Termite bioturbation effects on electro-chemical properties of Ferralsols in the Upper Katanga (D.R. Congo)

Abstract

Although the significant impact of mound-building termites on physical, chemical and biochemical soil properties over large areas of the (sub-) tropics has often been discussed, little is known about the influence of termites on electro-chemical properties of Ferralsols. In this study, we compared the curves describing the total cation exchange capacity (CEC T), the base cation exchange capacity (CEC B), and the anion exchange capacity (AEC) across a range of pH values ( charge fingerprint) and point of zero charge (pH 0) of Macrotermes falciger biogenic structures with soils not affected visually by termites (control soils). The results show that termite activities lowered considerably the pH 0 values, the actual AEC, the actual preferential adsorption of Al on the exchange complex (CEC T–CEC B) and the AEC variability (dAEC/dpH); and increased considerably the soil pH, the cation exchange capacities (CEC B and CEC T), the permanent negative charge ( σ p) and the CEC's variability (dCEC B/dpH and dCEC T/dpH). The lowering of pH 0 values (1.6-fold) was attributed to the bonding of negatively charged organic matter with protonated oxide sites and largely to the enrichment in permanent negative charge (about 2-fold), suggesting the termites' ability to change soil mineralogical properties. The mean pH 0–pH 0.002 values indicate the evolution of negative (− 2.0 to − 3.6 units) and positive (+ 0.6 units) charges on the variable charge components of mound and control soils, respectively. The study demonstrates that Macrotermes biogenic structures have a mixed charge system with higher permanent and variable charges than the surrounding Ferralsols.