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Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from Jawaharlal Nehru University, New Delhi, India

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Termites are ecosystem engineers who transform soil and sediments and make mounds. They transport and mix large quantities of sediments across the horizons of the mounds, modify their immediate environment at different depths. We have tried to understand the role of termites in weathering and geochemical transformations of homogeneous sediments of termite mounds of Delhi ridge area. The samples and respective parent sediments were collected from the seven locations of Jawaharlal Nehru University, New Delhi. It has been observed that bioturbation of termites caused fining of the mound samples compared to the parent sediments. The mound samples show higher weathering than the parent sediments. Carbonate precipitation in the alkaline conditions imposed by termites could have enriched Ca and Mg. Whereas, the clay enrichment caused K, Al enrichment. Fe got enriched in the oxic condition of mounds. Ti and Zr got enriched by the enrichment of finer grains of their minerals already present in the parent material. The enrichment of Co, Ni, Cu, Cr, and V show the biogeochemical role of the termites. The organic carbon brought by the termites, and iron oxides, both enriched phosphorus in the mounds. It has found that the termite mounds also have potential in sequestering CO2 by accumulating organic matter, precipitating carbonate minerals, and increasing chemical weathering of silicate minerals.
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Open access e-Journal
Earth Science India eISSN: 0974 8350
Vol. 10 (III), July, 2017, pp. 94 - 107
http://www.earthscienceindia.info/
Biological Weathering and Geochemical Fractionation by
Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India
Swati Singh1, Anurag Chaudhary1, Sumi Handique2, Saurabh K. Singh1 and
Jayant K. Tripathi1*
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India
2 Department of Environmental Sciences, Tezpur University, Assam, India
*Corresponding Author E-mail: jktrip@yahoo.com
ABSTRACT
Termites are ecosystem engineers who transform soil and sediments and make
mounds. They transport and mix large quantities of sediments across the horizons of the
mounds, modify their immediate environment at different depths. We have tried to
understand the role of termites in weathering and geochemical transformations of
homogeneous sediments of termite mounds of Delhi ridge area. The samples and
respective parent sediments were collected from the seven locations of Jawaharlal Nehru
University, New Delhi. It has been observed that bioturbation of termites caused fining of
the mound samples compared to the parent sediments. The mound samples show higher
weathering than the parent sediments. Carbonate precipitation in the alkaline conditions
imposed by termites could have enriched Ca and Mg. Whereas, the clay enrichment
caused K, Al enrichment. Fe got enriched in the oxic condition of mounds. Ti and Zr got
enriched by the enrichment of finer grains of their minerals already present in the parent
material. The enrichment of Co, Ni, Cu, Cr, and V show the biogeochemical role of the
termites. The organic carbon brought by the termites, and iron oxides, both enriched
phosphorus in the mounds. It has found that the termite mounds also have potential in
sequestering CO2 by accumulating organic matter, precipitating carbonate minerals, and
increasing chemical weathering of silicate minerals.
Keyword: Termite, Bioturbation, Geochemistry, Weathering, Trace elements
INTRODUCTION
Termite mounds are earthen nests commonly found all over the tropics and subtropics
region of the world. Termites (Isoptera) are the most significant soil ecosystem engineers in the
tropics and play a key function in the operation of many tropical and subtropical ecosystems
(Bignell, 2006). The functional domain (physical sphere of influence at the point scale) of termite
is termed as termitosphere (Lavelle et al., 1997; Dangerfield et al., 1998: Jouquet et al., 2006).
Termites build their mounds using aggregates of soil material from several meters depth which
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
95
results in a huge quantity of soil bioturbation (Grassé, 1984). Termites typically (passively) select
soil material for feeding, as mound materials are more fine-grained than the surrounding soil
(Arshad, 1981; Jouquet et al., 2002; Abe et al., 2009). They also feed on dead plant material
(litter) from the surroundings. Through their building and feeding activities, they play a key role in
the dynamics of clays and soil organic matter (SOM) in many tropical ecosystems (Jouquet et al.,
2007). Numerous studies have been done on the chemical and mineralogical composition of
mounds (Semhi et al., 2008; Abe et al., 2009). It has been revealed in some studies that clay
minerals in mounds can be dissimilar from those in the adjacent soil (Mahaney et al., 1999; Sako
et al., 2009), whereas some other studies did not find any disparity (Jouquet et al., 2005).
