Lec 1a: Life in Water - Water Properties

• All life basically is aquatic– Life on Earth evolved in and is sustained by water– Terrestrial organisms maintain an internal aquatic

environment for their organs and tissues

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• Determines human distribution and population sizes

• Water is both a renewable and a non-renewable resource

• Available fresh water is relatively scarce

Water Reservoirs

(Horne & Goldman, 1994)

Renewal Time300-11,000 yrs12,000 yrs60-300 yrs330 days

7-11 days7 days

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Human Water Use Summary – Pressures on a Key Resource

• Only 1% of water in lakes, 0.01% in rivers– (as % of inland liquid water)

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• U. S. water use ~2000 m3 / person /year –e.g. versus Israel ~500 m3 / person / year

• Much water use for industry and irrigation, not just home use (Fig 1.3)

• Surface water provides majority of water (Fig1.4)

Factors Affecting Human Need for Fresh Water

• Population pressure and growth– Now approximately 6.6 billion humans– Human population doubling every 50 years

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• Development and Technology–New technologies in manufacturing and agriculture often result in increased per capita need for fresh water–Development often interferes with the water cycle (e.g., reduction of vegetation, paving, etc.)

• Pollution–Reduces amount of fresh water available for use

92%

5% 3%

Sufficiency

Stress

Scarcity

58%24%

18%

Sufficiency

Stress

Scarcity

World Population and Water Supply 1995 & 2050

19955.7 billion

20509.4 billion

How Many People Can The Earth Support? Joel Cohen. Norton, New York, 1995. 532 pp.

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Human-Biological Interactions in the Water Cycle

Evaporation

Surface runoff

Deep storage

InterceptionTranspiration

Withdrawal fromdeep storage

Factories

WellsReservoirs

Agriculture

Ground water

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Water Properties

Depiction of the three phases of water: steam, liquid water, and ice

©Time, Inc. All rights reserved.8

(See Table 2.1 for a summary)

A. Basic Structure 1. Covalent bonding of 2H + O atoms 2. Polar-covalent bond 3. Inter-molecule attraction 4. H-bonds

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B. Cohesion 1. Wave formation and other water movements 2. Distribution of heat, gases, nutrients, plankton, etc.

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C. Surface Tension 1. Pressure needed to break surface 2. Only Hg is higher 3. Implications for organisms?

-Related to what characteristics?

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D. Liquid at ambient temperatures

E. Low density solid (ice floats!) -Critical for life on earth

F. High heat capacity-Specific Heat - 1.0 (also called Heat Capacity)

calories required to raise 1 g H2O 1OC

(e.g. from 14.5 to 15.5OC)

-Exceeded only byLiquid NH3 1.23Liquid H2 3.40

-Heat transfer by water is very important

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G. Good Solvent (for some things)Difference on land vs. water % of air as oxygen =21% Concentration =210 ml / L

What about in water? (at 15 degC and 1 atm)

Solubility of oxygen in water =34 ml / LSolubility of carbon dioxide in water =1019 ml / L ….Why the disparity?

So, volume of oxygen at equil. with air: = 34.1 ml/L * 21% = 7.16 ml / L (30x less than air!)

What is the effect of temperature on gas solubility? (in eq. with Atm)Water Temperature (deg C) ml / L

0 10.310 8.015 7.220 6.630 5.6

(This is why hot water supposedly freezes more quickly than cold water) 13

0 10 20 30 40

1

3

5

15

25

35

Density Difference (x 105/oC Lowering)

T(oC)

1.00000

0.99900

0.99800

0.99700

0.99600

0.99500

0.92

0.91

-5 0 5 10 20 25 3015

Temperature oC

Density

Liquid0.99987

Ice0.9168

8.5%Densitychange

H. Very viscous 1. 800x more dense than air 2. Water Temperature - Density Relationship

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Lake Thermal Profile - Time and Depth

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0

2

4

6

8

10

12

14

0 10 20 30

Temperature (oC)

Dep

th (

m)

0 3 6 9 12

DO (mg/L)

Hensley Reservoir (Madera Co)

June

0

2

4

6

8

10

12

14

0 10 20 30

Temperature (oC)

Dep

th (

m)

0 3 6 9 12

DO (mg/L)

August

0

2

4

6

8

10

12

14

0 10 20 30

Temperature (oC)

Dep

th (

m)

0 3 6 9 12

DO (mg/L)

December

OxygenTemperature

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Relationships among Water Viscosity, Inertia, and Physical Parameters

• Hydrogen bonding becomes more important at smaller scales, altering both viscosity and inertia

• Viscosity is the resistance to change in form (internal friction)

• Inertia is the resistance of a body to a change in its state of motion

• Reynolds number incorporates both 17

Reynolds Number (Re)• Inertia Fi = SU2 • Viscosity Fv = µSU/L (decreases w/ temp)

• Re = Fi/Fv = U L / µ

µ = dynamic viscosity = density U = velocity S = surface area L = length

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Reynolds number for some organisms

10-7 10-5 10-3 10-1 101

Size (m)

10-5

10-2

101

104

107

Re

Salmon

Mayfly larva

Copepod

Unicellular alga

Bacterium

A

10-6 10-4 10-2 100 102

Velocity (m s-1)

Salmon

Mayfly larva

Copepod

Unicellular alga

Bacterium

B

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Contrast of Properties Varied by Scale

Parameter Small organism (< 100 µm)

Large organism (> 1 cm)

Re Low High

Viscosity (Fu) High Low

Inertia (Fi) Low High

Body shape Variable Streamlined

Particle sinking rates Low High

Relative energy requirement for motility

High Low

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Stokes Law• Sinking rate of small spheres is a function

of size and density of the sphere and viscosity and density of water

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Stoke’s Law :

where: g = gravitational acceleration (m / s2) = coefficient of viscosity of the

medium (kg/m/s)densp = density of particle densm = density of fluid

r = radius of the particle

)dens(dens9η

2gr VelocitySinking mp

2

• Cells alter shape to change sinking rate (Melosira example)

Cell Morphology alters Sinking Rate

0 1 2 3 4 5 6 7

Volume (1000 µm3)

0

10

20

30

40

50

60

Sin

king

vel

ocity

(µ

m s

-1)

Sphere (1.25 g cm-3

)

Sphere (1.09 g cm-3

)

Melosira italica

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Water Chemical and Physical Properties Summary

• Hydrogen bonding• High density, surface tension, heat of

vaporization, heat capacity, liquid at earth’s surface, excellent solvent (important for weathering)

• Ions more soluble in warmer water, gasses less• Unusual relationship between temperature and

density• Influence of water physical properties on

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