Freshwater Algae: Identification and Use as Bioindicators

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106 3 ALGAE AS BIOINDICATORSDirective (WFD: European Union, 2000), which requiresMember States to monitor the ecology of waterbodies to achieve ‘good ecological status’. Macrophytesand attached algae together form one ‘biologicalelement’ that needs to be assessed underthis environmental programme (see also ‘multiproxyapproach’ – Section 3.2.2).Local water quality Various authors have analysedbenthic or epiphytic algal populations in relationto water quality, including the extensive periphytongrowths that occur in the littoral region of many lakes.These algae are particularly useful in relation to localwater conditions (e.g. localized accumulations ofmetal toxins, point source and diffuse loading at theedge of the lake), since their permanent location atparticular sites gives a high degree of spatial resolutionwithin the water body.Localized metal accumulations Cattaneo et al.(1995) studied periphyton growing epiphytically inmacrophyte beds of a fluvial lake in the St LawrenceRiver (Canada), to see if they could resolve periphytoncommunities in relation to water quality (toxicand non-toxic levels of mercury) under differing ecologicalconditions (e.g. fine versus coarse sediment).The periphyton, composed of green algae (40%),blue-greens (25%) diatoms (25%) and other phyla,was collected from various sites and analysed in termsof taxonomic composition and size profile. Multivariate(cluster and biotic index) analysis of periphytoncommunities gave greatest separation in relationto physical ecological (particularly substrate)conditions rather than water quality. The authors recommendedthat the use of benthic algae as aquaticbioindicators should involve sampling from similarsubstrate sites to eliminate ecological variation otherthan water quality.Point source and diffuse loading at the edge ofthe lake Water quality in the littoral zone may differconsiderably from that in the main part of the lake.This is partly due to the proximity of the terrestrialecosystem (with inflow from the surrounding catchmentarea) and partly due to the distinctive zone oflittoral macrophyte vegetation, making an importantbuffer zone between the shore and open water (Eloranta,2000). Analysis of littoral algae, either by multivariateanalysis or determination of bioindices, hasthe potential to provide information on water qualityat particular sites along the edge of the lake in relationto point discharges (stream inflows, industrialand sewage discharges) and diffuse loadings. The latterinclude input from surrounding agricultural land,discharges from domestic areas, traffic pollutants andloading from local ecosystems such as forests andpeat bogs (Eloranta, 2000) – Fig. 3.2.Sampling and analysis of littoral algae Althoughattached algal communities (as with phytoplankton)can theoretically be related to water qualityin terms of total biomass, this does not correlate wellwith nutrient loading (King et al., 2006) – chieflydue to grazing and (in eutrophic waters) competitionwith phytoplankton. Also, nutrients in the water canbe supplemented by nutrients arising from the substratum.Species counts, on the other hand, can provide auseful measure of water quality. Recent recommendationsfor littoral sampling (King et al., 2006: see alsoSection 2.10) concentrate particularly on diatoms –collecting specimens from stones and macrophytes(Fig. 2.29), since these substrata are particularly commonat the edge of lakes. Epipelic diatoms (present onmud and silt) are probably less useful as bioindicatorssince they are particularly liable to respond to substrate‘pore-water’ chemistry rather than general waterquality. The epipelic diatom community of manylowland lakes also tends to be dominated by Fragilariaspecies, which take advantage of favourablelight conditions in the shallow waters, but are poorindicators of water quality – having wide tolerance tonutrient concentrations. Having obtained samples andcarried out species counts of diatoms from habitatswithin the defined littoral sampling area, weightedaverageindices can be calculated as with river diatoms(Section 3.4.5/6) and related to water quality.3.2.2 Fossil algae as bioindicators: lakesediment analysisRecent water legislation, including the US CleanWater Act (Barbour et al., 2000) and the EuropeanCouncil Water Framework Directive (WFD: EuropeanUnion, 2000) have required the need to assesscurrent water status in relation to some baselinestate in the past. This baseline state (referred to as
