Abstract

Green roofs are emerging engineered ecosystems that provide multiple benefits, but many are constructed with nutrient-rich substrate and have been found to leach out high levels of phosphorus (P) in runoff. It is unclear, however, how long green roofs act as sources of P or what mechanisms are responsible for these net losses. We measured P concentrations in runoff water over 4 years from a 1-5 year old extensive green roof in Cincinnati, OH, USA, produced a model to predict runoff P levels into the future, and validated predictions using runoff from 2 nearby extensive green roofs. P concentrations in runoff from the focal green roof were on par with heavily fertilized agroecosystems and displayed strong seasonal dynamics and a rapid decline over the 4-year study. Runoff measurements and changes in substrate P content over a 2-year period were used to estimate a mass balance for green roof P. P loss from the substrate was substantial (4.55 +/- 2.3 g P/m(2)/yr), but only a small portion of the loss was attributable to leaching of P in runoff (0.19-0.65 g P/m(2)/yr). Missing P may be attributed to a combination of plant uptake and altered P form and binding strength, but further research is needed to precisely identify the mechanisms of P depletion. Our results also suggest that these and similar extensive green roofs are likely to act as environmentally significant sources of P for 10 or more years following roof installation, highlighting the need for reductions in initial substrate P content.

Keywords

Phosphate; Nutrient cycling; Nutrient retention; Time-series; Urban green infrastructure

Published in

Urban Ecosystems
2017, Volume: 20, number: 5, pages: 1121-1133
Publisher: SPRINGER

UKÄ Subject classification

Ecology


Publication identifier

DOI: https://doi.org/10.1007/s11252-017-0664-3

Permanent link to this page (URI)

https://res.slu.se/id/publ/109555