Comparative analysis of the impact of la

Journal of Geology and Mining Research Vol. 4(2), pp. 13-22, March 2012
Available online at http://www.academicjournals.org/JGMR
DOI: 10.5897/JGMR11.022
ISSN 2006-9766 ©2012 Academic Journals

Full Length Research Paper

Impact of degradation processes on physical and
chemical properties of soils in Delta State of the Niger
Delta
Ohwoghere Asuma, Oghenero
Department of Geology, Delta state University, Abraka, Delta State, Nigeria. E-mail: ohwonero@hotmail.com. Tel:
07051403616.
Accepted 9 February, 2012

A comparative analysis of the impact of three forms of soil degradations (bush burning, erosion and oil
spillage) on soils from selected towns in Delta State of the Niger Delta, was carried out on soil samples
collected from six soil profiles dug to depth of 0 to 200 cm to soils affected and unaffected by the three
soil degradation forms. The analysis revealed the soil matrix pH (pHKCl) to vary from 3.7 to 5.2 and the
soil matrix water (pHH2O) is from 4.4 to 6.2.The exchangeable bases of acidity concentration are higher
than those of exchangeable bases and generally the chemical characteristics of the soils are below the

critical levels required for soils needed for agricultural purposes. Bush burning has caused a depletion
in the values of carbon by 37%, organic matter by 35.5%, nitrogen by 48.8%, pH by 1.3%, silts by 30%,
and coarse sand by 13.04%, but it increased the values of sodium by 9.5%, potassium 52.9%, calcium
42.2% magnesium 31.8%, phosphorus 34%, lead 19.6%, iron 19.6%, nickel 0, 54%, vanadium 27.3%, clay
16.6% and fine sand 29.1%. Water erosion is responsible for decreasing the values of carbon by 64.2%,
organic matter by 64.1%, nitrogen by 63.6%, sodium by 26%, potassium by 28%, calcium by 50%,
magnesium by 32%, phosphorus by 36%, clay by 6.45%, silts by 14.2% and fine sand by 31.17%. In
addition, erosion has the pH of the soil increased by 21.6%, lead by 16.4% and coarse sand by 18.54%.
Oil spillage was responsible for extremely high increase in the amount of organic matter and related
elements - carbon and nitrogen. It caused an increased in the amount of carbon by 478%, organic
matter by 479%, nitrogen by 327%, potassium by 127%, calcium by 111%, sodium by 127%, phosphorus
by 72%, lead by 44%, nickel by 11.7%, vanadium by 60.7%, pH by 4.8%, silt by 66.6% and coarse sand
by 21%, while magnesium, clay and fine sand were decreased by 77%, 15% and 10.29 respectively.
Finally, the paper concludes that other forms of soil degradation such as bush burning and water
erosion are also capable of causing degradation to an alarming rate just like oil spillage and should be
taken seriously. Efforts should be directed just as it is in oil spillage, to ensure the prevention of
indiscriminate bush burning through the raising of awareness among rural dwellers and water erosion
control habits should be cultivated.
Key words: Soil degradation, impact, soil fertility, oil spillage, bush burning and water erosion.
INTRODUCTION

The physical, chemical and biological processes are
causes of soil degradation (Lal, 1994). Destruction of soil
structures, leaching, soil crusting, soil compaction, water
erosion, desertification and pollution of the environment
are some of the physical soil degradation processes. The
chemical processes include acidification, leaching,
salinization, cation exchange capacity reduction and

decreasing soil fertility. The biological process causing
land degradation is decrease in the total biomass, carbon
as well as soil biogenity and biodiversity.
Globally, soils that were once very productive are now
unproductive due to subjection of soils to degradation by
either anthropogenic or natural processes of degradation,
or even both. According to Lal and Stewart (1990), the

14

J. Geol. Min. Res.

problem of soil degradation has been in existence for as
long as settled agriculture, and its impact on human
welfare and global environment are now higher than in
the past. In the past, the flourished of any civilization has
direct relationship with the fertility of soils. So, as the
fertility of the soil decreases so the cultures and
civilization that depend on it. Evidence emanating from
archeological studies has shown that soil degradation
has lead to the extinction of the Harappen civilization in
Western Indian, Mesopotamia in West Asia, the ancient
kingdom of Babylon in Far East and the Mayan culture in
Central American (Olson, 1981).
Over the millennia (UNEP, 1986) has estimated that
about two billion hectares of lands that were once
productive has been turned unproductive as a result of
soil degradation. The destructive impact of soil
degradation has resulted in a lot of controversies and
consequently given rise to two schools of thought; one
argues that Soil damage is a global threat on the basis of
the adverse effects it has on biomass productivity and

