USE OF THE TROPHIC DIATOM INDEX TO MONITOR EUTROPHICATION IN RIVERS

Pergamon

@

PII: S0043-1354(97)00157-7

Waf.Res. Vol. 32,No. 1,pp. 236-242,1998 ~ 1998ElsevierScienceLtd. All rights reserved Printed in Great Britain 0043-1354/98$19.00+ 0.00

USE OF THE TROPHIC DIATOM INDEX TO MONITOR EUTROPHICATION IN RIVERS M. G. KELLY Bowburn Consultancy, 23 Clarence Street, Bowburn,Durham DH65BB, U.K. (Received August 1996; accepted in revisedform

April 1997)

Abstract-The performance of the trophic diatom index (TDI), a new index of trophic status in rivers, was evaluated at sites above and belowmajor sewageworks where nutrient removal is beingconsidered. Somemodificationsto the index are proposed as a result. These includechangingthe scale from 1 (low nutrients) to 5 (highnutrients) to G1OO,the removalof taxa that are predominatelyplanktonic from the index, and some minor adjustments to taxa sensitivitiesand indicator values. More detailed guidelines on the choice of sample site are also proposed. In particular, it is important that sites in the “recovery zone” downstreamof sewageworksarechosensothattheinfluence ofthegrosseffectsoforganicpollution

ontheindexisminimised. A “look-up”chartto aiddatainterpretationisalsodescribed.TherevisedTDI is nowrecommended to regulatoryorganisations as a toolforassessingeutrophicationin rivers.G 1998 ElsevierScienceLtd.All rightsreserved Key

words—algae,diatoms, rivers, monitoring, eutrophication, phosphorus, water quality

result, was designedto be robust and easilylearnt. It uses the weighted average equation of Zelinka and Concern over the impact of nutrients on rivers in Marvan (1961)to interpret benthic diatom commuEurope has increased since the publication of the nity structure in terms of the nutrient concentrations European Community’s Urban Wastewater Treat- in the river. (No attempt has been made at this stage ment Directive (UWWTD: European Community, to separate the effects of N and P.) A particularly 1991). A key component of this directive was the important feature is an ability to separate nutrientidentification of “sensitiveareas” (SAS)where more rich waters from those that are organically-polluted stringent wastewater treatment was required to (Kelly and Whitton, 1995). This arose from an prevent or reverse eutrophication (European Com- observation early in the study that high nutrient munity, 1991). In practical terms (given the high concentrations (e.g. >0.5 mg 1-1filtrable reactive P) capital cost of nutrient stripping), it is important to were often associated with rich diatom and identify sites where there are clear ecologicalchanges macrophyte floras and invertebrate faunas. Sites downstreamof a sewagetreatment works(STW)that dominated by the typical indicators of organic can be attributed to increased nutrient concen- pollution were associated with a much lower species trations, rather than to other components of the diversity. discharge (Kelly et al., 1996). Once it had been developed,an evaluation exercise Until this legislation, there were no robust was carried out, in which staffin three NRA Regions monitoring tools available with which the impact of weretaught the basicsof diatom identificationbefore nutrients on U.K. rivers could be assessed. Two using the index in monitoring exercisesrelevant to indicesthat have recentlybeen developedto meet this their circumstances. Experiences from this exercise need are the Trophic Diatom Index (TDI: Kelly and were pooled to produce a new version of the TDI Whitton, 1995)and the macrophyte Mean Trophic along with some more detailed guidelineson how it Rank (MTR: Holmes, 1996). Both have been could be used to monitor the impact of large STWS. evaluated extensivelyby the National Rivers Authority (NRA: now Environment Agency), and this MATERIALSAND METHODS paper reports modificationsto the original versionof the TDI, and describeshow it can be used in practice The following NRA Regions were involved: Anglian to assessthe impact of nutrients downstreamof large Region (Eastern and Northern Areas: East Anglia); (> 10,000 population equivalent) sewage works Sevem-Trent Region (Upper Trent Area: Midlands) and Thames Region (tributaries of River Thames: Southern (termed “qualifying discharges”, QDs). England),In addition, a separate evaluationwas performed The TDI was designedwith the practical needs of by the author in the River Wear (Northumbria and busy water industry biologists in mind and, as a Yorkshire Region). INTRODUCTION