Therefore, termites play a vital function in nutrient cycling and clay distribution in tropical and
subtropical soils (Lee and Wood, 1971; Black and Okwakol, 1997). Termites increase the fertility
of soil by increasing the porosity during the process of the mound formation. Termite mounds are
also known as nutrient accumulators, which can further increase the fertility of soil when it gets
eroded and spread over to the adjacent soil. The nutrient accumulation in the termite mound
makes it attractive for geophagy in Africa and some parts of Asia (Klaus and Schmid, 1998; Mills
et al., 2009).
Although the termites are important soil fauna and provide important ecological services,
they have not received requisite attention. The present study is a contribution to evaluate the
effect of termite activities on texture, geochemistry, mineralogy, and organic carbon content of
the loessic sediments in the Jawaharlal Nehru campus of New Delhi, India (Tripathi and Rajamani,
1999).
STUDY AREA
The study area, Jawaharlal Nehru University campus comes under the National capital
territory of Delhi (Fig. 1). The JNU campus lies on the plateau of the famous Delhi ridge at an
elevation of 250300 m height above the mean sea level, rising about 100 m above the adjacent
area. The area has a semi-arid climate with most common vegetation as deciduous trees,
xerophytic trees and shrubs. The Delhi ridge is an extension of the Aravalli hills, composed of
quartzites of the Middle Proterozoic Alwar Group of the Delhi Supergroup (Tripathi and Rajamani,
2003). The aeolian processes associated with the prevailing W to SW winds have been selectively
transporting fertile silt materials from the Thar Desert to the Delhi ridge (Tripathi and Rajamani,
1999).
MATERIAL AND METHOD
For the present study, approximately 2 kg of termite mound samples and respective
parent sediments samples were collected from seven locations on the JNU campus. For termite
mound samples (Fig. 2), small chunks were collected from various locations across the mound,
which were homogenized to form a representative sample. The respective parent sediments
material were collected from a distance of 10 m from the mound base after removing upper few
centimeters layer to avoid any surface contamination.
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
96
Fig. 1: Sampling locations of the termite mound sediments. The parent material samples were
collected from around 10 meters away of the termite mound sediments.
(a)
(b)
Fig. 2. Side (a) and top (b) view of termite mounds.
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
97
To determine the texture, the sediment samples were pretreated to deflocculate
aggregates by removing carbonate and organic content with HCl and H2O2 respectively
(Jackson, 1958). The sediment samples were then subjected to wet pipette method to extract
finer fraction (<63µm) (Galehouse, 1971; Pandarinath, 2003) using sodium hexmetaphosphate
(calgon) as the deflocculater of the clay particles. The dried weight of the samples were used
for calculation of percent weight of each size fraction after the correction for the calgon. Dry
sieving has been done for the coarser fraction (>63 µm) using set of ASTM sieves (500 µm, 350
µm, 250 µm, 171 µm, 125 µm, 88 µm, 63 µm and pan).
Homogenized samples (100 g) were ground to ~ 200 mesh (0.72 mm sieve size) in the
agate ball mill for geochemical and mineralogical analysis. The mineralogy of the processed
samples was determined using X-ray diffractograms (XRD) obtained from a Philips X’PERT
diffractometer. Geochemical analysis of the sediment samples were done by wavelength
dispersive X-ray fluorescence (XRF, PANalytical, Axios) for major oxides and trace elements.
Pellets (0.2mm thickness and 4 cm diameter) for the XRF analysis were prepared by thoroughly
mixing a few drops of 4% polyvinyl with 8 gm powered sediments samples in agate pestle. The
mixture was then pressed at 2500 psi in pellet holder to form pellets. International standards
(BHVO-2, GSP-2, MBH, SDC-1) were routinely run to assess the accuracies of analysis as well
as the calibration. The CIA has been calculated after the formula given by Nesbitt and Young
(1989) [        ], where, CaO
represents CaO in the silicate fraction only The excess of molar CaO contributed by CaCO3
minerals has been corrected by taking molar CaO equal to molar Na2O values in the formula
(Tripathi et al., 2007).
The organic matter in the sediment samples was estimated by the loss on ignition (LOI)
method (Dean, 1974). Sample (1g) weighed in a silica crucible were kept overnight in a muffle
furnace to remove moisture. After that, samples were first ignited at 5500 C for 4 hours to
combust organic matter from the sediments as CO2. Organic matter was calculated by using the
formula:     

  , where DW105 is the dry weight of the sample
after heating at 1050C and DW550 represents the dry weight of the sample after heating to 550
°C (all in g). TOC was estimated by a procedure developed by Walkely (1947) and revised by
Pathak et al. (2013).
