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CHAPTER t
INTRODUCTION
1. INTRODUCTION
Urbanization can be characterized by an increase in human habitation,
coupled with increased per capita energy consumption and extensive
modification of the landscape, creating a system that does not depend
principally on local natural resources to persist. Urbanization tenn can
be used as a convenient shorthand for the ecological forcing functions
created by the growth of cities and associated human activities. However,
the individual components (e.g., structures, physical and chemical
environments, populations, communities, ecosystems, and human
culture) must be quantified and correlations among them assessed to
discover the ecologically important impacts of urban development and·
change (McDonnell and Pickett, 1990).
Urbanization of the globe is accelerating, with potentially large impacts
on vegetation in cities and surrounding areas (Pickett et al., 2001). Plants
in urban ecosystems are exposed to many pollutants and higher
temperatures, C02 and nitrogen deposition than plants in rural areas
(Gregg et al., 2003). Natural and undisturbed forests may prove to be the
indicators of urbanization impact. The degree and rate at which
pollutants alter nutrient cycles in forest ecosystems are greatly
dependent on inherent soil properties (Johnson et al., 1982).
Since the middle of the 18th century the chemical composition of the
1
atmosphertc precipitation has attracted attention of researchers.
Recently the data on the element content of dry and wet depositions has
been widely used to evaluate anthropogenic geochemical impact on the
environment. The atmosphertc pollution of soil and plants by heavy
metals may present sertous hazard to the ecosystem (Zolotareva, 1983).
More than half of the world's population now resides in cities, and urban
areas produce 78% of greenhouse gases but account for only 2% of
Earth's land surface (Grtmm et at, 2000). In the past, soil research
focused largely on agrtcultural and forest soils but now there is much
stronger interest in urban soils because of the dramatic increase of the
urban population (De Kimpe and Morel. 2000).
Increasing urbanization, defined as aggregation of human population
with subsequent perturbation of the environment (Bornkamm et al.,
1982), has led to a large increase in the range of pollutants which can
have an adverse impact on forest ecosystems.
As per the National Forest Policy, 1988, one third of the country's total
geographical area is required to be under forest cover. Since then, focus
has been shifted from commercial exploitation of forest wealth to their
conservation. The conservation of forests has assumed greater
significance in view of dependence of vast rural population on such
resources. India with 2% of the world>s geographical area has to sustain
2
17% of the world's human population and 20% of cattle population. The
per capita availability of forests in the country is 0.08 ha which is much
below the global average.
1.1. Urbanization and Environmental Gradient
The established and successful gradient paradigm (Whittaker, 1967;
Austin, 1987; Stevens, 1989) provides a useful basis for ecological
studies of the spatial varying effects of urbanization (Ter Brank and
Prentice, 1988). The gradient paradigm can be summarized as the view
that environmental variation is ordered space, and that spatial
environmental patterns govern the corresponding function of ecosystems.
The degree of the environmental change determines in part, the
steepness of the gradient system structure and function.
Because urban areas appear so often as a dense, highly developed core,
surrounded by irregular rings of diminishing development (Dickinson,
1966), the gradient paradigm is a powerful organizing tool for observing
urban influences on ecosystems. Like natural environmental gradients,
urbanization should present ecologists with a rich spatial array to use in
explaining or predicting environmental and ecological effects. Urban
rural gradients, moreover, provide an opportunity to explicitly examine
the role of humans.
Urban and peri-urban trees and other vegetation can mitigate air
3
pollution by absorbing gaseous compounds and intercepting air-borne
particulate matter (McPherson, Nowak and Rowntree, 1994). The more
forested outlying zones and large parks within the city centre are a few
degrees cooler than the urban "heat islands" of contiguous built-up
areas. The dampening effect on ambient temperature is due to. both
shading and evapotranspiration by urban trees (Akbari et al., 1992).
