SCOPE 53 - Methods to Assess the Effects of Chemicals On Ecosystems

5.1 BACKGROUND

5.1.1 POLLUTION AND OTHER DEGRADATION FACTORS

Water pollution often represents a very complex set of factors that degrade aquatic systems. Intervention in the return of a river to its prepolluted condition can attack the mosaic of habitats; for example, the erection of a large dam can modify biological structures and reduce the consumer populations (invertebrates and fish) as much as the effects of industrial discharges to surface water. Estimating the degree of overall degradation of a site due to pollutant load requires targeted objectives that depend upon different methods of remediation. 

5.1.2 MANIFESTATIONS OF POLLUTION DAMAGE

In a lake or stream, the consequences of various discharges depend on the flow of the river and the assimilation capacity of the receiving environment. This ability to transform and transfer allochtonous river drift depends on the physical, chemical, and biological characteristics of the system in question. Three possibilities exist:

The introduction and dissemination of toxic or inhibiting substances. When nutrients are unlikely to enter the trophic structure (due perhaps to toxic inhibitory substances), pollution causes a gradual and eventually complete disappearance of species in the biological structure, as has been demonstrated for some pesticides, cyanides, detergents, and metals.

Excessive amounts of nutritive substances (organic matter, including nutrients). When the river drift of nutritive substances is progressive yet still within the assimilation capacity of the system, eutrophication (i.e., complexation of the biological structure) may be only temporarily accelerated. 

The amount of river drift presumed to be nutritive exceeds the assimilation capability of the receiving water. This condition results in the gradual development of a pollution condition characterized by the accentuated simplification of the consuming biological structure. The accumulation of unused substances implies a chemical modification of the environment of which several parameters first reach, and then exceed, the tolerance limits of an increasingly large number of species; the simplification of the consuming biological structure worsens this process, which accelerates exponentially.

Pollution of an aquatic system is manifested at the population level by three phenomena. Modification of the structure of the initial population results in the development of a few saprophage or euryoeces populations, such as Oligochetes or the Hydropsychidae, and the decrease in abundance of other more sensitive organisms, such as certain Heptageniidae or Plecopters. Simultaneously, progressive desertion of habitat by lentic facies in favour of lotic facies can be observed, whereby species of the initial population do not appear or disappear¾a process termed "imposed habitat changes" (Verneaux, 1973). Appearance, then proliferation, of species elective of specific river drift occurs; for example, this may occur because of intense development of certain algae, bacteria, and fungi (Cladophoraceae, Spirogyra, Sphaerotilus, Leptomitus, Fusarium, Cellolobacteria, Ferrobacteria, and Sulphobacteria) downstream from organic or specific discharges. Gradual disappearance in a specified order of all or part of the initial population then follows. These phenomena emphasize the differences between the eufunctional and dysfunctional systems, regardless of their potential trophic level. Eutrophication corresponds to an increase in biodiversity, and is, therefore, the opposite of the adverse effect of pollution or of the general system degradation phenomena which produce a decrease in the biodiversity of consuming organisms. Thus, an environment can be polytrophic without being eutrophic; and, for numerous reasons, a polluted environment may become dystrophic.

5.1.3 SPECIALIZED AND PRACTICAL METHODS

Analysis of published findings unveils the contrast between the large number of biological analyses performed, whose variety justifies both the statement by Bartsch and Ingram (1966) that "there are as many methods as biologists working on this topic" and the observation that few proposals include a complete, precise, and standardized protocol used as a standard by others. Depending on the specialization of the analysts, the protocols show great variety in the types of organisms, sampling procedures, taxonomic units selected, and procedures for data analysis.

The great variety of techniques employed in biocenotic testing requires that quantitative data be representative of the taxokenoses, and underscores the perception that each investigator develops and uses custom-tailored methods based on biological and ecological peculiarities of the group of organisms in question, characteristics of the investigated biotopes, work scale, and objectives of the investigations.

When a method of comparative analysis is proposed, defining appropriate and specific sampling protocols is problematic, because the parts of the method are interdependent. The macrobenthos sampling techniques that are employed jointly during seminars organized by the European Commission on biological indicators have shown the superior efficacy of a differentiated sampling protocol, in which the number of readings and the habitat categories are predefined (Verneaux et al., 1982)¾in contrast to other techniques in which the types of habitats are either not defined or are subjected to unrestricted research for a given time duration (Mouthon and Faessel, 1978).

