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Water quality

Water quality determines the 'usability' of water for particular purposes, such as providing essential ecosystem services. Water quality tests give information about the health of a waterway. By testing water over a period of time, the changes in the quality of the water can be identified. Water quality parameters including temperature, pH, salinity, turbidity, available phosphate and dissolved oxygen can be tested with a Waterwatch kit.

Acidity or alkalinity of water

pH is a measure of the acidity or alkalinity of water, represented on a scale of 1-14, where 7 is pH neutral. It is measured by visually assessing the colour change (chemical reaction with universal indicator) of a pH strip, after it has been left in the water for five minutes. There are a number of reasons that water may have extreme pH values:

Acidic values (1-6)

Geology and soil composition of a catchment affect pH. Acid soils (different from acid sulfate soils) and rocks such as basalt, granite and sandstone contribute to lower pH in water.

Acid sulfate soils are a major problem in estuarine areas. These soils form in anaerobic environments that are rich in sulphur, such as at the bottom of estuaries.

Runoff from bushland areas is slightly acidic. This is due to tannic acids (tannins) which are found naturally in leaves. Tannins are also responsible for giving water a tea-like colour.

Alkaline values (8-14)

Basic rocks such as limestone contribute to higher pH values. Runoff such as fertilisers and detergents cause increased alkalinity.

Extreme values of pH can cause problems for aquatic fauna. For example, fi h may develop skin irritations, ulcers and impaired gill functioning as a result of water that is too acidic.

Temperature

Temperature of a waterway is significant as it affects the amount of dissolved oxygen in the water. The amount of oxygen that will dissolve in water increases as temperature decreases. Temperature also affects the rate of photosyntheses of plants, the metabolic rate of aquatic animlas, rates of development, timing and success of reproduction, mobility and migration patterns. Life cycles of aquatic organisms are often related to changes in temperature. Seasonality, shading and water storages play a large role for temperature.

Salinity

Salinity is a measure of the dissolved salts in the water. Salinity (in freshwater streams) is usually highest during periods of low fl ows. Salinity is measured as EC (Electrical Conductivity), which is the property of a substance which enables it to serve as a meduim for electricity to travel. Salty water conducts electricity more readily than purer water. Sources of salinity include urban and rural runoff containing salt, fertilisers and organic matter. Land use issues related to high levels of salinity include clearing of vegetation and the resultant rise in the water table, excessive irrigation, groundwater seepage and runoff containing dissolved solids from industry, sewage, agriculture and stormwater.

Areas in the tidal limit of rivers which flow into the sea will experience fluctuations in salinity between high and low tide.

Water containing an EC level of over 800uS/cm is unsuitable for irrigation of many plants and tastes unpleasant to drink. Due to the sensitivity and tolerance of different plants to EC, plants can be used as indicators of soil salinity.

Turbidity

Turbidity is a measure of the ability of light to pass through water, that is, a measure of the water's murkiness. Measuring murkiness gives an estimate of suspended solids in the water. Turbidity is measured in Nephelometric Turbidity Units (NTU's).

Suspended solids usually enter the water as a result of soil erosion from disturbed/degraded land or can be traced to the inflow of effluent from sewage plants or industry. Suspended solids also occur naturally in the water from bank and channel erosion; however this process has been accelerated by human use of waterways. High turbidity affects submerged plants by preventing sunlight from reaching them for photosynthesis. High turbidity also has the capacity to significantly increase water temperature.

Available Phosphate

Phosphorus is a nutrient essential to the growth of plants and animals. Waterwatch measures Available Phosphate (APO4). APO4 is a measurement of the phosphate compounds that are soluble in water and therefore available to be absorbed by plants. The concentrations of phosphate in Australian soils and water are naturally low. High phosphate levels could lead to water bodies choked with weeds or algae, changes in aquatic flora and fauna composition and increased fluctuations of dissolved oxygen levels. The main sources of phosphorus in local catchments are:

  • sediments from eroded rocks and soil
  • effluent from waste water treatment plants and on site sewage disposal units
  • detergents and fertilisers that have been washed down drains or that have run off from properties due to poor land management practices and stormwater pollution
  • decaying organic matter
  • industrial waste

Dissolved Oxygen

Dissolved Oxygen is vital for the survival of fish, aquatic invertebrates and amphibians. Dissolved oxygen levels in waterways depend on the physical, chemical and biological activities occurring in the water body.

Oxygen enters the water by photosynthesis of aquatic plants, surface contact and wave action.

Oxygen is lost from water when temperature and salinity increases, and consumption and decay of organic matter occur. Prolonged low oxygen levels have very detrimental effects on waterways.