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)UrbanisationLand clearing

Pressure from pollutionToxinsAcid/base

Pressure from stress (water usage)StagnationWater levels

Importance of aquatic ecosystems

BiodiversitySpecies richness/trophic structure

BreedingBreeding grounds for many species

Buffer systemsPhysical and chemical

SinksResting places for sediments and chemicals

Only part of the hydrological cycleWhat 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 FreshwaterLentic (standing) Systems

Lakes, ponds, dams etc

QHow are they formed?Glacial activityTectonic activityErosionMan Made

Classification of Lentic Waters

ClassificationsOligotrophic

Newer, colder, deeper waters that are low in life and relatively unproductive (low PP).

EutrophicOlder, warmer, shallower waters that are high in

life and highly productive (high PP)

MesotrophicSomewhere in-between (i.e. Lake Macquarie)

Freshwater Lentic Systems

Q. What physical properties can they exhibit?DepthSurface areaLightTemperatureInputs and outputsAltitudeLongitude and latitude

Lentic WaterDepth, surface area & volume

Surface AreaDepth

Volume

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 temperatureAltitude, 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           Depth• Red             5 m• Orange       15m• Yellow            30m• Green            60m• Blue            75m• Indigo            85m• Violet           100m    

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

Relating depth with light

IR Reds Greens Blues

Loss of intensityand separationof wavelengths

Lentic water and light

Compensation Depth

Limnetic zone

Profundal zone

RiparianEdge

RiparianEdgeLittoral 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)

Epilimnion

Metalimnion(Thermocline)

Hypolimnion

>20OC

>4 but <20OC

4OCDo you remember the properties of water?

Decreasing temperature

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 Effectsmore 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

output

How long does it take to change over theentire volume of a water body? The question‘residence time’ is very important in ecologyand environmental chemistry/engineering.

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 flowThey exhibit turbulenceThey have significant energyGenerally lower in volumeBut 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 ProfilesVelocity profile for a wide river

Velocity ProfilesVelocity 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 matterCPOM vs FPOMGravel, sand, silt

Determinant in ‘floral’ species distributionLarge plants with roots need fine matterAlgae / bacteria like low energy areas

Determinant in animal species distributionAnimals (zooplankton→fish) follow plants