The general sampling methods should include monitoring of:

1. "drift" organisms directly in the water;

2. impact of periphyton "growth" and macrobenthos levels on the local nutrient supplies; and

3. micro-organisms (including periphyton), macrobenthos, and plants (such as mosses) that concentrate micropollutants (Mouvet, 1986) on the artificial supplies or substrates.

Although the number of comparative analysis protocols is rather small, the sampling techniques are apparently subjected to successive revisions (Downing and Rigler, 1984). Virtually all organisms, from unicellular ones to fish, have been used as indicators for a given component of freshwater quality. Studies pertaining to stagnant water (lakes, ponds) especially employ planktonic organisms and organisms related to streams, the benthic organisms. A distinction must be made between essentially fundamental biocenotic analyses, which require a determination of the species, and practical methods in which identification is restricted to units of taxonomic groups that can be identified by non-specialized operators. 

Although methods using Diatoms (Descy and Coste, 1991), Mollusks (Mouthon, 1993), and the Oligochaetes (Lafont et al., 1991) exist, the most frequently employed practical methods involve the simplified analysis of the macrobenthos of streams. In France, the dulcicole macroscopic invertebrates include approximately 150 families, 700 genera, and 2200 listed species (Ilies et al., 1978).

Depending on the nature of the organisms employed and the objectives being pursued, two main trends can be distinguished in the assessment of water quality and the biogenic tendencies of systems:

1. assessments based on the presence of organisms considered indicators of a specific type of contamination (which includes analyses for bacterial contamination and those involving "biotic indices"); and  

2. global approaches, based on the investigation of all or part of the aquatic populations, for which the absence of some organisms is as significant as the development of populations of other organisms. 

5.1.4 PROCEDURES FOR DATA ANALYSIS

Based on fundamental parameters for the analysis of populations by specific variety (or taxonomic richness) and density (or abundance) of individual organisms, the criteria have evolved from a simple comparison of specific indicators to the interpretation of biological structures in relation to reference organizations (biotypology) established in the abstract space of mathematical analyses. Direct comparisons of species indices provide observations that are especially interesting when they allow specification of biocenotic evolution. No specific analytical procedure is required, and the value of the conclusions depends on the precision of the findings and on the biological and ecological knowledge of the operators.

Graphic procedures or simple formulas such as species deficit ("Artenfehlbetrag;" Kothé, 1962) allow a global or group-by-group visualization of the changes which have an impact on biocenoses. The advantage of such determinations is that they offer a most complete perspective of the population of a location at a given time, that can be used as a reference for subsequent studies. This situation mandates that choices regarding impact studies be made by a recognized expert to have some value. Furthermore, true impact studies must be provisional; for that reason, they require access to biological and parametric models. Such access is a very rare occurrence. 

From the baseline parameters to study the populations formed by the taxonomic variety and abundance of individual organisms, authors have proposed numerous indices of diversity and regularity, of which the most frequently used are that of Shannon (1948) with incorporation of measurement of the regularity ("evenness") of taxonomic distribution, including "equitability," "diversity," and "redundance" (Lloyd and Gehlardi, 1964;  Patten, 1962; Hurlbert, 1971). These techniques are discussed and critiqued in the works of Margalef (1974), Pielou (1975), and Legendre and Legendre (1979). The main deficiency of these indices seems to be that similar values are offered for situations that may be very different.

The structure of populations can be investigated by their distributions of variety and abundance. Applying the log-normal model of Preston (1948) to the analysis of populations of benthic Diatoms, Patrick et al. (1954) proposed to use the flattening of the Gaussian curve, a function of the number of species and the standard deviation, as the indicator of water quality. Without consideration for some distributions resulting in different curves, the examination of numerous readings shows that, according to the taxons in question and to sampling procedures and types of environments, highly divergent structures are obtained, and they are well suited for the adjustment of the most diverse functions (binomial, positive and negative, logarithmic, exponential, linear) when multiple peaks do not appear. However, modifications that involve the distributions may constitute a useful contribution to the formulation of interpretative hypotheses (Amanieu et al., 1981).

