V. Artemiadou , M. Lazaridou-Dimitriadou
Dept. of Zoology, School of Biology, Aristotle University of Thessaloniki, 54006
Thessaloniki Greece.
E-mail: luteus@bio.auth.gr, mlazarid@bio.auth.gr , Tel. +30-31-998373,
Fax: +30-31-998269,
Abstract
The biological approach for the evaluation of the freshwater quality is expanding both in Europe and in the USA. In Greece there is not yet a suitable evaluation system as in the rest of the European countries. This study focuses on the attempt to modify the European biotic indices and scores according to Greek data. It considers additional taxa of benthic macroivertebrates, good biomonitoring organisms, it includes the reappraisal of the taxa used and it takes into account the abundance and the type of the substrate.
Introduction
Humans fully depend on the available quantities of freshwater. Until now, most of the methods used for the determination of freshwater quality are based on the physical and chemical characteristics of the rivers or the lakes. In The European
Union there are several Directives concerning the water quality, which is estimated according the concentrations of various physicochemical parameters. Nevertheless, since humans are part of the biosphere and depend their existence on the goods and the services which biosphere offers to them, they should evaluate and monitor their sources using biological criteria (20).
From the beginning of the century it was already known that living organisms could provide useful information for the status of a water body and until now they prove to have several advantages comparing to physicochemical methods (10, 27). The integrated assessment of water quality though, requires the combination of these two different approaches (26, 9). In Europe, over 50 evaluation systems based on living organisms have been developed until now (27, 9). Among the systems based on animals, the ones, which use benthic macroinvertebrates, seem to be the more suitable
(27, 16, 26, 10).
The European legislation contains a proposal Directive [COM (97) 49 final amended by COM (98) 76 final], which defines the "ecological" water quality and obliges the member states to establish national monitoring networks that will consider living organisms and especially benthic macroinvertebrates. Although, almost each
European Union country has developed its own evaluation system (28, 9) and established its own national monitoring network, in Greece there is neither a monitoring network nor a Greek evaluation system. Until now there is a limited number of studies testing the applicability of European biotic indices and scores in rivers (21, 2, 31, 4, 8, 22, 13, 25, 33, 23, 24, 19, 11, 18, 5, 28). Most of them concluded that the major problems in the appliance of these European systems were that they did not consider some taxa found in Greek rivers and they did not take into

account the abundance and the type of the substrate and so they were inconsistent in evaluating good or moderate quality of water bodies. They were really applicable though in excellent or poor quality waters.
The present attempt focuses on the selection and modification according to the Greek data, of existing European biotic indices and/or scores (Spanish and British as well) based on benthic macroinvertebrates, in order to reflect the hydrological and climatological peculiarities of the Greek rivers, which affect the biota.
Materials and methods
Data sources
The attempt to create a Greek evaluation system is based on data derived from previous studies on several rivers. These are a) Aliakmon river (NW Greece, 2, 4, 8,
33, 24), b) Axios river (NW Greece, 22, 19, 5), c) Aggitis river (N.E. Greece, 31) and d) Skouries and Olympias streams (Halkidiki, N. Greece, 13, 25).
Sampling method
The benthic macroinvertebrate sampling method used in all the above studies was the semi quantitative 3-minute kick/sweep method (16, 26, 27). According to it, a standard pond net (surface 575 cm2, mesh size 900 μ.m, depth 27,5 cm) is placed against the river current. At the same time the bottom of the river is disturbed and the benthic macroinvertebrates are drifted in the net. Each sample derives from a 3minute kick/sweep attempt, which covers all the different microhabitats in the river site.
Selection of the type of the Greek evaluation system
There are several types of European biotic indices or scores (27). The Greek evaluation system is based on a biotic score, which includes only the taxonomic level of family (with the exception the class of Oligochaeta) and gives a high value to the sensitive to lack of oxygen families and a low one to the tolerant taxonomic groups.
The gum of the values of the families present in the sample is the final value of the evaluation system. In addition, the average value of the biotic score is calculated by dividing the above sum with the number of the present taxa (at family level).
Additional taxonomic groups
According to all the above studies in the Greek rivers, the Greek benthic macrofauna consists of more taxonomic groups than the European biotic indices and scores include (e.g. the BMWP' score). The BMWP' score (1) is selected as the basis for the
Greek evaluation system, since it includes the most macroinvertebrate families found in our rivers.
Additionally, according to Illies (34) some other families are expected in Greek rivers.
Based on this information, some families were added and scored in the Greek evaluation system.
Appraisal of the benthic macroinvertebrate families
The evaluation of the families expected in Greek rivers but not found in the samples of the above studies was based on data from bibliography regarding their tolerance to polluted water. The appraisal of the families collected in the samples but not included in the BMWP’ score and the reappraisal of the rest of them were based on the methodology developed by Walley & Hawkes (32) for the British BMWP score and its average, the ASPT. In the present study this methodology was applied to Greek data using as a basis the Spanish BMWP' score and its average ASPT' and not the
British ones.

