Impact of Urban Pollution from the Hanoi Area on Benthic Diatom Communities Collected from the Red, Nhue and Tolich Rivers (Vietnam)

The effects of urban pollution from Hanoi city on the benthic diatom communities of the Nhue–Tolich river system were studied during the 2003 dry season. Benthic diatoms were allowed to grow on glass slides suspended in the water flow for 4 weeks. To reveal the relationship between water quality and diatom communities, Canonical correspondence analysis (CCA) was used on data concerning relative abundances of diatom species and environmental variables. Two diatom indices, IPS and DAIpo, were applied to evaluate water quality in the three rivers. A total of 291 diatom taxa were found in the Red, Nhue and Tolich Rivers. These were mainly cosmopolitan taxa, with some tropical, subtropical and endemic taxa. The most abundant taxa at the Red site were Aulacoseira granulata, Achnanthidium minutissimum, Encyonema minutum, Navicula recens and other halophilous taxa such as Nitzschia kurzii, Seminavis strigosa, Entomoneis paludosa, Bacillaria paradoxa. Diatom assemblages at the Tolich site consisted mainly of Nitzschia umbonata, Nitzschia palea and Eolimna minima. Diatom density ranged from 660 to 30,000 cells/cm². Environmental variables and diatom assemblage composition at all sites were significantly correlated. Two diatom indices gave similar results and indicate the Tolich River with the lowest values as a highly polluted site.     

Distribution of Epilithic Diatoms in Response to Environmental Conditions in an Urban Tropical Stream, Central Kenya

Use of diatoms in monitoring water quality is well acknowledged in developed countries, but only recently has the assessment started gaining importance in developing countries. Diatoms can be obtained from natural and artificial substrates. Appreciating the differences and similarities of diatom assemblages on both substrates may contribute to a better understanding and standardization particularly during monitoring of water quality. During this study we assessed diatom assemblages, biodiversity and trophic indices in relation to water quality along the Nairobi River. Fifteen sites were sampled in September 2000 during the dry season. Diatoms were collected from natural substrates (stones, pebbles) and artificial substrates (100% acrylic wool). On artificial and natural substrates, a total of 190 and 151 taxa were found, respectively, the majority of these taxa (80%) have cosmopolitan distribution and are also widespread throughout tropical African. Species composition changed downstream, five taxa dominated upper and mid stream sites whereas lower stream sites were dominated by one or two taxa. Species richness, diversity, dominance and evenness were positively correlated with NO₃, O₂ and altitude but decreased markedly downstream with a simultaneous increase in total dissolved solids, alkalinity, chemical oxygen demand and PO₄. Ordination and classification (CANOCO and TWINSPAN) showed that diatom assemblages in the Nairobi River responded strongly to water quality changes with respect to concentrations of NO₃, NO₂, total dissolved solids and temperature. Taxa common at less impacted upstream sites included Gomphonema gracilis, Anomoeoneis brachysira and Fragilaria biceps; while common taxa at midstream sites with agricultural catchments were Gomphonema parvulum, Navicula cryptocephala, N. schroeteri, N. bryophila, N. halophila, Nitzschia linearis var. linearis and Cymbella silesica. Achnanthes minutissima var. saprophila, Gomphonema angustum, Navicula subminuscula, N. arvensis, Nitzschia palea and N. umbonata were most common at urban sites, which were polluted by residential and industrial effluents. Trophic diatom indices suggested that water quality was poor at most sites in the Nairobi River. Most sites along the river had low Generic Diatom Index values, GDI (<12) and high Trophic Diatom Index values, TDI 73–78 (median = 76) and 75–84 (median = 77) for artificial and natural substrates, respectively. This study showed that diatoms' response on natural and artificial substrates were similar and reflected environmental conditions correctly.     

