Temporal And Spatial Pattern Of Aquatic Plant Diversity And Establishment Of Water Quality Assessment Model Based On Aquatic Plants In The Hanjiang River

A series of water conservancy projects on Hanjiang River,such as the South-toNorth Water Diversion,the Yangtze to Han River Water Diversion,the Han to Wei River Water Diversion,and the Cascade Projects,have transformed the Hanjiang River from a natural river into an important functional river that integrates ecological services such as water regulation,flood control,shipping,power generation and irrigation.The original natural environment of the Hanjiang River has undergone dramatic changes during the development of modernization.Signs of serious degradation have appeared in the natural ecosystem of the Hanjing River—— simplified ecosystem structure,reduced biodiversity,disappearance of rare species,frequent occurrence of water blooms,etc.The damage of the ecosystem will cause long-term irreversible impact on the water environment of the river basin.Therefore,it is especially important to monitoring the water environmental health of water source area for sustainable development.The first phase of the South-toNorth Water Diversion Project and its supporting projects have been officially completed for almost 5 years.The works focusd on the investigation and assessment of the water ecological environment and water quality in the mid-lower reaches of the Hanjiang River are relatively rare in recent years.Therefore,it is urgent to carry out systematic investigation of water ecological environment,water quality problem identification and water quality evaluation in the mid-lower reaches of the Hanjiang River.Aquatic plants,as important producers in river ecosystem,not only play important roles in river water environment health,but also can reflect the change of water environment quality.Based on the field investigation and monitoring of aquatic plant species and communities in the mid-lower reaches of the Hanjiang River and historical water quality monitoring data since 2010,this paper studied and analyzed the survey results and established a model with mathematical methods.The main works of this study are as follows: 1).Summaried the aquatic plant species of the mid-lower reaches of Hanjiang River and analyzed the species composition.2).Analyzed the temporal and spatial patterns of aquatic plant communities and their diversity structure in mid-lower Hanjiang River.3).Identify the impact of water conservancy construction on the aquatic plant community structure in the mid-lower reaches of Hanjiang River.4).The water quality in the mid-lower reaches of the Hanjiang River was evaluated,and the sources of pollution were identified.5)The mathematical model for evaluating the tropical status of the middle reaches of the Hanjiang River using aquatic plants was established,and the tropic status of the rivers in the middle reaches of the Hanjiang River in 2017 was evaluated.1.In this study,104 species of aquatic plants belonging to 62 genera and 33 families in the mid-lower reaches of Hanjiang River were recorded.Among them,there are 5 species of pteridophyta,92 species of angiospermae(57 species of monocotyledons plants,35 species of dicotyledonous plants,4 species of algae and 3 species of bryophyte plants.There are 5 form of life styles(emergent,floating-leaved,free drifting and helophytes).Among them,there are 46 species of helophytes and 26 species of submerged plants.Cyperaceae have the most species among families and the species number is 17.Potamogeton have the most species among genus and the species number is 8.There are 13 area types of aquatic plants in the mid-lower reaches of the Hanjiang River,most of the genus are cosmopolitan,and the proportion of tropical and temperate components is almost the same.2.The dominant species of aquatic plants in the middle reaches of Hanjiang River are Hydrilla verticillata(Lf)Royle,Potamogeton perfoliatus L.,Elodea nattallii(Planch.)St.John and Stucknia pectinatus(L.)Borner.The dominant species of aquatic plants in the lower reaches of Hanjiang River are Eichhornia Crassipes(Mart.)Solms and Hydrocharis dubia(Bl.)Backer.The aquatic plants in the middle reaches of the Hanjiang River have higher diversity than the downstream.3.Obvious community succession were seen in Danjiangkou,Laohekou and Xiangyang river sections when the South-to-North Water Diversion Project completed.After water diversion,the diversity of aquatic plant communities in the mid-lower reaches of Hanjiang River decreased,the proportion of free drifting plants and floating-leaved plants increased,while the propotion of emergent plants decreased.4.From 2010 to 2015,the average annual water quality of the five river sections in the mid-lower reaches of Hanjiang River were in line with the water function zone classification standard,reaching the standard of Class II water.According to the average of the comprehensive pollution index,the water quality of the five river sections was ranked as follows,Laohekou section > Xiangyang section > Danjiangkou section > Xiantao section > Hankou section.5.The main sewage pressure in the middle reaches of Hanjiang River was agricultural pollution,and the lower reaches was mainly domestic sewage.From 2010 to 2015,there were five major pollution items in the mid-lower reaches of Hanjiang River,including total phosphorus,ammonia nitrogen,permanganate index,petroleum and lead.6.The middle reaches of Hanjiang River are facing great eutrophication pressure after the implementation of the South-to-North Water Diversion Project.7.The determination coefficient of the linear relation corresponding to the optimal total tropical sensentive value(TTSV)in aquatic plants is high,which proves that the model based on aquatic plants to evaluate the water tropical status is established.The relative error of the model is within a reasonable range,which proves that the model is effective.