Trees and other urban forest vegetation facilitate soil water infiltration
and lower surface runoff in built-up central urban districts as well as
outlying zones, and they are an important mediator in urban
hydrological cycles (Loucks, 1993). At the level of individual urban sites,
there are significant local micro-climatic impacts of vegetation, including
influences on daily and seasonal temperature fluctuations, wind speed
and frost protection, depending on plant type and location (McPherson,
1993; Akbari et al., 1992).
1.2. Urbanization and forest soil
Soils form the major biogeochemical link between the forest biota they
support and atmospheric deposition. Soils function as nutrient reservoirs
upon which forest ecosystems rely, but nutrient reserves and availability
in soils may be altered by deposition of airborne pollutants (MacDonald
et al., 1991).
Particles are transferred from the atmosphere to forest soils directly by
4
dry deposition and precipitation scavenging (Bell and Treshow, 2002). A
very large number of human activities generate small particles (0.1-5 JID1)
with high concentrations of trace metals. Depending on weather
conditions, these particles may remain airborne for days or weeks and be
transported hundreds or thousands of km from their source. The
evidence that forest soils may be the ultimate or temporary repository for
the trace elements associated with these particles is substantial. Soils
particularly the clay and organic colloidal components have a very high
affinity for heavy metals.
Effland and Pouyat (1997) discussed the concept of soil in both urban
and rural environments to illustrate the obvious need to increase our
understanding of urban soils. They described spatial variability of the
urban soil system.
Parks and open spaces, serving important social and environmental
functions, are valued leisure and amenity resources in cities. It is widely
recognized that urban parks can cleanse the air, reduce the noise and
can ameliorate the microclimate. However, a few researchers, taking into
account of the size of parks and the urban pollution loading, are ...
skeptical of the efficacy of urban parks in improving the urban
environmental quality (Jacobs, 1969). While there have been a large
number of studies on the microclimatic effects of urban parks
5
(McPherosn et at, 1994; Avissar, 1996; Sornken-Smith and Oke, 1998;
Nowak et al., 2002), -there are relatively few reports ( Givoni, 1991;
Harrop et al., 1990; Ozdenix, 1992; Okuda et al., 1994) on the effects of
urban parks on the atmospheric and acoustic environment.
Atmospheric deposition processes have long been recognized as
important components of nutrient cycles in ecosystems. Air pollutant
emissions have, however, modified the depositions to the extent of
adversely affecting the soil properties, health of plants including forest
trees and normal nutrient cycling patterns (Agarwal, 2002; Fried Land
and Miller, 1999). Sulphur emissions are rising in many developing
nations across the world (Galloway, 1995). The rate of pollutant
deposition is controlled by environmental and biological variables (Lovett
and Kinskman, 1990). The chemical constituents of deposition interact
with surfaces in the canopy and are released to the forest floor primarily
as throughfall.
Air pollution constitutes a major environmental problem over large areas
of the world. The forest ecosystem in the Kola Peninsula, Russia, has
been affected by air pollution from the nickel processing industry for
. several decades. The high concentrations of sulfur dioxide cause severe
damage to vegetation due to direct injuries (Smith, 1981; Schulze, et al.,
1989; Aamlid and Venn, 1993).
6
Studies on the chemical composition of rainwater, d:ry deposition and
aerosols have been underway at Agra since 1990. These studies reveal
that although the ambient concentrations of acid precursor gases S02
and NOx are high, the depositions are alkaline in nature. This is mainly
because the aerosol is dominated by particles of soil-origin which
neutralize any acidity produced in depositions (Lakhani et al., 2007).
Atmospheric release of acidic pollutants includes sulphur and nitrogen
compounds in both gaseous and particulate phases and has the
potential to cause adverse health effects and other· environmental
damages. The main sources of atmospheric acidity are the gaseous
emissions of S02 and N02 generated by civil and industrial activities.
There are two major issues of air quality in pollutants monitored under
National Air Quality Monitoring Program in India, (i) conSistently high
particulate mater (PM) levels and (ii) consistently rising levels of oxides of
nitrogen (NOx) (Sharma et al., 2004). The levels of S02 in India have
dropped conSiderably after the introduction of low sulfur diesel (less than
0.25% sulfur) in the year 2000 (CPCB 2001).
