Freshwater Algae: Identification and Use as Bioindicators

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120 3 ALGAE AS BIOINDICATORSTable 3.8 Freshwater and Saltwater Wetland Diatoms (Florida, USA): SalinityOptima and Tolerance (Data from Gaiser et al., 2005)SpeciesSalinityOptimum*SalinityTolerance*Diatoms with lowest salinity optimaAchnanthidium minutissimum 1.80 0.20Nitzschia nana 1.83 0.72Navicula subrostella 1.84 0.21A. Open freshwater marshlandNitzschia palea var. debilis 2.06 1.24Encyonema evergladianum 2.25 1.51Brachysira neoexilis 2.69 1.77B. Forested freshwater marshlandNitzschia semirobusta 2.19 0.86Fragilaria synegrotesca 3.41 2.68Mastogloia smithii 4.20 2.75C. Mangrove Saltwater swampAmphora sp. 11.79 1.57Achnanthes nitidiformis 17.28 0.51Tryblionella granulata 18.38 0.92Diatoms with highest salinity optimaCaloneis sp. 20.52 1.06Tryblionella debilis 20.86 1.33Mastogloia elegans 20.99 1.03Diatoms are listed in relation to: Dominant species in three major wetland ecosystems (A,B,C) Three species with lowest salinity optima (Ecosystem A), shaded area – top of table Three species with highest salinity optima (Ecosystem C), shaded area – bottom of table.*Salinity values given as ppt. Optimum and tolerance levels for individual species are derivedfrom environmental analyses (see text).Predictive model The salinity optima and tolerance data shown in Table 3.8 were derived from environmentalsamples. Analysis of diatom species composition and salinity (along with other water parameters) wascarried out over a wide range of sites. Salinity optima for individual species were determined from those siteswhere the species had greatest abundance, and salinity tolerance was recorded as the range of salinities overwhich the species occurred.The species-related data was incorporated into a computer model that could predict ambient salinity (inan unknown environment) from diatom community analysis. Environmental salinity at a particular site wasdetermined as the mean of the salinity optima of all species present, weighted for their abundances. Predictedvalues for salinity based on such diatom calibration models are highly accurate (error
3.4 RIVERS 1213.4 RiversUntil recently, monitoring of river water qualityin many countries (Kwandrans et al., 1998) wasbased mainly on Escherichia coli titre (sewage contamination)and chlorophyll-a concentration (trophicstatus). Chlorophyll-a classification of the FrenchNational Basin Network (RNB), for example, distinguishedfive water quality levels (Prygiel andCoste, 1996): normal (chlorophyll-a concentration≤10 µgml −1 ), moderate pollution (10–≤60), distinctpollution (60–≤120), severe pollution (120–≤300)and catastrophic pollution (>300).The use of microalgae as bioindicators was pioneeredby Patrick (Patrick et al., 1954) and has concentratedparticularly on benthic organisms, since therapid transit of phytoplankton with water flow meansthat these algae have little time to adapt to environmentalchanges at any point in the river system.In contrast, benthic algae (periphyton and biofilms)are permanently located at particular sites, integratingphysical and chemical characteristics over time,and are ideal for monitoring environmental quality.Examples of benthic algae present on rocks andstones within a fast-flowing stream are shown inFig. 2.23. The use of the periphyton communityfor biomonitoring normally involves either the entirecommunity, or one particular taxonomic group – thediatoms.3.4.1 The periphyton communityAnalysis of the entire periphyton community clearlygives a broader taxonomic assessment of the benthicalgal population compared to diatoms only,but the predominance of filamentous algae makesquantitative analysis difficult. Various authors haveused periphyton analysis to characterize water quality,including a study of fluvial lakes by Cattaneoet al. (1995 – Section 3.2.1). This showedthat epiphytic communities could be monitored bothin terms of size structure and taxonomic composition,leading to statistical resolution of physical(substrate) and water quality (mercury toxicity)parameters.3.4.2 River diatomsContemporary biomonitoring of river water qualityhas tended to concentrate on just one periphyton constituent– the diatoms. These have various advantagesas bioindicators – including predictable tolerancesto environmental variables, widespread occurrencewithin lotic systems, ease of counting and a speciesdiversity that permits a detailed evaluation of environmentalparameters. The major drawbacks to diatomsin this respect is the requirement for complexspecimen preparation and the need for expert identification.Attached diatoms can be found on a variety of substratesincluding sand, gravel, stones, rock, wood andaquatic macrophytes (Table 2.6). The composition ofthe communities that develop is in response to waterflow, natural water chemistry, eutrophication, toxicpollution and grazing.Various authors have proposed precise protocolsfor the collection, specimen preparation and numericalanalysis of benthic diatoms to ensure uniformityof water quality assessment (see below). More generalaspects of periphyton sampling are discussed inSection 2.10.Sample collectionThe sampling procedure proposed by Round (1993)involves collection of diatom samples from a reachof a river where there is a continuous flow of waterover stones. About five small stones (up to 10 cmin diameter) are taken from the river bed, avoidingthose covered with green algal or moss growths. Thediatom flora can be removed from the stones either inthe field or back in the laboratory. As an alternativeto natural communities, artificial substrates can beused to collect diatoms at selected sample sites. Theseovercome the heterogeneity of natural substrata andconsequently standardize comparisons between collectionsites, but presuppose that the full spectrum ofalgal species will grow on artificial media. Dela-Cruzet al. (2006) used this approach to sample diatomsin south-eastern Australian rivers, suspending glassslides in a sampling frame 0.5 m below the water surface.Slides were exposed over a 4-week period to
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 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: 3.3 WETLANDS 119therefore directly
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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