Marina Potapova

MORPHOLOGICAL AND ECOLOGICAL VARIATION WITHIN THE ACHNANTHIDIUM MINUTISSIMUM (BACILLARIOPHYCEAE) SPECIES COMPLEX1

Variation of frustular morphology within the Achnanthidium minutissimum (Kütz.) Czarn. species complex was studied in type populations of 12 described taxa and in 30 recent North American river samples. The SEM observations in this study and other publications showed that ultrastructural characters on their own do not discriminate among taxa within the A. minutissimum complex. Therefore, an attempt was made to use other characters, such as valve shape and striation pattern, to delineate morphological groups. The sliding‐landmarks method was used to obtain valve‐shape descriptors. These shape variables were combined with conventional morphological characters in multivariate analyses. It was shown that some historically recognized taxa are morphologically distinct, while others are difficult to differentiate. Morphological grouping of “old” taxa most similar to A. minutissimum did not correspond to their taxonomic hierarchy in contemporary diatom floras. Morphometric analysis of a data set of 728 specimens from North American rivers revealed six morphological groups, although it was impossible to draw clear boundaries among them. These morphological groups differed significantly in their ecological characteristics and could be recommended as indicators of water quality. Application of the discriminant function analysis based on shape variables and striation pattern showed that North American specimens could be more consistently classified into the six groups identified in our analysis than into historically recognized taxa.

Quantifying species indicator values for trophic diatom indices : a comparison of approaches

This study compares two approaches for constructing diatom-based indices for monitoring river eutrophication. The first approach is based on weighted averaging of species indicator values with the underlying assumption that species have symmetrical unimodal distributions along the nutrient gradient, and their distributions are sufficiently described by a single indicator value per species. The second approach uses multiple indicator values for individual taxa and is based on the possibility that species have complex asymmetrical response curves. Multiple indicator values represent relative probabilities that a species would be found within certain ranges of nutrient concentration. We used 155 benthic diatom samples collected from rivers in the Northern Piedmont ecoregion (Northeastern U.S.A.) to construct two datasets: one used for developing models and indices, and another for testing them. To characterize the shape of species response curves we analyzed changes in the relative abundance of 118 diatom taxa common in this dataset along the total phosphorus (TP) gradient by fitting parametric and non-parametric regression models. We found that only 34 diatoms had symmetrical unimodal response to TP. Among several indices that use a single indicator value for each species, the best was the weighted averaging partial least square (WA-PLS) inference model. The correlation coefficient between observed and inferred TP in the test dataset was 0.67. The best index that employed multiple indicator values for each species had approximately the same predictive power as the WA-PLS based index, but in addition, this index provided a sample-specific measure of uncertainty for the TP estimation.

Biological assessments of Appalachian streams based on predictive models for fish, macroinvertebrate, and diatom assemblages

Abstract We developed empirical models for fish, macroinvertebrate, and diatom assemblages to assess the biological condition of 268 streams sampled from 1993 to 2002 in 7 major river basins in the Appalachian region of the USA. These models estimate the expected taxonomic composition at each site based on observed variation in taxonomic composition at reference sites. The index, O/E, is the ratio of the number of predicted taxa that were observed (O) to that expected (E) to occur at a site and is a measure of taxonomic completeness. We compared how O/E for each assemblage varied among major landuse settings and whether impaired assemblages were associated with particular physicochemical conditions. We also examined concordance among assemblages in their response to stress. Biological, chemical, and physical data were collected following consistent protocols. We used land-cover criteria, published data, and topographic maps to classify sites by major landuse setting. Fish, macroinvertebrate, and diatom assemblages had been sampled at 73, 108, and 52, respectively, of the least disturbed sites used to establish reference conditions. The models accounted for a substantial portion of the natural variation in taxonomic composition across sites that was associated with biogeographic, climatic, and basin-scale factors and generally were unbiased across the range of environmental gradients observed in the region. Assessments at nonreference sites showed that impairment of fish and macroinvertebrate assemblages was most strongly associated with agriculture and urban land uses, whereas impairment of diatom assemblages was most strongly associated with mining in the basin. Concordance in assessments among assemblages was not strong. Assessments based on 2 assemblages differed in 28 to 57% of cases, and assessments were never concordant for cases where all 3 assemblages were sampled. Furthermore, only ½ of these cases would have been assessed as ecologically impaired had only 1 assemblage been sampled. Differences between observed and predicted frequencies of occurrence for individual taxa were generally consistent with known tolerances to environmental stressors and might aid in identifying causes of biological impairment.

Choice of substrate in algae-based water-quality assessment

Abstract Our study investigated whether algae-based water-quality assessments are affected by differences between algal assemblages on hard substrates (rocks, wood) and soft substrates (fine-grained sediments). We analyzed a US Geological Survey National Water-Quality Assessment (NAWQA) 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.

