2-the aquatic environment
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aquatic environmentTRANSCRIPT
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The Aquatic Environment
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The Aquatic Environment
• Water is the essential substance of life• 75 to 95 percent of the weight of all living cells
is water• Water covers 75 percent of the planet's
surface and is the dominant environment on Earth– Saltwater (marine)– Freshwater
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Water Cycles between Earth and the Atmosphere
• The water (or hydrologic) cycle is the process by which water travels in a sequence from the air to Earth and returns to the atmosphere
• Solar radiation is the driving force behind the water cycle because it provides energy for the evaporation of water
© 2012 Pearson Education, Inc.Figure 3.1
Industrial useEvapotranspiration
Evaporation
River
Transpiration
Surfacerunoff
Groundwater Deep seepageDeep storage
Domestic useInfiltration
Interception
Precipitation
The Water Cycle
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• Water vapor in the atmosphere eventually falls in some form of precipitation
• Interception occurs when precipitation falls onto vegetation, dead organic matter, and urban structures or streets. This water evaporates directly back to the atmosphere
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• Precipitation that reaches the soil moves into the ground by infiltration– Surface runoff occurs when the soil is saturated– The water that seeps down to an impervious layer
of rock collects as groundwater
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• Evapotranspiration is the total amount of evaporating water from ground and vegetation
(surface evaporation + transpiration)
– water in terrestrial and aquatic environments.– Transpiration is the evaporation of water from the
internal surfaces of plants
Which of these is the largest reservoir of freshwater on Earth?
A. the atmosphereB. groundwaterC. lakesD. oceansE. polar ice caps and glaciers
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Precipitation385,000
Evaporation425,000
Atmosphere13
Vapor transport40,000
Precipitation111,000
Polar iceand Glaciers25,000 x 103Transpiration and Evaporation
71,000
Soil moisture67
Lake229
Ocean1.37 × 109 km3
River40,000 Groundwater
4,000
The Global Water Cycle
97% of water resides in the ocean2% resides in polar ice and glaaciers
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Hydrogen
(a)
OxygenIn water (H2O), the atoms are asymmetrically bound to one another
The hydrogen atoms share an electron with the oxygen atom through a covalent bond
What is Water?
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Figure 3.3b Hydrogen
(b)
+ –
Oxygen
Water is a Polar Molecule
Because electrons are unequally shared and spend more time around oxygen, water is considered a polar molecule
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Hydrogen
(c)
Oxygen
Because of this Polarity,It attracts other water
molecules
Hydrogen bonding between water molecules
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Hydrogen
(d)
Oxygen The Structure of Liquid Water
Hydrogen bonds break and reform easily
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What happens when water freezes?
• Water molecules in solid form (ice) are spaced farther apart (have more space) than water molecules in liquid
• Water becomes less dense as it converts from liquid to solid– This allows for insulation of water bodies so that
they do not freeze solid
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Hydrogen
(e)
Oxygen
Ice is less dense than liquid water
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–8 –4 0 4 8 12 16 20Temperature (°C)
Meltingor
freezing
Water
Maximum density at 4°C
Dens
ity (g
/cm
3 )
Ice
1.0004
1.0000
0.9996
0.9992
0.9988
0.9984
0.9178
0.9174
0.9170
Density of Wateras a function
of Temperature
4oC = ~ 39oF
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The Specific Heat of Water
• Specific heat of water = 1– Specific heat is the energy (measured in
calories) required to raise 1 gram of water 1°C• Water must absorb (or lose) great quantities of
heat to change its temperature– This helps to buffer aquatic habitats and is important
for thermal regulation within living organisms

Latent HeatHeat needed to change physical state of water
Figure 3.6
Hydrogen bond
Ice:Hydrogen bonds
are stable
Liquid water:Hydrogen bonds
break and re-form
Ice floats on top of lakes because it is denser than water
How does this protect the organisms living below the ice?
What would happen to organisms on Earth if water did not have a high specific
heat or Latent heat?
