Marina Potapova | Drexel University (original) (raw)

Papers by Marina Potapova

Scientific Data

Sediment diatoms are widely used to track environmental histories of lakes and their watersheds, ... more Sediment diatoms are widely used to track environmental histories of lakes and their watersheds, but merging datasets generated by different researchers for further large-scale studies is challenging because of taxonomic discrepancies caused by rapidly evolving diatom nomenclature and taxonomic concepts. We collated five datasets of lake sediment diatoms from the Northeastern USA using a harmonization process which included updating synonyms, tracking the identity of inconsistently identified taxa, and grouping those that could not be resolved taxonomically. Each harmonization step led to an increase in variation explained by environmental variables and a parallel reduction of variation attributable to taxonomic inconsistency. To maximize future use of the data and underlying specimens we provide the original and harmonized counts for 1327 core samples from 607 lakes, name translation schemes, sample metadata, specimen museum locations, and the Northeast Lakes Voucher Flora, which i...

FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. F... more FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. Figs 107–111. Cavinula scutiformis (Grunow ex A. Schmidt) Mann & Stickle. Figs 112–122. Cavinula hilliardii Manguin ex Kociolek & Reviers. Figs 123,124. Cavinula variostriata (Krasske) Mann in Round, Crawford & Mann. Figs 125, 126. Cavinula lapidosa (Krasske) Mann. Figs 127–131. Cavinula pusio (Cleve) H. Lange-Bertalot in Werum & Lange-Bertalot. Figs 103, 104. W. Smith, Omersby, 1853 (type slide). Figs 126, 128. BRM N14/87a (Krasske material near Hessen). Scale bar: 10 µm.

Diatom Research

Cyclotella lacuskarluki Manguin ex Kociolek & Reviers is a small diatom known only from the o... more Cyclotella lacuskarluki Manguin ex Kociolek & Reviers is a small diatom known only from the original drawing that provides little information on the morphology of this taxon. As Manguin’s original materials are lost, recently collected samples from Lake Karluk, Alaska, the type locality of the species, were studied with light and scanning electron microscopy to determine its identity. As a result of this investigation, C. lacuskarluki is transferred here to the genus Discostella. Discostella lacuskarluki is 2.5–7 µm in diameter, has a shallow mantle, a stellar pattern of alveoli in the valve centre that may be reduced or completely absent, bifurcating costae and 4–5 marginal fultoportulae opening externally by short thickened tubes with round openings. We observed this species in numerous lakes across Alaska, in Lake Tahoe, Nevada, in several lakes across Canada, and in tundra and tree-line lakes of Northeastern Siberia. Although direct comparison with other Discostella species is difficult because the small size of these diatoms requires high-resolution imagery to reveal ultrastructural details, it appears that D. lacuskarluki is conspecific with D. tatrica Procházková et al. recently described from lakes of Central Europe and also reported from the European part of Russia. It is also conspecific with D. nipponica (Skvotzov) Tuji & D. M. Williams known from Japan. The apparent wide distributional range of this species indicates that it has been overlooked and commonly reported as D. pseudostelligera or D. stelligera in arctic, boreal and alpine lakes.

Nova Hedwigia, 2014

The goal of this study was an inventory of diatoms of Bering Island, the largest of the Commander... more The goal of this study was an inventory of diatoms of Bering Island, the largest of the Commander Islands located east of Kamchatka Peninsula, Russia. Diatom samples were collected in summer 2008 from 85 sites, mostly from ponds, small lakes, rivers, and streams. A total of 313 species and infraspecifi c diatom taxa were found. The diatom fl ora of the island was mostly comprised of species characteristic for northern and alpine regions of Eurasia and North America, but several species were so far found only in Asia, or North America, or in both Eastern Asia and North America, were also observed. Five new species, Eunotia ninae Potapova, sp. nov., E. prilezhaevii Potapova, sp. nov., Diadesmis mochalovae Potapova, sp. nov., Psammothidium strelnikovae Potapova, sp. nov., and Pinnularia beringensis Potapova, sp. nov., are described and a new combination Placoneis cuneata (M. Moller ex Foged) Potapova is established. This study provides information for future analysis of biogeograhical patterns of diatoms and may serve as a baseline for assessing the changes in diatom assemblages caused by climate change and human impacts.

