Brent T. Aulenbach Joshua C. Henley Kristina G. Hopkins 20230404 tabular digital data Reston, VA U.S. Geological Survey https://doi.org/10.5066/P9G8HZTY Brent T. Aulenbach Joshua C. Henley Kristina G. Hopkins 2023 publication USGS Scientific Investigations Report 2023-5035 Reston, Virginia U.S. Geological Survey 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 purpose of this dataset is to provide annual and study period streamwater constituent load and yield estimates in support of the USGS Scientific Investigations Report " Hydrology, water-quality, and watershed characteristics in 15 watersheds in Gwinnett County, Georgia, 2002-20". This study is part of a long-term program to monitor and analyze the hydrologic and water-quality conditions of 15 watersheds in Gwinnett County, Georgia by the USGS in cooperation with Gwinnett County Department of Water Resources. 20021001 20200930 publication date Complete None planned -84.2721 -83.8468 34.1514 33.7676 ISO 19115 Topic Category inlandWaters USGS Thesaurus surface water quality streamflow mathematical modeling Marine Realms Information Bank (MRIB) keywords watershed USGS Metadata Identifier USGS:635048e2d34e47431c15c602 Geographic Names Information System Gwinnett County State of Georgia None. Please see 'Distribution Info' for details. None. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. Brent T Aulenbach U.S. Geological Survey, Southeast Region Research Hydrologist mailing address

1770 Corporate Drive Suite 500

Norcross GA 30093 US 678-924-6626 678-924-6710 btaulenb@usgs.gov Funded through a cooperative agreement between Gwinnett County Department of Water Resources and the U.S. Geological Survey MacOS Big Sur, version 11.7.1; Microsoft Excel for Mac, version 16.67, 15_GwinnettCoGa_Loads.csv 325 KB Estimates of uncertainty of loads and yields that were calculated using LOADEST are provided as 95-percent confidence intervals. Estimates of uncertainty were not reported for loads and yield calculated using the Beale ratio estimator approach because these estimates of error are poor when using small numbers of samples such as the case herein. No formal logical accuracy tests were conducted. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. Streamwater constituent loads were estimated for 13 Gwinnett County, Georgia watersheds for 12 water-quality constituents for the period water years 2003 to 2020. For constituent-watershed combinations that had moderate to strong concentration-model relations, as indicated by concentration model R-square >0.20, a regression-model approach was deemed most appropriate and was used to estimate loads. In a regression-model approach, concentration is estimated as a function of continuously measured explanatory variables, such as discharge and day of year (Johnson, 1979; Crawford, 1991; Cohn and others, 1992). Loads were estimated using an 11-parameter regression model, which was a function of discharge, base flow, season, turbidity, and time (trend), and had separate model parameters for the intercept, streamflow, and turbidity variables to account for different relations during base-flow and stormflow conditions. The optimal set of model terms was determined using a forward-stepwise regression with the corrected Akaike Information Criterion (AICc; Akaike, 1974; Burnham and Anderson, 2002). Model-term selection was done using JMP(R) statistical data analysis software version 16.1.0 (SAS Institute Inc., 1989-2021) employing an ordinary least squares (OLS) fitting approach. For models that included turbidity as an explanatory variable, a second model without turbidity terms was fit to prevent gaps in load estimates when turbidity data was not available. Final model fits were done using the USGS LOAD ESTimator software (LOADEST; Runkel and others, 2004). The adjusted maximum likelihood estimates (AMLE) algorithm (Cohn, 1988; Cohn and others, 1989, 1992) was used to fit the models and estimate loads. The AMLE approach appropriately handle left-censored water-quality data--concentrations that are below the analytical