About
The purpose of the Reference Site Visualization Tool is to make the reference site data that are used to set condition benchmarks in the National Aquatic Resource Surveys (NARS) easier to access and visualize. The tool also describes the steps involved in the reference site approach to setting benchmarks which is the approach used to set condition benchmarks for several of the environmental indicators reported on in the NARS. For those indicators using the reference site approach to set benchmarks, the reference site data included in this tool can be used to reproduce the condition benchmarks published in the most recent technical reports (2017 National Lakes Assessment, 2018/2019 National Rivers and Streams Assessment, 2016 National Wetland Condition Assessment). These resulting benchmarks are ultimately used to assign condition classes (good, fair, poor) to surveyed sites. The site navigation section below describes each section of the tool in more detail.
Site Navigation
The download tab can be used to view and download any of the reference site data that were used in the benchmark setting process. It is important to note that there may be some reference sites that passed the NARS reference site screens, but are not available to query via the Reference Site Visualization Tool because they were removed prior to being used to set benchmarks. For example, when deriving an indicator benchmark from the distribution of reference site values in a region, a common procedure is to remove reference sites with indicator values too far outside the typical range prior to deriving the benchmarks from the distribution. These 'outlier' reference sites are not included in this tool because they were not used to set indicator benchmarks.
In the download tab, reference site subsets can be selected by:
- 1) Survey (NRSA = National Rivers and Streams Assessment, NLA = National Lakes Assessment, or NWCA = National Wetlands Condition Assessment)
- 2) Indicator (any environmental indicator for which reference sites were used to set benchmarks)
- 3) Region (state or EPA region)
- 4) Any combination of the first three selections
After selecting which reference sites to view, four tabs with data will be returned:
- 1) An interactive map with pins representing the locations of the selected reference sites (pins can be clicked to view details about specific reference sites)
- 2) A table with the selected reference site data
- 3) Metadata describing what each column in the dataset represents
- 4) A list of acronyms encountered in the data and what each acronym stands for
Data can also be downloaded as an excel workbook with three sheets (reference site data, metadata, and acronyms)
The view tab can be used to view how the reference sites were used to set benchmarks for each survey/indicator/region and learn the screens that reference sites needed to pass to be considered in reference condition (i.e., least-disturbed). For example, to view all of the reference sites used to set benchmarks for chlorophyll-a in the upper midwest ecoregion in the National Lakes Assessment, a user would select National Lakes Assessment/chlorophyll-a/upper midwest in the three drop-down menus in the sidebar panel. After clicking SELECT, an interactive map of the reference sites, summary of the reference site screening process, and visual of how the benchmark values were derived from the reference sites will be returned.
There are 3 sub-tabs in the view tab:
- 1) In the 'Site Map' tab, the selection of reference sites can be viewed as pins on an interactive map and clicked on for more details.
- 2) In the 'Screening Process' tab, a summary of the screens that the reference sites passed in order to be considered least-disturbed can be viewed.
- 3) In the 'Indicator Benchmarks' tab, the distribution of indicator values from the selection of reference sites and the benchmark values that were derived from the distribution of indicator values can be viewed.
Background
What are reference sites?
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Reference sites in the National Aquatic Resource Surveys (NARS) are sites that are considered to be in least-disturbed condition for a given region (often aggregate ecoregion). Therefore, reference sites in the NARS are also known as least-disturbed sites because they are in the best condition compared to what is available for a given region. During the reference site evaluation process, Environmental Protection Agency scientists compare sites against several environmental screens. To be considered in reference condition, a site must pass all of the screens. See
Stoddard et al. 2007
for a thorough discussion on the concept of reference condition.
What is the reference site approach for setting benchmarks?
- The reference site approach for setting environmental benchmarks is one of the approaches used in the NARS to set condition benchmarks (e.g., good, fair, poor condition) for the environmental indicators. In the reference site approach, benchmarks for a given region are derived from the distribution of indicator values at reference sites in that region. For example, the benchmark for poor/fair condition is often set as the 5th or 95th percentile of the reference site distribution. Whether the benchmark is the 5th or 95th percentile depends on the indicator and if lower or higher values indicate better condition. Similarly, the benchmark for fair/good condition is often the 25th or 75th percentile.
Disclaimer
The United States Environmental Protection Agency (EPA) Reference Site Visualization Tool and code is provided on an "as is" basis and the user assumes responsibility for its use. EPA has relinquished control of the information and no longer has responsibility to protect the integrity, confidentiality, or availability of the information. Any reference to specific commercial products, processes, or services by service mark, trademark, manufacturer, or otherwise, does not constitute or imply their endorsement, recommendation or favoring by EPA. The EPA seal and logo shall not be used in any manner to imply endorsement of any commercial product or activity by EPA or the United States Government.