Freshwater Science, 2012

Stream indicators used to make assessments of biological condition are influenced by many possibl... more Stream indicators used to make assessments of biological condition are influenced by many possible sources of variability. To examine this issue, we used multiple-year and multiple-reach diatom, fish, and invertebrate data collected from 20 least-disturbed and 46 developed stream segments between 1993 and 2004 as part of the US Geological Survey National Water Quality Assessment Program. We used a variancecomponent model to summarize the relative and absolute magnitude of 4 variance components (among-site, among-year, site 3 year interaction, and residual) in indicator values (observed/expected ratio [O/E] and regional multimetric indices [MMI]) among assemblages and between basin types (least-disturbed and developed). We used multiple-reach samples to evaluate discordance in site assessments of biological condition caused by sampling variability. Overall, patterns in variance partitioning were similar among assemblages and basin types with one exception. Among-site variance dominated the relative contribution to the total variance (64-80% of total variance), residual variance (sampling variance) accounted for more variability (8-26%) than interaction variance (5-12%), and among-year variance was always negligible (0-0.2%). The exception to this general pattern was for invertebrates at least-disturbed sites where variability in O/E indicators was partitioned between among-site and residual (sampling) variance (among-site = 36%, residual = 64%). This pattern was not observed for fish and diatom indicators (O/E and regional MMI). We suspect that unexplained sampling variability is what largely remained after the invertebrate indicators (O/E predictive models) had accounted for environmental differences among least-disturbed sites. The influence of sampling variability on discordance of within-site assessments was assemblage or basin-type specific. Discordance among assessments was nearly 23 greater in developed basins (29-31%) than in least-disturbed sites (15-16%) for invertebrates and diatoms, whereas discordance among assessments based on fish did not differ between basin types (least-disturbed = 16%, developed = 17%). Assessments made using invertebrate and diatom indicators from a single reach disagreed with other samples collected within the same stream segment nearly M of the time in developed basins, compared to N for all other cases.

Proceedings of the Academy of Natural Sciences of Philadelphia, 2010

Proceedings of the Academy of Natural Sciences of Philadelphia, 2011

Proceedings of the Academy of Natural Sciences of Philadelphia, 2013

The goal of this study was to investigate type materials of 22 Navicula species described by Ruth... more The goal of this study was to investigate type materials of 22 Navicula species described by Ruth Patrick in 1959. Type specimens of two species could not be found on the holotype slides. The holotypes of 20 other taxa were located and imaged. Specimens of 11 taxa from type materials or from the type localities were investigated with electron microscopy and the details of their ultrastructure were described. On the basis of this examination, six Navicula species were transferred to other genera. The following new combinations were made: Hippodonta dulcis Potapova nom. nov., H. gravistriata (Patrick) Potapova comb. nov., Fallacia latelolongitudinalis (Patrick) Potapova comb. nov., F. duomedia (Patrick) Potapova comb. nov., Sellaphora subfasciata Potapova nom. nov., and S. secura (Patrick) Potapova comb. nov. Based on the available data, nine species described by Patrick were found to be taxonomic synonyms of taxa described earlier by other authors. Future studies of more abundant populations of Patrick's species and type materials of the taxa assumed to be synonymous, may, however, reveal differences between them and prove some of Patrick's taxa to be separate species.

Proceedings of the Academy of Natural Sciences of Philadelphia, 2013

Type material of the diatom species Eunotia arcuoides Foged, housed at the ANSP Diatom Herbarium ... more Type material of the diatom species Eunotia arcuoides Foged, housed at the ANSP Diatom Herbarium and at the Natural History Museum of Denmark, is investigated with light and electron microscopy, and a lectotype specimen of this species is designated. Eunotia arcuoides is a poorly known species that shares a number of morphological characters with a few Eunotia taxa known from alkaline waters. Among other characters of this species, we describe an unusual "epithemioid" or "amphoroid" shape of the frustule and a unique round helictoglossa. Eunotia arcuoides has equally wide dorsal and ventral parts of the mantle, and the valve faces in recently formed frustules are parallel. The girdle bands are, however, wider in their dorsal parts compared to ventral parts, so that the cells become progressively more amphoroid as they grow and more girdle bands are added.

