This U.S. Geological Survey data release presents tabular daily data on nitrate plus nitrite nitrogen and total nitrogen loads for the Connecticut River at Middle Haddam, Connecticut, from December 6, 2008, to September 30, 2014. The data release contains total nitrogen concentration estimates at 15-minute intervals from December 2011 to September 2014. The data release also includes tabular information on the total nitrogen loads from the Connecticut River at Thompsonville, Connecticut, from October 1, 2008, to September 30, 2014. Load data for each site and constituent include the daily loads and upper and lower 95-percent prediction intervals (where applicable); the method used in the load calculation for each site is also included in this data release.

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.

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.

Total Nitrogen (TN) rloadest models were developed to compute TN flux at School Branch at three USGS monitoring stations: School Branch at Maloney Road near Brownsburg, Indiana (03353415); School Branch at CR750N at Brownsburg, Indiana (03353420); and School Branch at Noble Drive at Brownsburg, Indiana (03353430). Frequently, TN models developed in rloadest regress discrete TN concentrations against concurrent daily mean streamflow values. However, due to the flashy nature of streamflows on School Branch, the developed TN models regressed discrete TN concentrations against the closest unit-value (15-minute) streamflows. Once TN flux models were calibrated, unit-value streamflows were used to estimate average TN fluxes for selected time periods, which in turn were used to compute loads. This data release contains calibration data sets and R code used to create regression models for estimating daily flux of total nitrogen and summary information for the models for each site.

Total Nitrogen (TN) rloadest models were developed to compute TN flux at School Branch at three USGS monitoring stations: School Branch at Maloney Road near Brownsburg, Indiana (03353415); School Branch at CR750N at Brownsburg, Indiana (03353420); and School Branch at Noble Drive at Brownsburg, Indiana (03353430). Frequently, TN models developed in rloadest regress discrete TN concentrations against concurrent daily mean streamflow values. However, due to the flashy nature of streamflows on School Branch, the developed TN models regressed discrete TN concentrations against the closest unit-value (15-minute) streamflows. Once TN flux models were calibrated, unit-value streamflows were used to estimate average TN fluxes for selected time periods, which in turn were used to compute loads. This data release contains calibration data sets and R code used to create regression models for estimating daily flux of total nitrogen and summary information for the models for each site.

The purpose of this data release is to provide the original data, analysis methods, and nitrogen loading models in support of a study of the upper South Platte River annual total nitrogen loads attributed to atmospheric deposition of reactive nitrogen during 2017-2018. The data release includes water-quality and stream discharge data and associated predictive regression models used in the estimation of South Platte River nitrogen loads upstream from Weldona, Colorado and sub-basin runoff coefficients for the reach between Chatfield Dam and the South Platte River at Denver gage. The water-quality data were obtained from monthly unfiltered grab samples collected by the Denver Department of Public Health and Environment and analyzed by Standard Methods 4500-NO2-B (nitrite); 4500-NO3-F (nitrate); and 4500-NORG-B+NH3 (Total Kjeldahl Nitrogen). Stream discharge data were obtained for gaging stations from the National Water Information System and Colorado Division of Water Resources with two exceptions as follows. The Englewood wastewater reclamation facility discharge data were supplied by the facility. Discharge values for site N25E were calculated by subtracting the discharge from Cherry Creek at Denver (site W17) from the discharge at South Platte River at Denver. In addition to supplying the data used to calculate nitrogen loads and sub-basin runoff coefficients, this data release also provides the equations and diagnostic statistics for the models developed using the LOADEST software configured for R (rloadest package). Data users are referred to R help to define the many diagnostic statistics presented.