3.2 LAKES 107‘reference conditions’) defines an earlier situationwhen there was no significant anthropogenic influenceon the water body. In the United Kingdom, thisreference baseline is generally set at about 1850,prior to the modern era of industrialization and agriculturalintensification. Having defined the referenceconditions, contemporary analyses can then be usedto make a comparative assessment of human influenceson lake biology, hydromorphology and waterchemistry. For a particular water body, the absenceof long-term contemporary data means that referenceconditions have to be assessed on a retrospective basis,including the use of palaeolimnology – the studyof the lake sediment record. The use of lake sedimentsto generate a historical record only gives reliableresults under conditions of optimal algal preservation(see below) and if the sediments are undisturbed bywind, bottom-feeding fish and invertebrates.Lake sediments – algal accumulation andpreservationContinuous sedimentation of phytoplankton from thesurface waters (euphotic zone) of lakes leads to thebuild-up of sediment, with the accumulation of bothplanktonic and benthic algal remains at the bottom ofthe water column. In a highly productive lake such asRostherne Mere, United Kingdom (Fig. 3.5), the wetsedimentation rate in the deepest parts of the waterbody has been estimated at 20 mm year −1 (Prartanoand Wolff, 1998), with subsequent compression asfurther sedimentation and decomposition occurs. Decompositionof algal remains leads to the loss of mostorganic biomass, and algal identification is largelybased on the relatively resistant inorganic (siliceous)components of diatoms and chrysophytes (Section1.9). Optimal preservation of this cell wall materialrequires anaerobic conditions, and sediment samplesare best taken from central deep parts of the lakerather than from shallow regions such as the littoralzone (Livingstone, 1984).Diatom bioindicators within sedimentsWithin lake sediments, diatoms have been particularlyuseful as bioindicators (Section 1.10) of pastlake acidification (Battarbee et al., 1999), pointsources of eutrophication (Anderson et al., 1990)and total phosphorus concentration (Hall and Smol,1999). The widespread use of lake sediment diatomsfor reconstruction of past water quality is supportedby the European Diatom Database Initiative (EDDI).This web-based information system is designed toenhance the application of diatom analysis to problemsof surface water acidification, eutrophicationand climate change. The EDDI has been producedby combining and harmonizing data from a series ofsmaller datasets from around Europe and includes adiatom slide archive, electronic images of diatoms,new training sets for environmental reconstruction(see below) and applications software for manipulatingdata. In addition to the EDDI, other databases arealso available – including a large-scale database forbenthic diatoms (Gosselain et al., 2005).Diatoms within sediments are chemically cleanedto reveal frustule structure (Section 2.5.4), identifiedand species counts expressed as percentage total. Numerousexamples of cleaned diatom images from lakesediments are shown in Chapter 4. As with fossilchrysophytes (Section 1.9), subsequent analysis ofdiatom species counts to provide information on waterquality can involve the use of transfer functions,species assemblages and may be part of a multiproxyapproach. The data obtained, coupled with radiometricdating of sediment cores, provide information ontimes and rates of change and help in setting targetsfor specific restoration procedures to be carried out.Transfer functions Transfer functions are mathematicalmodels that allow contemporary data to beapplied to fossil diatom assemblages for the quantitativereconstruction of (otherwise unknown) past waterquality. Various authors (Bennion et al., 2004; Tayloret al., 2006; Bennion and Battarbee, 2007) have describedthe use of this approach, which is as follows. Generation of a predictive equation (transfer function)from a large number of lakes, in each caserelating the dataset of modern surface-sediment diatomssamples to lake water quality data (Bennionet al., 1996). The ‘training set’ of lakes shouldmatch the lake under study in terms of geographicregion and lake morphology, and should have arange of water quality characteristics extending
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 11 and 12: 3.2 LAKES 109sites (Fig. 3.3 A, B,
Page 13 and 14: 3.2 LAKES 111Phytoplankton net prod
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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