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Terrestrial Carbon Sequestration Through Mined Land Restoration
By: Anuj Kumar Singh1
and Jamaluddin2
Introduction
The most important natural
resource, upon which all human activities are based since time immemorial, is
land. Man’s inexorable progress towards development has, however, considerably
damaged our land resource base. Further, land also suffers from various kinds of
soil erosion, degradation and deforestation. Mining is one of the reasons
responsible for extensive land degradation in India and worldwide. The mining
spoils, literally termed as dumps that result from excavation and dumping create
stark hostile conditions for vegetatal growth and establishment. Mine spoils
represent very rigorous conditions because of low organic matter content, low
organic carbon, deficiency of soil nutrients, unfavorable pH, either coarse
texture or compacted structures of spoil materials. As a result, the vegetation
cover in and around mines is usually greatly reduced. Regeneration through
natural succession on such highly degraded sites is very slow and mostly results
in a low diversity of plant communities. In the process of mines restoration,
afforestation of spoils by suitable plant species supplemented with microbial
Biofertilizers and certain mulches is a universally accepted technology.
Afforestation of mined spoils not only serves the purpose of land restoration
but also provides other very important ecological services like carbon
sequestration and consequently greenhouse gas mitigation. Many research
organizations and industries have been developing technologies to mitigate
carbon dioxide (CO2) concentrations. The available options include
separation and capture of CO2 from the energy system and
sequestration in the deep ocean, sequestration in the geologic formations,
sequestration in the depleted oil reserves, sequestration in the explored coal
seam, and terrestrial sequestration in plants and soil. Out of many available
technologies, afforestation approach is universally accepted due to its economic
feasibility and practicability. Terrestrial ecosystems which consist of
vegetation and soils are considered to be a major sink for carbon at present
time. Carbon sequestration by plants is a natural process and does not require
any specific sophisticated technological inputs. This article aims to discuss
possibilities of carbon sequestration through afforestation approach of
restoration of mine spoils spread almost in all states of the country.
A brief on status of mining
leases and wastelands in India
The status of mining leases
as on 31.3.2007 indicates that 7,734 mining leases were under mining operations
in the country in 23 states covering an area of 445,847 ha for 60 metallic and
non-metallic minerals excluding lignite, coal, petroleum, natural gas, atomic
minerals and minor minerals. During 2006-07, the state wise break up of leases
indicates Andhra Pradesh is leading with 1,507 mining leases followed by
Rajasthan (1,433), Gujarat (1,060), Madhya Pradesh (765), Tamil Nadu (461),
Karnataka (455), Orissa (380), Jharkhand (323), Chhattisgarh (313), Maharashtra
(262) and Goa (252).These eleven states together accounted for about 93% of the
total mining leases in force.
Area wise, Rajasthan with
24% of mining lease area was ahead in 2006-07 followed by Orissa (14.89%),
Andhra Pradesh (11.64%), Karnataka (8.30%), Jharkhand (7.80%), Gujarat (5.22%),
Madhya Pradesh (4.66%), Goa (4.08%), Chhattisgarh (4.03%) and Maharashtra
(3.82%). These ten states accounted for about 88.5% of the total mining lease
areas in force and the remaining 11.5% was accounted for by the rest of the
thirteen states. As on 31.06.2007, mineral wise, limestone ranks first with 1537
mining leases spread across the country covering an area of 106857.64 ha.
Further, in addition to mined out areas there are a number of categories of
lands lying unproductive and defined as wasteland. The estimates of extent of
area suffering from land degradation vary from 38.40 Mha to 187 Mha National
Remote Sensing Agency (now National Remote Sensing Centre) has estimated the
extent of wastelands to be 63.85 Mha which is about 20% of the total
geographical area. To harness the full potential of the available land resources
and prevent its further degradation, wasteland development is of great
significance. The problem of degraded land and its management is complex and
multi-dimensional and its development requires a scientific, holistic and
integrated approach.
