Diatom communities of acidic mountain streams in Poland

A comparison has been made of the species composition of diatom communities developing in acidic Polish mountain streams which flow over calcium-poor substrates: sandstones in the Silesian Beskid (section of the Western Carpathians), the witokrzyskie Mts, and over granite in the Karkonosze range (in the Sudetic Mts). The number of taxa and diversity of the diatom assemblages decreased along a decreasing pH gradient. The correlation between pH and the number of taxa was positive and significant (r ² = 0.69, p < 0.005). A small number of species (< 20) and low diversity were found in the communities developing in strongly acidic streams such as in the witokrzyskie Mts with pH 4.1–5.2, and in the Silesian Beskid with pH 3.5–4.0. In the stream of the Karkonosze Mts, with pH 5.2–6.0, the communities were characterized by their greater number of species and higher diversity.Acidobiontic and acidophilous diatoms were generally dominant. The pH-indiferent forms were less abundant, and their proportion increased above pH 5.0. Eunotia exigua, E. paludosa var. trinacria, E. tenella and Pinnularia subcapitata dominated in streams with the lowest pH, while E. exigua, E. sudetica and Achnanthes kryophila predominated in a stream with water pH above 5.2. Eunotia exigua, a common acidobiontic species was present in all the examined communities, and was a strong dominant in waters of pH 5.0. A corresponding decrease in abundance of E. exigua was observed with an increase in pH.     

Diatom assemblies in some moorland pools in the Drenthian district (the Netherlands)

The results are presented of a survey of diatom assemblies in a number of moorland pools and lakes in the Dwingeloo area of Drenthe. Four assemblies, with some intermediate ones, are described. (1) An assembly characterized by an abundance ofFrustulia rhomboides var.saxonica, Eunotia lunaris, E. veneris var.rhomboidea andTabellaria flocculosa and found in oligotrophic water with a pH in the range 3.1–4.2 (2) An assembly solely consisting ofEunotia exigua which occurs in oligo-minerotrophic pools with brownish deposits of iron compounds and a pH of about 3.5. (3) An assembly consisting of 100%Eunotia paludosa found in the ombrotrophic habitat of emerged stands ofSphagnum with a pH averaging 3.1. This species was found in nearly all localities sampled. (4) An assembly characterized by the sympatric occurrence ofMelosira italica, Nitzschia gandersheimiensis, Gomphonema parvulum andTabellaria flocculosa and found in mesotrophic, disturbed habitats with an average pH of about 4.5. For the delimitation of these assemblies a cluster analysis was carried out by means of the TABORD computerprogram.     

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.     

Diatom and micro-invertebrate communities and environmental determinants in the western Australian wheatbelt: a response to salinization

Diatom and micro-invertebrate communities were analyzed in 56 lentic wetlands from the wheatbelt of Western Australia. Sixteen water quality parameters were measured at each habitat and were tested as determinants of diatom and micro-invertebrate distribution. Nearly all waters were dominated by Na¹⁺ and Cl^1– and over half had low buffering capacity (<2 meq/L as TCO). Salinities ranged from <1 to > 240 mS/cm; some hypersaline habitats had pH values as low as 2.1, but most sites were alkaline.Diatoms (165 taxa) were present in all habitats, with indications that assemblages are correlated with land-use practices, i.e., historical clearing of native vegetation for dryland agriculture with resultant hydrological problems of salinization and water-logging. A non-metric multidimensional ordination showed pH, salinity, TCO, and total phosphorus to be significantly correlated with diatom community structure. Principal components analysis showed similar patterns. A salinity index was also developed for numerically important diatom taxa. Principal components analysis showed similar patterns. Certain tolerant Bacillariales, including Hantzschia amphioxys, Nitzschia hybrida, Tryblionella hungarica, and N.recta, were numerically important taxa in wetlands with visible signs of salinization.Micro-invertebrates (143 taxa) were present in habitats with salinities up to 200 mS/cm. Multidimensional ordinations showed salinity to be significantly correlated with micro-invertebrate community structure. The cladoceran Daphniopsis queenslandensis, ostracods Australocypris insularis, Mytilocypris tasmanica chapmani, and Platycypris baueri, and copepods Apocyclops dengizicus and Mesochra nr. flava were numerically important micro-invertebrates in moderate to high salinity environments, including those with signs of salinization. The diatoms, Navicula minuscula var. muralis and Pinnularia divergentissa var.subrostrata, and the copepod, Calamoecia trilobata, were common inhabitants of the extreme hypersaline (75 mS/cm), acidic (<4) habitats. Diatom communities were similar to those previously reported for other regions in Australia subjected to salinization; there were some differences in micro-invertebrate communities.     

