Geoderma 192 (2013) 304–315

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Clay composition and properties in termite mounds of the Lubumbashi area,D.R. Congo

B.B. Mujinya a,b, F. Mees c, H. Erens a, M. Dumon a, G. Baert a,d, P. Boeckx e, M. Ngongo b, E. Van Ranst a,⁎a Department of Geology and Soil Science (WE13), Laboratory of Soil Science, Ghent University, Krijgslaan 281/S8, B-9000 Gent, Belgiumb Department of General Agricultural Sciences, Laboratory of Soil Science, University of Lubumbashi, P.O. Box 1825, Lubumbashi, Democratic Republic of Congoc Department of Geology and Mineralogy, Royal Museum for Central Africa, Leuvensesteenweg 13, B-3080 Tervuren, Belgiumd Faculty of Applied Bio-engineering, University College Ghent, Schoonmeersstraat 52, B-9000 Gent, Belgiume Department of Applied Analytical and Physical Chemistry, Isotope Bioscience Laboratory—ISOFYS, Ghent University, Coupure 653, B-9000 Gent, Belgium

⁎ Corresponding author. Tel.: +32 92644626; fax: +E-mail addresses: bazirake_4@hotmail.com (B.B. Mu

(E. Van Ranst).

0016-7061/$ – see front matter © 2012 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.geoderma.2012.08.010

a b s t r a c t

a r t i c l e i n f o

Article history:Received 17 April 2012Received in revised form 13 August 2012Accepted 17 August 2012Available online xxxx

Keywords:Macrotermes falcigerWater-dispersible clayClay mineralogySesquioxidesMicromorphologyFerralsols

The influence of Macrotermes falciger activity on clays, sesquioxides and water-dispersible clay (WDC) con-tent was investigated by a physico-chemical, mineralogical and micromorphological study of termitemound and control soil profiles at various sites near Lubumbashi, SE Katanga, D.R. Congo. X-ray diffractionreveals that the termite-mound materials are enriched in 2:1 clays, especially mica and expandable clay min-erals, and selective dissolution analyses show that they contain greater relative amounts of Mn oxides andpoorly crystalline Fe oxides, relative to the surrounding Ferralsols. The water-dispersible clay (WDC) contentis much higher (4–87 fold) in epigeal mound parts than in the control soils. Enrichment in 2:1 clays of themounds is attributed to upward transport of mica and smectite as part of soil aggregates or saprolite mate-rials used in mound construction. The difference in nature and abundance of sesquioxides between termitemound and control soil is related to a difference in moisture regime, whereby the basal part of the moundsare characterized by conditions with alternating reducing/oxidizing conditions, in contrast to the surround-ing well-drained ferralitic soils. The much greater degree of clay dispersibility in termite mound materialsthan in the surrounding soils is mainly due to differences in clay properties, primarily surface charge charac-teristics, and to differences in Fe oxide content and mode of occurrence. The high water-dispersible clay con-tent of termite mound materials is confirmed by micromorphological features, including abundant claycoatings and fragments of coatings.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Termites of the genus Macrotermes (Isoptera, sub-familyMacrotermitinae) build their mounds using aggregates of soil materialfrom up to several meters depth, and feed on dead plant material gath-ered from the surrounding area (Grassé, 1984). Through their buildingand feeding activities, they play a key role in the dynamics of clays andsoil organic matter (SOM) in many tropical ecosystems (Jouquet et al.,2007). Collection of soil material by Macrotermitinae termites istypically (passively) selective, whereby mound materials are morefine-grained than the surrounding soil (Abe et al., 2009b; Arshad,1981; Jouquet et al., 2002a). Macrotermes mounds are frequentlyenriched in soluble salts (e.g. ammonium nitrate), exchangeable basiccations (Ca2+,Mg2+, andK+), andCaCO3 compared to the adjacent top-soil (Abe et al., 2009a, 2009b; Jouquet et al., 2005; Mujinya et al., 2010,2011; Watson, 1975). Some studies have shown that clay minerals inMacrotermitinaemounds can be different from those in the surrounding

32 92644997.jinya), eric.vanranst@ugent.be

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soil (Boyer, 1982; Leprun and Roy-Noël, 1976; Mahaney et al., 1999;Sako et al., 2009; Sys, 1957), whereas other studies did not reveal anydifference (Jouquet et al., 2005). In laboratory experiments, a subtlemodification of mineralogical properties of clayminerals in soil materialreworked by fungus-growing termites has been observed (Jouquet et al.,2002b, 2007). Other studies, based on field sampling, have documenteddifferences between mound and soil materials related to the nature ofsoil sesquioxides (Abe andWakatsuki, 2010; Obi et al., 2008), and vari-ous charge properties (Mujinya et al., 2010). However, up to now, an in-tegrated study that assesses the influence of termite activity both on clayminerals and on soil sesquioxides has yet to be performed.

Some of the soil properties that can bemodified byMacrotermitinaetermite activity have great influence on structural features, such as bulkdensity and structural stability (Holt and Lepage, 2000; Jouquet et al.,2011), as documented by various studies (e.g. Aloni, 1975; Contour-Ansel et al., 2000; Garnier-Sillam et al., 1988; Jouquet et al., 2003,2004). In this type of study, a distinction should be made betweenmacro-aggregate stability, reflected by water-stable aggregate abun-dance, and micro-aggregate stability, reflected by dispersible clay con-tent (Amézketa, 1999; Quirk and Murray, 1991). To our knowledge,no information exists on clay dispersibility in termite moundmaterials.

Table 1General information on sites and classification of the selected pedons.

Site 1 Site 2 Site 3 Site 4

Coordinates S 11° 36′ 1.1″E 27° 29′ 7″

S 11° 35′ 34.0″E 27° 28′ 47″

S 11° 34′18.18″E 27° 29′ 2″

S 11° 36′28.1″E 27° 28′35.9″

Parent rocks Kakontwedolomite

Conglomerate Stratifieddolomite

Shale

Sys and Schmitz(1959)

Red latosol Yellowish-redlatosol

Red latosol Yellowlatosol

WRB, 2006a,c Ferralsol Ferralsol Ferralsol FerralsolElevation 1281 m 1304 m 1323 m 1268 mSlope positionb Lower slope Upper slope Crest or

summitLowerslope

a IUSS (2006).b FAO (2006).c Ngongo et al. (2009).

Table 2Surface charge properties of the material of selected termite-mound units and the con-trol soils at Sites 1 to 3 (after Mujinya et al., 2010).

Properties Sampling units

Central hive Mound foot Control soil

pH0.002 6.7 (1.21)a 5.9 (0.54)a 4.7 (0.15)apH0 3.3 (0.09)a 3.3 (0.07)a 5.2 (0.66)bpH0–pH0.002 −3.4 (1.27)a −2.6 (0.48)a 0.4 (0.79)bσp (cmolc kg−1) at soil pH −4.9 (0.36)a −5.0 (0.22)a −2.4 (0.55)bCECT (cmolc kg−1) 9.4 (2.46)a 6.8 (0.77)a 2.4 (0.09)bCECB (cmolc kg−1) 9.0 (2.76)a 6.7 (0.87)a 2.1 (0.18)bAEC (cmolc kg−1) 0.1 (0.01)a 0.1 (0.01)a 0.5 (0.23)aCECT–AEC (cmolc kg−1) 9.2 (2.45)a 6.7 (0.77)a 2.0 (0.26)bσp/CECT (%) 59.8 (16.4)a 75.1(7.2)a 99.8(24.0)a

pH0=point of zero charge; σp=permanent surface charge; CECT=total cationexchange capacity; CECB=base cation exchange capacity; AEC=anion exchangecapacity; CECT–AEC=net negative charge. Mean values with the same letter are notsignificantly different (Pb0.05).

305B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

In soils, clay dispersibility is influenced by various properties, suchas clay content, composition and surface charge characteristics(Chorom and Rengasamy, 1995; Gillman, 1974), electrolyte composi-tion and concentration (Emerson, 1971; Gupta et al., 1984), Fe, Al andSi oxide contents (Goldberg and Forster, 1990; Pinheiro-Dick andSchwertmann, 1996), and organic matter content (Amézketa, 1999).The fraction of clay that disperses in water (water-dispersible clay,WDC) controls a range of soil physical properties such as swelling, fri-ability, hydraulic conductivity, surface sealing, crusting, and suscepti-bility to erosion (Kjaergaard et al., 2004).