environment quality, and it should therefore be taken
seriously (Pimentel et al., 1995; Dregne and Chou, 1994).
The other thought believes that soil is one of the factors
of production and if soil degradation is a severe issue,
why market forces have not taken care of it? The
supporter of this thought, argues that land manager
(farmers) as land users will not allowed to degrade to the
degree of affecting profit (Crosson,1997). The later
school of thought may have thought in this line because
of the use of fertilizers, but forgetting that fertilizers
themselves are also responsible for environmental
degradation and this may also be restricted to the
developed countries, but not the developing countries
where farmers are peasant and poor, and at such could
not afford fertilizer to improve the fertility of soils.
Soil degradation is actually the decline in the quality of
land and its utility. It occurs in various ways such as soil
leaching, exposure of plant and tree roots, soil sealing
and silt accumulation in lowland areas and waterlogging
of soil, soil compaction, gully and inter-rill erosion (Lal,

1988).Other causes of soil damage include the
indiscriminate disposal of industrial effluents and
municipal wastes on soil land, bush burning and oil
spillage. It has been estimated that one sixth of the world
soils have already been damaged by water and wind
erosion (UNEP, 1986). In addition another report has it
that over 3.5 million tones of soil are lost annually in
Nigeria to land degradation (Onyegoche, 1980).
In south central Nigeria, about 2.3 million tones of soil
are lost annually and this has caused a great reduction in
agricultural yield (Dike, 1995). In July, 2005, about
10,000 barrel was spilled at Otujeremi, Ughelli South
local government area, Delta state from the facility of
shell thereby causing soil damage and water pollution
(Ohwoghere-Asuma et al., 2005).
Delta state is one of the highest oil producing states
and agrarian region within the Niger Delta. The land use

pattern in the state is subdivided into agricultural and
industrial purposes. The agricultural activities of the

people include cultivation of cassava, corn, and plantain,
cash crops like rubber, palm trees and fish farming
(ponds). Bush fallow constitute the bulk of land use
except areas where plantains, rubbers and palm trees
are cultivated. Yet the state still ranks low in agricultural
productivities in Nigeria, a reason attributable to the
abundant oil and gas resources that often prevents
harnessing of the agricultural potentials and also the
people engage in subsistence agriculture. Industrial land
use includes sand mining for building and road
construction and host to oil installations. The activities of
oil prospecting and production companies and other
forms of degradation are responsible for the deficiency in
soil nutrients availability, which often lead to low
agricultural productivities in the state.
All studies regarding soil damages in the state are often
restricted to oil spillage, gas flaring and other related
forms of soil damages caused by the oil industry. This no
doubt has resulted in the neglect of other forms of soil
damage like water erosion and bush burning which are

also responsible for environmental degradation in the
Niger delta. The aim of this study therefore, is to analyze
comparatively, the degree and extent of impact of soil
degradation processes: oil spillage, water erosion and
bush burning, with a view of quantifying the severity of
each and ascertaining the extent of impact on the
physical and chemical quality of soils in selected areas in
Delta state.
MATERIALS AND METHODS
The study areas are located across three selected towns in Delta
state that have been affected by different forms of land degradation
that are distinctively different from one another. The areas include:
Ovu, which is affected by bush burning as farming is the main
occupation of the people (Ethiope East); Agbor also an agrarian
region, which is an area susceptible to water erosion because of
the slight topography relief of the area (Ika north) and Uzere, an
area that is host to lot of oil installations in the south of the state
(Isoko south). Ovu and Uzere are respectively flat and low lying
topography. These towns are located in latitude 5° 13’ and 6°22’
and longitude 6° 03’ and 6° 25’. The soil types of the study areas

are typical of tropical climate with higher temperature and heavy
rainfall. These soils are what Bašić et al. (2003) described as
ferrasols.
The climate is humid and tropical with a rainy and dry season in a
year. The rainy season spans from April to October and the dry
season from November to March. The area is characterized by
mean annual rainfall that may vary from 2300 to 2500 mm and
mean temperature that ranges from 27 to 32°C (Nwajei, 1993).
Geologically, it is made up of coastal plain sand, deltaic plain and
Sombreiro and meander belt (Reyment, 1965; Short and Stauble,
1965).
Sample collection
Two soil profiles were dug to depth of 200 cm at Ovu into soil
unaffected and affected by bush burning on 26th March 2006; at

Ohwoghere

Uzere into soil affected and unaffected by oil spillage on 12th, July
2003; at Agbor into soil damaged (gentle slope) and undamaged by
water erosion on 10th of August 2006 . Soil samples were taken

from specific interval ranging from 0 to 200 cm (Tables 1 to 3). A
total of 30 samples were collected from six locations, bagged,
labeled and subsequently taken to the department of soil science’s
laboratory, University of Nigeria, Nsukka for physical and chemical
analysis.

