An integrated assessment framework to evaluate conservation practices and environmental and economic benefits: A case for central Iowa

Date: 
Jul 2023

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.

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.

Publications created

Development, Iowa State University, Ames, IA. https://www.card.iastate.edu/ag_policy_review/.

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.

 

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