The heavily silicifi ed and coarsely ornamented Aulacoseira canadensis (Hustedt) Simonsen and Aul... more The heavily silicifi ed and coarsely ornamented Aulacoseira canadensis (Hustedt) Simonsen and Aulacoseira crassipunctata Krammer are morphologically similar and often confused in collections from North America. Re-examination of samples and permanent slides from several collections derived from biological monitoring and research programs allowed us to clarify their ecology and spatial distribution. The extinct A. canadensis was widely distributed in Miocene times in northwestern North America. Its occurrence in recent benthic diatom samples is due to erosion of diatomites located in catchments of rivers and lakes. A. canadensis may be conspecifi c with Melosira youngi Skvortzov, M. praegranulata Jousé, and M. praeislandica Jousé, which are other Miocene diatoms described and frequently reported from East Asia. Previously known from northern Europe, A. crassipunctata is restricted in North America to the eastern part of the continent. Living populations are found along the East Coast from South Carolina to Labrador and westward to northern Québec and northern Minnesota. As deduced from fossil assemblages, A. canadensis probably required slightly acidic oligotrophic waters of low conductivity and high dissolved organic carbon. Lakes and streams that support A. crassipunctata have low conductivity, high dissolved organic carbon, and a pH of 5-6. Under the light microscope these taxa may be distinguished by shape of the ringleist, size of the mantle areolae, and distance between the mantle areolae. They also differ by the presence of rimoportulae (found only in A. canadensis) and shape of the linking spines. Résumé: Aulacoseira canadensis (Hustedt) Simonsen et Aulacoseira crassipunctata Krammer sont morphologiquement similaires et sont souvent confondues dans les collections de l'Amérique du Nord. Elles sont toutes les deux fortement silicifi ées et ornementées grossièrement. Un réexamen d'échantillons et de lames permanentes provenant d'études de biosuivi et de programmes de recherche, nous ont permis de clarifi er leur écologie et leur distribution spatiale. A. canadensis, une espèce éteinte, était autrefois répartie dans la portion Nord-Ouest de l'Amérique du Nord au Miocène. Sa présence dans les échantillons de diatomées benthiques récents est due à l'érosion de dépôts de diatomites localisés dans le bassin versant des lacs et rivières. A. canadensis est peut-être la même espèce que Melosira youngi Skvortzov, M. praegranulata Jousé et M. praeilsandica Jousé, qui sont d'autres diatomées du Miocène décrites et fréquemment rapportées en Asie de l'Est. Connue auparavant en Europe du Nord, A. crassipunctata est restreinte à la partie Est du continent en Amérique du Nord. Des populations vivantes sont trouvées le long de la Côte-Est, de la Caroline du Sud au Labrador, et à l'ouest, au nord du Québec et au nord du Minnesota. Tel que déduit eschweizerbartxxx Loren Bahls et al. 168

Diatom identification guide & ecological resource for water resource managers, ecologists, taxono... more Diatom identification guide & ecological resource for water resource managers, ecologists, taxonomists, analysts, systematists, students, and the public. http://westerndiatoms.colorado.edu/

