An integrated assessment framework to evaluate conservation practices and environmental and economic benefits: A case for central Iowa
Issue
The Iowa Nutrient Reduction Strategy (INRS) aims to reduce nutrient discharge into Iowa streams and water bodies. Its goal is to decrease nutrient losses by 45% by 2035, aligning with the Gulf Hypoxia Action Plan. Challenges persist as nitrogen and phosphorus levels remain high in Iowa streams, leading to algae blooms, eutrophication and fish kills. Economic studies often underestimate benefits of conservation practices due to a limited understanding of ecosystem services, however, ecohydrological models, such as the Soil and Water Assessment Tool (SWAT), are recommended to test optimal management systems and provide inputs for economic models.
Objective
Researchers plan to develop a model that connects SWAT with an Economic Benefit Model for the Des Moines River Basin (DMRB) in central Iowa that can better quantify the benefits of adopting conservation practices in the region.
Approach
To address these issues, the team will use a methodology that integrates simulation models, data and economic analysis to assess the impact of best management practices on water quality and associated economic implications.
Project Updates
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
June 2024
During this period, researchers engaged in an intensive process of testing the Soil and Water Assessment Model (SWAT) Des Moines River Basin (DMRB) model for accurate representation of manure and fertilizer applications in the basin study area. The northern half of the study area is characterized by a dense network of confined animal feeding operations (CAFOs), which are dominated by swine production and beef cattle feedlots. This results in extensive amounts of manure nutrients that need to be applied to cropland landscapes, after accounting for storage and other aspects of nutrient losses. Inorganic fertilizer is also also used extensively throughout the study area. Research is ongoing to refine the accuracy of the model output. This includes meeting with State Geologist Keith Schilling and Calvin Wolter (retired from IDNR; working on contract with Univ. of Iowa IIHR scientists) to discuss these issues. Wolter, especially, has considerable experience analyzing nutrient budgets for the state of Iowa and has a lot of knowledge regarding nutrient application practices.
Other activities and accomplishments
Three presentations have been given or are scheduled:
- Gassman P, Brighenti T, Ji Y, Thompson J. 2024. Application of the Soil and Water Assessment Tool (SWAT) Model to Assess Mitigation Strategies for Diffuse Nutrient Pollution in Iowa, United States. Ag Eng 2024, Athens, Greece, July 1-3. https://pcoconvin.eventsair.com/ageng24/program-overview.
- Gassman P, Brighenti T, Ji Y, Thompson J. 2024. Application of the Soil and Water Assessment Tool (SWAT) Model to Assess Mitigation Strategies for Diffuse Nutrient Pollution in Iowa, United States. 2024 International SWAT Conference, Strasbourg, France, July 9-12. https://swat.tamu.edu/conferences/2024-france/.
- Gassman P, Brighenti T, Ji Y, Thompson J. 2024. Application of an Integrated Modeling System to Assess Nutrient Loss Mitigation Strategies for the Des Moines River Basin in Iowa. 2024 Iowa Water Conference, Coralville, Iowa, September 10-11, 2024. https://www.regcytes.extension .iastate.edu/iwc2022/.
One paper was submitted to a peer-review journal.
One related funding proposal was submitted by Philip Gassman: Climate-resilient production systems for a competitive dairy industry RFP, to: USDA-NIFA-NLGCA-010248; Capacity Building Grants for Non-Land Grant Colleges of Agriculture Program Research.
December 2023
We have performed an initial analysis of our proposed INRC research using the Soil and Water Assessment Tool (SWAT) model for the Des Moines River Basin (DMRB), as reported in the CARD APR article that is listed in the “Publications created” box below. Extensive hydrological testing of the DMRB SWAT model has been conducted as reported earlier in a study published in Science of the Total Environment (https://doi.org/10.1016/j.scitotenv.2022.156302) and in a recent study published in Journal of the ASABE (see “Journal Articles Submitted” box). We investigated two different methods of simulating tile drainage in SWAT in the Journal of the ASABE study, and determined that the more physically-based approach that is based on modified Hooghoudt and Kirkham equations provided the most accurate replication of daily water balance and streamflow. The results reported in the APR article reflect non-calibrated nutrient and sediment simulations, and do not include manure nutrient applications in the DMRB (which are considerable), and thus must be considered preliminary results that will be revised as we incorporate more accurate nutrient inputs and perform more in-depth pollutant transport testing. However, the effects of cover crops, field buffers and the two practices stacked together were logical as shown in Table 1 and Figure 2. The linkage with the economic model was also performed which relied on Secchi Depth indicators in water bodies to estimate recreation and housing benefits. This initial application demonstrated that the modeling system is proving to be a robust tool that can be used to assess the impacts of different conservation practices on various nutrient indicators and provide important economic insights for water bodies, and housing developments surrounding those water bodies within the DMRB. We are now pursuing a much more accurate accounting of manure and fertilizer nutrient inputs to the DMRB model, and we have also entered the next phase of testing pollutant transport in the model.
Other activities and accomplishments
One publicaton: Brighenti, T.M., P.W. Gassman, W.J. Gutowski and J.R. Thompson. 2023. SWAT model comparison between two methods for calculating tile-drain flow via spatial and temporal calibration. Journal of the ASABE. 66(6). https://doi.org/10.13031/ja.15534.