Precipitation Drives Nitrogen Load Variability in Three Iowa Rivers

Kari A. Wolf; Satish C Gupta; Carl J. Rosen

doi:10.1016/j.ejrh.2020.100705

Precipitation Drives Nitrogen Load Variability in Three Iowa Rivers

Kari A. Wolf, Satish C Gupta, Carl J. Rosen

Soil, Water, and Climate

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Abstract

Study region: Iowa, a leading agricultural state in the United States is a major source of nitrogen (N) to the Mississippi River. Study Focus: The study evaluated the impact of changes in precipitation, land cover (area under soybean production, Sb), and N fertilizer application (N_app) on variations in streamflow (SF), baseflow (BF) and N-load in the Des Moines, the Iowa, and the Raccoon rivers. New hydrological insights for the region: Ln(SF) and Ln(BF) for all three rivers were influenced by the current year (P₁) and previous year (P₂) precipitations. Presence of P₂ in the regression suggested a deficit or excess soil water that influenced fillable pore space causing decreased or increased river flows. The Ln(N-load) for the Raccoon River was also related to P₁ and P₂ but the Ln(N-load) for the Des Moines and the Iowa rivers were related to P₁ with p-values of P₂ slightly above α = 0.05 for significance. Presence of P₂ in Ln(N-load) regression reflected changes in both fillable porosity and residual soil N. Contributions of Sb and N_app in explaining variations in predictor variables were none to minimal. We conclude that wet climate and not changes in Sb or N_app is the primary reason for recent higher N-loads in these rivers. Under current cropping systems, we suggest directing efforts on treating river water by expanding floodplain interactions to reduce downstream N-loads.

Original language	English (US)
Article number	100705
Journal	Journal of Hydrology: Regional Studies
Volume	30
DOIs	https://doi.org/10.1016/j.ejrh.2020.100705
State	Published - Aug 2020

Bibliographical note

Funding Information:
This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council (3006-11025-00060279). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler's help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments.

Funding Information:
This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council ( 3006-11025-00060279 ). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler’s help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments.

Publisher Copyright:
© 2020 The Authors

Keywords

Baseflow
Fertilizer use
Land cover
Precipitation
River N loads
Streamflow

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title = "Precipitation Drives Nitrogen Load Variability in Three Iowa Rivers",

abstract = "Study region: Iowa, a leading agricultural state in the United States is a major source of nitrogen (N) to the Mississippi River. Study Focus: The study evaluated the impact of changes in precipitation, land cover (area under soybean production, Sb), and N fertilizer application (Napp) on variations in streamflow (SF), baseflow (BF) and N-load in the Des Moines, the Iowa, and the Raccoon rivers. New hydrological insights for the region: Ln(SF) and Ln(BF) for all three rivers were influenced by the current year (P1) and previous year (P2) precipitations. Presence of P2 in the regression suggested a deficit or excess soil water that influenced fillable pore space causing decreased or increased river flows. The Ln(N-load) for the Raccoon River was also related to P1 and P2 but the Ln(N-load) for the Des Moines and the Iowa rivers were related to P1 with p-values of P2 slightly above α = 0.05 for significance. Presence of P2 in Ln(N-load) regression reflected changes in both fillable porosity and residual soil N. Contributions of Sb and Napp in explaining variations in predictor variables were none to minimal. We conclude that wet climate and not changes in Sb or Napp is the primary reason for recent higher N-loads in these rivers. Under current cropping systems, we suggest directing efforts on treating river water by expanding floodplain interactions to reduce downstream N-loads.",

keywords = "Baseflow, Fertilizer use, Land cover, Precipitation, River N loads, Streamflow",

author = "Wolf, {Kari A.} and Gupta, {Satish C} and Rosen, {Carl J.}",

note = "Funding Information: This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council (3006-11025-00060279). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler's help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments. Funding Information: This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council ( 3006-11025-00060279 ). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler{\textquoteright}s help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments. Publisher Copyright: {\textcopyright} 2020 The Authors",

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AU - Gupta, Satish C

AU - Rosen, Carl J.

N1 - Funding Information: This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council (3006-11025-00060279). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler's help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments. Funding Information: This research was partially supported by funds from the Minnesota Soybean Research and Promotion Council ( 3006-11025-00060279 ). Second author also acknowledges support provided by the Raymond Allmaras Endowed Professorship on Emerging Issues in Soil and Water. Authors gratefully acknowledge Nathaniel Baeumler’s help in running the regression analysis using the R statistical package. We also thank Jeff Mitchell, Laboratory Supervisor of the Des Moines River Water Works for sharing N-load and N concentration data for the Raccoon River. Authors also thank three anonymous reviewers for their helpful comments. Publisher Copyright: © 2020 The Authors

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N2 - Study region: Iowa, a leading agricultural state in the United States is a major source of nitrogen (N) to the Mississippi River. Study Focus: The study evaluated the impact of changes in precipitation, land cover (area under soybean production, Sb), and N fertilizer application (Napp) on variations in streamflow (SF), baseflow (BF) and N-load in the Des Moines, the Iowa, and the Raccoon rivers. New hydrological insights for the region: Ln(SF) and Ln(BF) for all three rivers were influenced by the current year (P1) and previous year (P2) precipitations. Presence of P2 in the regression suggested a deficit or excess soil water that influenced fillable pore space causing decreased or increased river flows. The Ln(N-load) for the Raccoon River was also related to P1 and P2 but the Ln(N-load) for the Des Moines and the Iowa rivers were related to P1 with p-values of P2 slightly above α = 0.05 for significance. Presence of P2 in Ln(N-load) regression reflected changes in both fillable porosity and residual soil N. Contributions of Sb and Napp in explaining variations in predictor variables were none to minimal. We conclude that wet climate and not changes in Sb or Napp is the primary reason for recent higher N-loads in these rivers. Under current cropping systems, we suggest directing efforts on treating river water by expanding floodplain interactions to reduce downstream N-loads.

AB - Study region: Iowa, a leading agricultural state in the United States is a major source of nitrogen (N) to the Mississippi River. Study Focus: The study evaluated the impact of changes in precipitation, land cover (area under soybean production, Sb), and N fertilizer application (Napp) on variations in streamflow (SF), baseflow (BF) and N-load in the Des Moines, the Iowa, and the Raccoon rivers. New hydrological insights for the region: Ln(SF) and Ln(BF) for all three rivers were influenced by the current year (P1) and previous year (P2) precipitations. Presence of P2 in the regression suggested a deficit or excess soil water that influenced fillable pore space causing decreased or increased river flows. The Ln(N-load) for the Raccoon River was also related to P1 and P2 but the Ln(N-load) for the Des Moines and the Iowa rivers were related to P1 with p-values of P2 slightly above α = 0.05 for significance. Presence of P2 in Ln(N-load) regression reflected changes in both fillable porosity and residual soil N. Contributions of Sb and Napp in explaining variations in predictor variables were none to minimal. We conclude that wet climate and not changes in Sb or Napp is the primary reason for recent higher N-loads in these rivers. Under current cropping systems, we suggest directing efforts on treating river water by expanding floodplain interactions to reduce downstream N-loads.

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KW - Fertilizer use

KW - Land cover

KW - Precipitation

KW - River N loads

KW - Streamflow

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Precipitation Drives Nitrogen Load Variability in Three Iowa Rivers

Abstract

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