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     

Land-use influence on stream water quality and diatom communities in Victoria, Australia: a response to secondary salinization

Diatom communities were analyzed in 39 streams located in drainages with varied land-use practices throughout Victoria, Australia. Thirteen water quality parameters were also measured in each stream. Most streams had low HCO₃ ^1- concentrations (low buffering capacity) with >90% of the waters dominated by Na¹⁺ and Cl^1-. Phosphate concentrations ranged from 0.003 to 2.0 mg/L. Diatom communities (245 taxa) were strongly correlated with land-use practices, i.e. historic clear cutting, and secondary salinization. Streams influenced by heavy irrigation practices and dryland farming had reduced species diversity and richness compared to systems with low to moderate land use. A nonmetric multidimensional ordination of diatom communities in the 39 streams was conducted. An ANOSIM on the ordination showed that diatom communities in upland watersheds with native forest canopies and low salinization, lowland streams in watersheds with cleared forest canopies, moderate agricultural utilization and salinization, and lowland streams in areas with high irrigation and salinization were all significantly different (p<0.001) from one another. Community ordination techniques showed that both specific conductance (salinity) and phosphorus interacted to determine stream diatom community structure in drainages with high secondary salinization. Drainages with low to moderate agricultural activity and low nutrients, but with a wide range of salinities showed strong associations with the diatom taxa Amphora coffeaeformis, Cymbella pusilla and Entomoneis paludosa, whereas, streams in regions with heavy agricultural practices and high phosphorus had Bacillaria paradoxa, Nitzschia hungarica, N. frustulum and Aulacoseira granulata as numerically important diatoms. In contrast, Rhizosolenia eriensis, Frustulia rhomboides, Eunotia pectinatus and Tabellaria flocculosa were strongly associated with upland streams with fast current, relatively low O-PO₄ ^3- concentrations, low pH, low salinity, and low temperature. In general, the diatom communities in saline streams (3 mS) were similar to those previously reported in saline lakes in Victoria.     

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.     

Moss-inhabiting diatom communities from Heard Island,sub-Antarctic

In this paper, we list 192 diatom taxa, collected from bryophyte samples from Heard Island (52°05S, 73°30E). The Heard Island diatom flora shows a marked similarity to those of the Crozet and Kerguelen archipelagos, and is quite dissimilar to the moss-dwelling diatom flora of Macquarie and Amsterdam Island. Based on species composition, three main groups of samples could be discerned. Each group represents a different habitat. Samples dominated by Diadesmis ingeae, Pinnularia borealis and several Psammothidium species seem to prefer the driest habitats. A special form of this community was found in shaded areas. Samples from wet habitats such as flush areas and pools were dominated by species such as Adlafia bryophila, Sellaphora tumida, Fragilaria capucina and Planothidium lanceolatum. An intermediate group was observed in more acid, but terrestrial, conditions, characterised by Eunotia paludosa and Chamaepinnularia soehrensis var. muscicola. These community patterns are similar to those found on other sub-Antarctic islands, and we suggest that a group of typical sub-Antarctic species and communities exists.     