1.3. Atmospheric deposition and soil pollution
Air pollution is an emerging and eXCiting issue in Asia. Particularly,
emission of sulphur dioxide and nitrogen oxides have being rising
7
steadily over the last few decades. Fast growth of cities together with
expansion of industries and transport systems has made the Asian
region increasingly exposed to these emissions. Projections indicate that
potentially large increases in emission may occur during the next 20-50
years, if the current trend persists. If this occurs, the impact that have
been experienced in Europe will become apparent in large 'part of Asia.
These problems include the reduction in crop yield by direct effects of
gases (Agrawal et al. 2005), acidification of lakes (Nilsson and Grennfelt,
2004) , impacts on human health, impacts of corrosion on human made
structures (Streaklov, 1993), impacts on soil fertility leading to damaging
changes in natural ecoysystem and impacts on forests and crop growth
in sensitive soils (Pearson and Stewart, 1993), impacts are most visible
. on a local scale. Coal consumption which acts as the main source of
energy production, has generated large amount of acid precursors and
has resulted in the acid deposition in some areas of the world.
The territories in the vicinity of Russia and Estonia are well-known for
acidic air pollutants which originate mainly from the power plants of
Narva (Synthesis Report, 1991). However, alkaline pollutants are even
more massive, causing a very exceptional environmental situation
(Haapala et al., 1996b).
8
Soils are dramatically altered by human activities in urban environments
and these alterations distinguish these soils from those in other systems
and within urban environments (Craul, 1999). Research has assessed
the unique physical, biological, and chemical properties of urban soils,
specifically; urban soil bulk density (Short et al., 1986; Jim, 1998), and
soil organic matter quantity and quality (Beyer et al., 1995, 1996; Pouyat
et al., 2002) have been studied and found to be affected by urban
conditions.
In forest ecosystems most of the N on the forest floor is contained within
the litter layer and the soil organic fraction (Rosswall, 1976; Tate, 1~87).
Less than 1 % of the total soil N is in inorganic forms readily available for
plant uptake. Therefore, in an unfertilized fotest soil N availability is
determined by the rate at which organic N pools are mineralized.
A recent nation-wide survey revealed that almost 50% of the Dutch
forests show a decreased vitality (State Forest Service, 1990a). In the
Netherlands, enhanced nitrogen deposition is considered to playa major
role in forest deterioration (Roelofs et al., 1985).
Wet removal process is effective only during monsoon period (June
September) when around 85% of annual rainfall occurs in India. During
rest of the year, dry conditions prevail which determine the atmospheriC
deposition chemistry in India. Ambient concentration and atmospheriC
9
reactions are controlled by continuous input of suspended dust particles
which are contributed by soil suspension during dry weather conditions.
Hence, dustfall deposition is a significant removal mechanism in India as
it provides a very good sink for acidic gaseous pollutants covering earth's
atmosphere (Kulshrestha et al., 2003).
Saxena et al. (1997) considered that besides wet depOSition, dry
deposition is another major atmospheric removal process of gases and
particulates to the earth's surface. The dry deposition of small acidifying
substances containing S042- and N03- contribute to the total acid input
to ecosystems. For large particles containing base cations the
understanding of deposition is important for interpretation of throughfall
measurements, nutrient cycling and assessment of critical loads.
Dry deposition of airborne pollutants contributes importantly to the
atmospheric load of ecosystems and is studied intensively. The dry
deposition process is influenced by numerous chemical, physical, and
biological aspects of the atmosphere, the deposited substance, and the
surface structure (Sehmel, 1980; Hosker and Lindberg, 1982). Factors
influencing the rate of dry deposition may· have different effects on the
deposition of particles and gases. Differences in factors influencing
deposition may occur within small distances and within. short periods of
time. Forest edges provide a situation where many factors regulating
10
deposition are changing within very small distances. In model studies,
Wiman andAgren (1985) showed that the higher wind speed atthe forest
edge increased the dry deposition of particles.