Dynamics of diatom colonization process in some rivers influenced by urban pollution (Hanoi, Vietnam)

Periphytic diatom communities’ colonization patterns were studied at three sampling stations of the Red–Nhue–Tolich hydrosystem presenting different urban pollution levels by using artificial substrates for 6 weeks in dry season 2005. Structural characteristics of periphytic diatoms developed on glass substrates at each sampling site were followed and compared. This experiment showed, through various general criteria (total diatom density, dry weight biomass) and specific criteria (relative diatom abundances, indices) that the structure of benthic diatoms developed on these substrates was strongly affected by pollution as early as the second week of colonization. Communities exposed to heavily and moderately polluted sites contained species which are known to be saprophilous or tolerant to organic pollution such as Nitzschia umbonata, Nitzschia palea, Cyclotella meneghiniana, Eolimna minima. Growth inhibition of diatom communities at the heavily polluted site was mostly related to a strong increase of organic load rather than to low metallic input, though metallic (Cd and Zn) burdens have been successfully quantified in the biofilms developed at the three studied sites. Nevertheless, no significant difference in species richness and diversity index between colonization duration times was observed. Based on values of diatom indices Indice de Polluosensibilité (IPS) and diatom assemblage index to organic water pollution (DAIPo), water quality could be classified as medium quality at Red site, polluted at NT₂ and heavily polluted at TL. Thus, the use of diatoms as a tool for water assessment appears suitable for monitoring rivers in Vietnam, as it is in several other countries.     

Can season interfere with diatom ecological quality assessment?

To understand whether seasons influence the ecological quality assessment of streams on the basis of diatoms, a study was undertaken in two lowland water courses located in northwest Portugal, between autumn 2008 and summer 2009. Temporal variation in the chemical pollution of these streams was small as revealed by a number of physical and chemical parameters analyzed. PERMANOVA global test revealed significant variation in water temperature among seasons. The diatom communities also showed a temporal variation although not all the seasons were statistically different. The multidimensional scaling analysis showed that the main differences in the diatom communities were between two groups of seasons: autumn/winter and spring/summer. Species such as Cocconeis pseudolineata, Gomphonema parvulum var. exilissimum, Fragilaria vaucheriae, Encyonema minutum, and Nitzschia recta were more abundant in spring/summer, while species such as Mayamaea atomus and Nitzschia pusilla were more abundant in autumn/winter. The BIOENV routine confirmed that the biological and temperature patterns are highly correlated. Despite the effects observed on diatom communities, these differences were buffered by the EQR (IPS) values which do not reflect seasonal differences. Therefore, the use of the index IPS seems to allow the monitoring of the streams’ ecological quality throughout the year without the interference of the natural temporal variability of diatom communities.     

Epilithic diatoms as indicators in tropical African rivers (Lake Victoria catchment)

We investigated epilithic diatoms in rivers draining to the Nyanza Bay in Lake Victoria (Kenya) with the aim of determining environmental gradients in the assemblages and testing the usefulness of diatom metrics from temperate regions. Spatial and temporal variations of assemblages were studied in 12 sites of three rivers. Kibos, Nyando, and Kisat rivers contained 224 diatom taxa collected on seven sampling occasions over 4 years. Species richness showed a marginal decrease downstream and was the lowest at sites with high conductivity and ammonia–nitrogen levels. Two-Way Indicator Species Analysis and Canonical Correspondence Analysis revealed two major groups of river sites. Conductivity, alkalinity, turbidity, dissolved oxygen, and silicate were the most important variables influencing species distribution. Ecological diatom metrics of temperate regions and the Specific Pollution sensitivity Index showed good relationships with environmental variables. Both diatom assemblages and averaged indicator values were strong in predicting sites of ecological deterioration and in differentiating an upstream site of better quality (drinking water supply of Kisumu), thereby confirming epilithic diatoms as suitable water quality indicators in equatorial rivers. The use of metrics initially designed for temperate rivers, however, appears less valuable in good quality tropical rivers because potential indicators are not considered.     

