Installation of intensive and extensive green roofs is becoming popular for reducing runoff from impervious surfaces in many cities around the world. Most studies on runoff quality from green roofs have been conducted in cooler northern climates. We examined the losses and gains of nutrients, cations and selected anions in planted and unplanted growth medium and compared these to initial growth medium (IGM) typically used for green roof modules in south-central Texas. Water extracts of growth medium and leachate from three replicates of unplanted growth medium and three planted species (Sedum kamtschaticum, Delosperma cooperi and Talinum calycinum) were examined. During the first 6 months after establishment we observed high losses of nitrate (25 to 44 mgkg −1 ), dissolved organic carbon (DOC: 155 to 190 mgkg −1 ) and nitrogen (DON: 9.0 to 11.2 mgkg −1 ) and orthophosphate-P (1 to 2 mgkg −1 ). Average leachate concentrations based on four rain events 6 months after establishment ranged from 0.3 to 6.6 mgL −1 in planted modules and 6.3 mgL −1 in unplanted modules for nitrate-N, 38 to 42 mgL −1 in planted modules and 32 mgL −1 in unplanted modules for DOC, 2.1 to 3.1 mgL −1 in planted modules and 2.1 mgL −1 in unplanted modules for DON and 0.27 to 0.37 mgL −1 in planted modules and 0.40 mgL −1 in unplanted modules for orthophosphate-P. We suggest that after the establishment of green roofs, leachate losses may contribute some runoff concentrations of nitrogen, carbon and phosphorous in urban areas.
The German FLL Guidelines for green roofs are designed to inform about state-of-the-art performance expectations for green roofs. North America is experiencing steady growth in the green roof market and has no single-source set of standards or guidelines; therefore there is a need to identify what type of guidance may be lacking. Seven domains of knowledge from the FLL Guidelines are compared to similar areas of content in North American documents. It was found that although there are several North American green roof guidelines in use, compared to the FLL Guidelines there are areas where knowledge is lacking: guidance for compatibility of system components, slope application, filter fabrics, root barriers, surface and subsurface drainage, growth media, and erosion control, as well as standards or postconstruction testing requirements for fabrics, bulk density of growth media, root barrier performance, drainage media, and growth media. A case study of the Chicago City Hall green roof examines its content compliance with FLL performance standards. Recommendations for further advancement of North American guidelines include the need for more collaborative research and development in efforts to advance existing and new guidelines across ecoregions.
Shallow-rooted plants were studied on unirrigated modular green roof trays. Four species had 100% survival, six had varied survival rates and five had no survivors. These outcomes suggest that water conservation practices can be an effective approach for green roofs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.