What do water quality parameters mean?

Water temperature is a physical property that expresses how hot or cold water is. Water temperature influences the majority of physical, biological, chemical, and ecosystem processes in aquatic environments. Changes to water temperature affects dissolved oxygen levels, algal blooms, solubility of metals and other toxins in water.

Temperature is measured in degrees Celsius.

Dissolved oxygen (DO) is the amount of oxygen present in water. DO is critical to fish and other aquatic organisms living in a water body. The concentration of DO reflects the balance between oxygen-consuming processes (e.g. respiration by fish and bacteria) and oxygen-releasing processes (e.g. photosynthesis by algae and plants and the physical transfer of oxygen from the air). It is generally measured in the field along with water temperature which has a strong influence on solubility of DO in water and therefore its concentration.

DO is an indicator of water quality for rivers and streams under Victoria’s Environment Reference Standards.

DO is measured in mg/L.

Electrical conductivity (EC) or salinity, measures the total concentration of inorganic ions in the water. It determines the ability of water to conduct an electric current. Freshwaters are generally considered to have an EC of less than 1000 µS/cm. Measures of salinity and EC indicate whether the chemical nature of aquatic ecosystems is being altered and provides a warning of the potential loss of native biota.

EC is an indicator of water quality for rivers and streams under Victoria’s Environment Reference Standards.

EC is measured in microsiemens per centimetre (μS/cm).

Turbidity is a measure of how clear water is and is related to the amount of material suspended in water.

Turbidity is an indicator of water quality for rivers and streams under Victoria’s Environment Reference Standards.

Turbidity is measured in NTU.

pH is a value that represents the acidity or alkalinity of an aqueous solution. It is defined as the negative logarithm of the hydrogen ion concentration of the solution. The pH of a waterbody can be impacted by its underlying geology, organic matter and biological activity, nutrient levels, and temperature. Most natural freshwaters have a pH range of 6.8-8.

Naturally occurring low pH is sometimes caused by the breakdown of plant matter. These low pH waters are known as humic waters and can have pH as low as 4.5. There are numerous humic waterbodies across Victoria including the Gippsland Lakes and Lake Colac. Naturally occurring high pH waterbodies occur where the natural geology contains alkaline properties. Alkaline waterbodies are often high in salts. There are numerous alkaline waterbodies across Victoria including Lake Buloke and Lake Corangamite.

pH is measured in pH units.

True colur is the colour in a water sample after it has been filtered to remove suspended materials. Colour can affect species composition and the mechanisms that can be used to treat water for drinking. True colour is measured by filtering the water sample to remove all suspended material, and measuring the colour of the filtered water, which represents colour due to dissolved components only.

Colour is measured in PCU.

Total suspended solids (TSS) a measure of material in suspension in the water column. Related to turbidity which measures water clarity as affected by material in suspension.

TSS is measured in mg/L.

Total dissolved solids (TDS) is a measure of the inorganic salts (and organic compounds) dissolved in water.

TDS is measured in mg/L.

Total nitrogen is the combination of total Kejdahl nitrogen plus nitrate and nitrite. Total nitrogen (TN) is often the nutrient liming plant growth in marine and sometimes estuarine environments.

Total nitrogen is an indicator of water quality for rivers and streams under Victoria’s Environment Reference Standards.

TN is measured in mg/L.

Total Kjeldahl nitrogen (TKN) is total organic nitrogen plus ammonium. It is important for biological wastewater treatment and is a limiting factor for the nutrient removal process.

TKN is measured in mg/L.

Nitrogen as ammonia (NH3) is an inorganic form of nitrogen available for plant growth but is toxic to aquatic biota at high concentrations with toxicity increasing with decreasing DO concentration.

Ammonia is measured in mg/L.

Oxidised nitrogen (NOx) is the combination of known nitrates and nitrites.

Nitrates and nitrites are readily available for plant growth in water. Elevated levels of nitrate has the potential to stimulate algal growth and hence to be a factor in nuisance algal blooms and eutrophication of waterways - usually from human wastes or fertilisers. At high enough levels, nitrate can be toxic to aquatic life.

Oxidised nitrogen, nitrates, and nitrites are measured in mg/L.

Phosphorus is a nutrient essential to life and is often the nutrient that limits plant growth in freshwater systems. Phosphorus exists in water as both dissolved and particulate forms. Total Phosphorus (TP) TP is the measure of all forms of phosphorus present. This includes dissolved organic phosphorus, dissolved inorganic phosphorus (such as orthophosphate) and particulate phosphorus.

TP is an indicator of water quality for rivers and streams under Victoria’s Environment Reference Standards and is useful for understanding the potential for eutrophication.

TP is measured in mg/L.

