Collaborative Research: Coupling Human Choice and Biogeochemical Cycling in Urban Ecosystems

Humans are increasingly living in urban ecosystems. Cities cover only one to two percent of Earth's surface, but they are important hotspots of biogeochemical cycling because they concentrate the consumption of food and energy that are produced beyond their boundaries. Cities therefore are largely unsustainable, requiring large imports of fossil fuels, food, and water. Furthermore, cities are important sources of greenhouse gas emissions and other pollutants resulting from fossil fuel combustion and waste generation that lead to nutrient loading downwind and downstream. Little is known about the socio-ecological coupling between human behavioral factors and biogeochemical cycles, however. This collaborative research project seeks to understand the coupling between household biogeochemical fluxes and socioeconomic factors along an urban to exurban gradient in the Minneapolis-St. Paul (Twin Cities) metropolitan region in Minnesota. The investigators will focus on household consumption because it contributes substantially to urban biogeochemical cycling and because it is potentially flexible and therefore amenable to reduction in response to changes in factors that influence household choices. As part of the ongoing Twin Cities Household Ecosystem Project (TCHEP), a social survey of 3,100 households was conducted along an urban-to-exurban gradient, and landscape characteristics were surveyed for a subset of households. Survey data about key behaviors that influence biogeochemical fluxes, such as motor vehicle travel, air travel, diet, pets, and lawn care, are used as input to a Household Flux Calculator to generate total and component carbon (C), nitrogen (N), and phosphorus (P) fluxes for each household. The survey also gathered demographic data and linked behaviors with household attitudes, norms, and perceived control. This project will use the TCHEP database to examine how behavioral, demographic, and biophysical factors influence household decisions and, thus, the fluxes of C, N, and P through households along a gradient of housing density. The investigators will determine the effect of consumption and pollution produced by single family households on fluxes of C, N, and P at the scale of the urban study region, and they will examine how behaviors can be influenced by messages exchanged through social networks to change consumption choices and elemental fluxes. The project therefore will examine the feedback loop between household choices and elemental fluxes. Elucidating the nature of such socio-environmental coupling should stimulate novel approaches to making cities more sustainable, reducing urban pollution, and reducing urban contributions to climate change.

The long-term goal of this project is to advance understanding of integrated human-biophysical interactions in urban ecosystems towards improved knowledge and management of urban biogeochemical cycles. The study will quantify the effect of behavioral flexibility and its underlying behavioral controls on elemental fluxes through households. Enhanced understanding of the coupling between human behavior and biogeochemistry is expected to transform approaches to reducing pollution through identification of behavioral changes that reduce pollutant sources. The project will provide extensive education and training of numerous undergraduate and graduate fellows s well as post-doctoral researchers. It will develop an interactive web page for non-scientists in collaboration with the Science Museum of Minnesota's Science Buzz web project. The investigators will use the HFC model as a teaching tool in undergraduate courses and disseminate the TCHEP survey tool, the TCHEP database, and the HFC tool through the world-wide web. Project outcomes should facilitate the development of new paradigms to pollution control that are based on source reduction, information feedback loops to guide adaptive management, and greater citizen involvement. This project is supported by the NSF Dynamics of Coupled Natural and Human Systems (CNH) Program.