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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #382150
Research Project: Sustainable and Resilient Cropping Systems for Midwestern Landscapes

Location: Agroecosystems Management Research

Title: Contribution of streambanks to phosphorus export from Iowa

Author
item SCHILLING, KEITH - Iowa Geological Survey
item ISENHART, THOMAS - Iowa State University
item WOLTER, CALVIN - Iowa Department Of Natural Resources
item STREETER, MATTHEW - Iowa Geological Survey
item Kovar, John

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2021
Publication Date: 12/13/2021
Citation: Schilling, K.E., Isenhart, T.M., Kovar, J.L. 2021. Contribution of streambanks to phosphorus export from Iowa. Journal of Soil and Water Conservation. 77(2):103-112. https://doi.org/10.2489/jswc.2022.00036.
DOI: https://doi.org/10.2489/jswc.2022.00036

Interpretive Summary: Losses of phosphorus (P) from agricultural lands represent a major cause of water quality impairment within Iowa and elsewhere. Producers and land managers have made progress over the last several decades in reducing soil-bound P losses from agricultural lands to receiving waters via soil erosion. However, there is a growing body of evidence that much of the sediment and P delivered to the surface waters from agricultural landscapes originates from streambanks. With a multi-step process, we estimated the contribution of streambank P sources to P export from the state of Iowa. Long-term, we estimate that streambanks contribute approximately 31% of the annual P export from Iowa. Despite limitations in our analysis, an improved understanding of streambank P contributions will help natural resource managers make improved recommendations for effective soil and water conservation practices that best reduce P loading to rivers. This study may be among the first to address the issue of streambank P at a scale that has confounded many state and regional nutrient assessments.

Technical Abstract: Nonpoint source contributions of phosphorus (P) from upland and channel sources contribute to development of hypoxic conditions in receiving waters around the world. Streambanks are thought to be a potentially large contributor to sediment P loads in agricultural watersheds but are often unaccounted for in P reduction strategies. In this analysis, we estimate the contribution of streambank sources to TP export from the state of Iowa, using a multi-step process and relate this to overall statewide P export. Mapping and field monitoring indicated that 35,200 m of 3.2 m high streambanks are actively eroding in Iowa rivers at an annual rate of 12.4 cm yr-1. With an average streambank soil TP concentration of 470 mg kg-1 and bulk density of 1.17 g/cm3, approximately 7,681 Mg of TP is annually eroded from streambanks and delivered to Iowa rivers. Over a long-term annual basis, we estimate that streambanks contribute approximately 31% of the riverine TP export from Iowa. Despite limitations in our analysis, an improved understanding of streambank P contributions will help natural resource managers make improved recommendations for effective soil and water conservation practices that best reduce P loading to rivers. Our study is believed to be among the first to address the issue of streambank P at a scale that has confounded many state and regional nutrient assessments.