High risk of increase in pollutant mobilisation through water erosion due to climatic change

It is currently estimated that 2.2 million tons of topsoil are eroded in the UK annually. When contaminated sites are eroded away by water erosion it is the off-site impacts which are a problem because the sediment produced is transported to water courses, lakes, estuaries and coastal zones. A recent survey by DEFRA showed that 20% of all UK watercourses were at risk of failing EC Water Framework Directive because of sediment movement due to water erosion. Read on to find out how this will get worse under a changed climate.

Sediment movement also causes blockage of watercourses and drains, which in turn increases risk of flooding and re-deposition of sediments to land. Contaminated sediments will cause the quality of water bodies to deteriorate. The impact of water erosion on soils from contaminated and brownfield sites is of prime concern because contaminated soils often have physical properties that make them particularly prone to erosion forces. These soils are potential sources of pollution owing to mobilisation and transportation of toxic compounds via water erosion processes.

Neglected metal-mine spoils are particularly prone to high contaminant movement via soil erosion. These sites often have large amounts of mineral wastes stored in spoil heaps with high concentrations of heavy metals. Weathering and leaching mobilises heavy metals, especially where pH is low, making them available to vegetation and wildlife, as well as increasing their concentrations in water supplies well beyond the abandoned mine site.

Sustainable management of these sites requires an understanding of the magnitude of current and future pollutant linkage between a contaminated site along a pathway to a receptor. Sites that are currently low risk may become high risk in the future if changes in rainfall and temperature patterns make the materials in these sites prone to mobilisation and transport elsewhere. Therefore, studies to predict effects of climate change on future pollutant movement between sites and to recommend changes in present management practices are essential.

De Munck et al. (2008) carried out a study, which will be soon available in the CAB Abstracts database, to examine how pollutant linkage will be influenced by predicted changes in precipitation and subsequent rainfall erosion of soils and spoils in the UK in the 21st century. They used two contrasting case scenarios (low and high greenhouse gas emissions) to run the model Revised Universal Soil Loss Equation 2 (RUSLE2) for a case representing a high risk of pollutant linkage through water erosion. Results for 2 regions showed a significant and gradual increase in erosion rates with time as a consequence of climate change (32% and 6% increase in erosion for the Southwest and Southeast regions of the UK, respectively) by 2080. Re-vegetation of the site showed a dramatic reduction in predicted future amounts of sediment production and resulting contaminant movement to well below existing levels. Robert (2008) recommended land use changes that are beneficial to soil protection against erosion are required to prevent them from becoming a risk.

The IPCC 2007 report on climate change predicted with a high degree of confidence that there will be significant changes in the patterns of future precipitation at a global scale. In the UK, winters are predicted to be up to 30% wetter and summers up to 50% drier for some regions by the 2080s (Hulme et al. 2002). This suggests that the scenarios considered in De Munck’s article are a possible future reality and the present recommendations with regard to protection of mine spoils should be taken on board to avoid future spoil erosion and contaminant movement owing to an increase in rainfall. The CABI Environmental Impact database also includes latest reports from other organisations researching on man's impact on the environment.

References

(1) De Munck, C. S., Hutchings, R.R. and Moffat, A.J. (2008). Impacts of climate change and establishing a vegetation cover on water erosion of contaminated spoils for two contrasting UK regional climates: a case study approach. Integrated Environmental Assessment and Management, Vol 4, No. 4, Pg 443-455.

(2) Robert, M. (2006) Global change and carbon cycle: the position of soils and agriculture. Chapter in: Soil erosion and carbon dynamics, pp. 3-12.

(3)  Hulme, M., Jenkins, G.J., Lu, X., Tumpenny, J.R., Mitchell, T.D., et al. (2002). Climate change scenarios for the United Kingdom: The UKCIP02 scientific report. Norwich (UK). Tyndall Centre for Climate Change Research, School of Environmental Science, University of East Anglia, 18 pp.