Exudates from Gracilaria chilensis stimulate settlement of epiphytic ulvoids

In the diatom communities of the Vanishing and Ornithologist Creek 74 taxa were found. Most of the taxa have a cosmopolitan range and are resistant to various environmental stresses. For example, Achnanthes lanceolata var. lanceolata, is found in all types of waters and in several ecological conditions. Achnanthes delicatula ssp. delicatula, Nitzschia frustulum, N. capitellata, Navicula mutica, and N. gregaria develop both in fresh and brackish waters. Some of the organisms also settle in terrestrial environments. Navicula atomus, N. mutica, Pinnularia borealis, and Hantzschia amphioxys are common soil algae. Navicula digitulus, N. contenta, N. cohnii and Achnanthes coarctata also live in an aerial environment. Navicula atomus is well developed in eutrophic waters and Nitzschia capitellata can tolerate a high level of pollution, while Nitzschia gracilis, Fragilaria capucina, and F. alpestris appear both in oligotrophic, and enriched waters. Stenotopic ecological features are shown by Achnanthes marginulata and Navicula digitulus — known from the Alps and the North, and Navicula muticopsis characteristic for Antarctic and Subantarctic.The index of diatom biomass, usually of low and medium value, was highest in the area of possible impact by a penguin colony.     

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.     

The effects of dissolved heavy metals on attached diatoms in the Uintah Basin of Utah,U.S.A.

The relationships of diatom species to dissolved heavy metals in the streams of the Uintah Basin of Utah were studied through four seasons of 1977–1978. Niche center gradient analysis, cluster analysis and correlation analysis were performed.Achnanthes minutissima, Cyclotella meneghiniana, Cymbella minuta, Gomphonema parvulum, Navicula secreta var.apiculata, Nitzschia frustulum, Nitzschia frustulum var.perminuta, Nitzschia frustulum var.perpusilla, Nitzschia palea, andSynedra ulna appear to be indicator species of high or low heavy metal concentrations. Several other species also showed meaningful relationships to high or low heavy metal concentrations.Dept. of Physics and Astronomy, Brigham Young UniversityDept. of Physics and Astronomy, Brigham Young University     

The diatom flora of the Salton Sea, California

We report on diatom species of the Salton Sea, a highly saline (43 g l^–1) inland lake in California. We identified and photographed all diatom taxa encountered in the phytoplankton and benthos of the Salton Sea and its immediate tributaries. Ninety-four taxa were distinguished based on their morphological features using light- and electron microscopy. In the Salton Sea, there are four general categories of diatom assemblages related to their habitats: (1) A planktonic assemblage composed of Chaetoceros muelleri var. subsalsum, Cyclotella choctawhatcheeana, Cyclotella sp., Cylindrotheca closterium, Pleurosigma ambrosianum, Thalassionema sp.; (2) a benthic assemblage with diatoms that live on the bottom (e.g. genera Caloneis, Diploneis, Entomoneis, Gyrosigma, Plagiotropis, Pleurosigma, Surirella and Tryblionella), or in algal mats (Proschkinia bulnheimii, several species of Navicula and Seminavis gracilenta); (3) an epiphytic community attached to the macroscopic green algae which grow on the rocks and other hard surfaces near shore (e.g. Achnanthes brevipes, Licmophora ehrenbergii, Tabularia parva); and (4) a freshwater assemblage composed of species that get washed in by the rivers and other inflows discharging into the Sea (e.g. Achnanthidium minutissimum, Cocconeis pediculus, Cyclotella atomus, C. scaldensis, Nitzschia elegantula, T. weissflogii). The most striking feature of the phytoplankton is the abundance of species formerly known only from marine environments; this is not surprising given the high salinity and the peculiar history of the lake.     

Methods of pH calibration of sedimentary diatom remains for reconstructing history of pH in lakes

