SUITMA 2005 Cairo - Remediation of contaminated brownfield land through planting community woodlands
SUITMA 2005 Cairo
| This abstract is about one of the papers of the Consumed mining and military areas theme of the SUITMA 2005 symposium. |
| Nicholas Dickinson,i | Christopher French,i |
| Philip Putwain.ii |
- i - School of Biological and Earth Sciences, Liverpool John Moores University, Liverpool, United Kingdom
- ii - Ecological Restoration Consultants, Neston, United Kingdom.
Regeneration and urban greening of former industrial landscapes in lowland England have been achieved through substantial tree planting. Less onerous risk assessment criteria for this type of soft end-use remediation, compared to land for food crops, may be somewhat contradictory because increased usage of the land may increase human exposure. We have investigated whether tree planting provides an effective long-term management of risk associated with residual contamination through phytoextraction and/or phytostabilisation.
Results presented here describe 7 years of experimental fieldwork at more than 50 trial plots at over 20 sites in NW England. Trace element mobility has been quantified and we have focussed on contaminant hotspots and the potential for site clean-up by tree harvest. Dispersion patterns of trace elements were measured and mapped at sites variously contaminated with As, Cd, Cu, Ni, Pb, Zn and B, planted with 5 taxa of Salix, 2 Populus hybrids, Alnus, Betula and Larix. Soils at the sites were often shallow and poorly developed, but low pH (that may enhance metal mobility) was unusual, and there were obvious opportunities for organic amendments to build the soils. Heterogenous spatial dispersion of metals existed at all sites; this points to the importance of appropriate sampling regimes for soils contaminated by urban, industrial and traffic fallout. In our field-based studies, mass balance models are used (i) to quantify the dispersion and mobility of potentially-toxic elements at typical brownfield sites and (ii) to assess the feasibility of influencing contaminant hotspots through uptake and harvest of short-rotation coppice.
Predictive models based on stem and foliage harvest data show that significant amounts of Cd and Zn could be removed from soil by repeated harvest. Over a typical 20 year life cycle of the crop this could amount to removal from the land of 5.6 kg Cd ha-1 (a reduction of 6 ppm) and 96 kg Zn ha-1 (a reduction of 100ppm) by the most efficient taxa (Salix x calodendron). Phytoextraction of Cd using short-rotation coppice may provide an efficient and cost-effective method of clean-up for low-level contamination of brownfield land where this metal frequently cause concern; other elements have little risk associated with human exposure (e.g. Zn, Ni, Cu) or are insufficiently mobile in soil-plant systems (e.g. Pb, Cr). Tree planting provides aesthetic improvement and economic benefits. Time scales are long but we argue this could be improved by careful targeting of hotspots, clone selection, and final harvest of the root bole.