According to it, it is accepted that a) the BMWP' score of each family provides the real organism's sensitivity to pollution, b) the ASPT' (the average of BMWP') reflects the quality of a site precisely and c) the total average of the ASPT' values of all the sites where a family was found is a reliable statistical method according to which it is easy to rank the sensitivity of the families and to check the value of the family score.
The method considers the different substrate and categorizes the samples into three groups. The reappraisal was performed only for the families found at more than five sites in at least two substrate categories
Consideration of the abundance
The abundance is not considered by the Spanish BMWP' and the British one. In the present study, we tried to take it into account using as a basis the Chandler score (7).
This score distinguishes the abundance of the benthic macroinvertebrates into five categories.
Substrate
The substrate composition is one of the major factors affecting the benthic biocommunities. The only index that considers the diversity of the substrate is the
Lincoln Index ( 12). According to it, the sampling site is characterized either rich if it includes a lot of different microhabitats or poor if it contains few. After the distinction, we calculate the final score of the families and its average and according to the semi sum of these two values the water quality is characterized as "excellent",
"good", "moderate", "poor" and "very poor".
Results
In 293 samples collected from 66 different sites, 114 taxa of benthic macroinvertebrates were collected. Concerning the families that may be found in Greek rivers, six of them belong to the Ephemeroptera class. From these, one is already included in the Spanish score (Oligoneuriidae), while two others are not taken into account in the Greek evaluation system (Prosopistomatidae and Palingeniidae), since there is not enough information on their tolerance level to pollution and their preferences to habitat type. Regarding Trichoptera class, the family Calamoceratidae is not considered in the Greek evaluation system due to lack of information on its tolerance.
Epallagidae is the only family of Odonata class, which is not included in any of the
European scores. Due to very small piece of information, it is not taken into account in the Greek evaluation system either. Finally, two Dipteran families, three of
Hemiptera-Heteroptera and three of Gastropoda are included in the Greek evaluation system.
The evaluation of the tolerance of the above families is based on reference information and it is presented in Figure 1.
Regarding the evaluation of families collected in more than 5 samples in at least two substrate categories (32), the results of their reappraisal are presented in Figures 2a and 2b. According to them, 13 families are reaccredited the same score, 21 took higher value than their initial in the Spanish BMWP' and 23 were accredited lower score than in the beginning in the BMWP'.

Discussion
According to Extence et α1. (12), an evaluation system suitable for the monitoring of freshwater quality should combine several characteristics: a) be based on tested sampling methods, b) be simple and representative of the existing biocommunities, c) be easily applied in all types of rivers and by non specialists and d) be cost effective.
Considering all the above we tried to make the less compromises in the time required, the simplicity during a monitoring routine and the accuracy and precision of the performance of an evaluation system. So the selected sampling method for the
Greek evaluation system is the 3 min kick/sweep, too. It is a semi quantitative method in which the factor of space is replaced by the factor of time (3 minutes). Although several studies refer to the different number of samples that should be collected (26,
3), two samples seem to be sufficient (6). However, the most important point is to cover all the different microhabitats during the 3 minutes of a sampling attempt.
Altough in the case of deep rivers artificial substrate samplers are preferable
(26, 16, 27), their appliance in Greek rivers proved to be ineffective, while the usage of the pond net along the banks of the river gave satisfactory results (11). This is because the diversity of the taxa is higher at the banks than in the middle of the river, since the substrate is not as fine as in the middle and usually there is aquatic or bankside vegetation which is used either for shelter or for food (17).
The type of the evaluation system chosen for the creation of the Greek system is the "score", according to previous studies in Greek rivers, which indicated that
European "scores" gave more satisfactory results than European indices. Additionally, scores include more information of a biocommunity, since they consider almost all the taxa present there. On the contrary, the value of the indices is

