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Layer: Total Nitrogen (ID:9)

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Description: <div><div><b>Description:</b> National Measured Total Nitrogen Data derived from data stored in the U.S. EPA Water Quality Portal.</div><div><b>Forms Retained:</b> Total Nitrogen</div><div><b>Data Date Range:</b> 01/2000 – 12/2023</div><div><b>Acquisition Date:</b> 1/22/2024</div><div><b>Query Links:</b> <a href="https://www.waterqualitydata.us/#sampleMedia=Water&amp;characteristicName=Nitrogen&amp;startDateLo=01-01-2000&amp;startDateHi=12-31-2023&amp;mimeType=csv&amp;dataProfile=narrowResult&amp;providers=NWIS&amp;providers=STEWARDS&amp;providers=STORET" target="_blank">https://www.waterqualitydata.us/#sampleMedia=Water&amp;characteristicName=Nitrogen&amp;startDateLo=01-01-2000&amp;startDateHi=12-31-2023&amp;mimeType=csv&amp;dataProfile=narrowResult&amp;providers=NWIS&amp;providers=STEWARDS&amp;providers=STORET</a></div><div><b>Min. Value:</b> -9</div><div><b>Max. Value:</b> 53200</div><div><b>Units in Source/Original Dataset:</b> &lt;Null&gt;, #/100mL, %, cm3/g @STP, cm3/g STP, mg N/l******, mg/l, mg/L, MPN/100mL, None, NTU, ppb, ppm, ug, ug/L, umol/ umol/L, uS/cm</div></div><div><br /></div><div><div><b>Background</b></div><div>Total nitrogen (TN) in freshwater refers to the sum of all nitrogen species present, including organic nitrogen, ammonia (NH₄⁺/NH₃), nitrate (NO₃⁻), and nitrite (NO₂⁻). It plays a critical role in aquatic ecosystems by supporting primary production, as nitrogen is an essential nutrient for the growth of phytoplankton and aquatic plants. However, excessive nitrogen levels can lead to eutrophication, a process where nutrient over-enrichment promotes excessive algal growth, which can result in oxygen depletion, harmful algal blooms (HABs), and declines in biodiversity (Smith et al., 1999).</div><div><br /></div><div>Nutrient species such as nitrogen are often reported in several forms. For example, nitrate may be reported as nitrate (NO3), nitrate as N or nitrate nitrogen (NO3-N), or nitrate ion (NO3- or Nitrate as NO3). Nitrate as nitrogen is an especially common way of reporting nitrate concentrations. Nitrate as nitrogen means that the concentration is provided in terms of the element nitrogen, isolating the nitrogen portion of the nitrate rather than the nitrate portion including the oxygen. Nitrate as nitrogen is determined by dividing the atomic weight of nitrogen (14.0067) by the molecular weight of a nitrate ion (62.0049). For example, a nitrate concentration reported as 62 mg/L nitrate ion can also be expressed as 14 mg/L nitrate as nitrogen. Analysts should verify that nutrient concentrations are converted to comparable formats (generally in elemental form as nitrogen).</div></div><div><br /></div><div><div><b>Dataset</b></div><div>This dataset focuses primarily on samples reported as total nitrogen and no speciation aggregations or conversions were performed.  In some cases, components of a desired parameter are monitored and reported instead of the desired parameter. To take full advantage of available monitoring data, one might want to convert from one parameter to another. For example, if nitrate+nitrite data are desired, you might first use any reported values for “nitrate+nitrite” and then secondarily sum other reported values of “nitrate” and “nitrite” when each are reported separately. Total nitrogen values could be obtained using a similar procedure. Many analyses report both total nitrogen and components of total nitrogen, so summation will be needed only in cases where total nitrogen is not reported. When several nutrient species are reported, an opportunity to check that the component species are less than the totals should be used (e.g., SRP &lt; TP, NH3N &lt; TKN). A 2012 USGS report assessing precision and bias of total nitrogen sampling found that measuring total nitrogen directly to be the most accurate (priority 1 and 2), followed by summing dissolved and particulate nitrogen (priority 3), followed by summing TKN and nitrate + nitrite (priority 4) (Table 1)(Rus, 2012).