桂江流域附生硅藻群落特征及影响因素

研究了桂江流域水质、土地利用、地理因素对河流附生硅藻群落的影响。结果显示,桂江流域电导率(Conductivity,Cond.)由下游至源头呈降低趋势,其它水质参数变化趋势不明显。主成分分析(Principle Component Analysis,PCA)显示前两个主成分共解释了56.2%的水质特征,第一轴反映了氨氮(NH4-N)、硝氮(NO3-N)、总氮(Total Nitrogen,TN)的变化梯度,第二轴反映了水温(WT)、pH、Cond.、溶解氧(Dissolve Oxygen,DO)的变化梯度。桂江流域硅藻特定污染敏感指数(Specific PolluoSensitivity Index,IPS)和硅藻生物指数(Biological Diatom Index,IBD)下游低于源头,差异不显著,与多项水质、土地利用以及地理因子呈线性显著相关。24个样地共发现112种硅藻,丰富度大于5%的37种,丰富度最大的几个种类依次为Achnanthidium minutissimum,A.pusilla,A.tropica,Cymbella laevis。对应分析(Corresponding Analysis,CA)显示桂江流域存在3个差异较大的硅藻群落,流域下游以Nitzschia recta为优势种,A.lanceolata、Amphora montan、Planothidium frequentissimum在中下游丰度较高,上游区域种类较多。典型相关分析(Canonical Correspondence Analysis,CCA)排序前两轴解释了硅藻群落变异程度的28.60%,CCA排序轴1与水质(Cond.、WT、NH4-N、NO3-N、TN)和土地利用(城市面积、农田面积、植被覆盖)显著负相关,与地理因素(流域面积、海拔、坡度)显著正相关,第二轴与浊度(NTU)显著正相关(P<0.05)。偏典型相关分析(Partial CCAAnalyses)显示,土地利用、地理因子、水质分别解释了桂江流域硅藻群落变异的7.20%,17.50%,48.50%。结果表明,桂江流域附生硅藻群落结构是水质、地理因子和土地利用共同作用的结果,水质起决定性作用,电导和不同形态的氮是影响附生硅藻群落结构的主要水质因素。     

Changes in the algal composition and water quality of the Sundays River,Karoo, South Africa,from source to estuary

A first survey was done on algae present in the Sundays River from its source to its confluence with the sea. Species found in the upstream sections of the river included indicators of good water quality, but the quality deteriorated downstream with peaks in algal abundance being ascribed to peaks in nutrient concentrations. Cyanobacteria and euglenoids were present in the upper and middle reaches of the river, but were absent downstream. Dinoflagellates became more important downstream, especially in the estuary. Dominant species, reaching high concentrations along the river, included Nitzschia frustulum, Nitzschia capitellata, Carteria klebsii, Chlorella vulgaris and Anabaena species. The presence of the diatom Eolimna comperei is a first record of its occurrence in South Africa. The Sundays River can be described as a brackish, hard water system with high nutrient concentrations in certain sections. The most important contributors to high nutrient concentrations were point sources in the vicinity of towns along the river banks, as well as diffuse sources contributing to high nitrogen concentrations in the fertile Sundays River valley. Increasing salinities were due to pollution, evaporation and agricultural activities in the valley.     

七项河流附着硅藻指数在东江的适用性评估

综合运用因子分析、聚类分析、箱型图分析等统计方法评估了河流附着硅藻生物指数(Biological Diatom Index,IBD)、硅藻营养化指数(Trophic Diatom Index,TDI)、斯雷德切克指数(Sládecˇek’s Index,SLA)、特定污染敏感指数(Specific Polluosensitivity Index,IPS)、硅藻属指数(Generic Diatom Index,IDG)、戴斯指数(Descy Index,DESCY)和欧盟硅藻指数(European Economic Community Index,CEE)在东江流域河流水质评价中的适用性。结果显示:SLA与IPS,CEE显著相关(P<0.05),CEE与TDI不相关,其余指标间均极显著相关(P<0.01)。SLA与13项水质理化指标均无相关性,TDI与含氯度(Cl)显著负相关,CEE与溶解氧(DO)、电导率(Cond.)、总氮(TN)显著正相关(P<0.05),其余指标与氨氮(NH4-N)、pH不存在线性相关,与五日生化需氧量(BOD5)、高锰酸盐指数(CODKMnO4)、亚硝氮(NO2-N)、硝氮(NO3-N),总磷(TP)具极显著相关性(P<0.01)。13项水质理化指标中主成分负荷贡献大于50%的八项理化参数DO、BOD5、CODKMnO4、TN、NO3-N、NO2-N、TP和SiO2将试验区水质分为四组。IPS、IBD、IDG和CEE与水质物化分类一致性较好。IPS、IBD、IDG和CEE的逐步判别分析(引入P=0.20,剔除P=0.25)显示IPS和CEE都只选出了NO2-N,分类判别的正确率分别为55.6%和48.1%;IBD引入了NO2-N,CODKMnO4和DO 3个解释变量,判别正确率74.1%;IDG引入BOD5和NO3-N两个变量,分组正确率63.0%。硅藻群落聚类显示,IBD和IDG在水质物化分类的箱型图中呈现出明显合理的趋势。以上研究表明IBD和IDG硅藻指数最适合用于东江河流水质生物监测与评价。     

