3

CHAPTER
The Aquatic
Environment
© 2016 Pearson Education, Ltd.

Elements of ECOLOGY Lecture Presentation by

NINTH EDITION, GLOBAL EDITION
Carla Ann Hass
Penn State University
Thomas M. Smith • Robert Leo Smith
 Chapter 3 The Aquatic Environment

§ What percent of the weight of a living cell is water?

§ What percentage of Earth’s surface is covered in
water?
§ Where is water found on Earth?

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 Section 3.1 Water Cycles between Earth and the
Atmosphere
§ What does it mean to say that water cycles?
§ Why is solar radiation important in the water cycle?
§ What processes on Earth involve water moving from
one place to another?

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 Section 3.1 Water Cycles between Earth and the
Atmosphere
§ Processes and parts of the water cycle include:
§ precipitation
§ interception
§ infiltration
§ runoff
§ groundwater
§ deep seepage/deep storage
§ evapotranspiration
§ evaporation
§ transpiration

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Figure 3.1

Precipitation

Evaporation

Evaporation Interception

Transpiration

Surface
runoff
Infiltration
River

Groundwater
Deep seepage

Deep storage

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 Section 3.1 Water Cycles between Earth and the
Atmosphere
§ What is a reservoir in the water cycle?
§ What is a flux in the water cycle?

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 Section 3.1 Water Cycles between Earth and the
Atmosphere
§ A reservoir is where water is held. What are the six
reservoirs?
§ Flux is the movement of water from one reservoir to
another. What are the six fluxes?
§ How do you determine turnover time?

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Figure 3.2

Vapor transport
40,000 Precipitation
111,000
Atmosphere Polar ice
13 and Glaciers
29,000
Transpiration and Evaporation
Evaporation 71,000
425,000 Lake
Precipitation Soil moisture 229
385,000 67

River
40,000 Groundwater
Ocean
4000
1.37 ´ 106

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 Which of these is the largest reservoir of freshwater on
Earth?

A. the atmosphere
B. groundwater
C. lakes
D. oceans
E. polar ice caps and glaciers

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Figure 3.2

Vapor transport
40,000 Precipitation
111,000
Atmosphere Polar ice
13 and Glaciers
29,000
Transpiration and Evaporation
Evaporation 71,000
425,000 Lake
Precipitation Soil moisture 229
385,000 67

River
40,000 Groundwater
Ocean
4000
1.37 ´ 106

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 Which of these is the largest reservoir of freshwater on
Earth?

A. the atmosphere
B. groundwater
C. lakes
D. oceans
E. polar ice caps and glaciers

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 Evaporation from the oceans exceeds precipitation
into the oceans. Which of these processes or parts of
the water cycle does not contribute water to the
oceans?

A. transpiration by marine algae

B. melting ice from polar ice caps
C. groundwater seepage
D. rivers
E. All of these processes or parts of the water cycle
add water to the oceans.

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 Evaporation from the oceans exceeds precipitation
into the oceans. Which of these processes or parts of
the water cycle does not contribute water to the
oceans?

A. transpiration by marine algae

B. melting ice from polar ice caps
C. groundwater seepage
D. rivers
E. All of these processes or parts of the water cycle
add water to the oceans.

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 Section 3.2 Water Has Important Physical
Properties
§ What is the chemical symbol for water?
§ How are the hydrogen and oxygen atoms bound
together within a water molecule?
§ How do these chemical bonds affect the polarity of
the molecule?

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Figure 3.3a

Hydrogen
Oxygen

(a)

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 Section 3.2 Water Has Important Physical
Properties
§ Water = H2O
§ Oxygen has eight protons in its nucleus
§ the electrons shared with each hydrogen are more
strongly attracted to the oxygen
§ Gives the oxygen a slight negative (-) charge and
the hydrogens a slight positive (+) charge, resulting
in a polar molecule.