236

Trophic diatom index

237

A totalof 23QDson 11riverswereexaminedduringthe Performance of the TDI evaluationexercise.For eightof theseQDs,samplingwas The summer of 1996 was characterised by an confined to sites immediatelyabove and below the discharge.The remainder were sampled as part of broader unusually long period of low flows in U.K. rivers, surveys of nutrients within particular catchments. leading to development of large phytoplankton Methods were identical to those described in Kelly and Whitton (1995)with epilithic samples being collectedfrom populations at positions farther upstream than is the upper surfacesof at least fivecobblesor bouldersat each normally the case. Valvesof centric diatoms such as samplingsite. These were prepared by standard techniques Cyclotella and Stephanodiscus (normally only abun(Hendey,1974),and clean valvesweremountedin Naphrax. dant in lowland, eutrophic conditions)were found in At least 200 valves were identified per sample. As far as high numbers in benthic diatom films. In addition, possible,two samples(August and October) were collected from sites above and below discharges, according to some sites in southern England downstream of impoundmentsbut upstream of STWSalso contained standard NRA guidelines. The initial version of the TDI was derived empirically high numbers of planktonic diatoms. In the case of from graphs summarizing percent count vs. dissolved the River Wear, 32°/0of the benthic diatom film was phosphorus concentrations for 86 taxa (genera plus key indicator species: Kelly and Whitton, 1995).It produced composed of Cyclotella at a site in the upper part of values from 1 (low nutrient concentrations)to 5 (veryhigh the catchment (Table 1)becauseof the long period of nutrient concentrations). However, NRA staff involvedin low flows.Phytoplankton populations rarely develop the evaluationexpresseda clear preferencefor an indexthat in this part of the River Wear (where nutrient produced integer values over an extendednumericalrange. concentrationsare generallylow)and this population The TDI was therefore modified to extend from O (low nutrient concentrations) to 100 (very high nutrient of CycloteZZaskewedthe TDI, compared to the value whenplanktonic taxa were removed(Table 1),which concentrations). This was achieved as follows: was closerto valuesof TDI recordedfrom the site on TDI = (WMS X 25) – 25, previous visits. For this reason, all predominately where TDI = Trophic Diatom Index and WMS = planktonic taxa have been removedfrom the revised Weighted mean sensitivity,calculated as: version of the TDI. Other modifications to the TDI included slight ~ (ljSjVj changes to sensitivitiesand indicator values of some WMS =’~ taxa when case studies produced anomalous results, ~UjV, also, the addition of some extra, readily-identified j= taxa, wheresplittingthesefrom the genusadded more where aj = abundance (proportion) of speciesj in sample, ecological information. One genus where problems sf= pollutionsensitivity(l–5) of speciesj and Vj= indicator remain is IVitzschia, owing largely to taxonomic value (l–3). sj was derived empirically. In addition, a second value, the percentage pollution difficulties.Although species such as N. palea are tolerant valves (YoPTV)is also calculated to estimate the important indicators of organicpollution; others (e.g. influence of organic pollution on the indication of N. fonticola) prefer cleaner water (Coste, 1994). eutrophication at the site. O/OPTV is calculated as the sum of valves belonging to taxa generally regarded as Readily-recognizedspeciessuch as N. amphibia and particularly tolerant to organic pollution. Becausetheseare N. dissipata are included in the TDI as separate most abundantin situations where very high phosphorus categories;however,there remain a large number of concentrations are correlated with elevated values of speciesthat are relativelydifficultfor non-specialists determinants such as suspendedsolids,biochemicaloxygen to separate. demand and ammonia, phosphorus cannot be assumed to The full list of taxa and their sensitivities and be the limiting variable. YoPTVis less an indicator of organic pollution than of the reliability of the TDI as an indicator values is given as Appendix 1. 1

estimator of eutrophication at the site. In the author’s experience, O/OPTVvalues < 20°/0 of the total count generallyindicatethat organicpollutionis absent or mild in its effects.