RESULT AND DISCUSSION
The textural analysis of the samples suggests that the parent material of mounts is silty
sand sediments; whereas, the termite mound samples are mostly sandy mud (Table-1, Fig. 3).
The clay content has been found in higher proportion in the termite mounds than in the adjacent
parent materials (Table-1) due to termites’ preference for sticky finer soil material (clay rich) which
is used as a cementing material for construction of their nests (Lee and Wood, 1971; Donovan et
al., 2001). Modifications in soil texture of termite mound samples have been suggested due to the
overturning of the soil by the action of termites (Donovan et al., 2001; Jouquet et al., 2002b) in
which they easily ingest finer particles. The average bulk mineral compositions of the parent
material and termite mound, as estimated from the XRD, do not show any significant variation in
their mineral composition. They predominantly consist of quartz, feldspar, muscovite, and chlorite,
typical of the silty loessic sediments deposited on the quartzite rocks of JNU campus (Tripathi
and Rajamani, 1999).
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
98
Table-1: Textural properties of the termite mound (T) and respective parent material (P)
Fig. 3: Ternary diagram showing grain size distribution of the parent sediment samples ( ) and
termite mound samples ( ).
Type
Coarse
sand
Fine
sand
Silt
(total)
Clay
T
7.8
10.2
62
20
P
29.8
21.3
41.9
7
T
6.2
12.8
57.3
23.7
P
24
27.8
38.2
10
T
8
3.7
54.3
34
P
23
35.1
33
8.9
T
13.2
15.5
47.6
23.7
P
27.8
28.7
36.7
6.8
T
5.4
9.6
48
37
P
30.6
22.1
34.2
13.1
T
5
9.8
51.3
33.9
P
22
29.4
37.9
10.7
NEG
T
9.6
10.5
51.2
28.7
P
17.6
29.2
38
15.2
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
99
In general termite mound samples have higher organic matter and total organic carbon as
compared to the respective parent sediments (Table-2). These are found to be 2-4 times enriched
in the termite mound samples than the parent soil. The termites cause bioturbation of the soil
during the mound formation. They ingest upon the soil particles which pass through their gut,
thereby increasing the organic matter content of the soils. The increase in the organic matter
could also be the results of the fecal matter deposit of the termites on the mound. Also, the fecal
matter is used by many species of the termites as cementing material along with the clays for the
mound formation. The termites also feed on the litter thereby decomposing and which in turn
increases the concentration of the organic matter in the mound samples (Holt and Lepage, 2000;
Harry et al., 2001).
Table-2: Organic matter, total organic carbon, and CIA (all in %) of the termite mound sample
(T) and respective parent material (P).
Type
OM
TOC
CIA
T
8.2
4.2
74.0
P
2.2
1.0
64.9
T
5.8
2.8
77.1
P
2.4
1.1
62.0
T
6.6
3.5
80.7
P
2.0
0.9
66.4
T
4.4
2.4
76.3
P
1.5
0.7
68.8
T
6.2
3.5
79.3
P
2.4
1.1
72.0
T
5.5
2.6
75.7
P
2.8
1.3
71.7
T
7.4
3.6
76.4
P
3.4
1.5
70.4
Major element oxide compositions of the samples used in the present study for the termite
mound and respective parent material is given in Table-3. The parent samples show high silica
values, i.e., 67.81 78.08 %, as shown by the high quartz proportions. Whereas, the respective
termite mound samples show the relatively lower concentration of silica, i.e., 56.35 61.60 %.
Similarly, Na2O (0.82% - 1.44 %) shows higher concentration in the parent material as compared
to the termite mound samples. TiO2 concentration was found to be in the range of 0.5 - 0.9 % in
the parent sediment, whereas it was found to be in the range 0.81 to 1.06 % in the termite mound
samples. Iron oxide, FeO was found to vary between 3.38 and 4.67 in the parent material and
between 4.71 and 5.81% in the termite mounds. Exchangeable cations such as Ca, Mg and K are
also present in higher concentrations in the mound samples.
