Water Licencing

Prior to the 1980's most of Australia had unregulated water usage from the rivers and bore supplies.  What this meant was that anyone who wanted draw water from a river or bore applied for a licence and got it.  At its peak the entire flow of the Murray River could be drained by NSW users if they acted on thier permits.  With the drought that occurred in the late 1970's early 1980's, and the deteriorating condition of the Murray Darling system at this time, it was decided to begin water regulation, particularly for the these rivers and the catchment areas.

So all existing licence users had to reapply for water rights.  If they applied they got them.  However if you did not then your licence lapsed.  This has reduced the amount of water that was drawn from water supplies.

Licences are now traded on the market so if you want to increase the amount of water usage, you needed to buy one off someone who was selling.  These were not transferable to different waterways.  The amount of water that could be captured was limited to 10% of the water falling on a stakeholders land. Beyond that a water licence was again needed.

To this day there is considerable tension between irrigators and conservationists about what the right balance of water is for maintaining the environment while not decreasing food production.

The reason that Australia has a problem with water largely revolves around its scarcity. Because of this whole ecosystems have evolved to rely on seasonal variations of water like in the Snowy River, or cycles of drought and flood like the Murray Darling.  Alterations to this can affect ecosystems and river health. In the worst case scenario the river may be classed as dead and the quality of the water decline to the point where it is unusable by all. 

Pesticides Alternatives

One of the problems of repeated applications of pesticide is the emergence of resistant populations and the removal of beneficial species, often the predators of the pests.  Generally predators take longer to have their numbers recover after the application of pesticide compared to the pests.  This window of time allows the pest to increase its numbers unchecked.  As a result the farmer is required to apply more pesticide, making it harder for predators to recover.  This cycle is perpetuated and is called the pesticide treadmill.

By trying alternative methods, there are many benefits:

1. Only the pest species are targeted.
2. No chemical residues
3. Often more cost effective (particularly in the long term)
4. May lead to the eradication of the pest all together.


Some examples of this are:

1. Pheromone traps, these are effective when females use a chemical scent to signal to males they are ready to mate. By using the hormone, males can be lured to traps.

2.  Introduction of diseases - disease tends to be pest specific.  However it may require regular reapplication and disease resistance may emerge.

3. Introduction of predators - Again this can be considered if the predator does not target non pest species.  A case where this went horribly wrong was the cane toad.

4.  Sterile male release.  By releasing sterile males, the females lay eggs that wont hatch.  However, sterile males need to be released repeatedly.    

DDT - a quick finishing comment

As you would now be aware, DDT appears to have many long term environmental effects particularly the problems of biomagnification and bioaccumulation.  When levels get to a certain point, it then begins to have noticeable effects on animals, such as eggshell thickness in birds etc.  I should also point out that if enough DDT or other toxic substance accumulates in your body, it will eventually kill you.  Combined effects of biomagnification and bioaccumulation meant that the effects of DDT were first noticeable in fish eating birds.  The reason for this because the food chain can have 4-5 links which enhances the biomagnification effect for the top predator.

In addition, the effects of DDT and similar pesticides may affect nervous system development in young children. Evidence for this was shown comparing 2 groups of children with varying degrees of exposure.  The high exposure kids had reduced coordination, memory and fine motor skills.

Potentially more alarming is the estrogenic (feminising) effect that DDT and its breakdown products have.  It could well be affecting fertility of many male animals, including humans and, may be linked to other defects involved in the formation of male reproductive systems.

DDT is also non specific, that is it will kill target species, but also species that just have the misfortune to be around.  This includes potential pollinators.  As a result farmers have looked beyond pesticides when they can, and are trying differing strategies.  This is the basis of our next module.

Work to do for the next week

We have finished Salinity!

This is a topic that is asked either directly or indirectly without fail in the HSC exams in the extended response section.  The case study is often referred to as well.

Make sure that you have a good idea about causes of salinity, types of salinity, combating salinity AND the reasons the methods to treat salinity are used.


At the end of next week I would like the section 3 of your dot point summary notes completed.  This includes everything about salinity.  If you have not completed your class notes regarding the Wagga Wagga case study, you will need to do this in your own time.  I will be  more than happy to help at homework club or a nominated lunchtime.

Next thing we do is start looking at the effects on the environment of pesticides. 

DDT and other pesticides

Brief History

DDT was introduced into the environment on a large during the latter parts of WWII to eradicate malaria which is transmitted by mosquitoes.  It was so effective that it was offered to farmers to spray on crops and to local governments to control mosquitoes and other biting insects which cause human discomfort.

In the late 1950's and early 1960's a number of wildlife ecologists had noticed a decline in a number of fish eating birds in a number of ecosystems.  This was caused by thinning of eggshells when the bird laid eggs.  When they sat on them to incubate they broke and so the chicks failed to develop.

Another problem was that DDT was being detected in significant amounts in dairy products in Europe.  This is because the substance is soluble in fat and so would appear in high amounts.  Then it was detected in human breast milk.

DDT has a number of characteristics that lead to these observations:
1. Long stability and activity.  It can act in a sprayed area for a long time.
2. Fat soluble.  This means that it is stored in the fats and oils that are produced by plants and animals.
3.  It is not metabolised (broken down) by living things very easily.

Because of this, the amount of DDT can build up in tissues, if the rate of intake is more rapid than breakdown.  This is called BIOACCUMULATION.  For example if a human can break down 5 units of DDT/year but takes in 11, he/she will accumulate 6 units DDT every year.  After 10 year, 60 units will be stored.

On top of this there is also BIOMAGNIFICATION.  This is where the accumulation of DDT is magnified every level on the food chain.



Looking at the example here the DDT is in very low levels in the water.  However, it is picked up and stored in the tissues of zooplankton.  Then if the minnows eat 12 zooplankton, they get 0.48 ppm DDT, then if the needlefish eat 4 minnows they get their 2 ppm of DDT.  The bird only has to eat 13 needlefish to get the dosage as shown in the figure.  Biomagnification shows large jumps in the amount of DDT at each stage of a food chain, that is, the dose is magnified.  Even though low levels of environmental DDT wouldn't affect the bird if it was the only means of exposure, the fact that the concentrations get so high through the food chain means that it will have an effect on birds, and in this case its eggshells.

With the detection of DDT in human breast milk and foods that humans consume at levels considered high, countries began banning its use in that late 1960's onwards.  Other pesticides such as organophosphates suffered the same fate a bit later for the same reasons.

DDT is still used in limited amounts in countries with high malaria risks.