Carbon dynamics in forests &
plantations
The process of
photosynthesis combines atmospheric carbon dioxide with water, subsequently
releasing oxygen into the atmosphere and incorporating the carbon atoms into the
cells of plants. Additionally, forest soils capture carbon. Trees, unlike annual
plants that die and decompose yearly, are long-lived plants that develop a large
biomass, thereby capturing large amounts of carbon over a growth cycle of many
decades. Thus, a forest ecosystem can capture and retain large volumes of carbon
over long periods. Forests operate both as vehicles for capturing additional
carbon and as carbon reservoirs. A young forest, when growing rapidly can
sequester relatively large volumes of additional carbon. An old-growth forest
acts as a reservoir, holding large volumes of carbon even if it is not
experiencing net growth. Thus, a young forest holds less carbon, but it is
sequestering additional carbon over time. An old forest may not be capturing any
new carbon but can continue to hold large volumes of carbon as biomass over long
periods of time. Managed forests offer the opportunity for influencing forest
growth rates and providing for full stocking, both of which allow for more
carbon sequestration. Forest systems operate on a cycle of many decades and
centuries, rather than annually or over a few years as would be the case with
most crops and non-tree vegetation. As forest biomass expands, the amount of
carbon contained in plant increases. As the biomass contract, the forest holds
less carbon. In an unmanaged state, forests ebb and flow in response to
disturbances in the natural system. Forest disturbance regimes are part of the
natural ecological system, with wind, disease, fire and other natural, i.e.,
non-anthropogenic, events causing forest destruction and death. These events
result in the release of carbon into the atmosphere but also are typically
followed by the regrowth of the forest, which, in turn, begins a new process of
carbon buildup in the forest. In some cases, these disturbances are catastrophic
in that large areas of the forest landscape are disturbed, as with large
wildfires such as are common in many pine and boreal forests. In other cases,
the disturbances are highly localized, as with an occasional tree death due to
disease or old age such as is common in many tropical forests. Carbon release is
occasioned by the disturbance and often in the decay and decomposition of dead
matter that follows. However, most natural forests have provisions for natural
regeneration and regrowth, which, once again, captures carbon. Thus carbon is
recycled in the forest ecosystem.
Afforestation Approach
Soil acts as a critical
controlling component in the development of any ecosystem. Mine spoils are not
suitable for both plant and microbial growth because of low organic matter
content, unfavorable pH, drought arising from coarse texture or oxygen
deficiency due to compaction. The other limiting factors for revegetation of
mine spoil may be salinity, alkalinity, poor water holding capacity, inadequate
supply of plant nutrients and accelerated rate of erosion. Numerous studies
have demonstrated that land restoration benefits from plantations because it
allows jump start succession. The catalytic effects of plantations are due to
changes in under story microclimatic conditions (increased soil moisture,
reduced temperature etc.), increased vegetational structure complexity,
development of litter and humus layers and the soil physical and chemical
environment and accelerating development of diversity on degraded sites.
Plantations have an important role in protecting the soil surface from erosion
and altering the accumulation of fine particles. They can reverse degradation
process by stabilizing soil through development of extensive root systems.
Plantation of suitable species speed up succession that fulfills revegetation
goal. Besides controlling leaching of nutrients through soil erosion increases
plant diversity. Earlier studies indicated that well adapted plant species could
be recommended to establish self-sustaining cover, which require little
maintenance activities. In restoration, emphasis is given first to build soil
organic matter, nutrients and vegetation cover to accelerate natural recovery
process. Plantation can be used as a tool for mine spoil restoration as well as
carbon sequestration.
Once plantation is established,
plants increase soil organic matter, lower soil bulk density, moderate soil pH
and bring mineral nutrients to the surface and accumulate them in available
form. The plants accumulate these nutrients and re-deposit them on the soil
surface in organic matter, from which nutrients are much more readily available
for microbial breakdown. Once the soil characteristics have been restored, it is
not difficult to form the full suit of self sustained plantation on mined lands.
Some of the plant species viz. Jatropha curcas, Pongamia pinnata, Ailanthus
excelsa and Withania somnifara have been successfully tried on
limestone mined out areas of Madhya Pradesh in India. These important biodiesel
and medicinal plant species are suitably surviving and also have attracted
different other shrubs, grasses and tree species to grow. A number of
restoration ecologists have suggested many approaches for restoration of mined
land; however afforestation approach is uniformly accepted. The major aims of
restoration of mined spoils should be:
-
Speedy development of vegetal cover capable of reducing erosion and
pollution.
-
To provide ecological site stability in terms of favorable soil environment
to support colonization of diverse flora and fauna
-
Enrichment of soil nutrient
levels, weathering of overburden materials and humification of organic
matter.
-
Bio-rejuvenation of soil
system. Growth and survival of above ground and under ground flora.