Choice of sample sites

Current NRA guidelinesfor samplingQDs specify that samples should be collected from within 500m RESULTSAND DISCUSSION of the outfall. However,it was clear from this study Full details of water chemistry,diatom community that samples from immediatelybelow STWStended composition and TDI for each site are contairtedin to have high concentrations of taxa indicative of a separate report (Kelly, 1996).The main results of organic pollution, which tended to swamp the “signal” from those taxa that weregood indicators of the exerciseare described below. Table 1. Effectof planktonicdiatomson TDI in R. Wear,Summer1996(seealso Table 4) Above Below WittOn-le-Wear HouselopBeck HousclopBeck NZ 109356 NZ 170309 NZ 105357 Grid reference 27,5 28.5 38 Distancefrom source 0 5.3 32.8 Cyclotella(percentageof total) 47 74 58 TDI (includingplankton) 46 66 58 TDI (excludingplankton) 0 11 2 Difference(%)

M. G. Kelly

238

Table 2. Impact of Raunds STW on Hog’s Dyke (tributary of River Nene, Northamptonshire),August 1995.Medianorthophosphateis basedon a dataset of elevensamplescollectedover 12monthsprior to collectionof diatomsample, Only taxa > 10”Aat one site are included.

Grid reference Median orthophosphate(mg 1-‘) BMWP (ASPT) Dominant taxa Amphora pediculus (%) Small Nauicrda spp. (%) Rlroicosphenrirabbrt-viata (%)

Above STW

BelowSTW

SK 028377

SK 046371

0.35 41 (4.1)

3.5 6 (2.0)

52

N.D. 94

7 23

TDI 95 & 8 94 Percentageoollutiontolerant valves -. ND.: not detectedin sample;+ presentin samplebut <0.5% of total; BMWP: BiologicalMonitoring Working Party score; ASPT: Average Score Per Taxon.

inorganic nutrient enrichment. This is illustrated by samples from above and below Raunds STW, a QD discharging into a tributary of the River Nene (designatedas an SA)in Northamptonshire (Table2). A tenfold increase in median P concentration was observed downstream of the STW. However, the primary impact of the discharge is not nutrients, as the Biological Monitoring Working Party (BMWP) score and Average Score Per Taxon (ASPT), both based on macroinvertebrates,drop downstream, and the percentage of pollution tolerant diatom taxa increasesfrom 8 to g4°/0. For this reason, it is difficult

an urban catchment, with several large STWSin a short distance. As a result, a clear “recovery zone” (serzsuHynes, 1960), is not able to develop until Frimley Bridge. However, at this point, the flora is noticeably more eutrophic than upstream of the discharges; the percentage of pollution tolerant taxa drops to 17% whilst the TDI remains high (Fig. 1). Similar observations were made on other rivers where data from several sites was available. In particular, samples collected from the recoveryzone proved particularly useful in interpreting the effects to draw any conclusions about the impact of of nutrients. At these sites, the proportion of taxa nutrients per se at Raunds STW from this limited tolerant to organicpollution had decreasedand those intolerant to organic pollution were again abundant. sampling programme. This contrasted with the situation where sampling These included some taxa that are found in quite was not limited to sites immediately above and eutrophic conditions but appear relativelyintolerant below the discharge. A sequence of samples was of organic pollution (or are outcompeted by collected from the River Backwater, a tributary better-adapted taxa). Examples include Anphora of the River Loddon and, ultimately, the Thames, pedictdus, Navicula tripunctata and Nitzschia dissiwhich illustrates this point well. This is largely pata. 80 60

20

0

sample

site

Fig. 1. Impact of STWSon TDI (vertical bars) and ‘70PTV(0—0) in the River Backwater, Southern England. Major STWSenter the river at Aldershot Town, Aldershot Military, Ash Vale (between Lynchford and Frimley Bridge) and Camberley (between Frimley Bridge and Sandhurst). Further discharges enter below Sandhurst, but these are omitted for the sake of clarity.