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
100
Table-3: Major oxides (%) and trace elements (ppm) chemistry of termite mound sample (T)
and respective parent material (P)
PSR
MAM
KAV
SRP
SLS
NEG
NWG
T
P
T
P
T
P
T
P
T
P
T
P
T
P
SiO2
60.6
75.1
56.4
70.8
59.0
78.1
61.5
69.4
58.4
69.5
61.6
69.2
58.5
67.8
TiO2
0.8
0.6
1.1
0.6
1.0
0.5
1.0
0.9
1.0
1.1
0.9
0.9
1.1
0.8
Al2O3
15.3
10.8
17.7
11.2
18.6
8.0
17.2
14.3
18.7
12.9
17.3
13.8
16.1
13.7
FeO
4.7
3.1
5.4
3.3
5.8
3.4
5.6
3.5
5.3
3.4
5.6
3.6
5.7
4.7
MnO
0.1
0.1
0.1
0.1
0.1
0.0
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
MgO
2.3
1.8
2.3
1.9
1.9
1.3
1.7
1.5
2.8
1.8
2.5
2.1
2.9
1.8
CaO
2.4
1.9
5.5
2.9
1.8
1.4
1.4
0.9
2.2
1.5
2.1
1.4
3.2
2.0
Na2O
0.9
1.2
0.8
1.4
0.7
1.2
0.7
0.9
0.7
0.8
0.8
1.0
0.8
1.0
K2O
2.2
1.7
2.3
2.0
2.0
1.3
2.8
2.1
2.7
2.4
2.2
2.1
2.2
1.9
P2O5
0.16
0.12
0.16
0.13
0.13
0.1
0.17
0.14
0.22
0.17
0.21
0.15
0.18
0.15
Ba
330
209
399
236
378
197
357
241
332
263
287
236
392
266
Sc
11
8
17
8
15
5
16
13
17
15
11
6
14
13
V
94
66
124
65
122
54
116
82
132
104
148
106
122
96
Cr
103
70
136
67
135
70
122
91
128
103
138
109
135
116
Co
12
3
15
4
18
3
13
11
16
6
13
6
12
4
Ni
51
37
62
35
69
27
82
53
94
83
91
74
83
54
Cu
33
27
29
15
32
21
41
27
46
31
50
33
42
19
Zn
82
73
75
65
75
69
97
82
98
86
147
126
87
78
Rb
110
94
112
96
106
74
97
113
127
136
110
110
109
102
Sr
182
158
211
184
147
126
156
134
146
128
183
164
205
179
Zr
457
400
549
352
506
439
582
511
452
455
538
410
596
414
A total of 11 trace elements were analyzed in the termite mound samples as well as the
respective parent samples. Almost all the elements in the mound samples are found to be present
in a higher concentration as compared to the respective parent material (Table-3). Ba in the parent
soil ranged between 197 ppm and 263 ppm whereas in the mound samples it was found to vary
from 287 ppm to 399 ppm. Trace elements such as Co, Cu, Ni and V are found to show maximum
variation. Cobalt in the mound samples varies between 12 and 18 ppm whereas in the parent soil
is ranges from 3 to 6 ppm. The concentration of copper in the termite mound samples are found
to range between 29 ppm and 50 ppm while in the parent soil samples it varies between 15 and
33 ppm. The nickel concentration in the mound samples is found to vary between 51 and 94 ppm
whereas in the parent sediments it has been found in the range of 27 ppm and 84 ppm.
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
101
The CIA values of the parent sediment samples have been found to range between 62
and 72% with an average of 68%. The CIA of the termite mound samples varies between 74 and
81% with an average value of 77%. This indicates that the termite mound samples contain
minerals with the higher degree of chemical weathering as compared to the respective parent
material samples. For the mound formation termites bring finer particles with the higher CIA from
the adjacent. Also, these particles pass through the gut of termite which results in the further
breakdown and geochemical changes. It is very difficult here to assign the extent of weathering
occurred in the guts of termites. The molar proportions of Al2O3, CaO + Na2O + K2O; and Al2O3,
CaO + Na2O + K2O and FeO + MgO are plotted on triangular plots, i.e., A-CN-K and A-CNK-FM,
separately (Nesbitt and Young, 1984, 1989) (Fig. 4). The parent material samples plot in the
relatively less weathered region of the A-CN-K ternary diagram, and the parent, as well as mound
samples both plot parallel to the ‘A–CN’ line. The termite mound samples plot above the parent
material, towards the A apex. In the A-CNK-FM diagram, the samples show slight enrichment of
FM component. To understand the enrichment of various elements (major and trace elements)
in the termite mound samples, their elemental values were normalized with the values of the
respective parent material samples (Fig. 5).
