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Biogeochemical Cycling of Cu Associated with Particulate Matter in Lake Superior

Biogeochemical Cycling of Cu Associated with Particulate Matter in Lake Superior. Jaebong Jeong Environmental Engineering Michigan Technological University. KITES Project ( K eweenaw I nterdisciplinary T ransport E xperiment in S uperior). Keweenaw Current. Offshore.

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Biogeochemical Cycling of Cu Associated with Particulate Matter in Lake Superior

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  1. Biogeochemical Cycling of Cu Associated with Particulate Matter in Lake Superior Jaebong Jeong Environmental Engineering Michigan Technological University

  2. KITES Project (Keweenaw Interdisciplinary Transport Experiment in Superior) Keweenaw Current Offshore Cross-margin transport Nearshore Courtesy of Judy Budd, MTU Thermal Bar (NOAA CoastWatch L. Superior Surface Temperature Imagery)

  3. My project: Cu cycling associated with particles (SP and mine tailings). Eagle Harbor Freda and Redridge Copper Harbor Gay Portage Canal & Torch Lake Houghton Ontonagon Keweenaw Peninsula

  4. Gay, MI Courtesy of Dave Bolgrien, EPA

  5. Freda Old Smelter Site

  6. Freda 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. 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

  11. Wisconsin red clay CH Transect EH Transect HN Transect Core Sediment (MCA2) Surface Sediment sampling Sites FR Transect Freda stamp sands ON Transect Ontonagon River sediments Major Sampling Sites Copper Harbor Eagle Harbor Redridge Freda Ontonagon

  12. Depth Profile of Cu in the Core Sediment MCA2-Surf [Cu]Tot (mmol/g sediment) Mean Mass Diameter (mm) MCA2-Cu • 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. MCA2-BG

  13. Longshore Transport ? Or Dissolution and Precipitation? Or Algae Uptake & Sink? MCA2 Copper Harbor Eagle Harbor Redridge Original dumping site of stamp sands Freda Ontonagon

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

  15. 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. Longshore & Cross-margin Transport Source Materials Settling Particles & Sediments In Lake Superior 7.06 (mg/g) Under water Cross-margin transport Total [Cu] (mg/g) Cu peak Surface Back Ground Longshore transport Settling Particles Freda Stamp Sands Ontonagon River Sediments Offshore @ the HN transect Wisconsin red clay Core Sediments • Concentrations of total Cu in the different particles.

  17. Sediment Trap Samples Copper Harbor Eagle Harbor HN Transect Cross-margin Transport Freda Ontonagon

  18. Total Cu Concentrations Bathymetry (m) 1974 Kraft (mg/kg) Grain Size of Sediments (mm) 2000 North Entry Our Data (mg/g) Redridge Freda North Entry Redridge Freda North Entry Redridge Freda Cu Concentrations in Surface Sediments

  19. Original Dumping Site Dissolved Cu Concentrations ? Contaminated Sediments with High Cu How the contaminated sediments in neashore contribute the dissolved Cu concentrations in the water column? Normal Lake Sediments

  20. Spatial Variations of Dissolved Cu 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.

  21. Nearshore/offshore gradients (HN Transect) What are the controlling factors for the gradients?

  22. Bruland, K. W., 1980 (North Pacific, Sept. 1977) Our data (L. Superior, Aug. 2000) 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.

  23. Our data 2000 Shafer and Armstrong 1990 Sigg 1987 Sunda and Susan 1995 Cu:C ratios in Settling Particles Log Cu:C • High Cu:C ratios in suspended particles give strong evidence that dissolved copper concentrations may be controlled by particles via sorption.

  24. DCM and BNL HN210, 2000 DCM BNL HN 110, August 22, 1999 Deep chlorophyll maximum (DCM) and Benthic nepheloid layer (BNL) are co-occur during summer due to biological activity and resuspension of sediments.

  25. Particle Scavenging @DCM TSP (mg/L) Transmissivity/100 (%) Particulate Cu (Fp, %) @ BNL Particulate Cu fractions are closely related to particle resuspension in the BNL. ON 210, August2000

  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?

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