Page 175 - Freshwater-Biology-and-Ecology-Handbook

For the official status classification, you must use spring/autumn data.
RICT2 is used across Great Britain and Northern Ireland and can:
• calculate the official general degradation status for river invertebrates
• predict the value of a wide range of biotic indices
• predict the probability of occurrence of species or higher taxa and their numerical abundance and
abundance category
• compare two status classifications and indicate the statistical significance of any difference, described
below.

Comprehensive user guides are available from the website, together with a template for
entering data and test data sets that you can use to try out the programs.

To determine the river invertebrate status, you will need the following information:
1. Biological data from your site, which must be suitable for RIVPACS, in the form of WHPT ASPT and
WHPT NTaxa from spring and autumn samples collected according to RIVPACS methods.
2. The environmental data needed by RIVPACS to predict the reference value of WHPT ASPT and WHPT
NTaxa, listed in Table 3.4; see also Chapter 2 Section 7.6. Bias value for single-season WHPT NTaxa,
see Section 2.5.
3. Details of the methods for collecting this data are described in the Environment Agency’s guides
Freshwater macro-invertebrate sampling in rivers and Freshwater macro-invertebrate analysis of riverine
samples, both of which can be downloaded from the user guides web page of the RICT2 website:
https://www.fba.org.uk/rivpacs-and-rict/rict-rivpacs-user-guides

RICT2 classification programmes will produce results for the predictions of WHPT ASPT and WHPT
NTaxa and for the status classification. The prediction results include the probability of belonging to each
RIVPACS end group. The end groups represent the river invertebrate community types recognised by
RIVPACS (43 end groups for GB and 11 end groups for NI). The suitability information relates to how similar
your site is to those included in the RIVPACS database – if it is not similar, the suitability indicates that the
prediction results, and therefore also the classification, are likely to be unreliable for that site. This is useful
when evaluating the weight of evidence provided by the classification.
The classification results include the probability of belonging to each of the status classes, the most
probable class and the EQR (observed/reference value) for WHPT NTaxa, for each season and for
the average between them (spring and autumn results are combined by averaging the EQRs). These
results are repeated for WHPT ASPT and then for MINTA, which is the definitive classification based on
whichever index indicates the poorest quality status class (MINTA = minimum of NTaxa and ASPT).

The probabilities of class are based on the frequency of each class from 100,000 Monte Carlo simulations,
each simulation varying according to the known distribution of sampling error and information from the
bias value entered by the user to represent laboratory error. The final class is based on the most probable
class indicated by the Monte Carlo simulations. MINTA results can seem counterintuitive – it is possible for
the MINTA class to be worse than either of the classes indicated by WHPT ASPT and WHPT NTaxa. This
happens occasionally, particularly when the probabilities of belonging to two classes are not very different.

Pairs of classification results can be compared and the statistical significance of any differences estimated
using RICT2’s Compare program. Classifications from the same site in different years or from different
sites in the same (or different) years can be compared. This is useful for checking that differences in class
between river basin management plans have or have not changed, or for comparing results upstream and
downstream from a discharge or other activity to determine its impact.

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