What Are the Main Water Quality Indicators and Parameters?
- Dissolved Oxygen (DO)
Oxygen in waters is essential for humans, plants, and animals. However, if there is an abnormally high level of oxygen in the water, this can create major problems for sustaining life. That is why measuring the quantity of dissolved oxygen – the amount of oxygen available to aquatic life – is important. The quantity of dissolved oxygen is a key indicator of water quality in streams and lakes. Factors affecting levels of dissolved oxygen include sources such as number of bacteria as well as the water temperature.
Taking fish as an example, analysis has shown all species and sizes of fish can live if the amount of dissolved oxygen in the water is in the range of 9.5 mg/L to 12 mg/L. Below that level, fewer fish survive; and if it is below 4.0 mg/L, no types of fish can do so.
- Turbidity and Total Suspended Solids (TSS)
Turbidity is a measure of how clean water is and its clarity.
The measurement of turbidity levels depends upon the concentration of Total Suspended Solids (TSS). TSS are particles larger than 2 microns found in the water, such as gravel, sand, silt, clay, and algae. When organic matter decays – for example from animals, plants, and algae – this becomes a suspended solid. Suspended sediments can also contain high amounts of pollutants including phosphorus, pesticides, or heavy metals. Lighter solids will settle at the bottom of a body of water; if there are a lot of solids present, the surface water becomes cloudy or less clear.
- Bioindicators
Bioindicators are organisms used to monitor the health of an ecosystem, for example the quantity of micro algae present in water. They are organic and natural indicators of environmental pollution – living organisms such as plants, planktons, animals and microbes – providing valuable information for assessing the quality of water as well an important indicator of water pollution.
Several factors influence bioindicators in the environment, including the amount of light, water, temperature, and suspended solids in water. Changes in the composition of bioindicators, positively or negatively, is an effective way to measure the environmental impact of human activities on the health our natural ecosystems.
- Nitrates
Nitrogen provides the essential nutrients for all living organisms.
However, large nitrate concentrations – often due to the flow of human and animal waste, industrial pollutants and agricultural activity – can increase algae growth and reduce the amount of dissolved oxygen in the water, killing fish and other aquatic life. High nitrate levels are similarly harmful to humans. Monitoring the nitrate level is consequently crucial for health promotion strategies and safeguarding marine life.
Optimum nitrate levels vary according to the species. A maximum level of 2 mg NO3-N/l protects most freshwater species with a maximum level of 20 mg NO3-N/l for other animals.
- pH scale
pH illustrates how acidic or basic a body of water is according to a logarithmic scale, a measurement of alkalinity. The value for pH is expressed on a scale ranging from 0 to 14. Low numbers indicate the degree of acidity in the water; higher numbers how basic water is. A score of 7 is neutral.
What causes the pH level in the water to change? Factors include acid rain, automobile pollution, agricultural runoff, spills due to accidents, overflows from sewers and other pollutants. Major changes to pH scales can have damaging impacts on water, fish, and aquatic life, so it is another key water quality indicator.
- Water Temperature
Water temperature is an indicator too of water quality – and various forms of aquatic organisms depend upon specific temperatures and water conditions for their optimal health. The water temperature will also affect other parameters of water quality, such as the dissolved oxygen and vulnerability of organisms to parasites, pollution, and disease.
The time of year is another factor, with temperatures varying according to the seasons.