</div></div><div><br /></div><div>Table 1. Total Nitrogen Prioritization<br /></div><div style="text-align:left;"><img alt="Nitrogen Priority" src="https://lh3.googleusercontent.com/pw/AP1GczM_REmTSRtpmyewaPmjtOx__MjBdE_rEo5FVeQ8nmNMVNeLgKxIND-4bWhXqMgR8ePhrQxSe1xCqQQcP5TS9J-RF0RgYHXlo0ud_pWYQ6EOPAfPQ8HYoZEnkMj9A79wsInHb4ha76u8yqZl9KaH8bvwGw=w764-h183-s-no-gm?authuser=0" /><br /></div><div style="text-align:left;"><br /></div><div style="text-align:left;">This dataset is a collection of surface water total nitrogen samples collected across the United States from 2000-2023 from the Water Quality Portal (WQP), which integrates publicly available water quality data from the USGS National Water Information System (NWIS) and the EPA Water Quality Exchange (WQX) Data Warehouse. These water quality data records are provided by many federal, state, and tribal organizations and other partners. Because these data are from secondary sources, the U.S. EPA cannot ensure that the information is accurate, current, or complete. Therefore, users should verify the data from the original sources before drawing site specific conclusions.<br /></div><div style="text-align:left;"><br /></div><div style="text-align:left;"><div>Quality Assurance/Quality Control (QA/QC) and Identified Issues </div><div>An automated Quality Assurance/Quality Control (QA/QC) protocol was developed using a mix of Python and R-scripts to remove or identify potentially erroneous values and outliers from the WQP data download. The quality of the WQP measured data was evaluated as follows.</div><div><div><ul><li>Generally – do not delete data. Add a screening/flagging column to keep track of decision-making to remove records/observations.</li><li>Review the geographic/temporal scope and data types of the acquired data to the project objectives—it might not be necessary to process all data from a given data set. Map stations in a GIS to further refine and select data based on analysis selection criteria: geographic area, watersheds, bounding box, waterbody type, etc. This also provides the opportunity to conduct quality assurance checks based on spatial location (e.g., are the “estuarine” sites located near the coast).</li><li>Check for duplicate entries. Identify and screen those samples that are duplicates. Check for samples or results that do not have stations.</li><li>Interpret data qualifiers and comments (spiked, blanks, duplicates, etc.)</li><ul><li>ActivityTypeCode – e.g., Quality Control Samples</li><li>ResultCommentText – e.g., Sample beyond holding time, sample temperature elevated</li><li>ResultLaboratoryCommentText – e.g., diluted sample: method hi range exceeded, holding time exceeded</li></ul><li>Check for missing values – Identify and flag entries with missing total nitrogen values.</li><li>Check for outliers – Detect potential outliers that deviate from expected total nitrogen ranges from surface samples collected across the continental United States (0 to 90) (USEPA, 2022).</li><li>Check for incorrect units in the ResultMeasure/MeasureUnitCode  variable and flag entries where the unit is different than mg/L (Table 2).</li><li>Convert all relevant total nitrogen values to mg/L (Table 2).</li><li>Review and flag samples identified in the WQP with sample processing issues (e.g., suspected contamination, exceeding sampling hold time, no reported value, below reporting value). Many of the samples that met these criteria were already found and identified by WQP QA/QC data process.</li><li>Summary statistics – Calculate basic statistics (mean, median, standard deviation, range, last measurement, maximum, minimum).</li></ul></div></div><div style="text-align:center;"><img alt="Unit conversion to mg/l for measured total nitrogen samples." src="https://lh3.googleusercontent.com/pw/AP1GczMiu4KaD-lJLaTCzmAO6f93eoNL5gS-kEa_UgamlQ1M-9kRuL2PMjZbErDMx3gBHdejK0sSBeGIChX9EMY69yPeraFR4fzKxeqX--exB_t2Rn044uOMRV9Fm2Zqd1XaTD0j4kOmWUIyFKcxbDsU8MlLbQ=w670-h568-s-no-gm?authuser=0" /><br /></div><div style="text-align:center;"><i><b>Table 2</b>. Unit conversion to mg/l for measured total nitrogen samples.