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Relating Surface Water Alkalinity and Regional Geology

Relating Surface Water Alkalinity and Regional Geology. Martha Conklin, Jean Morrill, Roger Bales, Ray Brice & Jonathon Whittier Hydrology and Water Resources University of Arizona Tucson, AZ. H 2 O. Ca 2+. CaCO 3. HCO 3 -. CO 3 2-. H +. Alkalinity: Weathering of rocks.

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Relating Surface Water Alkalinity and Regional Geology

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  1. Relating Surface Water Alkalinity and Regional Geology Martha Conklin, Jean Morrill, Roger Bales, Ray Brice & Jonathon Whittier Hydrology and Water Resources University of Arizona Tucson, AZ

  2. H2O Ca2+ CaCO3 HCO3- CO32- H+ Alkalinity: Weathering of rocks CaCO3 + H+  Ca2+ + CO32- + H+  Ca2+ + HCO3-

  3. Questions • Why do GLOBE schools report a lower average alkalinity that non-GLOBE sites over the United States? • Does regional geology explain the differences in alkalinity values?

  4. % of Sites with average  Value Average Alkalinity (mg/L as CaCO3) GLOBE & USGS Data Comparison

  5. Why is GLOBE mean alkalinity lower than WQN mean for United States? • Distribution of GLOBE schools. • Stream size: GLOBE samples streams; USGS samples rivers. • Local watershed geology influences water alkalinity.

  6. Why is alkalinity related to bedrock geology? • Marine and continental sedimentary rocks • Limestone is primarily composed of CaCO3. • Dolomite is composed of CaMg(CO3)2 • Most igneous and metamorphic rocks contain very little CaCO3, but instead are mostly less soluble silicates and metal (hydr)oxides.

  7. Rock Type LIMESTONE Other MARINE SEDIMENTS CONTINENTAL SEDIMENTS IGNEOUS Alkalinity HIGH MODERATE TO HIGH MODERATE LOW Expectations

  8. Limestone Other Marine Sedimentary Continental Sedimentary Igneous and Metamorphic Geology Classifications

  9. mg/L as CaCO3 GLOBE Alkalinity Sites

  10. GLOBE & WQN Alkalinity Sites

  11. mg/L as CaCO3 State Average Alkalinity

  12. mg/L as CaCO3 Limestone and Dolomite

  13. mg/L as CaCO3 Other Marine Sedimentary

  14. mg/L as CaCO3 Continental Sedimentary

  15. mg/L as CaCO3 Igneous and Metamorphic

  16. mg/L as CaCO3

  17. Average Alkalinty (mg/L as CaCO3)

  18. Conclusions & Future Research • There are distinct geographical patterns for alkalinity in the US. • GLOBE trends are similar to USGS trends • There is good agreement with bedrock; can we improve it by looking at soils? • Expand rock categories to incorporate more detailed information on carbonate content. • Expand analysis to other countries (as GLOBE schools help us find bedrock & soil data!)

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