Diatoms as water quality indicators in the upper reaches of the Great Fish River,Eastern Cape,South Africa

This study focused on the spring-fed upper reaches of the economically important Great Fish River with the aim of determining if diatoms could be used for biomonitoring in semi-arid conditions in southern Africa. Five sites were monitored monthly from 2010 to 2012. Of the 269 diatom taxa belonging to 51 genera identified, the dominant taxa were mostly those considered to be pollution-tolerant: Amphora pediculus, Craticula buderi, Fragilaria biceps, Nitzschia frustulum, Nitzschia paleacea, Planothidium lanceolatum and Rhopalodia gibba. A number of diatom-based numerical indices were used to infer water quality, including the generic diatom index, the specific pollution sensitivity index, the biological diatom index, and percentage pollution-tolerant valves, which forms part of the UK trophic diatom index. All index scores showed the Great Fish River to be impacted, and showed significant correlations of diatom species abundance with pH, NO₃-N, electrical conductivity, NH4-N and CaCO_3. Analysis revealed EC and NO3-N as the main environmental drivers affecting diatom community composition, followed by pH and PO4-P. The percentage of diatom deformities at all sites was high, at 3.5%. Diatom indices showed the river to be impacted by decades of agricultural activity, which was confirmed by chemical water analysis. Thus diatom indices can be used for biomonitoring in semi-arid areas.     

Use of benthic diatom communities to evaluate water quality in rivers of southern Poland

Biological and chemical data were processed to estimate trophic stage and degree of pollution in several streams and rivers in southern Poland. The majority were eutrophic and some of them heavily polluted; only a few were oligo-mesotrophic. The differences in the water quality of the rivers were reflected by different types of diatom community and also by the values for some diatom indices, which were calculated using the latest version of the 'Omnidia' database software. Except for the Sládeček's index, all diatom indices correlated significantly with organic load (COD), oxygen concentration, conductivity and most of the measured ions. Some indices showed a significant negative correlation with trophic level (expressed by NH₄-N and PO₄-P). In general, IPS (Specific Pollution Sensitivity Index) and GDI (Generic Diatom Index) indices gave the best results. Among the investigated diatom communities, only a few taxa indicated oligo-mesotrophy and oligo-β-mesosaprobity. Most of the sites were characterised by a greater relative contribution of eutraphent and tolerant ones as well as α-mesosaprobic and polysaprobic diatoms. This study suggests that the structure of benthic diatom communities and diatom indices, especially GDI, can be applied for monitoring rivers in Poland. This revised version was published online in June 2006 with corrections to the Cover Date.     

Attached diatom communities from the lower Truckee River,summer and fall, 1986

The algal flora of the Truckee River below Reno, Washoe County, Nevada was examined during the summer and fall months of 1986. This reach of the lower Truckee River exhibited a substantial gradient in dissolved inorganic nitrogen associated with sources which included treated wastewater from the Reno metropolitan area. The algal communities were similar to those of other river systems of the Great Basin. Cyanophyta and Chlorophyta formed encrusting mats on the substrate, with the nitrogen fixer Calothrix atricha relatively abundant upstream from the nitrogen source. Diatoms were abundant within and upon this mat. A total of 139 diatom taxa and 11 taxa other than diatoms was identified from this flora. Several of the diatom taxa, including Achnanthes minutissima, Diatoma vulgare, Nitzschia dissipata, and Nitzschia palea, demonstrated distinct downriver patterns in relative abundance.     

