Urbanization and the concentration of industrial sites in coastal regions have led to a strong risk of heavy metals contamination in the neighbouring marine environment. Analysis of dated sediment cores from these environments may allow historical trends of heavy metal input to be reconstructed, and recent and historical inputs of metal contaminants to be compared. In this work we have assessed the depth profile of lead concentrations; converted lead profile to time-based profiles using(210)Pb sediment dating method; established site-specific baseline value for lead and estimated lead enrichment factors (EF) in sediment cores from Msimbazi estuary in Tanzania. The core bottom was estimated to date back about 59 years. Lead concentrations ranged from 11.5 (mgkg(-1)DW) in 1961 to 50.1 (mgkg(-1)DW) in 2006. Sediment layers deposited during late 1950`s and 1960`s were assumed to represent baseline values of lead concentrations because they correlate well with the documented population growth and increase of industrial and agricultural activities in the catchment. Iron-based enrichment factors illustrate that no enrichment of lead (EF <= 1) between 1957 and 1971. The upper sections of the core indicate that sediments of Msimbazi have experienced minor (1 < EF < 3) to moderate (3 <= EF < 5) enrichment of lead over time.

This study aimed to reconstruct the sedimentation rates over time and identify the changing sources of sediment in a major hydropower reservoir in Tanzania, the Nyumba ya Mungu (NYM). Fallout ²¹⁰Pb measurements were used to estimate age of sediment deposits and broad changes in sedimentation rates were reconstructed. Sedimentation peaks were cross referenced to geochemical profiles of allogenic and autogenic elemental constituents of the sediment column to confirm a causal link. Finally, geochemical fingerprinting of the sediment cores and potential sources were compared using a Bayesian mixing model (MixSIAR) to attribute the dominant riverine and land use sources to the reservoir together with changes through recent decades. Reservoir sedimentation generally increased from 0.1 g cm⁻² yr⁻¹ in the lower sediment column to 1.7 g cm⁻² yr⁻¹ in the most recent deposits. These results correlated to changes in allogenic and autogenic tracers. The model output pointed to one of two major tributaries, the Kikuletwa River with 60.3%, as the dominant source of sediment to the entire reservoir, while the other tributary, Ruvu River, contributed approximately 39.7%. However, downcore unmixing results indicated that the latest increases in sedimentation seem to be mainly driven by an increased contribution from the Ruvu River. Cultivated land (CU) was shown to be the main land use source of riverine sediment, accounting for 38.4% and 44.6% in Kikuletwa and Ruvu rivers respectively. This study explicitly demonstrated that the integration of sediment tracing and dating tools can be used for quantifying the dominant source of sediment infilling in East African hydropower reservoirs. The results underscore the necessity for catchment-wide management plans that target the reduction of both hillslope erosion reduction and the sediment connectivity from hillslope source areas to rivers and reservoirs, which will help to maintain and enhance food, water and energy security in Eastern Africa.

Assessment of public exposure to background radiation was performed in Manyoni, Tanzania to address public concerns following the discovery of uranium deposits in their neighborhoods. Results show that the highest concentrations of radionuclides are 112, 95 and 463 Bq.kg-1 for 226Ra, 232Th and 40K, respectively. The highest annual effective dose to the public is 2.91 mSv.y-1 with a mean value of 1.29 mSv.y-1. Authorities may use these results to address public concerns as well as the baseline information. Further investigations on public exposures in Manyoni are recommended.

Land use conversion is generally accompanied by large changes in soil organic carbon (SOC). SOC influences soil erodibility through its broad control on aggregate stability, soil structure and infiltration capacity. However, soil erodibility is also influenced by soil properties, clay mineralogy and other human activities. This study aimed to evaluate soil organic carbon as proxy of soil erosion risk in the Nyumba ya Mungu (NYM) catchment in Northern Tanzania. Soil organic carbon (SOC) was measured by an AgroCares scanner from which the soil organic matter (SOM) was derived using the conversional van Bemmelen factor of 1.72. A regression analysis performed between the measured loss on ignition (LOI) values and SOM from the AgroScanner showed a strong positive correlation in all land use classes (LOI_FL R² = 0.85, r = 0.93, p < 0.0001; LOI_CL R² = 0.86, r = 0.93, p = 0.0001; LOI_GL R² = 0.68, r = 0.83, p = 0.003; LOI_BS R² = 0.88, r = 0.94, p = 0.0001; LOI_BL R² = 0.83, r = 0.91, p = 0.0002). This indicates that SOC from the soil scanner provided a good representation of the actual SOM present in soils. The study also revealed significant differences in the soil aggregate stability (WSA) and SOM stock between the different land use types in the Upper Pangani Basin. The WSA decreases approximately in the following order: grassland > forest land > bare land > cultivated > bush land. Land use change can thus potentially increase the susceptibility of soil to erosion risk when SOC is reduced. Since WSA was directly related to SOM, the study indicates that, where formal measurements are limited, this simple and inexpensive aggregate stability test can be used by farmers to monitor changes in their soils after management changes and to tentatively assess SOC and soil health.

Phosphate fertilizers improve phosphorus-depleted agricultural soil for better plant growth; however, overuse may lead to human health issues. Analyzed soil samples were treated with five phosphate fertilizers and Spinacia oleracea to quantify the levels of natural radionuclides 232Th, 226Ra, and...