1. Hydrogeochemistry “Geochemistry of Natural Waters” “Geochemistry of Natural Waters” No wastewater, water resources No wastewater, water resources Study chemistry of rivers, lakes, ground water, oceans etc. Study chemistry of rivers, lakes, ground water, oceans etc.

2. Questions considered: Why do different waters have different chemical compositions? Why do different waters have different chemical compositions? What controls the compositions? What controls the compositions? How do compositions vary with setting? How do compositions vary with setting? How do they vary with time? How do they vary with time?

3. Why consider these questions? Diagenesis Diagenesis Chemical (and physical) alteration of solid material (low T and P) Chemical (and physical) alteration of solid material (low T and P) Material: rocks, sediments, minerals, plants, animals, bacteria Material: rocks, sediments, minerals, plants, animals, bacteria Often involves gas phases Often involves gas phases

4. Why consider these questions Hydrology and Hydrogeology Hydrology and Hydrogeology Variations in chemical composition can be used to understand (map) flow paths Variations in chemical composition can be used to understand (map) flow paths Flow can alter chemistry Flow can alter chemistry Diagenesis and hydrology are linked Diagenesis and hydrology are linked

5. Hydrologic cycle Free water distribution Free water distribution 96% in oceans 96% in oceans 3% in ice 3% in ice 1% in ground water 1% in ground water 0.01% in streams and lakes 0.01% in streams and lakes 0.001% in atmosphere 0.001% in atmosphere

6. The hydrologic cycle – this figure is for water How would dissolved mass be included in this?

7. Reservoirs = location of water (e.g. lake, ocean, river etc.) Reservoirs = location of water (e.g. lake, ocean, river etc.) Flux = motion of water between reservoirs Flux = motion of water between reservoirs Units = mass per time (per area) Units = mass per time (per area) Hydrologic cycle = closed loop of the flux of material Hydrologic cycle = closed loop of the flux of material

8. Flux = can be motion of any material (e.g. water, solutes, students in room) Flux = can be motion of any material (e.g. water, solutes, students in room) Flux only applicable if cycle is steady state Flux only applicable if cycle is steady state Not changing through time Not changing through time Input = output Input = output

9. For systems in steady state – can consider the “Residence Time” For systems in steady state – can consider the “Residence Time” Average time that material is in reservoir Average time that material is in reservoir Definition Definition T= A/J Where: A = abundance (not concentration of material J = flux of material (into or out of)

10. System not in steady state called transient System not in steady state called transient Best defined by “Response time” Best defined by “Response time” The amount of time for mass to change to certain value The amount of time for mass to change to certain value Typically doubling or halving. Typically doubling or halving. Sometimes considered “e-folding time” Sometimes considered “e-folding time” Amount of time for exponentially growing quantity to increase by a factor of e. Amount of time for exponentially growing quantity to increase by a factor of e. Exponential decay = time to decrease by a factor of 1/e Exponential decay = time to decrease by a factor of 1/e

11. Quantification of hydrologic cycle – a box model

12. A more complicated (complete?) box model

13. A natural system: Suwannnee River What are the values water and mass for each box? Abundance in reservoir What are values for arrows? Fluxes

14. Quick discussion of chemical changes in hydrologic cycle Rain Rain Streams Streams GW GW Meteoric vs non-meteoric water Meteoric vs non-meteoric water

15. Chemical (and Isotopic) composition of water Chemical (and Isotopic) composition of water Natural water always in contact with soluble material – air, sediments, rocks, organic matter Natural water always in contact with soluble material – air, sediments, rocks, organic matter Consequence – no natural water is “pure” Consequence – no natural water is “pure”

16. Importance Importance Dissolution of gases (e.g., CO 2 ) Dissolution of gases (e.g., CO 2 ) Dissolution of solid phases –porosity Dissolution of solid phases –porosity Precipitation of solid phases –cements Precipitation of solid phases –cements Coupled with hydrologic cycle - controls flux of material Coupled with hydrologic cycle - controls flux of material

17. Rain water chemistry Na + concentrations Cl - concentrations What might be the most likely source for Na and Cl? How could you test to see if this hypothesis is true? What are implications if this is true,e.g. what and where are other sources?

