Aquatic Ecology
Lecture 1:
General Principles of Aquatic Ecology
What is it?
Aquatic ecology is the study of water
based ecosystems
Complexity depends upon how ‘close’ we
look at any particular system
They are under extreme ‘pressure’
Very, very important…WHY???
Q. What pressure are they under?
Pressure from development (i.e. loss)
Urbanisation
Land clearing
Pressure from pollution
Toxins
Acid/base
Pressure from stress (water usage)
Stagnation
Water levels
Importance of aquatic ecosystems
 Biodiversity
Species richness/trophic structure
 Breeding
Breeding grounds for many species
 Buffer systems
Physical and chemical
 Sinks
Resting places for sediments and chemicals
 Only part of the hydrological cycle
What other parts are there?
The important questions of
Aquatic Ecosystems
Q. What are they really?
Q. How many types are there?
Classification
Q. What are the physical properties?
Q. What are the chemical properties?
Q. What are the biological properties?
What is an aquatic ecosystem?
They are an area of water, in which
‘significant’ biological activity can occur
This definition excludes most groundwater
systems
Aquatic ecosystems can involve flowing or
still water, and can be fresh or saline
How many types are there?
Several, depending on how close we look!
Freshwater (Limnology)
Lakes (lentic)
Rivers (lotic)
Brackish water (inter-tidal)
Marine water (Oceanography)
Still Freshwater
Lentic (standing) Systems
Lakes, ponds, dams etc
QHow are they formed?
Glacial activity
Tectonic activity
Erosion
Man Made
Classification of Lentic Waters
Classifications
Oligotrophic
Newer, colder, deeper waters that are low in life
and relatively unproductive (low PP).
Eutrophic
Older, warmer, shallower waters that are high in
life and highly productive (high PP)
Mesotrophic
Somewhere in-between (i.e. Lake Macquarie)
Freshwater Lentic Systems
Q. What physical properties can they exhibit?
Depth
Surface area
Light
Temperature
Inputs and outputs
Altitude
Longitude and latitude
Lentic Water
Depth, surface area & volume
Volume
Depth
Surface Area
Q. What is the issue with depth?
The depth of water determines the amount
of light (which affects what???)
The depth of the water also determines
some attributes of temperature
Altitude, latitude and longitude also affect this
Relating depth with light
There is a relationship with depth and light
intensity, as well as a depth/wavelength
relationship
Light intensity decreases with depth
Some wavelength’s of light travel deeper
Relating depth with light
Within the photic zone, the colours of the
light spectrum are able to penetrate
through water before being absorbed at
varying depths. The following data
illustrates how the light spectrum is
affected by depth:
Relating depth with light
(these values are not valid for all waters)
•
•
•
•
•
•
•
•
Colour
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Depth
5m
15m
30m
60m
75m
85m
100m
Relating depth with light
 Photic zone
 light is sufficient for photosynthesis to 100
(or 200 m)




Dysphotic zone
light is too weak for photosynthesis
< 5% sunlight
100 to 200 m
 Aphotic zone
 no light
Relating depth with light
IR
Reds
Greens
Blues
Loss of intensity
and separation
of wavelengths
Lentic water and light
Riparian
Edge
Littoral Zone
Riparian
Edge
Limnetic zone
Compensation Depth
Profundal zone
compensation depth:
the depth
at which the daily or seasonal amount of
light is sufficient for photosynthesis to
supply algal metabolic needs without
growth
Depth & Light
Depth & Light
This is obviously an important aspect of
aquatic ecology.
Without light, no photosynthesis occurs
and PP is very low.
In the profundal zone, different (anerobic)
chemistry applies
Depth & Light
Anaerobic zones have ‘no’ oxygen (DO2)
This results in ‘reduction’ chemistry, where
chemicals such as methane (CH4) instead
of oxidised chemicals such as CO2 being
formed.
Example found in swamp gas (CH4, H2S)
Temperature Gradients
(thermal stratification)
>20OC
Epilimnion
Metalimnion
(Thermocline)
Hypolimnion
>4 but <20OC
4OC
Decreasing temperature
Do you remember
the properties of
water?
Temperature Effects
 Can
control
distribution,
degree
of
activity,
and
reproduction of an organism
 Temperature controls the rate of chemical reactions
within organisms, thus their rate of growth and activity
 10OC rise in temperature, doubles the activity
 Polar organisms grow slower, reproduce less frequently, and
live longer than tropical organisms
 Tolerance to variation in temperature varies greatly between
species and within an organism’s lifespan
 Temperature can indirectly control organisms by limiting their
predators or restricting pathogens
Temperature Effects
 more activity with higher temperature
Salinity
 Can control the distribution of organisms and force
them to migrate in response to changes
 Availability of various dissolved chemicals (calcium
and silicon) can limit an organism’s ability to
construct shells
 Epipelagic organisms are more tolerant to changes,
since they are more accustomed to them
 Marine organisms’ body fluids have the same
proportion of salts than sea water, but lower salinity
Inputs and outputs
Input
How long does it take to change over the
entire volume of a water body? The question
‘residence time’ is very important in ecology
and environmental chemistry/engineering.
output
Significance?
 The residence time for water equates to the
residence time for chemicals such as nutrients
 If there is a long residence time, then there is a
good chance of algal blooms if nutrient overload
occurs
 This is very important for ecologists who will
determine the fate of organisms as a result of
eutrophication
Freshwater Lotic Systems
(Rivers & Streams)
Freshwater Lotic Systems
Q. How do rivers, streams and creeks differ
from lentic systems?
They exhibit significant rates of flow
They exhibit turbulence
They have significant energy
Generally lower in volume
But what are they really?
What is a river?
 A silly question?.......No!
 Rivers form because of gravity
 A river, stream or creek is simply a ‘catchments’
delivery/removal system
 Mother nature’s pipelines
 Paths of least resistance
A Rivers Flow
 There are two aspects of flow that can be
measured;
The Flow Rate (Velocity, V) (which is a measure of
the speed at which the water is moving i.e. 2 m/s
The volumetric flow rate (which is the volume of the
water in 2 m/s)
Q. How could these be relevant pieces of information?
Turbulence
Turbulence is the degree of agitation in the
water
This can dramatically affect all aspects of
water including biotic structure and DO2
levels
Proportional to flow rate and surface
features of the river
Velocity Profiles
Velocity profile for a wide river
Velocity Profiles
Velocity profile for a narrow creek
Effects of the velocity profile
Q. What effects does velocity have?
Distribution of organisms within the river
Distribution of sediments
More importantly, how does this affect our
sampling of these waters?
Flow Rate & Energy
Flow Rate & Energy
Results in distribution of matter
CPOM vs FPOM
Gravel, sand, silt
Determinant in ‘floral’ species distribution
Large plants with roots need fine matter
Algae / bacteria like low energy areas
Determinant in animal species distribution
Animals (zooplankton→fish) follow plants