Freshwater Algae: Identification and Use as Bioindicators

3.4 RIVERS 129any irregular conclusions that might have arisenfrom use of a single index. Different indices havebeen compared for assessment of water qualitywithin different river systems, where there is variationin trophic status (inorganic nutrients – particularlyphosphates and nitrates) and a range ofother factors such as salinity, organic pollution(related to biological oxygen demand – BOD)and industrial contamination (metal pollution andacidity).A summary of studies is shown in Table 3.14, withsome detailed examples below. In general, differentdiatom indices give broadly comparable results. Variousstudies (e.g. Case studies 3 and 4 below) do indicate,however, that the IPS index is particularly usefulfor monitoring general changes in water quality. Thisindex best reflects the combined effects of eutrophication,organic pollution and elevated salt concentrations,since it usually integrates all diatom speciesrecorded within the samples.Case study 3.2 Field studies using different diatom indices (Table 3.14)1. Greek rivers: variation in trophic status, organic and inorganic chemical pollutants. Iliopoulou-Georgudakiet al. (2003) used IPS, Descy 1979 and CEE indices as they were considered more representative of environmentalconditions. The indices gave exactly comparable results.2. Selected rivers in England and Scotland. Ranging from nutrient-poor upland streams to lowland rivers subjectto varied eutrophication and contamination with organic pollutants, pumped minewater, heavy metals andagricultural run-off.Kelly et al. (1995) assessed water quality using four indices based on diatom genera (GDI) and species (SPI,TDI-P and TDI-NP). The high correlation between indices across the different river sites suggested that anycould be used individually for routine monitoring and that diatom recognition to genus rather than specieslevel was adequate.3. Metal pollution in lowland river. DeJongeet al. (2008) assessed diatom populations in relation to metal(ZN) contamination and related physicochemical variables. The IPS index best reflected changes in waterquality (pH, conductivity, oxygen concentration, inorganic nutrients), and was the only diatom index thatindicated a significant difference between control and contaminated sites.4. Rivers of southern Poland: variation in trophic status and organic pollution. Kwandrans et al. (1998) usedthe suite of 8 diatom indices contained in the OMNIDIA database software to evaluate water quality in thisriver system. Except for Sladek’s index, indices typically showed significant correlations with each other andalso with parameters of water quality: organic load (BOD), oxygen concentration, conductivity, measuredion concentrations and trophic level (NH 4 -N, PO 4 -P). Two particular indices – IPS and GDI, gave the bestenvironmental resolution in terms of correlation with water quality variables (see Table 3.6) and showingclear differences between the separate river groups.Although the diatom indicator system emerged as a useful tool to evaluate general water quality, someindices were not able to differentiate between adverse effects of eutrophication (inorganic nutrients) andorganic material pollution. Abundance of key indicator species, however, such as Achnanthes minutissima(highly sensitive towards organic pollution) and Amphora pediculus (eutrophic species, sensitive to organicpollution) can be useful in evaluating the type of pollution involved.