Harmonization is more important than experience—results of the first Nordic–Baltic diatom intercalibration exercise 2007 (stream monitoring)

The goal of this study was a harmonization of diatom identification and counting among diatomists from the Scandinavian and Baltic countries to improve the comparison of diatom studies in this geographical area. An analysis of the results of 25 diatomists following the European standard EN 14407 during an intercalibration exercise showed that a high similarity was achieved by harmonization and not because of a long experience with diatoms. Sources of error were wrong calibration scales, overlooking of small taxa, especially small Navicula s.l., misidentifications (Eunotia rhomboidea was mistaken for Eunotia incisa) and unclear separation between certain taxa in the identification literature. The latter was discussed during a workshop with focus on the Achnanthes minutissima group, the separation of Fragilaria capucina var. gracilis from F. capucina var. rumpens, and Nitzschia palea var. palea from N. palea var. debilis. The exercise showed also that the Swedish standard diatom method tested here worked fine with acceptable error for the indices IPS (Indice de Polluo-sensibilité Spécifique) and ACID (ACidity Index for Diatoms) when diatomists with a low similarity (Bray–Curtis <60%) with the auditor in at least one of the samples are excluded.     

Distribution patterns of benthic diatoms in a Pampean river exposed to seasonal floods: the Cuarto River (Argentina)

The diatom community growing on cobbles and sand substrata along the Cuarto River (Córdoba, Argentina) was studied during 2000 and 2001. Multivariate analyses of the data (PCA and CCA) showed distinct differences in water chemistry and substrata types between the upstream sites (sites 1–10) and downstream sites (sites 11–19). Sites 1–10 supported an epilithic diatom community associated with low water conductivity and gravel substrata. This consisted of adnate Achnanthes (A. biasolettiana, A. minutissima), as well as stalked (Gomphonema aff. angustum, Reimeria uniseriata, Fragilaria capucina var. rumpens) or prostrate (Nitzschia lacuum) taxa. Downstream sites were associated with high conductivity, fast flowing waters and finer substrata (sand, silt), and were colonised by prostrate diatoms, including several species of Navicula (N. pupula, N. mutica, N. veneta, N. insociabilis) and Nitzschia (N. umbonata, N. palea). Variations in water flow caused significant changes in the diatom communities of the river. During periods of low flow (winter and autumn), chain forming (Diatoma vulgaris, D. moniliformis) or stalked (Synedra ulna) taxa partially replaced the former community of Navicula and Nitzschia in the downstream sites. High flow (in summer) led to diatoms of large size being replaced by smaller size diatoms, such as Achnanthes lanceolata, Navicula mutica, Hantzschia amphioxys and Amphora montana. The severe effect of floods in the lower part of the Cuarto led to these taxa having a much higher proportion in the lower stretch of the river, taking advantage of the subaerial conditions created by the floods. Local episodes of water pollution were associated with a transient shift towards the dominance of Navicula pupula, Synedra ulna, Nitzschia lacuum and Reimeria uniseriata during winter, when inputs were least diluted because of the low flow.     

Diatom communities in small water bodies at H. Arctowski Polish Antarctic Station (King George Island, South Shetland Islands, Antarctica)

An investigation of ponds, puddles and slow-flowing waters situated in the area of the Polish Antarctic Station distinguished two groups of diatom communities. The first group characterized waters poor in nutrients and brackish. The number of taxa, abundance of species and diatom biomass index were all low. Nitzschia homburgiensis, Achnanthes laevis var. quadratarea and A. delicatula prevailed. The second group characterized water richer in nutrients and brackish. The number of species was also low, but the diatom biomass index was higher. Nitzschia gracilis, Navicula gregaria and Navicula wiesneri formed large populations. Received: 17 May 1996 / Accepted: 20 September 1997     

Non-wadeable river bioassessment: spatial variation of benthic diatom assemblages in Pacific Northwest rivers,USA

Current bioassessment efforts are focused on small wadeable streams, at least partly because assessing ecological conditions in non-wadeable large rivers poses many additional challenges. In this study, we sampled 20 sites in each of seven large rivers in the Pacific Northwest, USA, to characterize variation of benthic diatom assemblages among and within rivers relative to environmental conditions. Analysis of similarity (ANOSIM) indicated that diatom assemblages were significantly different among all the seven rivers draining different ecoregions. Longitudinal patterns in diatom assemblages showed river-specific features. Bray–Curtis dissimilarity index values did not increase as a function of spatial distance among the sampled reaches within any river but the Malheur. Standardized Mantel r of association between assemblage similarity and spatial distance among sites ranged from a high of 0.69 (Malheur) to a low of 0.18 (Chehalis). In the Malheur River, % monoraphids, nitrogen-tolerant taxa, and beta-mesosaprobous taxa all decreased longitudinally while % motile taxa, especially Nitzschia, showed an opposite trend, reflecting a strong in-stream water quality gradient. Similar longitudinal trends in water quality were observed in other rivers but benthic diatom assemblages showed either weak response patterns or no patterns. Our study indicated that benthic diatom assemblages can clearly reflect among-river factors. The relationships between benthic diatom assemblages and water quality within each river may depend on the strength of the water quality gradients, interactive effects of water quality and habitat conditions, and diatom sampling design.     

