Freshwater Algae: Identification and Use as Bioindicators

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122 3 ALGAE AS BIOINDICATORSallow adequate recruitment and colonization of periphyticdiatoms before identifying and enumeratingthe assemblages.Specimen preparationThe diatoms are then cleaned by acid digestion, andan aliquot of cleaned sample is then mounted on amicroscope slide in a suitable high refractive indexmounting medium such as Naphrax. Canada balsamshould not be used as it does not have a high enoughrefractive index to allow resolution of the markingson the diatom frustule.Cleaning diatoms and mounting them in Naphraxmeans that identification and counts are made frompermanent prepared slides, rather than from volumeor sedimentation chambers (Section 2.5.2). It is normalto use a ×10 eyepiece and a ×100 oil immersionobjective lens on the microscope for this purpose. Beforecounting it is always desirable to scan the slideat a ×200 or ×400 magnification to determine whichare the dominant species.Numerical analysisDiatoms on the slide are identified to either genusor species level and a total of 100–500+ counted,depending on the requirements of the analysis beingused. Once the counting has been completed and theresults recorded in a standardized format, the datamay be processed.In recent times there has developed a dual approachto analysis of periphytic diatoms in relation to waterquality: evaluation of the entire diatom community (Section3.4.3), often involving multivariate analysis determination of numerical indices based on keybioindicator species (Section 3.4.4).Individual studies have either used these approachesin combination (e.g. Dela-Cruz et al., 2006)or separately.3.4.3 Evaluation of the diatom communityThe term ‘diatom community’ refers to all the diatomspecies present within an environmental sample.Species counts can either be expressed directly(number of organisms per unit area of substratum) oras a proportion of the total count. Evaluation of thediatom community in relation to water quality mayeither involve analysis based on main species, or amore complex statistical approach using multivariatetechniques.Main speciesVarious authors have considered different levels ofwater quality in terms of distinctive diatom assemblages.Round (1993) proposed the following classification,based on results from a range of British rivers.In this assessment five major zones (categories) ofincreasing pollution (inorganic and organic solublenutrients) were described:Zone 1: Clean water in the uppermost reachesof a river (low pH) Here the dominant specieswere the small Eunotia exigua and Achnanthes microcephala,both of which attached strongly to stonesurfaces.Zone 2: Richer in nutrients and a little higherpH (around 5.6–7.1) This zone was dominatedby Hannaea arcus, Fragilaria capucina var lanceolataand Achnanthes minutissima. Tabellaria flocculosaand Peronia fibula were also common in someinstances.Zone 3: Nutrient rich with a higher pH(6.5–7.3) Dominant diatoms included Achnanthesminutissima with Cymbella minuta in the middlereaches and Cocconeis placetula, Reimeria sinuateand Amphora pediculus in the lower reaches.Zone 4: Eutrophic but flora restricted throughother inputs Fewer sites in this category werefound and more work was considered necessary toprecisely typify its flora. However the major diatomassociated with the decline in water quality was
3.4 RIVERS 123Gomphonema parvulum together with the absence ofspecies in the Amphora, Cocconeis, Reimeria group.Zone 5: Severely polluted sites, where the diatomflora is very restricted As with Zone 4 notmany sites in this category have been investigated andmore work is needed. The flora was frequently dominatedby small species of Navicula (e.g. N. atomusand N. pelliculosa). Detailed identification of thesesmall species can be difficult, especially if only a lightmicroscope is available. Round (1993) concluded thatidentification to species level for these was unnecessaryand merely to record their presence in largenumbers is enough. If the pollution is not extremethere may be associated species present such as Gomphonemaparvulum, Amphora veneta and Naviculaaccomoda. Other pollution-tolerant species includeNavicula goeppertiana and Gomphonema augur.Round’s diatom assessment for British rivers iscompared with those of other analysts in Table 3.9 forcategories of moderate and severe nutrient pollution.Although there is substantial similarity in terms ofspecies composition, differences do occur – to someextent reflecting differences in river sizes and geographicallocation. These differences highlight theproblems involved in attempting to establish standardspecies listings for water quality evaluation.Multivariate analysisMultivariate analysis can be used to compare diatomassemblages and to make an objective assessment ofspecies groupings in relation to environmental parameters.Soininen et al. (2004) analysed benthic diatomcommunities in approximately 200 Finnish streamsites to determine the major environmental correlatesin boreal running waters. Multivariate statistical analysiswas used to define: diatom assemblage types key indicator species that differentiated betweenthe various assemblage groups relative contribution of local environmental factorsand broader geographical parameters in determiningdiatom community structure.The results showed that the ∼200 sites sampledcould be resolved into major groupings which correspondedto distinctive ecoregions (Table 3.10). Environmentalparameters characterizing these groupsrelated to water quality (conductivity, total P concentration,water humic content), local hydrology andregional factors. The impact of local hydrology isshown by the presence of planktonic diatoms in benthicsamples where rivers are connecting lakes (GroupD) or have numerous ponds and lakes within the watercourses(Group J). Group H had a very distinctdiatom flora characteristic of this extreme subarcticregion.These authors concluded that although analysisof diatom communities provides a useful indicationof water quality, hydrology and regional factorsmust also be taken into account. The different diatomcommunities identified in this study comparedwell with those documented for stream macroinvertabrates,suggesting that bioassessment of borealwaters in Finland would benefit from integrated monitoringof these two taxonomic groups.3.4.4 Human impacts and diatom indicesDiatom indices have been widely used in assessingwater quality and in monitoring human impacts onfreshwater systems. The latter can be considered eitherin terms of change from an original state, or inrelation to specific human effects.Change from a ‘natural’ communityThe use of benthic diatom populations to assessanthropogenic impacts on water quality impliescomparison of current conditions to a natural originalcommunity, with deviation from this due to humanactivities such as eutrophication, toxic pollutionand changes in hydrology. This concept is implicitin some major research programmes, such as theEuropean Council Water Framework Directive(WFD: European Union, 2000) where the baselineis referred to as ‘reference conditions.’ In the caseof lakes (Section 3.2.2), reference conditions canbe determined by on-site extrapolation into the past
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: 3.4 RIVERS 1213.4 RiversUntil recen
Page 27 and 28: 3.4 RIVERS 125Table 3.10 Benthic Di
Page 29 and 30: 3.4 RIVERS 127Palmer’s Index (Pal
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

Freshwater Algae: Identification and Use as Bioindicators

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