2-the aquatic environment

© 2012 Pearson Education, Inc.

The Aquatic Environment


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


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


• 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


• 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


• 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



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


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?


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


Hydrogen

(c)

Oxygen

Because of this Polarity,It attracts other water

molecules

Hydrogen bonding between water molecules


Hydrogen

(d)

Oxygen The Structure of Liquid Water

Hydrogen bonds break and reform easily


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


Hydrogen

(e)

Oxygen

Ice is less dense than liquid water


–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


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?


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


Hydrogen bonding of water molecules provides surface tension


• 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


Streamlined bodies offer the least resistance to the viscosity of water

Electromagnetic Spectrum


Not all light penetrates water Equally


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?


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


Density Changes with Water Depth

The hypolimnion has the higher density


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?


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)


The Polarity of Water accounts for its Solvent Nature


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?


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


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

2-the aquatic environment

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