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CHAPTER 5 3.1.18 3.1.18 TRPI (Total Reactive Phosphorus Index)

(110)
(109)
and Everall et al. (2019)
– relates river invertebrates to
The Total Reactive Phosphorus Index (TRPI) – Everall (2010)
the concentration of total reactive phosphorus (TRP) in rivers. Phosphorus is usually the limiting nutrient for plant growth in
rivers, so its enrichment is a key driver of eutrophication. The main artificial sources in freshwaters are sewage discharges
and agricultural run-off.
TRPI – Total Reactive Phosphorus Index

The Total Reactive Phosphorus Index relates river invertebrates to the concentration of total reactive phosphorus in rivers.

The index is based on an analysis of the relationship into 5 river types as well as keeping RIVPACS spring and
between TRP and river invertebrates by Paisley et al. autumn data separate. The river types were differentiated
(2003, 2011) (111) (112) using information theory and neural using neural network analysis, which identified altitude,
networks to analyse data from the Environment Agency’s alkalinity and substrate composition as the key controls to
national general quality assessment survey of river quality the macroinvertebrate community response to TRP. (44)
in England and Wales in 1995. This data, and therefore
TRPI, is based on 76 families of invertebrates analysed TRPI is based on the mutual information between the
to the level used in BMWP (Section 3.1.4, ie RIVPACS occurrence of a taxon and TRP concentrations for each
Taxon Level TL1). Only sites in GQA classes a (very type/season. Mutual information (MI) is a measure of
good biological quality) and b (good biological quality) the amount of information one random variable contains
were analysed, but sites with total ammoniacal nitrogen about another. The sensitivity groups do not relate
concentrations greater than 0.15 mg/l or 5-day biochemical to concentrations of TRP but to the strength of the
oxygen demand greater than 2.25 mg/l were excluded, association between the taxon and TRP. The sensitivity
to remove sites suffering from organic pollution, as well group to which a BMWP family belongs and its RIVPACS
as some other outliers. To reduce the influence of natural log 10 abundance category are used to identify a nutrient
environmental pressures and season, the data was split score (Table 5.9).

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