Communities caring for catchments
Module 1 - background
Waterwatch Australia Steering Committee
Environment Australia, June 2003
ISBN 0 6425 4856 0
Aquaculture in estuaries. Estuaries are often the site of aquaculture industries. Estuaries are also important nursery grounds for many species of fish. Water quality in estuaries is affected by human activities upstream and the amount of tidal flushing as well as effluent from aquaculture.
Construction activities can harm nearby waters in three ways. The first occurs when natural land cover is disturbed during excavation and grading operations. Soil stripped of its protective vegetation can be easily washed into nearby surface waters. Second, stormwater run-off often carries material used on the site, such as oil, grease, paints, glues, preservatives, acids, cleaning solutions and solvents, into nearby lakes or streams. Third, badly designed and managed projects can accelerate run-off and cause erosion.
Croplands and pastures. Run-off from croplands and pastures may carry chemicals, sediments, nutrients, bacteria and organic material into nearby lakes and streams. Nitrates and pesticides can seep from agricultural lands and contaminate underlying groundwater supplies. Sediment is often the main pollutant entering waters in these areas. Cropland and pasture erosion is the most significant source of sediment. Good water quality and soil erosion management practices by individual land managers are the key to stopping valuable soil loss. This also protects water quality by preventing movement of sediment and other pollutants from croplands to waters.
Dams along a watercourse may change the water conditions, not merely during and immediately after their construction, but through their existence. Upstream, the raised water level behind the dam wall increases stream width and depth and this will affect erosion, sediment load and water temperature. Downstream the dam will suppress the natural fluctuations in the flow. The need to produce electricity at certain times will lead to large and/or repeated releases of stored water, or even cause the stream to dry up, if all the inflow is retained. These changes affect the stream characteristics, especially water temperature, when discharges are drawn from the relatively deep and cold water in the storage. As many large dams are in unpolluted remote areas, the changes in water flow may harm relatively sensitive ecosystems.
Draining wetlands. Wetlands are complex natural systems that provide an important habitat for many species and act to filter water and remove many pollutants. Draining of wetlands can result in release of acid drainage from acid-sulfate soils.
Fertilisers. Nitrogen, phosphorus and potassium are the three primary nutrients applied to crops, gardens and lawns as fertilisers. Phosphorus entering water bodies in run-off from over-fertilised areas can cause heavy algal blooms and excessive weed growth, making waters unsuitable for drinking, swimming, waterskiing and other uses. The presence of nitrates in rural well water presents a risk to infants who may develop methaemoglobinaemia (blue-baby syndrome). Studies have indicated that nitrogen in fertilisers and manures are probable sources of elevated nitrate concentrations in rural groundwater supplies.
Forest practices. Waters in forested areas are usually of high quality, so pollution, if it does occur, is likely to harm a valuable and relatively sensitive ecosystem. Forestry activities that can transfer pollutants or sediments from land to water are:
Golf courses are great places for recreation but to keep them in peak condition the grounds person may use lots of fertilisers and pesticides. The water hazards and the creeks that flow through golf courses can be affected by these activities. It is also possible that the groundwater in the area may be affected.
Livestock operations. Animal feedlots are pens and buildings used to confine animals for feeding, breeding, raising, or holding purposes. They include open ranges used for feeding and raising animals and/or poultry, but do not include pastures. Poor feedlot management can allow stormwater run-off to carry pollutants from accumulating manure into surface and groundwaters. Feedlots can create significant pollution problems. Pollutants include nutrients, organic materials and bacteria that may affect humans and animals. High nitrate levels in the groundwater have been associated with improper storage of animal manure.
Mining operations can cause dramatic changes in surrounding catchments. Lakes, streams and groundwater can be polluted by sediments, tailings, dust, chemicals and wastes from open pit, strip and underground mines.
On-site sewage disposal systems. Many homes are not connected to municipal wastewater treatment systems and rely on septic tanks and trenches for sewage treatment. If they are well designed, installed and maintained, septic systems will safely treat wastewater for 20 to 50 years. Improper design, installation or operation of septic systems or holding tanks can lead to pollution of ground or surface waters by bacteria, nutrients and household toxic chemicals.
Pesticides (biocides) are used to control undesirable plants or animals. They include herbicides, insecticides and fungicides. Pesticides are used on agricultural lands, on urban lawns and gardens, as well as in lakes to control some weeds, and in forest management.
Septic systems use natural decomposition to treat wastes. Holding tanks do not treat wastes, but simply contain them on-site. Septic systems and holding tanks must be periodically pumped out or cleaned. Care must be taken in the disposal of materials removed when cleaning. Solids cleaned out of septic systems can be land-spread since they are partially treated, but continuous spreading on a single site should be avoided. Wastes removed from holding tanks need additional treatment as they have usually undergone little decomposition.
Urbanisation and stormwater. The urbanisation of land concentrates people, and therefore the pollutants that result from their lifestyles, in areas that are largely covered with non-absorbing surfaces such as buildings, driveways, roads, footpaths and parking lots. This combination of people, pollutants and pavement produces 'urban run-off' that may carry a greater pollutant load than municipal sewage. The amount of pollutants carried in urban run-off is influenced by:
Pollutants transported in urban stormwater systems to nearby waters include: