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Microplastics, as a new type of water pollutant, are receiving increasing attention. Due to their widespread distribution, being difficult to degrade, and toxic properties to organisms, they pose a serious threat to the health of freshwater ecosystems. This paper reviews the definition, classification, sources, as well as distribution and migration patterns of microplastics in the freshwater environment. It also discusses the toxicological effects of microplastics on freshwater organisms and the application of physical, chemical, and biotechnological technologies in the removal of microplastics. Microplastics can be categorized into primary and secondary microplastics based on types, sizes, and sources. Comprehensive analysis indicates that selecting appropriate microplastic collection and pretreatment methods is fundamental for quantitative and qualitative analysis and other research. The distribution and migration of microplastics are influenced by factors such as geographical locations, wind, water flow, and flow rate. Studies have shown that microplastics exert toxic effects on the growth and reproduction of freshwater organisms by adsorbing toxic chemicals and microbes on the surfaces, and that microplastics even affect the food chain and the health of freshwater ecosystems. To address these issues, this paper reviews the current applications of physical technologies such as adsorption, membrane filtration and sedimentation, chemical technologies such as coagulation and flocculation processes, oxidation, polymerization and photocatalytic degradation, and biological technologies such as microbial degradation. The paper concludes by proposing research prospects in four aspects: analytical methods for microplastics, environmental toxicity studies, removal technologies, and policies and regulations. This paper aims to provide ideas and references for incorporating microplastic indicators into the health assessment system of rivers and lakes and to offer management strategies for the river and lake health evaluation system.

To understand the niche and interspecific association of the dominant phytoplankton species during winter in the Pearl River estuaries, this paper selects eight Pearl River estuaries as the study area. Phytoplankton and environmental factors were detected in eight Pearl River estuaries in December 2019. The dominance value, niche width, niche overlap, variance ratio method, chi-squared test (χ2), and CCA are utilized to analyze the niche and interspecific association with respect to the dominant phytoplankton species. The results are as follows.① 54 species belonging to 6 phyla are identified, of which 7 species from 30 genera are the dominant species.② The niche width of the dominant species and the niche overlap values vary greatly among species pairs. Aulacoseira granulata has strong adaptability to the aquatic environment and exhibits a wide range of ecological adaptability. The niche overlap value of Skeletonema costatum is low, and interspecific competition is weak. ③ The phytoplankton of the Pearl River Estuary is generally in an early stage of succession and there is a trend of positive succession. The linkage community in the Pearl between species is not strong and the interspecific relationship is loose. The dominant phytoplankton species have not yet reached a relative dynamic equilibrium among themselves and between the dominant species and the environment, and the dominant species are in the stage of development. ④Ammonia nitrogen, total organic carbon (TOC), and turbidity are the main environmental factors affecting the distribution and ecological position of the dominant phytoplankton species in the eight Pearl River estuaries.