Aquatic pollution assessment based on attached diatom communities in the Pinang River Basin,Malaysia

The diatom communities collected from artificial substrates (glass slides) at 12 sampling sites along Pinang River Basin were analysed. Species composition was highly variable among sampling sites, and the highest diversity value (mean H = 3.56 bit/individual) and species richness (mean S = 17.32) was recorded at a polluted station in an estuary, which received salt-water intrusion during high tide. The downstream sampling stations were heavily organically polluted with Saprobic Index values ranging between 2.81 and 3.10, while upstream stations were relatively clean with Saprobic Index values recorded between 1.40 and 1.96. The diatom community structure and the specific sensitivity of certain diatom species can be related to the degree of water quality in Pinang River Basin. The abundance of certain diatom species could be used as biological indicators to measure impacts of river pollution.     

Diatom assemblages of the Cuyahoga river,N. E. Ohio (USA)

The Cuyahoga River is a heavily polluted tributary of Lake Erie located in N. E. Ohio (USA).One hundred seventy taxa of diatoms were identified from seven locations along the Cuyahoga River. The most frequently collected diatoms from each station were Cyclotella meneghiniana, Gomphonema parvulum, Navicula cryptocephala, N. cryptocephala var. veneta, N. lanceolata, N. menisculus, N. minima, N. minuscula, N. pelliculosa, Nitzschia amphibia, N. ovalis, N. palea, and Rhoicosphenia curvata.In the most heavily damaged region of the river these widely-distributed taxa were the only frequently collected diatoms.The relatively undamaged section of the river contained 94% more taxa than the most heavily damaged section. Chief among these additional taxa were Achnanthes lanceolata, A. lanceolata var. dubia, Cocconeisplacentula, Fragilaria vaucheriae, Melosira varians, Meridion circulare, Navicula mutica var. tropica, N. symetrica, Nitzschia dissipata, Stephanodiscus astraea, and Synedra rumpens.The degree of similarity between diatom assemblages along the Cuyahoga River as measured by a modification of Sørensen's index of similarity in species-frequency of occurrence composition was related to the degree of chemical-physical water quality similarities and to the extent of similarity between areas of geologic and biologic substrates. The most dissimilar diatom assemblages usually occurred between locations that were the most dissimilar with respect to chemical-physical water quality conditions rather than to dissimilarities with respect to sediment-substrate composition.     

Diatoms as indicators of stream quality in the Kathmandu Valley and Middle Hills of Nepal and India