The pH history of lakes can be inferred from diatom remains in dated sediment cores. To derive transfer functions for pH inference in acidic lakes, we counted diatoms in surface-sediment from 31 soft-water lakes in n. New England (NE) and 36 in Norway (N), covering pH 4.4–7.1. Cluster analysis of each data set indicates that pH 6 is an upper limit for a group of similar diatom assemblages. For each set, we developed multiple linear regressions to relate three versions of the diatom data to pH of surface-waters: (1) relative frequencies of selected diatom taxa, (2) the first principal component (1 PC) of these frequencies, and (3) the frequencies of Hustedt pH groups. Also, simple linear regressions were developed for two versions: (1) Index B and (2) Index Alpha, both based on pH groups. Regressions were run separately for lakes with pH 6; these are most relevant for pH inference in acidic lakes. The best regressions (N: taxa & 1 PC taxa) have r² 0.69–0.91 and S_e 0.24–0.31 pH units, the worst (NE: log alpha) have r² 0.27–0.57 and S_e 0.51. In all cases, errors for NE are greater than N, partly due to greater diversity of NE lakes. Regressions based on pH groups (directly & by indices) have smaller r² and larger S_e than those based on taxa and 1 taxa. The Index Alpha is least useful because its requirement for alkaline diatom units is unsatisfied at many acidic lakes. Regressions based on taxa may give erratic pH inferences due to sensitivity to unusual frequencies of individual taxa; this effect is reduced by using 1 PC taxa. Four regressions based on pH 6 lakes were used for inferring pH in a ²¹⁰Pb dated core from Nedre Målmesvatn, N (now pH 4.6). There is good agreement among three of the four (not for the regression based directly on taxa) that there has been a decrease of ca. 0.6 pH units starting in the late 1800's.     

A review on the occurrence and taxonomy of heterotrophic protists in extreme acidic environments of pH values ≤ 3

The occurrence and some important taxonomic problems of heterotrophic protists from extremely acidic (pH 3) environments are briefly discussed. Almost all information on the occurrence of heterotrophic protists from extremely acidic environments is restricted to acid mine drainage (AMD) or streams influenced by AMD. Most of the information is provided for ciliates. Very little information is available on the occurrence of flagellates, rhizopods and heliozoa in this environment. Within the ciliates Urotricha, Vorticella and Oxytricha dominate in acidic mining lakes. Actinophrys sp. is the most important heliozoan in these environments. There are many taxonomic problems which are not solved so far. Live observations and taxonomic methods adapted to the extreme chemical matrix are necessary for correct identification.     

Effects of water quality and season on diatom community structure in the Damour River,Lebanon

The diatom flora in the lower Damour River, a small coastal river in Lebanon, was studied during 1981. The study area included the Damour estuary and a tributary, the el-Hamam River. Achnanthes minutissima was the most abundant diatom in the flora. Other dominant taxa included Nitzschia dissipata and Navicula cryptocephala var. veneta in the spring and Anomoeoneis vitrea in the fall. The diatom community structure was characterized by 1 or 2 dominant taxa, a few common and many rare taxa, but the taxa in these categories varied according to season and locality. The freshwater flora had a group of 20 taxa which were widely distributed in the study area throughout the study period. These taxa, in addition to a few taxa of more restricted seasonal occurrence, were the major contributers to the flora and are characteristic of this river system. Certain aspects of the flora were resistant to change. Others were more sensitive to environmental conditions. The estuarine flora reflected brackish conditions beginning in June and extending through October.     

Diatoms and their relationship to environmental variables from lakes and ponds on Bathurst Island, Nunavut, Canadian High Arctic

Baseline and historical environmental data are sparse in the High Arctic, however diatom assemblages preserved in high arctic lake and pond sediment profiles can provide proxy data of past environmental changes. Ecological data, however, are still sparse. Diatom taxa preserved in the surficial sediment of lakes and ponds on Bathurst Island (75° 42 N, 97° 21 W), Nunavut, Canadian High Arctic, and their relationship to 34 environmental variables were examined using multivariate statistics. A total of 148 diatom taxa were identified from the surface sediments of 29 study sites. Five environmental variables, Fe³⁺, Total Phosphorus (Unfiltered) (TPU), Total Nitrogen (TN), Temperature (TEMP) and pH significantly (P0.05) accounted for most of the variation in the diatom assemblages. TN was also significantly correlated to other variables (e.g. TPF, DOC, POC). A CCA constrained to TN indicated that this variable best explained the species distributions, and a weighted-averaging (WA) model was developed to infer nutrient levels from the relative abundances of the 58 dominant taxa. Interestingly, previous limnological work indicated that nitrogen most likely limited algal production in some of these high arctic sites. This model may be used to quantitatively estimate past TN levels from diatom assemblages preserved in sediment cores from Bathurst Island, and may provide a means to track past environmental changes in the High Arctic.     

