Dragonflies As A Bioindicator Of Water Bodies Conditions

Pollution is the introduction of specific contaminants into the natural environment (land, water, air), which alters the makeup of that aspect, making it unstable and unhealthy to support forms of life over a long period of time. There are numerous types of pollution such as chemical, noise, light, land, air and water pollution (Bradford, A. 2018). Pollutants in water include fertilizers, oil spillages, suspended matter, oxygen depletion and an excess of nutrients (i.e. from sewage) in the water, and these may be detrimental to the health of plants, animals and in turn humans too. Infected water can lead to respiratory problems, neurological problems, cholera and numerous other diseases. There are many informal settlements along the Jukskei River (i.e. in Alexandra, Johannesburg) where people use its water for drinking and other consumption and can therefore fall ill. Furthermore, humans eat the fish and plants that also consume the polluted water and can become infected. Polluted water can be consumed by plants and then absorbed by animals which eat the plants. This can interfere with food chains and destroy the ecosystem. It is therefore important to detect the levels of pollution in such rivers and find suitable methods to rectify the polluted water.

Bioindicators are living organisms that give us an indication about the health of an ecosystem due to their sensitivity to pollution, such as dragonflies and mayflies. Dragonflies require a clean and unpolluted environment in order to survive; therefore, they can be used as an indicator for a healthy environment and biodiversity. They also require healthy indigenous vegetation to provide sufficient oxygen to them, which will help their transformation process from nymphs to adults. Dragonflies spend most of their life cycle underwater; in rivers, ponds, streams and lakes and can therefore be used as an indicator of aquatic species present in the waterbody. They are commonly found in the tropical areas of the world. If dragonflies are absent from certain waterbodies, it could be an indication of excessive nutrients, contaminants and pesticides in the water from surrounding agricultural plantations, industries, urban landscapes and informal settlements.

There are other means in which one can determine the level of pollution and water quality. These include the monitoring of temperature and pH, amount of nitrates, nitrites and phosphates and the water flow, as well as conductivity and suspended sediment in the water. (Regional Aquatics Monitoring Program) An experiment will be conducted whereby the pH, temperature and presence of dragonflies of the Jukskei River will be tested and analyzed, in order to determine the water quality. The temperature of a waterbody is vital in determining the quality of the aquatic system because it affects many factors such as chemical and biological processes, dissolved oxygen and species composition of the aquatic system. (Regional Aquatics Monitoring Program) As temperature of the water increases, the solubility of the oxygen in the water decreases because cold water can hold more oxygen than warm water. This directly affects the organisms in the water because some aquatic species require large concentrations of oxygen to survive and other species require low concentrations of oxygen to survive. Temperature affects rates of reactions within the aquatic systems, such as metabolic rates. As temperature increases, the rates of reactions also increase. Many species rely on the temperature of the water for growth, migration and reproduction. The Tiger Fish, found in parts of the Jukskei River, begin to feed when the temperature warms up to about 20°C and start their migration and spawning in October when the weather begins to warm up. Therefore, any extreme alterations in water temperature can negatively affect the species and disrupt their routine in the waterbody. Certain aquatic species can only survive within a specific temperature range; high temperatures may cause their enzymes to denature and low temperatures may cause their enzymes to not work effectively which can be detrimental to their body functioning and survival.