Nutrient Concentrations, Loads, and Yields in the Middle Iowa River Basin, Iowa

Scientific Investigations Report 2020-5148
Prepared in cooperation with the Sac and Fox Tribe of the Mississippi in Iowa
By:  and 



Concentrations, loads, and yields of nitrate plus nitrite, total nitrogen, and total phosphorus were assessed in the Iowa River upstream from the Coralville Reservoir in east-central Iowa. The results of this study describe baseline nutrient transport during two historical reference periods, 1980–96 and 2006–10, that can be used to evaluate the progress of the implementation of reduction strategies in the Middle Iowa River Basin. Where available, nutrient data during the more recent period 2011–18 are also described. Data included nutrient concentrations and streamflow from multiple Federal, State, and Tribal agencies, and loads were computed using multiple techniques to provide valuable insights, which would otherwise not be possible.

Despite an upward trend for mean annual and base streamflow (the trend in high streamflow was not significant), average nutrient loads and yields in the Iowa River were smaller in the recent period (2011–18) than in either historical reference period. Notably smaller loads during the 2012 drought, however, caused pronounced skewed average loads for 2011–18. Comparisons among periods were difficult to make because of a short period of data upstream from Marshalltown, Iowa, at the upstream boundary of the study area and a lack of recent data near Marengo, Iowa, at the downstream boundary of the study area. Though spring and summer loads were a disproportionate part of annual loads, up to 90 percent, seasonal load comparisons to determine load reduction were more sensitive to one or the other historical period than was assessment of annual loads. Runoff-transport relations may provide an additional tool to assess load reduction.

Suggested Citation

Garrett, J.D., and Kalkhoff, S.J., 2021, Nutrient concentrations, loads, and yields in the Middle Iowa River Basin, Iowa: U.S. Geological Survey Scientific Investigations Report 2020–5148, 22 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Methods
  • Iowa River Nutrient Concentrations, Loads, and Yields
  • Summary
  • References Cited
  • Appendix 1. Tributary Sites
Publication type Report
Publication Subtype USGS Numbered Series
Title Nutrient concentrations, loads, and yields in the Middle Iowa River Basin, Iowa
Series title Scientific Investigations Report
Series number 2020-5148
DOI 10.3133/sir20205148
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Iowa Water Science Center, Illinois-Iowa-Missouri Water Science Center, Central Midwest Water Science Center
Description Report: vii, 22 p.; 1 Table; Dataset
Country United States
State Iowa
Other Geospatial Middle Iowa River Basin
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details