In the absence of precipitation, dry deposition can be a very important
mechanism for removing pollutants from the atmosphere. Even in such
places, as eastern England the ratio of dry to wet removal of 502 has
been estimated to be 2: 1 (Davies and Mitchell, 1983). If this is the case,
then in arid and semiarid regions such as much of western United States
and north and central India dry deposition is important. Dry deposition
is usually characterized by a deposition velocity, which is defined as the
flux of the species to the surface divided by the concentration at some
reference height. The amount of the species deposited per unit area per
second in a geographical location, i.e., the flux, can be calculated if the
deposition velocity and the pollutant concentration are known (Kumar et
al.,2005).
1.4. Trace metals,as soil contaminants
During the last two decades, the trace element literature appears to have
been dominated by their role as environmental contaminants, and
reflects that metals seems to be the most important group of
contaminants, even more than organiC chemicals. Indeed, 6 out of 11
most common contaminants at the U.S. National priority list sites are
11
metals i.e., Pb, As, Cr, Cd, Ni and Zn, in their decreasing order of
frequency of occurrence (USEPA, 1995).
The problems of environmental pollution from metals from anthropogenic
sources have begun to cause concern in the metropolitan cities of India.
In this regard, industrial and agricultural practices in particular are
responsible for widespread contamination of the environment in many
places. Therefore, the impacts of this poilution on the relationships
between animals and/human health, and exposure to such elements
through air, water and food, are an important area of environmental
research (Fifield and Haines, 1995).
Human activities worldwide are profoundly altering the distribution and
character of the world's forests (Noble and Dirzo 1997). In fact, research
in human ecology and the emerging field of forest history increasingly
showed that human influences have long been pervasive in many forests
(Lepofsky et al., 1996; Roosevelt et ai., 1996; Schnieder, 1996; Kirby and
Watkins, 1998; Agnoletti and Anderson, 2000).
In China, environmental pollution has been increasing for the last
decades. High atmospheric emission of sulfur has been, and still is, of
major concern (NEPA, 1997). Levels of heavy metals in Chinese cultivated
soils have been studied, but little information exists on heavy metal
contamination in forest soils.
12
The main cause of air pollution is fuel combustion. In India. 25% of the
total energy is consumed by transport sector only. which is reported to
be contributing more than 50% of air pollution problem in most of the
metro cities. and in some cases it was even up to 80%. As per an
estimate. in 2001. air pollution contribution of transport sector was
about 72% in Delhi and 48% in Mumbai .. In Beijing and Guangzhou.
automobile pollution contribution in terms of CO and NOx is estimated
to be more than 80 and 40% respectively (Goyalet al.. 2005).
Heavy metals are natural constituents of the earth crust. A number of
these elements are biologically essential and are introduced into aquatic
enrichments by various anthropogenic activities (Omar et al.. 2004).
Main anthropogenic sources of heavy metals exist in various industrial
point sources e.g.. present and former mining activities. foundries.
smelters and diffuse sources such as piping. constituents products.
combustion of by products. traffic. industrial and human activities
[Nilgun et al.. 2004}.
Heavy metals in the hydrosphere are important because they interact
with soil/sediment samples of geological origin. and subsequently can
influence biological processes. Plants, especially aquatic species, can
accumulate heavy metals. and act as indicators of the condition of the
water environment in which they are located (Ingole and Bhole. 2000).
13
Considerable amounts of lead have accumulated in soils all over the
world due to anthropogenic activities in the last few decades. This metal
is highly toxic for human and animals. So recognizing and characterizing
its behavior in soils is essential. Lead forms strong complexes with
organic matter, so it often suffers from almost complete retention within
soils (Wang et al., 1995).
Many heavy metals are biogene elements, i.e., they occur in limited
amounts in living organisms and play specific roles in them. However,
higher concentrations can cause complications. In recent years, due to
human activity, some heavy metals accumulate in topsoil, penetrate into
the food chain and effect human health.