18. Relative concentrations, Rainfall Pollution – H 2 SO 4 Gypsum dust SO 4 matches Ca SO 4 matches pH – H 2 SO 4 SO 4 marine influence – dimethyl sulfide Excess Ca, Mg, less Na and K from oceans

19. Temporal variations During storm During storm Rain starts salty, becomes fresher during strom Rain starts salty, becomes fresher during strom O and H isotopes also change during storm O and H isotopes also change during storm Snow melt initially saltier & lower pH Snow melt initially saltier & lower pH change in melting temperature change in melting temperature

20. Rainfall not the only mechanism to deposit material from atmosphere to land surface Rainfall not the only mechanism to deposit material from atmosphere to land surface Aerosol – suspension of fine solid or liquid in gas (e.g. atmosphere) Aerosol – suspension of fine solid or liquid in gas (e.g. atmosphere) Examples – smoke, haze over oceans, air pollution, smog Examples – smoke, haze over oceans, air pollution, smog

21. Dry deposition – aerosols Dry deposition – aerosols Dissolution of gases and aerosols by vegetation and wet surfaces Dissolution of gases and aerosols by vegetation and wet surfaces Sedimentation of large aerosols by gravity Sedimentation of large aerosols by gravity Occult deposition Occult deposition More general term - Dry deposition plus deposition from fog More general term - Dry deposition plus deposition from fog Dry and Occult deposition difficult to measure Dry and Occult deposition difficult to measure

22. Atmospheric deposition of material called “Throughfall” Atmospheric deposition of material called “Throughfall” Sum of solutes from precipitation, occult deposition, and dry deposition Sum of solutes from precipitation, occult deposition, and dry deposition A working definition A working definition Data Available Data Available National Atmospheric Deposition Program National Atmospheric Deposition Program napd.swsl.uiuc.edu napd.swsl.uiuc.edu

23. Compositional changes resulting from throughfall – NE US Open box – throughfall composition Closed box – incident precipitation composition

24. Hydrology/hydrogeology Atmospheric deposition leads to surface and ground water Atmospheric deposition leads to surface and ground water Variety of processes alter/move this water: Variety of processes alter/move this water: Evaporation Evaporation Transporation (vegetative induced evaporation Transporation (vegetative induced evaporation Evapotranspiration Evapotranspiration

25. Movement across/through land surface Movement across/through land surface Overland flow – heavy flow on land surface Overland flow – heavy flow on land surface Interflow – flow through soil zone Interflow – flow through soil zone Percolate into ground water Percolate into ground water

26. Conceptualizaton of water flow Through- fall Important to consider how each of these flow paths alter chemical compositions of water

27. Examples of changing chemistry Plants Plants Provide solutes, neutralize acidity, extract N and P species Provide solutes, neutralize acidity, extract N and P species Soil/minerals Soil/minerals Dissolve providing solutes Dissolve providing solutes Evaporation Evaporation Increase overall solute concentrations Increase overall solute concentrations Elevated concentrations lead to precipitation Elevated concentrations lead to precipitation Salts/cements Salts/cements

28. Stream Hydrology Baseflow Baseflow ground water source to streams ground water source to streams Allow streams to flow even in droughts Allow streams to flow even in droughts Augmentations of baseflow Augmentations of baseflow Interflow, overland flow, direct precipitation Interflow, overland flow, direct precipitation Result in flooding Result in flooding Chemical variations in time Chemical variations in time caused by variations in compositions of sources caused by variations in compositions of sources

29. Bank storage Bank storage Flooding causes hydraulic head of stream to be greater than hydraulic head of ground water Flooding causes hydraulic head of stream to be greater than hydraulic head of ground water Baseflow direction reversed Baseflow direction reversed Water flows from stream to ground water Water flows from stream to ground water Hyporheic flow Hyporheic flow Exchange of water with stream bed and stagnant areas of stream Exchange of water with stream bed and stagnant areas of stream Nutrient spiraling – chemical changes in composition because changing reservoir Nutrient spiraling – chemical changes in composition because changing reservoir

30. Stream compositions Generally little change downstream Generally little change downstream Short residence time in stream Short residence time in stream Little contact with solids Little contact with solids Changes usually biologically mediated Changes usually biologically mediated Nutrients (N, P, Si) uptake and release (Nutrient spiraling) Nutrients (N, P, Si) uptake and release (Nutrient spiraling) Pollutants Pollutants Chemistry changes with discharge Chemistry changes with discharge Chemistry changes with exchange of GW and SW Chemistry changes with exchange of GW and SW

31. Ground water Unconfined example Unconfined example Porosity – fraction of total solid that is void Porosity – fraction of total solid that is void Porosity filled w/ water or water + gas Porosity filled w/ water or water + gas Vadose zone – zone with gas plus water (unsaturated – can be confusing term) Vadose zone – zone with gas plus water (unsaturated – can be confusing term) Phreatic zone – all water (saturated zone) Phreatic zone – all water (saturated zone) Water table – separates vadose and phreatic zone Water table – separates vadose and phreatic zone