Laboratory analysis
Plant available heavy metals were extracted from a solution of
ammonium acetate, with pH of 4.8 and soil/solution in the ratio of
1:5. Sample was placed in an Erlenmeyer with 50 ml of extraction
solution of ammonium and acetic acid. Mechanical agitation was
done for 30 minutes and subsequently filtered in a dry flask on a
washed filtered with acetic acidic. Total concentration in mg/kg of
Pb, Fe, Ni and V were determined by atomic absorption
spectrophotometer Varian AAA 200 after calibration with standard
prepared in the acetate ammonium solution.
Soil reaction - pH of the active acidity (pHH2O) and reserve acidity
(pHKCl) of soil samples were determined by mixing a solution of 0.1
M potassium chloride with distilled water and soil in the proportion
of 1:2:5 using Beckman zeromatic pH meter (Peech, 1965) after

equilibration. The method of Walkley and Blacky (Mathieu and
Pieltain, 2003) that utilizes oxidation of organic carbon by
potassium dichromate (K2Cr2O7) in acid medium was used for the
detection of organic carbon.
Organic nitrogen was determined by the method of Kjeldahl
(Bremner,1965), nitrogenous organic matter is mineralized by 98%
hot concentrated sulphate acid (H2SO4), the carbon and hydrogen
are released to the state of dioxide, carbon and water. The nitrogen
transform into ammonium fixed by H2SO4. Exchangeable bases
were determined by the method of (Jackson, 1958) and
exchangeable acidity by the titrimetric method using potassium
chloride solution (McLean, 1965). Soil cation exchange capacity
was determined by the ammonium acetate method (Jackson,
1958).
Available phosphorous was determined in accordance with the
method prescribed by Bray and Kurtz (1945).The impact of soil
damage was calculated with soil or degradation index in
accordance with Barrow (1992) method.

RESULTS AND DISCUSSION

The result of the laboratory analysis of the soil is
presented in (Table 1). There is degree of similarity in
both physical and chemical characteristics of all the soil
samples analyzed. Texture ranges from fine through
medium to coarse grained soils (sandy, loamy, sand and
sandy loamy soils).This is an indication of soil property
derived from parent materials or the geologic processes
that contributed to their formation. These soils are similar
to those derived from unconsolidated coastal plain sand
or sandstone, deltaic plain, Sombreiro and meander belt
of the Delta (Akamigbo and Asadu, 1986).These soils are
also characterized by relatively low quantity of silt and
clay contents. The low content of silt and clay reflects
subjection of the soils to some degree of leaching, water
erosion and the source of the parent materials
(Akamigbo, 1984; Sanchez, 1976).

15

The pH of the soil and that of its solution tends to affect
the ability of the soil to either retain or release chemical
properties of soil. Unlike water, soil has two pH values;
the pH of the soil matrix known as (pHKCl) and that of the
soil water matrix (pHH2O). The (pHKCl) is often regarded as
the pH of the soil because it takes into account all the
physical and chemical characteristics (McBean and
Rovers, 1998). Consequently the pHKCl is used in this
study as the pH of the soil. The pHKCl of both undamaged
and damaged soils ranges from 3.6 to 5.2; this makes the
soils to be acidic.
Both the pH of soil matrix water (pHH2O) and the soil
matrix (pHKCl) are lower than that suggested by Odu et al.
(1985) as a standard for the purpose of agriculture (Table
3). The acidic nature is adduced to the leaching of the
elements that are responsible for the bases by heavy
rainfall that often characterized the areas during the wet
season.
The chemical properties of the soil are lower than the
critical levels required for soils needed for agricultural use
as suggested by Odu et al. (1985).This suggests that the
soils are generally poor and cannot be regarded as fertile
soils. The reason for unfavorable chemical properties
may be probably due to the geology and the local parent
material as demonstrated by Enwezor et al. (1981). Also
the organic carbon and nitrogen content in soil are
relatively low except in the soil damaged by petroleum.
The low organic carbon and nitrogen content is
attributable to increase mineralization of the soil elements
by temperature, leaching and burning in accordance with
the findings of Sims (1990).
The analysis also revealed low exchangeable cation
content. The inherent properties of the soil derived from
the local parent material may be the reason for this. This
is in accordance with Akamigbo (1990); Akamigbo and
Asadu (1986), who demonstrated that the exchangeable
cation and the acidity of soils are greatly controlled by the
parent material from which the soils are derived. Heavy
rainfall that characterized the areas may have promoted
high level of leaching, which is probably responsible for
the low exchangeable cation observed. Leaching has
contributed to the removal of the more mobile elements
responsible for the alkalinity of the soil leaving behind
those that are less mobile. This phenomenon has
resulted in soil rich in aluminum (Al+++) and hydrogen (H+)
cations, which are responsible for the acidity of soils. In
addition, the apparent cation exchange capacity (ACEC)
and the effective exchangeable capacity (ECEC) are also
low (Appendix). Soils of this kind are what King and Juo
(1981) called low activity clay (LAC) soils. Akamigbo and
Igwe (1990) called this type of soils that are low in ACEC
and ECEC as soil which are made of the 1:1 lattice clay
minerals (kaolinites), which is normal property of lateritic
soils (Bašić et al., 2003). This is also supported by the
finding of Enwezor et al. (1981), who also attributed such
soils low in CEC to the type of clay minerals present in
them.