The reactions involved are very . complex, with the rate of transfer
depending on many factors, mainly on the binding mechanisms of heavy
metals in soil solids, and on the amount and composition of the liqUid
phases (Breummer et at, 1986).
Throughout the world, there is a long tradition of farming intenSively
within and at the edge of cities (Smit et al., 1996). However, most of these
peri-urban lands (lands in the periphery of city) are contaminated with
pollutants including heavy metals such as Cu, Zn, Pb, Cd, Ni, and Hg~
These metals are contributed mainly through industrial effluents, sewage
and sludge, vehicular emission, diesel generators and application of
14
pesticides in agriculture. This loading of heavy metals often leads to
degradation of soil health and contamination of food chain mainly
through the vegetables grown on such soils (Jackson and Alloway, 1992;
Rattan et al., 2002).
The emission pathways of metal pollutants in to the atmosphere. are of
very diverse type viz. volcanic activity, emission through vegetation, soil
erosion and man-made. In other words, pollutants are emitted form
natural sources and anthropogenic sources. An accurate assessment of
natural source strength is quite difficult but also important, as for many
elements, natural emissions exceed those from anthropogenic sources.
Among the natural sources of trace metals, the wind blown dust and
volcanic eruptions are considered the most important (Thakur et al.,
2002).
Today's lead (Pb) and cadmium (Cd) pools of Swedish forest soils are
mainly originating from anthropogenic sources (Andersson et al., 1992;
Johansson et al., 1995). In southern Sweden the Pb pool of the top soil
has increased during 2000 years to 5 to 10 times the prehistoric or
'background' level (Johansson et at, 1995). While iron crusts (ferricretes)
are widespread in western and Central Mrica and Central Africa
Savannas, which are characterized by a contrasted seasonal climate,
they generally disappear in tropical rain forest regions, due to changed
climatic conditions.
15
1.5. Spatial Variability of Urban Soils
The recognition of long-range atmospheric transport as a significant
source of Pb· in terrestrial eco-systems happened independently in the
early 1970s in Scandinavia (Tyler, 1972) and in North America (Reiners
et al., 1975). Since then, considerable evidence has been presented on
both sides of the Atlantic (Page and Steinners, 1990; Tyler, 1992; Njastad
et al., 1994; Miller and Freidland, 1994; Johansson et al., 1995) on the
character and magnitude of the problem. Strong arguments have been
presented in favor of atmospheric deposition as a major source of Pb in
surface soils in different parts of the world.
Craul (1992) discussed urban soil variability in the context of vertical
and spatial (horizontal) variability. Vertical soil variability is observed as
soil horizon differentiation or lithologic discontinuities in both
undisturbed and disturbed soils. In urban soils, short-range vertical and
lateral changes in soil horizonation resulted from human activities.
Spatial variability can be separated into systematic and random variation
with both the scale of observations and our current knowledge base
determining the distribution of each component (Wilding and Drees,
1983). Nonagricultural human activity contributes to soil variability
through systematic variation such as replanting of a human stream
corridor to create riparian buffer zones, and roadway construction
16
alerting topography through sequential cut-and-fill operations. Random
variation may be expressed as a result of differential erosion and
sedimentation rates associated with land development activities. It is
obvious that most random variation in urban soil landscape· simply
reflects our present limited level of knowledge. As knowledge of the
interaction between nonagronomic human activity and urban soil
characteristics increases, random variation may be identified as
systematic soil variability (Wilding and Drees, 1983).
Spatial variability of urban soils is implied in modern soil survey reports
for urban areas by the identification and mapping of "soil series-urban
land complexes." The soil series or the lowest level of the USDA soil
classification. system is identified as soil covered by fill material to a
depth of 18" or more, or all or most of the soil has been cut away
(Reybold and Matthews, 1976). The transition between the "undisturbed"
soil and "urban land" are unnamed components of the soil complex. The
relative percentage of the three components (undisturbed soil, transition
and "urban land") varies based on the historical impact of nonagronomic
human activities such as grading and cut-and-fill operations. Spatial
variability occurs within both the natural soils (Baltimore and Beltsville
series) and the human-influenced regions "Urban land" of the soil map
delineations.
