While provisioning ecosystem services generated through agricultural production are high, this often comes at the expense of other ecosystem services. Approaches that support both farm income and a balanced array of ecosystem services are needed. We employed a landscape modeling approach to demonstrate the financial and ecosystem service outcomes of strategically restoring grassland cover within a Corn Belt agricultural watershed. We assessed potential changes associated with a “Baseline” land use scenario and two alternative scenarios for the Grand River Basin (Iowa and Missouri, USA). In a “Buffered” scenario we simulated the impacts of replacing cropland within 20 m of streams with restored native grassland cover. In a “Productivity-based” scenario we simulated the replacement of annual row crops on poorly performing croplands with native grassland cover. Grasslands comprised 0.4% of the Baseline scenario. Grassland was expanded to 0.8% of the watershed in the Buffered scenario, reducing annual nutrient and sediment loss by 1.44%, increasing soil carbon sequestration by 0.12% over 10 years, and increasing pollinator abundance by 0.01%. The estimated annual value of these enhancements was $1.7 million for nitrogen reduction, $0.1 million for phosphorus reduction, $0.5 million for sediment reduction, and $1.3 million for soil carbon sequestration. Grassland comprised 4.9% of the watershed in the Productivity-based scenario, reduced annual nutrient and sediment loss by 11.50%, increased soil carbon sequestration by 1.13% over 10 years, and increased pollinator abundance by 0.42%. The estimated annual value of enhancements was $18 million for nitrogen reduction, $1.4 million for phosphorus reduction, $2.5 million for sediment reduction, and $14 million for soil carbon sequestration. We also calculated the value of grassland biomass for a potential energy market. The benefit of producing and selling grassland biomass ranged -$445 to $1,291 ha−1 yr−1. Scaled to the watershed, annual revenues ranged -$7.3 million to $21.1 million for the Buffered scenario and -$44.2 million to $128.8 million for the Productivity-based scenario. This study was the first to quantify changes in revenue and the value of ecosystem services associated with grassland restoration in the Grand River Basin and can help inform discussion among watershed stakeholders.
Mapping the Soil Vulnerability Index across broad spatial extents to guide conservation efforts THE NEED FOR TARGETED AGRICULTURAL CONSERVATION The 2008 Gulf of Mexico Hypoxia Action Plan was developed in response to national water quality impairments that were largely caused by agricultural land uses within and around the US Corn Belt (Alexander et al. 2008; Mississippi River Gulf of Mexico Watershed Nutrient Task Force 2008). The plan prompted states to create nutrient reduction strategies to achieve a 45% reduction in total nitrogen (N) and total phosphorus (P) loads into the Mississippi River, and thereby alleviate the hypoxic zone in the Gulf of Mexico (Mississippi River Gulf of Mexico Watershed Nutrient Task Force 2008). Similar to other state strategies, the Iowa Nutrient Reduction Strategy (INRS) promotes the widespread and voluntary adoption of best management practices (BMPs) to achieve nutrient reduction goals. The INRS establishes goals of 41% and 29% reductions in total N and total P, respectively, from nonpoint sources from a 1980 to 1996 baseline (Iowa Department of Agriculture and Land Stewardship et al. 2017). These goals are largely dependent on regional conservation funding and infrastructure to inform and incentivize BMP adoption at individual farm scales (Zimmerman et al. 2019a). Although billions of dollars have been spent to promote conservation, Iowa continues to be a primary contributor to Gulf of Mexico hypoxia, and there is little evidence of progress toward meeting environmental quality goals (Schilling et al. 2020; Jones et al. 2018; Robertson et al. 2014; Alexander et al. 2008; Tomer and Locke 2011; Osmond et al. 2012). Lack of success at broad-scale conservation efforts can be blamed on a complex mix of social, economic, and ecological barriers (Atwell et al. 2009; Osmond et al. 2012; Mattia et al. 2018; Zimmerman et al. 2019a); however, the historical lack of spatial precision and consideration of hydrologic processes in BMP application is likely a significant factor (Osmond et al. 2012; Tomer and Locke
The Raccoon River Basin is the primary source for drinking water in Iowa's largest city and plays a major role in the Mississippi River Basin's high nutrient exports. Future climate change may have major impacts on the biological, physiological, and agronomic processes imposing a threat to ecosystem services. Efforts to reduce nitrogen (N) loads within this basin have included local litigation and the implementation of the Iowa Nutrient Reduction Strategy, which suggest incorporating bioenergy crops (i.e., miscanthus) within the current corn–soybean landscape to reach a 41% reduction in nitrate loads. This study focuses on simulating N export for historical and future land use scenarios by using an agroecosystem model (Agro‐IBIS) and a hydrology model (THMB) at the 500‐m resolution, similar to the scale of agricultural fields. Model simulations are driven by CMIP5 climate data for historical, mid‐century, and late‐century under the RCP 4.5 and 8.5 warming projections. Using recent crop profit analyses for the state of Iowa, profitability maps were generated and nitrogen leaching thresholds were used to determine where miscanthus should replace corn–soybean area to maximize reductions in N pollution. Our results show that miscanthus inclusion on low profit and high N leaching areas can result in a 4% reduction of N loss under current climate conditions and may reduce N loss by 21%–26% under future climate conditions, implying that water quality has the potential continue to improve under future climate conditions when strategically implemented conservation practices are included in future farm management plans.
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