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Vol. 17 No. 3 - July 2011

Biological Recultivation Of "industrial Deserts" Or "lunar Scapes"

By: M.N.V. Prasad*

"Industrial deserts" or "Lunar scapes" are large territories over-loaded with technogenic waste.  Soil washing and cleaning in such situation is cost prohibitive. Therefore, one of the emerging approaches is "biological recultivation". It has been satisfactorily implemented in USA and Russia by seeding of perennial grasses, tree and bushy species. 

The environmental problems associated with mining and industrialization are the cause for concern in India. Recently, the environment minister of India announced that the MOEF has planned to add five million hectares of forest cover and improve its quality in another five million hectares in the next ten years. All this is possible when we have robust lab-cum-field research program in biological recultivation.

Despite the wide ranging constraints at hazardous waste dump sites and substrates, there have been some important success stories in the direct restoration yielding significant biodiversity benefits. The principal restoration options, on a site-specific basis, are the ameliorative approach (improving the physical and chemical nature of the site) and the adaptive approach which seeks to achieve the ecological restoration goal of establishing ecosystem structure and function and thus biodiversity. Ecological restoration without ameliorative and adaptive approaches usually depend on:

  1. careful selection of suitable substrates for plant growth

  2. species with good  adaptability  and  suitability for ground stabilization

  3. the value of the species as wildlife habitat (and as forage for domestic animals),

  4. aesthetic value.

Indigenous species available as propagules do not always satisfy the above criteria, in which case native, but not locally indigenous, species can be sown as a supplement, usually in a way that provides a rapid solution to short-term problems such as erosion, but one which enables colonization by local volunteer species and thus facilitates succession to eventually restore the native ecosystem and biodiversity 

The use of metal tolerant plants, in particular of the temperate grasses Agrostis capillaris and Festuca rubra, is a proven reclamation technology of 20 years for a variety of mine tailings and metal contaminated soils

More recently, a technology has been promoted whereby the tolerance to metals of some plants is used in a different way. Some species are described as "hyper accumulators" in recognition of their ability to accumulate elements that are usually present in trace concentrations in plants. For highly toxic metal mine wastes, it has been suggested that such species could be manipulated to clean-up or 'bioremediate' soils and at the same time  stabilize and reclaim land for other purposes. Long term trials are also underway in the U.S.A. and Chile.

Revegetation is the basis for most contaminated land reclamation programs. The revegetated contaminated area must meet two basic objectives; (i) forage and habitat for livestock and wildlife suitable for the approved post mining land use must be provided, and (ii) erosion from the mined lands must be controlled to the same extent that erosion is controlled on undisturbed native lands. Vegetation grown on the mined area is the forage for animals, a basic part of the habitat for animals, and the principal means of controlling erosion from mined lands.

There is not a single "best" method in all circumstances for any of the reclamation operations. The procedures and techniques described in this article  have  proved successful in at least one and possibly more situations.

1. Revegetating contaminated site 

      The objective of a revegetation program is to establish desirable vegetation. The procedures described for establishing vegetation include the aspects such as, seed-bed preparation, farming practices, seed handling, planting, mulching, shrub establishment and reforestation. Revegetation  involves the following points/exercises.

a)      Preparing a revegetation package

b)      Cultivation practices

c)      Drill seeding practices

d)     Hydro seeding practices

e)      Mulching practices

f)       Seed handling

g)      Planting methods for permanent reclamation

h)      Broadcast seeding

i)        Transplanting live plants and planting plant parts.

j)        Seeding shrub seed

2. Seed technology

Seed quality is vitally important. The quality of the seed many a time determines the        success or failure of a revegetation effort.  This includes the following points/aspects.

a)      Seed procurement

b)      Preparing a seed bed and seedlings  

c)      Procuring seeds/propagules of seasonal  grasses 

d)     Sowing the seeds of good shrubs, under trees and trees

3. Surface Stabilization

It is an important facet of restoration ecology. If the reclaimed land surface is stable, then soil erosion from that land is controlled to the extent possible. Vegetative and non-vegetative methods for stabilizing the land surface or controlling erosion are practiced in different sites.

