Christopher A. Mason James E. Colgin James S. Webber Alexander M. Soroka 20250313 Data table Richmond, VA U.S. Geological Survey - ScienceBase https://doi.org/10.5066/P13P4TWR Nitrogen, phosphorus, and suspended-sediment loads, and changes in loads, in major rivers across the Chesapeake Bay watershed were calculated using monitoring data from the Chesapeake Bay Nontidal Network (NTN) stations for the period 1985 through 2023. Nutrient and suspended-sediment loads and changes in loads were determined by applying a weighted regression approach called WRTDS (Weighted Regression on Time, Discharge, and Season). Load results represent the total mass of nitrogen, phosphorus, and suspended sediment that was exported from each of the NTN watersheds. The files containing all outputs generated by WRTDS for all applicable NTN monitoring stations are provided in the "Attached Files" section. These datasets contain output from the WRTDS and WRTDS with Kalman filtering models. These models were run to document riverine loads and trends in nitrogen, phosphorus, and suspended sediment for two time periods: ~1985-2023 and 2014-2023. 19841001 20230930 ground condition Complete Irregular -79.167480469182 -74.904785156852 42.714410712674 36.208470061656 none water quality nutrients nitrogen phosphorus suspended sediment load analysis WRTDS Kalman filtering WRTDS-Kalman trends rivers weighted regression USGS Metadata Identifier USGS:67af5be2d34e5020fb91f09d USGS Thesaurus water quality nitrogen phosphorus none Chesapeake Bay Watershed United States New York Pennsylvania Maryland Delaware West Virginia Virginia Washington DC none none Christopher A. Mason USGS Virginia and West Virginia Water Science Center mailing and physical

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Richmond Virginia 23228 USA 804-261-2613 camason@usgs.gov This biennial update of nitrogen, phosphorus, and suspended-sediment loads and trends is performed in cooperation with Delaware Department of Natural Resources and Environmental Control, District Department of the Environment, Maryland Department of Natural Resources, New York State Department of Environmental Conservation, Pennsylvania Departmental Protection, Virginia Department of Environmental Quality, West Virginia Department of Environmental Protection, Environmental Protection Agency, Susquehanna River Basin Commission, and Chesapeake Bay Program Office. All model results are based on monitored and lab-derived water quality data and in-situ discharge measurements. All data were checked for outliers and for feasible ranges based on site-specific watershed area, frequency of storm sampling, and constituent levels relative to historic discharge. Data set 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. No formal positional accuracy tests were conducted No formal positional accuracy tests were conducted Methods: Loads were estimated using a weighted regression approach called Weighted Regressions on Time, Discharge, and Season with Kalman filtering (WRTDS-K; Zhang and Hirsch, 2019) and flow-normalized loads and trends were estimated using WRTDS (Hirsch and others, 2010), which are both included in the R (version 4.3.1) software package called EGRET - Exploration and Graphics for RivEr Trends (version 3.0.9; Hirsch and DeCicco, 2015). The application of WRTDS to generate the results provided in these tables is documented in Chanat and others (2016). USGS station and parameter code information can be viewed at waterdata.usgs.gov/nwis and nwis.waterdata.usgs.gov/usa/nwis/pmcodes, respectively. References Cited: Zhang, Q. and Hirsch, R. M., 2019, River water-quality concentration and flux estimation can be improved by accounting for serial correlation through an autoregressive model: Water Resources Research, 55, 9705– 9723. doi.org/10.1029/2019WR025338. 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 Research Association, v. 46, no. 5, p. 857-880 Hirsch, R.M. and De Cicco, Laura, 2015, User guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R packages for hydrologic data (version 2.0, February 2015): U.S. Geological Survey Techniques and Methods book 4, chap. A10, 93 p., http://dx.doi.org/10.3133/tm4A10.