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Figure 3.3b

Hydrogen
Oxygen

+ -

(b)

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 Section 3.2 Water Has Important Physical
Properties
§ This polarity allows water molecules to form
hydrogen bonds with each other
§ a slightly (+) hydrogen will link to a slightly (-) oxygen
§ these are weak bonds that are easily formed and
broken

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Figure 3.3c

Hydrogen
Oxygen

(c)

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 Section 3.2 Water Has Important Physical
Properties
§ Hydrogen bonding among water molecules confers
many of the special properties of water.
§ Review of chemistry – what are some of these
properties?

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 Section 3.2 Water Has Important Physical
Properties
§ Water has a high specific heat
§ It requires one calorie to raise one gram of water
1°C
§ for comparison, it requires 0.59 calories to raise one
gram of ethanol 1°C
§ water can store large amounts of heat energy with
only a small increase in temperature
§ Why is this important for organisms?

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 Section 3.2 Water Has Important Physical
Properties
§ Water has a high specific heat
§ It requires one calorie to raise one gram of water
1°C
§ for comparison, it requires 0.59 calories to raise one
gram of ethanol 1°C
§ water can store large amounts of heat energy with
only a small increase in temperature
§ Why is this important for organisms?
§ Waters serves as a buffer to temperature changes,
both internally and externally.

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 Section 3.2 Water Has Important Physical
Properties
§ Because of the high specific heat of water, changing
state among solid, liquid, and gas phases requires
large amounts of heat energy
§ Latent heat = the energy released or absorbed in
state changes
§ removing one calorie will reduce the temperature of
one gram of water from 1°C to 2°C
§ however, 80 calories must be removed to reduce one
gram of water to 0°C, converting it to ice

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 Section 3.2 Water Has Important Physical
Properties
§ Why does ice float?

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 Section 3.2 Water Has Important Physical
Properties
§ Ice floats because of the lattice formed by hydrogen
bonding among water molecules, the solid phase of
water is less dense than the liquid – the water
molecules are held farther apart
§ water is most dense at 4°C
§ Why is this important in aquatic environments?

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Figure 3.4

1.0004
Maximum density at 4°C

1.0000

Density (g/cm3) 0.9996

Water
0.9992 Melting
or
freezing
0.9988

0.9984

0.9178

0.9174
Ice

0.9170
-8 -4 0 4 8 12 16 20
Temperature (°C)
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 Section 3.2 Water Has Important Physical
Properties
§ Organisms can live under the ice during the winter.

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 Section 3.2 Water Has Important Physical
Properties
§ Cohesion – because of the hydrogen bonds
between them, water molecules stick together
§ at the interface with air, water molecules on the
surface bond more strongly to water molecules below
§ produces surface tension – surface of the water is
“tight”
§ this may create a barrier to small organisms
§ allows some organisms to walk on water

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Figure 3.5

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 Section 3.2 Water Has Important Physical
Properties
§ Cohesion also leads to high viscosity of water
§ Viscosity – force required for an object to move
through the liquid
§ water has a frictional resistance 100´ greater than air
§ What is a common body shape seen in aquatic
vertebrates?

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 Section 3.2 Water Has Important Physical
Properties
§ Many aquatic vertebrates have a streamlined
(torpedo) shape
§ helps to reduce frictional resistance
§ many examples of convergent evolution in fish,
reptiles, birds, and mammals

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Figure 3.6

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 Section 3.2 Water Has Important Physical
Properties
§ Density of water about 860´ greater than air
§ Buoyancy – upward force exerted when a body in
water weighs less than the water it displaces
§ Reduces the effect of gravity
§ organisms need less structural support
§ compare the skeleton of a bony fish to a terrestrial
vertebrate of the same size
§ organisms can be very large

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 Section 3.2 Water Has Important Physical
Properties
§ Density of water about 860´ greater than air
§ Water shows greater pressure increases with depth
than air
§ pressure increases by 1 atmosphere (atm) for each
10 m of depth

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 Section 3.2 Water Has Important Physical
Properties
§ Organisms in the very deep ocean can experience
1000 atms of pressure
§ 15,000 pounds per square inch compared to 14.7
pounds per square inch on the surface
§ Many show special adaptations
§ for example:
§ the lungs of deep-diving mammals collapse
§ oxygen is held by myoglobin in the muscles

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 Section 3.3 Light Varies with Depth in
Aquatic Environments
§ What happens when light strikes the surface of the
water?
§ Review
§ How does light intensity vary seasonally?
§ think back to Section 2.1

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 Section 3.3 Light Varies with Depth in
Aquatic Environments
§ When light strikes the surface of the water
§ some light is reflected and some light is transmitted
§ The lower the angle at which it strikes the surface,
the more light is reflected.
§ How does this vary during the day and seasonally?

