Macroinvertebrates can be seen with the naked eye and these are organisms that lack a backbone. In freshwater rivers and streams, they are typically dominated by larval insects. The community as a whole includes snails, insects, crayfish, worms, and many other related organisms. Because these organisms are near the base of the food chain, they tend to have a limited ability to relocate, and they tend to be very vulnerable to short-term and long-term changes in water quality; they can be used as indicators of in-stream quality and changes in water quality with time. Because of the many thousands of species and because of the complexity of the taxonomic system, we are providing general information on using macroinvertebrates to evaluate and benchmark in-stream water quality.
Table 1 | Definitions of best candidate benthic metrics and predicted direction of metric response to increasing perturbation
Composition measures can be characterized by several classes of information, i.e., the identity, key taxa, and relative abundance. Identity is the knowledge of individual taxa, associated ecological patterns, and environmental requirements (Barbour et al. 1995). Key taxa (i.e., those that are of special interest or ecologically important) provide information that is important to the condition of the targeted assemblage. The presence of exotic or nuisance species may be an important aspect of biotic interactions that relate to both identity and sensitivity. Measures of composition (or relative abundance) provide information on the make-up of the assemblage and the relative contribution of the populations to the total fauna (Table 2). Relative, rather than absolute, abundance is used because the relative contribution of individuals to the total fauna (a reflection of interactive principles) is more informative than abundance data on populations without a knowledge of the interaction among taxa (Plafkin et al. 1989, Barbour et al. 1995).
The premise is that a healthy and stable assemblage will be relatively consistent in its proportional representation, though individual abundances may vary in magnitude. Percentage of the dominant taxon is a simple measure of redundancy Plafkin et al. 1989). A high level of redundancy is equated with the dominance of a pollution-tolerant organism and a lowered diversity. Several diversity indices, which are measures of information content and incorporate both richness and evenness in their formulas, may function as viable metrics in some cases, but are usually redundant with taxa richness and % dominance (Barbour et al. 1996b).
Table 2 | Definitions of additional potential benthic metrics and predicted direction of metric response to increasing perturbation.
This site has the organisms arranged by their sensitivity to pollution, i.e.,
Group One Taxa - Pollution Sensitive Organisms (caddisfly larvae, dobson fly, may fly, water penny, riffle beetle, stonefly nymphs and, snails)
Group Two Taxa - Pollution Intermediate Organisms (beetle larvae, Damselfly Nymphs (Order Odonata), Dragonfly Nymphs (Order Odonata), Scuds (Order Amphipoda), Crayfish (Order Decapoda), Sowbugs (Order Isopoda), Clams (Class Bivalvia (aka Pelecypoda)), and Crane Fly Larvae (Family Tipulidae))
Group Three Taxa - Pollution-Tolerant Organisms (Aquatic Worms (Phylum Annelida and others), Pouch Snails (Class Gastropoda), Black Fly Larvae (Family Simuliidae), Leeches (Class Hirudinea), and Midge Larvae (Family Chironomidae))
Macro-invertebrate Data for the Susquehanna River Basin (Dates range from 1990 to 2017)