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.

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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).

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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.

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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.

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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