Spatial Distribution and Accumulation of Heavy Metals and Nutrients in Mangrove Sediments, Leaves, and Macro-invertebrates

This dataset examines the spatial distribution and bioaccumulation of heavy metals and nutrients in mangrove ecosystems along the Dar es Salaam coastline, Tanzania, under the hypothesis that locations nearer to the city exhibit elevated concentrations of heavy metals and nutrients compared to those situated farther away, attributable to urban wastewater, industrial effluents, and stormwater runoff. Data were gathered from three mangrove locations representing varying proximities to the city: Mtoni (adjacent to the city), Kunduchi (moderately distant from the city), and Ras Dege (remote from the city). The data encompass concentrations of six heavy metals (Cu, Zn, Pb, Cd, Cr, Ni) in surface sediments (0–30 cm), mangrove leaves of Avicennia marina, and the fiddler crab Uca inversa. Sediments were air-dried, homogenised, and subjected to acid digestion; leaves and crabs were manually collected, oven-dried, crushed, and digested; heavy metals were assessed using High-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS, Thermo Finnigan Element II), while nitrogen and phosphorus were quantified via DR 4000 spectrophotometer. Bioaccumulation factors (BAFs) were determined as the ratio of metal concentration in organisms to that in sediments. Results indicate that sediments serve as significant reservoirs for Zn, Pb, and Cr (most pronounced at Mtoni); crabs exhibit efficient bioaccumulation of Cu and Cd, but mangrove leaves demonstrate minimal metal transfer (BAFs < 1). Nutrient enrichment (N and P) is most pronounced at Mtoni and has a positive correlation with Zn, Pb, and Cu, suggesting shared anthropogenic causes. This data establishes a foundation for tracking heavy metal and nutrient contamination, endorses the utilisation of U. inversa and A. marina as bioindicators, and guides coastal pollution management and mangrove conservation initiatives.