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Other properties of Water help sustain life
• Cohesion is the linkage between and among water molecules due to hydrogen bonding
• Surface tension of water is the result of differences in attraction among water molecules between the surface of the water and air– The surface of water is able to support small
organisms
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Hydrogen bonding of water molecules provides surface tension
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• Viscosity is the property that measures the force necessary to separate the molecules.
• Aquatic organisms must cope with the frictional resistance of water and overcome viscosity– The frictional resistance of water is 100 times greater than
air!• Water has a high viscosity due largely to its greater
density (860 times that of air!)– Aquatic organisms experience buoyancy in water because of
the upward force of water acting on the less dense object
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Streamlined bodies offer the least resistance to the viscosity of water
Electromagnetic Spectrum
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Not all light penetrates water Equally
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Light Varies with Depth in Aquatic Environments
• Water reflects light depending upon the angle in which light strikes it
• The pattern of light absorption in water gives rise to unique adaptations in aquatic organisms– Body color or lack of pigmentation– Large eyes– Bioluminescence
Dept
h (m
)
0
20
30
40
50
60
70
80
90
100
Light (% surface)
Dept
h (m
)
Transmittance (%)0 20 40 60 80 100
RedOrange
Yellow
Green
Blue
400 500 600 700Wavelength (nanometers)
(a) (b)
10
0 20 40 60 80 1000
20
30
40
50
60
70
10
Attenuation of Light with Water Depth
Why is water blue?
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The thermocline is the region of the vertical depth profile where water temperature declines most rapidly
The thermocline depth depends on solar radiation input and level of mixing
The thermocline is located between the epilimnion (warm, lighter water above) and the hypolimnion (cold, denser water below)
Temperature Profile of Water
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Density Changes with Water Depth
The hypolimnion has the higher density
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0 5 10 15 20Water temperature (°C)
Summer
Fall
Winter
Wat
er d
epth
EpilimnionWarm, low-density,surface waters
ThermoclineZone of rapidtemperature change
HypolimnionCold, high-density,deep waters
Seasonal Changes in Water Temperature
*Temperate region profile
Where is prime real-estate during winter months?
Why?
• Would the vertical profile be seen in moving water?
• Why or why not?
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Water Functions as a Solvent
• Water can dissolve more substances than any other liquid. This is crucial to biological systems
• Water's dissolving "power" is a result of its polarity
• Every water molecule has a positive and negative side so it is attracted to other charged atoms and molecules (ions)
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The Polarity of Water accounts for its Solvent Nature
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Oxygen Diffuses from the Atmosphere to the Surface Waters
• Diffusion is the general tendency of molecules to move from a region of high concentration to one of lower concentration
• Oxygen and carbon dioxide diffuse from the atmosphere into the surface waters of aquatic environments– The rate of diffusion is dependent on the solubility
of oxygen (greater in cold water) and the diffusion gradient
0 2 4 6 8 10 12
Summer
Falloverturn
Winter Cold water increases oxygen solubility, however, Surface ice reduces the diffusion of oxygen from atmosphere into surfacewaters
Decline in oxygen reflectsthe demand and uptakeby decomposer organismsinhabiting the bottom zone
Oxygen (ppm)
Oxygen Stratification
• What types of organisms have evolved to survive life in deep waters?
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Acidity Has a Widespread Influence on Aquatic Environments
• The pH of aquatic environments influences distribution and abundance of organisms
• What changes the pH of aquatic environments?– Physiological processes– Concentration of toxic metals
• Aluminum dissolves as pH decreases and becomes more concentrated in aquatic environments
What is pH?
Acid
Base[H] lowest
[H] highest
[H] and [OH] equal
pH = -log[H+][H] and [OH] must always add to 14
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The Carbonic Acid Buffer System Removes Excess CO2
– This system generally acts as a buffer and keeps the pH of water within a narrow range
CO2 + H2O H2CO3 HCO3- + H+
HCO3- H+ + CO3
2-
Free CO2 HCO3 CO3
50
Perc
ent o
f tot
al C
O2
100
0
pH4 5 6 7 8 9 10 11 12
2–
Predominate forms of CO2 in water in relation to pH