Sources and historical records of metal(loid)s in river sediments from an agricultural tributary of Tuojiang river: Evidence from geochemical analyses and Pb isotope.

Clarifying the sources and historical variation of metal(loid)s in agricultural river sediments is vital for watershed contamination control and environmental improvements. In this study, a systematical geochemical investigation of Pb isotopic characteristics and the spatial-temporal distribution of metal(loid)s abundances was conducted to delineate the origins of metal(loid)s (Cd, Zn, Cu, Pb, Cr, and As) in sediments from an agricultural river, Sichuan Province, Southwest China. The results showed significant enrichment of Cd and Zn in the whole watershed, with substantial anthropogenic contributions of 86.1% and 63.1% for the surface sediments, and 79.1% and 67.9% for the core sediments, respectively. As was mainly derived from natural sources. Cu, Cr, and Pb were originated from the mixing sources of natural and anthropogenic processes. The anthropogenic origin of Cd, Zn, and Cu in the watershed was closely correlated with agricultural activities. The profile of EF-Cd and EF-Zn displayed an increasing trend from the 1960s-1990s, and then kept a high value, which was consistent with the development of national agricultural activities. Pb isotopic signatures suggested multiple sources of the anthropogenic Pb contamination, including industrial/sewage discharge, coal combustion, and vehicle exhaust. The average anthropogenic 206Pb/207Pb ratio (1.1585) approximated that of local aerosols (1.1660), suggesting aerosol deposition was a crucial pathway of anthropogenic Pb input to sediment. Furthermore, the anthropogenic Pb percentages (mean of 52.3 ± 10.3%) from the EF approach were in line with that from the Pb isotopic method (mean of 45.5 ± 13.3%) for sediments under intense anthropogenic impacts.

Scale effects of land use on river water quality: a case study of the Tuojiang River Basin, China.

Assessing the scale effects of land use on water quality is of great significance for effectively controlling nonpoint source (NPS) pollution in river basins. In this study, redundancy analysis (RDA) and stepwise multiple linear regression (SMLR) analysis were applied to assess the effects of land use on water quality across multiscales in the Tuojiang River Basin. All monitoring sections were classified into three groups according to the characteristics of land use and cluster analysis of water quality. Results showed that the improvement in water quality of rivers in the Tuojiang River Basin lies in the emphasis and protection of the small-scale scope. Concomitantly, the linkages between individual water quality parameter and land use were highly dependent on spatial scales and regional basis. For the upstream group A, urban land is the main source of COD and TN pollution, while industrial and rural residential land contributed the most to TP pollution. Water body exhibits favorable effects on ammonia nitrogen due to its absorption and degradation, together with the growth of phytoplankton within it. For group B in the middle-lower reaches, controlling the input of organic fertilizers in paddy field will effectively alleviate COD pollution. Increasing the proportion of grassland near the riparian zone can have a positive effect on TN and TP pollution. It should continue to strengthen the strict supervision of NH3-N concentration in wastewater discharge from industrial enterprises. Our results can provide important information for land use planning and making multiple scale measures for water quality conservation.

Insight into n-CaO2/SBC/Fe(II) Fenton-like system for glyphosate degradation: pH change, iron conversion, and mechanism.

Glyphosate has significant adverse effects on creature and ecological balance. Therefore, the efficient treatment of glyphosate wastewater is of great significance. In this study, nano calcium peroxide (n-CaO2) was loaded onto activated sludge biochar (SBC), and then Fe(II) was added to construct a Fenton-like system (n-CaO2/SBC/Fe(II)). SBC played the role of both a dispersant and catalyst, which greatly improved the removal capability of glyphosate. The removal efficiency of glyphosate in the n-CaO2/SBC/Fe(II) system was as high as 99.6%. The persistent free radicals (PFRs) on SBC can promote the conversion of Fe(III) to Fe(II) in the reaction system, and Fe(II) can be maintained at about 15 mg L-1 until the reaction reached equilibrium. Due to the synergistic effect of Fe(II) hydrolysis and SBC catalysis, n-CaO2/SBC/Fe(II) system can effectively remove glyphosate in a wide initial pH range (4.0-10.0), and the pH of the reaction system can be remained in a suitable environment (4.0-6.0) for Fenton-like reaction. Advanced oxidation and chemical precipitation were the main mechanisms for the removal of glyphosate. Most of glyphosate could be oxidized into H2PO-4 anions by breaking the bonds of C-P and C-N, and the H2PO-4 can be further adsorbed and bounded on the surface of the composites. This system overcomes the shortcomings of pH rising and Fe(III) precipitation in the CaO2-based oxidation systems, and realizes the efficient and complete degradation for glyphosate.

Micro-electrolysis based nitrate reduction from aqueous solution by CNTs-Al-Cu composite under alkaline environment.

CNTs-Al was prepared by ball milling combined with sintering process and then used for CNTs-Al-Cu synthesis with chemical deposition method. The obtained CNTs-Al-Cu composite was systematically characterized and its NO3--N reduction performance under alkaline condition was also evaluated. As indicated by the reduction batch experiment, 80.2% of NO3--N removal efficiency was obtained in 90 min at pH of 9. The product of the reduction process was dominated by NO2--N, which was further reduced to harmless N2. The reusability of CNTs-Al-Cu composite was evaluated, and the experiment results showed that 68.1% of NO3--N removal efficiency was maintained after 3 cycles of regeneration. Finally, based on the characterization results and kinetic analysis, it was concluded that micro-electrolysis was mainly responsible for the removal of NO3--N by CNTs-Al-Cu.

Phytoplankton dynamics and implications for eutrophication management in an urban river with a series of rubber dams.

Rubber dams are widely used in urban rivers for landscape construction and flood control. However, the increased water residence time by dams usually causes phytoplankton accumulation. Developing a greater understanding of the phytoplankton dynamics and the effecting factors is essential for the eutrophication control of dammed rivers. Here, we investigated the variations in biomass and structure of phytoplankton communities along an urban landscape river with 30 rubber dams, and the main controlling factors during a 2-yr field monitoring. The biomass of phytoplankton significantly increased from 12.7 µg/L-Chl a and 1.14 × 107 ind./L-cells at the natural river part above dams to 65.2 µg/L-Chl a and 1.16 × 108 ind./L-cells at the 30th dam on average. There were different dominant taxa of phytoplankton between river sections with and without dams in different seasons. As Bacillariophyta dominated at the natural river part above dams throughout the year, accounting for 64.6% on average, and dominated at the 13th and 30th dams during the cold seasons (69.6% on average). But during the warm seasons, Cyanophyta and Chlorophyta increased obviously in the dammed river sections and became dominant taxa at the 30th dam, accounting for 55.9% and 34.7% respectively. The α-diversity of phytoplankton decreased along the series of dams. While the ß-diversity between river sections with and without dams increased because of species replacement. Redundancy analysis revealed that nutrients, flow velocity and temperature were the main factors influencing the spatial-temporal variation in phytoplankton community structure in this river. High-frequency monitoring data further indicated that phosphorus and discharge explained most of the variations in phytoplankton biomass within the 13th dam impoundment. It suggested that management strategies should focus on reducing the phosphorus input concentration under 0.164 mg/L and increase the discharge higher than 0.64 m3/s during warm seasons, to prevent phytoplankton bloom and further eutrophication problems in this dammed river.