Optimizing Peri-URban Ecosystems (PURE) to re-couple urban-rural symbiosis.

Globally, rapid urbanization, along with economic development, is dramatically changing the balance of biogeochemical cycles, impacting upon ecosystem services and impinging on United Nation global sustainability goals (inter alia: sustainable cities and communities; responsible consumption and production; good health and well-being; clean water and sanitation, and; to protect and conserve life on land and below water). A key feature of the urban ecosystems is that nutrient stocks, carbon (C), nitrogen (N) and phosphorus (P), are being enriched. Furthermore, urban ecosystems are highly engineered, biogeochemical cycling of nutrients within urban ecosystems is spatially segregated, and nutrients exported (e.g. in food) from rural/peri-urban areas are not being returned to support primary production in these environments. To redress these imbalances we propose the concept of the Peri-URban Ecosystem (PURE). Through the merging of conceptual approaches that relate to Critical Zone science and the dynamics of successional climax PURE serves at the symbiotic interface between rural/natural and urban ecosystems and allow re-coupling of resource flows. PURE provides a framework for tackling the most pressing of societal challenges and supporting global sustainability goals.