17
1.6. Study Area
Delhi has seen rapid urbanization in the last few decades, which is
putting pressure on its green cover. The number of vehicles is also
increasing rapidly. Though, the introduction of eNG has significantly
reduced air pollution, there is no alternative to green cover for combating
air pollution on sustainable basis. There is a growing realization for
augmenting measures for ground water recharge where forests/trees can
play major role in reducing run off and securing water conservation.
As per the State of Forest Report, 2003 of Forest Survey of India,
Dehradun, the National Capital Territory has 268 km2 as forest and tree
cover against the total geographical area of 1483 km2 . This represents
18.07% of the total geographical area of the Delhi. The forest cover and
tree cover in the Ncr are represented with 170.17 km2 and 98 km2
respectively (Greening Delhi Action Plan, 2006-07).
1.6.1. Physiography
Delhi state can be studied into four physiographic units called as (i)
Aravalli (Delhi) ridge, (ii) flood plains on the Yamuna basin, (iii) Piedmont
plains and (iv) undulating to level plains of the Aravalli alluvium.
It is a prolongation of the Aravallihills and enters the southern border
and ends in the North of Delhi on the West bank of Yamuna. The ridge is
predominantly rocky with undulating· relief and steep slopes. The
18
southern part of the ridge forms a plateau and constitutes a large part of
Mehrauli block. Its maximum elevation in the area is 320.3 metres above
sea level.
1.6.2. Geology
The geological formation of Delhi state ranges from Algonkian to
Quaternary age. A spur of the Aravali hills enters the state through
Gurgaon and Faridabad districts of Haryana and expands into an
elongated ridge 5-6 km wide. In nutshell geology of Delhi state may be
described as: (i) Alwar Quartzites, (ii) Older Alluvium, (iii) Recent
Alluvium and (iv) Sand Dunes.
1.6.3. Soils
The soils of Delhi state are grouped under orders inceptisols (81.3%) and
Entisols (18.7%) as reported by Mahapatra et al. (2000). These soils are
alluvial in origin and influenced by annual rainfall and flooding of
Yamuna river due to rains during the months of June- September.
National Bureau of Soil Survey and Land Use Planning identified 15 soil
series named as: Razapur, Kakra, Hamidpur, Holambi, Daryapur, Garhi
and Palam (NBSS and LUP, 1979; Lal et al., 1994) in Delhi State.
1.6.4. Clay minerals
The surface soils of Delhi state comprise mostly of ferruginous lime
quartzite, grites and schistose rock minerals. Sen (1952) observed the
19
following mineral composition of the fine sand fraction: epidoteszoisite
32-50 per cent, hornblend 17-34 per cent, garnetkaynite-zircon-titanits
9-14 per cent, iron oxide 10-20 per cent, mica 1-2 per cent, tourmaline
1":3 per cent. In light fraction, feldspar and quartz were almost in equal
proportion.
In Delhi soils, dominant clay minerals are chlorite, illite and kaolinite.
ChatteIjee and Dhar (1968) reported the presence of illitie in these soils,
however, the presence of quartz and possibly of montmorillonite was also
indicated. Rao and ChatteIjee (1972) concluded that illite was the
dominant mineral in association with chlorite and traces of
montmorillonite. In lower layers of the profile, geothite may also be
found. Mohanty (1997) confirmed the dominance of illite in the soil clay
of Delhi but smectite was also found in variable quantities depending
upon the location and soil. depth. Mixed layer minerals including small
amount of chlorite (pedogenic) and kaolinite were also present in the
clay.
Being. one of the most polluted and one of the most densely populated
cities in India, Delhi is chosen for the present study. Delhi has a
vehicular population of around 6 million (Transport Dept., 2009), which
is greater than that of the other three metropolitans (Mumbai, Kolkata
and Chennai) taken together. It also houses three thermal power plants
20
within the city limits and around 1,29,000 small-scale industries that
are mainly concentrated in six large industrial areas within the city.