TWO COMMON NORTH AMERICAN DIATOMS, ACHNANTHIDIUM RIVULARE SP. NOV. AND A. DEFLEXUM (REIMER) KINGSTON: MORPHOLOGY, ECOLOGY AND COMPARISON WITH RELATED SPECIES

Two species of Achnanthidium, which are fairly common in benthic samples collected from North American rivers, have posed considerable identification problems for analysts enumerating diatoms for water quality assessment programs in the United States. Both diatoms belong to the apparently diverse and insufficiently studied group of Achnanthidiumspecies with terminal raphe fissures sharply bent to the same side of the valve. The goal of this study was to clarify the taxonomic position of these taxa and document their morphology, ecology and distribution. One of these, Achnanthidium rivulare Potapova & Ponader sp. nov., is especially abundant in soft-water, phosphorus-poor rivers of coastal regions of North America, and has been confused in the past with various species of Achnanthidium and Rossithidium. This species is most similar to Achnanthidium convergens (Kobayasi) Kobayasi known from Japan and A. crassum (Hustedt) Potapova & Ponader comb. nov. Achnanthidium crassum is a poorly known species; therefore, SEM observations of its type material from Sumatra and another population from Hawaii are presented here. A second problematic North American species is A. deflexum (Reimer) Kingston, a diatom very similar in its morphology to A. pyrenaicum (Hustedt) Kobayasi. Study of the type materials and a number of other collections of these species with SEM and morphometric analysis of selected populations allowed us to conclude that A. deflexum, known from North America, and A. pyrenaicum, reported from Europe and Japan, are not conspecific. The shape and size of the frustule and the shape of the external areolae foramina are consistently different between the two species. Both A. deflexum and A. pyrenaicum are alkaliphilous, calciphilous diatoms, found mostly in phosphorus-poor waters.

SMALL-CELLED NUPELA SPECIES FROM NORTH AMERICA

Three small-celled Nupela species were found in streams and moist habitats of the United States, with a concentration of locations in the eastern part of the country. Two new species are described here: N. neglecta Ponader, Lowe & Potapova and N. Carolina Potapova & Clason. These two species and Nupela wellneri (Lange-Bertalot) Lange-Bertalot have external hymenate occlusions of their areolae, which apparently are diagnostic for this genus. These often erode during sample preparation, and hence have not been previously recognized as a generic character. All three species were recorded primarily from epilithon and epiphyton of small, heavily shaded streams with low to moderate conductivity, and relatively high concentrations of dissolved silica, total nitrogen, and dissolved organic matter.

Patterns of Diatom Distribution in Relation to Salinity

The total concentration of dissolved salts and the ionic composition of water are known to be important ecological factors influencing diatom distribution. The difference in salt content between marine and inland waters has been regarded as a major boundary that only a few diatom lineages managed to cross and in only one direction, from marine to freshwater habitat. Certain concentrations of salts far below typical marine salinity (0.2–0.5 g/l) were also thought to represent important ecophysiological thresholds. Quantitative analyses of large diatom datasets collected from estuaries, coastal areas, lakes, and rivers reveal, however, a continuous turnover of diatom species and genera along salinity gradients. No portion of the salinity spectrum, except for the extremes, is characterized by a depauperate diatom flora. Recent advances in reconstructing the evolutionary history of diatoms indicate that salinity affinities shifted in many diatom lineages and more often than was thought previously. The relatively high number of diatom species and genera confined to the marine environment can be explained not by the existence of physiological salinity thresholds common to all diatoms, but by the spatial dominance and greater temporal stability of marine habitats in comparison to relatively ephemeral fresh and brackish water bodies. At present, there is no compelling evidence of any salinity thresholds acting as insurmountable obstacles in diatom evolution.

Aulacoseira pardata sp. nov., A. nivalis comb. nov., A. nivaloides comb. et stat. nov., and Their Occurrences in Western North America

ABSTRACT. The morphology of several “low-mantle” species of Aulacoseira found in Western North America is studied. A new taxon, Aulacoseira pardata sp. nov., is described. Aulacoseira pardata is similar to Aulacoseira distans and Aulacoseira lirata and has been confused in the past with these two taxa. Aulacoseira distans var. nivalis and Aulacoseira distans var. nivaloides bear significant morphological differences from Aulacoseira distans. These two varieties are therefore elevated to species status: Aulacoseira nivalis comb. nov. and Aulacoseira nivaloides comb. et stat. nov., respectively. New taxa: Aulacoseira pardata English and Potapova New combinations: Aulacoseira nivalis, Aulacoseira nivaloides.

New species and combinations in monoraphid diatoms (family Achnanthidiaceae) from North America

This article clarifies the taxonomy and nomenclature of several monoraphid diatom species found in rivers and lakes of North America. The morphology of these diatoms is studied with light and electron microscopy. A new combination Rossithidium anastasiae (Kaczmarska) Potapova is introduced for a species common in both Europe and North America and often misidentified as Achnanthes linearis (W. Smith) Grunow or R. linearis (W. Smith) Round et Bukhtiyarova. Achnanthes harveyi Reimer, often found in eastern North America, is transferred to Psammothidium Bukhtiyarova & Round on the basis of the convex raphe valve, uniseriate striae, and raphe structure. A new Psammothidium species, P. pennsylvanicum Potapova is described and compared with the most similar taxon, P. semiapertum (Hustedt) Aboal. Diatoms originally described as Achnanthes lutheri Hustedt and A. stewartii Patrick are transferred to the genus Platessa Lange-Bertalot on the basis of biseriate striae, flat valves, and the absence of terminal raphe fissures. Two new Platessa species, P. kingstonii Potapova and P. bahlsii Potapova are described from the eastern USA and compared with most similar species, P. lutheri (Hustedt) Potapova and P. conspicua (A. Mayer) Lange-Bertalot, respectively. Achnanthes lanceolata var. abbreviata Reimer, found in the southeastern USA, is shown to possess multiseriate striae and relatively long terminal raphe fissures characteristic for the genus Planothidium Round & Bukhtiyarova, to which it is transferred.

Variance partitioning of stream diatom, fish, and invertebrate indicators of biological condition

Abstract.  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 variance-component model to summarize the relative and absolute magnitude of 4 variance components (among-site, among-year, site × 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 2× 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 ⅓ of the time in developed basins, compared to ⅙ for all other cases.