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Chemistry and Biogeochemical Cycling: Chemicals dissolved in water

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Chemistry and Biogeochemical Cycling: Chemicals dissolved in water. Abundant. Less Abundant (not trace). Chemistry and Biogeochemical Cycling: Solubility of Gases. Chemistry and Biogeochemical Cycling: Oxygen Solubility and temperature. Chemistry and Biogeochemical Cycling:

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Presentation Transcript
slide1

Chemistry and Biogeochemical Cycling:

Chemicals dissolved in water

Abundant

Less Abundant (not trace)

slide3

Chemistry and Biogeochemical Cycling:

Oxygen Solubility and temperature

slide5

Chemistry and Biogeochemical Cycling:

supersaturation

http://weberian.handrewlynch.net/

slide6

Solubility of oxygen:

Differences in fresh and salt water

Thank you to Tianlu Shen for this question!

slide7

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.

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.

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.

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

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]

slide8

Chemistry and Biogeochemical Cycling:

Ph

In pure water …

and thus …

and since pH is defined as…

for pure water

,

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

slide10

Chemistry and Biogeochemical Cycling:

The carbonate system

taking the negative log of both sides …

and when

pH = pK1

and when

pH = pK2

slide11

Chemistry and Biogeochemical Cycling:

The carbonate system

  • at pH<pK1, carbonic acid dominates
  • at pH between pK1 and pK2, bicarbonate dominates; and
  • at pH>pK2, carbonate dominates
slide12

Chemistry and Biogeochemical Cycling:

The carbonate system

The fraction of DIC present in each form can be calculated as f (pH)

(Chapra, 1997, p. 685

slide13

Chemistry and Biogeochemical Cycling:

The carbonate system

and the concentration of each component is given by …

slide14

Chemistry and Biogeochemical Cycling:

The carbonate system

photosynthetic withdrawal of carbon dioxide …

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.

slide15

Chemistry and Biogeochemical Cycling:

The carbonate system

ss demo

slide16

Chemistry and Biogeochemical Cycling:

Whiting event in lake michigan

earthobservatory.nasa.gov

slide18

Chemistry and Biogeochemical Cycling:

Organic carbon - sources

allochthonous:

carbon fixed within the watershed

slide19

Chemistry and Biogeochemical Cycling:

Organic carbon - sources

autochthonous:

carbon fixed within the lake

slide20

Chemistry and Biogeochemical Cycling:

Organic carbon - sources

“don’t it make

your brown eyes blue”

slide21

Chemistry and Biogeochemical Cycling:

Organic carbon – Redox reactions

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,

slide22

Chemistry and Biogeochemical Cycling:

Organic carbon – Ecological Redox series

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).

slide23

Chemistry and Biogeochemical Cycling:

Organic carbon – Redox in sediments

slide24

Chemistry and Biogeochemical Cycling:

Organic carbon – carbon cycle

slide26

Chemistry and Biogeochemical Cycling:

Oxygen – photosynthesis and respiration

slide30

Chemistry and Biogeochemical Cycling:

Phosphorus – nutrient limitation

The Product

The Supplies

slide31

Chemistry and Biogeochemical Cycling:

Phosphorus – the divided lake

slide32

Chemistry and Biogeochemical Cycling:

Phosphorus – forms of p in lakes

PP

PIP

POP

particulate

TP

SRP

TDP

DOP

soluble

organic

inorganic

slide34

Chemistry and Biogeochemical Cycling:

iron

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

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