-
Creation of self sustaining ecosystem
Sequence of activities
under afforestation approach
I. Studies on mined lands,
overburden dumps and spoils
a) Ecological
survey of major vegetative association and natural succession
b)
Characterization of mine spoils and dumps and identification of limiting factors
for plant growth
II. Stabilization of sites through
mechanical measures
III. Selection of site specific
species suitable for the site
IV. Planting technique
V. Use of amendments – Application
of biofertilizers, mulching, manuring, fertilization
VI. Conservation of Moisture and
water harvesting
VII. Protection, Monitoring and
Evaluation
Selection of
site-specific species suitable for the site
For sustainable stability of the
ecosystem selection of most suitable species is important. The basis of species
selection is:
-
Indigenous species of the
particular eco-climatic or agro-climatic zone
-
Ecological survey for
identifying pioneering species of grasses, herbs, shrubs and trees
-
Species trial in nursery
The selected species should
be
-
Capable of colonizing degraded
areas
-
Fixing atmospheric N2 as well
as conserving soil
-
Capable of attracting birds and
other faunal population
-
Fast growing species should be
given preference
-
Preference should be given to
indigenous one over the exotic
Benefits of Mines
restoration
Mine reclamation,
reforestation, and forest management may provide ecological and economic
benefits. Environmental benefits include reclamation of sites and storage of
carbon in trees and soil. Beyond carbon sequestration, environmental benefits
also include improved air and water quality, enhanced of wildlife habitat,
reduction in soil erosion, and increased recreational opportunities.
Air Quality:
Improvements in air quality generated by reforestation extend beyond the
sequestration of carbon dioxide. Research has shown that reforestation benefits
air quality in other ways. The leaf and needle surfaces of trees remove air
pollutants such as nitrogen oxides, ammonia, and sulfur dioxide.
Wildlife Habitat:
Reforestation of land after it has been disturbed by surface mining can produce
valuable wildlife habitat by planting trees. This will in turn generate forest
litter, which is an important part of the food chain and enriches the soil. The
tree canopy moderates temperatures of rivers and streams, which aids the
survival of aquatic species. Providing habitat for endangered and threatened
species is another potential benefit.
Erosion and water
quality:
Reforestation can help remediate former mine lands by improving water quality.
Tree roots stabilize mine land soil, which is susceptible to erosion. By
stabilizing the soil, trees prevent sediment and nutrients from washing into
nearby streams and rivers.
Phytoremediation:
Revegetating mining sites can be viewed as habitat improvement or the
creation of a “living cap.” In addition, depending on the type of contamination
present and the type of trees planted, revegetation can simultaneously provide a
phytoremediation contribution. Phytoremediation is the use of vegetation for in
situ treatment of contaminated soils, sediments, and water. Phytoremediation has
an advantage of being less costly than many remediation alternatives. However,
the process requires considerable time and should be employed at sites where
remediation can occur over a long period of time. It is important to recognize
that planting trees for carbon sequestration purposes does not equate to
phytoremediation. Depending on the type of trees selected, reforesting a former
mine land to generate carbon credits may do nothing to extract or remediate any
existing contamination at the site. However, some tree types may serve to
phytostabilize the soluble metals in the ground water or soil as well as
creating a more suitable soil.
Biodiesel
production feedstock.
Apart from carbon sequestration and other environmental and ecological services;
restoration of mined lands through afforestation may up to some extent provide
India’s one of the big challenges of energy production. Afforestation of mined
lands by energy plants viz. Pongamia pinnata and Jatropha curcas
may prove as efficient utilization of wastelands particularly in tropical and
sub-tropical ecological settings. After initial establishment, these species
require nominal maintenance as both of the species are drought tolerant and well
adapted to harsh climatic conditions.
Conclusion
While the debate over
climate change continues, Government agencies, industry, and other organizations
are pursuing proactive approaches to reduce atmospheric carbon, including carbon
sequestration projects. Mine reclamation through reforestation and sustainable
forest management can provide two major benefits. Financial benefits include
revenue from new forests, job creation, and other impacts on local economies.
Environmental benefits include storing carbon in the trees and soil, enhancing
wildlife habitat, and improving air and water quality. Thus, restoration of
mined lands through afforestation adds to the planet's net carbon storage and
helps moderate global warming by slowing the growth of carbon emissions in the
atmosphere. Adoption of afforestation approach of mined lands restoration by
appropriate technology and plants species preferably oil yielding species of
Biodiesel importance are strongly recommended. Technologies like application of
biofertilizers and mulches may be of great help for establishment of plants on
mined lands. In this way, the waste of mines may be converted in wealth of mines
and the loss what the mining has made to the environment will be sufficiently
compensated.
1Department
of Forestry, Orissa University of Agriculture &Technology, Bhubaneswar-751003, [email protected]
2Emeritus
Scientist (CSIR) Department of Bioscience, R.D. University, Jabalpur, M.P.,
[email protected] |
