Benthic macroinvertebrates of selected rivers in Luzon [Philippines]

Rivers are important to human civilization being used as a source of water for drinking, domestic use, agriculture and industrial purposes. At the same time, materials can be extracted from the river to support life, such as fish, gravel and sand, and energy from the flowing water. As is, rivers are used as navigational channels, recreation sites, and waste discharge systems. Although the uses may be conflicting, a water quality classification scheme is put into place to safeguard the beneficial use of the rivers. From another perspective, the river is an important habitat of animals, such as the benthic macroinvertebrates which is largely composed of three animal phylla, Mollusca, Annelida, and Arthropoda. The arthropods and annelids represented by insects and oligochaetes, respectively are the predominant members of the macroinvertebrate community. The river, as a habitat, must be able to provide an environment where these animals can grow, develop, and reproduce. Under optimal conditions, the maximum potential for biotic development can be realized. In nature, where only near-to-ideal situations can be achieved, a survey of 11 rivers in Luzon shows that the rivers draining forested watersheds have higher macroinvertebrate diversity than those exhibiting different degrees of watershed development. Forested watersheds in Luzon may have as high as 22 insect Families (Okayan Creek) and at least six insect Families (Balatuin River, Laguna) can be observed in a river draining a lowland forest. On the other hand, rivers impacted by anthropogenic activities and natural disasters such as lahar flows can be devoid of any macroinvertebrates. Rivers (Balatuin River) impacted by anthropogenic activities can be colonized by at least by one insect Family, the Family Chironomidae. Since Chironomidae or midges are known to tolerate very low levels of dissolved oxygen, they may be found as the predominant group in rivers receiving domestic wastes. A higher number of insect Families, two to seven, are found in rivers (Togpon Creek) draining mining areas. It appears that these rivers receive high sediment load which appears to have a minimal effect on biodiversity than domestic wastes. Lahar deposit, also a form of sediment load, have a more devastating effect on the macroinvertebrate community. Rather than simple burial, the scouring effect of lahar causes the riverbed (Baquilan, Bucao, Maloma and Sto. Tomas) to be in a constant flux which does not provide the stability required by the macroinvertebrates.