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Carbon Dioxide  Sources and Sinks: Respiration and Photosynthesis  CO 2 + H 2 O ---h ---> Org-C + O 2 (photosynthesis)  Org-C + O 2 -----> CO 2 + H.

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Presentation on theme: "Carbon Dioxide  Sources and Sinks: Respiration and Photosynthesis  CO 2 + H 2 O ---h ---> Org-C + O 2 (photosynthesis)  Org-C + O 2 -----> CO 2 + H."— Presentation transcript:

1 Carbon Dioxide  Sources and Sinks: Respiration and Photosynthesis  CO 2 + H 2 O ---h ---> Org-C + O 2 (photosynthesis)  Org-C + O > CO 2 + H 2 O (respiration)  The CO 2 system is regulated by the acid/base chemistry of the carbonate system! (pH between )  Formation of calcareous sediments (CaCO 3 )  It is time to do some serious chemistry

2 Gas Exchange [CO 2 ] = K h p CO2

3 Hydration of CO 2

4 Forms of CO 2 in Water Carbonic acid (H 2 CO 3 ), Bicarbonate (HCO 3 - ), and Carbonate (CO 3 2- ). H 2 CO 3 = H + + HCO 3 - = 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 CO 2 = H 2 CO 3 + HCO 3 - +CO 3 2-  Total Alkalinity = HCO CO 3 2-  Another way of thinking about alkalinity is the charge of permanent cations - charge of permanent anions!

9 Lets pull this all together  TCO 2 = H 2 CO 3 + HCO 3 - +CO 3 2-  TA = HCO CO 3 2-  pH = -log(H + )

10 Lets pull this all together  TCO 2 = H 2 CO 3 + HCO 3 - +CO 3 2-  TA = HCO CO 3 2-  pH = -log(H + )

11 6 Equations, 8 Unknowns  Measure two variables to define the system.  pH  Total Alkalinity  pCO 2  We also need values for K 1, K 2, K*

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14 Lets solve using a dummy variable

15 Carbonate Solubility  Carbonate (CaCO 3 )  Aragonite (CaCO 3 )  CaCO 3 = Ca 2+ + CO 3 2-  Ksp vs. Ion Product  IP = [Ca 2+ ][CO 3 2- ] Equilibrium Ksp=IP  Ksp > IP precipitation  Ksp < IP dissolution  diss. produces 2 units of TA, 1 unit TCO 2  ppt. consumes 2 units of TA, 1 unit TCO 2

16 Lets focus on TA and TCO 2

17 Deffeyes’ Diagram pH 10 pH 8 pH 6

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

19 Deffeyes’ Diagram pH 10 pH 8 pH 6 CaCO 3 Biological Physical

20 Deffeyes’ Diagram pH 10 pH 8 pH 6 CaCO 3 Biological Physical

21 Deffeyes’ Diagram pH 10 pH 8 pH 6 CaCO 3 Biological Physical

22 Other Weak Acids?  H 3 PO 4 Orthophosphate  Triprotic Acid  pK 1 = 2.148, pK 2 = 7.199, pK 3 = 12.5

23 Distribution diagram for H 3 PO 4

24 Characterization of Phosphorus Total P 0.45  m filter Dissolved Particulate Inorganic Organic oxidation 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- PO4 3-

28 O2 vs PO4 plots PO4 3- O2

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

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


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