The migration of heavy metals from urban surface dust in simulated grass swales

: an evaluation of grass species aimed to assist retention of particulates in SUDS devices

Abstract

Urban environments possess large areas that are covered in impermeable surfaces, leading to problems with buildup of non-point pollutants on surfaces as well as increased volumes of runoff produced with rainfall events. Sustainable Urban Drainage Systems (SUDS) offer a means to mimic natural drainage processes to deal with the quality and quantity of runoff at the source. Vegetative SUDS such as swales and filter strips are two such systems that can be used to help manage drainage, removing the suspended solids and promoting infiltration of runoff into the soil. This study aimed to investigate whether particular grass species would be more suitable in these surfaces than others both in removing pollutants (e.g. Heavy Metals) and reducing flows. 
A pot based pollutant retention study was conducted using processed street dust from central Coventry as a simulated pollutant to be applied in different quantities to the grasses. Analysis was then conducted on compost cores, roots and shoots for heavy metals (Cd, Cu, Ni, Pb & Zn). Street dust was shown to be mainly concentrated in the top layer of compost for all the grass species with only the fine material migrating through the profile. None of the heavy metal concentrations in the roots were influenced by the addition of street dust whereas ANOVA analysis indicated that street dust treatments caused significant differences in heavy metal concentrations in shoots. A pattern of accumulation was illustrated by decreases in heavy metal concentrations in the compost which resulted in increased shoot concentrations. Development of root systems on or near the surface of the pots was possibly a reason for increased uptake of heavy metals by some species. Overall Agrostis canina and Poa pratensis showed the greatest accumulations compared to their controls although Agrostis capillaris syn.tenuis and Agrostis stolonifera also showing accumulation potential. 
Hydraulic trials involving the use of seed trays to mimic vegetative surfaces were subjected to simulated runoff to examine if particular grass species encouraged infiltration. The results showed that throughflow and hence infiltration was related to the distance travelled along the tray. The different species showed no significant difference between each other regarding encouraging infiltration. Overall the Bent species of grass (in particular Agrostis canina) were shown to promote more throughflow. Based on the two trials the ii Bents (in particular Agrostis canina) and Poa pratensis were deemed to be suitable species worthy of further investigation on a larger scale.

Date of Award	2010
Original language	English
Awarding Institution	Coventry University
Supervisor	SM Charlesworth (Supervisor) & James Bennett (Supervisor)