Freshwater Algae: Identification and Use as Bioindicators

112 3 ALGAE AS BIOINDICATORSblue-green algae are more typical of eutrophic waters.Such generalizations are not absolute, however, sincesome desmids (e.g. Cosmarium meneghinii, Staurastrumspp.) are typical of meso- and eutrophic lakes,while colonial blue-green algae such as Gomphosphaeriaare also found in oligotrophic waters.Although it is not possible to pin-point individualalgal species in relation to particular trophic states, itis possible to list organisms that are typical of summergrowths in different standing waters (Table 3.3).Identification of such indicator species, particularlyat high population levels, gives a good qualitativeindication of nutrient state. As an example of thisthe high-nutrient lake illustrated in Fig. 3.5 is characteristicof temperate eutrophic water bodies,with highproductivity, characteristic seasonal progression (Fig.2.8) and with the eutrophic bioindicator algae listed inTable 3.3. In addition to phytoplankton bioindicators,the trophic status of the lake is also reflected in extensivegrowths of attached algae such as CladophoraFigure 3.5 Eutrophic lake (Rostherne Mere, UnitedKingdom). The high nutrient status of the lake is indicatedby water analyses (mean annual total phosphorus>50 µgl −1 ), high productivity (maximum chlaconcentration typically >60 µgl −1 ) and characteristicbioindicator algae. These include planktonic blooms ofAnabaena, Aphanizomenon, Microcystis (colonial bluegreens)plus various eutrophic algae (see text). Attachedmacroalgae (Cladophora) and periphyton communities(present on the fringing reed beds Fig. 2.29) are alsowell-developed.(Fig. 2.28) and in the dense periphyton communities(Fig. 2.29) that occur in the littoral reed beds.Analysis of lake sediments (Capstick, unpublishedobservations) indicates increased eutrophication inrecent historical times, with higher proportions ofthe diatoms Asterionella formosa plus Aulacoseiragranulata var. angustissima and marked decreases inCyclotella ocellata and Tabellaria flocculosa (moretypical of low-nutrient waters) over the last 50 years.Although individual algal species can be rated primarilyin terms of trophic preferences, they are alsofrequently adapted to other related ecological factors. Acidity: oligotrophic waters are frequently slightlyacid with low Ca concentrations, and vice versa foreutrophic conditions. Nutrient balance: mesotrophic waters may benitrogen-limiting (high P/N ratio), promoting thegrowth of nitrogen-fixing (e.g. Anabaena) but notnon-fixing (e.g Oscillatoria) colonial blue-greenalgae. Long-term stability: In hypertrophic waters, dominationby particular algal groups may vary with thelong-term stability of the water body. High-nutrientlakes, with established populations of blue-greensand dinoflagellates, often have these as dominantalgae during the summer months. Small newlyformedponds, however, are often dominated byrapidly-growing chlorococcales (green algae) andeuglenoids. The latter are particularly prominent athigh levels of soluble organics (e.g. sewage ponds),using ammonium as a nitrogen source. Some of themost hypertrophic and ecologically-unstable watersare represented by artificially fertilized fishponds, such as those of the Třeboň wetlands, CzechRepublic (Pokorny et al., 2002a,b).In addition to considering individual algal species,taxonomic grouping (assemblages) may also beuseful environmental indicators. Reynolds (1980)considered species assemblages in relation to seasonalchanges and trophic status, with some groupings(e.g. Cyclotella comensis/Rhizosolenia) typicalof oligotrophic waters and others typical of eutrophic(e.g. Anabaena/Aphanizomeno/Gloeotrichia)