Khadija Semhi

IMPACT OF TERMITE ACTIVITY ON SOIL ENVIRONMENT: A PERSPECTIVE FROM THEIR SOLUBLE CHEMICAL COMPONENTS

An investigation on varied types of termite mounds relative to the nearby soils that are not inhabited by the termites in different places of Cameroon show that the activity of the termites is increasing the contents of most major and some trace elements in the termite mounds, except for Si and sometimes Fe, Mn, Na and K. These released elements are relocated into newly formed mineral phases that are dissolved by either H2O or dilute HCl leachings. The Ca and Mn released by the termite activity testify for crystallization of Ca-Mg carbonates and phosphates as well as of Fe oxy-hydroxides and/or Mn hydroxides. Termite activity also induces an increase in the lanthanide contents, the mound materials being especially enriched in light lanthanides relative to the corresponding soils without termite activity. The shapes of the patterns support precipitation of Mn-Fe oxy-hydroxides and Ca carbonates-phosphates. The increased amounts of Eu and Ce linked to termite activity seem to relate to the occurrence of reducing agents that are released by the termites, modifying Eu+3 into Eu+2 and Ce+4 into Ce+3, favoring in turn selective incorporation of Eu+2 and Ce3+ in the new phases of the termite mounds. Another consequence of the termite activity is the precipitation of H2O and HCl extractable phases having low Sr/Ca ratios. Even if the K/Rb values of the termite mounds are typical for common soil-forming silicate minerals, their relocation by an inorganic process alone does not explain an abnormally high ratio in the H2O leachable mineral phases. It was also shown that the main source for K and Rb of the dissolved phases is not only the interlayer site of clay particles, but also nutrients immobilized in and by the termites.

Rare earth element mobility during laterization of mafic rocks of the Oman ophiolite

Eleven samples representing a sequence of progressive alteration through a laterite profile of Upper Cretaceous age developed on a layered gabbro from the Oman ophiolite have been analyzed for their rare earth element (REE) contents. The results provide new insights into the fractionation and vertical movement of REEs during the laterization of mafic parent rocks. Compared to the fresh parent rock, from the same section nearly flat chondrite-normalized REE patterns are observed in the saprolite zone, while light REE (LREEs: La-Nd)-enriched patterns characterize the oxide and clay zones. The altered gabbro shows a depletion in middle REEs (MREEs: Sm-Ho) compared to its unaltered counterpart. A negative cerium (Ce) anomaly is observed in the upper part of the altered gabbro, while the lower part appears to be depleted in Ce. The similarity in the LREE-enriched fractionation patterns throughout the alteration profile suggests that the REE fractionation process is independent of the total REE content of the parent rock.

Geochemical background and contamination level assessment in Tunisian and Moroccan Mediterranean coastal lagoon sediments

The calculation of enrichment factors (EF) enables estimating contamination levels of trace elements in lagoon sediments. It is based on normalization to a conservative element and to a reference material. This reference can be from the literature or from analyses of local sediments or rocks which have to be representative of the studied site. Calculations of enrichment factors were applied to Cu, Pb, Zn, Sc and Al measured in three semi-arid coastal lagoons, El Kelbia and El Meleh in Tunisia, and Nador in Morocco. For El Meleh and El Kelbia lagoons, EF calculations were done using the post-Archean Australian shale as global reference material, and deep sediments as local reference material. For Nador Lagoon (Morocco), the chosen global and local reference materials are the continental crust and the Gourougou volcanic body, respectively. The comparison between results of both methods of EF calculations shows that using a global reference from the literature induces an underestimation of the contamination level. The use of a local reference allows a more reliable estimation of contamination levels in the studied lagoon. It appears that El Meleh Lagoon is moderately enriched in Pb, especially at the mouth of Oued and near agriculture activities. The Lagoon of Nador is severely contaminated with Zn, Pb and Cu near mine dumps and in the vicinity of cities. El Kelbia Lagoon shows a high enrichment in Pb near garbage dumps and main roads and an overall low to medium enrichment in Zn.

Groundwater recharge to ophiolite aquifer in North Oman: constrained by stable isotopes and geochemistry

Abstract The current study employs geochemical and isotopic tools to understand hydrochemical and recharge processes characterizing ophiolite aquifer in North Oman in conjunction with the Hajar Super Group (HSG) aquifer. A total of 57 samples were analyzed for major ions and stable isotopes 2H and 18O. The geochemical composition of groundwater indicates that water–rock interaction and mixing are the main processes controlling groundwater chemistry. Groundwater in the HSG is characterized by carbonate minerals dissolution contrary to the groundwater in the ophiolites where silicates dissolution dominates. This results in differences in the groundwater chemical composition in the two systems. Isotopic characteristics of precipitation collected during the study period indicate two main moisture sources from the Indian Ocean and the Mediterranean Sea. Groundwater δ2H and δ18O values suggest two recharge sources to the ophiolite aquifer: lateral flow from the HSG and direct infiltration. Recharge from direct infiltration in the highlands, which is depleted in δ2H and δ18O, retains the same isotopic signature of precipitation, whereas that in the low land substantially reflects an evaporation effect.