Phytotaxa

Cavinula Mann & Stickle is small genus presently comprising 25 taxa distinguished by the linear t... more Cavinula Mann & Stickle is small genus presently comprising 25 taxa distinguished by the linear to round-elliptical valve shape, uniseriate striae, presence of nodules and distinctive terminal pores. Most often the species from the genus have been reported from colder northern or alpine oligotrophic aquatic systems, or moist sub-aerial habitats. observation of samples from different localities reveals fourteen Cavinula taxa are distributed across North America. descriptions of confirmed species including designated types are provided with regard to their taxonomy, autecology, and distribution in Canada and uSA. light and Scanning electron Microscope observations of different samples and type material reveal high morphological variation within some of the taxa. two and three morphotypes are recognized within C. cocconeiformis and C. pseudoscutiformis. Cavinula kernii and C. maculata are recognized as new species and formal description and differential diagnosis are presented. the biogeography of the genus Cavinula in North America is represented by three groups of species. the first group comprises taxa with more restricted distribution in oligotrophic, cold and/or alpine environments from the Arctic Archipelago and the rocky Mountains in western North America. the second group comprises more tolerant species with broader distributions across a wider range of ecological conditions. the third group from south-eastern North America, represented by C. maculata, is found in low pH and specific conductance conditions with low nutrients. Globally, forty-one percent of the known taxa are present in North America. this number is subject to change after a better understanding of the different morphotypes and global taxa distributions.

Phytotaxa, 2014

Surirella terryi var. arctica has been described more than 50 years ago from northern Alaska. Sin... more Surirella terryi var. arctica has been described more than 50 years ago from northern Alaska. Since then, it has not been reported in the scientific literature except for a single record. We studied in detail the holotype slide and material of S. terryi var. arctica and several other samples from northern Alaska, and concluded that S. terryi var. arctica differs from the nominate variety and should be placed in a separate species. Surirella arctica comb. et stat. nov. is presented here including a detailed morphological description and light and scanning electron micrographs. Surirella arctica can be easily recognized due to the internally thickened median area and transverse costae, together forming a craticula-like structure on the interior valve surface. This feature is well visible in the light microscope and helps discriminating S. arctica from other Surirella species similar in valve shape, size and other morphological characters. These taxa include S. angusta, S. heardensis and an unknown species from Siberia and Mongolia. The presence of S. arctica has been confirmed to date only from the northern Alaska and likely from the high Arctic in Canada.

Phytotaxa, 2014

The examination of a moss sample collected from a lake in a remote mountainous region of Eastern ... more The examination of a moss sample collected from a lake in a remote mountainous region of Eastern Siberia revealed a diverse diatom flora that included four new species: Eunotia frigida, Brachysira subtile, Encyonopsis vasilievae, and Neidium rugosum. N. rugosum has been previously illustrated from several locations in the arctic and subarctic and is widely distributed across the circumpolar Arctic. The distribution of three other species is likely more limited. Besides these species, a number of rare diatoms were also found in the moss community. These include Neidium boyeri and Stauroneis crassula previously known only from North America; Encyonema sibericum so far only reported from Western Siberia, Encyonema lunatum var. borealis earlier found in Finland, and Eunotia ferefalcata, Pinnularia angustarea, and Naviculadicta mongolica so far reported only from Mongolia. This study contributes to the understanding of biogeographic patterns of diatom distribution.

Our study investigated whether algae-based water-quality assessments are affected by differences ... more Our study investigated whether algae-based water-quality assessments are affected by differences between algal assemblages on hard substrates (rocks, wood) and soft substrates (finegrained sediments). We analyzed a US Geological Survey National Water-Quality Assessment (NA-WQA) program data set that consisted of 1048 pairs of samples collected from hard and soft substrates at 551 river sampling locations throughout the US. Biovolume and diversity of algal assemblages, biovolume of major taxonomic groups, and abundance of motile diatoms differed significantly between samples collected from hard and soft substrates at the same sites. Ordinations of assemblages from hard and soft substrates were highly concordant and provided similar information on environmental gradients underlying species patterns. The strengths of relationships between composition of algal assemblages and water chemistry parameters (conductivity, pH, total P, and total N) did not differ consistently between substrate types. Performance of weighted averaging (WA) inference models did not differ between models based on assemblages from hard and soft substrates. Moreover, the predictive power of inference models developed from single-substrate data sets was not reduced when these models were applied to samples collected from other substrates. We concluded that the choice of substrate to sample should depend on the assessment indicators to be used. If indicators based on the autecologies of many algal taxa (e.g., inference models or autecological indices) are used, restricting samples to a single type of substrate is unnecessary. If algal diversity, total algal biovolume, or abundance of specific algal taxa is used, samples should be collected from a single type of substrate.