4. Husbandry (management)

After the vegetation is established, the husbandry (management) of the vegetation becomes critical for its survival and longevity. The revegetation will degenerate to less than desirable cover and production and to a less desired species composition without some type of management to sustain it. Native plant species evolved under same type of foraging pressure should be included in the revegetation programs. Therefore, some type of management that at least simulates "use" is vital for the maintenance of the revegetated stand. The husbandry practices should include mowing for weed control, regulated grazing, and burning.

5. Monitoring

It is important to know how the vegetation is progressing toward the desired stage. The monitoring should focus on status of weed infestation, invasion by alien plants, protection afforded to native species, record keeping and document management.

Sodding

It is a bioengineering technique that uses vegetation mats for soil stabilization and erosion control. Plant salvage and transplant techniques with perennial grasses have been used with success. Perennial grasses with sturdy adventitious root mat anchoring them in place are preferred. The following is a list of recommendations for using vegetation mats as bioengineering materials:

  • To anchor perennial solid/soil binding grass mats to a slope, mats can be cut to form any shape desired. A shallow, narrow trench built along the contour of a slope and planted with a vegetation mat may become an effective terrace.

  • The mat should remain attached to stable vegetation and thus be held in place from the top. The mat can be pegged to prevent ripping and sliding. This technique would be used to stabilize the contaminated soil.

  • Vegetation mats can be used as building bricks. Slice the mats into rectangular pieces and use them to construct a very steep, living wall. The bricks can be pegged to each other and to the underlying substrate. This technique may be useful around culverts or sunken walkways and controls erosion.

Following three basic techniques are being used in different parts of the world:

a) Land filling:  Putting the top fertile soil on the surface of the hazardous waste. An ash dump site is overlaid in strips (strip sodding) each 3 to 6 m wide. Such strips are sown with perennial grasses or planted with shrubs and trees in a parsimonious technique

b) Ferlilizer application: Mineral fertilizers (NPK) are necessary in certain instances. Application of phosphate fertilizer at a dose of 30 kg per hectare and nitrogen fertilizer @ 30 kg per hectare is a normal sodding practice in different parts of world.

c) Irrigation: Watering of the surface disposal areas with domestic effluents. This is done through the growing season. High productivity perennial grasses, trees and bushy shrubs are planted in strips or in clumps or patches which is important for erosion control.

Examples of Plants that have successfully revegetated the land of mine spoils in different parts of India are mentioned below.

Bauxite mined area of Madhya Pradesh: Grevillea pteridifolia. Eucalyptus camaldulensis, Shorea robusta.

Coal mine spoils of Madhya Pradesh: Eucalyptus hybrid, Eucalyptus camaldulensis, Acacia auriculiformis, Acacia nilotica, Dalbergia sissoo, Pongamia pinnata

Lime stone mine spoils of outer Himalayas: Salix tetrasperma, Leucaena leucocephala, Bauhinia retusa, Acacia catechu, Ipomea carnea, Eulaliopsis binata, Chrysopogon fulvus, Arundo donax, Agave americana, Pennisetum purpureum, Erythrina subersosa

Rock-phosphate mine spoils of Musoorie: Pennisetum purpureum, Saccharum spontaneum, Vitex negundo, Rumex hastatus. Mimosa himalayana, Buddlea asiatica, Dalbergia sissoo, Acacia catechu, Leucaena leucocephala and Salix tetrasperma, etc.

Lignite mine spoils of Tamil Nadu:  Eucalyptus species, Leucaena leucocephala, Acacia and Agave

Mica, copper, tungeston, marble, dolmite, limestone, and mine spoils of Rajasthan:

Acacia tortilis. Prosopis juliflora, Acacia Senegal, Salvadora oleodes, Tamarix articulata. Zizyphus nummularia, Grewia tenax, Cenchrus setigerus. Cymbopogon, Cynodon dactylon. Sporobollis marginatus and  Dichanthium annulatum

Iron ore wastes of Orissa: Leucaena leucocephala

Haematite, magnetite, manganese spoil from Karnataka: Albizia lebeck

*Department of Plant Sciences, University of Hyderabad, Hyderabad 500 046 (A.P.) India; E-Mail - prasad_mnv@yahoo.com; mnvsl@uohyd.ernet.in


This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.


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