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 Section 3.3 Light Varies with Depth in
Aquatic Environments
§ What happens to the light that is transmitted?
§ Suspended particles and organisms either absorb or
scatter the light
§ Water absorbs light
§ Review of physics
§ Which wavelengths are absorbed first? Why?
§ Which wavelengths penetrate the farthest?
§ How does this affect aquatic organisms?

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 Section 3.3 Light Varies with Depth in
Aquatic Environments
§ How does this affect photosynthesis?
§ What is true of photosynthetic pigments in deeper
water?
§ How does this affect vision?

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Figure 3.7

Light (% surface) Transmittance (%)

0 20 40 60 80 100 0 20 40 60 80 100
0 0
Red
10 10 Orange
20 20

30 30
Yellow
40 40 Green
Depth (m)

Depth (m)
50 50
Blue
60 60

70 70

80
400 500 600 700
90
Wavelength (nanometers)
100
(a) (b)

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 Section 3.4 Temperature Varies with Water
Depth
§ What happens when light strikes the surface of the
water?
§ Is the temperature profile of the water column the
same as the light profile?

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 Section 3.4 Temperature Varies with Water
Depth
§ Sunlight warms the surface waters
§ winds and waves mix the surface waters
§ Distributes heat vertically
§ decline in water temperature with depth slower than
decline in solar radiation
§ Below mixed layer, temperatures drop rapidly =
thermocline
§ Thermocline depth is variable
§ Below thermocline water temperature further
declines with depth but at a slower rate

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 Section 3.4 Temperature Varies with Water
Depth
§ Produces zonation
§ Epilimnion – upper layer of warm, less dense water
§ Hypolimnion – lower layer of cold, more dense water
§ Thermocline prevents mixing of these layers

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Figure 3.8

Temperature (°C) Density (kg/m3)

0 5 10 15 20 998.0 998.5 999.0 999.5 1000

Epilimnion
Warm, low-density,
Warm,
surface waters
low-density water
Thermocline
Zone of rapid
temperature change

Depth (m)
Hypolimnion
Cold, high-density,
deep waters Cold,
high-density water

(a) (b)

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 Section 3.4 Temperature Varies with Water
Depth
§ Seasonal changes in solar radiation can lead to
changes in the vertical temperature profile
§ Tropics – thermocline is permanent
§ surface water is always warmer
§ Temperate zone
§ summer – thermocline is present
§ surface water is warmest

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Figure 3.9

Water temperature (°C)

0 5 10 15 20

Water depth

Summer
Fall
Winter
Spring
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 Section 3.4 Temperature Varies with Water
Depth
§ Temperate zone
§ Fall – surface water begins to cool
§ cool water sinks
§ warmer water moves to the surface, also cools
§ eventually temperature becomes uniform
§ Turnover – this vertical mixing moves nutrient

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Figure 3.9

Water temperature (°C)

0 5 10 15 20

Water depth

Summer
Fall
Winter
Spring
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 Section 3.4 Temperature Varies with Water
Depth
§ Temperate Zone
§ winter – surface water cools
§ ice many form on the surface
§ water at the bottom is most dense 4°C
§ Spring – surface water begins to warm
§ temperature eventually becomes less uniform than
winter, especially at the surface
§ some turnover takes place

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Figure 3.9

Water temperature (°C)

0 5 10 15 20

Water depth

Summer
Fall
Winter
Spring
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 Section 3.4 Temperature Varies with Water
Depth
§ The temperature of a flowing body of water such as
a stream or river is variable
§ warm and cool, depending on the season
§ shaded areas are cooler than those exposed to
sunlight
§ Temperature affects stream community structure
§ cool water versus warm water organisms

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Figure 3.10

21.1°
Water temperatures at various locations along the stream
Air temperature 21°C 20.0°
20.0°

17.2°
16.1° 16.1°16.1°
15.6° 15.6°
13.9° 14.4°

1 km

Wooded boulder section

Beaver meadow

Marion
River
(Elev. 543 m)

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 Section 3.5 Water Functions as a Solvent

§ What happens when you stir sugar into a glass of

water?
§ Why does this happen?