Scientific Data

Sediment diatoms are widely used to track environmental histories of lakes and their watersheds, ... more Sediment diatoms are widely used to track environmental histories of lakes and their watersheds, but merging datasets generated by different researchers for further large-scale studies is challenging because of taxonomic discrepancies caused by rapidly evolving diatom nomenclature and taxonomic concepts. We collated five datasets of lake sediment diatoms from the Northeastern USA using a harmonization process which included updating synonyms, tracking the identity of inconsistently identified taxa, and grouping those that could not be resolved taxonomically. Each harmonization step led to an increase in variation explained by environmental variables and a parallel reduction of variation attributable to taxonomic inconsistency. To maximize future use of the data and underlying specimens we provide the original and harmonized counts for 1327 core samples from 607 lakes, name translation schemes, sample metadata, specimen museum locations, and the Northeast Lakes Voucher Flora, which i...

FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. F... more FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. Figs 107–111. Cavinula scutiformis (Grunow ex A. Schmidt) Mann & Stickle. Figs 112–122. Cavinula hilliardii Manguin ex Kociolek & Reviers. Figs 123,124. Cavinula variostriata (Krasske) Mann in Round, Crawford & Mann. Figs 125, 126. Cavinula lapidosa (Krasske) Mann. Figs 127–131. Cavinula pusio (Cleve) H. Lange-Bertalot in Werum & Lange-Bertalot. Figs 103, 104. W. Smith, Omersby, 1853 (type slide). Figs 126, 128. BRM N14/87a (Krasske material near Hessen). Scale bar: 10 µm.

Diatom Research

Cyclotella lacuskarluki Manguin ex Kociolek & Reviers is a small diatom known only from the o... more Cyclotella lacuskarluki Manguin ex Kociolek & Reviers is a small diatom known only from the original drawing that provides little information on the morphology of this taxon. As Manguin’s original materials are lost, recently collected samples from Lake Karluk, Alaska, the type locality of the species, were studied with light and scanning electron microscopy to determine its identity. As a result of this investigation, C. lacuskarluki is transferred here to the genus Discostella. Discostella lacuskarluki is 2.5–7 µm in diameter, has a shallow mantle, a stellar pattern of alveoli in the valve centre that may be reduced or completely absent, bifurcating costae and 4–5 marginal fultoportulae opening externally by short thickened tubes with round openings. We observed this species in numerous lakes across Alaska, in Lake Tahoe, Nevada, in several lakes across Canada, and in tundra and tree-line lakes of Northeastern Siberia. Although direct comparison with other Discostella species is difficult because the small size of these diatoms requires high-resolution imagery to reveal ultrastructural details, it appears that D. lacuskarluki is conspecific with D. tatrica Procházková et al. recently described from lakes of Central Europe and also reported from the European part of Russia. It is also conspecific with D. nipponica (Skvotzov) Tuji & D. M. Williams known from Japan. The apparent wide distributional range of this species indicates that it has been overlooked and commonly reported as D. pseudostelligera or D. stelligera in arctic, boreal and alpine lakes.

Nova Hedwigia, 2014

The goal of this study was an inventory of diatoms of Bering Island, the largest of the Commander... more The goal of this study was an inventory of diatoms of Bering Island, the largest of the Commander Islands located east of Kamchatka Peninsula, Russia. Diatom samples were collected in summer 2008 from 85 sites, mostly from ponds, small lakes, rivers, and streams. A total of 313 species and infraspecifi c diatom taxa were found. The diatom fl ora of the island was mostly comprised of species characteristic for northern and alpine regions of Eurasia and North America, but several species were so far found only in Asia, or North America, or in both Eastern Asia and North America, were also observed. Five new species, Eunotia ninae Potapova, sp. nov., E. prilezhaevii Potapova, sp. nov., Diadesmis mochalovae Potapova, sp. nov., Psammothidium strelnikovae Potapova, sp. nov., and Pinnularia beringensis Potapova, sp. nov., are described and a new combination Placoneis cuneata (M. Moller ex Foged) Potapova is established. This study provides information for future analysis of biogeograhical patterns of diatoms and may serve as a baseline for assessing the changes in diatom assemblages caused by climate change and human impacts.

