This U.S. Geological Survey (USGS) data release presents tabular data on nitrogen concentrations and loads for multiple nitrogen species, and river discharge data used in the analysis of data collected from October 1994 to September 2021. Data on flow and nitrogen concentrations were analyzed using the USGS Exploration and Graphics for RivEr Trends (EGRET) R package, and the method of Weighted Regression on Time Discharge and Season (WRTDS). Data and outputs summarized are for water-quality data collected from 17 water-quality monitoring stations in the Long Island Sound watershed. Specific data in tabular format for this release include: calculated annual nitrogen concentration and loads, calculated annual flow-normalized nitrogen concentrations and loads by water year (for sites with 20 years of data or more), and calculated annual seasonal loads of each nitrogen constituent by calendar year. Measured daily river discharge data and sampled nitrogen concentration data for each water-quality monitoring site are available as outputs accessible within R statistical software and as comma-separated values (CSV) files. This data release provides an update of data originally generated for use in nitrogen budget models for Long Island Sound (Vlahos and others, 2020), and the associated data release (Mullaney, 2020). Mullaney, J.R., 2020, Nitrogen concentrations and loads and seasonal nitrogen loads in selected Long Island Sound tributaries, water years 1995-2016: U.S. Geological Survey data release, https://doi.org/10.5066/P9AVXGBB. Vlahos, P., Whitney, M.M., Menniti, C., Mullaney, J.R., Morrison, J., Jia, Y., 2020, Nitrogen budgets of the Long Island Sound estuary: Estuarine, Coastal, and Shelf Science, v. 232, no 104693, https://doi.org/10.1016/j.ecss.2019.106493.

This U.S. Geological Survey (USGS) data release presents tabular data on nitrogen concentrations and loads for multiple nitrogen species, and river discharge data used in the analysis of data collected from October 1994 to September 2021. Data on flow and nitrogen concentrations were analyzed using the USGS Exploration and Graphics for RivEr Trends (EGRET) R package, and the method of Weighted Regression on Time Discharge and Season (WRTDS). Data and outputs summarized are for water-quality data collected from 17 water-quality monitoring stations in the Long Island Sound watershed. Specific data in tabular format for this release include: calculated annual nitrogen concentration and loads, calculated annual flow-normalized nitrogen concentrations and loads by water year (for sites with 20 years of data or more), and calculated annual seasonal loads of each nitrogen constituent by calendar year. Measured daily river discharge data and sampled nitrogen concentration data for each water-quality monitoring site are available as outputs accessible within R statistical software and as comma-separated values (CSV) files. This data release provides an update of data originally generated for use in nitrogen budget models for Long Island Sound (Vlahos and others, 2020), and the associated data release (Mullaney, 2020). Mullaney, J.R., 2020, Nitrogen concentrations and loads and seasonal nitrogen loads in selected Long Island Sound tributaries, water years 1995-2016: U.S. Geological Survey data release, https://doi.org/10.5066/P9AVXGBB. Vlahos, P., Whitney, M.M., Menniti, C., Mullaney, J.R., Morrison, J., Jia, Y., 2020, Nitrogen budgets of the Long Island Sound estuary: Estuarine, Coastal, and Shelf Science, v. 232, no 104693, https://doi.org/10.1016/j.ecss.2019.106493.

This U.S. Geological Survey data release presents tabular data on nitrogen concentrations and loads for multiple nitrogen species, and river discharge data used in the analysis of data collected from October 1994 to September 2016. Data on flow and nitrogen concentrations were analyzed using the USGS EGRET R package, and the method of WRTDS (Weighted Regression on Time Discharge and Season). Data and outputs summarized are for water-quality data collected from 18 water-quality monitoring stations in the Long Island Sound watershed. Specific data in tabular format for this release include: calculated annual nitrogen concentration and loads, calculated annual flow-normalized nitrogen concentrations and loads by water year (for sites with 20 years of data or more), and calculated annual seasonal loads of each nitrogen constituent by calendar year. Measured daily river discharge data and sampled nitrogen concentration data for each water-quality monitoring site are available as tables accessible within R statistical software.