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 Section 3.5 Water Functions as a Solvent

§ Water’s role as a solvent results from bonding within

the water molecule
§ positive charge on hydrogen atoms
§ negative charge on oxygen atom
§ Permanent dipole (two oppositely-charged poles)

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 Section 3.5 Water Functions as a Solvent

§ Water is a polar solvent

§ attracted to other charged molecules
§ Can dissolve polar compounds
§ example – sucrose in water (or tea)
§ has hydroxyl groups (-OH) which are slightly polar
§ these hold the sucrose molecules together
§ water interacts with these -OH groups, separates the
sucrose molecules

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 Section 3.5 Water Functions as a Solvent

§ Water can dissolve ionic compounds

§ Example – salt (NaCl) in water
§ composed of Na+ and Cl- ions
§ H atoms attract Na+ while O atoms attract Cl-
§ pulls molecules apart; they dissolve
§ Most of the salt in the oceans is from NaCl
§ Practical Salinity Units (psu) = gm Cl/kg H2O
§ Ocean salinity averages 35 percent

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Figure 3.11

K+ 1.1% Minor
constituents:
Ca2+ 1.2%
Salt Sr2+, Br-, C
35 grams Mg2+ 3.7% 0.7%
SO42-
7.7%

Water Na+
965 grams Cl-
30.6% 55.0%

Seawater
Salinity = 35%

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 Section 3.5 Water Functions as a Solvent

§ Minerals that are ionic compounds dissolve in water

§ Example
§ CaCO3 (calcium carbonate) in limestone rocks
§ composed of Ca2+ and HCO3- ions
§ dissolves until it reaches maximum solubility
§ then precipitates out and forms sediments

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ How are gases exchanged between water and the
atmosphere?
§ Which two gases are the most important for aquatic
organisms?

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Review
§ Diffusion – movement of molecules from an area of
high concentration to an area of low concentration
§ Diffusion is affected by solubility and the diffusion
gradient

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Solubility is a function of:
§ temperature – solubility decreases as temperature
increases
§ pressure – solubility increases as atmospheric
pressure increases
§ salinity – solubility decreases as salinity increases
§ Diffusion gradient – difference in concentration
between the air and water

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Gases diffuse much more slowly in water than in air
due to greater density and viscosity
§ Oxygen concentration can be limiting for organisms
in aquatic environments
§ in air = 21%
§ in water = 1%

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Oxygen moves from the atmosphere into surface
waters
§ then diffuses into waters below
§ currents and turbulence assist this process
§ Oxygen is lost through
§ uptake by aquatic organisms
§ increased water temperature

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Oxygen can be stratified in lakes and ponds during
the summer
§ Highest at the surface
§ Diffusion
§ photosynthesis
§ Lower with increasing depth
§ cellular respiration
§ What happens in the fall and spring?
§ Think back to temperature stratification.

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Turnover – as warm and cold waters rise and fall,
the deeper water is recharged with oxygen
§ What happens in the winter?
§ oxygen solubility is higher at lower temperatures
§ oxygen demand reduced for most organisms
§ but, ice reduces diffusion from the atmosphere

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Figure 3.12

0 Ice
Spring
1 Colder water increases
Summer
oxygen solubility. Formation
2 Fall of ice, however, can greatly
Winter reduce diffusion from
3 atmosphere into surface
waters.
4

5
Depth (m)

8
Decline in oxygen reflects
9 the demand and uptake
by decomposer organisms
10 inhabiting the bottom zone.
11
0 5 10 15 20 0 2 4 6 8 10 12
Temperature (°C) Oxygen (ppm)

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Oxygen is not distributed evenly in the oceans
§ Highest levels near the surface (upper 10 to 20
meters)
§ diffusion and photosynthesis
§ As depth increases, oxygen concentration
decreases

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 Section 3.6 Oxygen Diffuses from the
Atmosphere to Surface Waters
§ Oxygen minimum zone at 500 to 1000 meters
§ Why does concentration again increase as depth
increases below this zone?

