Page 67 - Freshwater-Biology-and-Ecology-Handbook

Table 1.13
A simplified list of quality elements particularly sensitive to the pressures affecting rivers. Biological elements actually respond
to the integrated effect of all pressures. From UK TAG, 2005, 12. Monitoring Networks (2)

Source Category of
Macrophyte Phytobenthos Fish Morphology Hydrology chemical substances
Pressure Effect Exposure Pressure Macroinvertebrates General Physico- Specific Pollutants Priority substances Priority hazardous

Nutrient Primary effect on biology Change in nutrient concentration in defined X X X Nutrient
water body. Enhanced biomass, changes
Enrichment to other primary producers. suite
Organic Primary effect on biology Increased organic enrichment; change in X X Organic
Enrichment biological community structure suite

Annex 8 and Primary effects on
Annex 10 sediment and water Increased concentrations of contaminants X X General X X X
(water column and sediments)
suite
pollutants quality
Hydrological Primary effect on biology Changed water levels from abstraction; X X X X X X General
altered flow regime impacting biology suite
Riparian and channel modification;
Morphological Primary effect on biology altered sediment characteristics (eg size); X X X X X
smothering and damage to river bed
Change in ANC & pH; change in biological Acidification
Acidification Primary effect on biology X X X
community & toxicity synergies suite

We can only tell if the biology is impacted if we know value of metric observed
what the biological composition should be under EQR =
natural conditions. value of metric at reference condition

Natural biological communities can vary enormously The observed value is what is seen from a sample and the
between locations because of differences in natural reference value is what it should be under near natural
conditions such as geology, temperature, altitude and conditions. EQRs normally range from zero to one, but they
hydrology. These variations can be as great as impacts from can exceed one. This is a consequence of defining reference
anthropogenic pressures. Knowing what the biological value as the average value of a metric at reference sites:
composition should be at any given location is therefore by definition, at some sites the value of the metric must be
imperative if we want to know the degree to which biological greater than the reference value. If an EQR is substantially
communities are impacted at that location. Natural biological less than one, the value of the metric is much lower than we
communities are grouped into different types with similar expect under natural unimpacted conditions, and, assuming
composition, and these are associated with different types that the metric is one that decreases with increasing
of natural environmental conditions. These typologies are impact, we can assume that the biological community is
recognised by WFD. A general typology is described in WFD poorer than it should be. If the EQR is around one, the site
Annex II, based on altitude, catchment area and geology is in high status around reference condition. If the value is
for rivers, and altitude, depth, surface area and geology for greater than one, the site is of high status and the biological
lakes; but individual biological quality elements have their community is better than average under natural conditions
own physico-chemical definitions or ‘typologies’ because – eg an exceptionally diverse site in a nature reserve. Class
different parameters determine the distribution of different boundaries for WFD biological status classifications are
natural biological communities. always expressed as EQRs. The boundary EQR values
represent particular degrees of deviation from the reference
The degree to which a biological quality element is impacted values. High status is represented by values relatively close
(ie the biological quality for a particular quality element) is to one (ie little or no deviation) and bad status by values
quantified by the degree to which it deviates from its natural much less than one (ie substantial deviation). The EQR
state. This is expressed as an ecological quality ratio (EQR), scale allows the biological quality of communities from very
which is actually a decimal fraction. A number of metrics can different environments to be directly comparable, despite
be used to quantify biological communities, such as number large differences in their natural biological communities. The
of taxa, abundance of particular species or groups, biotic concept of reference is described more fully in Section 5.7.
indices and diversity indices. Any of these can be expressed
as an ecological quality ratio.
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