The foremost feature of a diatom is the species-specific ornamentation of the silicon cell wall,

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.

Centric diatoms of 107 different Hungarian running waters were investigated. Among them the largest was the River Danube, from which more than one hundred plankton samples were analysed by scanning electron microscopy (SEM). Only one sample was analysed from creeks, which were the smallest running waters analysed in this study. There were also channels with slow currents flowing out of rivers or connecting different rivers. In total, 41 centric taxa belonging to 11 genera were found during this study. The average number of taxa found in a single watercourse was 7, the maximum 40 and the minimum 1. Cyclotella meneghiniana was the most frequently encountered species (present in 60% of sites). Twelve taxa were found in more than 20% of sites, 7 taxa between 5-10% and 6 taxa only in one site.

status of rivers using benthic diatoms were compared. Ecological status is estimated as the ratio between the observed value of a biological element and the value expected in the absence of significant human impact. Approaches to defining the 'reference sites', from which these 'expected' values were derived, varied from country to country. Minimum criteria were established as part of the exercise but there was still considerable variation between national reference values, reflecting typological differences that could not be resolved during the exercise. A simple multimetric index was developed to compare boundary values using two widely used diatom metrics. Boundary values for high/good status and good/moderate status set by each participant were converted to their equivalent values of this intercalibration metric using linear regression. Variation of ±0.05 EQR units around the median value was considered to be acceptable and the exercise provided a means for those Member States who fell significantly above or below this line to review their approaches and, if necessary, adjust their boundaries.