In the miombo ecosystem of SE Katanga, Democratic Republic ofCongo (D.R. Congo), large Macrotermes falciger mounds (~8 m high,~15 m wide) are common, with typical densities of 3 to 5 moundsper hectare (Aloni, 1975; Mujinya et al., 2011; Sys, 1957). Thesemounds represent a large volume of material that will be added tothe surrounding soils upon degradation, or when debris is spreadover the soil surface during land clearing and preparation. Thus,knowing the nature of mound materials, including water-dispersibleclay content, is important for the proper management of these soils.In the Lubumbashi area, SE Katanga, crop yields have been reportedto be lower at former mound sites, and surface sealing has been ob-served within those circular zones (Mujinya, unpublished data), indi-cating a negative effect on soil structure that can outweigh theexpected benefits from various compositional features of moundmaterials.

The present study investigates differences in clay composition andproperties between termite mounds and surrounding Ferralsols atvarious sites near Lubumbashi, D.R. Congo. It aims to assess the effectsof Macrotermes activity on the composition and distribution of clayminerals and Fe-, Al- and Mn-oxides, and to relate these effects towater-dispersible clay behaviour of mound materials.

2. Materials and methods

The study was conducted in the northern part of the Lubumbashiregion, Katanga, D.R. Congo (11°34′ to 11°37′S, 27°28′ to 27°30′E).The climate of Lubumbashi is classified as Cws6 following Köppenclassification system, characterized by a rainy season (November toMarch), a dry season (May to September), and two transition months(October, April). Mean annual precipitation is 1270 mm with ex-treme values of 717 and 1770 mm. Mean annual temperature isabout 20 °C; the coolest month is July (15.6 °C), and the warmest isOctober (23 °C) (Malaisse, 1974; Mbenza, 1990). The primary vegeta-tion of the Lubumbashi region is miombo woodland (Malaisse, 1974).The strong anthropogenic degradation of the vegetation, mainly char-coal production, resulted in woodland being substituted by a second-ary grass savannah in the peri-urban zone of Lubumbashi (Malaisse,1990).

The bedrock of the Lubumbashi region consists of a ~10,000 mthick sedimentary succession that belongs to the NeoproterozoicKatangan Supergroup (Kampunzu and Cailteux, 1999; Kampunzu etal., 2000). Based on the regional occurrence of two conglomerateunits, the Katangan sedimentary succession is subdivided in threelithostratigraphic groups, i.e. from base to top the Roan, Nguba andKundelungu Groups (Cailteux, 2003). The Roan Group comprisessiliciclastic and dolomitic rocks, whereas the Nguba and KundelunguGroups largely consist of siliciclastic rocks, with one major carbonateunit occurring as part of the Nguba Group (Kakontwe Limestone)(Batumike et al., 2006).

2.1. Materials

Termite mounds were selected based on soil type and on the na-ture of the parent material (Table 1). Soils at Site 1 and 3, derivedfrom dolomitic parent materials, are red (2.5YR 5/6, moist), deep,clayey or sandy clayey, well drained, and highly weathered. The soil

at Site 2, derived from conglomerate, is yellowish-red (5 YR 5/6,moist), deep, sandy clayey, well drained, and highly weathered. Thesoil at Site 4, derived from shale, is strong brown to yellowishbrown (7.5YR 5/8 to 10YR 5/4, moist), with a silty loam texture, mod-erately well drained, and highly weathered (Sys and Schmitz, 1959).The soils at all sites are classified as Ferralsols in the WRB classifica-tion system (Ngongo et al., 2009). Sites 1 to 3 were subjected to anearlier study of surface charge properties of mound materials(Mujinya et al., 2010), reported here in part in Table 2. In summary,compared to the control soil at each site, the termite moundmaterialshave a lower (1.6-fold) point of zero charge (pH0), lower (5-fold) ac-tual anion exchange capacity (AEC), much greater (3.2 to 4.6-fold) ac-tual base cation exchange capacity (CECB), and greater (~2-fold)amount of permanent negative charge (σp).

2.2. Mound and soil sampling

Mound and soil sampling strategies have been described else-where (Mujinya et al., 2010, 2011). At each of the first three sites(Sites 1 to 3), a profile of ~7 m height/depth and ~1.25 m width,extending from the top of the mound down through the various epi-geal units (outer crust, inner section, central hive) and into themound foot, was dug by hand within a large termite mound (~5 mhigh, ~15 m wide) (Fig. 1a). At each site, a soil profile was also exca-vated, ~7 m away from the edge of the mound, outside the zone withnoticeable termite activity (control soil). At Site 4 (Site 2 in Mujinyaet al., 2011), a cross-section of a termite mound (~5 m high, ~3 mdeep, ~18 m wide), extending laterally into the soil around themound (~3 m deep, ~9 m wide), was prepared (Fig. 1b), and a1×1 m sampling grid was imposed on the surface of the cross-

306 B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

section. At Sites 1 to 3, bulk samples for physico-chemical analyseswere taken for every mound-profile unit and for the control soil(Mujinya et al., 2010, 2011). At Site 4, bulk samples were collectedfor all compartments of a 1×1 m grid covering the entire transect(Mujinya et al., 2011), but only samples along the central column ofthe mound cross-section and a column outside the mound (controlsoil) were considered for this study. Undisturbed samples for a micro-morphological study were taken for all mound units (SP to OC; seeTables 3 and 5) at Sites 1 and 4, for selected intervals at Site 2 (CH,IS) and Site 3 (CH, IS, MF), and from the control soil at Sites 1 and 2.

2.3. Laboratory procedures

Analyses were conducted on air-dried fine earth (b2 mm). Totalclay (TC) content was determined using the pipette method, after

Centra

Inner s

± 5.7 m high

Soil surface

Pro

a

1.

Inner s

b Intact termite mound

18 + 9 m

Fig. 1. Photographs of two studied termite mounds during sampling. (a) Mound profile at Smite mound in the background.

removal of organic matter (H2O2 treatment) and carbonates (reactionwith acetic acid buffer) (van Reeuwijk, 2002). Water-dispersible clay(WDC) content was determined by mixing 10 g of soil with 400 ml ofdeionized water in a 1 L sedimentation bottle, shaking overnightwithout a dispersing agent, followed by clay content determinationusing the pipette method (van Reeuwijk, 2002).

Soil pH was measured potentiometrically in a 1:2.5 (W/V) suspen-sion, both in water and in 1 M KCl. Total organic carbon (Corg) andtotal inorganic carbon (TIC) were determined according to ISO10694 (2006) with a TOC-analyser (TOC-5050A Shimadzu), and TICwas expressed as CaCO3 equivalent. CEC (1 M NH4OAc at pH 7) wasdetermined following standard procedures (Van Ranst et al., 1999).Oxalate-extractable and dithionite–citrate–bicarbonate (DCB) ex-tractable Al, Fe andMn (Alo, Feo, Mno; Ald, Fed, Mnd) were determinedby selective extraction (van Reeuwijk, 2002), followed by inductively

l hive

ection

Outer crust

file

25 m

Mound foot

ection

3 m

± 5 m

ite 1, with indication of mound units. (b) Mound cross-section at Site 4, with intact ter-

Table 3Texture, total clay (TC) content, pH, CaCO3 content, and organic matter (Corg) content,for termite-mound profiles and control soils at Sites 1 to 4.

