| Description |
Humans alter urban biogeochemical cycles through additions of nitrogen (N) and carbon (C). Urban N inputs include fossil fuel combustion and fertilizer application, and C inputs arise from anthropogenic sources of CO2 and organic matter. In this dissertation, I evaluated relationships between socioeconomic status, sociodemographic status, traffic density, fertilizer use, and foliar and soil chemistry to improve understanding of the spatial distribution of N and C sources in cities. Initially, I asked whether median household income and housing age (a proxy for time since development) were associated with the foliar chemistry of trees in Los Angeles, CA and grasses and soils in Salt Lake Valley (SLV), UT. Next, I evaluated the impact of vehicle emissions and fertilizer application on urban trees in the SLV to better understand if these human activities serve as a proxy for median household income. To further investigate the connection between foliar chemistry variables and income, I assessed the role of traffic density on interactions between vehicle emissions and affluence in Utah. Finally, I investigated whether N inputs from urban N deposition alleviated N limitation to primary productivity in trees. Ultimately, this body of work contains the first evidence of linkages between foliar and soil chemistry and median household income. This finding underscores the value of incorporating human socioeconomic status into frameworks that aim to understand urban biogeochemical cycles. This study also contributed to a better understanding of the influence of vehicle emissions on urban vegetation. I found that the foliar chemistry of iv the urban trees in this study was impacted by high-traffic density roads within a 1000 m radius, rather than by roads only within their immediate proximity. This finding reveals that emissions from major roadways can have large spatial footprints. In addition, I found that atmospheric pollutant concentrations are associated with traffic density and income, with higher NOx concentrations in lower income neighborhoods than higher income neighborhoods. This relationship is likely the result of higher densities of high-traffic roads in low-income neighborhoods. NOx concentrations can have adverse impacts on the human respiratory system and on ecosystem dynamics - thus, understanding spatial patterns of NOx can help to mitigate these negative impacts. Finally, I found that despite fertilizer inputs and irrigation, street trees in downtown SLV are co-limited by N and water availability. In total, this study has contributed to a better understanding of human impacts on urban biogeochemical cycles and plant-human-atmosphere interactions. |
