The dataset are the data used to produce figure in manuscript. This dataset is associated with the following publication: Tang, M., D. Lytle, and J. Botkins. Accumulation and Release of Arsenic from Cast Iron: Impact of Initial Arsenic and Orthophosphate Concentrations. WATER RESEARCH. Elsevier Science Ltd, New York, NY, USA, 194: 116942, (2021).

This data release contains simulated orthophosphate concentrations (milligrams per liter) as a function of year, season, and flow for 53 monitoring stations in the Chesapeake Bay watershed. These data were generated for a study published in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2018.10.062). They were extracted from the Weighted Regressions in Time, Discharge and Season (WRTDS; Hirsch et al. 2010) models developed for each monitoring station using two functions in the EGRET R package: the flowDuration function and the plotConcTimeSmooth function. The flowDuration function in the EGRET package (Hirsch and DeCicco, 2015) was used to quantify the 5th and 95th percentile flows to represent low and high flows, respectively, for each season at each watershed. These discharge values are then used as input for the plotConcTimeSmooth function, along with a date to represent the midpoint of each calendar year season (January-March = winter, etc.). The midpoints for the seasons were 15-February, 15-May, 15-August, and 15-November for the winter, spring, summer, and fall seasons, respectively. The plotConcTimeSmooth function provides estimates of concentration for those dates at those flows for all years included in the analysis. Simulated concentrations for the years 2006 and 2014 were extracted from this output, and are the only years included in this data release. Sources: 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 Resources 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, 2018)

Water-quality data were collected by Providence Water, formerly referred to as Providence Water Supply Board (PWSB), from tributaries in the Scituate Reservoir drainage area, October 1, 2017 through September 30, 2024 (water years 2018 through 2024). Water-quality samples were collected by the PWSB either monthly or quarterly at fixed stations on 38 tributaries in the Scituate Reservoir drainage area, Rhode Island. These data were used to calculate instantaneous loads and yields of constituents in reports by the U.S. Geological Survey. Water-quality samples were collected following a strict sampling schedule so that water-quality samples would be representative of various weather conditions. Samples were analyzed at the PWSB water-quality laboratory at the P.J. Holton Water Purification Plant in Scituate, Rhode Island. Water-quality properties and constituent concentrations were measured by using unfiltered water samples. These water-quality properties included pH, alkalinity, color, turbidity, and concentrations of chloride, nitrite, nitrate, orthophosphate, and bacteria (Escherichia coli [E. coli] and total coliform). This data release will be updated to append additional water-quality data collected by the PWSB. First posted May 2021, ver. 1.0 Revised July 2022, ver. 2.0 Revised November 2023, ver. 3.0 Revised December 2025, ver. 4.0