1. Diatoms are recognised as indicators in temperate streams, but only recently have assessments begun of their value in indicating stream quality in the tropics and sub‐tropics. Here, we extend previous studies by assessing stream diatom assemblages in relation to water quality and habitat character in the Kathmandu Valley, and in the Middle Hills of Nepal and northern India. We also assessed whether the U.K. Trophic Diatom Index (TDI) was sufficiently portable to reveal pollution in Himalayan rivers. In the more urbanised and highly agricultural Kathmandu Valley, we compared diatom response to water quality classes indicated by a local invertebrate index, the Nepalese Biotic Score (NEPBIOS). 2. Thirty and 53 streams in the Kathmandu Valley (2000) and Middle Hills (1994–96), respectively, were sampled in October and November during stable flows following the monsoon. Diatoms were collected in riffles, water samples taken for chemical analysis, and habitat character of the stream channel, bank and catchment assessed using river habitat surveys. In the Kathmandu Valley, macroinvertebrates were collected by kick‐sampling. 3. In total, 113 diatom taxa were found in the Kathmandu Valley streams and 106 in the Middle Hills. Of 168 taxa recorded, 62 occurred only in the Kathmandu Valley, 56 only in the Middle Hills and 50 were common to both areas. Most taxa found only in the Kathmandu Valley belonged to the genus Navicula while most taxa confined to the Middle Hills were Achnanthes, Fragilaria and Gomphonema. 4. In the Kathmandu Valley, richness and diversity increased significantly with K, Cl, SO₄ and NO₃, but declined significantly with Al, Fe, surfactants and phenols. Richness here also varied with habitat structure, being lowest in fast flowing, shaded streams with coarse substrata in forested catchments. In all streams combined, richness increased significantly with Si, Na and PO₄, but declined significantly with increasing pH, Ca and Mg. 5. Diatom assemblage composition in the Kathmandu Valley strongly reflected water chemistry as revealed by cations (K, Na, Mg, Ca), anions (Cl, SO₄), nutrients (NO₃, PO₄, Si), and also substratum composition, flow character and catchment land use. The commonest taxa in base‐poor forested catchments were Achnanthes siamlinearis, A. subhudsonis, A. undata and an unidentified Gomphonema species; Cocconeis placentula and Navicula minima in agricultural catchments; and Mayamaea atomus var. alcimonica, M. atomus var. permitis, and Nitzschia palea at polluted sites near settlements. Diatom assemblages in none‐agricultural catchments of the Kathmandu Valley and Middle Hills were similar, but they contrasted strongly between urban or agricultural catchments of the Kathmandu Valley and the less intensively farmed catchments of the Middle Hills. 6. In keeping with variations in assemblage composition, most streams in the Kathmandu Valley had higher TDI values (33–87, median = 64) and more pollution tolerant taxa (0–78%, median = 16) than streams in the Middle Hills (25–82, median 45, 0–26%, median = 2). TDI values correlated significantly with measured PO₄, Si, and Na concentrations in the Kathmandu Valley, and with Si and Na concentrations in the Middle Hills. There was some consistency between water quality classes revealed by NEPBIOS and diatoms, but also some contrast. Water quality class I–II sites had lower TDI values and were less species rich than water quality II sites, however, there were no significant differences in detrended correspondence analysis (DCA) assemblage scores and relative abundances of pollution tolerant taxa between NEPBIOS classes. 7. While diatoms in the Middle Hills indicate unpolluted or only mildly enriched conditions, they reveal pronounced eutrophication and organic pollution in the densely populated Kathmandu Valley. In addition, diatoms appear to respond to altered habitats in rural agricultural and urban areas. As demands on water resources in this region are likely to increase, we advocate the continued development of diatoms as indicators using methods based on what appear to be consistent responses in the TDI between Europe and the Himalaya.     

Ecological status of some Finnish rivers evaluated using benthic diatom communities

The applicability of some diatom methods to quality assessment of differenttypes of Finnish rivers was compared using dominant taxa of diatomcommunities and nutrient level estimations using Trophic Diatom Index(TDI) and a new Phosphorus Diatom Equation (PDE) [Tot. P_calc (g l^-1) = 39 – 0.278 ol-% – 0.117 olme-% – 0.346me-% – 0.006 meeu-% + 1.193 eu-%; n = 97; r² = 0.742;SE = 17.4]. The overall quality estimations were done by Index ofPollution Sensitivity (IPS) and by Generic Diatom Index (GDI); limit valuesfor quality classes are proposed.     

A review of diatoms found in highly acidic environments

A review is presented of 28 studies in the literature of diatoms in environments at pH 3.5, including natural and anthropogenic acid sources. A total of 124 diatom taxa have been reported, but many are likely to have been accidental occurrences, because only a few specimens were found. Approximately 19 taxa abundant in at least one study or common in several studies are considered true inhabitants of highly acidic waters. These include: Achnanthes minutissima, Eunotia exigua, E. tenella, E. septentrionalis, E. osoresanensis, E. arcus, E. glacialis, E. pectinalis, Frustulia rhomboides, F. rhomboides var. saxonica, Nitzschia capitellata/subcapitellata, Nitzschia communis, Nitzschia pusilla, Nitzschia vasta, Pinnularia acoricola, P. obscura, P. braunii var. amphicephala, P. subcapitata and P. terminitina. There are inconsistencies in the taxonomy of several of these species and possible synonymies could lower the number of taxa to less than 9. Compared to diatom species richness in environments at pH 4.5–5.0, there are many fewer taxa in environments pH 3.5, suggesting a threshold between pH 4.5 and 3.5 below which many species are unable to maintain a population.