Chemistry and Biogeochemical Cycling: Chemicals dissolved in water Abundant Less Abundant (not...

Chemistry and Biogeochemical Cycling:Chemicals dissolved in water

2 2 2 3 3 3CO H O H CO H HCO H CO 2 2 2 3 3 3CO H O H CO H HCO H CO 2 2 2 3 3 3CO H O H CO H HCO H CO

2 2

23

,

,

Ca Mg

CO

Na

2 2

23

,Ca Mg

CO

2 3 24 3 4 4

,

, , , ,

Na K

SO Cl NO PO SiO

Abundant Less Abundant (not trace)

Chemistry and Biogeochemical Cycling:Solubility of Gases

Chemistry and Biogeochemical Cycling:Oxygen Solubility and temperature

Chemistry and Biogeochemical Cycling:Pressure and Solubility

Chemistry and Biogeochemical Cycling:supersaturation

http://weberian.handrewlynch.net/

Solubility of oxygen:Differences in fresh and salt water

Thank you to Tianlu Shen for this question!

Snoeyink, V.L. and D. Jenkins. 1980. Water Chemistry. John Wiley & Sons, New York, New York, 463 pp. [text]

http://www.ionizers.org/water.html [images]

Due to the polar nature of the water molecule, it associates with ions or other molecules (including other water molecules) possessing a positive or negative charge.

Solubility of oxygen:The salting out effect When dissolved in water,

NsCl dissociates into a positively charged sodium ion and a negatively charged chloride ion. Water molecules are attracted to these ions and orient around them as waters of hydration.

Thus, less oxygen will dissolve in water with a high salt content than in ‘fresh’ water.

Gases such as oxygen dissolve less readily in water that is bonded in this manner. We might say that the salt ‘competes’ with the gases for the water molecules. Where there is a great deal of salt present, as in marine waters, a significant number of water molecules are present as waters of hydration.

Chemistry and Biogeochemical Cycling:Ph


2 [ ] [ ]H O H OH

141 10 @ 25wK H OH x C 141 10 @ 25wK H OH x C 141 10 @ 25wK H OH x C

14[ ][ ] 1 10wK H OH x In pure water …

and since pH is defined as…

[ ] [ ]H OH and thus …7 1[ ] 10H moles L

log[ ]pH H , 7pH for pure water

[Note that a little H+ goes a long way in terms of effect!]


1 2

2 2 2 3 3 3

K K

CO H O H CO H HCO H CO


731 1

2 3

[ ][ ]5 10 ; 6.3

H HCOK x pK

H CO

2113

2 23

[ ][ ]5 10 ; 10.3

H COK x pK

HCO

Chemistry and Biogeochemical Cycling:the carbonate system


1 2

2 2 2 3 3 3

K K


taking the negative log of both sides …

31 2 3 3

2 3

[ ]log ; [ ] [ ]

[ ]

HCOpK pH H CO HCO

H CO

and when

pH = pK1

223

2 3 33

[ ]log ; [ ] [ ]

[ ]

COpK pH HCO CO

HCO

and whenpH = pK2

Chemistry and Biogeochemical Cycling:The carbonate system


0.0

0.2

0.4

0.6

0.8

1.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

f (T

-DIC

)

pH

2 3H CO 23CO

3HCO

1pH pK 2pH pK

• at pH<pK1, carbonic acid dominates• at pH between pK1 and pK2, bicarbonate dominates; and• at pH>pK2, carbonate dominates



The fraction of DIC present in each form can be calculated as f (pH)(Chapra, 1997, p. 685

2

2 3 21 1 2

13 2

1 1 2

2 1 23 2

1 1 2

[ ]( )

[ ] [ ]

[ ]( )

[ ] [ ]

( )[ ] [ ]

Hf H CO

H K H K K

K Hf HCO

H K H K K

K Kf CO

H K H K K




and the concentration of each component is given by …

2 3 2 3 ,

3 3 ,

2 23 3 ,

[ ] ( )

[ ] ( )

[ ] ( )

T DIC

T DIC

T DIC

H CO f H CO C

HCO f HCO C

CO f CO C



photosynthetic withdrawal of carbon dioxide …

1 2

2 2 2 3 3 3

K K


According to LeChatlier’s Principle, the equilibrium would move to the left, consuming H+ and raising the pH.

While, at first glance, this looks to reduce the concentration of carbonate, the increase in pH re-distributes the DIC species, leading to an increase in the carbonate concentration.


