A dynamic life cycle assessment of green infrastructures

As stormwater and its associated nutrients continue to impair our nation's waterways, green infrastructures (GIs) are increasingly applied in urban and suburban communities as a means to control combined sewer system overflows and stormwater related pollutants. Although GIs have been widely studied for their life cycle impacts and benefits, most of these studies adopt a static approach which prevents that information from being scaled or transferred to different spatial and temporal settings. To overcome this limitation, this research utilizes a dynamic life cycle assessment (LCA) approach to evaluate seven different GIs by integrating a traditional LCA with a system dynamics model which simulates the daily loadings and treatments of nutrients by the GIs across a 30-year life span. A base model was first developed, calibrated, and validated for seven GIs that are currently installed on the campus of the University of New Hampshire. The base model was then expanded to assess different scenarios in terms of geographic locations, land uses, GI design sizes, and climate changes. Our results show these aforementioned factors have significant influences on GIs' life cycle performances, with life cycle nitrogen reductions varying -100.90 to 512.09kgNeq. and life cycle phosphorous reductions varying from -23.77 to 63.43kg P eq. Furthermore, nutrient loading thresholds exist for certain GIs to offset nutrient emissions from their construction and maintenance activities. Accordingly, an optimal GI design size can be estimated for a given spatial and temporal setting. Such thresholds and optimal sizes are important to be identified to inform the decision-making and future planning of GIs.