1. Carbon Dioxide Sources and Sinks: Respiration and Photosynthesis
CO2 + H2O ---hn---> Org-C + O2 (photosynthesis)
Org-C + O > CO2 + H2O (respiration)
The CO2 system is regulated by the acid/base chemistry of the carbonate system! (pH between )
Formation of calcareous sediments (CaCO3)
It is time to do some serious chemistry

2. Gas Exchange
[CO2] = Kh pCO2

3. Hydration of CO2

4. Forms of CO2 in Water
Carbonic acid (H2CO3), Bicarbonate (HCO3- ), and Carbonate (CO32-).
H2CO3 = H+ + HCO3- = CO H+ (4)

5. Systematic treatment of Equilibria

6. The first dissociation (K1)

7. The 2nd Dissociation Constant (K2)

8. Carbonate Mass and Charge Balance
Total CO2 = H2CO3 + HCO3- +CO32-
Total Alkalinity = HCO3- + 2CO32-
Another way of thinking about alkalinity is the charge of permanent cations - charge of permanent anions!

9. Lets pull this all together
TCO2 = H2CO3 + HCO3- +CO32-
TA = HCO3- + 2CO32-
pH = -log(H+)

10. Lets pull this all together
TCO2 = H2CO3 + HCO3- +CO32-
TA = HCO3- + 2CO32-
pH = -log(H+)

11. 6 Equations, 8 Unknowns Measure two variables to define the system. pH
Total Alkalinity
pCO2
We also need values for K1, K2, K*

14. Lets solve using a dummy variable

15. Carbonate Solubility Carbonate (CaCO3) Aragonite (CaCO3)
CaCO3 = Ca2+ + CO32-
Ksp vs. Ion Product
IP = [Ca2+][CO32-]
@ Equilibrium Ksp=IP
Ksp > IP precipitation
Ksp < IP dissolution
diss. produces 2 units of TA, 1 unit TCO2
ppt. consumes 2 units of TA, 1 unit TCO2

16. Lets focus on TA and TCO2

17. Deffeyes’ Diagram
pH 10
pH 8
pH 6

18. How do we mess with the CO2 system
Carbonate precipitation or dissolution?
diss. produces 2 units of TA, 1 unit TCO2
ppt. consumes 2 units of TA, 1 unit TCO2
Photosynthesis or Respiration?
photo. Consume TCO2, TA = constant
respir. Produce TCO2, TA = constant
Evaporation/precipitation
Change in TCO2 = TA

19. Deffeyes’ Diagram
pH 10
CaCO3
pH 8
Biological
Physical
pH 6

20. Deffeyes’ Diagram
pH 10
pH 8
CaCO3
Physical
pH 6
Biological

21. Deffeyes’ Diagram
CaCO3
Biological
Physical
pH 10
pH 8
pH 6

22. Other Weak Acids? H3PO4 Orthophosphate Triprotic Acid
pK1 = 2.148, pK2 = 7.199, pK3 = 12.5

23. Distribution diagram for H3PO4

24. Characterization of Phosphorus
Total P
0.45 m filter
Dissolved
Particulate
oxidation
Inorganic
Organic
Inorganic
Organic
Reactive Phosphate

25. Distribution of Phosphate

26. What is the cause of the phosphate distribution?
Lets look at other nutrients and oxygen as a clue.

27. NO2 vs PO4 plots
NO2-
PO43-

28. O2 vs PO4 plots O2
PO43-

29. General Phosphorus Cycle
Animals
Plants
photsynth.
respiration
Dissolved
inorganic P

30. General Phosphorus Cycle
Animals
Plants
photsynth.
respiration
weathering
Dissolved
inorganic P
fecal pellets
bacteria
Dissolved and detrital
organic-P
Sediments