Impacts on Water Quality of Integrating Landscape Design with Conservation Practices for Biomass Production

This study analyzes the effects on water quality of landscape design integrated with conservation practices for biomass production, as a part of a multi-institute project that identifies opportunities for growing biomass with profitability and environmental sustainability. The work assesses how and to what degree nitrogen, phosphorus, and suspended sediments runoff can be reduced at various scales across a watershed. A pair of Soil Water Analysis Tool models were developed, calibrated, and validated with 20-year hydrology and water quality records for the South Fork Iowa River (SFIR) and the Headwaters of North Raccoon River (HNRR) watersheds in Iowa. The models were used to simulate a landscape design scenario in which a portion of low- or negative-productivity land is converted to grow switchgrass for feedstock. We further simulated conservation practices and management such as riparian buffers and cover crop applications when stover is harvested at a rate of 30%, 45%, and 70%. Results demonstrated promising improvement of water quality under these scenarios. Compared with the historical baseline, when switchgrass is grown in low- or negative-profit land, 6%–12% of nitrogen, phosphorus, and sediments loss could be avoided in the SFIR and HNRR watersheds. Applying rye as a cover crop could reduce 15%–30% of the loadings, and installing riparian buffers could reduce up to 17% of nitrogen, 37% of phosphorus, and 71% of sediments. The two watersheds responded to the scenarios differently. Across all scenarios, the SFIR watershed showed responses more pronounced in nitrogen reduction than the HNRR watershed.