Freshwater Algae: Identification and Use as Bioindicators

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126 3 ALGAE AS BIOINDICATORS(undisturbed) conditions and relating to five differentecoregions (i.e. river types with similar altitude rangeand geological characteristics). The six other communitieswere typical of rivers that had been disturbedby human activity. Although natural variability occurredwithin individual ecoregions (similar to thatnoted in Finnish rivers, see above), this was greatlyexceeded by the effects of pollution at the differentsampling sites. The study aimed to identify diatomindicators for different types of anthropogenic disturbanceby comparing benthic diatom communities innatural and disturbed sites.Use of bioindicatorsAn alternative approach to analysing human impact interms of general disturbance is to use diatom indiceswith indicator species that directly reflect particularenvironmental changes resulting from human activities.Individual species can be numerically weightedto reflect their degree of environmental specificity.Bioindicators may relate to single parameters suchas total-P (trophic diatom index – TDI; e.g. Hofman,1996) or reflect more general aspects of water quality,combining organic loading and inorganic nutrientconcentration (IPS: index of pollution sensitivity,GDI: generic diatom index). Diatom indicator listsfor other variables such as salinity, trophy, nitrogenmetabolism types, pH and Oxygen requirements havealso been published (van Dam et al., 1994).3.4.5 Calculation of diatom indicesAs with lake phytoplankton indices (Section 3.2.3)the benefit of river diatom indices is that they reducecomplex biological communities (involving a rangeof species) to a single numerical value. This providesa very simple quantitative evaluation which can be appreciatedand used by biologists and non-biologistsalike. The disadvantage of an index is that potentiallyuseful information may be lost as counts of individualspecies are brought together and combinedinto a general evaluation. Diatom indices, based onbioindicator algae, are either single or multiple taxonassessments.Single taxon assessmentIndices based on a single species represent a verysimple environmental approach. Kothe’s Index. This is referred to as the ‘speciesdeficiency index’ (F) and relates the number ofcells (N 1 ) of a particular key species at site 1 to thenumber (N x ) at site x, where:F = N 1 − N x× 100 (3.2)N 1This very simple index is assessing environmental impacton a single species. It assumes that site 1 is thetypical one for that river and that changes in the numbersof the selected species will occur at other sites(for example a decline with downstream pollution).Multiple taxon indicesMost diatom indices are based on multiple taxa (generaor species). They are determined either in termsof the presence/absence of key indicator species (e.g.Palmer’s index) or are based on the weighted averageequation of Zelinka and Marvan (1961):n∑a j s j v jj=1Index =(3.3)n∑a j v jj=1Where:a j = is the relative abundance (proportion) ofspecies j in the samples j = the pollution sensitivity of species jv j = the indicator value of species jn = is the number of species counted in the sample.Different indices adapt this equation in differentways, and the performance of a particular index dependson which taxa are used, the number of taxa andthe values given for the constants s and v for eachtaxon. The values of individual indices based on thisequation vary from 1 to a maximum value equal to thehighest value of s. Commonly used indices includethe following.
3.4 RIVERS 127Palmer’s Index (Palmer, 1969) Palmer’s index,applied to river diatoms, is derived from an extensiveliterature survey and is based on the occurrence of20 common diatom species, listing them accordingto their tolerance to organic pollution. The sequence,from least polluted to most polluted waters, includes:Fragilaria capucina → Achnanthes minutissima →Cocconeis placentula → Diatoma vulgare →Surirella ovata → Gomphonema parvulum →Synedra ulna → Nitzschia palea.As with the more general version of Palmer’s index(Section 3.2.3, Table 3.5) diatom species are rated ona scale 1 to 5 (intolerant to tolerant) and the index iscalculated by summing up the scores of all relevanttaxa present within the sample. Values >20 indicatehigh levels of organic pollution.Descy’s Index A frequently used index (Descy,1979). Values of s j range from 1 to 5 and v j from1 to 3 (equation 3.2) giving index values from 1 to5. These can then be related to water quality (Table3.12: Descy, 1979).Example The example of Descy Index (I d ) calculationshown in Table 3.13 is taken from the RiverSemois in Belgium (Round, 1993). The part of theriver investigated was heavily polluted with domesticsewage and contained the key diatom speciesNavicula accomoda, Nitzschia palea, Achnantheslanceolata and Gomphonema parvulum.TheI d valueobtained (1.0) signals heavy pollution, in agreementwith the observed sewage contamination.Some workers have reported that this index tendsto give high values and thus underestimates heavypollution (Leclercq and Maquet, 1987).CEE Index: Descy and Coste, 1991 This indexof general pollution is based on a total of 223 diatomtaxa. The index ranges from 0–10 (polluted to nonpollutedwater).GDI Index (generic diatom index): Coste andAyphassorho, 1991 An index of organic and inorganicnutrient pollution, based on 44 diatom genera.Values range from 1–5 (polluted to non-polluted water).IDAP Index: Prygiel et al., 1996 Index basedon a combination of 45 genera and 91 diatom species.Values range from 1–5 (polluted to non-polluted water).IPS Index (specific pollution index): Coste, inCEMAGREF, 1982 This index for pollution sensitivityis based on organic load and nutrient concentrations.Values range from 1–5 (polluted to nonpollutedwater).TDI (trophic diatom index): Kelly and Whitton,1995 In its original formulation, this indexwas based on a suite of 86 diatom taxa selectedfor their indicator value (tolerance to inorganicnutrients) and ease of identification. The index wasdetermined as the weighted mean sensitivity (WMS:equation 3.3), with pollution sensitivity values (s j )from 1–5, and indicator values (v j ) from 1–3. TheTable 3.12 Diatom Index and River Water Quality* (Descy 1979)Diatom Index (I d )River Water Quality>4.5 No pollution, the best biological quality4.0–4.5 Very slight pollution, near normal communities3.0–4.0 Toxic pollution at moderate level or nutrient enrichment (eutrophication).Community changes apparent and sensitive species disappearing2.0–3.0 Heavy pollution. Only pollution resistant species abundant or dominant. Sensitivespecies severely reduced1.0–2.0 Severe pollution. Only a few tolerant species survive. Very reduced diversity*Water quality considered in relation to toxic pollution (e.g. heavy metal content) or nutrient enrichment (eutrophication).
Page 1 and 2: 3Algae as BioindicatorsBiological i
Page 3 and 4: 3.1 BIOINDICATORS AND WATER QUALITY
Page 5 and 6: Table 3.3 Lake Trophic Status: Phyt
Page 8 and 9: 106 3 ALGAE AS BIOINDICATORSDirecti
Page 11 and 12: 3.2 LAKES 109sites (Fig. 3.3 A, B,
Page 13 and 14: 3.2 LAKES 111Phytoplankton net prod
Page 15 and 16: 3.2 LAKES 113and hypertrophic (Pedi
Page 17 and 18: 3.2 LAKES 115Table 3.5 Organic Poll
Page 19 and 20: 3.2 LAKES 117Table 3.7 Bioindicator
Page 21 and 22: 3.3 WETLANDS 119therefore directly
Page 23 and 24: 3.4 RIVERS 1213.4 RiversUntil recen
Page 25 and 26: 3.4 RIVERS 123Gomphonema parvulum t
Page 27: 3.4 RIVERS 125Table 3.10 Benthic Di
Page 31 and 32: 3.4 RIVERS 129any irregular conclus
Page 33 and 34: 3.4 RIVERS 131Case study 3.3Compari
Page 35 and 36: individual analysts can be measured
Page 37 and 38: 3.5 ESTUARIES 135potential role of

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