As benthic macroinvertebrates tend to remain in their original habitat, they are affected by local changes in water quality. Some are capable of tolerating higher loads of pollution than others. Thus if the pollution is severe, or is moderate but sustained over time, the whole community structure may simplify in favor of tolerant species. Although the abundance of certain species may increase, the diversity, and species richness (the number of different species in a given area) decreases. By assessing indicator species, diversity, and functional groups ofof the benthic macroinvertebrate community, it is possible to determine water quality.
There are four feeding groups of macroinvertebrates: shredders, filter-collectors, grazers, and predators (KY, 1995). Shredders such as stoneflies (plecoptera) feed on plant material and some animal material, which is generally dead, and break it into smaller particles through their feeding and digestive process. Collectors, such as caddisflies (trichoptera) and blackflies (diptera), feed on this fine particle material which they filter from the water. Grazers, such as snails and beetles, feed on algae and other plant material living on rocks and on plant surfaces. Predators such as dobsonflies (magaloptera) or dragonflies (odonata) feed on other macroinvertebrates. Individual species may be generalists, and fit into more than one of these groups (as opposed to specialists).
Note: except where otherwise indicated, the source is (De Lange 1994).
Although water resources with high water quality generally have diverse and rich macroinvertebrate fauna, certain pristine environments have low diversity of macroinvertebrate fauna because of the cold temperature and/or relatively low nutrient levels (Peckarsky et al. 1990). Headwaters and headwater streams may have only two dominant species. Although all classes of invertebrates may be found in headwater streams, crustaceans, caddisflies, leeches, mollusks, flatworms and blackflies tend to be found in such environments (De Lange 1994; Peckarsky et al. 1990).
The majority of macroinvertebrates are found in the riffles of streams. (KY, 1995). Riffles range from uneven bedrock to cobbles to boulders. The optimum riffle area is caused by gravel (1 inch) to cobbles (10 inches). The flow of water over these areas provides plentiful oxygen and food particles. Riffle-dwelling communities are made up of macroinvertebrates that generally require high dissolved oxygen levels and clean water. Most are intolerant of pollution.
Insects (Insecta) Stonefly larvae (Plecoptera) Stoneflies require high dissolved oxygen concentrations and tend to be found in cold, flowing water with a gravel or stone bottom. Some species may be found along lake shores with wave action (Peckarsky et al. 1990). Stonefly nymph groups may be shredders or predators. They may be specialists or generalists (Peckarsky et al. 1990). Dobsonfly larvae (Megaloptera) Generally found in the mud (unconsolidated bottoms) of lakes and wetlands but they can be found in any water type. With the exception of the wetland species, dobsonflies are generally found in well-oxygenated lakes and streams (Peckarsky et al. 1990). Dobsonflies are predators, feeding on other aquatic insects, annelid worms (oligochaetes), crustaceans, and mollusks (Peckarsky et al. 1990). Snipe fly larvae (Diptera Athericidae) Snipeflies will only inhabit the bottoms of very clean, flowing water types. Water spider (Argyroneta aquatica) Water spiders require waters with high oxygen levels lacking pollution. Mayflies (Ephemeroptera) Mayflies are most abundant in cool, unpolluted, headwater streams but they may be found in standing (lentic) water as well. They prefer clean water and an average oxygen supply, but some species can tolerate low dissolved-oxygen levels (e.g. Callibaetis spp.) (Peckarsky et al. 1990). Mayfly nymphs tend to be grazers, feeding on algae or detritus (Peckarsky et al. 1990). Caddisfly larvae (Trichoptera) Generally caddisfly larvae are found in clear flowing water and are sensitive to pollution and oxygen depletion. Caddisflies are found across a range of habitats from cool streams to warm streams, lakes, marshes, and ponds (Peckarsky et al. 1990). Caddisflies found in standing water can tolerate some pollution. Crustacea Scuds (Amphipoda) Freshwater scuds are found in unpolluted lakes, ponds, streams, springs, and subterranean waters (Pennak 1989). They require abundant dissolved oxygen and many species only inhabit cold waters.
Turbidity reduces light penetration and submersed aquatic plant productivity. Thus turbidity will affect those macroinvertebrates depending on plant matter for food and predator macroinvertebrates that rely heavily on visual location of prey. Filter feeders' filtering mechanisms may be blocked by sediment. As sedimentation increases, rock dwelling or attaching macroinvertebrates such as mayflies, stoneflies, and caddisflies, will be replaced by silt-tolerant oligochaetes, chironomids, and lunged snails. Insecta Black fly larvae (Diptera Simuliidae) Simuliidae are filter feeders that can filter very fine particles (Peckarsky et al. 1990). Midge larvae (Diptera-Chironomidae) Midges are found in all water types, including salt water. They live in the silt bottom, on solid substrates, or on aquatic plants. Crustacea Sowbugs/pillbugs (Isopoda-Asellidae) Moderately intolerant of pollution, isopods may be found in streams, headwaters, ponds, or shallow areas of lakes (Peckarsky et al. 1990). Isopods feed on dead animal and plant matter thus, they will increase in number under eutrophic conditions (Peckarsky et al. 1990). Mollusca Snails (Gastropoda) Snails with gills are sensitive to oxygen depletion. However, those with lungs (pulmonate snails) can tolerate water with little or no oxygen. Annelida Leeches (Hirudimea) Leeches are generally pollution tolerant, however, some species of leeches are much less pollution tolerant than others (Pennak 1989; Peckarsky et al. 1990). Leeches are found in warm water of shallow standing water (Peckarsky et al. 1990). They generally can not tolerate very acidic waters. They are also limited by low calcium content (Pennak 1989). Siltation does prevent leeches from attaching to stones or other objects. Leeches feed on dead organic matter, snails, insects, oligochaetes, and other small invertebrates (Pennak 1989).