Hydro-chemical evolution of groundwater in a sequence of Tertiary Formations in Northwest Oman

Tertiary Formations, which are widely spread in the Arab Peninsula, are fundamental to the oil industry in the world’s largest oil producing area. These formations host major aquifers that satisfy water demands for oil production such as steam injection and reservoir pressure maintenance . The current study investigates the hydro-chemical evolution of groundwater in a sequence of Tertiary Formations in Northwest Oman in the Kingdom of Saudi Arabia and the United Arab Emirates borders. Stable isotopes (18O and 2H) show three different groundwater types: (1) groundwater formed from precipitation originating from the Mediterranean Sea, (2) groundwater formed from mixing of northern (Mediterranean) and southern (Indian Ocean) moisture sources, and (3) groundwater affected by evaporation. Radiogenic isotopes 14C and 3H indicate younger groundwater close to the recharge source in North Oman Mountains and older age in the plain desert area that constitutes the discharge zone. Groundwater chemistry notably evolves from Ca–Mg–HCO3 dominant in the recharge area to Na–Cl–SO4 dominant type in the discharge zone. Water–rock interaction is the main process controlling groundwater chemistry in the recharge zone while evaporation becomes progressively effective down the gradient. The geochemistry and stable and radiogenic isotopes of the Tertiary Formations indicate that the study area has witnessed wet periods during the Early Holocene with surface water bodies formed by groundwater discharge at distal parts. The sustainability of such old groundwater that is being exploited for oil production should be thoroughly investigated to secure future oil production.

Toward the understanding of the treatment of textile industries’ effluents by clay: adsorption of anionic dye on kaolinite

Clays, particularly kaolinite, are promising adsorbents for the treatment of textile effluents, but there is a need of better understanding the mechanisms of adsorption, especially in the case of anionic dyes. Thus, the removal of RR120 anionic dye was investigated using Tunisian raw clay (TBK) composed of kaolinite and illite, and a standard kaolinite (KGa-2), and conducting batch experiments by varying different parameters (contact time, ionic strength, concentration, temperature). We investigated the clays’ surface charges by electrophoretic mobility measures and the dye-clay interactions during adsorption, by the streaming-induced potentials (SIP). The results showed that KGa-2 has higher adsorption capacity for RR120 dye than TBK clay, moreover enhanced by increasing the ionic strength and/or lowering the pH of the aqueous. The SIP results showed an increase of negative charges for both clays, reflecting the adsorption of the anionic dye on the positive charges of the amphoteric surfaces of the clays. The SIP magnitudes indicated a higher adsorption rate for KGa-2 in accordance with the kinetic study. The Sips model that described the best adsorption isotherms indicates lateral interactions of the dye molecules, stronger in the case of KGa-2 than TBK. Also, the dye molecules form a thinner layer on KGa-2 surfaces. In addition, the dye molecule’s structure was not altered, as verified by mass spectrometry. The adsorption process was feasible and spontaneous and favored at ambient temperature. Thus, kaolinite-rich clays are effective in the removal of anionic dyes in aqueous solution and potential good adsorbents in wastewater treatment.

Chemical effect of pesticide application on soils: evidence from rare earth elements

The main objective of this study is to investigate the distribution of rare earth elements (REEs) in Lolium perenne L. plant species which has been grown on vineyard soils treated with pesticide commonly used in the study area. These plants have been grown on two types of soils: (1) brown calcareous soils developed on loess and (2) brown to calcic brown soils developed on conglomerates. The significant correlation observed between the concentrations of phosphorus and the total amount of REEs, in addition to the enrichment in middle REEs (MREEs), suggests the complexation of REEs with phosphates and organic matter. The soils were enriched in REEs due to pesticide application but the plants were depleted. The ratio of REEs in plant over REEs in soil before application of pesticides is higher than that after application of pesticides. Application of pesticides to crops did not affect the fractionation of REEs neither in leaves nor in roots. No selectivity in uptake of REEs occurred because of pesticides except for Ce and Eu which show a negative anomaly relative to the other REEs.

An Overview of Stable Isotopes in Northern Oman’s Main Aquifers as an Insight into Recharge Process

This review presents a synthesis of literature published on deuterium and oxygen isotopes in groundwater collected from different aquifers in North Oman. The identification of the main hydrological processes which characterize the main aquifers in the North Oman was the main objective of several previous studies. The main focus was to identify zones and mechanisms of groundwater recharge to the different aquifers. Hajar Super group was identified as a main aquifer that receives recharge and transfer freshwater into neighboring aquifers namely ophiolite, alluvium, Hawasina and Tertiary aquifers. A mass balance was also applied in previous studies to groundwater alluvium aquifer and indicated that 2/3 of recharge occurs along the wadi channels and that 1/3 is from the subsurface. Recently it was estimated that 13–68% of groundwater in the ophiolite aquifer is coming from the HSG contrary to the previous estimates of 10%.

Research on Soil Erosion

edited by Danilo Godone and Silvia Stanchi, InTech, Croatia, 2012, 191 pp., €100, hbk (ISBN 978-953-51-0839-9) This book focuses on models for prediction of soil degradation. Erosion of soils can b...

Water quality in a protected natural wetland: El Kelbia sebkhet, Tunisia

Surface waters were collected from a Tunisian protected wetland, sebkhet El Kelbia, to determine their chemical composition and to characterize this ecosystem in terms of water quality. Mineralogical composition of sediments in this sebkhet consists of evaporites, clays, quartz, calcite and oxides. The average total nitrogen concentration was 0.325 μg/g (SD = 0.068), with 0.089 μg/g as nitrate, 0.018 μg/g as nitrite and 0.023 μg/g as ammonia. The total phosphorus concentration was 0.081 μg/g (SD = 0.011) with 0.044 μg/g determined as PO4 3−. The total dissolved elements not including silica are about 16–248 meq/L and are characterized by relatively high spatial variability in the lake basin. The average concentration of trace elements from the highest to the lowest is as follows: Sr > Fe > Pb > Ba > Cd > Cu > Mn > Cr. The quality of the wetland waters was examined by comparing the concentrations of dissolved trace and major elements with those of Tunisian and European standard values. The comparison revealed that the quality of the current waters of the protected El Kelbia lake is considered to be satisfactory, but there is a need to prevent any threat of contamination that may arise from Pb and Zn from past mining activities and unauthorized dumping.