Selection Of Suitable Aquatic Plants For Ecological Restoration Based On Quadruple Screening Method

The confluence area of river and lake of Wuxi City links the lakes with the urban rivers of Wuxi City.It is an ecological transition zone with strong energy flow and material circulation process of lakes in the river basin,and is the most complex area in the river network of the lakeside area.In most of the confluence area of river and lake in China,there were some problems,such as habitat deterioration,difficult to plant aquatic plants and so on.This study aimed at the status of scarcity of aquatic plants,low biodiversity and habitat destruction in estuarine waters.Quadruple screening method was used to select aquatic plants with high adaptability to hydraulic shocks in estuaries,good removal efficiency of nitrogen and phosphorus,and suitable for growth in the confluence area of river and lake.Firstly,on the basis of the investigation of indigenous aquatic plants in Wuxi area of Taihu Lake(including suitable habitat plants)and the summary of document,preliminary screening of non-ecological risk aquatic plants suitable for planting in the confluence area of river and lake of the project demonstration area,namely primary screening species.Secondly,the primary screening species were field trial planting in the confluence area of river and lake.In this process,the selection of habitats and the adaptability of plants to hydraulic shocks in estuaries are mainly studied.Thirdly,in order to screened out aquatic plants with better removal efficiency of nitrogen and phosphorus,we carried out research on removal effect of nitrogen and phosphorus secondary screening.Finally,self-competition and elimination of aquatic plant mixed communities were carried out,leaving the aquatic plants with strong competitiveness in the community.The main conclusions are as follows:(1)Primary screening results:investigation and analysis of aquatic plants and water quality in the confluence area of river and lake of the study area showed that the water quality of the confluence area of river and lake was seriously polluted,and the water quality reached eutrophication status,basically failed to meet the lake entry standard.The results of RDA analysis showed that the main environmental factors affecting the distribution of aquatic plants in the confluence area of river and lake were water depth,SD,DO and CODMn.There were 20 kinds of main aquatic plants in the confluence area of river and lake,and the species of aquatic plants were fewer and the main ones were emergent aquatic plant.Through the calculation and analysis of the wide distribution and dominant species of aquatic plants,combining common indigenous aquatic plants such as artificial wetlands and lakeside belts in Wuxi area.The preliminary screening species of aquatic plants suitable for the confluence area of river and lake wetland growth were as follows:Phragmites australis,Zizania latifolia,Typha orientalis,Alternanthera philoxerodies,Arundo donax,Lythrum salicaria,Thalia dealbata,Monochoria korsakowii,corus calamus,Pontederia cordata,Canna indica,Sagittaria trifolia var.Sinensis;Trapa bispinosa,Brasenia schreberi,Euryale ferox,Nuphar pumilum,Hydrocharis dubia;Ceratophyllum demersum,Hydrilla verticillata,Myriophyllum spicatum,Potamogeton crispus L,Vallisneria spiralis,Potamogeton malaianus(2)Subscreening results:17 aquatic plants were planted in the confluence area of river and lake area for testing its adaptability,through observed the growth morphological characteristics of aquatic plants,three physiological characteristics of aquatic plants were determined:root activity,malondialdehyde content and proline content.Finally,cluster analysis was carried out on these indexes.The adaptability of the growth environment in the confluence area of river and lake area was ranked and combined the widely distributed aquatic plants.12 species of aquatic plants suitable for growth in estuaries were screened:Phragmites australis,Zizania latifolia,Typha orientalis,Acorus calamus,Thalia dealbata,Arundo donax,Sagittaria trifolia var.Sinensis,Canna indica,Pontederia cordata,Hydrilla verticillata,Vallisneria spiralis.Ceratophyllum demersum(3)Three screening results:studied on Purification of Nitrogen and Phosphorus by Aquatic Plants.The biomass of aquatic plants,the content of nitrogen and phosphorus in plants and the removal rate of nitrogen and phosphorLus in water quality were analyzed.The results showed that the net increase in biomass of aquatic plants had obvious growth and difference during the experiment period.The net increase in biomass of stems and leaves was more obvious than that of roots.The growth biomass of emergent plants was more obvious than that of submerged plants.The contents of nitrogen and phosphorus in different parts of aquatic plants were also different.The contents of TN and TP in stems and leaves of aquatic plants ranged from 3.30 mg/g to 14.38 mg/g,0.57 mg/g to 2.86 mg/g.The contents of TN and TP in roots ranged from 3.73 mg/g to 7.49 mg/g,0.49 mg/g to 0.83 mg/g.The nitrogen and phosphorus content in stems and leaves of the same aquatic plant was higher than that in roots,the same was true of the contribution of nitrogen and phosphorus to water absorption.The removal of nitrogen and phosphorus in water is mainly based on the absorption of aquatic plants.Most of the nitrogen and phosphorus in water can be removed by harvesting the stems and leaves of plants.Seven aquatic plants with strong water purification ability can be obtained by plant nitrogen and phosphorus absorption contribution rate and the net increase in biomass:Sagittaria trifolia var.Sinensis,Pontederia cordata,Thalia dealbata,Canna indica,Vallisneria spiralis,Zizania latifolia,Acorus calamus.(4)Final screening results:the aquatic plants were planted in the confluence area of river and lake area with single and mixed species.The growth status of aquatic plants and the changes of plant biomass before and after planting were observed.We Evaluated the competitiveness of each aquatic plant by calculating competition indicators such as relative yield,aggressive and relative competition intensity of each plant.Based on the results of previous research,the aquatic plants that were suitable for ecological restoration in the lake estuary were:Zizania latifolia,Thalia dealbata,Sagittaria trifolia var.Sinensis,Vallisneria spiralis.In this study,quadruple screening of suitable aquatic plants for ecological restoration in the confluence area of river and lake of lakeside cities in Wuxi was carried out.The aquatic plants that were suitable for ecological restoration in the lake estuary were:Zizania latifolia,Thalia dealbata,Sagittaria trifolia var.Sinensis,Vallisneria spiralis.