0.0

0.2

0.4

0.6

0.8

1.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

f (T

-DIC

)

pH

2 3H CO 23CO

3HCO

1pH pK 2pH pK


ss demo

Chemistry and Biogeochemical Cycling:Whiting event in lake michigan


earthobservatory.nasa.gov

3

2 2, 3[ ][ ]sp CaCOk Ca CO

Chemistry and Biogeochemical Cycling:alkalinity


3 32Alk HCO CO OH H


Chemistry and Biogeochemical Cycling:Organic carbon - sources

allochthonous: carbon fixed within the watershed


autochthonous: carbon fixed within the lake


“don’t it make your brown eyes blue”

Chemistry and Biogeochemical Cycling:Organic carbon – Redox reactions

2 2( )C H O EA CO RS

2 2 2 2( )C H O O CO H O

2 2( )

(0) (4 )

C H O CO

C C

In each redox reaction, an electron donor contributes electrons and is oxidized (i.e. becomes more positive) and electron acceptor receives electrons and is reduced (i.e. becomes more negative).

For oxidation of organic carbon by oxygen,

the half-reactions are,

2 2

2 2(0) (4 )

O CO

O O

Chemistry and Biogeochemical Cycling:Organic carbon – Ecological Redox series

2 22 2C CO H O + O + H O

3 222 2 4H 5CO5CH O 7H O2N 4NO

+22

2+2 2 4H CO2MnO 2C 3H OH Mn O

+22

2+2 8H CO4Fe 7H O4OOHCH FeO

4 2 22 22 2H 2CO 2H2CH O O OS H S

2 24 CH2CH O + CO

Oxygen Reduction (aerobic respiration)

Nitrate reduction (denitrification)

Manganese Oxide Reduction

Iron Oxy-Hydroxide Reduction

Sulfate Reduction

Methanogenesis

Stoichiometry after Berg et al. 2003 and Boudreau 1996).

Chemistry and Biogeochemical Cycling:Organic carbon – Redox in sediments

Depletion ofDepletion of

Oxygen Nitrate

swi swi swi

methanogenesis methanogenesis methanogenesis

sulfate reduction

sulfate reduction

sulfate reduction

denitrification

denitrificationoxygen reduction

Chemistry and Biogeochemical Cycling:Organic carbon – carbon cycle

Chemistry and Biogeochemical Cycling:oxygen

22, 2,( )a sat measured

dOk O O

dt

la

Kk

H

0.864l wK U

( 20), ,20

Ta T ak k

Chemistry and Biogeochemical Cycling:Oxygen – photosynthesis and respiration

2 2 2 2( )CO H O C H O O

2 2 2 2( )C H O O CO H O

Chemistry and Biogeochemical Cycling:Nitrogen - species

Component Formula Significance

Nitrogen gas sources: atmosphere and denitrificationactivity: nitrogen fixationimpact: none

Ammonia sources: loads, direct excretion and DON diagenesisactivity: nitrification impact: plant nutrient (marine), toxic; oxygen demand

Nitrite sources: nitrification intermediate; transientactivity: nitrificationimpact: toxic; oxygen demand

Nitrate sources: loads, precipitation, nitrificationactivity: nitrification, denitrificationimpact: plant nutrient (marine)

DON/PON sources: loads, biosynthesis/decomposition of organic matter activity: ammonificationimpact: none

2N

3NH

3NO

3NO

AA

Chemistry and Biogeochemical Cycling:Nitrogen – amino acids

Chemistry and Biogeochemical Cycling:Nitrogen cycle

Chemistry and Biogeochemical Cycling:Phosphorus – nutrient limitation

The Supplies

The Product

Chemistry and Biogeochemical Cycling:Phosphorus – the divided lake

Chemistry and Biogeochemical Cycling:Phosphorus – forms of p in lakes

particulate

soluble

inorganic organic

PIP POP

SRP DOP

PP

TDP

TP

34PO 3

4R PO

Chemistry and Biogeochemical Cycling:Phosphorus cycle

Chemistry and Biogeochemical Cycling:iron

http://www.flickr.com/photos/inoneear/3498341514/

2

8

1

33

4

( ) 1

( ) 10

0

sp

spFe OH K

Fe OH K

Chemistry and Biogeochemical Cycling:sulfate

2 24SO S

Chemistry and Biogeochemical Cycling:silicon

Chemistry and Biogeochemical Cycling: Chemicals dissolved in water Abundant Less Abundant (not...

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