Assessing Nitrogen Risks in Urban Watersheds: Insights from the Upper White River in Marion County, Indiana

Abstract Nitrogen pollution in urban watersheds presents significant risks to both ecological health and human health by driving eutrophication and a cascade of related environmental issues. This study established and applied a comprehensive nitrogen risk assessment model to Marion County, Indiana, part of the Upper White River Watershed, to quantify and evaluate the sources and impacts of nitrogen pollution at the county and census tract level. Utilizing this data, the model comprehensively mapped nitrogen outputs from the following sources: electricity, fertilizer, food production and waste, natural gas, pet food and waste, transportation, and wastewater. The findings from 2019 revealed that the total nitrogen footprint of Marion County amounted to approximately 73.8 million kg of nitrogen, with the predominant contributions stemming from food production and waste (56%) and the energy sector (37%). These sectors highlight key areas where interventions can significantly reduce nitrogen outputs. The interactive web application developed alongside the model serves as a dynamic tool for stakeholders, enabling visualization distribution of nitrogen output, thereby supporting targeted policymaking and fostering community engagement in nitrogen management practices. By offering a detailed and scalable nitrogen assessment framework, this study contributes to the strategic planning necessary for sustainable urban development and environmental stewardship in rapidly urbanizing areas.