Ecological Water Quality Benchmarks for the Conterminous United States, Attributed to the NHDPlus version 2.1

This data release provides a variety of water quality benchmarks, compiled from multiple publications and attributed to the NHDPlus v2.1 hydrography, for the conterminous United States (CONUS) for use in integrated water availability studies for evaluating altered water conditions and potential ecological impacts. To avoid ambiguity in terms, for the purpose of this data release, we use the following definitions. Benchmark is used as a generic term to refer to any value used to evaluate or compare condition against. A variety of benchmark sub-categories exist, which are not mutually exclusive. Criteria are a type of benchmark that are used or suggested for regulatory purposes, including enforceable and nonenforceable standards. Thresholds are a class of benchmark that indicate a significant, pre-defined quantifiable change in condition. Background reference values are a class of benchmark that indicate conditions representative of no to minimal amounts of human activity or disturbance. Presumptive standards are a class of benchmark that lack a clear and quantifiable degree of impact and where negative effects are merely presumed to occur. Specifically, this data release primarily focuses on ecologically relevant water quality benchmarks for nutrients (nitrogen, phosphorus), salinity as specific conductance, and temperature. Additional benchmarks that exist in the source datasets for other factors (e.g., chlorophyll-a, turbidity, and fish and macroinvertebrate multimetric indices) are also provided for completeness and value-added utility, even if they were not the primary focus of this compilation. This dataset includes a compilation of ecologically relevant benchmarks from the following sources: 1. Environmental Protection Agency National Rivers and Streams Assessment. Benchmarks used in the 2018-2019 assessment cycle are provided for total nitrogen, total phosphorus, specific conductance, and fish and macroinvertebrate multimetric indices. Specifically, the background reference value cutoff of Good/Fair and the Fair/Poor benchmark used as a presumptive standard to evaluate potential ecosystem impacts are included for each water quality parameter and biological multimetric index. These benchmarks are spatially variable based on the specific National Rivers and Streams Assessment Ecoregion Level III aggregation (9 units). 2. Environmental Protection Agency Recommended Ecoregional Nutrient Criteria for Rivers and Streams, developed in the National Nutrient Strategy. Although not directly used for regulatory purposes, these criteria are intended as a recommended starting place to support development of jurisdiction-specific regulatory criteria. Criteria are provided for total nitrogen, total phosphorus, turbidity, and chlorophyll-a. These data are variable based on a specific National Nutrient Ecoregion Level III aggregation (14 units). 3. Specific Conductance benchmark of a natural background reference value from Olson and Cormier (2019). The natural background benchmark was derived from a machine-learning model from data at least-impacted sites across the conterminous United States. These data are spatially variable at each NHDPlus v2.1 COMID. 4. Newly calculated fish community temperature thresholds, combining previously published fish species distribution models and laboratory-derived maximum critical thermal limits (CTmax) for each species. Available for individual species or via summary metrics of CTmax thresholds for the fish community in each local stream reach. These data are spatially variable for each NHDPlus v2.1 COMID. As the various benchmarks originate from different methods, were derived for comparison against different condition levels, represent different time-scales of condition, and/or may have different quantified levels of impact, a thorough reading of the metadata is highly encouraged, especially Attribute Definitions, Logical Consistency, and Purpose. This may have profound implications for use in water availability and ecological condition studies. This data release contains four primary tabular datasets. The two primary national-scale datasets are provided in Parquet format (.parquet), an open-source, efficient, cloud-optimized tabular format for big which can be easily read in R, Python, and other open-source languages. Alternative .csv formats of these two conus datasets, with otherwise identical content, are provided for accessibility purposes and are compressed in a .zip format for long-term storage. In addition, two other files are provided exclusively in .csv format, including a crosswalk of taxonomic names used to reconcile across source datasets, and a data dictionary for the primary files. The files are: 1. water_quality_benchmarks.parquet - The main ecological benchmark dataset for all CONUS NHDPlus v2.1 network flowlines. 2. Temperature_CTmax_taxa_NHD_CONUS.parquet - The taxa-level temperature thresholds for all fish taxa predicted to be present in all CONUS NHDPlus v2.1 network flowlines. In tall format, with one row per unique taxa per unique flowline identifier. Used to produce the community level summaries contained in water_quality_benchmarks.parquet. 3. conus_benchmarks_csv_archive.zip - A compressed archive containing identical copies of the main CONUS ecological benchmark datasets listed above (files #1 and #2), but provided in .csv format for accessibility purposes. Files are contained in .zip compressed archives to minimize size for long-term storage purposes. 4. unique_tsn_crosswalk.csv - A dataset that lists the unique taxonomic identifiers and taxonomic serial numbers (TSN) used in processing the temperature threshold data and align taxa names used in source thermal benchmark data and in the fish species distribution models. 5. variable_lookup.csv - A data dictionary containing entity and attribute information about the variable names, descriptions, units, and data sources contained in the main water quality benchmark files provided at the CONUS scale (files #1 and #2). File also contains sciencebase identifiers to facilitate optional programmatic access to these data through cloud-based parquet retrieval tools.

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                                            {
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