1. EVPP 550 Waterscape Ecology and Management Professor R. Christian Jones Fall 2007

2. Water Chemistry – CO 2, alk, pH Global carbon cycle includes: –Photosynthesis –Respiration –Fossil Fuel combustion –Ocean interactions –Rock interactions (over long term)

3. Water Chemistry – CO 2, alk, pH Earth’s atmosphere contains relatively small amounts of CO 2 as compared to O 2 But the amount has increased greatly over the past several decades As a greenhouse gas, CO 2 is a major factor in the warming of Earth surface temperatures CO 2 is also intimately involved in the carbonate- bicarbonate buffering system that controls pH in most freshwaters Ice core data Direct Measurements

4. Water Chemistry – CO 2, alk, pH Carbon dioxide dissolves in water to produce carbonic acid Carbonic acid dissociates to produce bicarbonate and hydrogen ion (1 st dissociation of carbonic acid) Bicarbonate dissociates to produce carbonate and another hydrogen ion (2 nd dissociation of carbonic acid) CO 2 + H 2 0 ↔ H 2 CO 3 H 2 CO 3 ↔ HCO 3 - + H + HCO 3 - ↔ CO 3 -2 + H +

5. Water Chemistry – CO 2, alk, pH pH = -log [H+] pH is the negative log of the hydrogen ion concentration pH = 4 means [H+] = 10 -4 pH = 7 means [H+] = 10 -7 pH = 10 means [H+] = 10 -10

6. Water Chemistry – CO 2, alk, pH The relative amounts of carbonate, bicarbonate, and carbon dioxide-carbonic acid change with pH in a predictable manner based on dissociation equations At high pH, carbonate dominates At intermediate pH, bicarbonate dominates At low pH, carbon dioxide-carbonic acid dominates

7. Water Chemistry – CO 2, alk, pH Alkalinity is the ability of water to resist acidification If the carbonate-bicarbonate system is the major buffer, then pH change can be resisted as long as bicarbonate and carbonate are present since they can absorb hydrogen ions Alkalinity = [HCO 3 - ] + 2 x [CO 3 -2 ]

8. Water Chemistry – CO 2, alk, pH pH of rain in equilibrium with atmospheric CO2 is about 5.5 Pollutants such as sulfate and NOX decrease it futher The total amount of alkalinity in a given water body is based, not only on the input of CO 2 from the atmosphere, but even more so on sources of carbonate and bicarbonate from the watershed

9. Water Chemistry – CO 2, alk, pH For some purposes we need to know the total amount of dissolved inorganic carbon (DIC) in a water body This determines the carbon available for photosynthesis and also is needed to calculate the photosynthetic rate using the C-14 method DIC = [H 2 CO 3 ] + [HCO 3 - ] + [CO 3 -2 ] Based on equations in handout, if we know pH, alkalinity, and temperature, we can derive total DIC and concentration of all forms of DIC

10. Water Chemistry – CO 2, alk, pH Effect of photosynthesis on pH and carbonate system Effect of respiration on pH and carbonate system Psyn consumes CO 2, equilibrium shifts to left resulting in consumption of H + and increase in pH Resp releases CO 2, equilibrium shift to left resulting in release of H + and decrease in pH CO 2 + H 2 0 ↔ H 2 CO 3 ↔ HCO 3 - + H + ↔ CO 3 -2 + H +

11. Water Chemistry – CO 2, alk, pH Vertical profiles of pH

12. Water Chemistry – Dissolved Ions Sources –Atmosphere –Soil/rocks Dissolution Weathering –Sediments Measurement –Total Dissolved Solids (TDS) –aka Filterable Residue –Gravimetric procedure –Filter substantial volume of water, then evaporate filtrate until constant weight –Problems: some residues are volatile and some retain water

13. Water Chemistry – Dissolved Ions Range: 1 mg/L to 300,000 mg/L (saturated brine) Equivalent to 0.001 – 300 ppt Fresh water: < 1 ppt Ocean: 35 ppt Great Salt Lake: 220 ppt

14. Water Chemistry – Dissolved Ions Conductivity –Measures the ability of water to conduct an electrical current –Proportional to the number of ions in solution –Pure water has a very low conductance (<0.1 umho/cm = uS/cm) –Conductance is a rough measure of TDS which can be calibrated more accurately for a given waterbody Conductivity –Is a function of temperature so values need to be standardized to a given temperature, usually 25oC –Conductivity increases by a factor of about 0.025 per oC –So to get Specific Conductance (Conductivity standardized to 25oC): –Cond(25oC) = Cond (T) x 1.025^(25-T)

15. Water Chemistry – Dissolved Ions Anions –CO3-2 and HCO3- (70-75% by wt) –SO4-2 and Cl- also important Cations –Ca+2 (60%) –Mg+2 (15-20%) –Na+ (15-20%) –K+ (5-10%) Alkalinity –[CO3-2] + [HCO3-] –Acid buffering capacity Hardness –[Ca+2] + [Mg+2] –Reaction to soap –More soap required in hard water because Ca and Mg tie some of it up

16. Water Chemistry - Nitrogen Forms –N 2 = dissolved molecular nitrogen –NH 4 +, NH 3, NH 4 OH = ammonia nitrogen –NO 2 - = nitrite ion –NO 3 - = nitrate ion –Organic nitrogen: includes proteins, amino acids, urea, etc.