Site Unit Height/depth(cm)

Texture TC(g kg−1)

pH CaCO3

(g kg−1)Corg(g kg−1)

H2O KCl

1 OC 520–570 HC 598.4 4.8 4.1 0.0 10.2IS1 440–520 C 562.7 4.8 5.2 0.0 8.4CH 250–440 C 576.5 7.3 6.5 0.0 6.0IS2 70–250 C 580.0 4.8 4.6 0.5 7.1MF1–IS2 0–70 HC 600.9 4.3 4.2 0.9 13.1MF1 0–76 SiC 565.9 6.8 6.6 0.9 3.9MF2 76–210 C 557.5 7.6 7.4 1.9 1.7SL–MF2 210–280 SiC 531.7 8.0 7.5 3.3 1.1SL 280+ C 405.9 7.9 7.5 2.5 1.0CS1 0–100 C 552.0 4.4 4.3 0.0 0.3CS2 100–200 C 578.0 5.1 4.2 0.0 2.3

2 OC1 458–478 C 430.0 4.9 3.9 0.1 7.2OC2 409–458 C 424.8 4.9 3.7 0.1 6.9IS1 311–409 C 420.0 4.5 3.8 0.4 5.8CH 166–311 C 412.0 4.4 3.6 0.8 9.8IS2 0–166 C 420.0 3.7 3.6 0.6 12.0SL 0–70 CL 320.0 3.6 3.5 0.2 2.9SP1–SL 70–122 CL 330.4 3.7 3.3 0.0 2.6SP1 122–167 CL 290.0 4.4 4.3 0.0 1.9SP2 167+ L 230.0 7.8 7.7 0.4 2.7CS1 0–100 CL 338.0 5.0 5.1 0.0 2.9CS2 100–200 SiL 203.0 5.0 4.2 0.0 0.0

3 OC1 370–420 C 460.0 5.3 4.5 0.0 13.1OC2 271–370 C 520.0 5.1 4.3 0.3 5.9CH 170–271 C 512.8 7.7 6.8 0.0 3.2IS 68–170 C 520.0 6.9 6.5 0.5 5.0MF–IS 68–0–58 C 510.0 6.9 6.5 0.5 5.1MF 58+ C 514.4 5.2 4.7 0.4 4.3CS1 0–100 CL 318.0 5.0 4.0 0.0 21.9CS2 100–200 C 486.0 5.0 4.1 0.0 2.2

4 OCR 400–500 HC 694.6 6.0 5.4 0.0 11.3CH1 300–400 HC 686.7 8.1 7.5 1.0 6.1CH2 200–300 HC 695.7 8.1 7.6 1.5 4.2IS2 100–200 HC 685.6 8.3 7.8 8.7 2.3MF–IS2 0–100 HC 675.8 8.5 7.9 3.9 2.0MF 0–100 SiC 646.4 8.6 7.9 6.7 1.5SL 100–200 SiC 632.4 8.6 7.7 2.1 2.8SL–SP 200–300 C 580.9 6.0 4.8 0.0 1.7SP1 300–400 SiC 478.2 8.5 7.6 0.0 2.9SP2 400–500 SiC 447.2 8.6 7.7 0.0 2.4CS1 0–100 HC 730.0 5.3 4.1 0.0 0.4CS2 100–200 SiC 500.0 4.8 4.2 0.1 3.1

OC outer crust; OCR outer crust remnant; IS, IS1, IS2 inner section; CH, CH1, CH2 centralhive; MF, MF1, MF2 mound foot; SL stone layer; SP1, SP2 saprolite; MF–IS, MF–IS2, MF1–IS2, SL–MF2, SL–SP, SP1–SL transitional units; CS1, CS2 control soil.HC heavy clay; C clay; SiC silty clay; CL clay loam; SiL silt loam.

307B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

coupled plasma-optical emission spectroscopy analysis (ICP-OES720-ES Varian).

For mineralogical analysis, the total clay (b2 μm) fraction was sep-arated by successive sedimentation after dispersion with a Na2CO3

solution. Fine clay (b0.2 μm) was obtained by high-speed centrifuga-tion of suspensions of the total clay fraction (van Reeuwijk, 2002).X-ray diffraction (XRD) analysis was performed for non-orientedpowder samples of the total clay. For the fine clay, oriented sampleson glass slides were used, after Mg-saturation, Mg-saturationfollowed by glycolation, K-saturation, and K-saturation followed byheating at 250 °C. XRD patterns were recorded with a Philips diffrac-tometer (PW3710), using CuKα radiation (40 kV, 30 mA) and a scan-ning speed of 2.5 s per 0.02° 2θ.

Thin sections, mainly 9×12 cm large, were made for resin-impregnated undisturbed samples following standard methods(Murphy, 1986) and described using the concepts and terminologyof Stoops (2003).

2.4. Statistical analyses

A principal component analysis (PCA) was carried out on the dataset for 18 physico-chemical variables of termite mound materials toelucidate major variation and covariation patterns. A correlation ma-trix for clay dispersion parameters and selected physico-chemicalproperties was also calculated. All statistical calculations were carriedout using Statistica 7.1 for Windows using a significance level of 0.05.

3. Results

3.1. General physico-chemical properties

Most termite mounds contain a certain amount of CaCO3, in con-trast to the control soils (Table 3). CaCO3 content is greater at Sites1 and 4 than at both other sites. Corg contents are generally higherin the epigeous parts than in subsurface intervals and in controlsoils, with one exception (Site 3). The average CEC of termite-mound material is 1.7 to 2.3 times higher than that of the controlsoils.

3.2. Clay mineralogy

The total clay fraction of the control soils at all sites is overall dom-inated by kaolinite, with variable amounts of quartz, goethite and he-matite; mica occurs in significant quantities only at Site 4 (Table 4).The termite mound samples have a mineral composition similar tothat of the associated control soil, but typically with the additional oc-currence of mica. Besides, other clay minerals are present in some ter-mite mound samples, including 2:1 clays (1.4 nm reflection; CH1, Site4) and probably mixed-layer minerals, based on 2.8 nm reflections(CH, Site 1; MF, Site 3) and a broad 1.1 nm peak (SP2, Site 2). Thefine clay fraction of the control soils is dominated by kaolinite(Table 4; Fig. 2). The fine clay in the mound materials is equally richin kaolinite, but it also contains abundant smectite in three out offour studied mounds, as well as significant amounts of mica andmixed-layer clay minerals at all sites. The largest amount of smectiteand mixed-layer clays occurs in the SP2 interval at Site 2, where thecontrol soil also contains an admixture of these minerals.

3.3. Sesquioxide content and composition

At all sites, the average Fed content is lower for the epigeous partof the termite mound than for the subsurface part and for the controlsoil, which is more clearly expressed for Sites 2 and 4 (Table 5). Incontrast, the average Feo content is generally higher for the termite-mound profiles than for the surrounding soils. As a consequence,there is a clear difference in Feo/Fed ratio between both types of ma-terials, especially for Sites 2 and 4, albeit with low values for allsites (b0.08). Fed contents in epigeous mound parts are lowest atSite 4 and highest at Site 1.

The average Ald content of the epigeous part is slightly higher thanthat of the subsurface parts at each site, and it is generally lower thanthat of the control soil (CS1). The difference in Ald content betweentermite mound and control soil is highest at Site 4 (Table 5). Mnd

and Mno contents are higher in the termite-mound profiles than inthe control soils at all sites. The highest values for both parametersare recorded for the mound foot unit at Sites 1, 3 and 4, and for thesaprolite unit at Site 2.

3.4. Texture and water-dispersible clay content

TC contents are generally somewhat higher in the epigeousmound units than in the control soils and in the subsurface parts(Table 3). Texture classes range from clay to heavy clay in the epige-ous units, to loam in the subsurface units, and to silt loam in the

Table 4Mineralogical composition of the clay fraction and fine clay fraction of termite-mound materials and control soils, based on XRD analysis, for Site 1 to 4.

Site Height/depth(cm)

Unit Clay (b2 μm) Fine clay (b0.2 μm)

Qr Fd Ca Go He Ka Mi Sm Ml Ka Mi Ch Sm Ml

1 250–440 CH ++ − (+) ++ + + (+) − (+) +++ (+) ++ (+)280+ SL ++ (+) (+) ++ + ++ (+) − − +++ (+) ++ −0–100 CS1 + (+) − + + + − − − +++ − + − −

2 166–311 CH +++ + − ++ + ++ + − − +++ + + (+)167+ SP2 +++ (+) − ++ − ++ + − + +++ + +++ +0–100 CS1 +++ (+) (+) ++ + ++ (+) − − +++ (+) + (+)

3 170–271 CH + (+) − − ++ +++ + − − +++ + + (+)58+ MF + (+) − − + +++ + − (+) +++ (+) + (+)0–100 CS1 + (+) − − + +++ (+) − − +++ − − −

4 300–400 CH1 − + − − − +++ +++ (+) − ++ (+) (+) (+)400–500 SL − + + + − +++ +++ − − + + − (+)400–500 CS1 − + − − − ++ +++ (+) − ++ − (+) −

Qr, quartz; Ka, kaolinite; Go, goethite; He, hematite; Mi, mica; Fd, feldspar; Ca, calcite; Ch, chlorite; Sm, smectite; Ml, mixed-layer clays.+++, many; ++, common; +, few; (+), very few; −, absent (based on peak intensities).

