These days, mining has become a terrible threat to nature with its widespread damaging impacts on environment and ecosystem. The noxious impacts of mining are mainly due from mine tailings. The mine tailings are highly acidic as well as toxic with a number of heavy metals including Cu, Zn, Mn, Ni, As, Fe and Hg.
The abundance of heavy metals along with other harmful effects in the tailings and very low pH of the tailings degrade the natural ecosystem of the tailing dams to a problematic state. Among various techniques for rehabilitation of the ecosystems on tailing dams, introducing various grasses at mine tailing sites is the most efficient and healthy management technique.
Here are some grass species which can be introduced on tailing dams to rehabilitate their ecosystem.
Chrysopogon Zizanioides or vetiver grass, a perennial bunchgrass, is a unique grass variety used in many countries in the world for its numerous beneficial effects on soil and ecosystem including-rehabilitation of the ecosystem on tailing dam, soil and water conservation, sediment control, pollution control, waste water treatment, infrastructure stabilization etc.
Height: Up to 1.5 m or 5 ft.
Stem: Tall, erect and stiff stems.
Leaf: Long, thin and rigid leaves; grow up to 5 ft long and 0.3 inch wide.
Flower: Brownish-purple colored flowers.
Root system: Finely structured and very strong root system. Roots grow downward, generally 7 ft to 13 ft in depth.
Distribution: This grass is native to India and cultivated intensively in tropical regions.
Resistance: Resistant to frost and wildfire; highly resistant to drought.
How it helps in stabilizing the ecosystem: The roots of vetiver grow almost exclusively downward, in some cases deeper than some tree roots, which make it a very effective erosion control plant and a great stabilizing hedge for stream banks and terraces. Its deep root system binds the soils tightly and thus it cannot dislodge which ultimately prevent erosion, while its root system penetrates the compacted soils and make them loose. It is also effective in runoff alleviation and water conservation.
Vetiver Grass Technology (VGT) is highly effective in rehabilitation of the ecosystem on tailing dams; as vetiver grass has a strong finely structured and deep root system along with excellent tolerance to extreme climatic variations including submergence and extreme temperature, prolonged drought, flood etc. Vetiver grass is also tolerant to a wide range of soil pH, Al an Mn toxicities, and various heavy metals including As, Pb, Zn, Hg, Cd, Cr , Ni, Cu etc. In Australia vetiver grass has been effectively used to stabilize mining overburden and highly sodic, magnesic, saline and alkaline tailings of coal mine. Using this grass is also effective in stabilizing highly acidic and high As tailings of gold mines.
Cynodon Dactylon is a fast-growing and widely cultivated grass variety in worm climates. This grass is capable of quick recovering from damage, and highly tolerant to heat and drought. It is a great grass species to rehabilitate the soil and ecosystem.
Common Names: Bahama Grass, Couch Grass, Indian Doab, Devil’s Grass, Wire Grass etc.
Distribution: The grass is originated in Asia, especially in India; it has now become pan-tropical.
Stem: The erect, slightly flattened stems are tinged purple in color and grow 1-30 cm tall usually.
Leaf-Blade: Leaf-blades are short (generally 2-15 cm long), blades are grey-green in color having rough edges.
Flower: Flowers occur on 3-7 cm spikes; time of flowering is late summer.
Resistance: Resistant to heat and drought.
Root system: A deep root system; greater portion of the root mass is less than 24 inches under the surface but under drought the root system is capable of growing to over 2 m deep in a penetrable soil.
How it helps in stabilizing the ecosystem: This grass species is highly useful and is being used as lawn grass, pasture grass, and anti-erosion cover on dams in many countries. Cynodon dactylon is useful as a forage resource for milk cattle for the places where the soil is not suitable for growing crops like soyabean, maize etc.
Cynodon Dactylon is a great tool to rehabilitate the ecosystem on tailing dam, as it is capable of absorbing a wide range of metals and heavy metals of the dams including Mn, Zn, Cu, Pb, Cd, Co; it can grow well in the very low pH of the damaged soil. It can grow in dry season and wet season and also in times of heavy rainfall as well, when the toxic tailings are eroded and deposited on it.
Hyparrhenia Hirta is a tufted and wiry perennial grass. It is an invasive variety which can be used productively to rehabilitate the ecosystem on a tailing dam if managed carefully.
Common Names: Tambookie grass, common thatching grass, thatching grass, Coolatai grass.
Distribution: This grass is common in southern Africa. It occurs throughout Africa and also occurs in Pakistan.
Stem: It has upright flowering stems which are hairless. Stems may be covered with in a whitish powdery substance during their young stage.
Root system: Deep root system.
Resistance: Extremely tolerant to drought.
Flower: Whitish flowers occur throughout the year especially in the summer.
Leaf: Leaves are green to bluish green in color, generally 2-35 cm long and 2-4 mm wide. The hairless leaves are often tufted at the base of the plant.
How it helps in stabilizing the ecosystem: An excellent grass which efficiently protects the soils and stabilizes eroded soils, and hard gravelly soils. They are self fertile and drought resistant grass.
Hyparrhenia Hirta is an effective tool to rehabilitate the ecosystem on tailing dam, as it is capable of absorbing a wide range of metals and heavy metals of the dam including Mn, Zn, Cu, Pb, Cd, Co; it can grow well in the low pH of the damaged soil. Hyparrhenia Hirta is an efficient hyper-accumulator for heavy metals like Cu and Zn and thus it is useful in selecting grasses on the basis of target toxic metals. It also has a limitation in growing on the tailing dam, that is- it cannot grow under heavy rainfall.
Caution: Hyparrhenia Hirta is an invasive variety and must be managed with extreme care.