32. Ground water flow Flow through rocks controlled by permeability Flow through rocks controlled by permeability Water flows from high areas to low areas Water flows from high areas to low areas Head gradients Head gradients Water table mimics land topography Water table mimics land topography Flow rate depends on gradient and permeability Flow rate depends on gradient and permeability

33. Confined aquifers Regions with (semi) impermeable rocks Regions with (semi) impermeable rocks Confining unit Confining unit Confined aquifers have upper boundary in contact with confining unit Confined aquifers have upper boundary in contact with confining unit Water above confining unit is perched Water above confining unit is perched Level water will rise is pieziometric surface Level water will rise is pieziometric surface Hydrostatic head Hydrostatic head

34. Effects of confined aquifers GW withdrawal lowers head Perched aquifers, springs, water table mimic topography

35. Other types of water Meteoric water – rain, surface, ground water Meteoric water – rain, surface, ground water Water buried with sediments in lakes and oceans Water buried with sediments in lakes and oceans Formation waters Formation waters Pore waters Pore waters Interstitial water/fluids Interstitial water/fluids Typically old – greatly altered in composition Typically old – greatly altered in composition

36. Other water sources Dehydration of hydrated mineral phases Dehydration of hydrated mineral phases Clays, amphiboles, zeolites Clays, amphiboles, zeolites Metamorphic water Metamorphic water Water from origin of earth – mantle water Water from origin of earth – mantle water Juvenile water Juvenile water Both small volumetrically; important geological concequences Both small volumetrically; important geological concequences

37. Concentrations/Units Need common way to describe dissolved components Need common way to describe dissolved components Many ways to do this: Many ways to do this: Solutes: mass (e.g. g, kg) or moles Solutes: mass (e.g. g, kg) or moles Solvent: amount of solvent or solution Solvent: amount of solvent or solution Geology usually reported by mass – units of analyses Geology usually reported by mass – units of analyses Chemical calculations always by moles Chemical calculations always by moles

38. Concentration terminology Total dissolved solids (TDS) – mass of solid remaining after evaporation of water Total dissolved solids (TDS) – mass of solid remaining after evaporation of water Bicarbonate converted to carbonate Bicarbonate converted to carbonate Units of mass (e.g. g, kg, etc.) Units of mass (e.g. g, kg, etc.)

39. Salinity – similar to TDS except quantities of Br and I replaced with Cl Salinity – similar to TDS except quantities of Br and I replaced with Cl Operational definition Operational definition Cl titration includes Br and I Cl titration includes Br and I Salinity reported as ratio of electrical conductivity to standard Salinity reported as ratio of electrical conductivity to standard Originally “Copenhagen seawater” Originally “Copenhagen seawater” Now KCl standard Now KCl standard Ratio so dimensionless (commonly ppt, ‰, PSU, nothing) Ratio so dimensionless (commonly ppt, ‰, PSU, nothing)

40. Chlorinity Determined by titration with AgNO 3 Determined by titration with AgNO 3 Definition Definition Mass (g) of Ag necessary to precipitate Cl, Br, and I in 328.5233 g of seawater Mass (g) of Ag necessary to precipitate Cl, Br, and I in 328.5233 g of seawater Total number of grams of major components in seawater: Total number of grams of major components in seawater: g T = 1.81578*Cl(‰) g T = 1.81578*Cl(‰) S(‰) = 1.80655*Cl(‰) S(‰) = 1.80655*Cl(‰)

41. Water salinity Fresh water Fresh water Potable, generally < 1000 mg/L TDS Potable, generally < 1000 mg/L TDS Brackish Brackish Non-potable, but < seawater Non-potable, but < seawater Seawater, salinity 34 to 37‰ Seawater, salinity 34 to 37‰ Saline water/brine > seawater salinity Saline water/brine > seawater salinity

42. Other measures of TDS Refractive index Refractive index Amount of refraction of light passing through water Amount of refraction of light passing through water Linearly related to concentrations of salts Linearly related to concentrations of salts Conductivity/resistivity Conductivity/resistivity Current carried by solution is proportional to dissolved ions Current carried by solution is proportional to dissolved ions

43. Conductivity Inverse of resistance Inverse of resistance Units of Siemens/cm Units of Siemens/cm 1 Siemen = 1 Amp/volt = 1/Ohm = 1 Mho 1 Siemen = 1 Amp/volt = 1/Ohm = 1 Mho Conductance is T dependent Conductance is T dependent Typically normalized to 25º C Typically normalized to 25º C Called Specific Conductivity Called Specific Conductivity

44. Reporting units Need to report how much dissolved material (solute) in water, two ways: Need to report how much dissolved material (solute) in water, two ways: Moles Moles Mass Mass Need to report how much water (solvent) Need to report how much water (solvent) Volume of water, typically solution amount Volume of water, typically solution amount Mass of water, typically solvent amount Mass of water, typically solvent amount