17. Water Chemistry - Nitrogen Forms –Equilibrium between ammonia nitrogen forms is a function of temperature and pH

18. Water Chemistry - Nitrogen Transformations –Nitrogen fixation N2 → reduced organic N (like amino acid) Three groups of organisms can do this –Aerobic and anaerobic heterotrophic bacteria use organic matter as energy substrate/important in sediments –Cyanobacteria use light as energy source/important in open water/done in heterocysts/may occur in large blooms in midsummer in enriched lakes –Purple photosynthetic bacteria use light as energy source, but need anoxic conditions

19. Water Chemistry - Nitrogen Transformations –Nitrogen fixation –Rate of N fixation in water column is increased during N limitation –Rate of N limitation is related to light intensity implying that light energy is driving the process

20. Water Chemistry - Nitrogen Transformations –Assimilation of combined nitrogen NH4+ → reduced organic nitrogen (like amino acid) NO3- → reduced organic nitrogen (like amino acid) NH4+ is energetically more favorable as it is already reduced

21. Water Chemistry - Nitrogen Transformations –Proteolysis or ammonification Organic Nitrogen → NH4+ Proteolytic bacteria use energy released from this transformation for metabolism –Nitrification NH4+ → NO2- –Nitrosomonas uses energy released for metabolism NO2- → NO3- –Nitrobacter uses energy released for metabolism –Reaction occurs quickly so NO2- generally very low

22. Water Chemistry - Nitrogen Transformations –Denitrification NO3- → N2 Anaerobic/aerobic interface habitats such as mud-water interface Active in sediments and wetlands, may greatly deplete NO3 in groundwater

23. Water Chemistry - Nitrogen

29. Water Chemistry - Phosphorus Importance to organisms –Nucleic acids –Adenosine Triphosphate (high energy PO4 bonds) –Bones and other solid inclusions Sources –Erosion of igneous rocks –Dissolution of phosphate- containing sedimentary rocks –Guano beds, bone skeletons –Human and animal waste, detergents

30. Water Chemistry - Phosphorus Forms of phosphorus –In biological systems and in water, almost all P is in the PO4 form –Can be individual PO4-3 ions or PO4 group can be combined with organic molecules, either dissolved or particulate Analytic Forms –Phosphate ion aka orthophosphate aka soluble reactive phosphorus Measured on filtered samples –Total soluble phosphorus Measured on filtered sample after digestion –Total phosphorus Measured on whole water samples after digestion

31. Water Chemistry - Phosphorus Ortho-P –Only directly utilizable form of inorganic P –May be formed from organic P by enzymatic action –Reacts with other chemicals and adsorps to particles and elements like Fe Organic P = Total P – Ortho P –Often most P in lakes is tied up in organisms or detritus –Can cycle between ortho-P and organic P

32. Water Chemistry - Phosphorus P cycle in lakes

33. Water Chemistry - Phosphorus P cycle in lakes

34. Water Chemistry - Phosphorus P profiles in various lakes

35. Water Chemistry - Iron Iron is a necessary requirement for all living organisms (enzyme systems) Iron has two states –Fe+3 = ferric ion Forms insoluble compounds Found under oxic conditions –Fe+2 = ferrous ion Is generally soluble Found under anoxic conditions

36. Water Chemistry - Iron Even though generally insoluble in oxic epilimnion, Fe can be held there by chelators (compounds that weakly bind it to prevent precipitation, but may give it up to cells)

37. Water Chemistry - Iron Generally, however, in oxic conditions Fe is found in a precipitated oxide form such as Fe(OH)3 These iron precipitates help to bind PO4 in the sediments and keep it from migrating into the water column

38. Water Chemistry - Iron However, when anoxic conditions set in, the Fe(OH)3 dissolves and PO4-3 can be rapidly released fueling algal growth

39. Water Chemistry - Iron However, when anoxic conditions set in, the Fe(OH)3 dissolves and PO4-3 can be rapidly released fueling algal growth

40. Water Chemistry - Iron However, when anoxic conditions set in, the Fe(OH)3 dissolves and PO4-3 can be rapidly released fueling algal growth

41. Water Chemistry - Silicon Required for diatioms Removed from the water column during diatom growth and sinking May come to limit diatom growth during the growing season