The findings need to be compared with biological reference organisms. Whenever the environments under study have been previously investigated with exhaustive definition of the biological organizations in abstract mathematical terms, new findings can be analysed with the initial structure used as a reference (i.e., biotypology) (Verneaux, 1973). Whether a water flow is considered in isolation or as a hydrographic network, the replacement of one set of species with another throughout a water flow system is plotted into the first two axes of an AFC (Hill, 1974; Orlóci, 1975; Benzecri et al., 1973) by an ecological continuum of species in the shape of a U ("Guttman effect"), to which other specific structure can be compared).

Within a biogeographic area of interest, the essential problem is loss of reference, or loss of the assurance that a sufficient number of control (sampling) stations (which might have degraded to varying degrees) exist for the establishment of a minimum reference structure. Such frameworks were established for 12 water flows through the Doubs hydrographic network on the basis of findings made between 1969 and 1972. All subsequent modifications are interpreted in relation to this structure.

The species of the organisms are not determined, and, to assess the water quality, the water-sediment interface (i.e., a wholistic aquatic environment) is characterized with the aid of simple formulas or standard tables, taking into account the nature of the taxons and the taxonomic variety. Since these different methods have been synthesized (Hellawell, 1986), two methods will be described.

5.2 ANALYSIS OF BENTHIC COMMUNITIES AND THE QUALITY OF WATERWAYS 

Based on simplified analyses of the macrobenthos, biotic indices have been designed to allow numerous operators (taxonomic non-specialists given adequate training) to establish a balance and draw a large-scale map of the general status from a national hydrographic network (Verneaux and Tuffery, 1967). A notation table offers a direct index of the sampling station (0-10) as a function of the nature and variety of the fauna in relation to three benthic samples of 1/10 m² in running water (lotic facies) and three benthic samples in calm water (lentic facies). Despite its simplicity and its wide use in Europe in forms adapted to particular aspects of the networks, this method has low sensitivity. By contrast, the maximum index class (Ib = 9±1) represents suboptimal quality, explaining its use as a reference for, rather than an index of, the absence of pronounced degradation. Thus, the index is not a trend indicator.

Attempts to improve sensitivity and precision (Verneaux et al., 1976) have revealed that these objectives can be achieved for jurassic-type pre-mountain water streams; however, limitations then become enhanced. For instance, the relative quality of the systems is underestimated with little slope or warmer systems that are naturally less well suited to develop such organisms as Plecopters or Heptageniidae. Nevertheless, these tests have contributed to the definition of a more exact sampling protocol.

In parallel, Chandler (1970) proposed a similar method, relying on a score of  0-100 obtained from a table combining the nature and abundance of the fauna (five estimated classes) with specific identification of most indicator groups. From practical experience, the family constitutes the basic unit, and the abundance criteria are discarded (Armitage et al., 1983; Hellawell, 1986). Similar tests (experimental protocol Cb2) have shown that the continual presence of numerous families is inadequate for them to be selected as indicator taxons (Verneaux et al., 1981). These processes led to the proposal of a simplified protocol (Verneaux et al., 1982). The analysis of large amounts of data defined the following characteristics:

1. the minimum practical size of a sample as 1/20 m²; 

2.  the required and sufficient number of readings as 8;

3.  the precise sampling protocol that circumscribes the mosaic of habitats;

4. the listing of the taxons used (135, of which 38 served as indicators based on frequency and fidelity);and

5.  the table of standard index values (0-20) according to the nature and taxonomic variety of the benthic fauna collected by the proposed protocol.

The classification of indicators is accomplished using two series of factor analyses of the distribution of families in sampling stations with little or no degradation, and then with the Rhithron (a stream with predominantly Cyprinides) altered in various ways (Benzecri et al., 1973). The classification of the taxons according to their relative general tolerance was performed in a manner similar to that for fish (Verneaux, 1981). This relative ranking differs considerably from those hierarchies of the "score systems" (Armitage et al., 1983), in which the positions of some taxons seem to be the result of the fact that several readings were made in environments that had already been degraded considerably (i.e., "loss of reference").

