CONTAMINATION AND DISPOSAL OF WATER
Mosquitoes and other undesirable insects can breed in still water or moist places around a farm. In areas where serious mosquito-borne diseases (eg. Malaria, Ross River virus) are common it is extremely important to keep these insects in check. Fish or other insect-eating animals in the water will help reduce their numbers. If the water is chemically treated or sprayed periodically this can also keep insects at bay, but it will contaminate your drinking water.
WILLOWS AND WATERWAYS
Willows (Salix species) are commonly found growing along waterways in many parts of the world, including temperate Australia. While these plants are excellent for preventing erosion of the banks of dams and rivers, they can cause significant and undesirable changes to the ecology of the watercourse. Willows, unlike most other vegetation, can spread their roots into the bed of a watercourse, slowing the flow of water and reducing aeration. Willow leaves decompose much faster than many other types of leaves, creating a mass of organic matter in autumn when they drop and an under-supply the remainder of the year.
Research at the University of Tasmania has shown willows have a negative effect on populations of invertebrate animals.
Algae are small forms of plant life that thrive in moist, light and fertile conditions. Still, sunlit water, such as that found in dams, lakes, troughs and open storage tanks, stimulates the growth of algae. Runoff from fertilisers, especially those containing nitrogen and phosphorus, further encourages growth, to the point where the water becomes unpalatable and potentially poisonous to livestock, humans, fish and other aquatic organisms.
Several species of blue-green algae are toxic. A bloom of blue-green algae will discolour the water, turning it an acidic green colour. It may have an unpleasant odour. The bloom can develop very quickly – in less than a week – making the water unsuitable for irrigation and for watering livestock. As the bloom decomposes, it reduces oxygen in the water, and fish may die. Even after several months, the sun-dried surface scum can remain toxic to animals.
The best way to control algal blooms is to prevent them happening. Minimise nutrient runoff into dams by avoiding excessive fertiliser use on the farm; fencing out stock from dams – instead using gravity-fed troughs for drinking water; establishing buffer strips of vegetation (grasses, trees and shrubs) to help stop nutrients and eroded soil entering the dam; avoiding the domestic use of washing powders and detergents containing phosphates. Another method is building natural wetlands at the inlet of the dam, as a separate shallow lagoon. This will help reducing nutrient levels at the inflow.
Artificial aeration helps to control blooms by mixing water layers and increasing oxygen levels. The simplest method is to cascade the water into a holding tank or dam. Artificial aeration is expensive in the long term.
As a last resort, algal blooms can be treated in dams (but not streams or natural waterways) with algaecides but they must be used with caution – the algaecide must not impact groundwater or catchment areas. Consult a farm advisory officer for advice.
Canadian research has shown that farm productivity can increase if grazing animals are fenced away from watercourses running through a property. Stock should not have direct access to creeks or rivers. The research showed that the quality of livestock drinking water has a direct bearing on livestock health and profitability. Hence - don't allow water to be fouled, and the farm will be more productive! Significant reductions have also been noted in stream bank erosion as a result of decreased trampling by stock.
Reference: Dr Walter Williams et al. Land and Water Resources Research and Development Corporation. Acres Australia Vol 3 No. 6.
Excess rainwater runoff can be a cause of severe difficulty to the farmer, resulting in erosion and loss of valuable topsoil. Floods can also cause major losses through stock death, reduction in health of surviving stock, damage to fencing and structures (eg. sheds, bridges), temporary reduction in area for stock to graze, and boggy conditions for movement of stock and machinery.
There are some simple means by which flood damage can be minimised. These include:
- Ensuring that any structures such as sheds and shelters, and stored food (ie. hay and silage) are located as high as possible above natural flood plains.
- Soil that has vegetative cover will always stand up to flood better than bare ground. Overgrazing or cultivating soil at times of the year when floods are likely increases the potential for soil loss if flooding occurs.
- If possible, arrange fencing of low-lying land to include a few areas where stock can retreat as water rises.
- Have a procedure for evacuating stock in case of flood, including:
- Having suitable transport available (boats may be necessary in regularly flooded areas).
- Having a suitable place to take stock that has temporary provision for food, shelter and water.
- Regular monitoring of flood levels - don't leave it too late to act.
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