Water quality monitoring parameters

There are a range of water quality monitoring parameters that can provide information about the health of our waterways. Understanding these parameters and how they affect aquatic ecosystems is important if monitoring is to lead to actions to protect aquatic ecosystems.

Temperature

Monitoring water temperature

The main effect of water temperature on the environment is the amount of oxygen in the water. The amount of oxygen water can hold decreases as the temperature of the water increases. If water gets too hot there is less available oxygen for living things.

Temperature also affects the metabolic rate of aquatic animals, rates of development, breeding cycles, mobility, migration patterns and the sensitivity of organisms to toxins, parasites, and disease.

Life cycles of many organisms are related to temperature. Organisms can tolerate slow changes in temperature, but thermal stress can occur where the temperature changes more than 1 or 2°C in 24 hours.

Temperature is directly affected by depth of water, flow rate, season, and time of day. Other influences include air temperature, altitude, amount of sunlight and shade, turbidity, stormwater, and urban runoff and cold-water releases from dams.

Cool to moderate water temperatures increase oxygen levels, which promotes healthy ecosystems. Protecting riparian (wetland) vegetation will help our waterways to stay cool and healthy.

pH levels

Monitoring pH

pH is the measure of acidity or alkalinity of water. The pH scale ranges from of 1 (strongly acidic) through 7 (neutral) to 14 (strongly basic or alkaline).

Generally, the pH of fresh surface waters is between 6.5 and 8.0, and the pH of most marine waters is close to 8.2. A pH range of 6.5 to 8.2 is best for most fish and other aquatic organisms. Changes outside of this normal range can cause a reduction in species diversity.

pH can be affected by several factors. For example, water flowing through a basalt and sandstone country can cause the water to be slightly acidic. This can be a natural occurrence. On the other hand, the application of lime to agriculture land may raise the pH if washed into the waterways, while fertilisers may lower it.

Water with a pH less than 5.5 may cause the release of heavy metals trapped in sediments. Fish and other aquatic species may suffer skin irritations, tumours, ulcers, and impaired gill functioning. People may also incur skin and eye irritations because of affected water.

Dissolved oxygen

Dissolved oxygen (DO) is the volume of oxygen that is contained in water. It is vital for the survival of fish, aquatic invertebrates, and amphibians. Oxygen enters the water through photosynthesis of aquatic plants and algae as well as wave action from waterfalls and riffles. Oxygen can be lost when water temperature rises and salinity increases.

DO is recorded in units of milligrams of oxygen gas (O2) dissolved in each litre of water (i.e. mg/L) or as a percentage of the maximum amount of DO that is possible in a water body at a specified temperature and salinity (i.e. % saturation).

Salinity

Salinity is the measure of the dissolved salt content of a body of water. It can naturally be found in the landscape, soil, rocks, dissolved water, or groundwater. Salt naturally occurs in our landscape. Land use activities can mobilise natural salts causing concentration in certain areas. Salinity is measured by electrical conductivity.

Electrical conductivity

Electrical conductivity (EC) or 'conductivity' is a measure of the ability of water to conduct an electrical current. The ability to conduct an electric current is due to the presence of dissolved salts. EC is used to calculate salinity and the concentration of dissolved salts in a water body.

The formal unit for conductivity is siemens per metre (S/m). Microsiemens per centimetre (μS/cm) is more commonly used when measuring fresh or brackish waters. Millisiemens per centimetre (mS/cm) is used when measuring estuarine and marine waters.

Turbidity

Monitoring turbidity

Turbidity is the cloudiness or muddiness of water. Particles that hinder the transmission of light through the water include clay, silt, sand, algae, or plankton. Turbidity can potentially affect the rate of photosynthesis, and therefore the growth of plants or algae in the water body.

Turbidity can be measured directly using probes. Nephelometric Turbidity Units (NTU) is the unit of measurement for turbidity.

Increased turbidity can affect light penetration. This can reduce plant growth, oxygen production and long-term biodiversity. Land-based activities such as agriculture, removal of vegetation, stormwater and urban runoff and building sites without sediment and erosion control, can increase turbidity levels.

Water level/discharge

Water quality has a direct relationship with water quantity, hence the importance of monitoring discharge. Discharge monitoring allows for the assessment of water quality conditions and trends as well as determining the load, or amount, of a contaminant that is moving past a given point. Discharge also determines habitat availability and suitability so is important for fish and other flora and fauna.

We monitor water level and convert the level data to discharge via an equation. This conversion of stream height to flow/discharge requires the collection of gauging data at all stages and preferably over time. This method is common in monitoring discharge in freshwater systems.