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

This study considers the net impact of three main ecosystem services provided by urban green infrastructure: greenhouse gas mitigation (both sequestration and reduced emissions owing to energy conservation), urban water runoff mitigation, and air quality improvement. In each case the authors review the current understanding of the benefits provided, then describe any ecosystem disservices that are relevant to the biogeochemical process in question. For example, while trees have a beneficial impact on some aspects of air quality, they also produce BVOCs, a precursor to smog, and allergens. Other disservices include CO₂ emissions from maintenance, water demands, potentially higher concentrations of nutrient pollutants from green roofs, and the introduction of invasive species. Finally the net effect of each of these three regulating services is summarized. The authors highlight the uncertainties in the current state of knowledge and argue for the need for more research to honestly address whether the net impact of a particular green infrastructure implementation is beneficial.