16

J. Geol. Min. Res.

Depth ( cm)

Horizon
description

Clay %

Silt %

Fine sand %

Coarse sand %

Total sands %

Textural class

Bulk density

Total porosity

MWDW

MWDD

Table 1. Physical properties of soil in the study areas of Uzere, Ovu and Agbor.

Unaffected by oil spillage at Uzere

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

A
AB
Bt1
Bt2
Bt3

12
14
16
18
20

4
4
4
2
4

56
58
50
50
58

28
24
30
30
18

84
82
80
80
76

SL
SL
SL
SL
SL

1.25
1.33
1.32
1.33
1.34

52.8
49.4
49.8
49.4
49.4

0.823
0.921
0.821
0.792
0.785

1.121
1.232
1.032
0.982
0.973

Oil spilled site at Uzere

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

A
AB
Bt1
Bt2
Bt3

10
16
12
14
16

6
6
8
4
6

68
50
58
60
60

16
28
22
22
22

84
78
80
82
78

SL
SL
SL
SL
SL

1.25
1.29
1.30
1.31
1.34

52.8
51.3
50.9
50.5
49.4

0.721
0.832
0.711
0.716
0.720

0.940
1.021
0.933
0.920
0.932

Unaffected bush burning site at Ovu

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

A
AB
Bt1
Bt2
Bt3

12
10
12
12
14

2
6
4
4
4

20
20
34
34
36

66
64
50
50
82

86
84
84
84
85

SL
SL
SL
SL
SL

1.20
1.23
1.24
1.24
1.25

54.7
53.5
53.2
53.2
52.0

0.925
0.832
0.721
0.90
0.687

1.030
0.991
0.950
0.821
0.810

Bush burning site at Ovu

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

A
AB
Bt1
Bt2
Bt3

8
10
12
14
16

4
4
2
2
2

32
32
38
40
44

56
48
48
44
38

88
86
86
84
82

SL
SL
SL
SL
SL

1.20
1.27
1.21
1.21
1.26

54.7
54.7
54.3
54.3
52.4

0.723
0.845
0.713
0.713
0.706

0.921
0.950
0.920
0.810
0.805

Unaffected erosion site at Agbor

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

AP
AB
Bt1
Bt2
Bt3

6
8
16
18
18

4
6
2
2
2

36
26
40
40
38

64
60
62
40
42

90
82
82
80
80

S
SL
SL
SL
SL

1.25
1.27
1.30
1.32
1.34

52.8
52.0
50.9
50.1
49.4

0.924
0.897
0.798
0.873
0.850

1.024
0.987
0.981
0.950
0.930

Sample location

Ohwoghere

17

Table 1. Contd.

Erosion site at Agbor

0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

AP
AB
Bt1
Bt2
Bt3

6
12
14
14
16

3
3
2
2
2

5
33
30
30
30

56
56
52
50
50

91
88
82
80
80

S
SL
SL
SL
SL

1.25
1.26
1.29
1.32
1.34

52.8
52.4
51.3
50.1
49.4

0.821
0.802
0.798
0.789
0.780

0.936
0.912
0.891
0.901
0.891

SL = Sandy loamy, S = sand, MWDW = mean weight diameter of wet aggregate, MWDD =mean weight diameter of dry aggregate.

Table 2. Favorable nutrient supply of agricultural soils (Odu et al., 1985).

