Freshwater Algae: Identification and Use as Bioindicators

3.4 RIVERS 131Case study 3.3Comparisons of diatom indices with other bioindices1. Use of different bioindicators for assessing water quality in Greek Rivers. Iliopoulou-Georgudaki et al.(2003). This study was carried out on river sites with water quality ranging from very poor to very goodand used bioindices based on diatoms (see previously) plus four other groups of organisms. Sampling offish and macrophyte vegetation gave only limited environmental assessment, with macrophytes in particularbeing incapable of a graded response to varying degrees and kinds of stress. Macroinvertebrates and diatomsrecorded the full range of pollution conditions, but indices based on macroinvertebrates were consideredto be the most sensitive – responding more readily than diatoms to transient changes to environmentalstate.2. Selected rivers in England and Scotland. Kelly et al. (1995) found that their diatom indices were significantlycorrelated with two benthic macroinvertebrate indices – BMWP (Biological Monitoring Working Partyscores) and ASPT (Average Score Per Taxon), both used routinely for water quality monitoring in theUnited Kingdom.3. Metal pollution in lowland river. Comparison of macroinvertebrates and diatoms as bioindicators by DeJonge et al. (2008) showed that diatom communities most closely reflected changes in metal concentration,with distinct taxa being associated with low (e.g. Tabellaria flocculosa) moderate (Nitzschia palea) andhigh (Eolimna minima) zinc levels. In contrast to diatoms, macroinvertebrate communities most closelyfollowed physical-chemical variables and the effects of metal pollution. The combined use of both groupsfor biomonitoring was considered to be more appropriate than separate use of either.Comparison to other bioindicator organismsAlthough routine monitoring of all but the deepestrivers has been based for many years on macroinvertebrates(e.g. De Pauw and Hawkes, 1993), a rangeof other bioindicator organisms is available. Theseinclude diatoms, other algae, fish, aquatic and riparianmacrophytes. Various authors have made simultaneouscomparisons of some or all of these toassess the relative usefulness of particular groupsof organisms – with particular emphasis on diatomsand macroinvertebrates. In the examples below (continuedfrom the previous section), diatom communitiesshowed comparable changes to macroinvertebratesin relation to water quality, but (with theexception of the IPS index) were generally lesssensitive.Response to changes in water qualityOne important aspect of algal bioindicators is thatthey are able to detect a rapid change in water quality.Because of their shorter generation time, diatomcommunities are potentially able to respond morerapidly than other bioindicator groups (e.g. macroinvertebrates,fish), which integrate water quality overlonger time frames.The time sequence of diatom change can be investigatedby transferring diatom biofilms from pollutedto non-polluted waters, and record: how different diatom indices compare over fixedtime periods the time needed for different indices to indicate asignificant change in water quality.