detection limit--such that load estimates have negligible bias (Cohn and others, 1992). The regression-model approach load estimation methodology was modified using a time-step approach that accommodated incorporating storm-composited samples into the concentration-discharge relations (Landers and others, 2007; Joiner and others, 2014; Aulenbach and others, 2017; Aulenbach and others, 2022). This time step represents a typical storm duration, which were determined from the average of the 25th and 75th percentiles of the storm-sample durations for each watershed and ranged from 4 to 12 hours. The model calibration datasets were split into two time periods, water years 2003-10 and 2010-20, to better allow for temporal changes in the model parameter fits and improve the ability to detect trends while still having a sufficient number of concentrations for fitting the models (Aulenbach, 2013). Water year 2010 was included in both calibration periods because it divided the load estimation period in about two equal periods while avoiding starting or ending the calibration periods during drought that could induce trends in loads. Load estimates for water year 2010, therefore, are reported for both calibration periods and can be averaged to obtain a single annual estimate. The Beale ratio estimator (BRE; Beale, 1962) was used to estimate loads for constituents whose concentration models did not explain much of the variance in concentrations (R-squares <0.2, which indicates less than 20 percent of the variance explained) and, therefore, did not warrant using a regression-based load estimation approach. The BRE is a commonly used ratio estimator approach. In the BRE method, first the average sample-estimated load is adjusted by the ratio of the average annual flow and the sample average annual flow. This load is then corrected for bias by multiplying it by a factor that accounts for the covariance (correlation) between the flow and load values. Beale ratio estimator loads were estimated on an annual basis using just the samples collected from that year. Estimates of uncertainty were not reported for loads using this approach because calculations of error are poor when using small numbers of samples, as occurred herein. In a load estimation evaluation study using a constituent that did not have a strong concentration-discharge relation, the Beale ratio estimator statistically outperformed other averaging and regression-model based approaches (Dolan and others, 1981). The Beale ratio estimator is a well-suited load estimation approach for studies which have few discrete concentration samples (Quilbé and others, 2006). Loads for the cumulative watersheds area were determined by summing the loads of the 12 non-nested watersheds. The study watersheds area load uncertainties were determined by combining the uncertainties of the individual watershed loads in quadrature (that is, squared, added, and then taking the square root), which is an appropriate method for combining errors from multiple values (Kirchner, 2001). Streamwater constituent load estimate calculations were completed between November 1, 2021 and January 18, 2022. References: Akaike, H., 1974, A new look at the statistical model identification: IEEE Transactions on Automatic Control, v. 19, no. 6, p. 716-723, accessed July 11, 2020, at https://doi.org/10.1109/TAC.1974.1100705. Aulenbach, B.T., 2013, Improving regression-model-based streamwater constituent load estimates derived from serially correlated data: Journal of Hydrology (Amsterdam), v. 503, p. 55-66, accessed July 11, 2020, at https://doi.org/10.1016/j.jhydrol.2013.09.001. Aulenbach, B.T., Henley, J.C., and Hopkins, K.G., 2023, Hydrology, water-quality, and watershed characteristics in 15 watersheds in Gwinnett County, Georgia, water years 2002-20: U.S. Geological Survey Scientific Investigations Report 2023-5035. Aulenbach, B.T., Joiner, J.K., and Painter, J.A., 2017, Hydrology and water quality in 13 watersheds in Gwinnett County, Georgia, 2001-15: U.S. Geological Survey Scientific Investigations Report 