Elements
Organic matter
Carbon
Nitrogen
Available phosphorous
Calcium
Potassium
Magnesium
pH

Critical values
2 6%
1.513%
0.15%
15 ppm
2.6 Me/100 g
0.20 Me/100 g
0.40 Me/100 g
6.5 - 7.5

Table 3. Criteria for classification of soil property status (FAO Soil Bulletin 48).

Parameters
pH
Organic carbon (%)
CEC (Me/100 g)
Nitrogen (%)
Phosphorus (Mg/l)
Potassium (Mg/l)
Calcium (Mg/l)
Magnesium (Mg/l)

The soil content in terms of plant available
phosphorus (Appendix) is low compared to that
suggested by (FAO, 1988) showed in Table 3.

Low value
> 5.6
< 0.8
< 16
< 0.083
< 6
< 140
< 1500
< 190

Medium value
5.6 – 7.6
0.8-1,5
16 – 36
0.83
Jun-25
140 - 450
1500 - 6000
190 - 550

One of the reasons is that the soils have been
affected by high degree of weathering, as
suggested by Enwezor et al. (1977), but the other

High value
> 7.6
> 1.5
> 36
> 0.16
> 25
> 450
> 6000
>550

one is so known “acidic fixation” of phosphorus
+++
(P) in soils with low pHKCl enriched by Al
ions
as usually in laterites (Bašić et al., 2003). It

18

J. Geol. Min. Res.

Table 4. Comparison of the impacts of three forms of soil degradation processes on soil physical and chemical properties.

Nutrient elements
pH
Carbon
Organic matter
Nitrogen
Sodium
Potassium
Calcium
Magnesium
Phosphorus
Lead
Iron
Nickel
Vanadium
Clay
Silt
Fine sand
Coarse sand

Oil spillage at Uzere
4.8+
478.5+
479.5+
327+
127+
111+
17+
7772+
44+
21.811.7+
60.7+
1566.6+
10.2921+

Bush burning at Ovu
1.33735.548.89.5+
52.9+
42.2+
31.8+
819.6+
19.6+
0.54+
27.3+
16.6+
30.029.1+
13.04-

Erosion at Agbor
21.6+
64.164.163.6262850224116.411.44+
4.5+
12.7+
6.4514.231.1818.54+

+ = addition, - = removal.

also forms insoluble inorganic complexes of iron and
calcium as the soil becomes more acidic and
consequently, it is increasingly unavailable to plants as
result of its solubility. In addition phosphorus of organic
materials is often released by process of mineralization
involving soil organisms, which is a major characteristic
of tropical soils and this process is often very rapid in
soils with high moisture content, temperature and in welldrained similar to those of study areas.
The concentration of heavy metals in soils analyzed
(Fe, Ni, V, and Pb) is shown in Appendix. The high acidity
(pHKCl value that range from 3.7 to 5.2) nature of the soils
investigated favourable for the concentration of heavy
metals in soil. This is in accordance with the observation
of Pilchard et al. (2003); Teixeira et al. (2010), they
demonstrated that heavy metals have the tendency to
accumulate in the surface of soil horizons rich in organic
matter in acid medium with pH < 6.The heavy metals
detected in the analysis may have been originated from
decomposition of organic matter, they occurred in
association with organic matter in the undamaged soil or
they may have been formed from same geochemical
processes with organic matter.
It is observed however, that the value of the
concentration of heavy metals is less compared to the
concentration given by Aubert and Pinta (1977), which is
the tolerable or critical level for agricultural purposes.
According to them the critical level is total content
(extracted in aqua regia); lead 100 to 400 mg/kg, 50 to
100 mg/kg for vanadium and 100 mg/kg for nickel and
20,000 to 60,000 mg/kg for iron.

The impact of land degradation forms on the soil
Three soil degradation processes; oil spillage, bush
burning and water erosion are prevalent in the study
areas and the degree of impacts in terms of percentage
of the undamaged soils is presented in Table 4.The
burning of agricultural residue has contributed to the loss
of the fertility of soil. Burning of bush tends to increase
the temperature of the top three inches of the topsoil to
such a degree that carbon and nitrogen equilibrium in the
soil is destabilized. Consequently, carbon dioxide is lost
to the atmosphere, nitrogen is converted to nitrate and
fauna and bacteria are killed. In order to ascertain the
impact of bush burning on the soil, result of analysis of
damaged and undegraded soils was compared. It was
observed that bush burning has caused a reduction in the
values of carbon by 37%, organic matter by 35.5%,
nitrogen by 48.8%, pH by 1.3%, silts by 30%, and coarse
sand by 13.04%. Conversely, increase was recorded in
the following soil elements; the values of sodium content
was increased by 9.5%, potassium 52.9%, calcium
42.2% magnesium 31.8%, phosphorus 34%, lead 19.6%,
iron 19.6%, nickel,0,54%, vanadium 27.3%, clay 16.6%
and fine sand 29.1%. The increment recorded in calcium,
magnesium,
sodium,
potassium
and
available
phosphorus in the soil may have emanated from the
ashes produced by the burning of cut trees and grasses
during land preparation for cultivation (Levine, 1991).
This also helps to show that most of the elements are
constituent of plants and trees etc; hence they are
released as by product of burning.

