1. Chapter 9 – The continental environment

4. Simpler Box Model of Hydrologic Cycle

6. Weathering: the various physical and chemical processes that lead to the decomposition of minerals and the breakdown of rocks to form soil. 4 Types of Chemical Weathering Oxidation of minerals containing reduced elements 4FeS 2(pyrite) + 15O 2 + 8H 2 O  2Fe 2 O 3(hematite) + 8H 2 SO 4 Congruent dissolution by water – ions go directly into solution NaCl (halite)  Na + + Cl - Congruent dissolution by acid (written as carbonic) MgSiO 4 (olivine) + 4H 2 CO 3aq  2Mg 2+ + 4HCO 3 - + H 4 SiO 4aq Incongruent dissolution by acid (breaks down to ion and a different mineral) 2NaAlSi 3 O 8(Na-plagioclase) + 2H 2 CO 3aq + 9H 2 O  Al 2 Si 2 O 5 (OH) 4(kaolinite) + 2Na + + 2HCO 3 - + 4H 4 SiO 4aq Primary mineral secondary mineral

9. Dissolution of Silica (quartz and amorphous silica) SiO 2 + H 2 O  H 4 SiO 4 aq Log K sp = 1.8814 – 2.028 x 10 -3 T – 1560.46 / T Log K sp = 0.338037 – 7.8896 x 10 -4 T – 840.075 / T……opal ……quartz Si T = [H 4 SiO 4 ] Ka1Ka1 [H + ] + Ka1Ka1 [H + ] 2 Ka2Ka2 1 + Equations for silica dissolution

10. Figure 9-2. function of pH. pH = 9.83 and pH = 13.17 correspond to the first and second dissociation constants, respectively, of silicic acid. Solubility of silica increases at higher pH Opposite of CaCO 3 containing minerals Fossilization = SiO 2 replacement of CaCO 3

11. Dissolution of Al and Fe hydroxides Al(OH) 3  Al 3+ + 3OH - General eq. Total solubility of Al is determined by the sum of free Al + all the Al-OH aqueous complexes in solution. Complexes: AlOH 2+, Al(OH) 2 +, Al(OH) 3aq, Al(OH) - 4 Overall Al solubility eq:  Al = K sp / K 3 w ([H + ] 3 + K  1 [H + ] 2 + K  2 [H + ] + K  3 + K  4 /[H + ])

12. Figure 9-3. Total concentration of aluminum in solution, as a function of pH, for a solution in equilibrium with gibbsite. Al hydroxide solubility depends on the exact mineral but generally has a near mid pH minima increasing asymmetrically at lower and higher pHs.

13. Stablility diagrams Represent equilibria between minerals and aqueous solutions Derived from thermodynamic data Figure 9-4b. Mineral stability fields as delineated by equilibrium equations plotted in Figure 9-4a. The labeled curve indicates the changes in chemistry of a solution in equilibrium with albite during weathering in a closed system. See text for discussion. For the weathering of silicate minerals X and Y axis describe solution Chemistry Fields denote the ‘stable mineral’ in Equilibria with particular solution chemistry A  B  C  etc… represents the path of weathering starting with gibbsite In a closed system Flushing rates in non-closed systems Will effect solution chemistry during weathering And control final weathering product. Hence Dominance of different minerals in different Soil types

15. Groundwaters Water chemistry modified by the vadose zone, and during transport in the saturated zone In general, the older the water the higher the dissolved ion Conc. = higher conductivity

16. Surface and Groundwaters Graphical representations Stiff diagram

17. Piper Diagram Data used to generate the Piper Diagram is Found on Eby p. 324, Table 9-7 Plots each ion as a value normalized to 100% Data on the 2 triangles is Also projected on the quadrilateral

18. Ca Cl SO 4 Mg Na HCO3

19. Figure 9-7. Hydrochemical facies. After Back (1966).

20. Piper Diagram Data used to generate the Piper Diagram is Found on Eby p. 324, Table 9-7 Plots each ion as a value normalized to 100% Data on the 2 triangles is also projected on the quadrilateral Piper diagrams also provide indications of mixing of water masses 1 2 mix Straight line = mixture

21. Rivers Controls on river chemistry Gibbs Approach Precip – high (Na and Cl), tropical rivers Weathering – rock dominance, depends on rock type, climate, relief Evaporation and fractional crystallization

23. Controls on River chemistry Rock weathering controls River chemistry Stallard and Edmond approach

24. Sources of ions in river water by general rock type Ocean source + -

26. pH in groundwater and surface water controlled by: Ion exchange Carbonic acid system Water-mineral interactions Remember the carbonic acid system? As pH decreases buffering decreases

