Cities, and households within cities, are biogeochemical hotspots, because of their consumption of energy, materials, and food, and associated production of air and water pollution. In addition, households make environmentally relevant choices such as the size of home to purchase and where to live relative to workplaces. In the Twin Cities Household Ecosystem Project, we have been studying patterns and drivers of household fluxes of carbon (C), nitrogen (N), and phosphorus (P) in Minneapolis-Saint Paul, Minnesota using a hybrid approach that includes a large scale survey, including acquisition of respondents’ energy bills; county parcel data; and landscape measurements; all used as inputs to a Household Flux Calculator.
Results/Conclusions
Total fluxes of C, N, and P (and fluxes from specific contributing activities) were highly variable and often skewed among households, with a small number of households contributing disproportionately to total fluxes across all households. Carbon fluxes were dominated by home energy use, motor vehicle travel, and air travel, each being progressively more skewed among households. Nitrogen fluxes were dominated by human diet, fossil fuel emissions, and lawn fertilizer, whereas P fluxes were dominated by human diet, detergents, and pet diet. Both social and biophysical factors contributed to patterns of household biogeochemical fluxes. For example, greater household income (as expressed through larger homes, more vehicles, more frequent and longer air travel, and the like) was associated with greater household C fluxes. Not surprisingly, households that had longer commute distances had greater vehicle emissions. Less easily quantifiable factors like values, norms, and attitudes also influenced specific behaviors such as maintaining a lawn or using alternative transportation, rather than a car, for daily trips. For example, people who valued a green, neat, and tidy lawn and who placed importance on what others think were more likely to fertilize their lawn. On an individual level, achieving sustainable planetary stewardship in urban settings requires that individuals understand the importance of different household activities in affecting urban biogeochemistry. On a larger scale, policies to promote urban (and, ultimately, planetary) stewardship may be most effective if they are informed by knowledge of the social drivers of specific choices (including by households) that influence urban biogeochemistry.