Irish water quality rating

To use this freshwater scoring system within Species Diversity and Richness undertake the following steps

NB Species Diversity and Richness includes an example data set for this scoring system called IrishQ_test.csv which can be used and edited to understand how the data is structured.

A biological Assessment scheme suited to Irish rivers was devised by Toner in 1970 and later described by Flanagan and Toner (1972).  This scheme, called the Quality Rating System, has been in use since 1971 when the first national survey of river water quality was carried out by An Foras Forbartha (Flanagan and Toner, 1972). To use this method you must give the program observation data arranged as samples by family (see T-Group) or other appropriate taxon as specified in Table 1 below. It is important that you spell the names correctly as the program looks through the list of names and scores those that correspond with a standard list. Species Diversity and Richness includes an example data set for this scoring system called IrishQ_test.csv which can be used and edited to understand how the data is structured.

The Quality Rating System relates the relative abundance of five key groups of macro-invertebrates to water quality.  The scheme uses five basic water quality classes: Q1 - bad quality, Q2 - Poor quality, Q3 - doubtful quality, Q4 - fair quality, Q5 - good quality. In addition, the intermediate classes Q1-2, Q2-3, Q3-4 and Q4-5 are used to give an effective nine-point scale. Species Diversity and Richness reports the Q value as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 5. The Q value of 1.5 corresponds to the intermediate class Q1-2.

A summary of the scheme is given in Table 2. This table relates the relative-abundance of key macro-invertebrate groups to Q-Value.  Note that a distinction is made between eroding and depositing substrata.

While the Quality Rating System is based primarily on macro-invertebrate communities, other factors are also taken into account in assessing Q-Value, for examples the presence and abundance of macrophytes and algae, and the occurrence of slime growths. An overall assessment is also made of the individual sampling site's ecological type and its general suitability for macro-invertebrate communities.  These factors may result in a modification to the basic Q-Value derived solely from the decision tables shown in Table 2.

The full assessment of the site, from sampling to ascribing a Q-Value can be completed in the field within 20 to 30 minutes by an experienced biologist.  Where possible, preference to be given to riffled sites with turbulent flow conditions and hand-net sampling to be carried out according to ISO Standard 7828-1905. In deeper waters, dredge or grab sampling may be used, but with a few exceptions this is not necessary due to the shallow nature of most Irish rivers.  Kick sampling is carried out for 2 to 5 minutes and usually supplemented by a similar period hand picking animals from stones to ensure that those with efficient hold-fast mechanisms are represented in the sample.  The sample is decanted and cleared of debris and then transferred to a large white tray on the riverbank for examination.  A field inventory of the invertebrates and their relative abundance is then made in situ.  A general site description is recorded on the field sheet in addition to the macro-invertebrate list.  This includes measurements of dissolved oxygen (DO) and temperature, and descriptions of site substratum, water velocity, clarity and river flow conditions.  The presence and abundance of macrophytes, algal taxa and 'sewage fungus' are also recorded.  Reference faunal samples are retained, but routine laboratory sorting of samples and taxonomic identification of invertebrates to species level is not possible due to constraints of time and resources. Comparison of species lists made in the field with fully sorted and identified laboratory lists has shown that good accuracy can be achieved with field examination of samples, albeit at lower taxonomic detail. Field abundance values are, of necessity, semi-quantitative with each macro-invertebrate taxon being classified into one of 5 categories: 1-5, 6-20, 21-50, 51-100 and > 100 individuals. Again broad agreement has been found between field and laboratory assessments of abundance.

In terms of a programme aimed at assessing water quality in Irish rivers, the Quality Rating System has proved an efficient and reliable technique.  The Biological Survey of River Quality in Ireland has been in operation since 1971.  There has been very little modification of the scheme in that period. This has allowed long-term trends in water quality to be assessed.  Due to the limited resources involved in the biological survey (the survey is carried out by three biologists) it takes four years to complete the national survey - with seriously polluted rivers getting sampled on an annual basis.  Because there has not been a comprehensive physico-chemical river survey programme in the past, the biological survey of river quality has assumed an important role in the national reporting of water quality in Irish Rivers. 

Table 1, Summary of the 'Irish Quality Rating System: Macro-invertebrate group A, B, C, D and E.

Table 2. Decision tables for assigning Q-values based on the relative abundance of these groups at eroding and depositing sites.

Quality Rating                        Eroding Sites                                                

               A                B                C                D                E                

Q5                ++++                +++                ++                +                +-                

Q4                ++                ++++                +++                ++                +-                

Q3                -                +-                ++++                +++                ++                

Q2                -                -                +-                ++++                +++                

Q1                -                -                -                +-                ++++                

                                       Depositing Sites                                                

Q5                +-                ++++                +++                ++                +-                

Q4                -                ++                ++++                ++                +-                

Q3                -                +-                ++                +++                ++                

Q2                -                -                +-                +++                +++                

Q1                -                -                -                -                ++++        

Key:                ++++                Well represented or dominant

               +++                                May be Common

               ++                                May be present in small numbers

               +-                                Sparse or absent

               -                                Usually absent

Species Diversity and Richness selects the most appropriate Q rating by comparing the average score for each of the 5 groups of taxa defined in Table 1 against standard tables to find which quality rating which is most similar for eroding and depositing substrates. The similarity measure used is the Euclidean distance.

The standard tables of average scores used by Species Diversity and Richness to calculate the Irish quality rating are as follows:

Depositing sites