Freshwater Algae: Identification and Use as Bioindicators

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110 3 ALGAE AS BIOINDICATORSnutrient-adapted macrophytes and abundant zooplanktonpopulations.Other examples of a multiproxy approach to lakesediment analysis include the studies of Cattaneoet al. (1998) on heavy metal pollution in Italian Laked’Orta (Section 3.2.2) and studies on eutrophicationin six Irish lakes (Taylor et al., 2006). The latter studyinvolved sediment analysis of cladocerans, diatomsand pollen from mesotrophic-hypertrophic lakes, toreconstruct past variations in water quality and catchmentconditions over the past 200 years. The resultsshowed that five of the lakes were in a far more productivestate compared to the beginning of the sedimentrecord, with accelerated enrichment since 1980.3.2.3 Water quality parameters: inorganic andorganic nutrients, acidity and heavymetalsA wide range of chemical parameters can beconsidered in relation to general lake water quality– including total salt content (conductivity), inorganicnutrients (nitrogen and phosphorus), solubleorganic nutrients, acidity, heavy metal contaminationand presence of coloured matter (causedparticularly by humic materials). The diversity andinter-relationships of different lakes in relation tothese characteristics was emphasized by the studyof Rosen (1981), evaluating lake types and relatedplanktonic algae from August sampling of 1250Swedish standing waters. A summary from this studyof algae characteristic of Swedish acidified lakes,oligotrophic forest lakes (varying in phosphoruscontent and conductivity), humic lakes, mesotrophicand eutrophic lakes is given by Willen (2000).In this section, the role of algae as bioindicatorsis considered in reference to four main aspectsof lake water quality – inorganic nutrients,soluble organic nutrients, acidity and heavy metalcontamination.Inorganic nutrient status: oligotrophic toeutrophic lakesThe trophic classification of lakes, based primarilyon inorganic nutrient status, has become the majordescriptor of different lake types. Its importance reflects: the key role that nutrients have on the productivity,diversity and identity of algae and other lakeorganisms a major distinction between deep mountain lakes(typically oligotrophic) and shallow lowland lakes(typically eutrophic) the major impact that humans have on changingthe ecology of lakes, typically from oligotrophic toeutrophic ecological problems that may arise as lakes changefrom eutrophic to hypertrophic, leading to degenerativechanges that can only be reversed by humanintervention.The diverse ecological effects that increasing nutrientconcentrations have on lake ecology have beenwidely reported (e.g. Kalff, 2002; Sigee, 2004), includingthe ecological destabilization that occurs atvery high nutrient concentrations.Definition of terms Lake classification, fromoligotrophic (low nutrient) to mesotrophic and eutrophic(high nutrient), is based on the twin criteriaof productivity and inorganic nutrient concentration– particularly nitrates and phosphates. Variousschemes have been proposed to define these terms,including one developed by the Organization forEconomic Cooperation and Development (OECD,1982). This scheme (Table 3.2) uses fixed boundaryvalues for nutrient concentration (mean annualconcentration of total phosphorus), and productivity(chlorophyll-a concentration, Secchi depth). In thisscheme, for example, the mean annual concentrationof total phosphorus ranges from 4–10 µgl −1 foroligotrophic lakes, and 35–100 µgl −1 for eutrophicwaters. In addition to total phosphorus, boundariesfor the main soluble inorganic nutrients – orthophosphateand dissolved inorganic nitrogen (nitrate, nitrite,ammonia) have also been designated (TechnicalStandard Publication, 1982).
