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Trace Metal Signals in Hawaiian Sediments: Elucidating Background from Anthropogenic Signals

Trace Metal Signals in Hawaiian Sediments: Elucidating Background from Anthropogenic Signals. Eric Heinen De Carlo, Ph.D. Research Professor. Questions. What are “natural” TM levels in Hawai‘i? What are sources of TM?

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Trace Metal Signals in Hawaiian Sediments: Elucidating Background from Anthropogenic Signals

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  1. Trace Metal Signals in Hawaiian Sediments:Elucidating Background from Anthropogenic Signals Eric Heinen De Carlo, Ph.D. Research Professor

  2. Questions • What are “natural” TM levels in Hawai‘i? • What are sources of TM? • What are spatial and temporal variabilities of TM levels in the aquatic environment? • How do freshets mobilize anthropogenic TM? • How does surface water transport impact TM concentrations? • What are fate and impact of TM in Hawai‘ian waters?

  3. Background The concentration of a given TM observed in the absence of anthropogenic input Is this definition appropriate? What controls “background”? An alternative definition … The concentration of a given TM observed prior to the current activity/land use Geochemists prefer the former… but this is not necessarily appropriate for environmental and/or regulatory purposes…

  4. Approach • Examine various systems in Hawai‘i • Sample land, streams, lakes, estuaries, and the near-shore ocean • Collect time series samples in streams (base and storm flows) • Determine TM concentrations & isotopic compositions • Conduct laboratory experiments • Carry out statistical evaluation of data…

  5. Media of Interest for TM Studies • Water • Source rocks • Surface soils, soil cores (Honolulu) • Sediment cores (Ala Wai, Kane‘ohe Bay, Pololu wetlands, Lake Waiau) • Streambed sediments (USGS/NAWQA) • Suspended particulate matter • Road deposited sediment (RDS) • Other media (corals, tree rings)

  6. Important Local Factors: Topography, Wind and Rain • Influence rainfall patterns • Determine erosion • Affect sediment transport Uniform source materials (volcanic rocks)  Control (natural) composition

  7. Rainbow Falls (Hilo, Hawai‘i) during low and high flows (August 2000)

  8. Turbidity in Hawaiian Streams • Turbidity (in streams) due entirely to TSS • Relative inter stream homogeneity

  9. Site Selection Criteria • Areas expected to be “unimpacted” • Sites draining specific “land use” • “Integrator” sites • Where simple/specific processes dominate • Sites with well-characterized soil/rock types

  10. The Ala Wai Canal Watershed • Small well constrained watershed (crest to ocean ~9 km) • Steep (Elevation range 0-914 m) • High rainfall (and gradient ~450 to 50 cm) • Various land uses • Good USGS stream flow characterization

  11. Waiakeakua…a background site? • Conservation (mostly…) • Tributary to Mānoa Stream • Basalt substrate

  12. Kaimuki HS (KHS) an Integrator site • Urban setting • Modified stream channel • Below confluence of Mānoa and Palolo Streams • Carbonate substrate

  13. The Ala Wai Canal

  14. Metals in Mānoa Stream All concentrations in ppb

  15. Metals in Mānoa Stream, (Baseflow & Storms)

  16. Mean Enrichment Factors Mean conc. of TM at KHS Mean conc. of V at KHS Mean conc. of TM at WK Mean conc. of V at WK • EF = 1: No enrichment • EF > 1: Urban enrichment • EF < 1: Conservation land enrichment

  17. SPM (Mānoa Stream) Nickel (EF = 1.03) Chromium (EF = 0.94) Vanadium (reference) No apparent urban enrichment… yet HIGH levels!

  18. SPM (Mānoa Stream) Lead (EF = 5.58) Zinc (EF = 2.47) Copper (EF = 1.63) Strong urban enrichments suggest anthropogenic inputs

  19. SPM (Mānoa Stream) Barium (EF = 2.14) Cobalt (EF = 1.49) Copper

  20. SPM (Mānoa Stream) Arsenic (EF = 0.46) Strongest upper watershed enrichment of all TE Source???

  21. 0.2 2001 district averages based on >54 samples, WK average based on 53 storm samples

  22. Pb in Ala Wai Canal Sediments Historical trends from sediment cores

  23. “Background” vs. Canadian Sediment Guidelines Are Cu and Zn problems? (Cr even worse) All concentrations in mg/kg

  24. Pb in Streamed Sediments (NAWQA) Urban versus rural settings All concentrations in mg/kg

  25. Controls on Trace Element Concentrations • Rock Type (natural source) • Climate and Weathering • Soil Type (product of BGC reactions) • Mobility (Kd) of TE • Biological effects • Erosion/Local Transport • Local Anthropogenic Input • Long Range Transport/Input

  26. Rock Compositions Hawaii (volcanic) vs continental (granitic) settings

  27. Source Rock and Weathering Weathering depends on rock type and climate • Hawaii has primarily mafic and ultramafic rocks • Tropical and humid climate leads to fast weathering • TM levels depend on mobility From Physical Geology (Judson et al. 1987)