2017-5012, 82 p., accessed July 11, 2020, at https://doi.org/10.3133/sir20175012. Aulenbach, B.T., Kolb, K., Joiner, J.K., and Knaak, A.E., 2022, Hydrology and water quality in 15 watersheds in DeKalb County, Georgia, 2012-16: U.S. Geological Survey Scientific Investigations Report 2021-5126, 105 p., accessed August 8, 2022, at https://doi.org/10.3133/sir20215126. Beale, E.M.L., 1962, Some uses of computers in operational research: Industrielle Organisation, v. 31, p. 51-52. Burnham, K.P., and Anderson, D.R., 2002, Model selection and multimodel inference--A practical information-theoretic approach (Second Edition). Springer-Verlag, New York City, New York, ISBN: 13: 978-0387953649. Cohn, T.A., 1988, Adjusted maximum likelihood estimation of the moments of lognormal populations from type I censored samples: U.S. Geological Survey Open-File Report 88-350, 34 p., accessed July 11, 2020, at https://doi.org/10.3133/ofr88350. Cohn, T.A., Caulder, D.L., Gilroy, E.J., Zynjuk, L.D., and Summers, R.M., 1992, The validity of a simple statistical model for estimating fluvial constituent loads: An empirical study involving nutrient loads entering Chesapeake Bay: Water Resources Research, v. 28, no. 9, p. 2353-2363, accessed July 11, 2020, at https://doi.org/10.1029/92WR01008. Cohn, T.A., DeLong, L.L., Gilroy, E.J., Hirsch, R.M., and Wells, D.K., 1989, Estimating constituent loads: Water Resources Research, v. 25, no. 5, p. 937-942, accessed July 11, 2020, at https://doi.org/10.1029/WR025i005p00937. Crawford, C.G., 1991, Estimation of suspended-sediment rating curves and mean suspended-sediment loads: Journal of Hydrology, v. 129, p. 331-348, accessed July 11, 2020, at https://doi.org/10.1016/0022-1694(91)90057-O. Dolan, D.M., Yui, A.K., and Geist, R.D., 1981, Evaluation of river load estimation methods for total phosphorus: Journal of Great Lakes Research, v. 7, no. 3, p. 207-214, accessed July 11, 2020, at https://doi.org/10.1016/S0380-1330(81)72047-1. Johnson, A.H., 1979, Estimating solute transport in streams from grab samples: Water Resources Research, v. 15, no. 5, p. 1224-1228, accessed July 11, 2020, at https://doi.org/10.1029/WR015i005p01224. Joiner, J.K., Aulenbach, B.T., and Landers, M.N., 2014, Watershed characteristics and water-quality trends and loads in 12 watersheds in Gwinnett County, Georgia: U.S. Geological Survey Scientific Investigations Report 2014-5141, 79 p., accessed July 11, 2020, at https://doi.org/10.3133/sir20145141. Kirchner, James, 2001, Data analysis toolkit #5--Uncertainty analysis and error propagation: Analysis of Environmental Data Course, University of California, Berkeley, Calif., 8 p., accessed January 17, 2017, at http://seismo.berkeley.edu/~kirchner/eps_120/Toolkits/Toolkit_05.pdf. Landers, M.N., Ankcorn, P.D., and McFadden, K.W., 2007, Watershed effects on streamflow quantity and quality in six watersheds of Gwinnett County, Georgia: U.S. Geological Survey Scientific Investigations Report 2007-5132, 62 p., accessed July 11, 2020, at https://doi.org/10.3133/sir20075132. Quilbé, Renaud, Rousseau, A.N., Duchemin, Marc, Poulin, Annie, Gangbazo, Georges, and Villeneuve, Jean-Pierre, 2006, Selecting a calculation method to estimate sediment and nutrient loads in streams--Application to the Beaurivage River (Québec, Canada): Journal of Hydrology, v. 326, p. 295-310, accessed July 11, 2020, at https://doi.org/10.1016/j.jhydrol.2005.11.008. Runkel, R.L., Crawford, C.G., and Cohn, T.A., 2004, Load estimator (LOADEST)--A FORTRAN program for estimating constituent loads in streams and rivers: U.S. Geological Survey Techniques and Methods, book 4, chap. A5, 69 p., accessed July 11, 2020, at https://doi.org/10.3133/tm4A5. SAS Institute Inc., 1989-2021, JMP, ver. 16.1.0: Cary, North Carolina. 