5.3 BIOLOGICAL GENERAL QUALITY INDEX

This standard describes a method to determine the standardized global biological index published by Verneaux et al. (1982), which was promulgated under the name IBGN by AFNOR (1992). IBGN assesses the biogenic tendency of a waterstream station from the results of a macrofauna analysis that is considered to produce a comprehensive expression of the general quality of a waterstream station under otherwise constant conditions. When applied to an isolated site, the method determines the global biological quality within a range of parameters, whose maximum value corresponds to the optimal combination of set variety with the nature of the benthic macrofauna. When applied comparatively (e.g., upstream and downstream from a discharge), the method evaluates the effect of a disturbance on the receiving environment within the limits of its sensitivity.

The benthic macrofauna samples (diameter > 500 µm) are taken at each station, according to a sampling protocol that takes into account the different types of flexible net (diameter = 500 mm), using: retractable panels, removable base (1/20 m²), sampler "Surber" position, rack, metal frame, cutting blade, sampler "Shrimpnet" position, and habitats defined by the support structure and the flow speed.

Table 5.1. IBGN values according to the nature and the taxonomic variety of the macrofauna

Variety class ®		14	13	12	11	10	9	8	7	6	5	4	3	2	1
	åt=	>	49	44	40	36	32	28	24	20	16	12	9	6	3
Taxa	¯GI¯	50	45	41	37	33	29	25	21	17	13	10	7	4	1
Chloroperlidae
Perlidae	9	20	20	20	19	18	17	16	15	14	13	12	11	10	9
Perlodidae
Taeniopterygidae
Capniidae
Brachycentridae	8	20	20	19	18	17	16	15	14	13	12	11	10	9	8
Odontoceridae
Philopotamidae
Leuctridae
Gloososomatidae	7	20	19	18	17	16	15	14	13	12	11	10	9	8	7
Beraeidae
Goeridae
Leptophlebiidae
Nemouridae
Lepidostomatidae	6	19	18	17	16	15	14	13	121	11	10	9	8	7	6
Sericostomatidae
Ephemeridae
Hydroptilidae
Heptageniidae	5	18	17	16	15	14	13	12	11	10	9	8	7	6	5
Polymitarcidae
Potamanthidae
Leptoceridae
Polycentropodidae	4	17	16	15	14	13	12	11	10	9	8	7	6	5	4
Psychomyidae
Rhyacophilidae
Limnephilidaea
Hydropsychidae	3	16	15	14	13	12	11	10	9	8	7	6	5	4	3
Ephemerellidaea
Aphelocheiridae
Baetidaea
Caenidaea	2	15	14	13	12	11	10	9	8	7	6	5	4	3	2
Elmidaea
Gammaridaea
Mollusques
Chironomidaea
Asellidae	1	14	13	12	11	10	9	8	7	6	5	4	3	2	1
Achetes
Oligochetesa
aTaxa represented by at least 10 individuals, the others by at least 3 individuals.

A representative sample consists of eight samplings. The sorting and identification of the sampled taxons are performed to determine the taxonomic variety of the sample and its fauna indicator group. These two criteria allow a statement on the biogenic quality of the station using an index established with the help of Table 5.1.

The habitats located in calm water (lentic facies) are prospected with the help of a shrimper, using traction over 50 cm, or, by default, by back-and-forth movement over an equivalent surface (the additional surface compared with that of the Surber compensates for the loss of a portion of the individuals).

A ring-shaped illumination lens is used for the sorting in a binocular lens (stereoscopic microscope G £ 50) issued for the identification of the taxons. 

5.3.1 SAMPLING 

The IBGN is determined per station, which is defined as the segment of a water stream whose length is virtually equal to 10 times the width of the stream bed at the time of the sampling. The detection of disturbance is facilitated in extreme situations at the moment of low waters (minimum flow, maximum temperature) or during critical periods (discharges and seasonal human activities). The samples must be taken during a period of stabilized flow for at least 10 days. 

For each station, the benthic fauna sample consists of eight samplings of 1/20 m² each (volume sampled for the loose substrates: 0.5-1 L) performed separately in eight different habitats selected from among the combinations defined for each station. The eight samples together must provide a representative picture of the mosaic of habitats of the station. Each habitat is characterized by a support-speed set. 

In the absence of certain habitats, the samples can be obtained according to the strata. Each stratum, sampled separately, constitutes a complete sampling. For example, in the absence of a lentic habitat in a mountain stream, the surface of the grid is sampled; then, separately, the inside surface and the underlying substrate are sampled a second time. 

