Major Determinants of Water Quality

1. Major Determinants of Water Quality

2. Major Determinants of Water Quality and the Impact or Availability of Water Pollutants Organisms Solubility Oxygen pH

3. Solubility The ease with which substances dissolve in water Salts dissolve to produce ions in solution

4. Ions Ions are stable forms of elements that acquire an electrical charge by gaining or losing electrons 11 protons (+), 10 electrons (-) Sodium ion (Na+) 17 protons (+), 18 electrons (-) Chloride ion (Cl-) By losing an electron, sodium has more protons than electrons and becomes positively charged. By gaining an electron, chlorine has more electrons than protons and becomes negatively charged.

5. Dissolution and Solubility Cl- Cl Cl Na Cl Cl NaCl Solid Na+

6. Ionic Contaminants Pb2+ Hg2+ AsO4- PO4-3 NH4+ NO3- Cd2+ Natural and anthropogenic sources Weathering of Rock Industrial Processes Agriculture Solubility depends on the ion to which it is bonded

7. Forms and Solubility Pb2+ Hg2+ AsO4- PO4-3 NH4+ NO3- Cd2+ HgCl2 soluble PbCO3 poorly soluble FePO4 poorly soluble AlPO4 poorly soluble KH2PO4 soluble CdCO3 poorly soluble CdCl2 soluble The degree to which contaminants impact water quality is often determined by their solubility

8. Toxic organic pollutants including pesticides, and industrial products generally are not ionic and are not particularly soluble in water. DDT Dioxins PCBs Dioxin DDT PCB

9. Oxygen is also Water Soluble Solubility: 0.043 g/L (20oC) In water, about one out of every 100,000 molecules is oxygen

10. Temperature and Oxygen The solubility of oxygen in water is highly temperature dependent. Saturated Oxygen Content 10.1 mg/L 8.3 mg/L 15oC 25oC

11. Oxygen and Heat Add heat

12. Factors that Control O2 Content in Water Photosynthesis Agitation of Water Temperature Activity of Aerobic Heterotrophs

13. pH

14. pH is a Measure of H+ Concentration in Water H+ ion Responsible for Acidity Acid: any substance which increases the H+ concentration in water The greater the number of H+ ions, the greater the acidity Low pH = High amount of Hydrogen ions in water High pH = Low amount of Hydrogen ions in water

15. HCl H+ + Cl- HNO3 H+ + NO3- H2SO4 H+ + HSO4- Dissociation of acids

16. pH (hydrogen) H+ Low pH = High H+ Each unit decrease in pH represents a 10-fold increase in H+ concentration * pH 4 = 0.0001 g H+/ L pH 3 = 0.001 g H+/ L There is 10 times more H+ in water at pH 3 compared to pH 4

17. Extra Credit: • ____is a measure of H+ concentration in water • Oxygen is more or less soluble in warm water that cold. • Identify one ionic contaminant. • 4. ______are stable forms of elements that acquire • an electrical charge by gaining or losing electrons

18. pH and Availability of Nutrients and Metals

19. pH and Availability and Form of Nutrients Nitrogen When organisms decompose organic material nutrients are released including NH4+ NH4+ NH3 High pH Low pH low H+ conc. High H+ conc. soluble Gas

20. Nitrate and Ammonia NH4+ and NO3- Forms are controlled by organisms NH4+ is converted to NO3- by aerobic bacteria These bacteria, therefore, are controlled by oxygen levels They also are controlled by pH. They do not function well at low pH. NH4+ dominant at low pH NO3- dominant at higher pH

21. _ _ _ _ _ _ _ _ _ Soil particles possess a negative electrical charge Dominant Forms: NH4+ and NO3- Sources: fertilizers, manures, wastewater discharge NO3- is more mobile in the environment than NH4+ NH4+ NO3- Leaching to ground or surface water

22. Availability and Form of Nutrients Phosphorus dissolved dissolved H2PO4- HPO4-2 Low pH High pH High H+ conc. low H+ conc. CaHPO4 AlPO4 Solid (unavailable) Solid (unavailable) Dissolved (available) CaHPO4 + H+ = Ca2+ + H2PO4-

23. Acids and Metals

24. Minerals and Erosion KAlSi3O8 CaAl2Si2O8 NaAlSi3O8 Feldspars granite Acid KAlSi3O8 CaAl2Si2O8 NaAlSi3O8 Al3+ Acid Dissolved in water Acid Aluminum is toxic to plants and some organisms

25. Availability and Form of Metals PbCO3 + H+ Pb2+ + HCO3- dissolved (available) Solid (unavailable) CdSO4 + H+ Cd2+ + SO4-2 dissolved (available) Solid (unavailable) Acid dissolution of metals increases their mobility

26. oxygen FeS2 2H2SO4 water Mine Tailings There are approximately 420,000 abandoned mines in the states of California, Arizona and Nevada Cd, Pb, Zn, Cr, Cu, Al 2H+ + SO42- PbCO3 + H+ Pb2+ + HCO3- soluble solid Direct toxicity of H+ plus dissolution of associated metal contaminants such as arsenic, lead, and cadmium

27. pH and Acid Rainfall

28. Natural rainfall is acidic: pH 5.6 CO2 + H2O = H2CO3 H2CO3 => H+ + HCO3- Acid Pollution by sulfur dioxide and nitrogen oxides contributes additional acidity to rainfall. SO2 + H2O → H2SO4

29. National Surface Water Survey (EPA) Investigated the effects of acidic deposition in over 1,000 lakes Acid rain caused acidity in 75 percent of the acidic lakes and about 50 percent of the acidic streams Most lakes and streams have a pH between 6 and 8. In the Northeast U.S. many lakes have pH less than 5. Adirondacks and Catskill Mountains mid-Appalachian highlands Little Echo Pond has a pH of 4.2. The Canadian government has estimated that 14,000 lakes in eastern Canada are acidic.

30. Low pH can be directly toxic to fish and other species As acid rain flows through soils in a watershed, aluminum is released Low pH and increased aluminum levels cause chronic stress that may not kill individual fish, but leads to lower body weight and smaller size and makes fish less able to compete for food and habitat. Acid tolerances food Increasing acidity At pH 5, most fish eggs cannot hatch

31. Major Determinants of Water Quality and the Impact or Availability of Water Pollutants Organisms Solubility Oxygen pH

32. Next: The History of Sewage