Ohwoghere

Water erosion as a form of soil damage and land
degradation is often responsible for decline and increase
in the availability of minerals required for the productivity
of agricultural produces as presented in Table 4.The
analysis of the soils, both damaged and undamaged
revealed that erosion is responsible for the reduction of
values of carbon content by 64.2%, organic matter by
64.1%, nitrogen by 63.6%, sodium by 26%, potassium by
28%, calcium by 50%, magnesium by 32%, phosphorus
by 36%, clay by 6.45%, silts by 14.2% and fine sand by
31.17%.The reduction by water erosion is adduced to soil
particles and nutrients erosion as well as leaching as
demonstrated by Lal (1988). In addition, erosion has the
pH of the soil increased by 21.6%, lead by 16.4% and
coarse sand by 18.54%. It is an indication that erosion
has caused the reduction of the acidity and same time
increasing the alkalinity of the soil. The increase in
coarse sand due to erosion may results in enhanced
permeability, which is detrimental to the plants, as
nutrients will be leached from the root zone especially in
the study areas with high level of rainfall.
Oil spillage like other forms of land degradation has
drastic effect on the soil but with greater degree of impact
when compared to the other, the result of which is shown
in Table 4 and Appendix. The analysis of the soil sample
showed that oil spillage was responsible for astronomical
increase in the amount of organic matter and related
elements such as carbon and nitrogen. It caused an
increased in the amount of carbon by 478%, organic
matter by 479%, nitrogen by 327%, potassium by 127%,
calcium by 111%, sodium by 127%, phosphorus by 72%,
lead by 44%, nickel by 11.7%, vanadium by 60.7%, pH
by 4.8%, silt by 66.6% and coarse sand by 21%, while
magnesium, clay and fine sand were decreased by 77%,
15% and 10.295 respectively. The increment observed is
attributable to the natural components of petroleum,
which is organic in nature that is derived from the
biodegradation of plant materials and microorganisms.
The organic nature of petroleum is reflected by the high
quantity of organic matter released into to the soil form its
spillage. The outcome of the analysis is similar to the
findings of Odu (1978); Abii and Nwosu (2009). With this
finding, it is tempting to say oil spillage tends to enhance
the quality of the soil on the basis of the organic matter
added to it, but this is not so, as crude oil blocks the pore
spaces of soils, thereby preventing the aeration of the soil
needed for plant growth and organisms. In addition
increase in coarseness of the sand will tend to promote
the flow of crude oil from the top horizon to deeper
horizon. This is supported by the decrease of heavy
metals with depths observed in the study (Appendix), as
the only way this can happened is by vertical flow of the
crude oil to soil horizon below.
Conclusion
It has been established in the study that other processes

19

of soil damages and land degradation such as bush
burning and erosion are also capable of causing
degradation to an alarming rate just like oil spillage. As a
matter of necessity action should be take to curb the
indiscriminate bush burning prevalent in Delta state due
to its degrading effects on the soil’s nutrient availability.
Erosion control measures such as mulching and planting
of cover crops in farm land should be encouraged.
It has been ascertained in the study that bush burning
and erosion have negative affects on the organic matter
content, carbon and nitrogen, with water erosion
responsible for greater degree of reduction. While bush
burning is capable of causing the increase in the amount
of exchangeable cations observed in the study, erosion
on the other hand is responsible for the reduction of
these soil elements. A different scenario is observed with
oil spillage, which has the highest degree of addition of
organic matters, carbon, nitrogen, heavy metals, and the
exchangeable cations except magnesium to the soil it
degrades. This is not equivalent to improvement in the
soil fertility by it due blocking of pore spaces in the soil,
thus eliminating aeration and causing the death of soil
microorganisms.
It has been observed in the analysis that bush burning
was responsible for reduction of pH, while water erosion
and oil spillage have increased the pH, with erosion
causing the greatest increase. By increasing the pH of
the soil erosion and oil spillage invariably contribute to
the enrichment of the soil with exchangeable bases and
depletion of exchangeable acidity.
The soils analyzed in the study are acidic just like other
lateritic soils of rain forest origin. The acidic nature of the
soil tends to promote the accumulation of heavy metals in
soil horizons rich in organic matters.
The tendency of any soil to retain soil water depends to
a large extent on the fine – colloidal soil particles such as
clay and organic matter. Oil spillage and water erosion
reduced the ability of the soils to retain water as they are
responsible for the decrease in clay content as observed
in the study. Conversely bush burning enhances the
water retentive capacity of the soil as it has caused an
increase in the content of clay and fine sand. While oil
spillage and water erosion promotes the infiltration
capacity, bush burning tend to impairs it.
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Ohwoghere