Freshwater Science, 2012

Stream indicators used to make assessments of biological condition are influenced by many possibl... more Stream indicators used to make assessments of biological condition are influenced by many possible sources of variability. To examine this issue, we used multiple-year and multiple-reach diatom, fish, and invertebrate data collected from 20 least-disturbed and 46 developed stream segments between 1993 and 2004 as part of the US Geological Survey National Water Quality Assessment Program. We used a variancecomponent model to summarize the relative and absolute magnitude of 4 variance components (among-site, among-year, site 3 year interaction, and residual) in indicator values (observed/expected ratio [O/E] and regional multimetric indices [MMI]) among assemblages and between basin types (least-disturbed and developed). We used multiple-reach samples to evaluate discordance in site assessments of biological condition caused by sampling variability. Overall, patterns in variance partitioning were similar among assemblages and basin types with one exception. Among-site variance dominated the relative contribution to the total variance (64-80% of total variance), residual variance (sampling variance) accounted for more variability (8-26%) than interaction variance (5-12%), and among-year variance was always negligible (0-0.2%). The exception to this general pattern was for invertebrates at least-disturbed sites where variability in O/E indicators was partitioned between among-site and residual (sampling) variance (among-site = 36%, residual = 64%). This pattern was not observed for fish and diatom indicators (O/E and regional MMI). We suspect that unexplained sampling variability is what largely remained after the invertebrate indicators (O/E predictive models) had accounted for environmental differences among least-disturbed sites. The influence of sampling variability on discordance of within-site assessments was assemblage or basin-type specific. Discordance among assessments was nearly 23 greater in developed basins (29-31%) than in least-disturbed sites (15-16%) for invertebrates and diatoms, whereas discordance among assessments based on fish did not differ between basin types (least-disturbed = 16%, developed = 17%). Assessments made using invertebrate and diatom indicators from a single reach disagreed with other samples collected within the same stream segment nearly M of the time in developed basins, compared to N for all other cases.

Proceedings of the Academy of Natural Sciences of Philadelphia, 2010

Proceedings of the Academy of Natural Sciences of Philadelphia, 2011

Proceedings of the Academy of Natural Sciences of Philadelphia, 2013

The goal of this study was to investigate type materials of 22 Navicula species described by Ruth... more The goal of this study was to investigate type materials of 22 Navicula species described by Ruth Patrick in 1959. Type specimens of two species could not be found on the holotype slides. The holotypes of 20 other taxa were located and imaged. Specimens of 11 taxa from type materials or from the type localities were investigated with electron microscopy and the details of their ultrastructure were described. On the basis of this examination, six Navicula species were transferred to other genera. The following new combinations were made: Hippodonta dulcis Potapova nom. nov., H. gravistriata (Patrick) Potapova comb. nov., Fallacia latelolongitudinalis (Patrick) Potapova comb. nov., F. duomedia (Patrick) Potapova comb. nov., Sellaphora subfasciata Potapova nom. nov., and S. secura (Patrick) Potapova comb. nov. Based on the available data, nine species described by Patrick were found to be taxonomic synonyms of taxa described earlier by other authors. Future studies of more abundant populations of Patrick's species and type materials of the taxa assumed to be synonymous, may, however, reveal differences between them and prove some of Patrick's taxa to be separate species.

Proceedings of the Academy of Natural Sciences of Philadelphia, 2013

Type material of the diatom species Eunotia arcuoides Foged, housed at the ANSP Diatom Herbarium ... more Type material of the diatom species Eunotia arcuoides Foged, housed at the ANSP Diatom Herbarium and at the Natural History Museum of Denmark, is investigated with light and electron microscopy, and a lectotype specimen of this species is designated. Eunotia arcuoides is a poorly known species that shares a number of morphological characters with a few Eunotia taxa known from alkaline waters. Among other characters of this species, we describe an unusual "epithemioid" or "amphoroid" shape of the frustule and a unique round helictoglossa. Eunotia arcuoides has equally wide dorsal and ventral parts of the mantle, and the valve faces in recently formed frustules are parallel. The girdle bands are, however, wider in their dorsal parts compared to ventral parts, so that the cells become progressively more amphoroid as they grow and more girdle bands are added.

