seawaveQ—An R Package Providing a Model and Utilities for Analyzing Trends in Chemical Concentrations in Streams with a Seasonal Wave (seawave) and Adjustment for Streamflow (Q) and Other Ancillary Variables, Version 2.0.0

Open-File Report 2020-1082
National Water Quality Program
By:  and 

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Abstract

The seawaveQ R package provides functionality and help to fit a parametric regression model, SEAWAVE-Q, to pesticide concentration data from stream-water samples to assess trends. The model incorporates the strong seasonality and high degree of censoring common in pesticide data, and users can incorporate numerous ancillary variables such as streamflow anomalies. The model is fitted to pesticide data using maximum likelihood methods for censored data and is robust in terms of pesticide, stream location, and degree of censoring of the concentration data. This R package standardizes this methodology for trend analysis, documents the code, and provides help and tutorial information.

In previous investigations, the SEAWAVE-Q model assumed a linear trend across the period analyzed. For short trend periods, this assumption of a linear trend is adequate. However, as the period of record analyzed becomes longer, the assumption of linearity is problematic because of changes in pesticide regulation and use, some of which can be abrupt. In this update to the model, a restricted cubic spline option was added for long trend periods. This option allows for more flexibility in the time component of the model. Bootstrap functionality is included to determine statistical significance. Model results with the new restricted cubic spline option are compared to the linear trend option for two pesticide-site combinations.

Suggested Citation

Ryberg, K.R., and York, B.C., 2020, seawaveQ—An R package providing a model and utilities for analyzing trends in chemical concentrations in streams with a seasonal wave (seawave) and adjustment for streamflow (Q) and other ancillary variables, version 2.0.0: U.S. Geological Survey Open-File Report 2020–1082, 25 p., https://doi.org/10.3133/ofr20201082.

ISSN: 2331-1258 (online)

Table of Contents

  • Foreword
  • Abstract
  • Introduction
  • Description of the seawaveQ Package
  • Statistical Methodology of Original Model
  • Addition of Restricted Cubic Splines Option
  • Model Output
  • Load Calculation
  • Summary
  • Disclaimer
  • Acknowledgments
  • References Cited
  • Appendix 1. Vignette
  • Appendix 2. R Documentation
  • Appendix 3. Visualizations of the Seasonal Wave
  • Appendix 4. Model Comparisons

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title seawaveQ—An R package providing a model and utilities for analyzing trends in chemical concentrations in streams with a seasonal wave (seawave) and adjustment for streamflow (Q) and other ancillary variables, version 2.0.0
Series title Open-File Report
Series number 2020-1082
DOI 10.3133/ofr20201082
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) WMA - Earth System Processes Division
Description Report: vi, 25; 3 Appendixes
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
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