  28. Source Rock and Weathering-2 Data for Kauai basalt/saprolite, reproduced from Y.H. Li (2000)

  29. Effect of Soil Type Total Cu concentrations (mg/kg) in soils on various parent materials Sandy soils on drift (Arenosols, Podzols) 2-10Sandy soils on granite 10Silty clay loams on shales (Gleysols, Cambosols, etc.) 40Clays developed on clay rocks (Gleysols) 10-27Loams developed on basalt rock (Cambisols and others) 40-150Humic loams on chalk 7-28Organic rich loams on loess (Chernozems) (ave. 30) 1-100Soils developed on pumice (Lithosols/Arenosols) 3-25Tropical soils (Ferralsols) 8-128 From Heavy Metals in Soil (Alloway 1990) Table Courtesy of J. Fern, Earth Tech

  30. Distribution Coefficients (Kd) Kd = (Concentration of X)solid /(Concentration of X)liquid Data for Waiakeakua Stream (Irving, 1998)

  31. Solid Phase Partitioning • Used to evaluate TM associations • Control by source materials • Operational definition • Useful in evaluating mixtures of sources • Provides indication of “availability”

  32. Solid Phase Partitioning Acid Treatment on SPM Filtration 0.01N HNO3 Leach: Mobilize “available” metals (easily released fraction) SPM Replicate 1 15N HNO3 Leach: Mobilize all but most refractory metals Storm Water Sample SPM Replicate 2 SPM Replicate 3 Aqua Regia (HNO3/HCl) & HF: Total particulate dissolution (total metal concentration)

  33. SPM from MānoaStream 0.01N HNO3Leach (pH 2) 15N HNO3 Leach

  34. Biological Uptake? Hg (NAWQA) All concentrations in mg/kg

  35. Cadmium (NAWQA) All concentrations in mg/kg

  36. Copper (NAWQA) All concentrations in mg/kg

  37. Zinc (NAWQA) All concentrations in mg/kg

  38. Some Methods of Evaluating TM Data • Scatter plots of two or more TE • Box and whisker plots • Normalization to reference element(s) • Use of linear regressions (and deviations therefrom) • Frequency distributions • Cumulative frequency distributions • Principle Component Analysis (PCA)

  39. Box and Whisker Plots

  40. Normalization of Data • Normalization to reference element (RE) • Allows to evaluate mineralogically based variability (dilution or enrichment) • RE used should be relatively immobile (e.g., Al, Fe, Ti, but need to be careful…) • RE can also be an element such as Ca • Application to systems with mixed composition (e.g., laterite + carbonate in Ala Wai canal sediments)

  41. Ala Wai Sediments ???

  42. Linear Regressions-1 Data courtesy of W. Wen, Earth Tech, Honolulu, HI

  43. Linear Regressions-2

  44. Copper Concentration (mg/kg) Cumulative Frequency Diagrams • Linear scale • Use changes in slope (i.e., the inflectionpoint) to identify potential outliers • Trend of major data population lognormally distributed Slide Courtesy of J. Fern, Earth Tech

  45. Copper Concentration (mg/kg) Cumulative Frequency Diagrams • Log scale • Use changes in slope (i.e., the inflection point) to identify potential outliers • Inflection point observed on the log scale plot • The trend of data population is very clear Slide Courtesy of J. Fern, Earth Tech

  46. Principal Component Analysis • Large number of variables condensed into a few factors (simplify) • Extracted factors can be interpreted based on meaning of clumped variables (factor loads) • Factor scores assigned to each discrete sample allow inter-sample comparison • Variables examined: • Metal concentrations (Ala Wai & Kane`ohe)

  47. Principal Component Analysis Loads • Factor 1: • Pb, Zn, Cu, Ba (Co) • Anthropogenic • Factor 2: • Ni, V, Cr • Basalt source • Factor 3 (weak): • As, U, Cd • Agricultural

  48. Principal Component Analysis Scores F2 vs. F1 F3 vs. F1 Factor 1: Pb, Zn, Cu, Ba, Co / Factor 2: Ni, V, Cr / Factor 3: As, U, Cd

  49. Conclusions…or Food for Thought • Local vs. mainland reference conditions are clearly not the same  need locally relevant reference(s) • Variable local (natural) background  first order dependence on the matrix/mineralogy • “Natural” vs. “operational” background: use of an absolute definition or a working definition • Use of statistics is helpful, especially when additional data are unavailable or further sampling and analysis is not feasible • Use scientific method… it works!

  50. Acknowledgments Michael S. Tomlinson (M.S. 2002) Vincent L. Beltran (M.S. 2002) Mark M. Irving (Ph.D. 1998) Haisheng Li (M.S. 1996) Wendell (Xi Yuan) Wen (M.S. 1995) Khalil J. Spencer, Ph.D. (now at LANL) Chuck Fraley, Yvonne Parry Scott Narod, Vincent Todd, Norine Yeung • NOAA Sea Grant College Program • USGS NIWR • USGS Hawai‘i NAWQA • US EPA • Hawai‘i State DOH and DLNR • C&C Honolulu Dept. Env. Services • Earth Tech (Honolulu)

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