The heavily silicifi ed and coarsely ornamented Aulacoseira canadensis (Hustedt) Simonsen and Aul... more The heavily silicifi ed and coarsely ornamented Aulacoseira canadensis (Hustedt) Simonsen and Aulacoseira crassipunctata Krammer are morphologically similar and often confused in collections from North America. Re-examination of samples and permanent slides from several collections derived from biological monitoring and research programs allowed us to clarify their ecology and spatial distribution. The extinct A. canadensis was widely distributed in Miocene times in northwestern North America. Its occurrence in recent benthic diatom samples is due to erosion of diatomites located in catchments of rivers and lakes. A. canadensis may be conspecifi c with Melosira youngi Skvortzov, M. praegranulata Jousé, and M. praeislandica Jousé, which are other Miocene diatoms described and frequently reported from East Asia. Previously known from northern Europe, A. crassipunctata is restricted in North America to the eastern part of the continent. Living populations are found along the East Coast from South Carolina to Labrador and westward to northern Québec and northern Minnesota. As deduced from fossil assemblages, A. canadensis probably required slightly acidic oligotrophic waters of low conductivity and high dissolved organic carbon. Lakes and streams that support A. crassipunctata have low conductivity, high dissolved organic carbon, and a pH of 5-6. Under the light microscope these taxa may be distinguished by shape of the ringleist, size of the mantle areolae, and distance between the mantle areolae. They also differ by the presence of rimoportulae (found only in A. canadensis) and shape of the linking spines. Résumé: Aulacoseira canadensis (Hustedt) Simonsen et Aulacoseira crassipunctata Krammer sont morphologiquement similaires et sont souvent confondues dans les collections de l'Amérique du Nord. Elles sont toutes les deux fortement silicifi ées et ornementées grossièrement. Un réexamen d'échantillons et de lames permanentes provenant d'études de biosuivi et de programmes de recherche, nous ont permis de clarifi er leur écologie et leur distribution spatiale. A. canadensis, une espèce éteinte, était autrefois répartie dans la portion Nord-Ouest de l'Amérique du Nord au Miocène. Sa présence dans les échantillons de diatomées benthiques récents est due à l'érosion de dépôts de diatomites localisés dans le bassin versant des lacs et rivières. A. canadensis est peut-être la même espèce que Melosira youngi Skvortzov, M. praegranulata Jousé et M. praeilsandica Jousé, qui sont d'autres diatomées du Miocène décrites et fréquemment rapportées en Asie de l'Est. Connue auparavant en Europe du Nord, A. crassipunctata est restreinte à la partie Est du continent en Amérique du Nord. Des populations vivantes sont trouvées le long de la Côte-Est, de la Caroline du Sud au Labrador, et à l'ouest, au nord du Québec et au nord du Minnesota. Tel que déduit eschweizerbartxxx Loren Bahls et al. 168

Diatom identification guide & ecological resource for water resource managers, ecologists, taxono... more Diatom identification guide & ecological resource for water resource managers, ecologists, taxonomists, analysts, systematists, students, and the public. http://westerndiatoms.colorado.edu/