(accessed May 24, 2016) Chanat, J.G., Moyer, D.L., Blomquist, J.D., Hyer, K.E., and Langland, M.J., 2016, Application of a weighted regression model for reporting nutrient and sediment concentrations, fluxes, and trends in concentration and flux for the Chesapeake Bay Nontidal Water-Quality Monitoring Network, results through water year 2012: U.S. Geological Survey Scientific Investigations Report 2015-5133, 139 p. http://dx.doi.org/10.3133/sir20155133 20250301 AnnualResults.zip Files containing WRTDS and WRTDS-K annual estimates of concentration and load for all sites and constituents (multiple CSV spreadsheets in a compressed folder). Individual file nomenclature is as follows for (1) WRTDS outputs: USGS Station Number_Parameter Code (where, 00600-Total Nitrogen, 00631-Nitrate, 00665-Total Phosphorus, 00671-Orthophosphate, and 80154-Suspended Sediment)_AnnualResults.csv and (2) WRTDS-K outputs: USGS Station Number_Parameter Code (where, 00600-Total Nitrogen, 00631-Nitrate, 00665-Total Phosphorus, 00671-Orthophosphate, and 80154-Suspended Sediment)_AnnualResults_K.csv. Producer defined DecYear Mean value of individual daily Decimal Year values for all the days included in the year Producer defined Range varies by dataset Q ["_AnnualResults" versions only] Mean annual streamflow in cubic meters per second (m^3/s) U.S. Geological Survey Range varies by dataset Conc ["_AnnualResults" versions only] Model estimate of mean annual concentration in milligrams per liter (mg/L) U.S. Geological Survey Range varies by dataset Flux ["_AnnualResults" versions only] Model estimate of mean annual flux (or load) in kilograms per day (kg/day) Producer defined Range varies by dataset FNConc ["_AnnualResults" versions only] Model estimate of mean annual flow-normalized concentration in mg/L Producer defined Range varies by dataset FNFlux ["_AnnualResults" versions only] Model estimate of mean annual flow-normalized flux (or load) in kg/day Producer defined Range varies by dataset GenConc ["_AnnualResults_K" versions only] Model estimate of mean annual Kalman concentration in mg/L (note: "Gen" signifies the use of a random number generator for re-sampling during Kalman estimations) U.S. Geological Survey Range varies by dataset GenFlux ["_AnnualResults_K" versions only] Model estimate of mean annual Kalman flux (or load) in kg/day (note: "Gen" signifies the use of a random number generator for re-sampling during Kalman estimations) Producer defined Range varies by dataset PeriodLong Number of months included in the calculation of mean annual concentration and flux Producer defined Range varies by dataset PeriodStart Number representing the start month (10 = October) for the averaging period defined by PeriodLong Producer defined Range varies by dataset CIAnnualResults.zip File containing annual mean estimated concentration and flux with confidence intervals derived from bootstrapping, for long-term sites and constituents, using WRTDS (multiple CSV spreadsheets in a compressed folder). Individual file nomenclature is as follows for (1) WRTDS outputs: USGS Station Number_Parameter Code (where, 00600-Total Nitrogen, 00631-Nitrate, 00665-Total Phosphorus, 00671-Orthophosphate, and 80154-Suspended Sediment)_CIAnnualResults.csv. Producer defined Year Mean value of individual daily Decimal Year values for all the days included in the year. Year represents water year which extends from October 1 to September 30 (For example, 1985.248 = Water Year 1985) Producer defined Range varies by dataset FNConcLow Lower confidence limit (90 percent) on flow-normalized concentration in miligrams per liter (mg/L) Producer defined Range varies by dataset FNConcHigh Upper confidence limit (90 percent) on flow-normalized concentration in mg/L Producer defined Range varies by dataset FNFluxLow Lower confidence limit (90 percent) on flow-normalized flux (load) in kilograms per day (kg/day) Producer defined Range varies by dataset FNFluxHigh Upper confidence limit (90 percent) on flow-normalized flux (load) in kg/day Producer defined Range varies by dataset bootOut.csv WRTDS (from non-Kalman loads) trend results for all sites and constituents. Producer defined scenario StationNumber_ParameterCode_ModelScenario where(Station Number = USGS station ID; Parameter code = 00600 (Total Nitrogen), 00631 (Nitrate plus Nitrite), 00665 (Total Phosphorus), 00671 (Orthophosphate), 80154 (Suspended Sediment); Model Scenario = RIM_LT (RIM site; 1985 to 2023), RIM_10YR (RIM site; 2014 to 2023), NTN_ST_ALL_2023 (NTN site; 2014-2023), and NTN_LT_ALL_2023 (NTN site; ~1985-2023) Producer defined Range varies by dataset rejectC Logical variable: TRUE means we reject Ho (no change in flow-normalized concentration) when pValC< 0.1 (two sided), FALSE means we do not reject Ho when pValC >= 0.1 (two sided) Producer defined TRUE Reject Ho (no change in FN Conc) when pValC< 0.1 (two sided) Producer defined FALSE Do not reject Ho when pValC >= 0.1 (two sided) Producer defined pValC The two-sided p-value for the bootstrap trend test on FN Conc