Freshwater Algae: Identification and Use as Bioindicators

3.2 LAKES 109sites (Fig. 3.3 A, B, C), which indicated clear alterationsin water quality. In a number of deep lochs(C), limited eutrophication has occurred, with transitionfrom a Cyclotella/Achnanthes assemblage to aspecies combination (Asterionella/Aulacoseira) typicalof mesotrophic waters. Some shallow lochs (B)also showed nutrient increase, indicated by transitionfrom a non-planktonic (largely benthic) to a planktondominateddiatom population. In other cases, deepoligotrophic (E) and shallow (D) lochs showed littlechange in diatom assemblage, indicating minimalalteration in water quality.Multiproxy approach In a multiproxy approach,diatoms are just one of a number of groupsof organisms that are counted and analysed withinthe lake sediments (Bennion and Battarbee, 2007).For European limnologists, the stimulus for a multiproxyapproach has come with the most recent WaterFramework Directive (WFD; European Union,2000). This focuses on ecological integrity rather thansimply chemical water quality, for which the use ofhydro-chemical transfer functions and diatom speciesassemblage analysis are not sufficient.Multiproxy analysis uses as broad a range of organismswithin the food web (e.g. pelagic food web)as possible, commensurate with those biota with remainsthat persist in the sediment in an identifiableform. In addition to micro-algae (diatoms, chrysophytes),fossil indicators also include macroalgae(Charophyta), protozoa (thecamoebae), higher plants(pollen and macro-remains), invertebrates (chironomids,ostracods, cladocerans) and vertebrates (fishscales).This approach is illustrated by the study of Davidsonet al. (2005) on Groby Pool, United Kingdom,a shallow lake that has undergone nutrientenrichment in the past 200 years. Comparison of20-year slices from the sediment surface (recent:1980–2000) and base (reference: 1700–1720) indicatemajor changes in lake ecology (Fig. 3.4),driven primarily by alterations in water quality (Bennionand Battarbee, 2007). The ecological referencestate is one of dominance by benthic diatoms,colonization by low nutrient-adapted macro-algaeand higher plants, with detectable invertebrates restrictedto plant-associated Chydoridae. In contrastto this, the current-day ecosystem is much moreproductive – dominated by planktonic algae, highTOPPlanktonicStephanodiscusEpiphytic:CocconeisHigher plants:PotamogetonCallitricheNymphoeaZooplankton:CeriodaphniaBosminaDaphniaDominantdiatomsMacroalgae andhigher plantsInvertebratesBOTTOMBenthicFragilaria spp.Charophyta:Nitella, CharaHigher plants:Myriophyllum,UtriculariaPlant-associatedChydoridFigure 3.4 Multi-proxy palaeoecological analysis of a sediment core: Groby Pool, United Kingdom. Analysis of20-year slices from the top (recent ecology, ∼1980–2000) and bottom (reference ecology, ∼1700–1720) samples of thecore. Figure adapted and redrawn from Bennion and Battarbee (2007), original data from Davidson et al. (2005).