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Bioremediation of Urban Environmental Pollution by Ornamentals
By: S. C.
Sharma and
R. K. Roy
Earth was a
beautiful landscape but man has ruthlessly exploited for his greed specially in
the present century. With rapid industrialisation and random urbanisation
environmental pollution has become a serious problem. Over exploitation of open
spaces, ever-increasing number of automobiles and demographic pressure have
further aggravated the problem. There are various ways and means to mitigate
the urban environmental pollution. Planting of trees and shrubs for abatement
of pollution and improvement of environment is an effective way and well
recognized throughout the world. Earlier, the purpose of planting trees in
urban areas was purely aesthetic. The incessant increase of urban environmental
pollution has necessitated to reconsider the whole approach of urban
landscaping and its orientation in order to achieve duel effect i.e.
bioaesthetics and mitigation of pollution. Proper planning and planting scheme
depending upon the magnitude and type of pollution, selection of pollution
tolerant and dust scavenging trees and shrubs should be done for bioremediation
of urban environmental pollution. Pollution, the major problem in cities is
compounded by the fact that there is no exhaust for the polluted air to escape.
Landscape architects can solve the pollution problems related to urban
landscape by creating a micro-climate.
Planting
along the road:
Roads are
the important sites of the urban areas which contribute significantly in
mitigating pollution by planting trees on both sides. Unfortunately, in most of
the old Indian cities and towns, there is hardly any provision of sufficient
space for the same. However it is necessary to study the type of road, overhead
electrical cables, space available on both sides, central verge, traffic
triangles, round abouts, squares and other open space available before taking
up any plantation. It has been observed that trees and shrubs which are drought
/ frost resistant are generally tolerant to pollution.
Selection of
trees is another important task. Before selecting any plant species, it is
necessary to consider following characters : agro-climatic suitability; height
and spread; canopy architecture; growth rate and habit (straight undivided
trunk); aesthetic effect (foliage, conspicuous and attractive flower colour);
pollution tolerance and dust scavenging capacity. Some of the ornamental trees
which have aesthetic effect and tolerant to pollution have been screened and
recommended for planting along the roads. Acacia auriculiformis,
Ailanthus excelsa, Alstonia macrophylla, A. scholaris, Albizzia lebbek,
Bauhinia acuminata, B. purpurea, Butea monosperma, Cassia fistula, C.
marginata, C. siamea, Casuarina equisetifolia, Crataeva religiosa,
Drypetes roxburghii, Ficus benjamina, Lagerstroemia duperreana, L. flosreginae,
L. rosea, Mimusops elengi, Polyalthia longifolia, P. longifolia 'Angustifolia',
P. longifolia 'Pendula', Peltophorum ferrugineum, Tectona grandis, Terminalia
arjuna, T. muelleri, Thespesia populnea etc. Emphasis should be
given to the native plant species which are comparatively well acclimatised,
stress and pollution tolerant.
Central
Verge:
Central
verge of the two way roads in the cities and towns are often found neglected
and devoid of any planting. It is recommended that this area should be well
utilized by planting dwarf trees and shrubs. This will not only serve aesthetic
purpose but also functional being physical barrier for the glare of head lights
of the vehicles which is essential for effective and safe operation of the
roads during dark hours. Planting may be done either in single or double row
depending upon the space available. Since these plants are more close to the
automobile exhaust, their capacity for pollution tolerance should be considered
before selection. Following plant species have been reported as pollution
tolerant and recommended for plantation: Acalypha wilkesiana, Bougainvillea
'Chitra', 'H.C.Buck', 'Lady Mary Baring', 'Mary Palmer Special', 'Partha',
'Shubhra', 'Zulu Queen'; Caesalpinia pulcherrima, Callistemon lanceolatus,
C. polandii, Cassia surattensis, Duranta plumeri, Euphorbia milli,
Hamelia patens, Hibiscus rosa-sinensis, Ixora coccinea, Jatropha panduraefolia,
Lantana camara, L. depressa, Malpighia coccigera, M. glabra, Murraya
paniculata, Nerium oleander, Phyllanthus niruri, Rosa'Gruss an Teplitz',
Tabernaemontana coronaria, Thevetia neriifolia, Vinca rosea, Wadelia
lacinata etc.
Traffic
Island:
Traffic
islands at the main road intersections vary in shape and size from square,
triangle to round. Whatever may be the shape, these islands should be property
planted with the dwarf trees, shrubs and ground covers recommended for planting
along the road and central verge which will contribute effectively in
mitigating the air pollution.
Greenbelt:
Greenbelt is
defined as the mass plantation of pollution tolerant trees and shrubs in an
area for the purpose of minimizing air pollution by filtering, intercepting and
absorbing pollutants in an effective manner for improvement of the environment.
Every town and city must have certain area earmarked for the development of
greenbelts. The effectiveness of the greenbelt depends on the several factors
viz. climatic conditions, design, selection of plant species and its characters
and type of pollutants. The importance of greenbelt can be ascertained from the
estimate of cleansing capacity of 3.7 tonnes of CO2 from atmosphere
and supply of 2.5 tonnes of oxygen from one hectare of woodland. Following
trees and shrubs are recommended for planting in the greenbelt which have
aesthetic effect as well as pollution tolerant capacity: Acacia
auriculiformis, Albizzia lebbek, Azadirachta indica, Bougainvillea cultivars,
Bauhinia purpurea, Butea monosperma, Cassia siamea, C. surattensis,
Dalbergia sissoo, Ficus infectoria, Diospyros embryopteris,
Lagerstroemia duperreana, Melia azedarach, Millingtonia hortensis, Murraya
paniculata, Nerium oleander, Nyctanthes arbortristis, Parkinsonia aculeata,
Polyalthia longifolia, Putranjiva roxburghii, Terminalia arjuna,T muelleri,
Thevetia neriifolia etc.
Considering
the present scenario of urban environmental pollution, there is a growing need
for changing the approach of planting trees and other plant species. Inclusion
of the ornamental plants having pollution mitigating ability in the landscape
plan will serve the duel purpose in the long way for making the cities green
and pollution free. Proper planting scheme will bring life and colour in the
cement concrete jungle and healthy environment to the urbanities.
Dr. S.
C. Sharma is an Emeritus Scientist (CSIR) and Dr. R.K.Roy is a Scientist in
Botanic Garden at National Botanical Research Institute,
Lucknow,
India. |
