Effects of cascade dams on the occurrence and distribution of microplastics in surface sediments of Wujiang river basin, Southwestern China.

The influence of cascade dams on the migration of microplastics (MPs) was conducted by analyzing the spatial distribution of MPs in sediments of the Wujiang river basin (Wujiang river basin) in Southwest China. The results showed that the abundance of MPs in Wujiang river basin sediments ranged from 310 to 2620 items/kg dw (mean: 1354 items/kg dw, a high level compared with aquatic sediments worldwide). The main chemical components of these MPs were polypropylene and polyethylene. High abundance of MPs in tributary sediments suggested that tributary inputs contributed to the main stream and reservoirs. Statistical analysis showed that gross domestic product (GDP) and the basin area of cascade reservoirs, rather than hydraulic retention time and reservoir age, were the dominating factors in the distribution of MPs in the Wujiang river basin. The accumulation of MPs in cascade reservoirs implied the interception effect of cascade dams. The rapid development of cascade dam systems and the interception effect of dams should be taken into account when predicting the flux of MPs from rivers to the ocean. Heavy metals found on the surface of the MPs showed the compound pollution of MPs and heavy metals in dammed rivers and cascade reservoirs. Our results deepen the understanding of the migration of MPs in rivers alongside intensive cascade hydropower development.

Star sensor calibration with separation of intrinsic and extrinsic parameters.

The calibration method based on integrated modeling with intrinsic and extrinsic parameters is widely used for star sensors. However, the unified optimization of parameters results in the coupling between intrinsic and extrinsic parameters in this method, further influencing the calibration accuracy of the intrinsic parameters and causing certain limitations for the practical applications involving precise extrinsic parameters. A novel calibration method for star sensors with separation of intrinsic and extrinsic parameters is proposed in this paper to solve the issue. Firstly, the coupling form of intrinsic and extrinsic parameters in the integrated calibration model is analyzed, and the coupling degree is analyzed through the partial correlation coefficient (PCC). Then, on the basis of the analysis results, combined with the applications of star sensors in satellites and missiles, the extrinsic parameters coupled with the intrinsic parameters are separated individually, and the intrinsic and extrinsic parameters without coupling are optimized nonlinearly as a whole. The experimental results verify the validity of the proposed method.

Investigating the effect of dynamic traffic distribution on network-wide traffic emissions: An empirical study in Ningbo, China.

Urban road traffic is one of the primary sources of carbon emissions. Previous studies have demonstrated the close relationship between traffic flow characteristics and carbon emissions (CO2). However, the impact of dynamic traffic distribution on carbon emissions is rarely empirically studied on the network level. To fill this gap, this study proposes a dynamic network carbon emissions estimation method. The network-level traffic emissions are estimated by combining macroscopic emission models and recent advances in dynamic network traffic flow modeling, namely, Macroscopic Fundamental Diagram. The impact of traffic distribution and the penetration of battery electric vehicles on total network emissions are further investigated using the Monte Carlo method. The results indicate the substantial effect of network traffic distribution on carbon emissions. Using the urban expressway network in Ningbo as an example, in the scenario of 100% internal combustion engine vehicles, increasing the standard deviation of link-level traffic density from 0 to 15 veh/km-ln can result in an 8.9% network capacity drop and a 15.5% reduction in network carbon emissions. This effect can be moderated as the penetration rate of battery electric vehicles increases. Based on the empirical and simulating evidence, different expressway pollution management strategies can be implemented, such as petrol vehicle restrictions, ramp metering, congestion pricing, and perimeter control strategies.

Effects of cascade dam on the distribution of heavy metals and biogenic elements in sediments at the watershed scale, Southwest China.

