A Methods Manual for the Collection, Preparation and Analysis of ...

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4. ArchivingIt is important to retain a portion of the original sample throughout the preparation stageuntil the final slide has been made and examined under a microscope.After slide preparation, a portion of the cleaned suspension should be preserved andstored in a labeled vial with ethanol added to reach a final concentration of more than20% by volume, to prevent the growth of micro-organisms.Alternatively, two or three drops of a 5% aqueous solution of phenol (caution: thischemical is carcinogenic) may be added. The archiving of diatom material is necessaryin case further slides need to be made or if other workers wish to verify the results of adiatom community analysis after mounting and examining the sample themselves, or ifSEM studies on the material are to be undertaken.Finally, a slide should be stored in a herbarium or diatom collection to facilitate crossreferencing.Diatom slides provide a permanent historical record of water qualityconditions at a site and should be stored in order to ensure that they can be accessed forfuture analyses. It is recommended that at least two slides are prepared from each sample.One of these should be lodged in the appropriate national herbarium, for future reference.This is:The North-West University,Potchefstroom Campus,School of Environmental Sciences and Development,Division Botany,Private Bag X6001,Potchefstroom, 2520Type material should be lodged at:The Natural History MuseumCromwell RoadLondon, SW7 5BDUNITED KINGDOMDiatom slides sent to such institutions should be labeled with the following minimuminformation: Location (place name not just a number) Co-ordinates if available Date on which the sample was collected Substratum Name of the sampler Type of mountant Date on which the slide was prepared.39
5. Enumeration and simple biometricsDiatom counts, when analysed may be used to infer the average water quality at a particularsampling site. Once the sample has been counted in the correct manner the data can beentered into a computer data-base (“Omnidia”, Lecointe et al., 1993) from which severalcalculations can be made using a specific equation or using the sum of the water qualityoptima of all the species in the sample.Simply, each diatom species used in the calculation/equation is assigned two values; the firstvalue reflects the tolerance or affinity of the diatom to a certain water quality (good or bad)while the second value indicates how strong (or weak) the relationship is. These values arethen, in addition, weighted by the abundance of the diatom in the sample i.e. how many of theparticular diatom in the sample occur in relation to the total number counted. Below is theformula of Zelinka and Marvan (1961) on which most diatom indices are based:index n∑ j∑1nj1a jsjva jvjjWhere a j = abundance (proportion) of species j in sample, v j = indicator value and s j =pollution sensitivity of species j. The performance of the indices depends on the values givento the constants s and v for each taxon and the values of the index ranges from 1 to an upperlimit equal to the highest value of s.The aim of counting diatom units is to produce semi-quantitative data from which ecologicalconclusions can be drawn. With this in mind it is important to know how many valves tocount to get a reliable estimation of the relative species composition at a specific samplingsite. The total number of valves to be counted for each sample varies according to the purposeof the analysis and according to the need to produce statistically good results. The statisticalprecision of percentage counting depends on the frequency of the taxon in the sample count inrelation to the size of the sample count. In a South African study Schoeman (1973) made aseries of experimental counts in which 200, 300, 400, 500 and 800 valves per sample werecounted and their relative abundance calculated. When only 200 valves were counted,compared to when 800 valves were counted, the percentage differences of the relativeabundances of individual species were often as high as 6-7%. However, the results obtainedfrom counting 400 as opposed to 800 valves differed by only 1-2%. For this reason heconcluded that counting 400 valves was satisfactory for the calculation of relative abundanceof diatom species. Similarly, Battarbee (1986) demonstrated that there were markeddifferences in the percentages between counts of 100 and 200 valves, while there was littledifference between counts of 400 and 500. For this reason he recommended that a count of300 to 600 may be used for purposes of routine analysis. This range is supported by Prygiel etal. (2002) who, in an inter-comparison exercise, found that diatom index scores were not40
Page 1 and 2: A Methods Manual for theCollection,
Page 3 and 4: This report is part of a set on Dia
Page 5 and 6: FOREWORDThis method manual is inten
Page 7 and 8: TABLE OF CONTENTSNOTE TO THE USER .
Page 9 and 10: GLOSSARYAerophilic - Depending on f
Page 11 and 12: Phytoplankton - The phytoplankton c
Page 13 and 14: photomicrographs earned high praise
Page 15 and 16: 2. How do you recognise diatoms in
Page 17 and 18: 4. Diatoms - Colony formation and a
Page 19 and 20: 5.1 Pennate and Centric diatomsPenn
Page 22 and 23: SECTION 2: FIELD PROCEDURESTo facil
Page 24 and 25: depending on the period of exposure
Page 26 and 27: 2.3.2 Examination of fresh material
Page 28 and 29: 3. Toolkit for Fieldwork (field app
Page 30 and 31: 5. Site selection for water quality
Page 32 and 33: 6. Sampling locality details and fi
Page 34 and 35: 8. Choice of substrata (detail)Samp
Page 36 and 37: 10 Preservation of diatom material
Page 38 and 39: 1: Micro-pipette 1 ml with disposab
Page 40 and 41: 1.2 Pre-preparation examination of
Page 42 and 43: 1.3.2.3 Shake the sample well and p
Page 44 and 45: one is available the peroxide can b
Page 46 and 47: 2 Preparation of diatom slidesHealt
Page 48 and 49: 2.1.9 After the diatom-coated cover
Page 52 and 53: affected at counts of 300 and above
Page 54 and 55: 6. Counting records (electronic and
Page 56 and 57: The main source of variability is,
Page 58 and 59: 11. Key reference worksThere are se
Page 60: HARDING WR, ARCHIBALD CGM, TAYLOR J

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