27. Water-mineral interaction H + + CaCO 3  Ca 2+ + HCO 3 - … replaces bicarbonate ion needed for buffering, increases calcium conc. (and Mg is dolomite is present), raises pH Calcite Silicates Al 2 SiO 5 (OH) 4kaolinite + 6H +  2Al 3+ + 2H 4 SiO 4aq + H 2 O NaAlSi 3 O 8albite + 4 H 2 O + 4H +  Na + + Al 3+ + 3H 4 SiO 4aq KMg 1.5 Fe 1.5 (AlSi 3 O 10 )(OH 2 ) biotite + 10H +  K + + 1.5Mg 2+ + 1.5Fe 2+ + Al 3+ + 3H 4 SiO 4aq

28. Water-mineral interaction H + + CaCO 3  Ca 2+ + HCO 3 - … replaces bicarbonate ion needed for buffering, increases calcium conc. (and Mg is dolomite is present), raises pH Calcite Silicates Al 2 SiO 5 (OH) 4kaolinite + 6H +  2Al 3+ + 2H 4 SiO 4aq + H 2 O NaAlSi 3 O 8albite + 4 H 2 O + 4H +  Na + + Al 3+ + 3H 4 SiO 4aq KMg 1.5 Fe 1.5 (AlSi 3 O 10 )(OH 2 ) biotite + 10H +  K + + 1.5Mg 2+ + 1.5Fe 2+ + Al 3+ + 3H 4 SiO 4aq All the silicate weathering rxns release silicic acid and free aluminium. High free Aluminum conc. in acid lakes. Free Al is toxic to aquatic critters.

29. Read about the ‘Killer Lakes’ of Cameroon, Eby p. 336, Case Study 9-4

30. Eutrophication: a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes and can cause other organisms to die. Nutrients can come from many sources, such as fertilizers applied to agricultural fields, golf courses, and suburban lawns; deposition of nitrogen from the atmosphere; erosion of soil containing nutrients; and sewage treatment plant discharges. Water with a low concentration of dissolved oxygen is called hypoxic.

31. Structure and mixing of lake waters

32. C i F i + C h F h = C o F o + C e F e + R P e where C i is the concentration of the substance in the inlet water, F i is the flux of water into the lake, C h is the concentration of the substance in the hypolimnion, F h is the flux of water from the hypolimnion to the epilimnion, C o is the concentration of the substance in the outlet water, F o is the flux of water out of the lake, C e is the concentration of the substance in the epilimnion, F e is the flux of water from the epilimnion to the hypolimnion, and R P e is the rate of removal of the substance by particles in the epilimnion. The amount of the substance that is ultimately stored in the sediment is: R s = R P e + R P h – R d where R s is the rate at which the substance is sequestered in the sediment, R P h is the rate of removal of the substance by particles in the hypolimnion and R d is the rate of re-solution of the substance.

33. Soufrière Hills volcano (Montserrat)

34. Mt Ruapehu lahar event - New Zealand (March 18, 2007) Total dissolved solids > 80%

35. Tephra: air-fall material produced by a volcanic eruption regardless of composition or fragment size.

37. Metals sorption Figure 9-16. Adsorption of metal cations as a function of pH. From AQUATIC CHEMISTRY, 3rd Edition by W. Stumm and J. J. Morgan. Copyright © 1996. This material is used by permission of John Wiley & Sons, Inc. Depends on pH and charge to size ratio for individual metal Generally for the transition metals, the lower the pH the less sorption

38. Metals mobility depends on: ion exchange / sorption-desorption complex formation and chelation Ion exchange aA y + bBX  bB z + aAX…..’X’ denotes that A or B are stuck on a solid The exchange ratio between a and b (K a/b ) is: K a/b = [B z ] b [AX] a / [A y ] a [BX] b Example: Exchange between Na and Ca 2Na + + Ca solid  Ca 2+ + 2Na solid K Na/Ca = [Ca 2+ ] 1 [Na solid ] 2 / [Na 1+ ] 2 [Ca solid ] 1

39. Metals chelation Ligands – net negatively charge molecules that associate (attract) metals M 2n+ aq + nC 2 O 4 2-   M(C 2 O 4 ) n aq metalLigand (oxalate) Multidentate ligand has more than one binding atom Chelation occurs when complexes are formed with a multidentate ligand Oxalate is a common multidentate ligand produced biologically Metal-oxalate chelates have low solubility and will precipitate out. Therefore biological processes assist in metals precipitation through the oxalate chelation process.