Cascade dam has important effects on the magnitude and dynamics of sediment particles, heavy metals, and biogenic elements in reservoirs. However, systematic studies on the interception effect of cascade dam on the various elements that occur in rivers at the watershed scale are lacking. The aims of this study were to (1) assess the interception effect of a cascade dam on heavy metals and biogenic elements and (2) investigate the key factors of these effects of the cascade dam. Surface sediments were collected from 29 sites distributed in the Wujiang River Basin (WRB, a watershed scale in Southwest China), including from tributaries (7 sites), the main stream (13 sites), and cascade reservoirs (9 sites). In addition, the particle sizes, heavy metals (Fe, Mn, Zn, Cr, Cu, As, Pb, and Cd), and biogenic elements (TOC, TN, and TP) of sediments were analyzed. Compared with the tributaries, D50 (median particle size) was significantly reduced by 56.8% of cascade reservoirs. The proportion of 63-2,000 µm decreased from 13.78 to 1.34%, indicating that more coarse particles were intercepted in the cascade reservoirs. The contents of heavy metals (Fe, Zn, Cu, As, and Cd) declined significantly along the way. On the whole, the contents of TOC, TN, and TP were highest in the midstream and lower in the upstream and downstream. The hydrological condition (reservoir age, HRT, and flow) and the basin area and internal and external inputs of cascade reservoirs are important factors. The findings deepen the current understanding of the mechanisms by which cascade dam affects the river transport of heavy metals and biogenic elements at the watershed scale and provide an important reference for establishing hydropower developments along rivers and developing aquatic environment management strategies.

Oxygenation and synchronous control of nitrogen and phosphorus release at the sediment-water interface using oxygen nano-bubble modified material.

Synchronously controlling the nitrogen (N) and phosphorus (P) release from sediments is an important basis for eutrophication management in lakes, but it is still a technical challenge at present. Loading nano-bubbles on the surface of natural minerals to increase dissolved oxygen(DO) level at the sediment-water interface (SWI)provides a possible solution to this problem. In this study, oxygen nano-bubble modified mineral (ONBMM) technology was developed, and its efficiency of oxygenation at the SWI and effect on the removal of internal nutrient input were evaluated under simulated conditions. The results showed that ONBMM effectively improved DO levels near the SWI; the highest concentration reached 6.55 mgL-1. Meanwhile, adding ONBMM remarkably reduced the concentrations of total P(TP), total N(TN) and ammonia N(NH3-N) in the overlying water. Compared with the control group, the fluxes of TP, NH3-N, and TN loading from sediments in simulation cores treated with ONBMM reduced by 96.4%, 51.1%, and 24.9%, respectively. The high-resolution data obtained by DGT showed that ONBMM effectively inhibited the reduction and release of FeP through increasing the oxygen level at the SWI. The results of 16S rRNA high-throughput sequencing showed that adding ONBMM strengthened the role of nitrobacteria, denitrifying bacteria, and ammonia oxidation bacteria at the SWI. The ONBMM technology provides a new tool to achieve oxygenation at the SWI and in situ control of internal pollution in eutrophic lakes.

Removal of phosphate by aluminum-modified clay in a heavily polluted lake, Southwest China: Effectiveness and ecological risks.

Lake eutrophication is a main water environmental problem. When the extraneous nutrients are effectively controlled, nutrients in water mainly source from endogenous release from the sediment. In situ passivation is an important pollution control technique for endogenous pollution in lakes or reservoirs. This study focused on Qianling Lake, a cascade-channel lake in Southwest China polluted by phosphorus (P), which was selected for an in situ passivation project using a novel Al-based passivator on the polluted water area. Accordingly, the release of endogenous nutrients from the sediment can be controlled to remediate the polluted water, and the remediation effect and ecological risk of the passivation were evaluated. The results showed that after 12 months of passivation, the release of P from the sediments can be effectively inhibited. Concentrations of total P (TP) and Chl-a within water of the passivation area were reduced by approximately 80% and 70%. Meanwhile, water transparency and the content of dissolved oxygen were remarkably enhanced. The application of the passivator remarkably improved the water quality. P in water and at the sediment-water interface was fixed on the surface of sediment in the form of Al-combined state. This passivator exhibits favorable P-controlling performance in the restoration of lakes and reservoirs polluted by endogenous P. This aluminum-modified clay is an effective passivator for remediation of internal P pollution in potentially similar lakes and reservoirs.