Trophic diatom index

Another feature of the Backwater study also observed elsewhere was an increase in TDI and percentage pollution tolerant taxa above the point at which the first STW effluententered the river (Fig. 1). Pea Bridge, the first site on the River Backwater, is located upstream of Aldershot, whereas the site upstream of Aldershot Town STW lies between the town itself and the STW discharge. It would appear that urban runoff and intermittent storm sewer overflows in the town may affect water quality independent of the STW itself.

Use of “Look-up” chart to interpret data

As a consequenceof results such as those from the Backwater, a “look-up” chart has been developed that allowsdata to be plotted in two dimensions:one using the TDI to indicate the impact of eutrophication and the other indicating changes because of other factors. This allows complicated changes such as those seen in the River Backwater catchment to be readily interpreted (Fig. 2). The four horizontal categories are derived from table 6 of Kelly and Whitton (1995)and refer to the amount of organic pollution corresponding to the proportion of valves of tolerant taxa. These are, in brief: < 200/0 21-4070 41–60%

free from significant organic pollution

some evidence of organic pollution organic pollution likely to contribute sig-nifican-tly to eutrophication at site site heavily contaminated with organic pollution.

>61°A

---F e-l Pamantoftaxa

TDI o-9 10-19 20-29 30-39 40-49 50-59

<20%

toiarantto organkpollutbn 414096

214%

I

\

m

I

239

Vertical movement on the chart is interpreted as indicatingchangesresultingfrom increasedeutrophication, whereas horizontal movement indicates changes due to other factors. In practice, it is more commonto observediagonal movement(e.g.between “above Aldershot Town” and “above Aldershot Military”), indicating a combination of factors affectingthe diatom community. However, sampling farther downstream in the recovery zone enables changesin the flora as the river recoversfrom organic pollution to be observed.In the River Backwater, the look-up chart demonstrates that the lowermost site had a higher TDI, which could not be attributed merely to side-effectsof organic pollution. Problems of sample comparability”

collection

and “index

of

Samplingprotocols adopted in this study followed commonpractice (e.g. Round, 1993)in attempting to collect samples,as far as possible,from boulders and cobblesfree from filamentousalgae. In some areas of the U.K. (especially deep, slow-flowing rivers of southern and eastern England), this was difficult or impossible, and at some sites, TDI values were affected by high numbers of Rhoicosphenia abbreviate, abundant as an epiphyte of Cladophora glomerata.

Standardization of other factors, such as substrate composition, water depth and degree of shade between sites, also proved difficultand, whereas the significanceof these effectsis not yet clear, a simple evaluation of the extent to which sites differed in these characteristicswas thought to be valuable. The importance of standardising physical characteristics of sample reaches was recognised during development of the macrophyte MTR (Holmes, 1996),and an “index of comparability” was developed for this. This enabled workers to assess, semi-quantitatively, the extent to which two sites differedin their physical characteristics. A simplified version (Table 3) was therefore adopted for use with the TDI. When this was applied to the River Wear above and below Houselop Beck (whoseconfluenceis also the point of entry of the Bradley sewagedischarge), it was clear that, physically, the two sites were comparable (Table 4) and the amount of Cladophora observedat the two sites was low on both occasions.

ao-a9 70-79 50-89

F----------t----------tmiiair-t---------” Table 3. Explanationof ‘“Indexof comparability”used to compare Uhsmdhml<

a

-----------

.----------

-----------

-----------

I

1

t

I

290 Fig. 2. Practical example of “look-up” chart in action: River Backwater, S.E. England.u/s Aid. Townand u/s Aid. Military refer to’sites up~tream of Aldershot Town STW and Aldershot Military STW, respectively. Shaded areas refer to combinationsof TDI and percent tolerant taxa that are unlikelyto be encountered. See text for further details.

physicalcharacteristicsand cover of filamentousalgaebetween sites where TDI valueshave been calculated Index of com~atabilitv Criteria Depth,substrate,proportionsmotheredbyfdamenI

