[Spatial and Temporal Variation Characterization and Variability of Microplastics in Water-borne River and Reservoir]

Water-source rivers and reservoirs are crucial sources of drinking water for numerous urban and rural areas. In depth exploration of the occurrence characteristics and risk differences of microplastics （MPs） in these two types of water environments is of great significance for formulating targeted pollution control strategies for MPs. This study selected the Dongjiang River and Xinfengjiang Reservoir， important drinking water sources in Guangdong Province， China， as the research objects. Through a systematic investigation of the abundance， composition， and diversity of MPs in their surface water and sediments， the differences in the pollution characteristics of MPs in the two types of water environments under spatiotemporal changes were explored in depth. The research results showed that during the dry and wet seasons， the abundance ranges of MPs in the surface water of the Dongjiang River were 180-500 and 33-300 items·m^-3， respectively， and the corresponding abundance ranges of MPs in sediments were 145-1 610 and 105-410 items·kg^-1， respectively. In the Xinfengjiang Reservoir， the abundance ranges of MPs in the surface water during the dry and wet seasons were 120-750 and 233-733 items·m^-3， respectively， and the abundance ranges of MPs in sediments were 75-365 and 80-445 items·kg^-1， respectively. The detected MPs were predominately 0.1-1 mm， fibrous， and white， and PET， PP， PE， and CP were the dominant polymer types. During the dry season， the abundance of MPs in the surface water and sediments of the Dongjiang River was significantly higher than that in the wet season （P < 0.05）. However， the difference in the abundance of MPs in the Xinfengjiang Reservoir between the two water periods was not obvious， indicating that the impact of water period changes on the abundance of MPs in the two types of water environments was different. At the same time， the diversity indices of MPs in the two types of water environments both showed the characteristic that the dry season was significantly higher than the wet season （P < 0.05）， indicating that water period changes affected the diversity of MPs in the two water bodies by re-combining the composition of MPs. In addition， under different water periods， the distribution of MPs in the Dongjiang River and Xinfengjiang Reservoir showed a large spatial heterogeneity. The impact of water period changes on the lower reaches of the Dongjiang River was greater than that on the upper reaches， and the impact on the tributaries entering the Xinfengjiang Reservoir was greater than that on the reservoir body. Notably， the abundance of MPs in the Xinfengjiang Reservoir was significantly higher within the two water periods than that in the Dongjiang River （P < 0.05）， indicating that the Xinfengjiang Reservoir was an important pollution source of MPs in the Dongjiang River. The comparison results of the three risk indicators showed that the ecological risk of MPs in the surface water of the Xinfengjiang Reservoir in the dry season was higher than that in the Dongjiang River. The differences in the pollution characteristics of MPs in the two types of water environments in different water periods may have been closely related to the differences in the impacts of rainfall and flow on their respective pollution sources and hydrodynamic characteristics.