Coupling biogeochemical cycles in urban environments: ecosystem services, green solutions, and misconceptions

© The Ecological Society of America www.frontiersinecology.org H are increasingly influencing biogeochemical cycles at a global scale (Vitousek et al. 1997; Rojstaczer et al. 2001). From the publication of “man’s role in changing the face of the Earth” (Thomas 1956) to the recent syntheses on climate change (eg Solomon et al. 2007), the role of cities in altered biogeochemical cycles has received increasing attention; for the first time in human history, more people live in urban areas than in the countryside (UN 2010). As cities concentrate increasing numbers of people, they also concentrate and transform energy, materials, and waste in small areas. Although constraining populations to smaller areas may have advantages for land and other resource uses (Anderson et al. 1996), techniques and approaches need to be developed to design more efficient and sustainable cities. One approach to improving urban sustainability is to use “ecosystem services” to remediate pollution and other environmental problems (McPherson et al. 1998; Bolund and Hunhammar 1999; Nowak et al. 2002; McPherson et al. 2005; Oberndorfer et al. 2007). The Millennium Ecosystem Assessment (MA 2003) provided a framework for categorizing the societal benefits of ecosystems into different services: provisioning services (which provide food and materials), cultural services (which provide aesthetic and psychological benefits), and regulating services (which moderate environmental conditions and quality; Figure 1). Each of these services relies on fundamental ecological processes that are recognizable and in most cases measurable by members of the scientific community. Here we focus on the climate-, water-, and atmosphere-regulating services provided by planned urban green space, including but not limited to urban forests, parks, and gardens. Regulating services in green space are intimately linked to many fundamental biogeochemical processes, which are the biological and chemical processes that cycle and transform carbon (C), nutrients (eg nitrogen [N] and phosphorus [P]), water, and other materials in the environment. There is a growing body of literature about the potenCOUPLED BIOGEOCHEMICAL CYCLES