20220118 15_GwinnettCoGa_Loads.csv Comma Separated Value (CSV) file containing annual and model calibration period streamwater constituent load and yield estimates. Producer Defined Site_nu U.S. Geological Survey site number Producer Defined NA No station number for the combined study area watersheds Producer defined "02205865" Sweetwater Creek at Club Drive near Lilburn, Ga. Producer defined "02207120" Yellow River at Ga 124, near Lithonia, Ga. Producer defined "02207185" No Business Creek at Lee Road, below Snellville, Ga. Producer defined "02207385" Big Haynes Creek at Lenora Road, near Snellville, Ga. Producer defined "02207400" Brushy Fork Creek at Beaver Road, nr Loganville, Ga. Producer defined "02208150" Alcovy River at New Hope Road, near Grayson, Ga. Producer defined "02217274" Wheeler Creek at Bill Cheek Road, near Auburn, Ga. Producer defined "02218565" Apalachee River at Fence Road, near Dacula, Ga. Producer defined "02334480" Richland Creek at Suwanee Dam Road, near Buford, Ga. Producer defined "02334578" Level Creek at Suwanee Dam Road, near Suwanee, Ga. Producer defined "02334885" Suwanee Creek at Suwanee, Ga. Producer defined "02335350" Crooked Creek near Norcross, Ga. Producer defined "02336030" North Fork Peachtree Creek at Graves Rd, near Doraville, Ga. Producer defined Watershed Watershed names used in the associated U.S. Geological Survey Scientific Investigations Report. Watershed drainage area defined by site specified in value definition shown in parentheses Producer Defined Sweetwater Creek Sweetwater Creek at Club Drive near Lilburn, Ga. (USGS site number 02205865) Producer defined Yellow River near Lithonia Yellow River at Ga 124, near Lithonia, Ga. (USGS site number 02207120) Producer defined No Business Creek No Business Creek at Lee Road, below Snellville, Ga. (USGS site number 02207185) Producer defined Big Haynes Creek Big Haynes Creek at Lenora Road, near Snellville, Ga. (USGS site number 02207385) Producer defined Brushy Fork Creek Brushy Fork Creek at Beaver Road, nr Loganville, Ga. (USGS site number 02207400) Producer defined Alcovy River Alcovy River at New Hope Road, near Grayson, Ga. (USGS site number 02208150) Producer defined Wheeler Creek Wheeler Creek at Bill Cheek Road, near Auburn, Ga. (USGS site number 02217274) Producer defined Apalachee River Apalachee River at Fence Road, near Dacula, Ga. (USGS site number 02218565) Producer defined Richland Creek Richland Creek at Suwanee Dam Road, near Buford, Ga. (USGS site number 02334480) Producer defined Level Creek Level Creek at Suwanee Dam Road, near Suwanee, Ga. (USGS site number 02334578) Producer defined Suwanee Creek Suwanee Creek at Suwanee, Ga. (USGS site number 02334885) Producer defined Crooked Creek Crooked Creek near Norcross, Ga. (USGS site number 02335350) Producer defined North Fork Peachtree Creek North Fork Peachtree Creek at Graves Rd, near Doraville, Ga. (USGS site number 02336030) Producer defined Study watersheds area Study watersheds area is composed of the 12 non-nested watersheds Producer defined Constit Chemical constituent abbreviated name Producer Defined TSS Total suspended solids (USGS parameter code 00530) Producer defined SSC Suspended sediment concentration (USGS parameter code 80154) Producer defined TN Total nitrogen (USGS parameter code 00600) Producer defined NO3NO2 Total nitrate plus nitrite (USGS parameter code 00630) Producer defined DP Dissolved phosphorus (USGS parameter code 00666) Producer defined TP Total phosphorus (USGS parameter code 00665) Producer defined TOC Total organic carbon (USGS parameter code 00680) Producer defined Ca Total calcium (USGS parameter code 00916) Producer defined Mg Total magnesium (USGS parameter code 00927) Producer defined TPb Total lead (USGS parameter code 01051) Producer defined TZn Total zinc (USGS parameter code 01092) Producer defined TDS Total dissolved solids (USGS parameter code 70300) Producer defined Period_typ Time period type - whether the time period of load and yield represents a year or the model calibration period Producer Defined Annual Load and yield for an individual water year Producer defined Period Load and yield is for the model calibration period Producer defined Period Time period of load and yield, in water years Producer Defined 2003 2020 water year 1 N_years Number of years load and yield represent Producer Defined 1 11 