Identifying the Driving Factors of Water Quality in a Sub-Watershed of the Republican River Basin, Kansas USA.

Morgen Burke,Jeffrey VanLooy,Mojtaba Shahabi,Yeqian Xu,Haochi Zheng,Xiaodong Zhang

doi:10.3390/ijerph15051041

Morgen Burke, Jeffrey VanLooy + Show 4 more

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https://doi.org/10.3390/ijerph15051041

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Abstract

Studies have shown that the agricultural expansion and land use changes in the Midwest of the U.S. are major drivers for increased nonpoint source pollution throughout the regional river systems. In this study, we empirically examined the relationship of planted area and production of three dominant crops with nitrate flux in the Republican River, Kansas, a sub-watershed of Mississippi River Basin. Our results show that land use in the region could not explain the observed changes in nitrate flux in the river. Instead, after including explanatory variables such as precipitation, growing degree days, and well water irrigation in the regression model we found that irrigation and spring precipitation could explain >85% of the variability in nitrate flux from 2000 to 2014. This suggests that changes in crop acreage and production alone cannot explain variability in nitrate flux. Future agricultural policy for the region should focus on controlling both the timing and amount of fertilizer applied to the field to reduce the potential leaching of excess fertilizer through spring time runoff and/or over-irrigation into nearby river systems.

Highlights

Nonpoint source (NPS) pollution continues to be a major source of water quality impairment in the U.S In 2017, the U.S Environmental Protection Agency (EPA) reported that NPS from agriculture was one of the most common sources of pollutants for streams and lakes [1]
To examine how land use varies across the Republican River, we used ArcGIS Desktop 10.3.1 (Environmental Systems Research Institute, Redlands, CA, USA) to clip the U.S Department of Agriculture (USDA) Cropland Data Layer (CDL) [17] to the boundary of the River Basin (RRB)
Our study found a strong relationship between springtime precipitation and well water irrigation, and nitrate flux for the Hardy-Clay Watershed (HCW)

Summary

Introduction

Nonpoint source (NPS) pollution continues to be a major source of water quality impairment in the U.S In 2017, the U.S Environmental Protection Agency (EPA) reported that NPS from agriculture was one of the most common sources of pollutants for streams and lakes [1]. Agricultural production practices often result in over-application of fertilizers, which can cause leaching of excess nitrogen and phosphorous into nearby aquatic ecosystems through runoff [2]. Carpenter et al [3] estimated an average of 44 kg/ha yr of phosphorous is applied for agricultural production in the U.S but only 18 kg/ha yr is harvested, resulting in an estimated 2% to 30% of phosphorous applied to cropland potentially leaching into nearby surface water. Basin, many of these pollutants make their way to the coast and end up in the Gulf of Mexico. Nitrogen concentrations in the Gulf of Mexico have more than tripled since 1970 [4], and the hypoxic conditions caused by the increased nitrogen loads continue to impair the gulf’s ecosystems [5,6]

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