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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 is a set of light microscope images grouped into 1154 morphological operational taxonomic units. Post-hoc harmonization enables data quality control when other approaches (e.g., upfront management of taxonomic consistency) are not possible. Measurement(s) diatom taxa • abundance Technology Type(s) observation • literature review • digital curation Sample Characteristic - Organism Bacillariophyta Sample Characteristic - Environment Lakes Sample Characteristic - Location Northeastern Unites States of America [ABSTRACT FROM AUTHOR]

Diatoms have been successfully used as indicators of past and present environmental conditions in freshwater and marine habitats, but their diversity and indicative properties in microtidal coastal wetlands of temperate zone are relatively poorly studied. The goal of this study was to determine whether diatoms can be used as indicators of sea level and nutrient content in coastal wetlands of the mid-Atlantic region of the USA. Our exploratory analyses indicated that benthic and marsh soil diatom assemblages were jointly controlled by tidal elevation, salinity, sediment texture, and nutrient content, while the relative importance of these factors varied among datasets targeting different environmental gradients. The habitat type could be correctly inferred from diatom assemblage composition in 79% of samples. A diatom-based model developed for inferring sediment nitrogen content had an average accuracy of prediction of 12.5% of observed nitrogen range. Models for inferring tidal exposure from diatom assemblage data provided assessment with 11–16% accuracy as estimated by the bootstrapped root mean square errors of prediction, which is similar to the accuracy of models based on other microfossils. These results show that despite inherent challenges, such as tidal redistribution of diatom frustules across the intertidal zone, diatoms can be successfully used as an independent source of evidence in paleoreconstructions of sea-level change and nitrogen enrichment, as well as for monitoring current nutrient pollution in mid-Atlantic wetlands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]