45. Molar units Number of molecules (atoms, ions etc) in one liter of solution Number of molecules (atoms, ions etc) in one liter of solution Most common – easy to measure solution volumes Most common – easy to measure solution volumes Units are M, mM, µM (big M) Units are M, mM, µM (big M) Example Example Na 2 SO 4 = 2Na + + SO 4 2- 1 mole sodium sulfate makes 2 moles Na and 1 mole SO4

46. Molal Units Number of molecules (atoms, ions etc) in one kg of solvent Number of molecules (atoms, ions etc) in one kg of solvent Abbreviation: m or mm or  m (little m) Abbreviation: m or mm or  m (little m) More difficult to measure weight of solvent, not used so often More difficult to measure weight of solvent, not used so often Difficult to determine amount of solvent in natural waters with dissolved components Difficult to determine amount of solvent in natural waters with dissolved components

47. Why use molar units? Reaction stoichiometry is written in terms of moles, not mass Reaction stoichiometry is written in terms of moles, not mass CaCO 3 = Ca 2+ + CO 3 2- 100 g = 1 mole 40 g = 1 mole 60 g = 1 mole Simple to convert between mass (easily measured) and moles

48. Mass – Mole conversion easy Based on Avagadro’s number = 6.022 x 10 23 Based on Avagadro’s number = 6.022 x 10 23 1 Mole is Avogadro’s number of stuff 1 Mole is Avogadro’s number of stuff Defined by number of atoms in 12 g of 12 C Defined by number of atoms in 12 g of 12 C

49. Example Nitrate a pollution of concern Nitrate a pollution of concern Commonly measured as mass Commonly measured as mass Reported as mass of N in NO 3 Reported as mass of N in NO 3 N is the element of concern N is the element of concern If not specified, concentrations could be very different If not specified, concentrations could be very different Moles of NO 3 and N are identical Moles of NO 3 and N are identical

50. Alternative – Weight units Mass per unit volume Mass per unit volume For example: g/L or mg/L For example: g/L or mg/L If very dilute solution If very dilute solution Mass per unit volume about the same as mass per mass Mass per unit volume about the same as mass per mass 1L water ~ 1000 g, variable with T, P and X 1L water ~ 1000 g, variable with T, P and X

51. Alternative – charge units Equivalents – molar number of charges per volume Equivalents – molar number of charges per volume eq/L or meq/L eq/L or meq/L Used to plot piper diagrams Used to plot piper diagrams Used to calculate electrical neutrality of solutions Used to calculate electrical neutrality of solutions

52. Calculation: Calculation: Moles (or millimoles) of ion times its charge Moles (or millimoles) of ion times its charge Na 2 SO 4 = 2Na + + SO 4 2- 1 mole of Na = 1 eq Na solution 1 mole of SO 4 = 2 eq SO 4 solution Although different number of moles, solution is still electrically neutral

53. Example Example

54. Charge Balance Electrical neutrality provides good check on analytical error Electrical neutrality provides good check on analytical error Charge Balance Error – CBE Charge Balance Error – CBE CBE =  m c Z c -  m a Z a  m c Z c +  m a Z a

55. Possible causes of errors Significant component not measured Significant component not measured Commonly alkalinity – can be estimated by charge balance Commonly alkalinity – can be estimated by charge balance Analytical error Analytical error +5% difference OK – acceptable +5% difference OK – acceptable + 3% good + 3% good 0% probably impossible 0% probably impossible

56. Piper Diagrams Two triangular diagrams Two triangular diagrams Projected on quadralinear diagram Projected on quadralinear diagram Very useful figure for comparing concentrations of water Very useful figure for comparing concentrations of water

57. Santa Fe water chemistry

58. Construction Convert concentrations to meq/L Convert concentrations to meq/L Use major cations and anions concentrations Use major cations and anions concentrations Cations = Ca, Mg, Na + K Cations = Ca, Mg, Na + K Anions = SO 4, Cl, HCO 3 + CO 3 (or alkalinity) Anions = SO 4, Cl, HCO 3 + CO 3 (or alkalinity)

59. Calculate %’s of each element on ternary diagram Calculate %’s of each element on ternary diagram For example Ca is: For example Ca is: Plot %’s on ternary diagrams Plot %’s on ternary diagrams Project each % onto diamond diagrams Project each % onto diamond diagrams [Ca] [Ca] + [Mg] + [Na + K ] *100

60. Composition: Ca = 22.3% Mg = 13.7% Na+K = 64% Alkalinity = 31.3% Sulfate = 54.5% Chloride = 14.2%