Such a mixed land-use pattern is expected to cause considerable
pollution of the natural resources, especially soil. Highly urbanized zones
of Delhi are thus likely to impact the soils of surrounding regions.
Keeping this in mind, the present study was designed in order to assess
the impact of urbanization on forest soils in the National Capital Region
of Delhi. The study sites are located on approximately 15 km wide x 70
km long· transect that extended from suburban Bawana, New Delhi
through highly urbanized Central Ridge and South Central Ridge, New
Delhi to comparatively less urbanized Asola Wildlife Sanctuary, New
Delhi and forested area in District Faridabad, Haryana.
f' 1. 7. Significance of study
~ The pollution gradient has provided an opportunity to study the effects of . "'. ~ pollutant deposition on forest ecosystems under natural conditions on a
~ regional basis (MacDonald et al., 1991). Undisturbed forest soil can be
~ taken into account for the study of air pollution gradient; according to
~ wind direction. Soil (surface and profile) may be analysed and the soil ()'
'0 characteristics can provide some understanding of the type of pollutants .'-0
~ deposited over a long period of time. The gradient of air pollutant f'.
... deposition from higher to lower concentration and its subsequent effect LV)
~ on profile of undisturbed forest soil is the matter of Significance.
21
The degree of urbanization changes the functioning of natural
ecosystems. The specific micro-climate conditions in the cities also
facilitate the changes in soils as an important component of urban
enVironment· (Scharenbroch et at, 2005). The determination of the
. characteristics and specific properties of soils is of a great importance for
human health (Simpson, 1996). City soils are very variable and on one
hand have characteristic close to the characteristics of natural soils and
on the other hand soils formed totally as a result of human actiVity.
Urban soils show differences in comparison with the soils in natural
ecosystems (Kabata-Pendias 1992) and for many soil quality parameters
the intrinsic local scale variability can be significant (Hursthouse et al.
2004).
Atmospheric depositions were observed in seasonally dry tropical
enVironment of India by Singh and Agrawal (2005) and emphasized the
anthropogenic influence on chemical composition of depositions. Urban
to-rural gradient studies were helpful in order to understand the effect of
urban development on the functioning of forest ecosystems (McDonnell et
al., 1997). The results revealed a complex urban-rural enVironmental
gradient.
Spatial variation in heavy metal contents (Singh and Kumar, 2006) was
reported in soils and vegetable samples of peri-urban sites in New Delhi,
India. Considering the above studies, possible transport of pollutants
22
from their source to rural areas as a matter of urban to rural gradient
seems to be important.
The dustfall deposition fluxes were calculated by Kulshrestha et al.,
(2003) in Delhi, India and concluded that fluxes were higher for Ca which
suggested that dustfall mainly comprises of soil particles and 504 and
N03 are thought to be originated by anthropogenic activities.
As the city forests are important resources, from the point of view of
maintenance of the local climatic conditions on one hand and acting as
bio indicator of urban atmospheric pollution on the other, preservation of
such forests is of paramount importance to safeguard the urban
environmental quality.
The study area, NCR of Delhi, is reported in the recent times to have
witnessed the degradation in its environmental quality, due to rapid
growth in developmental activities. A variety of industries, besides huge
volume of traffic emits and leads to the deposition of large quantities of
chemical species and may eventually prove to be detrimental to the
health of forest soil.
Thus the changes occurring in soil characteristics need to be
scientifically recorded so that proper assessment of their impacts on the
health of soil and human beings can be made.
23
1.S. Objectives
1. To detennine the physico-chemical properties of soil at five different
forest sites in the National Capital Region of Delhi.
2. To evaluate spatial variability of forest soils from urban to peri-urban
areas in the NCR of Delhi.
3. To assess the spatial distribution of atmospheric deposition and to
establish the inter relationship between atmospheric deposition and
forest soil characteristics.
4. To establish the link if any between urbanization and forest soil
characteristics.
5. To suggest remedial measures to minimize the urban impacts on
forest soils.
24