40. Metal Cycles Geosphere  atmosphere via Volcanoes, dust Geosphere  hydrosphere via ocean vents Short residence time in atmosphere Hydrosphere transport controlled by redox, pH, mineralogy Biosphere important in establishing redox, pH, etc

41. Heavy metals At # > 20 Fate and transport determined strongly by element-type -Transition metals - Zn, Cd, Pb -As, Se -Hg Transition metals Usually occur at divalent, or trivalent cations With the exception of V, these metals will ppt at high pH (forming oxyhydroxides, or metal carbonates) Complex with humic material (Mn 2+ <Cd 2+ <Co 2+ <Ni 2+ <Zn 2+ <Pb 2+ <Cu 2+ <VO 2+ ) Adsorption decreases with decreasing pH

42. Arsenic and Selenium Occur primarily as neutral or negatively charged species (H 2 AsO 4 -, HAsO 4 2-, H 3 AsO 3, H 2 AsO 3 -, SeO 4 -, HSeO 3 -, SeO 3 2- ) Adsorption increases with decreasing pH When reduced S is present, both As and Se incorporated into S minerals Changing redox conditions can either immobilize or liberate As or Se depending on the presence of other elements……difficult to predict mobility Major anthropogenic source of Se is coal combustion

43. Mercury Most redox conditions allow for elemental Hg Elemental Hg is inert = not immediately hazardous, long half life High redox = Hg 2+ or Hg(OH) 2aq Low redox + sulfur = HgS (cinnabar) Global mercury cycling dominated by atm transport and deposition on land Some anaerobic bacteria methylate Hg CH 3 Hg= methyl mercury, (CH 3 ) 2 Hg = dimethyl mercury easy biotic uptake bioconcentration toxic

44. Radioactive materials Making fissionable nuclear fuel 235 U Natural uranium ore = 99.275% 238 U, 0.719 % 235 U Extraction  enrichment (1.8 – 3.7% 235 U)

45. Nuclear Fission 235 U + 1 0 n  fission fragments + 2 or 3 neutrons + energy neutron In order to get the reaction to go, the impacting neutron must be slowed down. Neutrons are slowed either with water or with graphite (Chernobyl) depending on the type of reactor. Water-type reactors are self quenching because the ability of water to slow down neutrons decreases as water heats up (negative feedback) Graphite-type reactors behave the opposite

46. Radioactive wastes from fission High level = very radioactive and long half-life Low level = not so radioactive and short half-life Yucca Mountain

47. Yucca mountain is made of volcanic tuff U is more mobile in oxidizing conditions Mobility of nuclear waste elements

48. Oklo – the fossil natural nuclear reactor Uranium ores in Oklo, Gabon contain little 235 U because of prior fission rxns Original U minerals (2 billion years ago) dispersed in a sandstone conglomerate. Relative abundance of 235 U vs 238 U was much higher then the U minerals were dissolved and redeposited as UO 2 at a redox boundary (U concentrated to 50-70%) Interstitial water moderated the fission like a present day reactor. When the water was steamed away due to the heat release from fission, reaction stopped. More water infiltrated and reaction fired up again, on off on off etc. for 500,000 yrs Large quantities of fission products exist today Site used to study migration and retention of fission wastes

49. Nonmetals Carbon – see chapter 5 Halogens Negative charge so sorption is less important Solubility controls mobility Fluorine concentrations determined by availbility and solubility of fluorite (CaF 2 ) Chlorine and bromine used as hydrologic tracer because once dissolved they largely behave conservatively -no volatile derivatives -little to no adsorption -little to no biological uptake -care taken to discount anthropogenic inputs

50. Nitrogen Oxidized and mobile = NO 3 - Reduced and sorptive = NH 4 +

51. Phosphorous Source is weathering of P containing rocks (e.g. apatites) Mobility and abundance controlled by solubility, adsorption, biological uptake, redox Phosphate (PO 4 3- ) strongly adsorbed to ferric (Fe 3+ ) oxides and oxyhydroxides (Fe(OH) 3…..at high redox Low redox (e.g. anoxia) desorbs phosphate and releases it in the water Freshwater eutrophication due to phosphate Anoxia associated with eutrophication keeps resupplying phosphate (+ feedback)

52. Sulfur HSO 4 -, SO 4 2-, H 2 S, HS - Most natural Eh and pH waters sulfate dominates Low Eh’s sulfide dominates. Which sulfide species at low Eh and high pH? Which sulfide at high Eh and low pH? Very low Eh (deep sediments) metal sulfide minerals ppt out (e.g. pyrite) Sulfate mobility controlled by adsorption (divalent anions preferentially adsorbed over monovalent anions like Cl - or NO 3 - ), and biology. Similar to phosphate, sulfate is adsorbed by Al and Fe oxides