Environmental DNA Metabarcoding Technology To Monitor The Diversity Of Aquatic Insects In The Dongjiang River Basin

Rivers are carriers of life in water and carry the flow of matter and energy of aquatic ecosystems.Human-induced climate change,hydrological rhythm changes,eutrophication and other problems have caused great disturbances to river ecosystems.Aquatic insects play an important role in freshwater ecosystems and are often used as biological indicators due to their sensitivity to environmental changes.Monitoring aquatic insect populations to assess the impacts of human disturbance and climate change on freshwater ecosystems is particularly important.However,traditional ecological surveys have major shortcomings,such as time-consuming and labor-intensive,difficult taxonomic identification,and inability to carry out long-term,highfrequency monitoring.The dataset monitored based on environmental DNA(hereinafter referred to as e DNA)technology can provide a multi-level perspective,which is of great significance for fully understanding the biodiversity changes of aquatic insects in subtropical rivers in China.Dongjiang is an important part of China’s South China economic and ecological region,covering Guangdong Province and parts of Jiangxi Province.The area through which it flows is densely populated and economically developed,accounting for 70% of the province’s GDP.Dongjiang also shoulders the important task of supplying water resources to the Hong Kong Special Administrative Region,which is a veritable water of life,politics and economy.Due to the high utilization of water resources in the basin and the impact of human interference on growth,the ecological environment and water resources of the Dongjiang River Basin have been greatly threatened.Solutions need to be further explored to achieve sustainable watershed development.In this study,the main stream of the Dongjiang River and its main tributaries were used to investigate the aquatic insect taxa at 51 sampling points in the study area using e DNA technology,and the spatial patterns of aquatic insect community diversity and functional diversity were analyzed.Analyze the impact of different water collection on the assessment of aquatic insect biodiversity in water bodies,and clarify the optimal water collection required by e DNA technology to detect aquatic insects in streams and rivers;Combined with the physical and chemical parameters of water,the main environmental factors affecting the changes of aquatic insect communities in the study area were elucidated.Use the Aquatic Insect Biological Index to assess the health of river ecosystems.The main findings are as follows:1.The data show that the amount of water extracted significantly affects the species monitoring of aquatic insects,for stream water,the collection of 2L surface water can monitor 80%of species,while for mainstream rivers,at least 4L of surface water is required to complete 80%of species monitoring.To improve the accuracy or repeatability of monitoring between replicate samples,5L of surface water can be collected for stable monitoring results regardless of stream and main stream.2.In 2021,the survey of aquatic insects in the Dongjiang River Basin obtained a total of 166 species in 6 orders,20 families,89 genera,and 166 species.Among them,diptera and mayfly are the two dominant groups,accounting for 99.88% of the total reads.The three families of Rockworm(69.20%),Tetrapodidae(14.36%)and Mosquitoes(14.26%)accounted for 97.82% of the total number of reads.After the correlation analysis of diversity index and environmental factors,it was found that species richness,Shannon Wiener index,Simpson index,functional richness and functional number dispersion were positively correlated with the distance from estuary.The functional uniformity index was negatively correlated with the distance from the estuary.Altitude is the most important environmental factor affecting species richness,and permammolate is an important environmental factor affecting species richness.Altitude,dissolved oxygen,and permathate are important environmental factors affecting functional richness.3.The ecological health of the four rivers in the Dongjiang River Basin was evaluated by FBI(Section Biological Index,hereinafter referred to as FBI)and WQI(Comprehensive Water Quality Labeling Index,hereinafter referred to as WQI)index.The water quality of the headwaters of the Dongjiang River and the Hun River is in good condition,and as the river flows downstream,the middle reaches of the Dongjiang River and the Xizhi River basin are in a general water quality state,while the water quality of the lower reaches of the Dongjiang River and the Shima River is poor.The Dongjiang River Basin as a whole is in the general level of water quality standards,and the water quality status is upstream> midstream > downstream,and there are no health and very poor grades in the water quality assessment.In general,the diversity of aquatic insect species,functional diversity and water quality status in the Dongjiang River Basin were as follows:upstream> middle > downstream.This paper aims to use e DNA to monitor the diversity of aquatic insects in the Dongjiang River Basin.It can provide important datasets and technical support for the application of e DNA technology in aquatic insect monitoring and ecosystem management in subtropical rivers.