Filterable reactive phosphorus (FRP) is the measure of only the dissolved bioavailable orthophosphate in water. FRP indicates the immediate potential for utilisation by organisms.

FRP is measured in mg/L.

Total reactive phosphorus (TRP) is the amount of phosphorus that is readily available and reactive in the water. This usually refers to the inorganic orthophosphate form of phosphorus. Orthophosphate can be directly utilised by aquatic plants and algae, hence it provides understanding of the potential for algal blooms

TRP is measured in mg/L.

Biological oxygen demand (BOD) is the oxygen (in mg) consumed by aerobic organisms per litre of water sample over 5 days of incubation. It indicates the degree to which there is organic matter in the water whose decomposition will use up oxygen levels and can indicate risk for low DO levels that may stress biological organisms.

BOD is measured in mg/L.

Dissolved organic carbon (DOC) is the measure of the amount of organic matter dissolved in water. High levels of DOC can interfere with the effectiveness of some treatment processes for drinking water.

DOC is measured in mg/L.

Total organic carbon (TOC) is a measure of the amount of organic compound in water. Organic matter can enter water naturally. TOC depletes oxygen levels in water. TOC can affect drinking water quality, via reaction with chlorine creating disinfection by-products. TOC is measured in mg/L.

Chlorophyll a is the level of chlorophyll a, a green pigment found in plants (and including algae). Analyses for pigments such as chlorophyll and especially chlorophyll ‘a’ are widely used to assess the abundance of algae present in suspension in natural waters.

Chlorophyll a is measured in μg/L.

Phaeophytin is one of the breakdown products of chlorophyll. It remains pigmented but is not active in photosynthesis. The ratio of chlorophyll ‘a’ to phaeophytin ‘a’ serves as a good indicator of the physiological condition of phytoplankton of the sample. In typical water bodies, phaeophytin will contribute between 16% and 60% of the overall absorption.

Phaeophytin is measured in μg/L.

E.coli is bacteria traditionally used as an indicator to assess the level of faecal contamination of waters from both humans and animals. E.coli is measured in org/100mL/

Total alkalinity is a measure of the buffer capacity of waters, which is its ability to resist changes in pH or neutralize acids. In poorly buffered waters (eg billabongs) water can greatly vary in pH every day because of diurnal biological processes. Total alkalinity is a combination of all carbonates, bicarbonate, and hydroxide ions. Total alkalinity is measured in mg/L.

Bicarbonate alkalinity (HCO3) is a measure of the ability of most rivers to buffer (resist) changes in water due to the presence of bicarbonate ions (HCO3-). Bicarbonate ions are contributed to the system mainly from dissolution of rocks and soils within the catchment.

Bicarbonate alkalinity is measured in mg/L.

Carbonate alkalinity (CaCO3) is a measure of carbonate ions which contribute to the alkalinity of the water (along with bicarbonate ions and hydroxide ions).

Carbonate alkalinity is measured in mg/L.

Alkalinity as hardness (CaCO3) is the sum of multivalent metal ions in solution and is expressed as a concentration of CaCO3. High levels of CaCO3 in waters, primarily groundwater, can impact on pipes used for distribution, and use for industrial and domestic purposes.

Alkalinity as Hardness is measured in mg/L.

Alkalinity as hydroxide (OH-) is a measure of the quantitative capacity of aqueous media to react with hydroxyl ions. The equivalent sum of the bases that are titratable with strong acid. Alkalinity is a capacity factor that represents the acid-neutralising capacity of an aqueous system.

Alkalinity as hydroxide is measured in mg/L.

Calcium (Ca) is an important determinant of water hardness. It also functions as a pH stabilizer because of its buffering qualities. Calcium is linked to improved taste of water. Calcium is measured in mg/L.

Chloride (Cl) is a naturally occurring ion that is present in both fresh and salt water. Chloride is most commonly derived from dissolved salts such as sodium chloride or magnesium chloride. Chloride is essential in small amounts for normal cellular function in plants and animals. Chloride can be an indicator of seawater intrusion in groundwater. Chloride is measured in mg/L.

Fluoride (F) is added to drinking water in most Victorian sites to enhance teeth health, and is naturally occurring at sufficient levels in few places. It can have toxic impacts on fish at sufficient levels. Fluoride is measured in mg/L.

Ionic balance is an important water quality parameter that refers to balance between positively charged ions (cations) and negatively charged ions (anions) in water (electroneutrality). Imbalances can affect aquatic ecosystems, industrial process and human health. Ionic balance is expressed as ratio or percentage. Ionic balance is measured in %.

Magnesium (Mg+) is a cation contributing to water hardness. Magnesium is an important mineral for human, animal and plant health though excessive amounts can impact both. Magnesium is measured in mg/L.