5.3.2 SAMPLING PROTOCOL 

The samples are taken with the help of the sampling devices. Each sample is immediately fixed on site by the addition of a 10 percent (v/v) formaldehyde solution, placed in a plastic bag, transported packed in ice, and then stored in the refrigerator. The surface speeds are estimated for each habitat. 

The support categories (S) are studied in the order of the succession (from 9-0). This table layout recommends that the habitats most friendly to fauna should be prospected first. For each support category , the sampling is made in the speed class where the support is best represented. The speed classes (5 to 1) are listed in decreasing order.

When a monotonous station (straightened course, silted bed, or canal) does not include the eight different types of support, the number of samplings is extended to eight through samplings taken of the dominant support. The percentage of coverage of each habitat (SV set) can be estimated from the following:

5.3.3 BIOLOGICAL ANALYSIS

5.3.3.1 List of taxons

The selected taxonomic unit is the family with the exception of some fauna groups (branches or classes) with little representation or where the taxonomic analysis unveiled specializations. The repertory includes 138 taxons which may be included in the overall variety (åt), of which 38 are indicator taxons that form the nine indicator fauna groups (GI in Table 5.1). The Mollusks and the Achetes are also listed.

The collected organisms are sorted and determined according to larval, nymph or adult stage, provided that this latter stage is aquatic. Empty sheaths or shells are not taken into account.

To facilitate the interpretation of the results, the samplings should not be mixed and the fauna list of the station should be prepared by indicating the distribution of the taxons in the eight habitats.

5.3.3.2 Determination of the global biological index (IBGN)

The IBGN is determined on the basis of the information in Table 5.1, which lists the nine indicator fauna groups (GI) and the 14 taxonomic variety classes. The following must be determined sequentially:

1. The taxonomic variety of the sample (åt), equal to the total number of taxons collected even if they are represented only by a single individual. This number is compared to the classes included in Table 5.1.

2. Indicator fauna class (GI) considering only the indicator taxa represented in the samples by at least three individuals or 10 individuals depending on the taxons. GI is determined by prospecting the taxa listed in Table 5.1 from top to bottom (GI 9 to GI 1) and halting the examination at the first significant presence (n > 3 individuals or > 10 individuals) of a taxon in the list on the ordinate of  Table 5.1. IBGN can be derived from the åt and GI values. For example:

GI = 8, åt = 33 >>> IBGN = 17
GI = 5, åt = 30 >>> IBGN = 13
GI =3, åt = 14 >>> IBGN = 7

Because of the significant absence of indicator taxa (3 or 10 individuals), the IBGN score equals 0.

5.3.3.3 Test report

For each station, the test report must include the date; the exact geographic location (Lambert coordinates); the ecological type, if known; the distance from the source; the altitude; the length of the wet bed at the time of the sampling; the water temperature; the nature of the support and the flow rate pertaining to the eight samplings performed for the station (SV set) with an indication of the dominant habitat or, preferably, the approximate collected classes; the list of sampled taxons with their distribution over the eight habitats, with a possible indication of their relative abundance; the taxonomic variety of the sample (åt); the indicator fauna group (sequence number of GI); and the standardized global biological index (IBGN). 

For cartographic representation of the results, each segment of the stream can be assigned one of the following colours, depending on the value of IBGN:

    
The IBG variations throughout a segment or a water stream in its entirety can be plotted in a graph where the distance from the source is the abscissa and the index values are the ordinate.

5.3.4 EXAMPLE

An illustration has been prepared by the author of the Pont de Fleurey on the Dessoubre stream (affluent of the Doubs) at Jura Massif in France. The Dessoubre, a mesorhithron stream with the association Tadpole-Trout-Grayling-Minnow-Loach, presents a habitat diversity and a water quality corresponding to its ecology type. The start of a trend manifested by the most stenoecious fauna to leave the habitats of the lenitic facies should be noted. In 1981, this station was one of the stations used for the sampling of the range of index values in search of optimal values.