3.2 LAKES 111Phytoplankton net production (biomass) is determinedeither as chlorophyll-a concentration(mean/maximum annual concentration in surface waters)or as Secchi depth (mean/maximum annualvalue). Examples of total volumes of planktonic algaeat different trophic levels (Norwegian lakes) arealso given in Table 3.2, together with characteristicbioindicator algae.Algae as bioindicators of inorganic trophicstatusPlanktonic algae within lake surface (epilimnion)samples can be used to define lake trophic status interms of their overall productivity (Table 3.2) andspecies composition (Table 3.3). Species compositioncan be related to trophic status in four mainways – seasonal succession, biodiversity, bioindicatorspecies and determination of bioindices.1. Seasonal succession. In temperate lakes, thedevelopment of algal biomass and the sequence ofphytoplankton populations (seasonal succession) directlyrelate to nutrient availability. In all cases theseason commences with a diatom bloom, but subsequentprogression (Reynolds, 1990) can be separatedinto four main categories (Table 3.3). Oligotrophic lakes. In low nutrient lakes the springdiatom bloom is prolonged, and diatoms may dominatefor the whole growth period. Chrysophytes(Uroglena) and desmids (Staurastrum) may alsobe present, and in some lakes Ceratium and Gomphosphaeriamay be able to grow in the nutrientdepletedwaters by migrating down the water columnto higher nutrient conditions. Mesotrophic lakes. These have a shorter diatombloom (dominated by Asterionella), often followedby a chrysophyte phase then mid-summer dinoflagellate,blue-green and green algal blooms. Eutrophic lakes. In high nutrient lakes, the springdiatom bloom is further limited, leading to a clearwaterphase (dominated by unicellular algae), followedby a mid-summer bloom in which largeunicellular (Ceratium), colonial filamentous (Anabaena)and globular (Microcystis) blue-greenspredominate. Hypertrophic lakes. These include artificially fertilizedfish ponds (Pechar et al., 2002) and lakes withsewage discharges, and are dominated throughoutthe season by small unicellular algae withshort life cycles. The algae form a successionof dense populations, out-competing larger colonialorganisms which are unable to establishthemselves.2. Species diversity. Bioindices of species diversitycan be derived from species counts and fall intothree main categories (Sigee, 2004) – species richness(Margalef index), species evenness/dominance(Pielou index, Simpson index) and a combination ofrichness and dominance (Shannon–Wiener index).One of the most commonly-used indices (d), developedby Margalef (1958), combines data on the totalnumber of species identified (S) and total number ofindividuals (N), where:d = (S − 1)/ log e N (3.1)During the summer growth phase, species diversityis typically low in oligotrophic lakes, rising progressivelyin mesotrophic and eutrophic lakes, but fallingagain in some eutrophic/hypertrophic lakes wheresmall numbers of species may out-compete other algae.The effects of increasing nutrient levels on algaldiversity (d) are illustrated by Reynolds (1990),with summer-growth values of 3–6 for the nutrientdeficientNorth Basin of Lake Windermere (UnitedKingdom) – falling to levels of 2–4 in a nutrientrichlake (Crose Mere, United Kingdom) and 0.2–2for a hypertrophic water body (fertilized enclosure,Blelham Tarn, United Kingdom).3. Bioindicator species. Some algal species andtaxonomic groups show clear preferences for particularlake conditions, and can this act as potentialbioindicators. In a broad comparison of oligotrophicversus eutrophic waters, desmids (green algae) tendto occur mainly in low nutrient waters while colonial
Page 1 and 2: 3Algae as BioindicatorsBiological i
Page 3 and 4: 3.1 BIOINDICATORS AND WATER QUALITY
Page 5 and 6: Table 3.3 Lake Trophic Status: Phyt
Page 8 and 9: 106 3 ALGAE AS BIOINDICATORSDirecti
Page 11: 3.2 LAKES 109sites (Fig. 3.3 A, B,
Page 15 and 16: 3.2 LAKES 113and hypertrophic (Pedi
Page 17 and 18: 3.2 LAKES 115Table 3.5 Organic Poll
Page 19 and 20: 3.2 LAKES 117Table 3.7 Bioindicator
Page 21 and 22: 3.3 WETLANDS 119therefore directly
Page 23 and 24: 3.4 RIVERS 1213.4 RiversUntil recen
Page 25 and 26: 3.4 RIVERS 123Gomphonema parvulum t
Page 27 and 28: 3.4 RIVERS 125Table 3.10 Benthic Di
Page 29 and 30: 3.4 RIVERS 127Palmer’s Index (Pal
Page 31 and 32: 3.4 RIVERS 129any irregular conclus
Page 33 and 34: 3.4 RIVERS 131Case study 3.3Compari
Page 35 and 36: individual analysts can be measured
Page 37 and 38: 3.5 ESTUARIES 135potential role of

Freshwater Algae: Identification and Use as Bioindicators

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