Matched Riverbank–Channel Elemental Profiles along the Tigris River: An Exploratory Compositional Survey

Riverbank soils and channel sediments are dynamically exchanged during erosion and deposition, yet their geochemical relationships are rarely evaluated as matched observations. This study compared channel sediment and right- and left-bank surface soils at seven Tigris River reaches between Baghdad and Wasit during summer 2024. Forty-one elements were screened by energy-dispersive X-ray fluorescence. The 21 samples were analysed as seven matched reach sets of three samples each using exact restricted element-wise permutation, Monte Carlo restricted multivariate permutation, false-discovery-rate control, centered log-ratio transformation, principal component analysis, Ward clustering, and Aitchison distance. The first two CLR principal components explained 57.1% of compositional variance. The exploratory matched-set compositional test indicated no statistically detectable consistent sample-type effect (Monte Carlo restricted-permutation p = 0.1439, R²=0.200). After element-wise FDR correction, the survey provided insufficient evidence of a consistent difference among the three media for any of the 41 elements. The magnitude and direction of channel–bank contrasts varied among reaches, and the descriptive sequence of site-specific Aitchison distances was not monotonic. The observed profiles are consistent with, but do not demonstrate, local hydraulic sorting and bank–channel exchange; they do not establish metal bioavailability, ecological risk, or river-water suitability. The matched survey design and compositional framework provide a transparent baseline for targeted monitoring of Tigris sediment redistribution.