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Spatial and temporal distribution of trace metals and their cycling is a key issue for understanding the ongoing biogeochemical processes in coastal environments. Sediment cores were collected from six different sampling locations from the Rufiji delta mangrove forests in southeastern coastal Tanzania that are perceived to be impacted by urban development and agricultural activities in the catchment, and pollution in upstream sections of the Rufiji River. The chronology and sediment accumulation rates at these sampling sites were derived based on the distribution of 210Pbexcess method. The trace metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were sequentially extracted as per the BCR method and analyzed. The results indicate that the mass accumulation rates range from 0.40 g cm−2 year−1 (cores NR3 and NR4) to 1.75 g cm−2 year−1 (core SR1). Trace metals in the cores are mainly associated with the residual phase and their abundances in sediments are ranked as Cr > Zn > Ni > Cu > Pb > Cd. The results imply that trace metals in the Rufiji delta mangroves are mainly of crustal origin, and they are less sensitive to weathering. Further, these metals are least available for uptake by plants and they pose limited threat to the biota.

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Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.

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This study reports on the adsorption isotherm and kinetics of arsenic and/or fluoride by the hybrid iron-aluminum electrocoagulation in a batch reactor. The experiments were performed at a condition of current density J = 9.9 mAcm −2 ; time = 50 min; and pH = 7.5, at variable initial concentrations. The flocs surfaces were characterized using Fourier transform infrared spectroscopy and X-ray powder diffraction that revealed presence of AlAsO 4 •2(H 2 O), AlF 2 OH, and FeOOAs.Adsorption of fluoride and arsenic in both systems followed Freundlich and Langmuir models. The adsorption processes for fluoride and arsenic were spontaneous and physical in nature with monolayer maximum adsorption capacities of 76.4 and 1.14 mg/g, respectively in single systems. In a binary component system, the adsorption capacity of arsenic was 0.06 mg/g while that of fluoride became 75.6 mg/g as evaluated using extended Langmuir and extended Freundlich models. Moreover, the kinetics of fluoride and/or arsenic adsorption followed the pseudo second-order model. The remediation of fluoride and arsenic from water by Al-Fe oxyhydroxide were found to be through ionic exchange and electrostatic attraction, respectively.

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