308 B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

surrounding soil. At Sites 1 and 2, the TC content of the subsurfacemound parts is similar to that of the control soils at the correspondingdepth. Site 4 has the highest TC contents, both for the termite-moundprofile and for the control soil (Table 3).

WDC contents are generally much higher for the termite moundsthan for the control soils (Fig. 3). The average WDC contents of theepigeous mound units are 4 to 87 times higher than those of the con-trol soils, whereas TC contents are only up to double the control soilvalue (Table 3). The interval with the highest WDC contents is notthe same at all sites (MF1–IS2 at Site 1, IS2 at Site 2, IS at Site 3, CH1

at Site 4). The average WDC content of the epigeous parts is highestat Sites 1 and 4. The clay-dispersion ratio (CDR), defined as the ratiobetween WDC and TC values, generally follow the trend of WDC con-tents. It ranges from 0.30 to 0.60 for termite mound materials, andfrom 0.01 to 0.38 for the control soils.

Applying principal component analysis to the available data, half(52.0%) of the total variance can be explained by the first two princi-pal components (Fig. 4). Clay dispersibility appears to be most relatedto the first component, which explains 30.3% of the total variability.This axis separates samples with high WDC, CDR, TC, Alo, Ald Ald/Fed, Alo/Feo and CEC values from samples with high Fed content.Axis 2 (21.7% of the total variability) groups samples with highCaCO3, Feo, Mno, Mnd, Feo/Fed, Mnd/Fed and pH values. The correlationmatrix for clay dispersion and selected physico-chemical propertiesin termite moundmaterials (Table 6) shows that WDC content is pos-itively correlated with TC, pH, CaCO3, Alo, Ald/Fed, Feo/Fed, Alo/Feo andCEC values, and that it is negatively correlated with Fed content. CDRonly significantly correlated with Fed and CEC values.

3.5. Micromorphological features of clay and sesquioxide occurrences

At Site 1, clay coatings and infillings occur in the OC and SL inter-vals (Fig. 5a), and they are absent in all intervening units. A similarpattern is recognized for Site 4, where clay coatings/infillings onlyoccur in the outer part (OCR, CH1) and basal part (MF–IS2, MF) ofthe mound (Fig. 5b and c). For Sites 2 and 3, for which thin sectioncoverage is largely limited to the central part of the mound, onlyminor amounts of clay coatings are recognized, for a single CH unitsample (Site 2). At Site 1, the clay coatings are orange brown, limpid,and partly laminated. At Site 4, the coatings are yellowish to orangebrown and lamination is more rare. At both sites, the coatings in thehighest interval (OC, OCR) are covered by micromass material in sev-eral pores (Fig. 5b). In all samples with clay coatings, part of these fea-tures are undisturbed (Fig. 5a and c), but associated deformedcoatings are generally common (Fig. 5d).

All thin sections show small aggregates of mainly orange brownlimpid fine material, grading to yellowish at Site 4. A laminated fabricis common for aggregates from all sites (Fig. 5e). At Site 1, the aggre-gates are most abundant in intervals with clay coatings, but this rela-tionship is not recognized for the other sites. The aggregates arepartly clustered, and some occurrences at Site 4 are confined tosharply delimited small patches with a different micromass than thesurrounding material (Fig. 5f). The aggregates also occur in both ref-erence soil samples, with possible associated deformed clay coatingsat one site (Site 2). Similar orange brown limpid material occurswithin or along some of the petroplinthite fragments which are pres-ent in the SL unit and in some higher intervals.

Orthic iron oxide nodules with gradual boundaries occur in alllower intervals at Site 1, from the MF1–IS2 interval downward. AtSite 4, they occur in all intervals except the outermost unit (OCR),but they are most abundant in the basal part of the profile (MF, SL,SL–SP). Iron oxide nodules also occur in most samples from Site 2.At Site 4, iron oxide hypocoatings occur in several lower units of themound. Site 4 is the site with the least reddish color of the micromass(yellowish brown), in comparison with Site 2 (orange brown) and es-pecially with Sites 1 and 3 (dark reddish).

4. Discussion

4.1. Clay composition

The present study shows that termite mound materials areenriched in 2:1 clays minerals in comparison with the control soils,where clay minerals other than kaolinite are mostly absent. Thehigher (about 2-fold) amount of permanent surface charge (σp) fortermite mound structures compared to the control soils (Table 2) iscompatible with 2:1 clay enrichment. The occurrence of montmoril-lonite in Macrotermes mounds built on kaolinitic soils of the Lubum-bashi region has previously already been reported (Fripiat et al.,1957; Sys, 1957), and similar observations have been made else-where (Boyer, 1982; Leprun and Roy-Noël, 1976; Sako et al., 2009).Our data suggest that 2:1 clay mineral enrichment is a ubiquitousphenomenon in M. falciger mounds on Ferralsols of the Lubumbashiregion. Differences in the composition and nature of the clay fractionbetween termite mounds and the surrounding soils can in principlebe explained by the introduction of materials with a different claycomposition by termites during nest construction, or by transforma-tion or neoformation of clay minerals within the mound (Boyer,1982; Fripiat et al., 1957; Leprun and Roy-Noël, 1976). Clay mineraltransformation inside the mound has been simulated in laboratoryconditions, whereby an observed increase in the proportion of

Fig. 2. XRD patterns of Na-, Mg- and K-saturated oriented fine clays, glycolation of the Mg-saturated sample and heating at 250 °C of the K-saturated sample, for termite moundmaterials and control soils at Sites 1 to 4.

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Table 5DCB-extractable Al, Fe and Mn (Xd), and oxalate-extractable Al, Fe anf Mn (Xo), for termite-mound profiles and control soils at Sites 1 to 4.

Site Unit Height/depth (cm) DCB extractable Oxalate extractable Ratios

Ald Fed Mnd Alo Feo Mno Feo/Fed Alo/Ald Ald/Fed Alo/Feo Mnd/Fed

(g kg−1)

1 OC 520–570 12.8 66.0 0.5 1.3 2.0 0.4 0.03 0.10 0.19 0.62 0.01IS1 440–520 10.8 62.7 0.5 1.0 1.6 0.4 0.03 0.09 0.17 0.59 0.01CH 250–440 10.5 63.0 0.6 1.0 1.6 0.6 0.03 0.09 0.17 0.59 0.01IS2 70-250 9.9 61.4 0.3 0.7 1.4 0.2 0.02 0.08 0.16 0.53 0.00MF1–IS2 0–70 10.8 61.6 0.5 1.0 1.9 0.3 0.03 0.09 0.18 0.53 0.01MF1 0–76 10.4 62.1 0.9 0.7 1.4 0.8 0.02 0.07 0.17 0.51 0.01MF2 76–210 10.2 61.8 1.1 0.7 1.3 1.1 0.02 0.07 0.16 0.51 0.02SL–MF2 210–280 10.5 62.4 0.7 0.7 1.3 0.6 0.02 0.07 0.17 0.57 0.01SL 280+ 11.0 89.2 0.7 0.7 1.2 0.6 0.01 0.06 0.12 0.57 0.01CS1 0–100 12.0 61.7 0.2 1.2 1.0 b0.1 0.02 0.10 0.20 1.21 b0.01CS2 100–200 12.5 65.9 0.2 1.2 0.9 b0.1 0.01 0.09 0.19 1.25 b0.01

2 OC1 458–478 7.5 49.2 0.7 0.9 1.9 0.7 0.04 0.12 0.15 0.49 0.01OC2 409–458 7.2 47.9 0.9 0.7 1.9 0.9 0.04 0.10 0.15 0.39 0.02IS1 311–409 6.9 46.6 1.0 0.8 1.7 0.9 0.04 0.12 0.15 0.50 0.02CH 166–311 6.8 44.1 0.3 1.1 1.9 0.2 0.04 0.16 0.16 0.57 0.01IS2 0–166 7.6 44.4 0.3 1.1 1.8 0.2 0.04 0.15 0.17 0.64 0.01SL 0–70 7.9 78.8 0.5 0.8 2.2 0.3 0.03 0.10 0.10 0.37 0.01SP1–SL 70–122 6.4 58.2 0.4 0.5 1.5 0.3 0.03 0.08 0.11 0.32 0.01SP1 122–167 6.5 76.1 1.9 0.6 1.8 1.9 0.02 0.10 0.09 0.35 0.02SP2 167+ 5.0 75.7 3.9 0.5 3.0 3.9 0.04 0.10 0.07 0.16 0.05CS1 0–100 9.6 83.2 0.8 0.8 0.7 0.2 0.01 0.08 0.12 1.24 0.01CS2 100–200 4.5 65.6 0.1 0.3 0.2 0.1 0.00 0.06 0.07 1.84 b0.01