The general occurrence of “plastid initials” and their development into plastids in cortical cells of woody plants in winter

Summary Electron microscopic studies revealed that plastid initials, presumed precursors of plastids, occur in cortical cells of the following plants studied in February and March: Betula ermanii Cham.; Prunus sargentii Rhed.; Pyrus communis L.; Ribes sinanense F. Maekawa; Salix matsudana Koidz. forma tortuosa Rhed.; and Sambucus sieboldiana var. miquelii Hara. Since plastid initials were found previously in Malus pumila Mill., Morus bombycis Koidz. and Populus euramericana cv. gelrica (Sagisaka 1991), plastid initials have been found in all woody plants examined to date. In P. euramericana cv. gelrica, at later stages of the development of the initials in March, the conglomerates of plastid initials became heterogeneous in terms of size, extent of thylakoid formation and ability to form starch granules. The formation of prolamellar structures was frequently observed in cells of Magnolia kobus var. borealis Sarg., which was sampled on April 19. These observations suggest the course of events in the development of the plastid initial and the continuity of the life of amyloplasts over a year in the life of woody plants.     

Diatoms from Indonesian mangroves and their suitability as sea-level indicators for tropical environments

We collected modern diatom samples from two mangrove environments of Sulawesi, Indonesia to provide a much needed dataset for the reconstruction of sea level from tropical environments. The diatom assemblages are dominated by mesohalobous species (e.g. Amphora coffeaeformis, Amphora turgida, Achnanthes delicatula, Nitzschia sigma and Tryblionella balatonis) and oligohalobous (e.g. Amphora veneta, Diploneis ovalis and Progonoia didiomatia) taxa. Both study sites show strong vertical zonations, which suggests that duration and frequency of intertidal exposure are important factors in controlling the relative abundance of diatoms. The assemblages can be generally divided into a mixed assemblage of mesohalobous, oligohalobous–halophilous and oligohalobous-indifferent diatoms that are found from the dense mangrove vegetation towards the landward edge of the transects, and mesohalobous diatom assemblages that are located within the fringing Rhizophora and tidal flat environments. We subsequently developed a diatom-based transfer function, which is a quantitative approach to sea-level reconstruction. The relationship between observed and diatom-predicted elevations suggests accurate and precise reconstructions are possible. The error estimate (± 0.15 m) is comparable to diatom-based transfer functions from temperate marshes.     

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.     

SURVEY OF BENTHIC DIATOM COMMUNITIES FROM LOTIC SYSTEMS WITHIN THE WESTERN ALLEGHENY PLATEAU

Over the course of 3 years (1997–1999), 72 stream sites were sampled for epilithic diatom communities. The analysis of these samples has led to the identification of over 325 species of diatoms. In addition to sampling the diatom community, selected physical and chemical parameters were recorded from each stream reach. These parameters included pH, specific conductance, current velocity, SRP, nitrate, silica, and total alkalinity. Canonical Correspondence Analysis (CCA) was used to identify influential environmental parameters and to assess the response of the diatom community to prominent anthropogenic inputs in the region (i.e. coal mine drainage, eutrophication). The initial analyses indicate that pH was the most influential environmental parameter along the first CCA axis. This shift was not unexpected, as acid mine drainage (AMD) in the region leads to a wide range of pH values (2.8–7.93). The highly acidic sites were characterized by species of the genus Eunotia (specifically E. exigua and E. steineckei), Frustulia rhomboides, and Pinnularia subcapitata. Furthermore, Achnanthidium minutissimum was the most widely distributed of the diatom species encountered, being found at 94% of the sites sampled. Streams that fluctuated between acidic and circumneutral pH (termed “teeter‐totter”) had greater abundances of Brachysira vitrea than other streams in this survey. Further implications for the use of these diatom communities as biomonitoring tools and the distribution of assemblages within the Western Allegheny Plateau will be discussed.