11 111 [v

tous algae and degree of shade are broadly comparablefor the twosites Oneofthesefactorsmarkedlydifferentbetweensites

Two of thesefactorsmarkedlydifferentbetween sites Threeor fourofthesefactorsaremarkedlydifferent betweensites

240

M. G. Kelly Table4. Comparisonof physicalfeaturesand abundanceof tilamentousalgae at the River Wear, above and below

Width (m) Depth (cm) Substrate: bouldersand cobbles(%) pebblesand gravel(%) Percentageof substratesmotheredby: (a) fdamentousalgae (b) other macrophytes Shading Habitat TDI (excludingplankton)

BradleySTW Above BradleySTW

BelowBradleySTW

Approx. 10 Approx. 30

Approx. 15 Approx. 30

70 30

80 20

10 o 10-20%denselyshaded in summer Riffle 46

5 0 lcL20°/0denselyshaded in summer Mixture of run and riflle 66

For this reason, an “index of compatabiiity” of I can be applied to the difference between the two sites, indicatingthat these non-water quality factors can be ruled out in this case as the cause of the changein the TDI. An additional benefitof this approach is that it focuses attention during selectionof sample sites on environmentalfactors that might be influencingTDI values at a site. Use of herbaria

A problem throughout the study related to the general lack of information about the relationship between spatial and temporal changes in diatom communities. Information on how diatom community composition had changed over time would have been very helpfulfor interpreting likelyconsequences of nutrient stripping on rivers. To aid future studies, therefore, copies of all slides prepared during these studies were lodged in the appropriate national herbaria. This means that a permanent historical record of diatom communitiesis establishedfor each site not biased, as paper records are, by legislative requirements and logistical constraints prevailing at the time of sample collection. General discussion

The control of river eutrophication presents new challengesto regulatoryorganisationsthat go beyond simply developingand using new indices such as the TDI and MTR. Although increases in nutrient concentrations and changes in the photosynthetic biota (as measured by TDI and MTR) were observed downstream of most of the STWSstudied, it was not possible to ascribe the latter unequivocally to the former, especially in lowland areas where nutrient concentrations above the first major discharge are often high. Part of the aim of the TDI is to provide a monitoring tool that separates the influence of nutrients from that of other constituents of a sewage discharge (Kelly et al., 1996), and the use of “look-up” charts (Fig. 2) appears to be one option with potential for separating these impacts, and indeed may have applications for the MTR in the future as well. Whereasa clear increasein TDI downstreamof an STW (as interpreted by a “look-up” chart: Fig. 2)

may be evidence that nutrient reduction may be an appropriate strategy, no change is not evidencethat it will not. It should be interpreted as indicating that any ecological response might not be noticeable without a reduction in nutrients from upstream sources (although this lies outside the jurisdiction of the UWWTD). However, studies of nutrient reduction in lakes (e.g. Sas, 1989)have demonstrated that nutrient reduction only leadsto a floristicchange at a relativelylate stage. Dependingupon the starting concentration and the scale of the reduction, other possibilities include no effect at all, changes in resource acquisition strategies of dominant taxa and biomass reduction without floristic change (Sas, 1989). Both the TDI and MTR (Holmes, 1996) measurefloristicchangesbut not changesin biomass, and there is a clear need for robust techniques that are able to do this. There have been two consequences of the evaluation exercisedescribedin this paper: the first is that the TDI, in its modifiedform, is now being used widely within the Environment Agency (which took over the NRA’s role in April 1996),and the second is that it has helped to provoke a debate about the ecologicalconsequencesof eutrophication in rivers. Whilstthe consequencesof organicpollution in rivers and eutrophication in lakes are relativelywellknown, some of the problems met as the TDI #al’wvaluated related to a basic lack of understanding of the dynamics of river eutrophication. An explanatory paradigm would provide a basis for placing sampling sites (for both TDI and other indices)with respect to a discharge, and for predicting the ecologicaleffects of a change in nutrient concentration. The TDI is now recommended to regulatory organisationsas a tool for assessingeutrophication in rivers. Severalof the aspects raised in this paper (e.g. effectsof urban runoff and storm sewers and effects immediately downstream of discharges) are concerned not with the index itselfbut with how it is best used within monitoring systemsdesignedto produce information on which robust decisions concerning capital expenditure at STWS can be based. These points underline the importance of catchment-based approaches in assessingthe impact of nutrients and the effectivenessof likely nutrient control schemes, rather than simply evaluating the impact of isolated