3 OC1 370–420 4.9 44.5 0.2 0.8 1.6 0.1 0.04 0.16 0.11 0.51 b0.01OC2 271–370 4.1 44.2 0.3 0.7 1.4 0.2 0.03 0.16 0.09 0.46 0.01CH 170–271 3.6 44.1 0.4 0.6 0.9 0.3 0.02 0.17 0.08 0.70 0.01IS 68–170 3.8 45.0 0.5 0.8 2.7 0.4 0.06 0.22 0.08 0.31 0.01MF–IS 68–0–58 4.0 44.0 0.5 0.7 1.6 0.4 0.04 0.17 0.09 0.42 0.01MF 58+ 3.6 46.4 0.4 0.5 1.3 0.3 0.03 0.13 0.08 0.37 0.01CS1 0–100 4.0 38.5 0.1 1.2 1.0 b0.1 0.03 0.29 0.10 1.19 b0.01CS2 100–200 4.9 51.6 0.2 0.9 0.9 b0.1 0.02 0.19 0.09 0.99 b0.01

4 OCR 400–500 8.5 36.8 0.5 1.2 1.6 0.5 0.04 0.14 0.23 0.75 0.01CH1 300–400 7.7 35.8 0.6 1.2 1.9 0.6 0.05 0.15 0.22 0.61 0.02CH2 200–300 8.1 38.4 0.8 1.1 1.7 0.6 0.04 0.13 0.21 0.63 0.02IS2 100–200 7.4 35.9 0.8 1.1 3.0 0.5 0.08 0.15 0.21 0.37 0.02MF–IS2 0–100 7.6 38.0 0.9 1.0 1.9 0.6 0.05 0.13 0.20 0.53 0.02MF 0–100 6.9 35.8 1.0 0.9 1.9 0.7 0.05 0.13 0.19 0.48 0.03SL 100–200 5.3 32.1 0.5 0.9 1.7 0.3 0.05 0.18 0.16 0.56 0.01SL–SP 200–300 Nd Nd Nd 1.2 2.0 0.7 Nd Nd Nd 0.60 NdSP1 300–400 4.9 87.9 0.2 0.7 2.6 0.2 0.03 0.14 0.06 0.28 b0.01SP2 400–500 5.4 74.7 0.1 0.9 1.7 0.1 0.02 0.17 0.07 0.56 b0.01CS1 0–100 11.9 49.0 0.2 1.6 0.9 0.1 0.02 0.14 0.24 1.87 b0.01CS2 100–200 10.7 52.1 0.2 1.0 0.9 b0.1 0.02 0.09 0.20 1.15 b0.01

OC=outer crust, OCR=outer crust remnant, IS, IS1 and IS2=inner section, CH, CH1 and CH2=central hive, MF, MF1 and MF2=mound foot, SL=stone layer, SP1 and SP2=sapro-lite, MF–IS, MF–IS2, MF1− IS2, SL–MF2, SL–SP, SP1–SL=transitional units, CS1 and CS2=control soil.Nd, not determined.

310 B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

expandable layers has been attributed to the release of non-exchangeable potassium from illite interlayers, by interaction withtermite saliva and associated microorganisms (Jouquet et al., 2002b,2007). For the sites of the present study this illite-to-smectite trans-formation hypothesis (see also Boyer, 1982) is only a possible expla-nation of the occurrence of smectite and mixed layer minerals, as itdoes not account for the significant difference in mica content be-tween mound and control soil. Smectite, occurring as a discrete min-eral phase, was most likely simply brought up by termites as part ofnest construction materials, which were also mica-bearing. Theminor amounts of expandable clay minerals that occur in some con-trol soils are probably derived from the termite mounds by erosionor other types of reworking. This is supported by the higher contentof these minerals in the control soil at the site where they are mostabundant within the mound. Initial results of an ongoing study oflong cored sections beneath Macrotermes mounds in the Lubumbashiarea (Dumon, unpublished data) demonstrate the occurrence ofabundant smectite at depth at all three coring sites. Initial petro-graphical data for these levels show that smectite formed as aweathering product in the saprolite, compatible with smectite occur-rence in the fine clay fraction of derived materials.

4.2. Sesquioxides

Our results show that average Fed contents are lower in the epigeousmound part than in the surrounding soil at all sites, and that Feo con-tents are higher, in contrast to earlier findings (Abe and Wakatsuki,2010). The resulting higher Feo/Fed ratios suggest that this part of themounds contains higher relative amount of poorly crystalline oxides(Boero and Schwertmann, 1987; Pinheiro-Dick and Schwertmann,1996; Blume and Schwertmann, 1969). High Feo/Fed ratios generally in-dicate periodic redox conditions that promote dissolution of pre-existing well-crystallized oxides and inhibit formation of secondarycrystalline oxides by periodic dissolution and relatively fast precipita-tion of iron oxides (Boero and Schwertmann, 1987). The lower Fedvalues imply an overall loss of iron during these processes.Macrotermesmounds are known to be sites with frequent water saturation, relatedmainly to the local development of a fluctuating perched water tablebeneath the mound structure, where the top of poorly permeable sub-surface intervals is commonly lowered by the translocation of soil ma-terials by termites (Hesse, 1955; Turner, 2006). This is consistent withthe occurrence of iron oxide redistribution processes in the studied ter-mite mounds (Mujinya et al., 2011), suggested by the recognition of

Fig. 3.Water-dispersible clay (WDC) content, clay-dispersion ratio (CDR), and difference between total clay (TC) andWDC contents, for termite-mound profiles and control soils atSites 1 to 4. OC: outer crust; OCR: outer crust remnant; IS, IS1, IS2: inner section; CH, CH1, CH2: central hive; MF, MF1, MF2: mound foot; SL: stone layer; SP1, SP2: saprolite; MF–IS,MF–IS2, MF1–IS2, SL–MF2, SL–SP, SP1–SL: transitional units; CS1, CS2: control soil.

311B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

prominent mottling in the field and by the recognition of iron oxidenodules and hypocoatings in thin sections. Therefore, the difference iniron oxide crystallinity between termite mounds and nearby controlsoils is most likely due to alternating reducing and oxidizing conditionsin themounds, resulting from seasonal water saturation variability. Fe–Mn oxide concentrations and depletion features are abundant up toconsiderable height within the termite mound soil at Site 4 (Mujinyaet al., 2011), which is compatible with the high Feo/Fed ratios and an ab-sence of hematite in the clay fraction that is observed for this site.

Similarly, the higher Mnd content of termite mound materials ascompared to control soils is supported by morphological evidence ofFe–Mn oxide features in the mounds (Mujinya et al., 2011).

The variations in average Fed content of epigeous moundmaterialsbetween sites reflect differences in the abundance of well-crystallizediron oxides (goethite and hematite) as part of the clay fraction. Ald isprobably mainly derived from Al-substituted iron oxides. The degreeof crystallinity of iron oxides decreases with increasing degree ofAl-for-Fe substitution (Schwertmann and Wolska, 1990; Taylor andSchwertmann, 1978). Mineralogical composition is also a factor,

whereby goethite in soils commonly has a greater degree of Al substi-tution than co-existent hematite (Schwertmann and Kämpf, 1985).The latter could explain the lower Ald content of mound and soil ma-terials at the site containing hematite as the only iron oxide (Site 3).Periodic reducing conditions favor the formation of more stableAl-substituted goethite over persistence of hematite (Schwertmannand Kämpf, 1985).

4.3. Influence of clay mineralogy and soil properties on clay dispersibility

4.3.1. Effect of physico-chemical propertiesDifferences in averageWDC content between sites are reflected by

differences in pH, for the epigeous mound units. Clay dispersion canincrease with increasing soil pH (e.g. Chorom et al., 1994; Suarez etal., 1984), in view of the relationship between pH and soil particlecharge (Chorom and Rengasamy, 1995; Qafoku et al., 2004; Sumner,1993), but no direct causal relationship between pH and WDC con-tent is apparent for the studied termite mound materials (seeTable 6). pH generally follows the trend of CaCO3 content (Tables 3

Fig. 4. Correlation circle of principal component analysis (PCA) on 18 physico-chemicalvariables of termite mound materials.

