This dataset contains quality assurance sample concentrations for 19 constituents for the 15 monitored watersheds in Gwinnett County, Georgia, from 2000 to 2020. Samples include 431 replicate pairs and 335 field blanks. Replicate sampling allows for comparison of water quality to assess the combined variability in sample representativeness and laboratory precision and can also be used to identify possible sample contamination. Field blanks, samples of deionized “blank” water collected using the same sampling equipment and similar methodology as routine samples, were used to identify any possible contamination from field collection equipment and methodology.

The dataset contains annual and model calibration period streamwater constituent load and yield estimates for 13 watersheds in Gwinnett County, Georgia for the water years 2003 to 2020. Loads and yields were estimated for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The USGS LOADEST load estimation software, which employs a regression-model estimation approach, was used for constituents that had at least a minimal relation with the model explanatory variables, as indicated by concentration model R-square >0.20. The Beale ratio estimator was used to estimate loads for constituents that had weak concentration-model relations, concentration model R-squares <0.20. Loads and yields are provided for the 13 individual study watersheds and for the study watersheds area. The period of loads available varies by watershed depending upon when monitoring and constituent analysis started. Uncertainties in load and yield estimates that were calculated using LOADEST are provided as 95-percent confidence intervals of the estimates.

The dataset contains annual and model calibration period streamwater constituent load and yield estimates for 13 watersheds in Gwinnett County, Georgia for the water years 2003 to 2020. Loads and yields were estimated for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The USGS LOADEST load estimation software, which employs a regression-model estimation approach, was used for constituents that had at least a minimal relation with the model explanatory variables, as indicated by concentration model R-square >0.20. The Beale ratio estimator was used to estimate loads for constituents that had weak concentration-model relations, concentration model R-squares <0.20. Loads and yields are provided for the 13 individual study watersheds and for the study watersheds area. The period of loads available varies by watershed depending upon when monitoring and constituent analysis started. Uncertainties in load and yield estimates that were calculated using LOADEST are provided as 95-percent confidence intervals of the estimates.

The dataset contains model coefficients and statistics for the 488 regression models used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for two calibration periods, water years 2003-2010 and 2010-2020. Model terms were selected from an 11-parameter equation, which was a function of discharge, base flow, season, turbidity, and time (trend), using a forward stepwise ordinary least squares regression approach. Model coefficients were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit both with and without turbidity explanatory variables for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The dataset includes a summary of sample concentrations used to calibration the models (period of samples collected, number of concentrations, number of censored concentrations, and number of outliers removed), model coefficients, and selected model statistics (concentration and load model R-squares, estimated residual variance, serial correlation in the model residuals, and Turnbull-Weiss normality test statistic of residuals). Portable document format files of LOADEST output are provided for each model in a “zip” file that contain model diagnostic statistics and plots for evaluating model fits.

The dataset contains model coefficients and statistics for the 488 regression models used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for two calibration periods, water years 2003-2010 and 2010-2020. Model terms were selected from an 11-parameter equation, which was a function of discharge, base flow, season, turbidity, and time (trend), using a forward stepwise ordinary least squares regression approach. Model coefficients were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit both with and without turbidity explanatory variables for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. The dataset includes a summary of sample concentrations used to calibration the models (period of samples collected, number of concentrations, number of censored concentrations, and number of outliers removed), model coefficients, and selected model statistics (concentration and load model R-squares, estimated residual variance, serial correlation in the model residuals, and Turnbull-Weiss normality test statistic of residuals). Portable document format files of LOADEST output are provided for each model in a “zip” file that contain model diagnostic statistics and plots for evaluating model fits.

This dataset contains a list of outlier sample concentrations identified for 17 water quality constituents from streamwater sample collected at 15 study watersheds in Gwinnett County, Georgia for water years 2003 to 2020. The 17 water quality constituents are: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), suspended sediment concentration (SSC), total nitrogen (TN), total nitrate plus nitrite (NO3NO2), total ammonia plus organic nitrogen (TKN), dissolved ammonia (NH3), total phosphorus (TP), dissolved phosphorus (DP), total organic carbon (TOC), total calcium (Ca), total magnesium (Mg), total copper (TCu), total lead (TPb), total zinc (TZn), and total dissolved solids (TDS). 885 outlier concentrations were identified. Outliers were excluded from model calibration datasets used to estimate streamwater constituent loads for 12 of these constituents. Outlier concentrations were removed because they had a high influence on the model fits of the concentration relations, which could substantially affect model predictions. Identified outliers were also excluded from loads that were calculated using the Beale ratio estimator. Notes on reason(s) for considering a concentration as an outlier are included.

This dataset contains a list of outlier sample concentrations identified for 17 water quality constituents from streamwater sample collected at 15 study watersheds in Gwinnett County, Georgia for water years 2003 to 2020. The 17 water quality constituents are: biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), suspended sediment concentration (SSC), total nitrogen (TN), total nitrate plus nitrite (NO3NO2), total ammonia plus organic nitrogen (TKN), dissolved ammonia (NH3), total phosphorus (TP), dissolved phosphorus (DP), total organic carbon (TOC), total calcium (Ca), total magnesium (Mg), total copper (TCu), total lead (TPb), total zinc (TZn), and total dissolved solids (TDS). 885 outlier concentrations were identified. Outliers were excluded from model calibration datasets used to estimate streamwater constituent loads for 12 of these constituents. Outlier concentrations were removed because they had a high influence on the model fits of the concentration relations, which could substantially affect model predictions. Identified outliers were also excluded from loads that were calculated using the Beale ratio estimator. Notes on reason(s) for considering a concentration as an outlier are included.

The dataset contains the sample constituent concentrations and explanatory variable values used for fitting the load regression models that were then used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for water years 2003 to 2020. Load regression models were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. Explanatory variables include a storm condition indicator variable, season, time and time-squared (trend), and the natural logarithms of streamflow, streamflow during base-flow conditions, base flow, turbidity, and turbidity during stormflow conditions.

The dataset contains the sample constituent concentrations and explanatory variable values used for fitting the load regression models that were then used to estimate streamwater constituent loads for 13 watersheds in Gwinnett County, Georgia for water years 2003 to 2020. Load regression models were fit using U.S. Geological Survey (USGS) LOADEST load estimation software. Models were fit for 12 water-quality constituents: total suspended solids, suspended sediment concentration, total nitrogen, total nitrate plus nitrite, total phosphorus, dissolved phosphorus, total organic carbon, total calcium, total magnesium, total lead, total zinc, and total dissolved solids. Explanatory variables include a storm condition indicator variable, season, time and time-squared (trend), and the natural logarithms of streamflow, streamflow during base-flow conditions, base flow, turbidity, and turbidity during stormflow conditions.

This dataset contains the daily average base flow, as determined by hydrograph separation, for 14 watersheds in Gwinnett County, Georgia for October 2001 through September 2020. Hydrograph separations were done using the Web-based Hydrograph Analysis Tool (WHAT) using the simple local minimum method on the daily average streamflows, which are also provided in this dataset. Base flow along with the calculated base-flow index (the proportion of base flow to total flow) were used to characterize groundwater recharge and the relative degree of storm runoff in the watersheds. Base flow was also used as predictor variable in models for estimating streamwater constituent loads for 12 water-quality constituents at 13 of the study watersheds.