21

APPENDIX
Table 1. Chemical properties of soil not affected by oil spillage in Uzere.

Depth
(cm)
0 - 20
20- 45
45- 85
85-125
125-200

pH
KCl
4.1
4.8
4.2
4.5
4.4

H2O
5.1
5.4
5.6
5.3
5.4

Organic matter (%)
c
O.M
N
0.64
1.1
0.056
0.28
0.48 0.015
0.16
0.28 0.012
0.13
0.22 0.015
0.10
0.17 0.013

Na+
0.05
0.04
0.04
0.03
0.03

Exchangeable bases (Meg/100 g)
K+
Ca2+
Mg2+ ACEC
ECEC
0.04
.03
0.3
5
4.3
0.03
1.4
0.7
5
4.6
0.03
0.9
0.8
5
4.2
0.04
o.5
1.2
6
4.4
0.04
0.4
0.5
5
3.6

Exchangeable acidity (Meg/100 g)
Al3+
H+
P(mg/kg)
EA
2.8
0.8
2.0
3.6
2.0
0.4
1.4
2.4
1.6
0.8
1.4
2.4
1.9
0.7
1.3
2.6
2.0
0.6
1.4
2.6

Pb2+
7.25
5.33
1.5
1.0
0.0

Heavy metals (mg/kg)
Fe2+
Ni2+
V+
38.0
180.1
6.11
40.0
175.2
5.60
18
33.5
3.20
9.3
25.o
2.10
8.2
10
1.80

Table 2. Chemical properties of soil affected by oil spillage at Uzere.

Depth
(cm)
0-20
20-45
45-85
85-125
125-200

KCl
4.7
4.6
4.5
4.5
4.6

pH
H2O
5.8
5.6
5.6
5.7
5.5

Organic matter (%)
C
O.M
N
1.40
2.40 0.096
1.84
3.16 0.999
1.74
2.96 0.099
1.32
2.28 0.095
1.30
2.24 0.090

+

Na
0.10
0.10
0.09
0.06
0.06

Exchangeable bases (Meg/100 g)
+
2+
2+
K
Ca
Mg
ACEC ECEC
0.12
0.40
0.10
6
3.3
0.14
1.5
0.20
5
4.1
0.08
1.5
0.20
5
4.1
0.02
0.40
0.20
4
2.6
0.02
0.40
0.10
3
2.6

Exchangeable acidity (Meg/100 g)
3+
+
Al
H
P(mg/kg)
EA
1.8
0.8
3.4
2.6
1.4
0.8
2.0
2.2
1.4
0.8
2.0
2.2
1.3
0.6
2.5
1.9
1.4
0.7
3.0
2.1

Heavy metals (mg/kg)
2+
2+
2+
+
Pb
Fe
Ni
V
1.6
31
2043
17.3
3.56
30
1932
11.2
1.2
20.2
55.2
2.3
1.05
5.2
15.7
1.1
0
2.5
5.3
1.07

Exchangeable acidity (Meg/100 g)
3+
+
Al
H
P mg/kg)
EA
2.8
0.8
2.2
3.6
1.6
0.6
1.4
2.2
2.0
0.4
1.4
2.4
2.5
0.5
1.2
3.0
2.0
0.6
1.3
2.6

Heavy metals (mg/kg)
2+
2+
2+
+
Pb
Fe
Ni
V
3.56
26
188.5
9.17
5.38
25
178.5
7.64
0.0
0.0
0.0
0.0
0,0
0.0
0.0
0.0
0.0
0.0
0.0
0.0

Table 3. Chemical properties of soil not affected by bush burning at Ovu.

