This data release supports an analysis of changes in dissolved organic carbon (DOC) concentration and in the slope of the concentration-discharge relation in the Sleepers River Research Watershed W9 near North Danville, Vermont 1991 to 2018. The data release includes pre-processed model inputs and model outputs. W9 is a 40.5 hectares forested sub-watershed of the Sleepers River Research Watershed that was originally established by the U.S. Department of Agriculture in 1959 and has been intensively studied by the USGS since 1991. The W9 headwater sub-watershed drains to Pope Brook and is gaged at USGS station ID 01135100. Pope Brook flows into Sleepers River and ultimately into the Connecticut River. Two models were used to analyze concentration-discharge relations: the Weighted Regressions on Time, Discharge and Season (WRTDS) model (Hirsch and others, 2010) and the Hydrograph Separation model (HYSEP) (Sloto and Crouse, 1996). The WRTDS model used discharge data downloaded from Shanley and others (2021) and DOC data downloaded from Matt and others (2021). The HYSEP model used discharge data downloaded from Shanley and others (2021). The WRTDS model was used to estimate daily concentrations and fluxes of DOC and the HYSEP model was used to estimate the fraction of daily discharge that could be classified as stormflow (event flow) as opposed to base flow. In a separate analysis, regression models were used to estimate DOC concentrations for an identical average daily discharge hydrologic record. The observed calendar year 2007 record was chosen for this analysis. The average daily discharge in 2007 was similar to the long-term average daily discharge, the timing of the spring runoff was closely aligned with the average, there was a characteristic period of low flow in late summer, and there were several typical large runoff events in early summer and fall. Daily discharge for calendar year 2007 was inserted into the original discharge record after calendar year 1997 (early period) or 2010 (recent period) using dates from 1998 or 2011. The original data from the second half of each of these periods (January 1,1998 through May 16, 2006) and (January 1, 2011 through December 31, 2018), respectively, were incremented by one year. Therefore, in this analysis the dates for the early period spanned 9/30/1991 to 5/16/2006 and the dates for the recent period spanned 5/17/2006 to 12/31/2019. Note: the input and output data files that contain 2007 in the filenames include this synthetic or modified daily discharge data and therefore would not match the observed records. This data release is structured as a set of comma-separated values (CSV) files, including a site file (Site_Information.csv), 17 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 identifier, site name, latitude, longitude, horizontal datum, land surface elevation, vertical datum, and drainage area. There are five pairs of input files. There are two input files for each WRTDS run including a daily discharge file and a daily DOC concentration file, for example "W9Daily.csv" and "W9Sample.csv" for the full period 9/30/1991 to 12/31/2018 for discharge and concentration, respectively. The other input file pairs are "W9DailyEarly.csv" and "W9DailyRecent.csv" and "W9DailyEarly2007.csv" and "W9DailyRecent2007.csv." The last two files contain the identical hydrologic record spliced into the middle of each period. There is one WRTDS output file for each of the paired input and output files noted: "DailyOutput_W9.csv" (full period); "DailyOutput_W9Early.csv" (early period); "DailyOutput_W9Recent.csv" (recent period); "DailyOutput_W9Early20072.csv" (early period with identical hydrologic record spliced into the middle); "DailyOutput_W9Recent20073.csv" (recent period with identical hydrologic record spliced into the middle). There is one output file from the HYSEP model "Baseflow_Daily_01135100.csv" that contains the estimated discharge associated with base flow. References: 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 Association, v. 46, no. 5, p. 857–880, http://dx.doi.org/10.1111/j.1752-1688.2010.00482.x. Matt, S., Shanley, J. B., Chalmers, A. T., Sebestyen, S. D., Merriam, J. L., Bailey, S. W., Campbell, J., Ryan, K. A., Denner, J. C., Clark, Stewart C., and Schuster, P. F., 2021, Aqueous chemistry database, Sleepers River Research Watershed, Danville, Vermont, 1991-2018., https://doi.org/10.5066/P9380HQG Shanley, J.B., Chalmers, A.T., Denner, J.C., and Clark, S.F., 2021, Five-minute discharge; daily precipitation, stream runoff, and maximum and minimum air temperature; and annual precipitation and runoff for W-9 catchment, Sleepers River Research Watershed near Danville, Vermont, 1991-2018: U.S. Geological Survey data release, https://doi.org/10.5066/P929KMVK Sloto, R.A., and Crouse, M.Y., 1996, HYSEP: A Computer Program for Streamflow Hydrograph Separation and Analysis: U.S. Geological Survey Water-Resources Investigations Report 1996–4040, 46 p., https://pubs.er.usgs.gov/publication/wri964040. The W9Info2.csv file is used by WRTDS to assign the appropriate information for the analysis for this watershed.