Land Remediation

Land remediation is the process by which land resources are restored to their former state or “baseline condition”. This is the condition of the natural resource and its services which would have existed had environmental damage not occurred. Remediation involves land management practices which can remove, control, contain or reduce environmental risks, so that the site no longer poses any significant threat to human health or the environment. This status should apply to both current, and any future proposed land use.

The need for land remediation

Throughout the world, demands on finite land resources are ever increasing, and, if unchecked, can lead to irreversible land degradation, as the land is used beyond its inherent “capacity”. According to the Millennium Ecosystem Assessment (2005), “human actions are depleting Earth’s natural capital, putting such strain on the environment that the ability of the planet’s ecosystems to sustain future generations can no longer be taken for granted”. In developing countries, economic demands for self sufficiency in food production force farmers onto marginal lands where steep slopes and infertile soils result in erosion rates far in excess of soil formation rates. Loss of the soil resource limits crop yields and productivity, requiring further extension onto other marginal areas, leading to a negative feedback cycle of declining yields and greater demands on poorer land resources. In addition to declining soil resources on-site, eroded sediment poses environmental risks to water resources due to sedimentation in water-bodies and channels, and declines in water quality due to turbidity. In this example, the need for land remediation by soil conservation techniques is critical to control environmental degradation, so that agricultural, and thus economic and social development can be sustained.

Conversely, in the developed world, the need for agricultural land has declined in recent years due to readily available and cost-competitive food imports. However, economic and social trends have led to a rapid expansion of residential, industrial, commercial and infrastructural land use. For example in England alone, over the next 20 years, over 200,000 new homes will be required per annum to meet housing demands 13 . Given such forecasts and the limited land resource available, particularly where demands are highest, the UK government has had to reconsider land use policy, with greater focus being placed on using brown – rather than green-field sites 17 . The government’s target is for 60% of all “new build” homes to be on brown-field sites.

Inevitably some of these sites have adverse “environmental footprints” from previous land use – such as contamination by industrial by products, or physical limitations such as shallow water tables, degraded soils or steep slopes. Without appropriate management, these sites may suffer environmental damage in terms of loss of ecological habitat, the ability of the soil resource to mitigate the effects of climate change and transport of pollutants to water courses.

If these sites are to be used in the future, legislation exists to ensure conditions there meet regulatory standards of environmental quality (e.g. Dutch Standards in the EU and EPA Standards in the US). The challenge is to manage the physical, biological and chemical status of these sites in the short and long term, so that these standards are met, and the precious land resource is both well protected and “fit for purpose”.

Drivers behind land remediation

Legislation relating to land remediation is widespread, with mandatory and voluntary regulations and guidelines at the local, national and EU level. Fundamental to these regulations are EU Directives such as the Environmental Liability Directive 5 , the Water Framework Directive 4 and the Soil Framework Directive 6 . The latter is one component of the EU’s Thematic Strategy for Soil Protection, which recognises the importance of soil as a natural resource, in terms of the environmental functions and services performed by soil, namely:

• Production of food, fibre and bio-fuels, agricultural and industrial raw materials
• Provision of biodiversity through habitat creation for micro- and macro-organisms and creation of a gene reservoir
• Storage of water, nutrients, air, organic matter, carbon sequestration and trace elements

The Thematic Strategy also identifies a number of threats associated with human activities, such as inappropriate land use, which can significantly impede these vital functions and services. These are:

• Soil erosion
• Organic matter decline
• Compaction
• Salinisation
• Landslides
• Soil contamination
• Soil sealing
• Loss of biodiversity

Where and when these threats occur (and producing an inventory of affected sites is a priority for the European Commission), the Thematic Strategy emphasises the need for effective land remediation to mitigate any potential or actual environmental damage.

Solutions

Remedial measures are defined as “any action, or combination of actions, including mitigating or interim measures to restore, rehabilitate or replace damaged natural resources and/or impaired services, or to provide an equivalent alternative to those resources or services” 5 . One approach to land remediation is to consider the transition from degraded to non-degraded land as two phases 12 . The first phase is concerned with the abiotic barriers to successful remediation, as shown in Figure 1 – this is the reclamation phase. The second (restoration) phase deals with the biotic barriers, and will involve measures designed to restore ecosystem function, services and structure.