years 1 Model_type Load estimation model type(s) - study watersheds area loads and yields can be composed of multiple model types Producer Defined Q & QT LOADEST Streamflow-only and streamflow-turbidity load models - includes both a model without turbidity model parameters and a model with at least one of the two turbidity model parameters Producer defined BRE Beale ratio estimator Producer defined QOnly LOADEST Streamflow-only load model - model does not include turbidity model parameters Producer defined QOnly; Q & QT Includes model types: (1) LOADEST streamflow-only load model and (2) LOADEST streamflow-only and streamflow-turbidity load models Producer defined BRE; QOnly; Q & QT Includes model types: (1) LOADEST streamflow-only load model, (2) LOADEST streamflow-only and streamflow-turbidity load models, and (3) Beale ratio estimator Producer defined Calib_Prd Model calibration period, in water years (WYs). The model calibration datasets were split into two time periods, WYs 2003-2010 and 2010-2020. The early calibration period sometimes started later than WY 2003 depending on when the water-quality constituent was routinely sampled and analyzed for the particular site. Loads were estimated for the Sweetwater Creek watershed starting in WY 2011 because monitoring started later at that site Producer Defined 2011-2020 Water years 2011 to 2020. This period pertains just to the Sweetwater Creek at Club Drive near Lilburn, Ga. site because monitoring did not begin until part-way through water year 2010 Producer defined 2003-2010 Water years 2003 to 2010 Producer defined 2010-2020 Water years 2010 to 2020 Producer defined 2003-2010; 2010-2020 Load and yield for study watersheds area for water year 2010 are an average of loads and yields from model calibration datasets water years 2003 to 2010 and 2010 to 2020 Producer defined 2006-2010 Water years 2006 to 2010 Producer defined 2005-2010 Water years 2005 to 2010 Producer defined 2004-2010 Water years 2004 to 2010 Producer defined 2004*-2010 Water years 2004* to 2010. Study watersheds area load and yield estimates for water year 2004 were scaled to the study watersheds drainage area to account for missing load and yield estimates from some watersheds for total calcium and total magnesium in water year 2004. Insufficient data to calculate study watershed area loads and yields in water year 2003. *Model calibration start year varied by watershed Producer defined 2004*-2010; 2010-2020 Load and yield for study watersheds area for water year 2010 are an average of loads and yields from model calibration datasets water years 2004* to 2010 and 2010 to 2020. *Model calibration start year varied by watershed Producer defined 2008-2010 Water years 2008 to 2010 Producer defined 2007-2010 Water years 2007 to 2010 Producer defined 2003*-2010 Water years 2003 to 2010. Study watersheds area load and yield estimates for water years 2003 - 2007 for total lead and 2003 - 2004 for total zinc were scaled to the study watersheds drainage area to account for missing load and yield estimates from some watersheds. *Model calibration start year varied by watershed Producer defined 2003*-2010; 2010-2020 Load and yield for study watersheds area for water year 2010 are an average of loads and yields from model calibration datasets water years 2003* to 2010 and 2010 to 2020. *Model calibration start year varied by watershed Producer defined 2006*-2010 Water years 2006* to 2010. Insufficient data to calculate study watershed area loads and yields in water years 2003 - 2005 for dissolved phosphorus. *Model calibration start year varied by watershed Producer defined 2006*-2010; 2010-2020 Load and yield for study watersheds area for water year 2010 are an average of loads and yields from model calibration datasets water years 2006* to 2010 and 2010 to 2020. *Model calibration start year varied by watershed Producer defined 2005*-2010 Water years 2005* to 2010. Insufficient data to calculate study watershed area loads and yields in water years 2003 and 2004 for total organic carbon. *Model calibration