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, Staur<strong>as</strong>trumspp.) are typical of meso- <strong>and</strong> eutrophic lakes,while colonial blue-green algae such <strong>as</strong> 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 st<strong>and</strong>ing waters (Table 3.3).<strong>Identification</strong> 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 se<strong>as</strong>onal progression (Fig.2.8) <strong>and</strong> 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 <strong>as</strong> 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 ) <strong>and</strong> characteristicbioindicator algae. These include planktonic blooms ofAnabaena, Aphanizomenon, Microcystis (colonial bluegreens)plus various eutrophic algae (see text). Attachedmacroalgae (Cladophora) <strong>and</strong> periphyton communities(present on the fringing reed beds Fig. 2.29) are alsowell-developed.(Fig. 2.28) <strong>and</strong> in the dense periphyton communities(Fig. 2.29) that occur in the littoral reed beds.Analysis of lake sediments (Capstick, unpublishedobservations) indicates incre<strong>as</strong>ed eutrophication inrecent historical times, with higher proportions ofthe diatoms Asterionella formosa plus Aulacoseiragranulata var. angustissima <strong>and</strong> marked decre<strong>as</strong>es inCyclotella ocellata <strong>and</strong> Tabellaria flocculosa (moretypical of low-nutrient waters) over the l<strong>as</strong>t 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, <strong>and</strong> 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-greens<strong>and</strong> dinoflagellates, often have these <strong>as</strong> dominantalgae during the summer months. Small newlyformedponds, however, are often dominated byrapidly-growing chlorococcales (green algae) <strong>and</strong>euglenoids. The latter are particularly prominent athigh levels of soluble organics (e.g. sewage ponds),using ammonium <strong>as</strong> a nitrogen source. Some of themost hypertrophic <strong>and</strong> ecologically-unstable watersare represented by artificially fertilized fishponds, such <strong>as</strong> those of the Třeboň wetl<strong>and</strong>s, CzechRepublic (Pokorny et al., 2002a,b).In addition to considering individual algal species,taxonomic grouping (<strong>as</strong>semblages) may also beuseful environmental indicators. Reynolds (1980)considered species <strong>as</strong>semblages in relation to se<strong>as</strong>onalchanges <strong>and</strong> trophic status, with some groupings(e.g. Cyclotella comensis/Rhizosolenia) typicalof oligotrophic waters <strong>and</strong> others typical of eutrophic(e.g. Anabaena/Aphanizomeno/Gloeotrichia)
3.2 LAKES 113<strong>and</strong> hypertrophic (Pedi<strong>as</strong>trum/Coel<strong>as</strong>trum/Oocystis)states. Consideration of algae <strong>as</strong> groups rather thanindividual species leads on to quantitative analysis<strong>and</strong> determination of trophic indices.4. Phytoplankton trophic indices. In mixed phytoplanktonsamples, algal counts can be quantitativelyexpressed <strong>as</strong> biotic indices to characterize laketrophic status (Willen, 2000). These indices occur atthree levels of complexity (Table 3.4).1. Indices b<strong>as</strong>ed on major taxonomic groups Earlyphytoplankton indices, developed by Thunmark(1945), Nygaard (1949) <strong>and</strong> Stockner (1972) usedmajor taxonomic groups that were considered typicalof oligotrophic (particularly desmids) or eutrophic(chlorococcales, blue-greens, euglenoids) conditions.The proportions of eutrophic/oligotrophic speciesgenerated a simple ratio which could be used to designatetrophic status (Table 3.4a). Using the chlorophyceanindex of Thunmark (1945), for example,counts of chlorococcalean <strong>and</strong> desmid species canbe expressed <strong>as</strong> a ratio, which indicates trophic statusover the range oligotrophy (1).Although such indices provided useful information(see below), they tended to lack environmentalresolution since many algal cl<strong>as</strong>ses turn out to be heterogeneous– containing species typical of oligo- <strong>and</strong>eutrophic lakes. Problems were also encountered insome of the early studies with sampling procedures,Table 3.4Lake Trophic IndicesIndex Calculation Result Reference(a) Major taxonomic groups: numbers of speciesChlorophycean index Chlorococcales spp./Desmidiales spp. 1 = eutrophyMyxophycean index Cyanophyta spp./Desmidiales 1 = eutrophyDiatom indexCentrales spp./PennalesEuglenophycean index Euglenophyta/Cyanophyta + ChlorophytaA/C diatom index Araphid pennate/centric diatom spp. 2 = eutrophy