Browsing by Author "Sawe, Shovi"

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Assessing the impact of phosphate fertilizer application on radionuclide accumulation in soil and Spinacia oleracea
(Journal of Ecological Engineering, 2025-06-23) Mankala, James; Sawe, Shovi; Moirana, Ruth
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 232 Th, 226 Ra, and 40 K. The study aimed to investigate how phosphate fertilizers contribute to the accumulation of radionuclides 232 Th, 226 Ra, and 40 K in Spinacia oleracea using a high-performance germanium detector. Results revealed the mean activity concentrations in agricultural soil mixed with phosphate fertilizer were 232 Th (66.66 ± 6.39 Bq/kg), 226 Ra (54.78 ± 5.41 Bq/kg), and 40 K (837.17 ± 62.89 Bq/kg); Spinacia oleracea were 232 Th (5.79 ± 0.83 Bq/kg), 226 Ra (40.24 ± 5.38 Bq/ kg), and 40 K (1268.12 ± 129.95 Bq/kg). The soil-to-plant transfer factors were 232 Th (0.244), 226 Ra (0.572), and 40K (1.756). The mean annual limits on the intake of radionuclides were 232 Th (231.67 ± 33.20 Bq/kg), 226 Ra (1609.53 ± 215.33 Bq/kg), and 40 K (50724.67 ± 5,198.13 Bq/kg). The mean annual effective dose was 0.849 ± 0.103 mSv/year, and the internal radiation index was 0.504 ± 0.059 Bq/kg. The results indicate that the mean activity concentrations of 232 Th, 226 Ra and 40 K are below standards but exceed those of the control sample, suggesting regular monitoring of phosphate fertilizer quantity applied to the soil for cultivation.
Assessment of Potentially Toxic Metals in Fish from Lake Manyara, Northern Tanzania
(Springer US, 2023-09) Sawe, Shovi; Amasi, Aloyce; Wynants, Maarten
Elemental tracer concentrations of copper, lead, nickel and zinc, were assessed in the muscles of Oreochromis amphimelas and Clarias gariepinus from Lake Manyara, Tanzania, to evaluate their safety to consumers, specifcally humans. Results revealed that no elemental concentrations exceeded the FAO permissible levels, indicating fsh from all sites are safe for human consumption. However, based on the highest found concentration of Pb, we recommend a maximum consumption of 2.2 kg of fsh from Lake Manyara per week. No signifcant diferences were observed in the metal concentrations between the two fsh species, suggesting there is no bioaccumulation in the food chain. Moreover, no signifcant diferences were found between fsh landing sites, indicating there are no regions in the lake with higher pollution. These fndings indicate that PTM concentrations have not increased to toxic levels due to increased mobilisation from the catchment. Continued monitoring of potential toxic metal concentrations in fsh is recommended due to endorheic nature of Lake Manyara and increasing anthropogenic activities in its catchment area.
Evaluating Soil Carbon as a Proxy for Erosion Risk in the Spatio-Temporal Complex Hydropower Catchment in Upper Pangani, Northern Tanzania
(MDPI, 2021-10-15) Amasi, Aloyce; Wynants, Maarten; Kawala, Remigius; Sawe, Shovi; Blake, William; Mtei, Kelvin
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 mineral ogy 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 (LOIFL R 2 = 0.85, r = 0.93, p < 0.0001; LOICL R 2 = 0.86, r = 0.93, p = 0.0001; LOIGL R 2 = 0.68, r = 0.83, p = 0.003; LOIBS R 2 = 0.88, r = 0.94, p = 0.0001; LOIBL R 2 = 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.
Reconstructing the Changes in Sedimentation and Source Provenance in East African Hydropower Reservoirs: A Case Study of Nyumba ya Mungu in Tanzania
(MDPI, 2021-08-08) Amasi, Aloyce; Wynants, Maarten; Kawalla, Remegius; Sawe, Shovi; Munishi, Linus; Blake, William; Mtei, Kelvin
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 catchmentwide 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.