5.4 DETERMINATION OF THE GENERAL BIOLOGICAL QUALITY OF LAKES

5.4.1 BASIS

Although benthic macrofauna, because of its variety and abundance, constituted the material of choice for the establishment of practical biological methods for the assessment of the general status of streams, at present no similar methods can be applied to still-water systems, although Limnology emerged with lacustrine investigations. This can be explained by several factors.

5.4.1.1 The nature of the organisms

Whereas benthos constitutes the core of the organism of streams, lakes are, however, characterized by microscopic planktonic organisms (phytoplankton and zooplankton) that have very brief developmental cycles, and present significant spatial and time-related variations. Thus, this material is difficult to use to determine the significance to the entire system. Therefore, employment of the zoomacrobenthos, whose integration power is much greater, has been projected. However, a portion of the species only colonizes in the littoral zones whose habitat mosaics prove to be very different from one lacustrine basin to the next. Brinkhurst (1974) shows the general phenomenon of a decrease in fauna (here, generic) variety with depth.

The main components of the macrobenthos capable of colonizing lacustrine sediments up to depths of 250-300 m belong to the "difficult groups," such as Mollusks, more specifically Pisidies, the Oligochetes (Brinkhurst, 1974), and especially the Chironomide dipters for which the analysis of a great number of species associations has offered for a long time the basis for lacustrine biotypology with the work of the great forerunners such as Thienemann (1920-1931) or Brundin in the late 1940s. The studies of comparative biocenotics, performed with this material, can be conducted only by true specialists, which unfortunately is increasingly less the case.

5.4.1.2 Interpretation ambiguities

While simplified methods are proposed based on the single phytoplankton or on the basis of the species of a single faunistic class, order, or family, the challenge is in uncovering the meaning of the analytical findings, especially when a global qualitative perspective requires considerable integration of widely diverse information. Therefore, the indices proposed by Lafont et al. (1991) by a simplified analysis of the Oligochete populations objectively express the biological quality of the water-sediment interface; Saether (1979) considers the communities of Chironomide dipters of the deep zone to be the indicators of the "quality of the waters," and links his results to a "trophic level" relative to the system, pollutions, and dysfunctions that are included and not differentiated.

The application of this method to the lakes of the Jura approximates "eutrophic" effects; the phytoplanktonic biomasses mark a varied range of partial primary productions, and physicochemical analyses of the sediment reveal a great variety of sedimentological types. Yet, equally apparent is the absence of relationships between the global sedimentary composition (% carbonates and MO), the primary production, and the depths of the basins.

Two main conclusions can be drawn from these comparisons:

1. The need to differentiate the trophic level from the nutritive substance content which express a potential and the "trophic status" of a system, by expressing a functioning or dysfunctioning mode whose sediments and fauna supply images for which interpretations must be found.

2. The usefulness to have available a practical biological method for the assessment of the general biogenic aptitude of a lake, which would offer sufficient synthetic significance.

Besides the recent proposals of Lafont et al. (1991) and Mouthon 1993) which propose, respectively, simple assessment methods for the biological quality of lacustine systems on the basis of Oligochetes and Mollusks, all other proposals tend to define different "trophic levels," but not the resulting biogenic aptitudes.

5.4.1.3 IBL: A method to evaluate the biogenic quality of lakes

An experimental classification of lacustrine systems based on a comparative analysis of the benthic fauna has been proposed. This method is called the Lacustrine Biogenic Index (IBL; Verneaux, 1993), and includes a comparative sampling protocol, original biologic descriptors, and a standard table that allows the definition of the biological type and the biogenic index of a lake.

Sampling

Only fine sediment over 5 cm is collected using a modified Ekman bucket with the addition of lateral ballast as well as a penetration limiter. Coarse substrates and hydrophytes are avoided, as are certain sites such as beaches, harbours or substrate enclosures. Two samplings are performed each station to form a station sample; and two depths, to which two isobaths correspond, are prospected (Zo at 2-2.5 m; and Zf at ³/₄ Z maximum relative depth). The number of stations per isobath is proportional to the length of each isobath, and should be determined using the following factors:

 
 where L is the length of the isobath in question, expressed in km.

The stations are distributed regularly (virtually in an equidistant manner) over each isobath. The samples are taken during a single sampling trip during an isothermia period which follows thawing and springtime circulation. Depending on the altitude, in the Jura lakes the expeditions took place in April or in May. Each sample (consisting of two samplings) is filtered through a conic net with a mesh width of 250 µm; then 5 percent formaldehyde solution is added and the sample is then placed in a plastic bag with the air removed. The samples are transported on ice, and stored in a refrigerator.

