Maximizing ecosystem services on an urban college campus: Modeling nutrient cycling and human health impacts on institutional urban lands

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Shannon Hahn, Evelyn Jauregui, Christie Manning and Christine S. O'Connell, Environmental Studies, Macalester College, St. Paul, MN, Michael Frazier, Facilities Services, Macalester College, St. Paul, MN

Background/Question/Methods
Institutions that manage urban land have the ability to influence nutrient cycling - and, thus, ecosystem services - in urban areas. Macalester College, an urban campus in St. Paul, Minnesota, manages roughly 20 hectares (ha) of land. Macalester currently maintains approximately half of their grounds as turfgrass, an ideal cover for high-traffic areas and recreation. However, turfgrass is energy intensive to maintain, inefficient at carbon sequestration, and requires regular fertilization which leads to nutrient pollution. In this project, we assessed Macalester’s current grounds to provide recommendations for future land management practices that would increase sustainability (defined as prioritizing ecosystem services which improve human health, limit nutrient pollution, increase carbon sequestration, require low management, and are economically feasible). We used geospatial data to measure campus land cover types and used a nutrient model, iTree, to model nutrient cycling on Macalester’s campus under 3 alternate landscape plans: business-as-usual (BAU); replacing lawn area with native shrubs and herbaceous plants; and replacing lawn area with shrubs, herbaceous plants and planting trees. We then compared the future nutrient cycling, carbon footprint, and human health impacts of these alternative land management strategies.



Results/Conclusions
Macalester campus currently maintains 5.3 ha of tree cover and a total pervious area of 12.0 ha. They maintain 6.9 ha of turf grass, which they fertilize each year with a total of 190.4 kg nitrogen (N) ha-1 yr-1 and 104.2 kg phosphorus (P) ha-1 yr-1. We found that, if Macalester were to increase tree cover to 30% campus area (7.1 ha), convert 0.64 ha of lawn to low-input native gardens, and follow Minnesota fertilization best practices, then these changes, driven by an increase in tree cover, will sequester 26.9 tonnes (7.7 tonnes more than BAU) of carbon per year, as well as remove harmful chemicals including 5.1 kg carbon monoxide, 4.4 kg sulfur dioxide, 38.2 kg nitrogen dioxide, 289.4 kg ozone, 132.0 kg PM10 particulates and 13.6 kg PM2.5 particulates. This would result in a human health benefit valued at $4,051 per year. Broadly, we find that converting campus landscape from turfgrass to non-turfgrass land cover enhances the capacity to manage for a more conservative nutrient cycle, higher carbon sequestration, and increased air quality. In this way, urban institutions may have broad-reaching impacts on human health and urban ecosystems.