The measures employed in both phases of land remediation may be based on physical, biological or chemical processes, or a combination of these. In many countries, there is no standard methodology or approach for planning or implementation, probably because each site has its own unique characteristics and challenges 7 .

Site assessment – Assessing the extent, degree and source of any environmental damage is critical in the process of remediating degraded land. Site surveys and investigations require objective data on land resource quality, namely the physical, chemical and biological condition of the site, and the past and present stresses operating there. One approach is to consider the “capability” of the land for various end land uses.

Here, emphasis is placed on the physical (abiotic) characteristics of the site in terms of soil texture, permeability, structure, slope gradient and erosion status (although it could be argued that these also reflect the site’s biotic status). Developed in the US, primarily for agricultural land use planning, land capability classification is a useful “check list” of factors affecting land quality, and thus the capacity to support different proposed land uses sustainably (e.g. which will not lead to excessive loss of the soil resource through erosion processes or damage to infrastructure by flooding). Variations exist for recreational 1 and urban land use planning 8 .

Site assessment should also consider any operational and environmental constraints at the site, such as specific site designation (e.g. in the UK, Sites of Special Scientific Interest) and legal responsibilities /constraints, as outlined in pertinent environmental law. Site investigations should include on-site and off-site surveys, such as the degree of soil erosion both at the site, and the off-site consequences of this degradation further downstream. Data sources may be field based, or rely on information archives such as national or local soil surveys.

The scale of survey will be dictated by the purpose of the remediation / final land use, and the data available – spatial scales may vary from individual soil auger holes on a point basis, to remotely sensed, satellite imagery at 1:10,000 or even smaller scales, which may cover several square kilometres. The quality of the data will also be determined by the temporal scale of monitoring – some previously surveyed data may become obsolete over time. Any site assessment must consider the proposed end application, as quality standards may vary between proposed land uses. Finally, sampling and analytical protocols may not be universally applicable – they will vary over a range of site conditions and intended end land uses.

Abiotic (physical) land remediation measures – Remediating land from a degraded to an “in-tact” state (Figure 1) may first require engineering of the physical landscape. Steep slopes, soil compaction and sealing, excessive loading by overburden or inadequate provision of drainage can lead to landscape instability in the form of landslides, erosion, excessive surface runoff and flooding, all of which limit ecosystem functions and services.

In the reclamation of such degraded land, an understanding of the fundamental properties of soil and water, including hydrology, hydraulics and geotechnics is essential. These disciplines are also the basis for designing, laying out and re constructing the physical landscape of the site to minimise degradation processes, and protect the environment. Thus, land remediation often starts with the selection, design and engineering of appropriate physical structures such as channels, weirs, spillways, terraces, berms and culverts to control these environmental threats, and create a landscape suitable for the intended end land use.

Once the abiotic/physical barriers to successful remediation are crossed, the second phase of the remediation process can be implemented, whereby the biotic / biological status of the site is restored.

Biotic (biological) land remediation measures – Abiotic or physical reclamation is only the first phase of land remediation. Restoring the ecological functions and services of a site, and preventing further degradation can be achieved with bio- and phyto-remediation techniques. Micro-organisms such as fungi, bacteria, vegetation and their enzymes can restore, rehabilitate and reclaim damaged soil resources.

However, conditions must be favourable for these biota, and physical remediation alone may not be able to create a “healthy” substrate. Soil amendments (sources of carbon and nutrients) may be added (in the form of compost, organo-mineral fertilisers, treated sewage sludge etc.) to provide sustenance for (micro)biological communities. Current research at Cranfield University (Department of Natural Resources) is assessing the ability of soil amendments (composts sourced from green and food wastes, zeolite and organo mineral fertilisers) to remediate contaminated land (including mine tailings and colliery spoils) for the production of vegetation, including bioenergy crops.

Biotic remediation occurs at many spatial scales – from the ability of vegetation to affect hydrological and hydraulic processes operating at the site 2 15 down to microscopic organisms improving soil structure. For example, the stability of soil aggregates can be increased by the production of metabolic products (e.g. plant exudates and mucilage) binding soil particles together, and via physical enmeshment by filamentous organisms 3 16 .

Improving soil structure leads to a better environment for further biological processes to occur (e.g. vegetation establishment, diversification of microbiological communities), as well increasing soil water storage, infiltration and resistance to erosion.