Trophic diatom index discharges, Although this necessarily involves more

effort, it will result in stronger cases and a greater likelihood of improvements in ecological quality following nutrient stripping. Acknowledgements—I thank the National Rivers Authority (now the Environment Agency) for funding both the

development of the TDI and the evaluation exercise. In particular, I thank Anne Lewis for managing the project, and NRA staff directlyinvolvedin collectingdata reported here (Chris Adams, David Balbi, Alison Hutchings, Anna McQueen, Ruth Maddocks, Alan Tubbs). I also thank Brian Whitton for useful discussions.The viewsexpressed in this paper are not necessarilythose of the Environment Agency.

REFERENCES

Coste M. (1994) Proposition

d’une codification des denominations de diatomees adaptee a la gestion des inventaires et aux calculs d’indices diatomiques (Proposal for the coding of names of diatoms for the management of inventories and calculation of diatom-based indices). CEMAGREF, Bordeaux, France. European Community (1991) Council directive of 21 May 1991 concerning urban waste water treatment (91/271/ EEC). Oj7iciaIJ. Eur. Community Ser. L. 135, 40-52.

HendeyN. I. (1974)The permanganatemethodfor cleaning freshly gathered diatoms. Microscopy 32, 423-426.

241

Holmes N. T. H. (1996) The Use of Riuerine Macrophytes for the Assessment of Trophic Status: Review of 1994/95 Data and Refinements for Future Use. A Report to the National Rivers Authority. National Rivers Authority, Peterborough, U.K. Hynes H. B. N. (1960) The Biology of Polluted Waters. Liverpool University Press, Liverpool, U.K. Kelly M. G. (1996) The Use of Diatoms to Monitor Nutrients in Rivers. R&D Project Record E1/i618/5.Environment

Agency,Bristol, U.K. KellyM. G. and Whitton B. A. (1995)The Trophic Diatom Index: a new index for monitoring eutrophication in rivers. J. Appl. Phycol. 7, 433444. Kelly M. G., Whitton B. A. and Lewis A. (1996)Use of diatoms to monitor eutrophicationin U.K. rivers. In Use of Algae to Monitor Rivers (Edited by Whitton B. A. and Rott, E.), .up. . 79–86. University of Innsbruck Press, Innsbruck. Round F. E. (1993)A review and methods for the use of epilithicdiatoms for detectingand monitoringchangesin river water quality 1993.Methods for the Examination of Waters and Associated Materials. Her Majesty’sStationery Office,London. Sas H. (1989) Lake Restoration by Reduction of Nutrient Loading: Expectations,

Experiences,

Extrapolations.

Academia Verlag Richarz GmbH., St Augustin. Zelinka, M. and Marvan P. (1961) Zur Prazisierung der biologischen Klassifikation der Reinheit fliessender Gewasser (Towards a precise biologicalclassificationof the purity of flowingwaters). Archivftir Hydrobiologie 57, 389+07.

APPENDIX1 Taxon sensitivities(s) and indicatorvalues(v)used for the TD1.Predominatelyplanktonictaxa and thosetolerant to organicpollutionare also identified.*A changesinceKellyand Whitton (1995).A workedexampleof how to calculatethe TDI is givenin Appendix1 of Kelly and Whitton (1995). s v Comment Taxon Achanthoceras o 0 Moved from Auheya(plankton) IncludesA. rastrata, A. calcar, etc. 2 5 Achnattthes (Achnanthidium) Iattceolara-type Achnanthea (Achrranlhidium)mirrutissima-type 2 2 IncludesA. microcephala,A. biasolettiana 1 Includingnther Achnanthidiurnspp. 3 Achnaruhes (other) Achnanthidium See Achrtamhes spp. 1 3 Amphipleura Amphora pedicrdus Amphora (other) Anomoeoneis Asterionelhr Attheya Ardacosira Brachysira Caloneis Ceratoneis arcus Chaetoceras Cocconeis pediculus Cocconeis placentrda Cocconeis (other) Ctenophora prdchella Cyclostephanos Cyclotella Cymatopleura Cymbella a@ris Cymbella delicatula Cymbella microcephala Cymbella (large forms) Cymbella (other) Denticrda tenuis Dialoma tenue Diatoma rmlgare Diatoma (other) Didymosphenia geminata Dirrloneis E~erbeckia arenaria Encyonema minutum/silesiacum