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Figure 3.13

0
Oxygen
minimum
1000 zone
Depth (m)

2000

3000

4000

5000
0 1 2 3 4 5 6
cm3 O2 per liter
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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ What is the carbon dioxide – carbonic acid-
bicarbonate system?
§ How does it affect the pH of water?

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ Carbon dioxide diffuses from the atmosphere into
the water
§ Carbon dioxide reacts with water to produce
carbonic acid
§ CO2 + H2O equilibrium H2CO3
§ Carbonic acid dissociates into hydrogen and
bicarbonate ions
§ H2CO3 equilibrium HCO-3 + H+
§ Bicarbonate can dissociate into hydrogen and
carbonate ions
§ HCO3- equilibrium H+ + CO32-
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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ Carbon dioxide – carbonic acid – bicarbonate
system tends to stay in equilibrium
§ Example:
§ if algaes remove CO2 through photosynthesis,
carbonic acid and bicarbonate will produce more CO2
to restore equilibrium

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ Hydrogen ions (H+) are produced and absorbed by
these reactions
§ Acidity – the abundance of hydrogen ions in a
solution
§ acidic solutions have a large number of H+ and few
OH- (hydroxyl ions)
§ alkaline solutions have a large number of OH- and
few H+
§ pH – the negative logarithm (base 10) of the
concentration of H+ in solution

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ In pure water (a neutral solution)
§ A small fraction of water molecules dissociate into
ions
§ H2O → H+ + OH-
§ Ratio of H+ to OH- is 1:1
§ Concentration is 10-7 moles/liter
§ pH = -log(10-7) = 7

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ Solution departs from neutrality when the
concentration of one ion increases or decreases
relative to the other
§ Example – pH 6
§ H+ ions increase in concentration to 10-6 moles/liter
§ OH- decrease in concentration to 10-8 moles/liter
§ The pH scale goes from 1 to 14
§ pH > 7.0 = alkaline
§ pH < 7.0 = acidic

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ Presence of CO2 affects the pH of water as a result
of the absorption and production of H+
§ This allows the carbon dioxide-carbonic acid-
bicarbonate system to act as a buffer against large
changes in pH
§ If pH = 7, HCO3- more abundant
§ If pH is lower, CO2 more abundant
§ If pH is higher, CO32- more abundant

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Figure 3.14

100
Free CO2 HCO3 CO32-
Percent of total CO2

50

0
4 5 6 7 8 9 10 11 12
pH

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ pH range of natural waters between 2 and 12
§ Rocks underlying a watershed affect its pH
§ watersheds dominated by limestone CaCO3
§ higher pH and well-buffered
§ watersheds dominated by sandstone or granite
§ lower pH, less well-buffered
§ Seawater is slightly alkaline (pH 7.5 to 8.4)
§ sodium, potassium and calcium are alkaline ions

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 Section 3.7 Acidity Has a Widespread
Influence on Aquatic Environments
§ How does pH affect aquatic organisms?
§ Directly influences physiological processes
§ most organisms cannot reproduce below pH 4.5
§ Indirectly influences through heavy metal
concentration
§ acidic waters contain high concentrations of
aluminum
§ aluminum is insoluble in neutral or alkaline waters

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ What are the different types of water movement?
§ How does this affect aquatic environments?