based on the presence or the absence of specific taxa sensitive to pollution.
Additionally, the fact that only one taxonomical level (family level) is used in the
European scores, makes their appliance easy, since the identification of the benthic macroinvertebrates down to this level is not difficult, although not very detailed. The results derived from family level are better comparable and sometimes more informative than the ones based on species or genus identification level (14).
The dependence of sampling on the season (14, 3) could be overcome if samples are collected in all four seasons. In the case where only one sampling can be performed, then the ideal time regarding Europe is in the end of spring or in the beginning of summer (16, 26). Score values are also affected by the magnitude of the sample
(number of 3 min attempts), but the differences are not significant between two or three attempts (26, 3).
Among the European scores, the one preferred to be the basis of the Greek evaluation system is the Spanish BMWP' score and its average ASPT'. Since it is adapted for rivers in the continental Europe where the benthic macrofauna is reacher
(10), it includes more families than the respective British one.
Concerning the families that may be or have been found in Greek rivers but are not considered in the European scores, they are accredited scores according to reference information. Three of them belong to the Ephemeroptera class, from which two (Polymitarcidae and Isonychiidae) are considered to be moderately tolerant, since they can be found in water with high BOD; and one sensitive (15) (Figure 1).
Regarding Trichoptera, three families have been collected in our samples and will be included in the Greek evaluation system. According to Tachet et α1. (30) and to Illies
(34) two of them (Thremmatidae and Helicopsychidae) prefer small streams with high oxygen level and are characterized as very sensitive, while the third one (Ecnomidae) appears more tolerant (Figure 10). The two Dipteran families Rhagionidae and
Syrphidae are accredited very low scores (Figure 1), since they are very tolerant to organic pollution (34, 29). Concerning Hemiptera-Heteroptera, most of the species of the three families live in lentic water areas with vegetation and appear to survive in polluted sites, since they 1ive on the surface of the water (30). Therefore they are accredited low scores (Figure 1 ). Finally, all the additional families of Gastropoda are considered tolerant to organic pollution and live next to aquatic vegetation (17).
In the BMWP' score and in the British one, all the sensitive taxa are crowded in the score "10", since the value "9" does not exist (32). After the reappraisal of the benthic macroinvertebrate taxa, some of them were accredited score "9". In this way, differences among sensitive taxa can be accredited. In addition, the appraisal of each family in the Spanish BMWP' and in the British one was based on the more tolerant species of the family, in order to avoid overestimation of its sensitivity. In this case, some families are accredited lower values than their really should (32). This is one reason why after the reappraisal (Figure 2a), the score of some families (eg.
Nemouridae, Rhyacophilidae et al.) raised. In the case of Chironomidae and of
Oligochaeta, the species, which contain hemoglobine and are coloured red, obtained lower values than the rest belonging to this family and class respectively.
One more factor that affects the score of the families is the lack of knowledge concerning the tolerance of each species of a family. As a consequence, the evaluation of the families of one class with the same score actually reflects the average sensitivity of the class and not the sensitivity of the family (32). For example, many
Dipteran families have the value 4 in the British BMWP or the Spanish BMWP', while after the reappraisal for the Greek evaluation system, some of them showed different scores (Figures 2a and 2b). Different new scores were observed for various

families. When the new scores were in agreement with reference information, they were accepted. In the opposite case, they were rejected.
The abundance influences the evaluation of the freshwater quality, since it gives more accurate information for the biocommunity (7). Regarding that the absolute abundance varies significantly even under natural conditions (20) and that the sampling method is semi quantitative, only the relative abundance of the benthic taxa can be considered in the Greek evaluation system. According to it, the taxa are characterized as "present", "common" and "abundant" in an attempt to simplify the
Chandler score (7). If their score is more than 6 when "present" (relative abundance lower than 1 %), it raises in the case of being "common" or "abundant", if it is lower than 5, it decreases and if it is 6 or 5 does not change.
Substrate and aquatic or bankside vegetation determine the composition of the benthic macrofauna (17). In an attempt to consider their influence, the methodology of Lincoln Index (Extence et α1., 1987) was followed and slightly modified: the criteria to characterize a site as poor are set more specifically. Poor sites are the ones whose substrate consists more than 70% of sand and silt and the vegetation cover is
10% or less.
The present study is the first attempt to create an evaluation system of the water quality in Greek rivers. The preliminary forms of the Greek evaluation system
(GES) and its average (GES divided by number of taxa) have been already tested but on a limited number of samples. Although their performance was satisfying, it must be tested in more rivers in order to reach a final form and be safely used for monitoring freshwater quality in Greece.
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