BackgroundThe regression of similarity against distance unites several ecological phenomena, and thus provides a highly useful approach for illustrating the spatial turnover across sites. Our aim was to test whether the rates of decay in community similarity differ between diatom growth forms suggested to show different dispersal ability. We hypothesized that the diatom group with lower dispersal ability (i.e. periphyton) would show higher distance decay rates than a group with higher dispersal ability (i.e. plankton).Methods/Principal findingsPeriphyton and phytoplankton samples were gathered at sites distributed over an area of approximately 800 km length in the Negro River, Amazon basin, Brazil, South America (3°08′00″S; 59°54′30″W). Distance decay relationships were then estimated using distance-based regressions, and the coefficients of these regressions were compared among the groups with different dispersal abilities to assess our predictions. We found evidence that different tributaries and reaches of the Negro River harbor different diatom communities. As expected, the rates of distance decay in community similarity were higher for periphyton than for phytoplankton indicating the lower dispersal ability of periphytic taxa.Conclusions/SignificanceOur study demonstrates that the comparison of distance decay relationships among taxa with similar ecological requirements, but with different growth form and thus dispersal ability provides a sound approach to evaluate the effects of dispersal ability on beta diversity patterns. Our results are also in line with the growing body of evidence indicating that microorganisms exhibit biogeographic patterns. Finally, we underscore that clumbing all microbial taxa into one group may be a flawed approach to test whether microbes exhibit biogeographic patterns.

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Abstract:Connectivity between different landscape units and flow paths to the stream has gained much attention in hydrological science. Recent work has focused on the threshold sequencing of spatial sources in upland forested watersheds, connectivity and its spatial patterns in the hillslope-riparian-stream continuum. Fast flow path connectivity in the HRS continuum is still difficult to decipher because of the scale-limitations of hydrometric and tracer methods. Such connectivity may be strongly non-linear and controls streamflow response and chemistry. Recently, diatoms, one of the most common and diverse algal groups, were used to detect the onset and cessation of surface runoff to small headwater streams and constrain hydrograph separation methods. In this work, we investigate the potential for diatoms to determine fast flow path connectivity between their habitat and the stream over various scaled catchments. We used seven nested sub-catchments (0.45 to 247 km 2 ) with uniform and mixed geologies and land use types within the Attert River catchment (Luxembourg) for testing our hypothesis. We categorized the prevailing diatom communities based on their habitat in the hillslope-riparian-stream continuum of one headwater catchment and sampled a storm event for diatom communities in every catchment. We present the diatom dynamics during the event hydrograph. We also outline different occurring species of diatoms and present that combinations of species or individual species can be used as a tracer for source area connectivity. Further, we show that the occurrence of aerial diatom species decreases by a power law with scale, potentially limiting the scale of application. Finally, we discuss how diatoms could indicate temporal variability of contributions from different physiographic units.

Abstract. Diatoms (Bacillariophyta) are one of the most common and diverse algal groups (ca. 200 000 species, ≈ 10-200 µm, unicellular, eukaryotic). Here we investigate the potential of aerial diatoms (i.e. diatoms nearly exclusively occurring outside water bodies, in wet, moist or temporarily dry places) to infer surface hydrological connectivity between hillslope-riparian-stream (HRS) landscape units during storm runoff events. We present data from the Weierbach catchment (0.45 km 2 , northwestern Luxembourg) that quantify the relative abundance of aerial diatom species on hillslopes and in riparian zones (i.e. surface soils, litter, bryophytes and vegetation) and within streams (i.e. stream water, epilithon and epipelon). We tested the hypothesis that different diatom species assemblages inhabit specific moisture domains of the catchment (i.e. HRS units) and, consequently, the presence of certain species assemblages in the stream during runoff events offers the potential for recording whether there was hydrological connectivity between these domains or not. We found that a higher percentage of aerial diatom species was present in samples collected from the riparian and hillslope zones than inside the stream. However, diatoms were absent on hillslopes covered by dry litter and the quantities of diatoms (in absolute numbers) were small in the rest of hillslope samples. This limits their use for inferring hillslope-riparian zone connectivity. Our results also showed that aerial diatom abundance in the stream increased systematically during all sampled events (n = 11, 2011-2012) in response to incident precipitation and increasing discharge. This transport of aerial diatoms during events suggested a rapid connectivity between the soil surface and the stream. Diatom transport data were compared to twocomponent hydrograph separation, and end-member mixing analysis (EMMA) using stream water chemistry and stable isotope data. Hillslope overland flow was insignificant during most sampled events. This research suggests that diatoms were likely sourced exclusively from the riparian zone, since it was not only the largest aerial diatom reservoir, but also since soil water from the riparian zone was a major streamflow source during rainfall events under both wet and dry antecedent conditions. In comparison to other tracer methods, diatoms require taxonomy knowledge and a rather large processing time. However, they can provide unequivocal evidence of hydrological connectivity and potentially be used at larger catchment scales.

