Assessment of the Geochemical Characteristics of Water and Surface Sediments of Rufiji Mangrove Forest, Tanzania

Abstract

This study was carried out to investigate the geochemical characteristics of the Rufiji mangrove systems using mineralogy and heavy metal analyses. Rufiji mangrove sediments showed predominance of fine grain size fractions with silt as the major component. Stoichiometric ratios of nutrients revealed phosphorus enrichment in Rufiji sediment. The overall order of heavy metal concentrations in sediments was: Fe > Mg > Mn > Zn > Cr > Ni > Pb > Cu > Co > Cd. There was no relationship between grain size and some of the heavy metal concentrations, except for Co, Cr, Fe, and Mg which negatively correlated with sand, and positively correlated with silt. The findings indicated minor enrichments for Pb and Zn, and no enrichment for all other metals. The estimated geo-accumulation index demonstrated very low values (Igeo < 0) in almost all metals, except Zn (Igeo > 1.0) at station 3, indicating that sediments of the Rufiji mangrove ecosystem are unpolluted to moderately polluted. Ongoing research on the transport of nutrients, distribution and behaviour of anthropogenic chemicals throughout the estuary, and over different seasons, may provide further insights on the processes and factors which modulate the spatial and temporal variability in geochemistry of this rich and diverse tropical estuarine system.

Keywords: Rufiji mangrove; Enrichment factor; Geoaccumulation index; heavy metal.