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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 #352686
Title: Phosphorus transformations in stream bank sediments in Iowa, USA, at varying redox potentials

Author
item RAHUTOMO, SUROSO - Iowa State University
item Kovar, John
item THOMPSON, MICHAEL - Iowa State University

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2018
Publication Date: 9/15/2018
Publication URL: http://handle.nal.usda.gov/10113/6294897
Citation: Rahutomo, S., Kovar, J.L., Thompson, M.L. 2018. Phosphorus transformations in stream bank sediments in Iowa, USA, at varying redox potentials. Journal of Soils and Sediments. 19:1029-1039. https://doi.org/10.1007/s11368-018-2139-4.
DOI: https://doi.org/10.1007/s11368-018-2139-4

Interpretive Summary: Stream bank erosion is one of the main sources of suspended sediments in stream water. The sediments carry phosphorus (P) that may be released to the water. With a controlled laboratory study, we investigated the different forms of P in stream bank sediments in relation to oxygen levels in the stream water. Depending on the form, P can be released to the water as oxygen levels decrease, a common occurrence in summer months. Samples representing four major types of sediments were collected from the banks of Walnut Creek in Jasper County, Iowa: Camp Creek, Roberts Creek, and Gunder members of the Holocene-age De Forest Formation and Pre-Illinoian Till, a glacial deposit that is older than 500,000 y. We compared three treatments: incubation with ambient air, incubation without oxygen, and incubation without oxygen and with addition of glucose to stimulate microbial activity. After each treatment, soil P fractions were determined and classified as water-extractable P, slowly cycling P, stable P, and residual P. Variations in oxygen levels did not affect the total P, stable P, or residual P in the sediments. In contrast, we found that the amount of somewhat soluble P increased at the same time that slowly cycling P associated with iron (Fe) decreased, especially in the three Holocene-age sediments. These sediments appear to have a greater potential to contribute to elevated levels of P in the stream water under low oxygen levels. The results of this work will contribute useful information to watershed scientists, local environmental groups, and NRCS personnel interested in improving water quality in this and similar watersheds.

Technical Abstract: Streambank erosion is one of the main sources of suspended sediments in stream water, and it often carries phosphorus with it. With a controlled laboratory study, we investigated the changes in different forms of P in stream bank sediments at varying redox potential. We hypothesized that there could be increases in labile forms of solid-phase P under low redox conditions. Sediment samples representing four major stratigraphic units were collected from alluvial banks of Walnut Creek in Jasper County, Iowa: Camp Creek, Roberts Creek, and Gunder members of the Holocene-age De Forest Formation and Pre-Illinoian Till, a glacial deposit that is older than 500,000 y. We compared three treatments: no anaerobic incubation, anaerobic incubation, and anaerobic incubation with addition of glucose. After each treatment, soil P fractions were determined and classified as water-extractable P, labile P, slowly cycling P, stable P, and residual P. Labile P is extractable with 0.5 M NaHCO3, slowly cycling P is extractable with 0.1 M NaOH or 1 M HCl, stable P is extractable with concentrated HCl, and residual P is associated with acid-insoluble compounds in the soil. Redox potential of the equilibrated systems was significantly less when sediments were incubated anaerobically than when they were not incubated, especially when glucose was added to the anaerobic incubation. Variations in redox potential did not significantly affect the total P, organic or inorganic stable P, or residual P in the sediments. In contrast, we found that the amount of inorganic labile P increased at the same time that slowly cycling P associated with Fe increased. The forms of P in the four bank sediments were redistributed by reducing conditions. There was an increase in the concentration of inorganic labile P which coincided with a decrease in slowly cycling P associated with Fe, especially in the Holocene-age sediments. These sediments appear to have a greater potential to contribute to elevated levels of P in the stream water when they are subjected to low redox potential in the stream environment.