lec 1a: life in water - water properties all life basically is aquatic –life on earth evolved in...
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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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3
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
organisms23