Producer defined Range varies by dataset estC The WRTDS estimate of the change in the flow-normalized concentration over the period being considered in the trend test in milligrams per liter (mg/L) Producer defined Range varies by dataset lowC The lower 90 percent confidence interval (CI) for the trend in mg/L Producer defined Range varies by dataset upC The upper 90 percent CI for the trend in mg/L Producer defined Range varies by dataset lowC50 The lower 50 percent CI for the trend in mg/L Producer defined Range varies by dataset upC50 The upper 50 percent CI for the trend in mg/L Producer defined Range varies by dataset lowC95 The lower 95 percent CI for the trend in mg/L Producer defined Range varies by dataset upC95 The upper 95 percent CI for the trend in mg/L Producer defined Range varies by dataset likeCUp The likelihood that the trend in flow-normalized concentration is actually upwards, a probability Producer defined Range varies by dataset likeCDown The likelihood that the trend in flow-normalized concentration is actually downwards, a probability Producer defined Range varies by dataset rejectF Logical variable, TRUE means we reject Ho (no change in flow-normalized flux) when pValF< 0.1 (two sided), FALSE means we do not reject Ho when pValF >= 0.1 (two sided) Producer defined TRUE reject Ho (no change in flow-normalized flux) when pValF< 0.1 (two sided) Producer defined FALSE do not reject Ho when pValF >= 0.1 (two sided) Producer defined pValF The two-sided p-value for the bootstrap trend test on flow-normalized flux Producer defined Range varies by dataset estF The WRTDS estimate of the change in the flow-normalized flux over the period being considered in millions of kilograms per year (10^6 kg/year) Producer defined Range varies by dataset lowF The lower 90 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset upF The upper 90 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset lowF50 The lower 50 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset upF50 The upper 50 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset lowF95 The lower 95 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset upF95 The upper 95 percent CI for the trend in 10^6 kg/year Producer defined Range varies by dataset likeFUp The likelihood that the trend in flow-normalized flux is actually upwards, a probability Producer defined Range varies by dataset likeFDown The likelihood that the trend in flow-normalized flux is actually downwards, a probability Producer defined Range varies by dataset baseConc Flow-normalized concentration for first year of trend period, in mg/L (to use if you want to compute the trends in percentage terms) Producer defined Range varies by dataset baseFlux Flow-normalized flux for first year of trend period, in 10^6 kg/year (to use if you want to compute the trends in percentage terms) Producer defined Range varies by dataset iBoot The number of bootstrap iterations that were used in the test (will be some value between 39 and 100) Producer defined Range varies by dataset flowTrends.csv A table of streamflow trends (mean) computed for the long-term time period ~1985-2023, where applicable. Producer defined STAID USGS Station ID USGS Standard Gaging Station Number USGS Standard Gaging Station Number slopeEst_mean Trend slope expressed in percent change. The slope is computed using a Thiel-Sen estimator and represents total change in the mean from 1985-2023. Producer defined -0.59 1.3 pValue_mean The p-value score of the mean streamflow trend's statistical significance. Producer defined 0.05 1 eList.zip A list (.RData file) which specifies the objects that contain all of the data and the statistical model outputs. Additional arguments are available in the eList for setting details of the graphical output or model estimation parameters. Number of eLists available for each site and constituent combination is based on the beginning of water quality and discharge record availability. Producer defined U.S. Geological Survey - ScienceBase U.S. Geological Survey - ScienceBase mailing and physical

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Denver CO 80225 USA 1-888-275-8747 sciencebase@usgs.gov Although these data have been processed successfully on a computer system at 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. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 20250313 Christopher A. Mason U.S. Geological Survey Physical Scientist mailing and physical

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Richmond VA 23228 USA 804-261-2613 camason@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998