Fig. 4: A-CN-K and A-CNK-FM plots for parent material and termite mounds. A-CN-K plot
suggests that termite mound samples exhibit a higher degree of weathering (a), A-CNK-
FM plot indicates slight enrichment in FM content (b).
A significant loss of Na has been observed during weathering and formation of termite
mound soil. Mounds have been found enriched in exchangeable basic cations, especially Ca and
Mg, due to the presence of their carbonates precipitated during evaporation of water in the porous
mounds sediments. Similar precipitations were also observed by others (Watson, 1975; Jouquet
et al., 2005; Abe et al., 2009; Mujinya et al., 2010, 2011). The high pH for the precipitation is
maintained by the termites in the mounds as soil particles probably undergo modifications through
their gut because of the extremely alkaline pH, reaching values up to 12 (Brune and Kühl, 1999;
Brauman, 2000; Ohkuma, 2003). Al and K show a greater enrichment during the formation of
termite mounds, which is in agreement with the increase in the clay content of the termite mounds
as compared to the respective parent samples. The greater enrichment of these elements could
be possible because of fractionation of micaceous minerals to the mounds while bringing the finer
sediments to the mounds by the termites.
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
102
Fig. 5: Parent soil log normalized diagram indicates enrichment of various elements in the termite
mounds.
The enrichment in the Fe concentration could be due to the formation of iron
oxyhydroxides during the mound formation, which is responsible for reddening of the mounds
sediments. The depletion of silica in the termite mound samples is the result of the decrease in
the coarser fraction, i.e., sand enriched in quartz. The increase in the concentration of phosphorus
in the termite mound samples against the respective parent material could be due to the high
organic matter content in the termite mound samples as well as the increase in the iron oxide
concentration. They both get enriched in phosphorus, first one being available and second one
being unavailable forms (Mishra et al., 2013). Termite mound also shows enrichment of various
trace and nutrient elements such as Ba, V, Co, Cu, Ni, Zn and Zr. Nutrient enrichment in the
mounds samples could be due to the enrichment of organic matter by the activity of termites in
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
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the mound and preferential selection of fine soil particles (Liu et al., 2007; Mills et al., 2009).
Organic matter and clays provide adsorption sites for metal which could be the reason for the
enrichment of major and trace elements (Fig. 6 and 7).
Fig. 6: Variation digrams of various elements with clay percent.
Also, many trace elements such as Co, Ni, Cu, Zn are found in metalloproteins which are
vital for the metabolic processes (Frausto da Silva and Williams, 2001). Co is a key requirement
for gut bacteria in the termites (Milewski and Diamond, 2000). Ti and Zr seem to have
concentrated due to depletion of silica rich coarser grains (e.g., quartz), and in a result relative
increase in the silt size Ti and Zr phases of the sediments (Tripathi and Rajamani, 1999).
CONCLUSION
The observations from the present study on the termite mound samples suggest that (1)
bioturbation caused by the action of termite results in the fining of the soils samples compared to
the adjacent parent sediment samples, (2) the termite mound soil samples have been found more
weathered in nature than the parent sediments samples, (3) the mound samples are found to be
enriched in the exchangeable bases, such as Ca, Mg, by carbonate precipitation, K and Al by the
clay/micaceous enrichment, and other major elements such as Fe by iron oxide precipitation in
the porous aerated mounds, (4) the mound samples are found to be enriched in the trace
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
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elements with the highest enrichment for Co, Ni, Cu, Cr and V possibly due to higher clay and
organic matter concentration in the mound samples, where termite may have played their
biogeochemical role, (5) the organic carbon and iron oxides are responsible for the enrichment of
phosphorus in the mounds as available and unavailable forms, respectively, and (6) the increased
organic matter, higher weathering index and precipitation of carbonates, all indicate potential of
termites in the CO2 sequestration.
Fig. 7: Variation digrams of various elements with organic matter content.
Acknowledgement: SS acknowledges Council of Scientific and Industrial Research (CSIR) for a research
fellowship. JKT acknowledges the Department of Science and Technology (DST), India for the DST-
Biological Weathering and Geochemical Fractionation by Termites: A Case Study of Loessic Sediments from
Jawaharlal Nehru University, New Delhi, India: Singh et al.
105
PURSE research grants to Jawaharlal Nehru University. Authors duly acknowledge the reviewer and the
editor.
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(Received: 20.05.2017; Accepted: 20.07.2017)
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