312 B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

and 6, Fig. 4; see also Mujinya et al., 2011), which therefore also cor-relates with WDC content, despite its flocculating effect. An indirectrelationship between pH and WDC content must be assumed, where-by conditions favoring calcite precipitation also promote high claymobility.

4.3.2. Effect of sesquioxidesWDC content generally decreases with increasing DCB-extractable

iron oxide content. The important effect of iron oxides on aggregatestability, especially in highly weathered soils, is well documentedand understood (e.g. Amézketa, 1999; Barthès et al., 2008; Bronickand Lal, 2005; Pinheiro-Dick and Schwertmann, 1996; Seta andKarathanasis, 1996). The stabilizing effect of sesquioxides mainly

Table 6Partial correlation matrix (r) for WDC content (g kg−1), CDR values and selected soilproperties for termite mound soils.

WDC CDR

TC 0.80*** 0.31CaCO3 0.38* 0.16Corg 0.23 0.30pH soilpHH2O 0.43** 0.33pHKCl 0.42* 0.30ΔpH −0.15 −0.15

DCB extractableAld 0.17 0.01Fed −0.60*** −0.39*Mnd −0.23 0.04

Oxalate extractableAlo 0.43* 0.15Feo −0.18 −0.11Mno −0.22 0.07

RatiosFeo/Fed 0.39* 0.22Alo/Ald 0.20 0.17Alo/Feo 0.52*** 0.30*CEC 0.45** 0.37*

*,**,***=significant at Pb0.05, Pb0.01 and Pb0.001, respectively.

acts at the level of soil microaggregates, and is attributed to their floc-culation capacity, their binding effect in the interaction between clayparticles and organic molecules, and their potential precipitation asgels on clay surfaces (Amézketa, 1999). The strong negative correla-tion (r=−0.60, Pb0.01; see also Fig. 4) between WDC and Fed con-tents is consistent with the favorable effect of iron oxides on soilaggregation.

The positive correlations (r=0.52, Pb0.01) betweenWDC contentand Alo/Feo suggest a dispersive effect of poorly crystalline Fe oxidesin termite mound soils, in which Alo and Feo seem to be linked.There is also a weak but very significant positive correlation betweenAlo and Corg contents (r=0.46, Pb0.01), suggesting a role of complex-ation by organic matter. Although there are indications for links be-tween SOM-sesquioxide interaction and dispersion (e.g. Bartoli etal., 1992), they cannot be invoked for the present study. The parame-ters for which the mentioned correlations have been noted may wellhave no causal relationship.

4.3.3. Effects of clay mineralogy and surface charge characteristicsBecause of their high physico-chemical interaction capacity (large

specific surface area, high CEC), smectitic and illitic clays are moresensitive to aggregation than low-activity clays such as kaolinite(Amézketa, 1999; Bronick and Lal, 2005). Dispersion and swelling ofclays are indirectly interrelated phenomena within the soil matrix(Frenkel et al., 1978). Soils dominated by 2:1 clay minerals, especiallyexpandable clays, are more dispersive than those dominated by 1:1minerals. This agrees with the higher dispersibility of termite-mound materials, enriched in mica and expandable clays, as com-pared to the control soils, dominated by kaolinite. The site with thehighest average CDR value for the epigeous mound units has the in-terval with highest smectite content of the fine clay fraction (Site2). However, the highest CDR values were recorded for the site withonly a small relative amount of 2:1 clay minerals (Site 3). Further-more, the σp of the control soils constitutes nearly the entirety (99.8%) of the low CECT (2.4±0.09 cmolc kg−1 soil) (Mujinya et al.,2010). These observations indicate that clay mineralogy alone cannotfully explain the difference in clay dispersibility between termitemounds and the surrounding Ferralsols.

Rather than being determined by mineralogical composition, claydispersibility in the Macrotermes mounds seems to be related to sur-face charge properties. This is suggested by the weak but significantpositive correlation between CEC and WDC content (r=0.45,Pb0.05, see also Fig. 4). Furthermore, surface charge properties ofmound and soil materials (Mujinya et al., 2010) generally reflect thetrends in the clay dispersion. The higher (3.3- to 4.6-fold) net nega-tive charge (CECT–AEC) exhibited by mound materials as comparedto that of the surrounding Ferralsols causes a considerable differencein dispersibility in water (cf. Chorom and Rengasamy, 1995). Further-more, pH0 is ~1.6 times lower for termite mounds than for the controlsoil, and pH is ~1.2 to 1.4 times higher (Mujinya et al., 2010). WDCcontent becomes negligible when soil pH is near its pH0 (Gillman,1974), which are conditions that are met in the control soil, whereaspH–pH0 values −3.6 to −2.6 for the mound materials, favoring claydispersion.

4.3.4. Significance of micromorphological featuresThe occurrence of fine clay coatings and derived features is a record

of clay dispersibility within the termite mounds. In more general terms,their presence is also a unique example of the development of clay coat-ings in recent surface deposits. The pattern observed for both moundswith the most complete thin section coverage, showing clay accumula-tion in the outer and basal part of the structure, is not clearly correlatedwith variations in other studied properties, including WDC content.Note that the latter is a measure of clay dispersibility, not of the amountof clay that has been translocated following dispersion. The occurrenceof clay coatings in the outer part of the mounds is most likely related

Fig. 5.Micromorphological features of clay occurrences (plain-polarized light). (a) Undisturbed fine clay infilling with crescent fabric (OC unit, Site 1). (b) Fine clay coating, coveredby coarser material (OCR unit, Site 4). (c) Fine clay coatings in the basal part of a termite mound (MF–IS2 unit, Site 4). (d) Deformed coatings, grading to fragmented features (ar-rows) (CH1 unit, Site 4). (e) Aggregate of orange brown fine material, with prominent lamination (SL unit, Site 1). (f) High concentration of orange brown aggregates in sharplydelimited lens with brownish micromass (arrows) (SL–SP unit, Site 4).

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to direct rainfall on the mound surface during the rainy season, and thebasal occurrence can be linked to water stagnation, as recorded bymot-tling. The absence of clay coatings in the intervening intervals is mostprobably related to a lack of illuvial clay deposition rather thanpostdepositional destruction. This is suggested by the association be-tween coatings and fragments of coatings at Site 1, implying that nocomplete destruction of clay coatings occurs. The nature of the coatingsindicates good dispersion and the occurrence of successive stages withslightly different conditions, resulting in the deposition of laminatedfine clay coatings. Coatings occurring in the outer crust formed by depo-sition following short-distance translocation. Only the formation ofcoarser coatings of micromass material that cover the fine clay coatingsin the outer part of the mounds does not require conditions with claydispersion. Although clay illuviation is recognized for several termitemounds investigated for the present study, it has previously only rarelybeen reported for this type of structure. Observations are limited to lay-ered coatings with silt and sand (Wielemaker, 1984), which might notbe illuvial.

The nature and abundance of fragments of clay coatings, as well astheir associationwith intact and deformed coatings, show that the frag-ments are largely derived from coatings that formedwithin themound.

Zones with high concentration of fragments of clay coatings and withaberrant micromass are deformed pellets (see also Wielemaker,1984), illustrating a manner in which termite activity contributes tofragmentation and translocation of illuvial clay accumulations. Frag-ments of clay coatings that occur in the control soil could be derivedfrom reworked mound material, although the deformed coatings thatare occasionally associated with these fragments suggest that clay coat-ings also formed in situ outside the mounds. Fragments of clay coatingshave been described in one earlier study (Wielemaker, 1984), and oneoccurrence of similar features has been interpreted as being derivedfrom the soil beneath the mound (Miedema et al., 1994).

The occurrence of iron oxide nodules is an expression of intensivecyclic oxido-reduction. The nodules are formed by redistribution ofiron oxides, typically reprecipitating in the form of poorly crystallinecompounds.