This U.S. Geological Survey data release presents tabular data on nitrogen concentrations and loads for multiple nitrogen species, and river discharge data used in the analysis of data collected from October 1994 to September 2016. Data on flow and nitrogen concentrations were analyzed using the USGS EGRET R package, and the method of WRTDS (Weighted Regression on Time Discharge and Season). Data and outputs summarized are for water-quality data collected from 18 water-quality monitoring stations in the Long Island Sound watershed. Specific data in tabular format for this release include: calculated annual nitrogen concentration and loads, calculated annual flow-normalized nitrogen concentrations and loads by water year (for sites with 20 years of data or more), and calculated annual seasonal loads of each nitrogen constituent by calendar year. Measured daily river discharge data and sampled nitrogen concentration data for each water-quality monitoring site are available as tables accessible within R statistical software.

During the spring and summer of 2022, the U.S. Geological Survey collected water-quality samples for nutrient analysis at 45 stations across the state of Connecticut and adjacent areas of New York and Rhode Island to better understand the groundwater discharge component of nitrogen loading to the Long Island Sound. The targeted stations were located in small drainage basins (less than 50 square kilometers) in the southern portion of the Long Island Sound watershed. Sites were selected randomly from groups based on expected drivers or controls on baseflow nitrogen loads. Factors used in the grouping included four metrics calculated for the upstream watershed: percent impervious cover, septic system density, percent agricultural or turf grass land cover, and percent coarse-grained stratified sediments. The water-quality samples and instantaneous discharge measurements were collected under baseflow conditions during two separate synoptic sampling events, one in the nongrowing season (April 2022) and one in the growing season (June and July 2022). Instantaneous discharge measurements were collected in addition to water-quality samples to enable the calculations of nitrogen loads and yields. The water-quality samples were analyzed for physical properties and concentrations of chloride, nutrient species, and dissolved organic carbon; some analyses were performed past analytical method holding times. This data release includes site characteristics and geospatial data for potential and final (selected) sites, as well as field data, analytical results, and calculated nitrogen loads and yields for the final sites. Column names, units and descriptions are provided in data_dictionary.txt and a lookup table for method codes is provided in MethodLookupTable.txt. Note that many station identifiers (site_no) have a leading "0" that should be retained.

During the spring and summer of 2022, the U.S. Geological Survey collected water-quality samples for nutrient analysis at 45 stations across the state of Connecticut and adjacent areas of New York and Rhode Island to better understand the groundwater discharge component of nitrogen loading to the Long Island Sound. The targeted stations were located in small drainage basins (less than 50 square kilometers) in the southern portion of the Long Island Sound watershed. Sites were selected randomly from groups based on expected drivers or controls on baseflow nitrogen loads. Factors used in the grouping included four metrics calculated for the upstream watershed: percent impervious cover, septic system density, percent agricultural or turf grass land cover, and percent coarse-grained stratified sediments. The water-quality samples and instantaneous discharge measurements were collected under baseflow conditions during two separate synoptic sampling events, one in the nongrowing season (April 2022) and one in the growing season (June and July 2022). Instantaneous discharge measurements were collected in addition to water-quality samples to enable the calculations of nitrogen loads and yields. The water-quality samples were analyzed for physical properties and concentrations of chloride, nutrient species, and dissolved organic carbon; some analyses were performed past analytical method holding times. This data release includes site characteristics and geospatial data for potential and final (selected) sites, as well as field data, analytical results, and calculated nitrogen loads and yields for the final sites. Column names, units and descriptions are provided in data_dictionary.txt and a lookup table for method codes is provided in MethodLookupTable.txt. Note that many station identifiers (site_no) have a leading "0" that should be retained.

