Revision History for OFR 2020-1014

Aldo V. Vecchia and Rochelle A. Nustad

Time-Series Model, Statistical Methods, and Software Documentation for R–QWTREND—An R Package for Analyzing Trends in Stream-Water Quality

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Posted online May 13, 2020

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Revised and reposted November 30, 2021, version 1.1

Appendix 1 was modified. R-QWTREND was updated to extend the maximum period of a time-series model to 100 years. Previously, the time-series model was limited to 50 years. The qwtrend2018v4.exe file was the only file revised to accomplish this extension. No other changes were made.  

Note to users about interpretation of results in the QWMODOUT5D output file: There are four columns of concentration in base-10 logarithm units in QWMODOUT5D: frvar, fadat, fadat2, fapfdat.  Other than fapfdat, concentrations can be back-transformed to the original units by exponentiating 10 to the power of the concentration (10^concentration).  See the accompanying report (Vecchia and Nustad, 2020) for details on what the concentrations in each column represent.

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Revised and reposted March 28, 2023, version 1.2

Appendix 1 was modified. In this version of R-QWTREND, a rounding issue in prepQWdataV4.txt, the file that prepares water-quality and streamflow data for trend analysis, has been fixed. Previously, water-quality observations in the first 15 days of February, May, August, and November were unexpectedly filtered out unless they occurred on the 3rd, 8th, or 13th day of the month. If the previous version of R-QWTREND was used for trend analysis, results will change slightly for some sites with this updated version, but most results will be minimally impacted. To follow along with the “R-QWTREND Sofware Documentation” section of OFR 2020-1014, the user may use prepQWdataV4old.txt to get exact results. See the StartQWTrendV4.R file for further instructions.