start year varied by watershed Producer defined 2005*-2010; 2010-2020 Load and yield for study watersheds area for water year 2010 are an average of loads and yields from model calibration datasets water years 2005* to 2010 and 2010 to 2020. *Model calibration start year varied by watershed Producer defined Runoff Average streamflow for period. Values reported to three significant figures Producer Defined 7.48 47.1 inches per year Load Streamwater constituent load expressed as a mean daily flux. Loads for the period can be calculated by multiplying this value by the number of days in the period. Values reported to three significant figures Producer Defined 0.00801 1900000.0 pounds per day Load_95L Streamwater constituent load 95% confidence interval lower limit expressed as a daily flux. Values reported to three significant figures Producer Defined NA No Data - confidence intervals provided only for LOADEST load estimates, not for Beale ratio estimator load estimates Producer defined 0.00646 1510000.0 pounds per day Load_95U Streamwater constituent load 95% confidence interval upper limit expressed as a daily flux. Values reported to three significant figures Producer Defined NA No Data - confidence intervals provided only for LOADEST load estimates, not for Beale ratio estimator load estimates Producer defined 0.00958 2950000.0 pounds per day Yield Streamwater constituent yield - load per unit area. Values reported to three significant figures Producer Defined 0.00262 18800.0 pounds per acre per year Yield_95L Streamwater constituent yield 95% confidence interval lower limit. Values reported to three significant figures Producer Defined NA No Data - confidence intervals provided only for LOADEST estimates, not for Beale ratio estimator estimates Producer defined 0.00174 8980.0 pounds per acre per year Yield_95U Streamwater constituent yield 95% confidence interval upper limit. Values reported to three significant figures Producer Defined NA No Data - confidence intervals provided only for LOADEST estimates, not for Beale ratio estimator estimates Producer defined 0.00324 62500.0 pounds per acre per year The dataset contains annual and study period streamwater constituent load and yield estimates for 13 watersheds in Gwinnett County, Georgia for water years 2003 to 2020. Loads and yields were estimated for 12 water-quality constituents: total suspended solids (TSS), suspended sediment concentration (SSC), total nitrogen (TN), total nitrate plus nitrite (NO3+NO2), total phosphorus (TP), dissolved phosphorus (DP), total organic carbon (TOC), total calcium (Ca), total magnesium (Mg), total lead (TPb), total zinc (TZn), and total dissolved solids (TDS). The USGS LOADEST load estimation software, which employs a regression-model estimation approach, was used for constituents that had moderate to strong concentration-model relations, 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 cumulative area of the study watersheds. The period of loads available varies by watershed depending upon when monitoring and constituent analysis started. Uncertainties in loads and yields are provided as 95-percent confidence intervals for estimates that were calculated using LOADEST. Further details on load estimation methodologies are available in Aulenbach and others (2023). Aulenbach, B.T., Henley, J.C., and Hopkins, K.G., 2023, Hydrology, water-quality, and watershed characteristics in 15 watersheds in Gwinnett County, Georgia, water years 2002-20: U.S. Geological Survey Scientific Investigations Report 2023-5035. U.S. Geological Survey GS ScienceBase mailing address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 United States 1-888-275-8747 sciencebase@usgs.gov Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Digital Data https://doi.org/10.5066/P9G8HZTY None 20230404 Brent T Aulenbach U.S. Geological Survey, Southeast Region Research Hydrologist mailing address

1770 Corporate Drive Suite 500

Norcross GA 30093 US 678-924-6626 678-924-6710 btaulenb@usgs.gov FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998