Potassium (K+) is an essential nutrient for plant growth and human health. Monitoring and managing potassium levels in water is important to ensure optimal conditions for plant growth, protect aquatic ecosystems, and maintain the quality of water for various purposes. Potassium is measured in mg/L.

Silica (SiO4) is a measure of the silicate ion coming from silica (SiO2) as it dissolves in water. Monitoring and managing silica levels in water are important to prevent scaling and corrosion issues, ensure the efficiency of industrial processes, and protect aquatic ecosystems. Silica is measured in mg/L.

Total anions are the sum of all negatively charged ions. Total anions are measured in mg/L.

Sodium (Na+) levels in water can vary depending on the geological characteristics of the region, and the proximity to seawater. Monitoring and managing sodium levels in water are important for maintaining water quality, preventing soil salinity issues, and minimizing potential adverse impacts on human health and the environment. Sodium is measured in mg/L.

Sulphate (SO4) is a naturally occurring ion that can impact ecosystem health and contribute to corrosion and scaling issues in water distribution systems, plumbing, and industrial equipment. Sulphate is measured in mg/L.

Total cations are the sum of all positively charged ions. Total cations are measured in mg/L.

Aluminium (Al) can be present in water naturally through leaching from soil and rock. Aluminium is measured in mg/L.

Arsenic (As) is released into the environment naturally by the weathering of arsenic-containing rocks and volcanic activity though human activities account for twice the levels caused naturally. Several forms of arsenic occur in natural waters, the two most common being arsenic (III) and arsenic (V). Some compounds formed with arsenic are very toxic. Arsenic is measured in mg/L.

Cadmium (Cd) is found in low background levels in many natural waters. Cadmium may be accumulated by a numerous aquatic organisms, with bioconcentration factors in the order of 100 to 100,000. Cadmium is measured in mg/L.

Chromium (Cr) when in natural waters, is present mainly in the trivalent chromium (III) and hexavalent, chromium (VI) forms. The form of chromium present appears to significantly affect toxicity to aquatic organisms and the behaviour of chromium in the aquatic environment. Chromium is measured in mg/L.

Copper (Cu) is found at low concentrations in most marine, estuarine and fresh waters. It is an essential trace element required by most aquatic organisms, but toxic concentrations are not much higher than those that allow optimum growth of algae growth. Copper is readily accumulated by plants and animals; bioconcentration factors ranging from 100 to 26,000 have been recorded for various species of phytoplankton, zooplankton, macrophytes, macroinvertebrates and fish. Copper is measured in mg/L.

Iron (Fe) is the fourth most abundant element in the Earth’s crust. It is an essential trace element for both plants and animals, required by most organisms for essential growth and development, and iron deficiency could cause adverse biological effects. However, acute toxicity to aquatic insects has been reported at iron concentrations ranging from 320 to 16,000 µg/L. Iron is measured in mg/L.

Lead (Pb) is generally present in very low concentrations in natural water though human outputs of lead to the environment outweigh all natural sources. Lead reaches the aquatic environment through precipitation, fall-out of lead dust, street runoff and industrial and municipal wastewater discharges. Lead is measured in mg/L.

Manganese (Mn) is an essential trace element for microorganisms, plants and animals and can be bioconcentrated up to four orders of magnitude, possibly to facilitate essential uses. It is present in natural waters primarily in suspended form (like iron) and its toxicity is low compared to other trace metals. It is a common constituent of discharges from mining and smelting activities. Manganese is measured in mg/L.

Mercury (Hg) is of particular concern to the aquatic environment as inorganic forms of mercury (of relatively low toxicity and availability to bioconcentrate) may be converted by bacteria in situ into organomercury complexes (particularly methylmercury), which are more toxic and tend to bioaccumulate. Bioconcentration factors for methylmercury for fish are consequently very high, ranging from 106 to 108. Mercury is measured in mg/L.

Molybdenum (Mo) is found naturally in water in low concentrations. Higher concentrations can be found in water from mining, agriculture, or fly-ash deposits from coal-fuelled power stations. Application of fertilisers may also increase the concentration of molybdenum in ground and surface water. Molybdenum is measured in mg/L.

Nickel (Ni) is found at low background concentrations in most natural waters and is an essential trace element for aquatic organisms but may be toxic at higher concentrations. Nickel is measured in mg/L.

Selenium (Se) is generally found in very low concentrations in natural water. Selenium is measured in mg/L.

Zinc (Zn) can enter the environment from both natural processes (e.g. weathering and erosion) and anthropogenic (e.g. zinc production, waste incineration, urban runoff) processes. Zinc is an essential trace element required by most organisms for their growth and development. It is found in most natural waters at low concentrations. Zinc toxicity is hardness dependent. Zinc is measured in mg/L.