Phytotaxa

Cavinula Mann & Stickle is small genus presently comprising 25 taxa distinguished by the linear t... more Cavinula Mann & Stickle is small genus presently comprising 25 taxa distinguished by the linear to round-elliptical valve shape, uniseriate striae, presence of nodules and distinctive terminal pores. Most often the species from the genus have been reported from colder northern or alpine oligotrophic aquatic systems, or moist sub-aerial habitats. observation of samples from different localities reveals fourteen Cavinula taxa are distributed across North America. descriptions of confirmed species including designated types are provided with regard to their taxonomy, autecology, and distribution in Canada and uSA. light and Scanning electron Microscope observations of different samples and type material reveal high morphological variation within some of the taxa. two and three morphotypes are recognized within C. cocconeiformis and C. pseudoscutiformis. Cavinula kernii and C. maculata are recognized as new species and formal description and differential diagnosis are presented. the biogeography of the genus Cavinula in North America is represented by three groups of species. the first group comprises taxa with more restricted distribution in oligotrophic, cold and/or alpine environments from the Arctic Archipelago and the rocky Mountains in western North America. the second group comprises more tolerant species with broader distributions across a wider range of ecological conditions. the third group from south-eastern North America, represented by C. maculata, is found in low pH and specific conductance conditions with low nutrients. Globally, forty-one percent of the known taxa are present in North America. this number is subject to change after a better understanding of the different morphotypes and global taxa distributions.

Phytotaxa, 2014

Surirella terryi var. arctica has been described more than 50 years ago from northern Alaska. Sin... more Surirella terryi var. arctica has been described more than 50 years ago from northern Alaska. Since then, it has not been reported in the scientific literature except for a single record. We studied in detail the holotype slide and material of S. terryi var. arctica and several other samples from northern Alaska, and concluded that S. terryi var. arctica differs from the nominate variety and should be placed in a separate species. Surirella arctica comb. et stat. nov. is presented here including a detailed morphological description and light and scanning electron micrographs. Surirella arctica can be easily recognized due to the internally thickened median area and transverse costae, together forming a craticula-like structure on the interior valve surface. This feature is well visible in the light microscope and helps discriminating S. arctica from other Surirella species similar in valve shape, size and other morphological characters. These taxa include S. angusta, S. heardensis and an unknown species from Siberia and Mongolia. The presence of S. arctica has been confirmed to date only from the northern Alaska and likely from the high Arctic in Canada.

Phytotaxa, 2014

The examination of a moss sample collected from a lake in a remote mountainous region of Eastern ... more The examination of a moss sample collected from a lake in a remote mountainous region of Eastern Siberia revealed a diverse diatom flora that included four new species: Eunotia frigida, Brachysira subtile, Encyonopsis vasilievae, and Neidium rugosum. N. rugosum has been previously illustrated from several locations in the arctic and subarctic and is widely distributed across the circumpolar Arctic. The distribution of three other species is likely more limited. Besides these species, a number of rare diatoms were also found in the moss community. These include Neidium boyeri and Stauroneis crassula previously known only from North America; Encyonema sibericum so far only reported from Western Siberia, Encyonema lunatum var. borealis earlier found in Finland, and Eunotia ferefalcata, Pinnularia angustarea, and Naviculadicta mongolica so far reported only from Mongolia. This study contributes to the understanding of biogeographic patterns of diatom distribution.

Our study investigated whether algae-based water-quality assessments are affected by differences ... more Our study investigated whether algae-based water-quality assessments are affected by differences between algal assemblages on hard substrates (rocks, wood) and soft substrates (finegrained sediments). We analyzed a US Geological Survey National Water-Quality Assessment (NA-WQA) program data set that consisted of 1048 pairs of samples collected from hard and soft substrates at 551 river sampling locations throughout the US. Biovolume and diversity of algal assemblages, biovolume of major taxonomic groups, and abundance of motile diatoms differed significantly between samples collected from hard and soft substrates at the same sites. Ordinations of assemblages from hard and soft substrates were highly concordant and provided similar information on environmental gradients underlying species patterns. The strengths of relationships between composition of algal assemblages and water chemistry parameters (conductivity, pH, total P, and total N) did not differ consistently between substrate types. Performance of weighted averaging (WA) inference models did not differ between models based on assemblages from hard and soft substrates. Moreover, the predictive power of inference models developed from single-substrate data sets was not reduced when these models were applied to samples collected from other substrates. We concluded that the choice of substrate to sample should depend on the assessment indicators to be used. If indicators based on the autecologies of many algal taxa (e.g., inference models or autecological indices) are used, restricting samples to a single type of substrate is unnecessary. If algal diversity, total algal biovolume, or abundance of specific algal taxa is used, samples should be collected from a single type of substrate.