Depth
(cm)
0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

PH
KCl
4.7
4.6
4.5
4.5
4.6

H20
4.8
4.8
4.4
4.4
4.7

Organic matter (%)
c
O.M
N
1.32
2.27 0.098
0.56
0.96 0.040
0.48
0.83 0.040
0.35
0.60 0.040
0.32
0.55 0.038

+

Na
0.07
0.04
0.04
0.05
0.06

Exchangeable bases (Meg/100 g)
+
2+
2+
K
Ca
Mg
ACEC ECEC
0.07
0.09
0.10
3
5.4
0.04
0.05
0.50
4
3.3
0.04
0.02
0.20
3
2.9
0.05
0.30
0.30
3
3.7
0.03
0.35
0.40
5
3.4

22

J. Geol. Min. Res.

Table 4. Chemical properties of soil affected by bush burning at Ovu.

Depth
(cm)
0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

pH
KCl
3.7
3.7
3.7
3.8
3.6

H2O
4.4
4.5
4.7
4.6
4.4

Organic matter (%)
c
O.M
N
0.81
1.33
0.76
0.28
0.48
0.81
0.36
0.62
0.18
0.28
0.48
0.10
0.24
0.41
0.009

+

Na
0.04
0.04
0.05
0.03
0.03

Exchangeable bases (Meg/100 g)
K+
Ca2+ Mg2+ ACEC
ECEC
0.04 0.30
0.20
3
3.00
0.03 0.50
0.40
5
3.40
0.02 0.90
0.80
3
4.2
0.04 0.80
0.80
3
4.1
0.03 0.70
0.70
3
3.8

Exchangeable acidity (Meg/100 g)
Al3+
H+
EA
P mg/kg)
2.0
0.4
2.4
1.4
2.0
0.4
2.4
1.4
2.0
0.4
2.4
1.4
1.8
0.6
2.4
1.3
1.9
0.4
2.3
1.4

Heavy metals (ppm)
Pb
Fe2+
Ni2+
V+
3.56
30
175.5
8.66
7.4
31
194.3
12.7
0.0
0.0
0.00
0.0
0.0
0.0
0.00
0.0
0.0
0.0
0.00
9.17
2+

Table 5. Chemical properties of soil not affected by water erosion at Agbor.

Depth
(cm)
0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

pH
KCl
4.7
3.9
3.8
3.8
3.7

H2O
5.4
5.0
4.8
4.9
4.8

Organic matter (%)
C
O.M
N
1.28
2.20 0.096
0.52
0.90 0.049
0.56
0.96 0.049
0.52
0.90 0.046
0.50
0.86 0.046

+

Na
0.04
0.04
0.09
0.08
0.07

Exchangeable bases (Meg/100 g)
K+ Ca2+ Mg2+
ACEC
ECEC
0.6 1.0
0.20
4.0
4.0
0.6 1.1
0.40
3.5
4.1
0.8 1.1
0.10
3.6
3.6
0.7 1.0
0.10
3.2
2.9
0.8 0.8
0.10
3.0
2.8

Exchangeable acidity (Meg/100 g)
Al3+ H+
P Mg/kg
EA
2.8 0.4
5.0
2.3
2.8 0.4
2.0
3.2
1.0 2.8
1.8
6.0
1.7 0.5
1.7
2.2
1.8 0.4
1.8
2.2

Heavy metals (mg/kg)
Pb
Fe2+
Ni2+
V+
5.33
177
177.3 6.62
5.33
28
177.9 0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

Exchangeable acidity (Meg/100 g)
3+
+
Al
H
P(mg/kg)
EA
1.8
0.8
2.5
2.6
1.2
0.8
2.5
2.0
1.4
0.6
1.4
2.0
1.2
0.7
1.4
1.9
1.3
0.5
1.3
1.8

Heavy metals (mg/kg)
2+
2+
2+
+
Pb
Fe
Ni
V
5.33
40.0
191.4 10.1
7.11
28.00 179.7
7.4
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00

2+

Table 6. Chemical properties of soil affected by water erosion at Agbor.

Depth
(cm)
0 - 20
20 - 45
45 - 85
85 - 125
125 - 200

pH
KCl
5
5.2
5.2
5.2
5.1

H2O
5.5
5.3
6.2
6.1
6.2

Organic matter (%)
C
O.M
N
0.28
0.48 0.026
0.32
0.55 0.026
0.20
0.34 0.018
0.21
0.36 0.018
0.20
0.34 0.016

+

Na
0.08
0.05
0.06
0.05
0.04

Exchangeable bases (Meg/100 g)
+
2+
2+
K
Ca
Mg
ACEC ECEC
0.07
0.60
0.10
4.5
3.9
0.05
0.50
0.20
4.5
3.7
0.05
0.50
0.20
3.5
3.3
0.05
0.50
0.10
3.2
3.2
0.05
0.40
0.10
3.3
2.9