ARE STREET TREES BEING SUBSIDIZED BY HUMAN WASTE?
In this study, we explore whether street trees in Baltimore City are subsidized by leaky infrastructure (sanitary and potable water) typically associated with urban streets. To test this hypothesis, we examined the stable isotopic composition of foliage from 24 trees of the species Pyrus calleryana in southeastern Baltimore City. Trees were chosen to represent two major categories: “street trees” and “park trees” located within a large park. Nitrogen isotopic composition of foliage was expected to provide insight on the relative contributions of waste-water derived nitrate to tree nutrition, with higher d15N values suggesting access to sewage. We observe a large range in d15N values (1.3-10.4), with statistical differences (p<0.02) between street (mean=4.3) and park (mean=2.3) trees. These preliminary analyses suggest that nitrogen from human waste can be a significant source of nitrogen (and water) for street trees in Baltimore City with important implications for other cities characterized by aging infrastructure.