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Currents – streams and rivers
§ Waves – open body of water (lake or ocean),
breaking on a shore

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Stream character and structure are modified by
velocity of the current
§ Velocity is affected by
§ Shape and steepness of the stream channel
§ Stream channel width, depth roughness of bottom
§ Rainfall intensity
§ Rapidity of snow melt

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ In a fast stream:
§ velocity is 50 cm/second or higher
§ current removes all particles less than 5 mm in
diameter, leaving a stony bottom
§ high water volume increases the velocity
§ moves bottom stones and rubble
§ scours the streambed
§ cuts new banks and channels

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Over time, width, depth, volume increase
§ velocity decreases
§ silts and decaying matter accumulate on the bottom

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Figure 3.15

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Wind generates waves on
§ large lakes
§ open ocean
§ Frictional drag of wind on smooth surface → ripples
§ More wind applies more pressure → wave size
grows
§ When energy from wind = energy lost by breaking
waves, whitecaps form

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Waves approach land
§ Water becomes more shallow
§ Bottom of wave hits ocean floor
§ wavelength shortens
§ wave steepens
§ Eventually breaks – collapses forward
§ Energy dissipated as shore pounded or sand
removed

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 Section 3.8 Water Movements Shape
Freshwater and Marine Environments
§ Ocean currents are influenced by
§ Prevailing wind direction
§ Coriolis effect
§ Warm surface currents move N and S from equator
§ Bring up deep cold, oxygenated waters – upwelling

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Figure 3.16

Western
edge of
Northern continent Coriolis
equatorial Coriolis Wind effect
current effect
Equator

Southern
equatorial
current

N E Coastal
upwelling
(b)
Equatorial W
upwelling S Deep water
(a) Surface water
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 Section 3.9 Tides Dominate the Marine
Coastal Environment
§ What causes ocean tides?
§ What is meant when the intertidal zone is called “an
environment of extremes”?

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 Section 3.9 Tides Dominate the Marine
Coastal Environment
§ Tides affect life on the ocean shores
§ Result from the gravitation pull of the moon and the
sun
§ Each causes two bulges on opposite sides of the
earth
§ Lunar tides:
§ bulge on the moon side due to gravitation attraction
§ bulge on the opposite side because gravitation force
at that point is less than at Earth’s center

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Figure 3.17

Sun
New
moon
T
A N

Spring tide

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 Section 3.9 Tides Dominate the Marine
Coastal Environment
§ Solar tides are similar to lunar tides
§ Sun has a weaker gravitational pull on tides
§ Solar tides partially masked by lunar tides, except
when the moon is new and when it is full
§ at these times, planets are nearly in line
§ gravitational pulls of the moon and sun are additive
§ leads to very large high tides

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 Section 3.9 Tides Dominate the Marine
Coastal Environment
§ Tides vary from day to day following the phases of
the moon. They are also affected by:
§ gravitational pull of the moon and the sun (which vary
because of Earth’s elliptical orbit)
§ water depth
§ winds (onshore and offshore)
§ shore contour
§ wave action

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 Section 3.9 Tides Dominate the Marine
Coastal Environment
§ Intertidal zone – lies between the water lines for high
and low tide
§ Daily periods of submergence and exposure
§ Organisms high in the intertidal zone are exposed to
environmental extremes
§ wide temperature fluctuations
§ intense solar radiation
§ dessication
§ air

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 Section 3.10 The Transition Zone between Freshwater and
Saltwater Environments Presents Unique Constraints

§ What is an estuary?
§ Where would you find estuaries?
§ Why is an estuary environment challenging for
aquatic organisms?

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 Section 3.10 The Transition Zone between Freshwater and
Saltwater Environments Presents Unique Constraints

§ Estuary – where freshwater and saltwater mix

§ Temperatures fluctuate daily and seasonally
§ Salinity varies vertically
§ saltwater is more dense than freshwater
§ currents and winds can mix the water
§ Salinity varies horizontally
§ the waters with the lowest salinity are at the river
mouth
§ the waters with the highest salinity are at the sea

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 Section 3.10 The Transition Zone between Freshwater and
Saltwater Environments Presents Unique Constraints

§ Coriolis effect leads to variation in salinity

§ In the Northern Hemisphere:
§ outflowing freshwater and inflowing seawater are
deflected to the right
§ higher salinity on the left side of the estuary

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Figure 3.18

High-
tide 30‰ 25‰ 20‰ 15‰ 10‰ 5‰ 0
shoreline
River
mouth

Low- 25‰ 15‰ 5‰

tide 20‰ 10‰ 0
shoreline Low High
tide
tide

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 Section 3.10 The Transition Zone between Freshwater and
Saltwater Environments Presents Unique Constraints

§ Organisms living in an estuary have adaptions to

these changes in salinity
§ physiological
§ bull sharks are able to live in both marine and
freshwater environments through adjustments in
osmoregulation
§ behavioral
§ fish can move to area of suitable salinity

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 This figure shows that in an estuary, near the mouth of
a river, salinity

A. is the same at both high and low tide.

B. is higher at low tide, and lower at high tide.
C. is lower at low tide and higher at high tide.
D. decreases as you move toward the ocean.