The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency's Long Island Sound Study (https://longislandsoundstudy.net), characterized nitrogen export from forested watersheds and whether nitrogen loading has been increasing or decreasing to help inform Long Island Sound management strategies. The Weighted Regressions on Time, Discharge, and Season (WRTDS; Hirsch and others, 2010) method was used to estimate annual concentrations and fluxes of nitrogen species using long-term records (14 to 37 years in length) of stream total nitrogen, dissolved organic nitrogen, nitrate, and ammonium concentrations and daily discharge data from 17 watersheds located in the Long Island Sound basin or in nearby areas of Massachusetts, New Hampshire, or New York. This data release contains the input water-quality and discharge data, annual outputs (including concentrations, fluxes, yields, and confidence intervals about these estimates), statistical tests for trends between the periods of water years 1999-2000 and 2016-2018, and model diagnostic statistics. These datasets are organized into one zip file (WRTDSeLists.zip) and six comma-separated values (csv) data files (StationInformation.csv, AnnualResults.csv, TrendResults.csv, ModelStatistics.csv, InputWaterQuality.csv, and InputStreamflow.csv). The csv file (StationInformation.csv) contains information about the stations and input datasets. Finally, a short R script (SampleScript.R) is included to facilitate viewing the input and output data and to re-run the model. Reference: Hirsch, R.M., Moyer, D.L., and Archfield, S.A., 2010, Weighted Regressions on Time, Discharge, and Season (WRTDS), with an application to Chesapeake Bay River inputs: Journal of the American Water Resources Association, v. 46, no. 5, p. 857–880.

A monthly model of groundwater-transported nitrogen loads was developed for 12-digit hydrologic unit code (HUC12) watersheds on the north shore of Long Island Sound in coastal Connecticut and adjacent areas of New York and Rhode Island. As part of the analysis, potential management actions that upgraded septic systems or reduced fertilizer application to areas of turf-grass were also simulated. This compilation includes a zipped file (Tables.zip) of aggregated model outputs and datasets used in the model development. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each table and a data dictionary (data_dictionary.csv) that includes the variable name, data type, units, reasonable values, and a description for each column in the tables. This compilation also includes a zipped file of supplemental figures (Figure.zip) that were not included in the main report. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each figure. Finally, this compilation includes a shapefile of the HUC12 basins as used in this study. For the purposes of this study the seaward boundaries of the HUC12 basins were extended to include adjacent coastal waters and the shapefiles were delineated using the model grid. For these reasons the shapefiles will differ slightly from other geospatial datasets of the HUC12 basins. Complete model inputs and outputs are available in the model archives accessible at https://doi.org/10.5066/P1HKENGV and https://doi.org/10.5066/P1GUC7FE.

A monthly model of groundwater-transported nitrogen loads was developed for 12-digit hydrologic unit code (HUC12) watersheds on the north shore of Long Island Sound in coastal Connecticut and adjacent areas of New York and Rhode Island. As part of the analysis, potential management actions that upgraded septic systems or reduced fertilizer application to areas of turf-grass were also simulated. This compilation includes a zipped file (Tables.zip) of aggregated model outputs and datasets used in the model development. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each table and a data dictionary (data_dictionary.csv) that includes the variable name, data type, units, reasonable values, and a description for each column in the tables. This compilation also includes a zipped file of supplemental figures (Figure.zip) that were not included in the main report. The zipped file contains a file dictionary (file_dictionary.csv) that includes the file name, title, and caption for each figure. Finally, this compilation includes a shapefile of the HUC12 basins as used in this study. For the purposes of this study the seaward boundaries of the HUC12 basins were extended to include adjacent coastal waters and the shapefiles were delineated using the model grid. For these reasons the shapefiles will differ slightly from other geospatial datasets of the HUC12 basins. Complete model inputs and outputs are available in the model archives accessible at https://doi.org/10.5066/P1HKENGV and https://doi.org/10.5066/P1GUC7FE.

This data release contains estimated seasonal total nitrogen (TN) and total phosphorus (TP) loads during 2005 through 2020 in selected streams of the watersheds draining to Washington waters of the Salish Sea (Puget Sound region). Two load estimation methods were used: Fluxmaster (Schwarz and others, 2006, https://doi.org/10.3133/tm6B3) and Weighted Regression on Time, Discharge, and Season (WRTDS) with Kalman filtering (Hirsch and De Cicco, 2015, https://doi.org/10.1016/j.envsoft.2015.07.017). Together with the water-quality data, streamflow data, and estimated nitrogen and phosphorus loads, this release also provides copies of computer programming script that can be used to recreate the load estimates or modified for similar applications (see Process Steps). Seasonal TN and TP loads paired with streamflow were estimated at 50 locations. For convenience, seasonal summaries are also provided of observed streamflow at 128 locations and of observed water temperature at 29 locations.