Evaluation and auditing – Carrying out a comprehensive and appropriate ecological audit of the site post-remediation is essential in ecosystem management, because it will help assess the sustainability and success of the project. Rigorous auditing requires the selection of an appropriate methodology, and the ability to evaluate, present and interpret data, as with initial site assessment techniques.

Survey techniques should use the most effective sampling methods, such as diversity indices and indicator species. Vegetation community classification and ordination methods which relate species community distribution to the environment are also very important. Microbiological measurements may consider key indicators of success, such as community size, composition and activity 9 .

Environmental Impact Assessment (EIA) now forms an integral part of the planning process in many land remediation projects. The method relies on careful selection of screening and scoping criteria to aid identification, prediction and quantification of impacts. Methods used range from simple checklists through to more complex matrix, networks or systems modelling techniques. All EIA approaches should include economic and social impacts of remediation techniques.

Conclusions

Implementation of successful land remediation requires an understanding of the controlling elements associated with the soil ecosystem, and of the interaction of pedo-transfer functions occurring at the soil/air/vegetation and landscape interface. A multi- and trans disciplinary approach is needed to address the complex issues surrounding land degradation and remediation. Practitioners need to have a comprehensive skills portfolio, covering the physical, biological and chemical sciences, environmental and civil engineering as well as management skills to integrate these diverse disciplines 10 .

References

1 Canada Land Inventory, 1969. Land Capability Classification for Outdoor Recreation , Report No. 6 . Queens Printer , Ottawa

2 Coppin, N.J. and Richards, I.G. (eds.). 1990. The use of vegetation in civil engineering. CIRIA Research Project No. 379. Butterworths. 49-85, 199-215.

3 Edgerton, D.L., Harris, J.A., Birch, P. & Bullock, P. 1995. Linear relationship between aggregate stability and microbial biomass in three restored soils. Soil Biology and Biochemistry, 27, 1499-1501.

4 European Commission, 2000. Water Framework Directive 2000/60/EC http:// ec.europa.eu/environment/water/water-framework/index_en.html

5 European Commission, 2004. Directive 2004/35/Ce of the European Parliament and of the Council of 21 April 2004 on environmental liability with regard to the prevention and remedying of environmental damage. Directive 2004/35/EC (OJ L 143, 30.4.2004,). Official Journal of the European Union. 30.4.2004.

6 European Commission, 2006. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions – Thematic Strategy for Soil Protection [SEC(2006)620] [SEC(2006)1165].

7 Forkin, J. 2005. A framework for the management of land reclamation and restoration projects. Unpublished M.Sc. thesis. Cranfield University.

8 Hannam, I.D. and Hicks, R.W. 1980. ‘Soil Conservation and Urban Land Use Planning’. Journal of the Soil Conservation Service of New South Wales 36:134-145.

9 Harris, J.A. 2003. Measurements of the soil microbial community for estimating the success of restoration. European Journal of Soil Science, 54, 801-808.

10 Harris, J.A. and Leeds-Harrison, P.B. 2003. The restoration engineer – a new breed of environmental professional. Journal of the I.Agr. Engrs., Vol. 58, No. 3.

11 Harris, J.A., Birch, P. & Palmer, J. 1996. Land restoration and reclamation; principles and practice. Longman Higher Education, Harlow, Essex.

12 Hobbs, R.J. & Harris, J.A. (2001). Restoration ecology: repairing the Earth’s ecosystems in the new millennium. Restoration Ecology, 9, 239-246.

13 Joseph Rowntree Foundation, 2002. Britain’s housing in 2022. More shortages and homelessness? A working paper for Tackling disadvantage: A twenty-year enterprise, due for completion December 2002

14 Millennium Ecosystem Assessment. 2005. http://www.millenniumassessment.org/en/index.aspx

15 Morgan, R.P.C. and Rickson, R.J. (eds.). 1995. Slope stabilisation and erosion control: a bioengineering approach. Spon.

16 Ritz, K. and Young, I.M. 2004. Interactions between soil structure and fungi. Mycologist (2004), 18: 52-59. Cambridge University Press

17 Urban Task Force, 2005. Towards a strong urban renaissance. Independent report by members of the Urban Task Force chaired by Lord Rogers of Riverside.

Published: 10th Jun 2007 in AWE International