As cities develop, more land is converted into impervious surfaces,
which do not allow water to infiltrate. Careful urban planning is needed
to ensure that the hydrologic cycle and water quality of the catchment
areas are not affected. There are techniques that can attenuate peak
flow during rain events and reduce the amount of metals, nutrients, and
bacteria that enter the urban water cycle. This brief gives a short
introduction on bioretention systems and documents the effectiveness of
some 36 plant species in removing water pollutants. A summary on the
maintenance requirements is also presented.