Sorting and determination of the taxa

The samples are analysed separately. The macroinvertebrates are identified but not counted out. The selected taxonomic unit is genus except for the Oligochetes, Nematodes, Hydracarians, and Ceratopogonidae. A listing shows the fauna data and the frequency of each taxon is expressed in percentage of occurrence in relation to the no and nf counts of the stations (or the samples per isobath).

Descriptors employed

The quality coefficient of the fauna of the fine sediment is determined where the found taxa are classified in the decreasing order of sensitivity to the physicochemical quality of the water-sediment interface. Only taxon indicators are selected whose frequency is at least equal to 50 percent of the number of samples no taken at depth Zo. The descriptors include: vo = fauna variety ( generic) at depth Zo, qo = quality of the fauna at depth Zo, and df = bathymetric distribution coefficient at depth Zf

where k = 0.047 vo + 1, F = relative faunistic deficit index, and F = ?df ^. qo. For example, if vo = 38 and F = 0.77 for type B₄, then biogenic index/20 = 15; and if vo = 23 and F = 0.38 for type B₃ then biogenic index/20 = 08.

Qualitative levels include eubiotic lake, eumerobiotic lake, merobiotic lake, merodysbiotic lake, and dysbiotic lake; and the quantitative levels include oligobiotic lake, oligomesobiotic lake, mesobiotic lake, mesopolybiotic lake, and polybiotic lake. The combinations of the two series of information is used to define the type of lake as either euoligobiotic or mesomerobiotic or dyspolybiotic lake.

Interpretation

The variety of endobenthic fauna sampled in the littoral zone beyond the river zone (Zo = -2, -2.5 m) constitutes a good indication of the biogenic potential of the system in relation to consumer organisms. The fauna distribution index (F) which takes into account the nature of the fauna (qo) and the significance of the corrected relative fauna deficit (df) expresses the operating mode of the system. The index (IBL) constitutes a mark of the resulting biogenic aptitude trend that can assume the same values in the cases of different figures. For example, an oligotrophic lake that is both eubiotic and oligobiotic (type Al, IBL = 10) with highly oxygenated water but with few minerals, and a hypertrophic lake (type D4, IBL = 10) of moderate depth and very rich in mineral salts and deoxygenated as of moderate depth have the same biogenic index of 10. The determination of the biological type of the lake allows an interpretation of the resulting biogenic index. The general quality of the water, corresponding to categories A, B, C, D, E, can be expressed by five colours ranging from blue to red to indicate decreasing quality.

5.5 REFERENCES

AFNOR (1992) Détermination de l'indice biologique global normalisé (IBGN) [Determination of the Standardized Global Biological Index (IBGN)]. Report No. NF T 90350. AFNOR, Paris, 9 pp.

Amanieu, M., Gonzales, I.L., and Guelorget, O. (1981) Critères de choix d'un modèle de distribution d'abondance. Application à des communautés animales en Ecologie benthique [Selection criteria for an abundance distribution model. Application to the animal communities in benthic ecology]. Oecol. Gen. 2, 265-286.

Armitage, R.D., Mass, D., Wright, J.F., and Furse, M. T. (1983) The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running-water sites. Water Res. 17, 333-347.

Bartsch, A.F., and Ingram, W.M. (1966) Biological analysis of water pollution in North America. Verh. Int. Verein. Limnol. 16, 786-800.

Benzecri, J.P., et al. (1973) L 'Analyse des Données. I: La Taxinomie. L 'Analyse des Correspondances. [Data Analysis. I: Taxonomy. II: Analysis of Correlations] Dunod, Paris, 615 pp and 619 pp.

Brinkhurst, R.O. (1974) Factors mediating interspecific aggregation of tubificid oligochaetes. J. Fish Res. Bd. Can. 31, 460.

Chandler, J.R. (1970) A biological approach to water quality management. Water Pollut. Control 69, 415-422.

Descy, J.P., and Coste, M. (1991) A test of methods for assessing water quality based on diatoms. Verh. Int. Verein. Limnol. 24, 2112-2116.

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