Freshwater Algae: Identification and Use as Bioindicators

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