Phosphorus (P) is an important nutrient required for plant growth. Land use influences concentration and bioavailability of P in agricultural soils. About 198 soil samples (0-30 cm soil depth) were collected from three land-use types (maize, paddy, and conserved areas) in Usangu basin located in Southern Highland Tanzania. The concentration of soil P determined were compared among different land-use types and locations. The total P (TP), complexed (Po), and bioavailable P (B-P) were measured. The concentration of TP and B-P was determined by acid digestion and Mehlich 3 method, respectivelly, The Po concentration in soil extract was obtained by subtracting B-P from TP. TP, B-P and Po concentration in collected soils samples were in range of; Total P (63.12-1350.9 mg/kg), Bioavailable P (0.52-49.87 mg/kg), and complexed P (62.60-1301.03 mg/kg). The cropping area had high TP but very low B-P, especially in paddy farming areas indicating cropping and associated activity decrease bioavailable P in agricultural soils. Furthermore, soils from cropping areas had higher Al, Fe, and Mg concentrations than conserved areas, which caused a substantial reduction in B-P due to increased P fixation and adsorption. It is important to note that converting natural land to farming land could potentially influence soil P dynamics thus affecting P bioavailability, crop productivity, and environmental safety.

Characterization of land use influence on soil phosphate bioavailability in Usangu agro-ecosystem-Tanzania

Abstract In this study, distribution and accumulation of trace elements (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) in water, tissues of aquatic organisms (e.g. fishes: Oreochromis niloticus, Platycephalus indicus, Clupanodon punctatus; crabs: Charybdis japonica, Portunus sanguinolentus, and Charybdis varuegata; prawns: Litopenaeus vannamei, Metapenaeus joyneri, Penaeus japonicas, Penaeus penicillatus; mollusks: Mytilus spp., Perna spp.), and trophic transfer in food web were investigated in Yundang Lagoon at Xiamen in China. Most of the studied metals such as Cr, Mn, Ni, Cu, Cd, and Pb were biodiluted in the food web except As which was biomagnified in the food web. Moreover, the target hazard quotient and total target hazard quotient risk values were higher than threshold limit values indicating that non-carcinogenic health risk to the inhabitants due to consumption of aquatic organisms.

Trophic transfer, bioaccumulation, and potential health risk of trace elements in water and aquatic organisms of Yundang Lagoon at Xiamen in China

Heavy metal pollution in sediments is a common environmental issue in small- and medium-sized reservoirs not only in China but also worldwide; however, few interpretations of the pollution pattern exist. Based on the analyses of accumulation characteristics, ecological risks, and source apportionments of eight heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in sediments, we derived a paradigm to describe the pollution pattern of heavy metals in sediments of a typical small- and medium-sized Tongjiqiao Reservoir. The results showed high levels of Cd, Hg, and As pollutants in the surface and upper sediment layers of the pre-dam area. Additionally, As, Cd, Hg, and Pb pollutants peaked in the middle layers of the inflow area, indicating a high ecological risk in these areas. The positive matrix factorization results implied that industrial, agricultural, and transportation activities were the main sources of heavy metals. The heavy metal pollution pattern exhibited three distinct stages: low contamination, rapid pollution, and pollution control. This pattern explains the heavy metal pollution process in the sediments and will provide scientific guidance for realizing the green and sustainable operation and development of the reservoir. 

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Understanding the Heavy Metal Pollution Pattern in Sediments of a Typical Small- and Medium-Sized Reservoir in China

Towards sustainability: Threat of water quality degradation and eutrophication in Usangu agro-ecosystem Tanzania.

Intensive paddy farming activities involve higher use of irrigation water and agrochemicals to increase crop productivity per unit area. However, a practice may result in environmental challenges due to nutrient loss and agro-chemicals contamination from agricultural fields. The present study characterized the relationship between agricultural soil phosphate (P) status and P levels in water bodies in Usangu agro-ecosystem (UA), the area famous for paddy rice production in Southern Highland Tanzania. The studied soil pH ranged from 6.4 to 7.6, while water pH was 4.9–6.8, which varied among study sites and negatively correlated to each other. This study found a positive correlation between P concentration (P < 0.001, R2 = 0.78) in agricultural soils and water samples in the study area, where P in soil were 1.66–17.56 mg/kg and 0.02–1.65 mg/L in water. This correlation pattern of P in soil and water indicates that increased P content in farming areas under poor management (flooding system of irrigation), as observed in the study area likely to influence increased levels of P in water bodies leading to water eutrophications, but also reducing the land productivity per unit area. The significant P enrichment (>1.65 mg/L) from agricultural fields to water bodies found in different water samples from irrigation schemes potentially leads to eutrophication. To sustainably manage P concentration in water bodies and increase land productivity per unit area, the hotspot for P loss to water bodies in the agro-ecosystem has to be identified and managed, but also flooding irrigation system standard in the study area has to be abandoned to reduce plant nutrient loss and contamination of water bodies. 

Increasing agricultural soil phosphate (P) status influences water P levels in paddy farming areas: Their implication on environmental quality

This study investigates the pollution status, spatial distribution of heavy metals including Cr, Mn, Ni, Cu, Zn, As, Cd and Pb, in sediments from the Longhu Lake, and evaluates possible ecological ...

https://www.tandfonline.com/doi/pdf/10.1080/26395940.2021.1894988

Ya Wang

Papers

Pollution status, spatial distribution and ecological risk of heavy metals in sediments of a drinking water lake in South Eastern China