Horizontal and vertical distribution of microplastics in dam reservoir after impoundment

Environmental fate of microplastics in alpine and canyon-type river-cascade reservoir systems: Large-scale investigation of the Yalong River in the eastern Qinghai-Tibet Plateau

Reservoirs are regarded as potential collection sites for microplastics (MPs), and ample water resources in plateau regions provide favorable natural conditions for hydroelectric power generation. However, research on the impact of cascade reservoir construction in the plateau region on the fate of MPs within the watershed is limited. In this study, the Yalong River, an alpine canyon river in the eastern Qinghai-Tibet Plateau, was selected as the research area. This study explored the distribution of MPs at various depths in water, sediment, and riverbank soil as well as the formation of "MP communities" within the river-cascade reservoir system. Furthermore, the effects of dam construction on MPs' migration in different environments were analyzed. The results revealed that the abundance of MPs in the water and sediment within the cascade reservoir area (CRA) was significantly higher than that in the river area (RA) (P < 0.001). Additionally, the trend of increasing MPs in water with decreasing altitude was notably slower in CRA. Regarding shape, the proportion of fibers in the water within the CRA was significantly lower than that in the RA, with a smaller vertical migration rate in the water than in the sediment. The proportion of MPs < 500 μm in the water within the CRA was significantly higher than that in the RA. High-density MPs were notably deposited in the reservoir sediments. The analysis of the MP communities revealed that the construction of cascade dams led to relative geographical isolation between different sampling sites, reducing the similarity of MP communities in the CRA. This study established a theoretical foundation for understanding the impact of cascade dam construction on the fate characteristics of MPs and their potential risks in plateau areas.

Occurrence of microplastic pollution in rivers globally: Driving factors of distribution and ecological risk assessment

Microplastics, as global emerging pollutants, have received significant attention worldwide due to their ubiquitous presence in the rivers. However, there is still a lack of clarity on the occurrence, driving factors, and ecological risks of microplastics in rivers worldwide. In this study, a global microplastic dataset based on 862 water samples and 445 sediment samples obtained from 63 articles was constructed, which revealed the temporal and spatial distribution of abundance and morphological characteristics of microplastics in rivers across the globe. In global rivers, the abundance of MPs in both water and sediment spans across 10 and 4 orders of magnitude, respectively. The MP comprehensive diversity index based on the physical morphological characteristics of MPs indicated a significant positive correlation between the pollution sources of MPs in different environmental media. Based on the data was aligned to the full-scale MPs, a novel framework was provided to evaluate the ecological risk of MPs and the interaction effects between the influencing factors driving the distribution characteristics of MPs in rivers around the world. The results obtained demonstrated a wide variation in the key driving factors affecting the distribution of microplastics in different environmental media (water and sediment) in rivers globally. The diversity indices of the morphological characteristics of MPs in densely populated areas of lower-middle income countries in Asia were significantly higher, implying that the sources of microplastics in these regions are more complex and extensive. More than half of the rivers are exposed to potential ecological risks of MPs; however, microplastics may pose only immediate risks to aquatic species in Burigang River, Bangladesh. This can provide valuable insights for formulating more effective scientific strategies for the management of MP pollution in rivers.

Effects of land use on soil microplastic distribution adjacent to Danjiangkou reservoir, China

As a new type of pollutant, microplastics (MPs) are an increasingly prominent threat to terrestrial ecosystems. However, the distribution, sources and influencing factors of MPs need to be further studied, especially in reservoir surrounding soil, a hot zone for MPs accumulation and a source of MPs in the watershed. Here, we detected MPs in 120 soil samples collected around Danjiangkou reservoir, with their amount ranging from 645 to 15,161 items/kg. The topsoil layer at 0-20 cm had lower levels of MPs (mean 3989 items/kg) than subsoils at 20-40 cm (mean 5620 items/kg). The most commonly detected types of MPs were polypropylene (26.4%) and polyamide (20.2%), with sizes ranging from 0.05 to 0.5 mm. With regard to shape, most MPs (67.7%) were fragmented, while fibers make up 25.3% of the MPs. Further analysis revealed that the number of villages had the highest driving force for the abundance of MPs with 51%, followed by pH 25% and land use types 10%. The water and sediment of reservoirs are important sources of agricultural soil microplastics. Paddy lands showed higher microplastics levels than orchards and dry croplands. The polymer risk index indicated that the agricultural soil near Danjiangkou reservoir had the highest MPs risk. This study highlights the importance of assessing MPs contamination in the agroecosystems surrounding reservoirs and provides valuable insight into clarify the ecological risks of MPs in the reservoir area.

Vertical Differentiation of Microplastics Influenced by Thermal Stratification in a Deep Reservoir

Microplastics (MPs) are an emerging environmental concern. However, vertical transport of MPs remains unclear, particularly in deep reservoirs with thermal stratification (TS). In this study, the vertical variation in MP organization, stability, migration, and the driving factors of the profile in a deep reservoir were comprehensively explored. This is the first observation that TS interfaces in a deep reservoir act as a buffer area to retard MP subsidence, especially at the interface between the epilimnion and the metalimnion. Interestingly, there was a size-selection phenomenon for MP sinking. In particular, the high accumulation of large-sized MPs (LMPs; >300 μm) indicated that LMPs were more susceptible to dramatic changes in water density at the TS interfaces. Furthermore, simultaneous analysis of water parameters and MP surface characteristics showed that the drivers of MP deposition were biological to abiotic transitions during different layers, which were influenced by algae and metals. Specifically, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and microscopic Fourier transform infrared analyses implied that the occurrence of metals on the MP surface can promote MP deposition in the hypolimnion. Our findings demonstrated that TS significantly influenced the MP fate in deep reservoirs, and the hotspot of MP exposure risk for vulnerable benthic organisms on the reservoir floor deserves more attention.

Effects of irrigation on the fate of microplastics in typical agricultural soil and freshwater environments in the upper irrigation area of the Yellow River

Agricultural activities are among the most significant sources of microplastics (MPs) in water. However, few studies have explored the effect of irrigation on the fate of MPs in agricultural systems. This study investigated the distribution of MPs in agricultural soil, surface water, and sediment of adjacent rivers, as well as the "MP communities" in various environments before and after irrigation in a typical agricultural irrigation area of the Yellow River. MPs were detected in all of the examined sites. The number of MPs in surface water and sediment increased after irrigation, whereas those in the surface soil of croplands decreased. In the vertical direction, irrigation accelerated the migration of MPs (< 100 µm) deep into the soil. The vertical mobility of fibers in soil was faster than that of other types of MPs. Moreover, irrigation decreased the correlation between soil properties and MPs in soils. MP community analysis indicated that irrigation enhanced the differences between MP communities among adjacent environments. Collectively, our findings confirmed that river water irrigation caused secondary MP pollution in the soil environment and accelerated MP pollution in deep soil. Therefore, this study provides a theoretical basis for the development of strategies for MP pollution control in agricultural soil.