<br /></i></div><div style="text-align:center;"><br /></div><div style="text-align:left;"><div>Examples of errors found in the source dataset include negative alkalinity values, units of measurements not consistent with alkalinity measurements (e.g., &lt;Null&gt;, CaCO3, ppm) and entries suspected to be µg/L but reported as mg/L based on the natural and anthropogenic ranges of alkalinity. Users should verify the data from the original sources before drawing site specific conclusions. Generally source specific issues within the dataset will become apparent as QC steps are performed and data Individual contributing organizations can be found in the final and original datasets if the end user would like to filter for specific sampling partners.</div><div><br /></div><div>The resulting dataset is presented as a summarized collection of information for each unique sampling location and the original data flagging process helps to exclude unreliable and errant values from the final statistics. The R code developed to perform the QA/QC steps are available from <a href="mailto:cormier.susan@epa.gov" target="_blank">cormier.susan@epa.gov</a></div></div><div><br /></div><div><br /></div><div><div><b>Terms of Use</b></div><div><b><br /></b></div><div><b>Freshwater Explorer Data Disclaimer</b></div><div>This data is intended for exploratory and discussion purposes. Although statutory provisions and U.S. Environmental Protection Agency (EPA) regulations contain legally binding requirements, these data and related information are not regulatory nor do they change or substitute for any provisions or regulations. The information does not substitute for the Clean Water Act, a National Pollutant Discharge Elimination System permit, or EPA or state regulations applicable to permits; nor is this material a permit or regulation itself. Thus, it does not impose legally binding requirements on EPA, states, tribes, or the regulatory community. This information does not confer legal rights or impose legal obligations on any member of the public. Mention of any trade names, products, or services is not and should not be interpreted as conveying official EPA approval, endorsement, or recommendation.</div><div><br /></div><div>While EPA has used its best efforts to include complete and accurate information in this system, EPA cannot be held responsible for errors or omissions and is not liable for any direct, indirect, or consequential damages resulting from using this secondary information. Some potential sources of error have been assessed by the U.S. EPA resulting in the removal of some samples from the original data sets. However, all sources of potential error cannot be eliminated from the measured data reported in the Freshwater Explorer or the data used to develop predictive models. Therefore, the U.S. EPA cannot fully ensure either the original data or the values calculated from them. Conclusions and assessments drawn from the use of the Freshwater Explorer are the responsibility of the user.</div><div><br /></div><div>Please check sources, scale, accuracy, dates, and other available information. Please confirm that you are using the most recent copy of both data and metadata. Reliance on the information contained in this system by any party cannot be used as a defense in any administrative or judicial proceeding.</div><div><br /></div><div>This dataset may be revised periodically. EPA can revise this dataset without public notice to reflect changes in EPA policy, guidance, and advancements in the field of biological assessments. EPA welcomes public input on this document at any time. Send comments to FreshwaterExplorer@epa.gov, Center for Environmental Measurement and Modeling, Office of Research and Development, U.S. Environmental Protection Agency, 26 W. Martin Luther King Dr, Cincinnati, OH 45268.