Water is considered one of the most indispensable resources and is the elixir of life for human beings other organisms of the environment and maintaining the balance of nature. Availability of safe drinking water is a worldwide problem especially in Pakistan where about 44 per cent of the population without access to clean water, while in rural areas 90 per cent of the population lacks such access. According to Pakistan Council of Research in Water Resources (PCRWR), about 200,000 children in Pakistan die every year of diarrheal diseases alone. Human activities (domestic, industrial, agricultural, artificial drainage and other different potential impacts) attributing negative effects on water quality and stream habitats (Saunders et al. 2002). As a resultant pollution produced generally change the water chemistry and decrease the dissolved oxygen. To estimate the level of various organic pollutants such as heavy metals, nitrates and phosphates is always expensive and difficult for the common people.
To assess the water impurities many fresh water organisms have been used in biological monitoring including bacteria, algae, vascular plants, macroinvertebrates and fish. Of these organisms macroinvertebrates includes molluscs, crustaceans, annelids and insects are frequently recommended for biomonitoring programs because of their diversity, ease of collection and ease of identification to levels for bioassessment. Biological assessments of human and environmental impacts on water quality and aquatic organisms have been used since the early 1900s by observing the presence and absence of sensitive organisms from a habitat (Paparisto et al. 2008).
For example 49 US states use macroinvertebrates in their water quality monitoring programs. Macroinvertebrates provide essential nutrients (proteins, lipids and energy) for secondary consumers (e.g. waterfowl, shorebirds, fish, amphibians and other vertebrate predators) and help in maintenance of water quality by facilitating organic decomposition and nutrient cycling (Batzer et al. 1999; Davis and Bidwell 2008). Because of their sensitivity to disturbance, aquatic macroinvertebrate communities are also excellent biological indicators for evaluating health of various wetland ecosystems. Additionally, the occurrence of these aquatic insects indicates the presence of more industrial effluents that has resulted in good growth of macrophytes in the river. From these techniques the use of macroinvertebrate which are an ideal indicators to assess water quality has become a standard addition to many countries; aquatic insects as bioindicators for water pollution is less expensive than the evaluation of physical and chemical parameters used in assessing quality (Arimoro and Ikomi 2009; Trigal et al. 2009; Lili et al. 2010).
Aquatic insects also play an important ecological role in nitrogen remobilization by eating small organisms and being consumed by other animals and fishes. Moreover aquatic insects are useful in assessing heavy metal pollution which is toxic even at very low concentration and to detect them at trace levels is very important. It is also important in terms of the environmental movement to be able to show how long metals stay in the water. The biological evaluation of water quality is linked to the number of pollution-tolerant organisms compared to the number of pollution intolerant ones. If the stream yields a higher proportion of pollution tolerant macroinvertebrates and no sensitive ones that could indicate poor water or habitat quality index. A more favorable water quality index would be characterized by finding sensitive organisms as well as tolerant organisms.
Every species has a certain range of physical and chemical conditions in which it can survive. Some organisms can survive in a wide range of conditions and can tolerate more pollution. Other organisms are very sensitive to changes in water conditions and cannot tolerate pollution. Examples of intolerant organisms are mayflies, stoneflies and some caddisflies (members of the Ephemeroptera, Plecoptera and Trichoptera orders respectively). Some pollution-tolerant organisms include leeches, aquatic worms and some Dipterous larvae. Water quality is evaluated by comparing the number of tolerant organisms to the number of intolerant organisms. A large number of pollution-tolerant organisms and few intolerant organisms may indicate poor water and/or habitat quality. However, pollution-tolerant organisms can also be found in a wide range of conditions, including pollution-free environments (Voshell and Reese 2002).
Despite the importance of aquatic insects regarding water quality assessment a very little scientific research work has been done on macroinvertebrates in Pakistan, a country which depends heavily on annual glacier melts and monsoon rains. The research on these organisms in relation to water quality variables would have been a great development especially in the rural areas where people are always struggling for the safe drinking water.
The authors are from the Department of Entomology, University of Agriculture Faisalabad, Pakistan. They can be reached at <firstname.lastname@example.org>