USGS

Water Resources of Colorado

Changes in Nutrient and Pesticide Concentrations in Urban and Agricultural Areas of the South Platte River Basin, Colorado, Wyoming, and Nebraska, 1994–2000

by Lori A. Sprague and Adrienne I. Greve

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 02-4270, 12 p., 5 figs.

This document also is available in pdf format: Adobe Acrobat IconWRIR 02-4270 (1.7 MB)
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Abstract

As part of the National Water-Quality Assessment (NAWQA) Program, the U.S. Geological Survey (USGS) monitored two sites on the main-stem South Platte River— an urban site in Denver and a mixed urban/agricultural site near Kersey—to determine changes in nutrient and pesticide concentrations from 1994 through 2000. Concentrations of nitrate, nitrite, ammonia, and orthophosphorus decreased at the Denver site during the study period, likely due to an increase in instream dilution of wastewater-treatment plant (WWTP) discharge and upgrades at the WWTPs. In contrast, only concentrations of orthophosphorus decreased at the Kersey site; agricultural inputs between Denver and Kersey may have offset the observed decreases in other nutrients upstream. During the extreme low-flow conditions in 1994, when there was relatively little snowmelt to dilute instream pesticide concentrations, total median pesticide concentrations at both sites were the highest of the study period. During the less extreme conditions in 1997 through 2000, greater amounts of snowmelt likely led to lower total median pesticide concentrations at both sites. Because pesticide-use data are not available, the contribution of changes in the amount and type of pesticides applied on the land to changes in the concentration of pesticides in the river is not known but likely was substantial. In general, insecticides predominated at the Denver site, whereas herbicides predominated at the Kersey site.


Contents

Abstract

Introduction

Why are we concerned about nutrients and pesticides?

How do nutrients and pesticides reach rivers?

How have nutrient concentrations changed in the South Platte River at Denver and near Kersey from 1994 through 2000?

How have pesticide concentrations changed in the South Platte River at Denver and near Kersey from 1994 through 2000?

What can be done to further reduce the concentrations of nutrients and pesticides in the South Platte River?

References

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