5 5 4

0 4

0 1

2 I

1 0 1 0

3

3 1

0

0

4 3 2 2

2 2 2

;Iankton See Achanthoceras Plankton See Hannaea

0 0 4

1 1 1 4 2 2 2 5 2 2

1 0 0 I 3 3 2 2

1 2 2 3

Plankton

Formerly Synedra pulchella Plankton Plankton

Nominally >70 pm. IncludesC. caespitosa, C. lanceolata* IncludesErcyonemaspp. Other Deruicrda SPP.are halophilous *

1 3

1

1

4 3

2 2

* Continued overleaf

242

M. G. Kelly

Taxon

s

v

Encyonema(other)

Comment See Cymbella (other)

Epithemia Eucocconeis Ermotia Fragilaria capucina Fragilaria crotonensis Fragilaria uaucheriae Fragilaria (other) Frustulia Gomphocymbella Gomphoneis Gomphonema angustatum Gomphonema oliuaceoides Gomphonema olivaceum Gomphonemaparrnrlum Gomphonema (other) Gyrosigma Hannaea arcus Hantzschia Martyana Melosira varians Meridion circrdare Navicrda cryptotenella-type Navicula gregaria Navicula lanceolata Navicula tripunctata Nauicrda (other)

2 5 5 3 5 1 5 5 4 2 5 5 5 4 4

2 3 2 3 1 2 3 1 2 2 3 2 1 2 2 1

Nauicrda (small species)

5

1

Neidium Nitzschia Nitzschia Nitzschia Nitzschia Nitzschia Nitzschia

acicrdaris anrphibia dissipafa pusilla section Sigmoideae

2 4 5 5 4 4

(other)

4

3 1 3 2 2 2 1

1 1 2

3 3 2

●

4 4 4 s 1

1 3 1 1 1

*

1

3 0

I

3 I

2

0 3 2 1 2

2 1 3 2

0 2 1 2 1

Plankton IncludingStaurosira See Gomphonema-other

I

Opephora Perania @buIa Pinnrdaria Pseudostaurosira breuistriata Psammodictyon Prarctastriata Reimeria sinuata Rhizosolenia Rhoicosphenia abbreviate Rhopalodia Sellaphora Semiobis Skeletonema Stauroneis Staurosirella Stenopterobia Stephanodiscus Surirella Synedra ulna Synedra (other) Tabellariafeneslrata Tabe[laria+ther Tabu[aria Tetracyclus Thalassiosira

o

o

1 I o 1 1 1 0 3 2 1 0

Tryblianella Urosolenia

o

0

Organicpollution-tolerant

Formerlyfreshwaterspeciesof Opephora IncludesN. nrenisculus, N. reichardtiana

Organicpollution-tolerant Organicpollution-tolerant Excludingsmallspecies(seebelow).Includingrelatedgenera such as Luticola, Cardrnda, etc. Nominally < 12f.tm.Including small speciesof Se/laphora, Diadesmis and related genera.Organicpollution-tolerant

* * * Ocnerallylarge (> 100#m) forms * IncludesN. palea plus Tryblionella and Psammodictyon. Organicpollution-tolerant See Martyana

See Nitzschia (other) See Urosolenia = R. curuata *

Includedwith small ALmictda 5 4 1

o 3 3

4 II 2 5 1

;Iankton

2

Plankton

Plankton

* Plankton See Nitzschia (other) Plankton