5. Conclusion

In agreement with some earlier reports, this study shows thatMacrotermes mounds are enriched in 2:1 layer silicates, especiallymica and expandable clay minerals, compared to the nearby Ferralsols,

314 B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

dominated by kaolinite. Our data suggest that this 2:1 clay enrichmentof Macrotermes mounds is a common phenomenon in the Lubumbashiregion, and is most probably due to upward transport of mica- andsmectite-bearing soil/saprolite material by termites. There are no indi-cations for subsequent termite-mediated illite-to-smectite transforma-tion. Selective extraction analysis shows that Macrotermes moundmaterials contain higher relative amounts of poorly crystalline Fe andMn oxides compared to the control soils. The observed difference insesquioxide abundance and forms between termite mound materialsand control soils is interpreted as the result of a difference in moistureregime between the generally well-drained ferralitic substrates andthe termite mounds that experience alternating reducing/oxidizingconditions within the basal part of the structure.

Water-dispersible clay content is much higher in epigeal parts ofMacrotermesmounds than in the surrounding Ferralsols. The similaritybetween the trends of clay-dispersion ratio (CDR) and CEC, and the sig-nificant (Pb0.05) correlation betweenWDC and Fed contents of termitemoundmaterials, suggests that the greater clay dispersibility in termitemoundmaterials ismainly due to differences in clay properties and ironoxide concentration and composition, whereby clay properties includesurface charge characteristics. Finally,micromorphological data providedirect evidence of the occurrence of clay dispersion and translocationwithin Macrotermes mounds. Thin section observations also documentcyclic variations in redox conditions.

Acknowledgments

This study was funded by the project G.0011.10 N of the Fund forScientific Research (Flanders), by the project ZRDC2008MP059 of theFlemish Interuniversity Council-University Development Co-operation(VLIR-UDC), and the Belgian Technical Cooperation (BTC).

References

Abe, S.S., Wakatsuki, T., 2010. Possible influence of termites (Macrotermes bellicosus)on forms and composition of free sesquioxides in tropical soils. Pedobiologia 53,301–306.

Abe, S.S., Yamamoto, S., Wakatsuki, T., 2009a. Physicochemical and morphologicalproperties of termite (Macrotermes bellicosus) mounds and surrounding pedonson a toposequence of an inland valley in the southern Guinea savanna zone ofNigeria. Soil Science & Plant Nutrition 55, 514–522.

Abe, S.S., Yamamoto, S., Wakatsuki, T., 2009b. Soil-particle selection by the mound-building termite Macrotermes bellicosus on a sandy loam soil catena in a Nigeriantropical savanna. Journal of Tropical Ecology 25, 449–452.

Aloni, J., 1975. Le sol et l'évolution morphologique des termitières géantes du Haut-Shaba (Rép. Zaïre). Pédologie 25, 25–39.

Amézketa, E., 1999. Soil aggregate stability: a review. Journal of Sustainable Agriculture14, 83–151.

Arshad, M.A., 1981. Physical and chemical properties of termite mounds of two speciesof Macrotermes (Isoptera, Termitidae) and the surrounding soils of the semiaridsavanna of Kenya. Soil Science 132, 161–174.

Barthès, B.G., Kouakoua, E., Larré-Larrouy, M.C., Razafimbelo, T.M., de Luca, E.F.,Azontonde, A., Neves, C.S.V.J., de Freitas, P.L., Feller, C.L., 2008. Texture andsesquioxide effects on water-stable aggregates and organic matter in some tropicalsoils. Geoderma 143, 14–25.

Bartoli, F., Philippy, R., Burtin, G., 1992. Poorly ordered hydrous Fe oxides, colloidal dis-persion and soil aggregation. II. Modification of silty soil aggregation with Fe(III)polycations and model humic macromolecules. Journal of Soil Science 43, 59–75.

Batumike, M.J., Kampunzu, A.B., Cailteux, J.L.H., 2006. Petrology and geochemistry ofthe Neoproterozoic Nguba and Kundelungu Groups, Katangan Supergroup, south-east Congo: implication for provenance, paleoweathering and geotectonic setting.Journal of African Earth Sciences 44, 97–115.

Blume, H.P., Schwertmann, U., 1969. Genetic evaluation of profile distribution of aluminum,iron, and manganese oxides. Soil Science Society of America Journal 33, 438–444.

Boero, V., Schwertmann, U., 1987. Occurrence and transformations of iron and manga-nese in a colluvial terra rossa toposequence of northern Italy. Catena 14, 519–531.

Boyer, P., 1982. Quelques aspects de l'action des termites du sol sur les argiles. ClayMinerals 17, 453–462.

Bronick, C.J., Lal, R., 2005. Soil structure and management: a review. Geoderma 124,3–22.

Cailteux, J.L.H., 2003. Proterozoic sediment-hosted base metal deposits of WesternGondwana, Abstract Volume of the Conference and Field Guidebook. 3rd IGCP-450 Meeting and Field Workshop, Lubumbashi, D.R. Congo, p. 223.

Chorom, M., Rengasamy, P., 1995. Dispersion and zeta potential of pure clays as relatedto net particle charge under varying pH, electrolyte concentration and cation type.European Journal of Soil Science 46, 657–665.

Chorom, M., Rengasamy, P., Murray, R.S., 1994. Clay dispersion as influenced by pH andnet particle charge of sodic soils. Australian Journal of Soil Research 32, 1243–1252.

Contour-Ansel, D., Garnier-Sillam, E., Lachaux, M., Croci, V., 2000. High performanceliquid chromatography studies on the polysaccharides in the walls of the moundsof two species of termite in Senegal, Cubitermes oculatus and Macrotermessubhyalinus: their origin and contribution to structural stability. Biology and Fertil-ity of Soils 31, 508–516.

Emerson, W.W., 1971. Determination of the contents of clay-sized particles in soils.Journal of Soil Science 22, 50–59.

FAO, 2006. Guidelines for Soil Description. Fourth Edition. Food and Agriculture Organiza-tion of the United Nations, Rome.

Frenkel, H., Goertzen, J.O., Rhoades, J.D., 1978. Effects of clay type and content, ex-changeable sodium percentage, and electrolyte concentration on clay dispersionand soil hydraulic conductivity. Soil Science Society of America Journal 42, 32–39.

Fripiat, J.J., Gastuche, M.C., Vielvoye, L., Sys, C., 1957. Les argiles des sols de la regiond'Elisabethville. Pédologie 7, 12–18.

Garnier-Sillam, E., Toutain, F., Renoux, J., 1988. Comparaison de l'influence de deuxtermitières (humivore et champignonniste) sur la stabilité structurale des solsforestiers tropicaux. Pedobiology 32, 89–97.

Gillman, G.P., 1974. The influence of net charge on water dispersible clay and sorbedsulphate. Australian Journal of Soil Research 12, 173–176.

Goldberg, S., Forster, H.S., 1990. Flocculation of reference clays and arid-zone soil clays.Soil Science Society of America Journal 54, 714–718.

Grassé, P.P., 1984. Termitologia. Tome, 2. Fondation des Societe´s, Constructions,Masson, Paris.

Gupta, R.K., Bhumbla, D.K., Abrol, I.P., 1984. Effect of sodicity, pH, organic matter andcalcium carbonate on the dispersion behaviour of soils. Soil Science 137, 245–251.

Hesse, P.R., 1955. A chemical and physical study of the soils of termite mounds in EastAfrica. Journal of Ecology 43, 449–461.

Holt, J.A., Lepage, M., 2000. Termites and soil properties. In: Abe, T., Bignell, D.E.,Higashi, M. (Eds.), Termites: Evolution, Sociality, Symbioses, Ecology. Kluwer Aca-demic Publishers, Dordrecht, pp. 389–407.

ISO 10694, 2006. Part IIIa. Sampling and analysis of soil. Determination of Organic Mat-ter Content. ISO, Geneva.

IUSS Working Group WRB, 2006. World Reference Base for Soil Resources 2006. WorldSoil Resources Reports No. 103. FAO, Rome.

Jouquet, P., Lepage, M., Velde, B., 2002a. Termite soil preferences and particleselections: strategies related to ecological requirements. Insectes Sociaux 49, 1–7.

Jouquet, P., Mamou, L., Lepage, M., Velde, B., 2002b. Effect of termites on clay mineralsin tropical soils fungus-growing termites as weathering agents. European Journalof Soil Science 53, 521–527.

Jouquet, P., Mery, T., Rouland, C., Lepage, M., 2003. Modulated effect of the termiteAncistrotermes cavithorax (Isoptera, Macrotermitinae) on soil propertiesaccording to the structures built. Sociobiology 42, 403–412.

Jouquet, P., Tessier, D., Lepage, M., 2004. The soil structural stability of termite nests:role of clays in Macrotermes bellicosus (Isoptera, Macrotermitinae) mound soils.European Journal of Soil Biology 40, 23–29.