© 2016 Pearson Education, Ltd.

Figure 3.18

High-
tide 30‰ 25‰ 20‰ 15‰ 10‰ 5‰ 0
shoreline
River
mouth

Low- 25‰ 15‰ 5‰

tide 20‰ 10‰ 0
shoreline Low High
tide
tide

© 2016 Pearson Education, Ltd.

 This figure shows that in an estuary, near the mouth of
a river, salinity

A. is the same at both high and low tide.

B. is higher at low tide, and lower at high tide.
C. is lower at low tide and higher at high tide.
D. decreases as you move toward the ocean.

© 2016 Pearson Education, Ltd.

 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ The pH of the oceans has been relatively steady at

8.2 for millions of years
§ As CO2 in the atmosphere has increased, more is
being taken up by ocean surface waters
§ How does this affect the pH of the oceans?
§ Think of the CO2 – bicarbonate – carbonic acid
system

© 2016 Pearson Education, Ltd.

 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ As atmospheric CO2 has increased, the pH of ocean

surface waters has fallen by 0.1 pH unit
§ this is a 25 percent increase in the hydrogen ion
concentration

© 2016 Pearson Education, Ltd.

Figure 3.19
400 8.38
(a) Mauna Loa CO2 record
8.33
375
8.28
350 8.23

CO2

pH
325 8.18
8.13
300
8.08
275 8.03
(b) Aragonite saturation state

4.50
Waragonite

4.00

3.50

3.00
(c) Calcite saturation state

6.50

160° W 158° W 156° W

Wcalcite

6.00 23° N
Station ALOHA
22°
5.50 21°
20°Station Mauna Loa
19°
5.00
1950 1960 1970 1980 1990 2000 2010 2020
Year
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 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ How will this affect marine organisms?

§ How does more CO2 affect photosynthetic
organisms?
§ How does increased acidity affect organisms with
hard shells?

© 2016 Pearson Education, Ltd.

 Section 3.10 The Transition Zone between Freshwater and
Saltwater Environments Presents Unique Constraints

§ Increased CO2 levels in surface waters may be

beneficial for photosynthetic organisms
§ More CO2 could allow higher rates of photosynthesis

© 2016 Pearson Education, Ltd.

 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ CaCO3 is formed through the reaction of calcium

(Ca2+) and carbonate ions (CO32-)
§ As the pH of the oceans falls, CO32- react with the
increasing number of H+
§ This reduces carbonate and increases bicarbonate
in the water

© 2016 Pearson Education, Ltd.

 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ Many marine organisms have shells made of

calcium carbonate – CaCO3
§ molluscs
§ echinoderms
§ corals
§ algaes
§ How does this decline in dissolved CaCO3 in the
oceans affect them?
§ How are these organisms’ shells made?

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 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ To make shells, these organisms precipitate

dissolved CaCO3 into solid CaCO3 structures
§ These structures are stable as long as the
surrounding seawater contains CaCO3 at saturation
concentrations.
§ If the carbonate ions decline, water is depleted of
two CaCO3 minerals important to calcification,
aragonite and calcite.
§ Changes in the pH of ocean water threaten these
shelled organisms.

© 2016 Pearson Education, Ltd.

 Ecological Issues & Applications: Rising Atmospheric
Concentrations of CO2 are Impacting Ocean Acidity

§ Review of studies investigating response of these

marine calcifying species to elevated CO2 levels:
§ degree of sensitivity varies
§ most showed negative effect on calcification rates
§ all studies with corals show adverse effect
§ What does this predict for the future of marine
ecosystems?

© 2016 Pearson Education, Ltd.

Figure 3.21

© 2016 Pearson Education, Ltd.