Quantifying the Effects of BMPs on Sediment and Phosphorus Delivery to a Range of Eastern Iowa Rivers

Date: 
Oct 2018

Issue

Over the last few decades, improvements in land management and installation of best management practices (BMPs) have significantly reduced field erosion, but water quality benefits have been poorly quantified. The Revised Universal Soil Loss Equation (RUSLE) is among the most widely used empirical models to estimate gross soil erosion at the plot scale, but it does not provide an estimation of the sediment exported from a watershed. Sediment delivery ratios (SDRs) are used to estimate the fraction of gross erosion that is exported from a watershed for a given time. The SDR concept can be expanded to include a Phosphorus Delivery Ratio (PDR) if total gross erosion of soil P is compared to total P export.

Objective

The objective of this project is to develop new SDR and PDR relations for the eastern Iowa landform region that accounts for the effects of BMPs and streambank erosion. The project will quantify the effectiveness of the existing BMPs and the future potential to reduce sediment and total P export from agricultural watersheds. Obtaining these results will serve as an important demonstration of the success of BMPs, plus motivation for future implementation.

Approach

The team will examine a subset of Iowa watersheds in eastern Iowa where they already have continuous turbidity and P measurements with which to estimate total sediment and P export. The eastern Iowa basins—two Rapid Creek subbasins, Rapid Creek, Clear Creek, and English River—provide a range of watershed sizes that will allow team members to scale the SDR/PDR curves for an eastern Iowa ecoregion. At the end of the one-year project, annual sediment and total P exported from these watersheds from sheet and rill and streambank erosion will be quantified, and new SDRs will be determined that considers the effects of existing BMPs on the landscape and contributions from streambank erosion.

Project Updates

March 2021

FINAL REPORT:


Figure 1: Location map of English River and Rapid Creek watersheds in Iowa with exploded county view, showing stream gauge sites and major rivers.

Our research findings were exciting and showed great progress in conservation over the past several decades in Iowa. Details are reported in the Journal of Soil and Water Conservation, March 2021.

Other activities and accomplishments

- 2 presentations

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