Freshwater Algae: Identification and Use as Bioindicators

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).