Jouquet, P., Barré, P., Lepage, M., Velde, B., 2005. Impact of subterranean fungus-growing termites (Isoptera, Macrotermitiane) on chosen soil properties in aWest African savanna. Biology and Fertility of Soils 41, 365–370.

Jouquet, P., Bottinelli, N., Lata, J.-C., Mora, P., Caquineau, S., 2007. Role of the fungus-growing termite Pseudacanthotermes spiniger (Isoptera, Macrotermitinae) in thedynamic of clay and soil organic matter content. An experimental analysis.Geoderma 139, 127–133.

Jouquet, P., Traoré, S., Choosai, C., Hartmann, C., Bignell, D., 2011. Influence of termiteson ecosystem services provided by termites. European Journal of Soil Biology 47,215–222.

Kampunzu, A.B., Cailteux, J., 1999. Tectonic evolution of the Lufilian arc (Central AfricaCopperbelt) during the Neoproterozoic Pan-African orogenesis. In: Cox, R., Ashwal,L.D. (Eds.), Proterozoic Geology of MadagascarGondwana Research 2, 401–421.

Kampunzu, A.B., Tembo, F., Matheis, G., Kapenda, D., Huntsman-Mapila, P., 2000. Geo-chemistry and tectonic setting of mafic igneous units in the NeoproterozoicKatangan Basin, Central Africa: implication for Rodinia Break up. Gondwana Re-search 3, 125–153.

Kjaergaard, C., de Jonge, L.W., Moldrup, P., Schjønning, P., 2004. Waterdispersiblecolloids: effects of measurement method, clay content, initial soil matric potential,and wetting rate. Vadose Zone Journal 3, 403–412.

Leprun, J.C., Roy-Noël, J., 1976. Minéralogie des argiles et répartition des nids épigés dedeux espèces du genre Macrotermes au Sénégal occidental (Presqu'île du Cap-Vert). Insectes Sociaux 23, 535–547.

Mahaney, W.C., Zippin, J., Milner, M.W., Sanmugadas, K., Hancock, R.G.V., Aufreiter, S.,1999. Chemistry, mineralogy and microbiology of termite mound soil eaten bythe chimpanzees of the Mahale Mountains, Western Tanzania. Journal of TropicalEcology 15, 565–766.

Malaisse, F., 1974. Phenology of the Zambezian Woodland Area with Emphasis on theMiombo Ecosystem. In: Lieth, Helmut (Ed.), Phenology and seasonality modeling.Ecological Studies, 8. Springer-Verlag, New York, pp. 269–286.

Malaisse, F., 1990. La couverture végétale. In: Bruneau, J.-C., Pain, M. (Eds.), Atlas deLubumbashi. Editions Publidix, Université Paris X-Nanterre, Nanterre, pp. 30–31.

Mbenza, M., 1990. Le climat de Lubumbashi. In: Bruneau, J.C., Pain, M. (Eds.), Atlas deLubumbashi. Editions Publidix, Université Paris X-Nanterre, Nanterre, pp. 30–31.

Miedema, R., Brouwer, J., Geiger, S.C., Vandenbeldt, R.J., 1994. Variability in the growth ofFaidherbia albida near Niamey, Niger, Africa: micromorphological aspects of termite

315B.B. Mujinya et al. / Geoderma 192 (2013) 304–315

activity. In: Ringrose-Voase, A.J., Humphreys, G.S. (Eds.), Soil Micromorphology:Studies in Management and Genesis. : Developments in Soil Science, 22. Elsevier,Amsterdam, pp. 411–419.

Mujinya, B.B., Van Ranst, E., Verdoodt, A., Baert, G., Ngongo, L.M., 2010. Termite biotur-bation effects on electro-chemical properties of Ferralsols in the Upper Katanga(D.R. Congo). Geoderma 158, 233–241.

Mujinya, B.B., Mees, F., Boeckx, P., Bodé, S., Baert, G., Erens, H., Delefortrie, S., Verdoodt,A., Ngongo, M., Van Ranst, E., 2011. The origin of carbonates in termite mounds ofthe Lubumbashi area, D.R. Congo. Geoderma 165, 95–105.

Murphy, C.P., 1986. Thin Section Preparation of Soils and Sediments. A B AcademicPublishers, Berkhamsted.

Ngongo, M.L., Van Ranst, E., Baert, G., Kasongo, E.L., Verdoodt, A., Mujinya, B.B.,Mukalay, J.M., 2009. Guide des Sols en République Démocratique du Congo,Tome I : Etude et Gestion. Don Bosco, Lubumbashi.

Obi, J.C., Ogunkunle, A.O., Olatunji, O.O., 2008. Extractable iron and aluminum distribu-tion in Macrotermitinae Nigeriensis infested guinea savanna Alfisol. AgriculturalJournal 3, 345–348.

Pinheiro-Dick, D., Schwertmann, U., 1996. Microaggregates from oxisols andinceptisols: dispersion through selective dissolutions and physicochemical treat-ments. Geoderma 74, 49–63.

Qafoku, N.P., Van Ranst, E., Noble, A., Baert, G., 2004. Variable charge soils: their miner-alogy, chemistry and management. Advances in Agronomy 84, 159–215.

Quirk, J.P., Murray, R.S., 1991. Towards a model for soil structural behavior. AustralianJournal of Soil Research 29, 829–867.

Sako, A., Mills, A.J., Roychoudhury, A.N., 2009. Rare earth and trace element geochem-istry of termite mounds in central and northeastern Namibia: mechanisms formicro-nutrient accumulation. Geoderma 153, 217–230.

Schwertmann, U., Kämpf, N., 1985. Properties of goethite and hematite in kaoliniticsoils of Southern and Central Brazil. Soil Science 139, 344–350.

Schwertmann, U., Wolska, E., 1990. The influence of aluminum on iron oxides. XV. Al-for-Fe substitution in synthetic lepidocrocite. Clays and Clay Minerals 38, 209–212.

Seta, A.K., Karathanasis, A.D., 1996. Water dispersible colloids and factors influencingtheir dispersibility from soil aggregates. Geoderma 74, 255–266.

Stoops, G., 2003. Guidelines for the Analysis and Description of Soil and Regolith ThinSections. Soil Sci. Soc. Am., Madison, Wisconsin.

Suarez, D.L., Rhoades, J.D., Lavado, R., Grieve, C.M., 1984. Effect of pH on saturated hy-draulic conductivity and soil dispersion. Soil Science Society of America Journal 48,50–55.

Sumner, M.E., 1993. Sodic soils: New perspectives. Australian Journal of Soil Research31, 683–750.

Sys, C., 1957. L'aménagement des sols de la région d'Elisabethville d'après leurscaractéristiques morphologiques et analytiques. Bulletin Agricole du Congo Belge48, 1425–1432.

Sys, C., Schmitz, A., 1959. Note explicative des cartes de sol et de la végétation duCongo-Belge et du Rwanda-Urundi; région d'Elisabethville (Haut-Katanga), N° 9;A, B et C. Publication INEAC, Bruxelles.

Taylor, R.M., Schwertmann, U., 1978. The influence of aluminium on iron oxides. Part 1.The influence of Al on Fe oxide formation from the Fe (II) system. Clays and ClayMinerals 26, 373–383.

Turner, J.S., 2006. Termites asmediators of thewater economy of arid savanna ecosystems.In: D'Odorico, P., Porporato, A. (Eds.), Dryland Ecohydrology. Springer, Netherlands,pp. 303–313.

Van Ranst, E., Verloo, M., Demeyer, A., Pauwels, J.M., 1999. Manual for the soil chemis-try and fertility laboratory-analytical methods for soils and plants, equipment, andmanagement of consumables. NUGI, 835. ISBN: 90-76603-01-4 (Belgium, 243 pp.).

van Reeuwijk, L.P., 2002. Procedures for Soil Analysis, 6th ed. International Soil Refer-ence and Information Centre (ISRIC), Wageningen. The Netherlands.

Watson, J.P., 1975. The composition of termite (Macrotermes spp.) mounds on soil de-rived from basic rock in three rainfall zones of Rhodesia. Geoderma 14, 147–158.

Wielemaker, W.G., 1984. Soil formation by termites. A study in the Kisii area, Kenya.PhD Dissertation, Wageningen Agricultural University, 132 pp.