Termite mounds as bioindicators of soil geochemistry in the Guinea and Sudan Savannah zones of northeastern Nigeria: A multi-parameter synthesis

Abstract

The capacity of termite mounds to reflect, amplify and transmit the geochemical signature of the local soil profile was evaluated through a multi-parameter synthesis integrating XRF oxide analysis, heavy metal distribution, NPK quantification and physical characterization of Nausititermes walkeri and Coptotermes acinoformis mound soils and adjacent control soils from nine communities across three ecological zones of Bauchi State, Nigeria. Across all analytical streams, results consistently reflected the geochemical signature of regional parent material: the oxide order SiO₂ > Al₂O₃ > Fe₂O₃ tracked the Guinea–Sudan savannah weathering gradient; Fe₂O₃ anomalies in Bauchi LGA mounds reflected Jos Plateau basement geology; heavy metal profiles showed Fe consistently highest and Cd consistently lowest across all sample types, though the relative order of Zn, Pb, Cr and Mn varied by LGA and sample type rather than following one fixed hierarchy (see the companion heavy-metal study for detail), with inter-metal correlations calculated from LGA-level means that are suggestive of, but cannot confirm, common geogenic sources (Zn–Cr: r = 0.997; Cd–Zn: r = 0.998, both from n = 3, 1 degree of freedom); and NPK patterns reflected local organic matter quality and subsoil mineral K content. ANOVA showed no significant differences between mound and control soils for most parameters (p > 0.05), consistent with, though not proof of, geochemical continuity between mound and parent soil. The synthesis supports a three-tier bioindicator framework: Tier 1 regional geochemistry signal (oxide order as ecological zone indicator); Tier 2 local subsurface anomaly signal (Fe, K₂O enrichment as geological anomaly indicators); Tier 3 fertility status signal (NPK enrichment ratios as soil fertility potential indicators). An operational mound geochemical sampling protocol with 5–6× cost savings versus conventional soil survey is proposed for Bauchi State.