Cities comprise less than 2% of the world’s surface but account for about half of the human population and are hotspots of global biogeochemical activity. In post-industrial cities, individual human choices and behaviors are primary drivers of urban biogeochemistry. To understand how human choices affect the fluxes of carbon (C) and nitrogen (N) through households, we surveyed 3,100 owner-occupied, single family homes along a gradient from the city center of Saint Paul, Minnesota, to the peri-urban zone of Anoka County, Minnesota (approximately 55 km distance). Our unique socio-biophysical survey allows us to estimate total C and N, fluxes through households and link human choices to those fluxes. Survey data were processed using our Household Flux Calculator and accounting tool that computes C and N fluxes through each household, defined to include daily activities on personal property plus personal travel. For each household, C and N fluxes were calculated for air and motor vehicle travel, household energy use, food consumption and disposal, inputs and recycling of paper and plastics, pet food consumption and waste production, and the household landscape.
Results/Conclusions

We hypothesized that household fluxes are highly variable and skewed, with a small fraction of the population contributing a disproportionate fraction of total fluxes. Early analyses confirm this hypothesis. Air travel is a large contributor to the total flux of C across the 3,100 household surveyed, but one tenth of the households contribute over 32% of the total flux of C. Similarly, most of the contribution of N to lawn due to fertilizer application is due to a small number of households (about 600) where N fertilizer application is in the range of 160 to 240 Kg N ha-1 yr-1. For over a third of surveyed household N fertilization did not occur. Most importantly, we conclude that a comprehensive model of urban biogeochemistry must integrate both human behaviors and biophysical processes. This type of integrative model is necessary for developing new approaches to reduce air and water pollution from urban ecosystems.