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Abstract:The identity and nomenclatural history of several small-celled naviculoid taxa are revisited. The species discussed here are important from the ecological point of view since they are often dominant in benthic freshwater communities. The original concepts of several species that have suffered major taxonomic drift due to their entangled nomenclatural history are discussed, and forgotten epithets are resurrected. We examined the original material of Navicula aggerica E. reichardt, Navicula atomoides GrunoW, N. crassulexigua e. reichardt, N. minima GrunoW, N. minima var. typica R. ross, N. minutissima (Kütz.) GrunoW, N. saugerresii desm., N. seminulum GrunoW, N. seminulum var. intermedia hust., N. seminulum var. radiosa hust., N. stroemii hust., N. subbacillum hust., N. subseminulum hust., N. tantula hust., N. vasta hust., N. ventraloides hust., Stauroneis fonticola hust., and Synedra minutissima Kütz. Several of these names were regarded as synonyms in many floristic works and, as such, remained forgotten or ignored. Analyses using light and scanning electron microscopy indicate conspecificity of Navicula minima (= Sellaphora seminulum sensu auct. nonnull.) with Sellaphora saugerresii (desm.) c.e. Wetzel et d.G. mann comb. nov., which has priority against N. minima. Synedra minutissima is lectotypified and transferred to Halamphora minutissima (Kütz.) C.E. Wetzel et compère comb. nov. Navicula minutissima (Kütz.) GrunoW 1860, nom. illeg. and Navicula minima GrunoW pro parte, typo excl. designate one and the same species (valid and legitimate), currently known as Sellaphora aggerica (E. reichardt) Falasco et ector. We consider Sellaphora atomoides (GrunoW) C.e. Wetzel et Van de VijVer comb. nov. (= Eolimna tantula sensu auct. nonnull.) and Sellaphora nigri (de not.) C.E. Wetzel et ector comb. nov. (= Eolimna minima sensu auct. nonnull.) to be separate species, although morphologically very similar. Sellaphora crassulexigua (e. reichardt) c.e. Wetzel et ector comb. nov. and Sellaphora subseminulum (hust.) C.e. Wetzel comb. nov. are rarely encountered, but usually found in calcareous springs and aerial habitats, respectively. All species are transferred to the genus Sellaphora on the basis of their valve morphology, pending molecular studies confirming the monophyly of the group once living material of each can be located and brought into clonal culture. Additionally, 64 established taxa from Navicula s.l., Eolimna or Naviculadicta are formally transferred to Sellaphora. Navicula subminuscula manGuin is formally transferred to the genus Craticula GrunoW.

This research aimed at developing the Trophic Water Quality Index (TWQI) for subtropical temperate Brazilian lotic systems based on a review of the indicative values of diatom species obtained using multivariate analysis techniques and considering the environmental gradient defined by a series of measured physical, chemical, and microbiological variables. Sampling was conducted from 2005 to 2009 in the Pardo River Hydrographic Basin, Rio Grande do Sul (RS), Brazil, and in the Andreas Stream Hydrographic Basin, RS, from 2012 to 2013. A total of 140 biological samples and 211 abiotic samples were collected. Data were analyzed by cluster analysis based on the Ward method and canonical correspondence analysis (CCA). The results indicated that total phosphate, turbidity, ammonia nitrogen, electrical conductivity, dissolved oxygen, and thermotolerant coliforms showed a significant correlation with the sample ordination made by CCA, in relation to a gradient of eutrophication. Eutrophication was operationally defined in a broad sense, including the problem of organic pollution and eutrophication of the water. The determination of the different tolerance degrees to eutrophication of the diatom taxa was used to assign trophic values of 1, 2.5, and 4 to species, corresponding to levels of low, medium, and high tolerance, respectively. By using the trophic values obtained for each diatom species, the TWQI constituted a new technological tool for environmental monitoring studies and showed a consistent, robust, and objective database for water quality assessment in subtropical temperate Brazilian lotic systems.

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