The purpose of this data release is to provide the original data, analysis methods, and nitrogen loading models in support of a study of the upper South Platte River annual total nitrogen loads attributed to atmospheric deposition of reactive nitrogen during 2017-2018. The data release includes water-quality and stream discharge data and associated predictive regression models used in the estimation of South Platte River nitrogen loads upstream from Weldona, Colorado and sub-basin runoff coefficients for the reach between Chatfield Dam and the South Platte River at Denver gage. The water-quality data were obtained from monthly unfiltered grab samples collected by the Denver Department of Public Health and Environment and analyzed by Standard Methods 4500-NO2-B (nitrite); 4500-NO3-F (nitrate); and 4500-NORG-B+NH3 (Total Kjeldahl Nitrogen). Stream discharge data were obtained for gaging stations from the National Water Information System and Colorado Division of Water Resources with two exceptions as follows. The Englewood wastewater reclamation facility discharge data were supplied by the facility. Discharge values for site N25E were calculated by subtracting the discharge from Cherry Creek at Denver (site W17) from the discharge at South Platte River at Denver. In addition to supplying the data used to calculate nitrogen loads and sub-basin runoff coefficients, this data release also provides the equations and diagnostic statistics for the models developed using the LOADEST software configured for R (rloadest package). Data users are referred to R help to define the many diagnostic statistics presented.

This data release provides data in support of an assessment of changes in slope of the concentration discharge relation for total organic carbon in eight major rivers at gaging stations in Connecticut from 1972 to 2019. The rivers include the Connecticut at Thompsonville (01184000), Housatonic at Stevenson (01205500), Quinebaug at Jewett City (01127000), Farmington at Tariffville (01189995), Shetucket at Willamantic (01122500), Naugatuck at Beacon Falls (011208500), Quinnipiac at Wallingford (01196500), and Salmon at East Hampton (01193500). The assessment is described in the article “An increase in the slope of the concentration discharge relation for total organic carbon in major rivers in New England, 1973 to 2019” (Huntington and Wieczorek, in review). Two models were used in this assessment; the Weighted Regressions on Time, Discharge and Season (WRTDS) model (Hirsch and others, 2010), and the Hydrograph Separation (HYSEP model) (Sloto and Crouse, 1996). Both models use data from the USGS National Water Information System (NWIS) database (USGS, 2020). The WRTDS model was used to estimate daily concentrations of various water quality constituents and the HYSEP model was used to estimate the fraction of daily discharge that could be classified as storm flow (event flow) as opposed to base flow. In a separate analysis, for the Connecticut, Farmington, and Quinnipiac Rivers, independent regression models for the early and recent periods were used to compare predicted TOC concentrations given a common daily discharge record for one year. A synthetic record was developed from the average daily discharges for these rivers for the period 10/1/1992 to 9/30/1998. To run the appropriate WRTDS model with this discharge record the dates for this synthetic record were set to 10/1/1983 to 9/30/1984 when run with the early period model and 10/1/2005 to 9/30/2006 when run with the recent period model. Using these synthetic discharge periods centered the synthetic year in the middle of each period thus controlling for any temporal trends in the C-Q relations during the periods. On the few days of the year during those periods when samples were collected for TOC analyses, the observed discharge in the actual record was substituted for the synthetic discharge so the original concentration discharge data pair would be used in the regression model. This data release is structured as a set of comma-separated values (CSV) files, including a site file, 44 data files, and a data dictionary (Data_Dictionary.csv), which provides information describing the content of each of the data files. The data dictionary contains the filename, data type, description, and units. The site-information file contains the USGS 8-digit site ID, site name, latitude, longitude, horizontal datum, land surface elevation, vertical datum, and drainage area. The data files contain input data for one set of model runs and output data for all model runs of the WRTDS model as follows: • There are six input files, one for the early period (1973 to 1995) and one for the recent period (1996 to 2019) for three rivers. These input files contain two columns (date and daily discharge). The file naming convention begins with WRTDS_INPUT_DAILY_Discharge_ and is followed by the date range and the USGS site ID for the specific river. For example, “WRTDS_INPUT_DAILY_Discharge_1996-2019_01196500.csv” is for the recent period for the Quinnipiac River at Wallingford • There are eight WRTDS model output files (one for each of the eight rivers) for the full period (1973 to 2019) that contain date, daily discharge, and estimated concentrations of total organic carbon, total nitrogen, total phosphorus, and sulfate. The file naming convention begins with WRTDS_Output_Daily_1973-2019_ and is followed by the USGS site ID for the specific river. For example, “WRTDS_Output_Daily_1973-2019_01184000.csv” is for the full period for the Connecticut River at Thompsonville. • There are eight WRTDS model