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Updated: Mar 18, 2026
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Measuring Phosphorus Release in Laboratory Microcosms for Water Quality Assessment
Published on: July 22, 2019
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Stream channel storage: Closing the watershed total phosphorus budget
William J Beck1, John L Kovar2, Thomas M Isenhart1
1Department of Natural Resource Ecology and Management, Iowa State University, Ames, Iowa, USA.
Journal of Environmental Quality
|March 17, 2026
Summary
In agricultural watersheds, remobilized phosphorus from in-channel sediments is the primary source of annual total phosphorus (TP) loads, not streambanks. Restoring watershed hydrology and floodplain connectivity is key to reducing TP loads.
Area of Science:
- Environmental Science
- Hydrology
- Agricultural Science
Background:
- Total phosphorus (TP) loading from agricultural watersheds is a significant environmental concern.
- Quantifying in-channel sediment contributions to TP loads is challenging but crucial for effective management.
- Walnut Creek watershed in Iowa serves as a case study for understanding phosphorus dynamics in agricultural landscapes.
Purpose of the Study:
- To develop a 3-year total phosphorus budget for the Walnut Creek watershed.
- To estimate the contribution of in-channel storage to annual TP loads.
- To identify key sources and pathways of TP export from the watershed.
Main Methods:
- Constructed a comprehensive TP budget using data on streambank erosion, overland flow, baseflow, and floodplain flux.
- Quantified phosphorus contributions from various sources including in-channel sediment remobilization.
- Analyzed the influence of hydrological conditions, including drought and high-discharge events, on TP loads.
Main Results:
- Remobilization of sediment-bound phosphorus from in-channel storage was the dominant contributor to annual TP loads.
- Overland flow was the second largest contributor to TP loads.
- Streambank erosion contributed minimally, and baseflow dissolved phosphorus was significant in drought years.
- Floodplain storage was negligible due to low peak flows and channel incision but represents a significant storage opportunity.
Conclusions:
- In-channel sediment P remobilization is the primary driver of annual TP loads in this agricultural watershed.
- Reducing peak flows through watershed hydrology restoration and enhancing channel-floodplain connectivity are critical for mitigating TP loads.
- Future climate scenarios and channel evolution may increase the impact of high-discharge events on TP export.
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