Nutrient Trading in Iowa: A Pilot Study in the Catfish Creek Watershed

Date: 
Feb 2014

Issue

Iowa’s economy is largely driven by agriculture, with more than 69 percent of the land planted in a principal crop in 2013. Fertilizer containing nitrogen (N) and phosphorus (P) is applied to farm fields to enhance soil fertility, but water quality can suffer when those nutrients leave farm fields. Financial incentives may be useful for farmers and landowners to implement nutrient reduction practices that improve water quality.

Objective

Nutrient trading provides one possible framework for nutrient reduction that could benefit both point source and nonpoint source contributors of N and P. The goal of nutrient trading is to improve water quality through nutrient reduction in an incentivized and economically advantageous way. Under this framework, contributors of N and P could generate tradable credits by adopting best management practices (BMPs) that reduce nutrient levels below required levels. Those who collect credits, such as farmers and landowners, could sell them to point source contributors downstream who also need to meet required nutrient levels or reductions. In this way, the credits provide an additional source of revenue to the sellers that could cover the cost of BMP implementation and potentially provide additional profit. This system also offers a potential cost savings to the buyer, since buying credits may be more cost effective than implementing more extensive and perhaps expensive measures.

Approach

This project will develop the scientific basis for a nutrient trading program in Iowa using the Catfish Creek Watershed near Dubuque as a pilot watershed. This will involve relating a given BMP to a nutrient load reduction. From this analysis, questions like the following can be answered: How does a given BMP equate to a nutrient load reduction (concentration or load)? How does the nutrient reduction change with differing hydrologic conditions or for different crop types/rotations? What type of variability is expected in nutrient reductions across a geologic region or landscape unit? Nitrogen is the primary nutrient to be studied initially since it is water soluble and strongly tied to streamflow and precipitation. Nutrient trading related to P will be assessed at a later time.

Project Updates

March 2016

FINAL REPORT

The goal of nutrient trading is to improve water quality through nutrient reduction in an incentivized and economically advantageous way. Under this framework, contributors of N and P could generate tradable credits by adopting best management practices (BMPs) that reduce nutrient levels below required levels. Using the Catfish Creek Watershed as a pilot watershed, a hydrologic model to determine nutrient fate and transport was developed and tested. This numerical tool can be used to evaluate different agricultural conservation practices for nutrient and flow reduction. Then these estimates can be used to develop the financial and social components of a nutrient trading system. The successful creation and implementation of a nutrient trading system in Catfish Creek will provide a blueprint for a similar system statewide.

December 2015

A physically based hydrologic and water quality model is being developed for Catfish Creek Watershed in eastern Iowa as part of a nutrient trading pilot study. The river network for the model has been refined to include streamflow contributions from 23 river branches, which includes about half of the second-order streams and all higher order streams. One water level sensor was installed near Dubuque to capture the combined streamflow response of the South Fork and Main Fork Catfish Creek branches. Measured data from this site will provide an additional resource for calibration and validation to ensure simulated results are in general agreement with actual observations. Findings from this work will provide the scientific basis for developing a nutrient trading system in Iowa to improve water quality.

September 2015

A physically based hydrologic and water quality model is being developed for Catfish Creek Watershed in eastern Iowa as part of a nutrient trading pilot study. An initial coupled surface-subsurface model has been developed that represents the various hydrologic processes in a physical manner, which will allow hydrologic and nutrient processes to be studied at scales ranging from a farm field (acres) to the catchment scale (square miles). Findings from this work will provide the scientific basis for developing a nutrient trading system in Iowa to improve water quality. Refining the nutrient load reduction estimates and their associated uncertainties provided by various agricultural conservation practices will assist non-point source contributors (farmers, landowners, etc.) in making more informed decisions about nutrient management that can help meet both individual and public needs.

June 2015

This nutrient trading project is in the latter stages of model development and the beginning phase of model calibration, with the Catfish Creek Watershed near Dubuque as a pilot study. Model development has involved data inventory of the watershed, terrain preprocessing in GIS and gathering the necessary model input datasets. Efforts are focused on calibrating the model to ensure outputs are reasonable, and the model has some predictive power for evaluating how the basin will respond under different hydrologic conditions. Two water quality and stream stage sensors deployed in the watershed will allow comparison of simulated and measured flow and water quality variables.

March 2015

Under a nutrient trading system in Iowa, point source contributors of nitrate and phosphorus could trade part of their nutrient load reduction responsibilities to landowners by offering cost-share incentives for installation of nonpoint source nutrient reduction practices. The focus of this project is to improve existing flow and nutrient reduction estimates for certain agricultural conservation practices. The Catfish Creek Watershed near Dubuque is being used as a pilot study. Several hydrologic and nutrient fate/transport models are being researched and tested. Model develop also is being performed for Catfish Creek, so watershed modeling can begin soon after a model is selected.

December 2014

Nutrient trading provides a possible framework for nutrient reduction that could benefit both point source and nonpoint source contributors of nitrogen and phosphorus. Those who collect credits, such as farmers and landowners, could sell them to point source contributors downstream who also need to meet required nutrient levels or reductions. This project will develop the scientific basis for an Iowa nutrient trading program using the Catfish Creek Watershed near Dubuque as a pilot watershed. Initial steps to assemble data and develop the project are underway, including meetings with the City of Dubuque and the Iowa League of Cities to discuss overall goals.

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