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Third national assessment

7.0 Glossary

Benthic invertebrate community – The varied populations of small animals (excluding fish and other vertebrates) that live in or on bottom sediment or a rocky substrate and that provide food resources for fish. Measuring changes in benthic invertebrate communities helps to understand changes in aquatic habitats and provides an evaluation of the aquatic food resources available to fish and an indication of change in water quality.

Body Condition – A measure of the physical condition of fish that describes the relationship between body weight and body length; condition essentially measures how “fat” fish are in each area investigated.

Control/impact design – A study design consisting of no less than one reference area, usually upstream from the mine or situated in a different watershed (not exposed to mine effluent), and one exposure area or a series of exposure areas, often downstream from the mine (exposed to mine effluent).

Critical effect size (CES) – A threshold above which an effect may be indicative of a higher risk to the environment. 

Density – The total number of individuals of all taxonomic categories collected at a sampling station, expressed per unit area.

Effect – In the context of the MMER, an effect on fish or the benthic invertebrate community is a statistically significant difference between measurements taken from the exposure area and from the reference area or measurements taken from sampling areas that have gradually decreasing effluent concentrations with increasing distance from a final discharge point. An effect on fish tissue is defined as measurements of concentrations of total mercury that exceed 0.5 µg/g wet weight in fish tissue taken in an exposure area and that are statistically higher than the concentrations of total mercury in fish tissue taken in a reference area.

Evenness index – A measure of how evenly individuals are distributed among the different taxa. This measure helps to evaluate changes in the relative abundance of taxa.

Exposure area – All fish habitat and waters frequented by fish that are exposed to effluent.

Gradient design – A study design in which sampling is done along a gradient of decreasing effluent concentration, starting with exposure areas close to the mine and progressing towards less exposed areas farther from the mine.

Inhibitory effect – Refers to a situation where the indicator being measured is smaller in the exposure area than in the reference area.

Liver condition (relative liver weight) – A measure of fish energy storage and/or response to toxicant exposure that describes the relationship between liver weight and body weight.

Reference area – Water frequented by fish that is not exposed to effluent and that has fish habitat that is as similar as possible to that of the exposure area.

Reference condition approach (RCA) – A study design involving the assessment of a large number of sites in reference areas for comparison to test (exposure area) sites.

Relative gonad weight – A measure of fish reproductive investment that describes the relationship between gonad weight and body weight.

Similarity Index – An index that measures the degree of difference in community structure (especially community taxonomic composition) between two sites. The higher the value, the greater the difference. The index is used to evaluate the amount of similarity between benthic invertebrate communities at different sites relative to reference conditions.

Stimulatory effects – Refers to a situation where the indicators being measured are larger in the exposure area than in the reference area.

Sublethal toxicity (SLT) tests – In the context of environmental effects monitoring, sublethal toxicity tests measure the effluent concentration for which a given effect level is observed on the organisms in a laboratory setting. Stimulation is sometimes observed instead of inhibition.  Stimulation refers to an increase in the growth of the organisms relative to controls after effluent exposure.  A sublethal toxicity test measures what is detrimental to the organism (e.g., effects on growth or reproduction), but below the level that directly causes death within the test period.

Taxon (plural taxa) – A taxonomic group into which an organism is classified based on structural similarities and evolutionary relationships with other organisms. Traditionally these groups are arranged hierarchically into species, genus, family, order, class, phylum, etc.

Taxon richness – The total number of different taxonomic categories collected in a sample or at a sampling station (e.g., number of species, number of families).

Weight-at-age – A measurement of the rate of growth of fish described by the relationship of size (weight) to age. Over the entire life span of a fish, the rate of increase in size may decline as the fish ages.

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