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Background and aims - A novel species of Navicula has been recently discovered in rivers of the central Appalachian Mountains, USA. The purpose of this paper is to formally establish this new species and to determine whether it had been overlooked in the past or is a recent arrival to the area. Methods - We studied historical collections made in Pennsylvania, Virginia and adjacent areas since the 1940s and housed at the ANSP Diatom Herbarium. Light and scanning electron microscopy was employed to study the morphology of the new species and similar Navicula taxa, including those commonly reported at the same locations, or originally described from the rivers of the eastern United States, such as N. radiosafallax, initially established as N. radiosa var. parva by J.H. Wallace. Key results - The new species has an unusual shape of the external raphe slit, which is undulate toward the proximal ends. This character was so far found in a single other Navicula species known only from Europe. Examination of historical materials confirmed that N. eileeniae was absent from collections made in the eastern United States before 2007, but has become progressively more common and abundant in the last decade. The prevalence of this species in streams of low to moderate mineral and nutrient content suggests that its recent expansion cannot be explained by pollution. Climate change is also unlikely to have caused the northward expansion of N. eileeniae, as it has never been recorded south from central Appalachia. Conclusions - The results of this study confirm that a population of previously unknown Navicula species has been expanding in Central Appalachia and suggest that rapid shifts of distributional ranges not readily explainable by environmental changes may occur in protists. [ABSTRACT FROM AUTHOR]

Abstract: Diatoms from the genus Achnanthidium are abundant in rivers, streams, and springs of the Appalachian Mountains. They inhabit clean and polluted waters, including those affected by acid mine drainage. The identification of Achnanthidium taxa is difficult due to their small cell size and insufficient information in the diatom floras. We studied the taxonomy and ecology of Achnanthidium in Appalachian rivers by analyzing a data set of benthic diatom samples and corresponding water chemistry data collected during several water-quality surveys from 181 sampling sites. Ten species were identified using scanning electron and light microscopy: A. alpestre (Lowe & Kociolek) Lowe & Kociolek, A. atomus (Hustedt) Monnier, Lange-Bertalot, & Ector, A. deflexum (Reimer) Kingston, A. duthii (Sreenivasa) Edlund, A. eutrophilum (Lange-Bertalot) Lange-Bertalot, A. cf. gracillimum (Meister) Lange-Bertalot, A. cf. latecephalum Kobayasi, A. minutissimum (Kützing) Czarnecki (sensu lato), A. reimeri (Camburn) comb. nov., and A. rivulare Potapova & Ponader. The distribution of common taxa in relation to water chemistry was studied by fitting non-parametric regression models (generalized additive models, GAM, and non-parametric multiplicative regression models, NPMR) to species relative abundances. Studied Achnanthidium species differed considerably in their responses to water chemistry. These results suggest that species-level identifications will lead to more accurate bioassessments. [Copyright &y& Elsevier]

Abstract: Two major arguments in favor of using diatoms in water-quality assessments are that their distributions are cosmopolitan and their ecology is well studied. If these assumptions are true, diatom-based monitoring tools could be considered universal and used in any geographic area. Indeed, some diatom metrics based on species indicator values developed in Europe are often used in North America and many other parts of the world. There is considerable evidence, however, that diatom metrics are less useful when applied in a geographic area other than where species relations with environmental characteristics were originally studied to construct the metrics. We used U.S. Geological Survey National Water-Quality Assessment program data to create diatom metrics for monitoring eutrophication, and show here that these metrics provide better assessments in U.S. rivers than similar metrics developed for European inland waters. We also demonstrate that metrics developed by studying diatom–nutrient relationships on the continental-scale can be further refined if combined with regional-scale studies. [Copyright &y& Elsevier]

Summary 1. We quantified the relationships between diatom relative abundance and water conductivity and ionic composition, using a dataset of 3239 benthic diatom samples collected from 1109 river sites throughout the U.S.A. [U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program dataset]. This dataset provided a unique opportunity to explore the autecology of freshwater diatoms over a broad range of environmental conditions. 2. Conductivity ranged from 10 to 14 500 μS cm-1 , but most of the rivers had moderate conductivity (interquartile range 180–618 μS cm-1 ). Calcium and bicarbonate were the dominant ions. Ionic composition, however, varied greatly because of the influence of natural and anthropogenic factors. 3. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that conductivity and abundances of major ions (HCO&formmu0; + CO&formmu1;, Cl- , SO&formmu2;, Ca2+ , Mg2+ , Na+ , K+ ) all explained a statistically significant amount of the variation in assemblage composition of benthic diatoms. Concentrations of HCO&formmu3; + CO&formmu4; and Ca2+ were the most significant sources of environmental variance. 4. The CCA showed that the gradient of ionic composition explaining most variation in diatom assemblage structure ranged from waters dominated by Ca2+ and HCO&formmu5; + CO&formmu6; to waters with higher proportions of Na+ , K+ , and Cl- . The CCA also revealed that the distributions of some diatoms correlated strongly with proportions of individual cations and anions, and with the ratio of monovalent to divalent cations. 5. We present species indicator values (optima) for conductivity, major ions and proportions of those ions. We also identify diatom taxa characteristic of specific major-ion chemistries. These species optima may be useful in future interpretations... [ABSTRACT FROM AUTHOR]