Continuous Turbidity Data Used to Compute Constituent Concentrations in the South Loup River, Nebraska, 2017–18

Scientific Investigations Report 2021-5120
Prepared in cooperation with the Lower Loup Natural Resources District
By:  and 



The South Loup River in central Nebraska has been impaired by bacteria since at least 2004, which has resulted in the river not meeting its intended use as a recreational waterway. As part of a strategy for reducing the bacterial load in the river, the U.S. Geological Survey, in cooperation with the Lower Loup Natural Resources District, made continuous estimates of Escherichia coli (E. coli) and nutrient concentrations during seasonal monitoring at the South Loup River at Saint Michael, Nebraska, during 2017–18. Continuous turbidity data were collected from mid-April through October in 2017 and 2018 and were paired with 35 co-occurring discrete water samples that were analyzed for E. coli, nutrients, and suspended solids. Surrogate models relating the discrete concentrations to the continuous turbidity data were developed using ordinary-least-squares regression and were evaluated for model performance and uncertainty. Although the model assumptions were met for E. coli, the imprecision of the E. coli model was considerably higher than the other constituents, probably because of measurement imprecision and greater sensitivity to environmental factors. Once the models were developed, the turbidity data were used to predict continuous constituent concentrations and corresponding prediction intervals, which were made available online as part of the U.S. Geological Survey National Water Information System database. It is expected that results from these models will provide stakeholders with an understanding of constituent concentrations during the 2017–18 monitoring period and the results will also provide a good reference point for any future comparisons.

Suggested Citation

Rus, D.L., and Densmore, B.K., 2021, Continuous turbidity data used to compute constituent concentrations in the South Loup River, Nebraska, 2017–18: U.S. Geological Survey Scientific Investigations Report 2021–5120, 10 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Methods
  • Surrogate Models Using Continuous Turbidity Data to Compute Constituent Concentrations
  • Summary
  • References Cited
  • Appendix 1. Paired Replicate Sampling Data
Publication type Report
Publication Subtype USGS Numbered Series
Title Continuous turbidity data used to compute constituent concentrations in the South Loup River, Nebraska, 2017–18
Series title Scientific Investigations Report
Series number 2021-5120
DOI 10.3133/sir20215120
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Nebraska Water Science Center
Description Report: vi, 10 p.; 2 Datasets
Country United States
State Nebraska
Other Geospatial South Loup River
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details