</div></div><div><br /></div></div><div><div><b>Credits (Attribution)</b></div><div><br /></div><div><b>Preferred Citation:</b> Leppo, E., Wharton, C., and Cormier. S. 2024. U.S. EPA Freshwater Explorer v2 national measured alkalinity metadata and dataset. USEPA. <a href="https://arcg.is/0OuDn80" target="_blank">https://arcg.is/0OuDn80</a></div></div><div><br /></div><div><b>Original data sources:</b> Water Quality Portal. Washington (DC): National Water Quality Monitoring Council, United States Geological Survey (USGS), Environmental Protection Agency (EPA); 2021. https://doi.org/10.5066/P9QRKUVJ. National Water Quality Monitoring Council, 2024 Water Quality Portal, accessed 01, 16, 2024, <a href="https://www.waterqualitydata.us/#sampleMedia=Water&amp;characteristicName=Alkalinity&amp;startDateLo=01-01-2000&amp;startDateHi=12-31-2023&amp;mimeType=csv&amp;sorted=no&amp;dataProfile=narrowResult&amp;providers=NWIS&amp;providers=STEWARDS&amp;providers=STORET, https://doi.org/10.5066/P9QRKUVJ." target="_blank">https://www.waterqualitydata.us/#sampleMedia=Water&amp;characteristicName=Alkalinity&amp;startDateLo=01-01-2000&amp;startDateHi=12-31-2023&amp;mimeType=csv&amp;sorted=no&amp;dataProfile=narrowResult&amp;providers=NWIS&amp;providers=STEWARDS&amp;providers=STORET, https://doi.org/10.5066/P9QRKUVJ.</a><br /></div><div><br /></div><div><div><b>References</b></div><div>Hunt, D.T.E. and A.L. Wilson. 1986. The Chemical Analysis of Water: General Principles and Techniques. 2nd ed. Royal Society of Chemistry, London, England.</div><div><br /></div><div>Youden, W.J. 1969. Ranking laboratories by round-robin tests. In Precision Measurement and Calibration. H.H. Ku, ed. NBS Special Publication 300, Vol. 1. U.S. GPO Washington, D.C.</div><div><br /></div><div>Hillman, D.C., J.F. Potter, and S.J. Simon. 1986. National Surface Water Survey, Eastern Lake Survey-Phase I, Analytical Methods Manual. EPA/600/4-86/009. U.S. Environmental Protection Agency, Las, Vegas, NV.</div><div><br /></div><div>U.S. EPA, 1987. Handbook of Methods for Acid Deposition Studies: Laboratory Analyses for Surface Water Chemistry. EPA/600/4-87/026. U.S. Environmental Protection Agency, Office of Research and Development, Washington D.C.</div><div><br /></div><div>Oblinger Childress, C. J., W. T. Foreman, B. F. Connor, and T. J. Maloney. 1999. New reporting procedures based on long-term method detection levels and some considerations for interpretations of water-quality data provided by the U.S. Geological Survey National Water Quality Laboratory. Open-File Report 99-193, US Geological Survey, Reston, Virginia.</div><div><br /></div><div>Rus, D.L., Patton, C.J., Mueller, D.K., and Crawford, C.G. 2012. Assessing Total Nitrogen in Surface-Water Samples-Precision and Bias of Analytical and Computational Methods. U.S. Geological Survey Scientific Investigation Report 2012-5281. 38 p. <a href="https://pubs.usgs.gov/sir/2012/5281/sir12_5281.pdf" target="_blank">https://pubs.usgs.gov/sir/2012/5281/sir12_5281.pdf</a></div><div><br /></div><div>Smith, V. H., Tilman, G. D., &amp; Nekola, J. C. (1999). Eutrophication: impacts of excess nutrient inputs on freshwater, marine, and terrestrial ecosystems. Environmental Pollution, 100(1-3), 179-196.</div><div><br /></div><div>USEPA. 2022. National Rivers and Streams Assessment 2023 - 2024: Laboratory Operations Manual. EPA841-B-22-008. U.S. Environmental Protection Agency, Office of Water, Washington, DC.</div><div><br /></div><div>USGS. 2024. Alkalinity Calculation Methods. <a href="https://or.water.usgs.gov/alk/methods.html" target="_blank">https://or.water.usgs.gov/alk/methods.html</a></div></div>

Copyright Text: Water Quality Portal. Washington (DC): National Water Quality Monitoring Council, United States Geological Survey (USGS), Environmental Protection Agency (EPA); 2021. https://doi.org/10.5066/P9QRKUVJ.

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