Sediments

Dissolved Cu Concentrations ?

Original

Dumping

Site

20

0

500

1000

1500

Freda HN ON

[Cu

] dis (

ng

/L)

Nearshore

Offshore

A

Spatial Variations of Dissolved Cu

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.

Transect

21

Nearshore/offshore gradients (HN Transect)

0

500

1000

1500

0 5 10 15 20 25

Distance (km)

[Cu

] dis (n

g/L

)

0.0

0.1

0.2

0.3

[Cu

] dis (

g/L

)Surface Water

Pore Water

What are the controlling factors for the gradients?

22

The Vertical Profiles of Dissolved Cu

Unlike Cu cycling in the Oceans, biological uptake and regeneration seem not to be the major processes of Cu cycling in L. Superior.

0

1

2

3

4

5

6

0 200 400 600 800 1000

[Cu] (ng/L)

Dep

th (

km)

Bruland, K. W., 1980 (North Pacific, Sept. 1977)

0

50

100

150

200

0 200 400 600 800 1000[Cu] (ng/L)

De

pth

(m

)

HN 010

ON 010

FR010

HN 210

ON 210

FR 100

Our data (L. Superior, Aug. 2000)

23

Cu:C ratios in Settling Particles

High Cu:C ratios in suspended particles give strong evidence that dissolved copper concentrations may be controlled by particles via sorption.

1

10

100

1000

LakeSuperior

LakeMichigan

LakeConstance

AlgaeCultures

North Pacific

RedfieldRatio

Sunda and Susan1995

Our data2000

Sigg1987

Shafer and Armstrong 1990

Log

Cu

:C

24

0

20

40

60

80

100

0 20 40 60 80 100

Dept

h (m

) Transmissivity (%)

Temperature (oC)

TSP (mg/L)*100

Fluorescence*1000

0

20

40

60

80

100

0 20 40 60 80 100

Dept

h (m

) Transmissivity (%)

Temperature (oC)

TSP (mg/L)*100

Fluorescence*1000

HN210, 2000

DCM and BNL

Deep chlorophyll maximum (DCM) and Benthic nepheloid layer (BNL) are co-occur during summer due to biological activity and resuspension of sediments.

HN 110, August 22, 1999

BNL

DCM

25

Particle Scavenging

Particulate Cu fractions are closely related to particle resuspension in the BNL.

0

50

100

150

200

0.0 0.2 0.4 0.6 0.8 1.0D

epth

(m)

ON 210, August2000

Transmissivity/100(%)

Particulate Cu (Fp, %)

TSP(mg/L)

@ BNL

@DCM

26

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.

27

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.

28

Questions?