Aquatic Pollution and Coastal Management

Unit 11 : Monitoring and control of pollution

11.9.Assessment Indices
There are various indices used to assess the effects of stressors on (aquatic) populations and communities:
Biotic Indices
Generally specific to the type of pollution or the geographical area, they are used to classify the degree of pollution by determining the tolerance of an indicator organism to a pollutant. Indicator species are assigned scores for their tolerance level. Biotic indices assume that polluted sites or systems will contain fewer species than unimpacted sites or systems and the species that are present will reflect their particular sensitivity to a pollutant. The measures are generally weighted and may include indices such as richness, pollution tolerance, trophic levels present, abundance, and deformities. These indices were originally devised for, and are most useful for, organic pollution .
Diversity Indices
The measure of the richness, or number of distinct taxa (e.g., orders, families, species) at a site, and the evenness, the relative abundance of different taxonomic groups, is determined by counts of all organisms collected.
Comparison, or similarity indices - The comparison of the community structure in richness and/or evenness over time or over space.
Both the diversity index and the similarity index may use the functional feeding group (e.g. herbivores, detritivores, carnivores) as a measure of the community integrity rather than taxa (i.e. species, genus, family).
On the level of the individual or species, biochemical and physiological indicators may be examined. Some benthic macroinvertebrates such as stoneflies (Plecoptera), caddisflies (Trichoptera), mayflies (Ephemeroptera), and shellfish, show increases or decreases of certain enzymes, changes in DNA, RNA, amino acids, and protein production, oxygen consumption and ion concentration, in response to environmental stressors such as temperature shifts, metals, and pesticides. Physiological indicators of contamination include deformities, sores, or lesions .
The EPA Rapid Bioassessment Protocol for Use in Streams and Rivers uses community diversity in assessing water quality. The absence of pollution sensitive benthic macroinvertebrate groups (Ephemeroptera, Pecoptera, and Trichoptera) and dominance of pollution-tolerant groups (Oligochaetes and Chironomids), is indicative of pollution. Overall, low richness of benthic macroinvertebrates may indicate impairment. However, naturally low nutrient levels in pristine headwaters may be the cause of low productivity and few benthic macroinvertebrate species exist in these conditions.
Pollutant stressors tend to cause slime and filamentous algae productivity and/or fewer fish species and more tolerant species than expected . The judgment of impairment, based on these indicators should be made by an experienced biologist.