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.