Carbon, nitrogen, and phosphorus fluxes in household ecosystems in the Minneapolis-Saint Paul, Minnesota, urban region.

Rapid worldwide urbanization calls for a better understanding of the biogeochemical cycling of those macroelements that have large environmental impacts in cities. This study, part of the Twin Cities Household Ecosystem Project, quantified fluxes of carbon (C), nitrogen (N), and phosphorus (P) at the scale of individual households in the Minneapolis-Saint Paul metropolitan area in Minnesota, USA. We estimated input and output fluxes associated with several components of household activities including air and motor vehicle travel, food consumption, home energy use, landscape, pets, and paper and plastic use for 360 owner-occupied, stand-alone households. A few component fluxes dominated total input fluxes of elements. For instance, air and motor vehicle transportation, together with home energy use, accounted for 85% of total C consumption and emissions. All total and component fluxes were skewed to varying degrees, suggesting that policies targeting disproportionately high fluxes could be an effective and efficient way to reduce pollution. For example, 20% of households contributed 75% of air travel emissions and 40% of motor vehicle emissions. Home energy use was more nearly normally distributed. Nitrogen fluxes were dominated by human diet and lawn fertilizer applications, which together accounted for 65% of total household N inputs. The majority of P inputs were associated with human diet, use of detergents, and pet food. A large portion of the variation among household fluxes of C, N, and P was related to a few biophysical variables. A better understanding of the biophysical, demographic, and behavioral drivers of household activities that contribute to C, N, and P fluxes is pivotal for developing accurate urban biogeochemical models and for informing policies aimed at reducing sources of pollution in urban ecosystems.