Studies On Water Purification Effect And Evaluation Of Aquatic Plants In Hefei Shushan Minqu Constructed Wetland

The Shushan Minqu constructed wetland is a demonstration project that aims to preserve the original site conditions and protect the water quality of reservoirs while at the same time highlighting the beauty of aquatic plants in Hefei.Due to the incomplete management of the wetland in the later period,together with the sewage discharge from the surrounding communities and the industrial park.The water quality of the wetland deteriorated and the plant landscape effect was not obvious.This article studies on the Aquatic Plants of the Shushan Minqu constructed wetland in Hefei.By investigating the species composition of aquatic plants;Collected the water of the Sedimentation tank,the Purification pool and the Comprehensive purification pool,then studied the changes of the pH,transparency,total nitrogen and total phosphorus in the water with seasonal changes at different sampling times;Collect the 7 aquatic plant root sediments including Thalia dealbata,Cattail,Reed,Water Lily,Cyperus alternifolius,Myriophyllum verticillatum L.,and Eichhornia crassipes,and through experiments to analyze the sedimentation of plants on the sediment;The 7 aquatic plants were used as experimental materials to analyze the ability of plants to accumulate nitrogen and phosphorus;Finally,the AHP method was used to comprehensively evaluate the actual landscape value of seven aquatic plants from the two aspects of plant purification function and ornamental value,to fully understand the ornamental value of aquatic plants and their ability to purify wastewater in wetland water systems,so as to provide scientific basis for the selection of wetland plants and ecological treatment of water eutrophication in the future.Draw the following conclusions:(1)During the period of April to October in 2017,Through investigation we discovered that the plant landscape of the Shushan Minqu constructed wetland is composed of two parts:wetland shoreline plant landscape and wetland water plant landscape.The data showed that there were 26 families,35 genus,and 36 species of aquatic plants in this constructed wetland.The families of the most plant species including Gramineae,Nymphaeaceae,Cyperaceae,Compositae and accounting for 11.1%,5.5%,8.3%,11.1%,and 5.5%,respectively.(2)To analyze the water samples in the Sedimentation tank,the Purification pool and the Comprehensive purification pool,we found that at the same sampling time,the pH variation range of the water bodies was 7.6~7.9,7.2~7.1,7.6~7.4,respectively.After the sewage flows through the three wastewater treatment processes,the pH value is reduced;the transparency of the water body varies from 13 to 15(cm),7 to 8(cm),and 12 to 14(cm).Although the transparency of the water has improved,the overall transparency has been poor;The range of variation of TN content was 4.5~5(mg/L),3.2~3.5(mg/L),and3.8~4.2(mg/L),respectively,and the range of TP content was 0.3~0.38(mg/L),0.17~0.25(mg/L),0.27~0.31(mg/L)respectively.The results showed that after the water flows through the three wastewater treatment processes,the content of TN and TP has decreased.(3)The order of the total nitrogen content in the root sediments of the 7 aquatic plants was as follows:Reed>Cattail>Thalia dealbata>Cyperus alternifolius>Myriophyllum verticillatum L.>Water Lily>Eichhornia crassipes.Among them,the content of total nitrogen in Reed root was the highest,which was 2.63 g/kg,and that of Eichhornia crassipes was the lowest,1.46 g/kg.The order of total phosphorus content in the sediments of the seven aquatic plants was as follows:Reed>Thalia dealbata>Cattail>Cyperus alternifolius>Water Lily>Eichhornia crassipes>Myriophyllum verticillatum L.Among them,the total phosphorus content in the sediment of the root of Reed was the highest,which was 3.21 g/kg,and the lowest was Myriophyllum verticillatum L.,2.03 g/kg.The results showed that Reeds had the best deposition and absorption of nitrogen and phosphorus in the sediment.(4)Through field surveys,we discovered that the period from April to July is the rapid growth period of the 7 aquatic plants.The growth of their plant height from April to July is Reed(154.23cm),Thalia dealbata(210.38cm),Cattail(161.65cm),Cyperus alternifolius(69.2 cm),Water Lily(12.93 cm),Eichhornia crassipes(11.45 cm),and Myriophyllum verticillatum L.(41.9 cm).The order of biomass of the 7 aquatic plants in October was Thalia dealbata>Reed>Cyperus alternifolius>Cattail>Water Lily>Eichhornia crassipes>Myriophyllum verticillatum L.,among which,the biomass of the Thalia dealbata was the highest,which was 2300 g/m~2.Myriophyllum verticillatum L.had the lowest biomass,which was 720 g/m~2.The order of nitrogen accumulation of the seven aquatic plants in October was Thalia dealbata>Reed>Cyperus alternifolius>Cattail>Myriophyllum verticillatum L.>Eichhornia crassipes>Water Lily,among them,the nitrogen accumulation amount of the Thalia dealbata was the highest,which was 60.75g/m~2,and the nitrogen accumulation of the Water Lily was the lowest,which was 29.8g/m~2.The order of phosphorus accumulation of 7 aquatic plants in October was Cattail>Reed>Thalia dealbata>Cyperus alternifolius>Water Lily>Eichhornia crassipes>Myriophyllum verticillatum L.,among which,the accumulation of phosphorus in Cattail was the highest,which was 5.4 g/m~2.The accumulation of phosphorus in Myriophyllum verticillatum L.was lowest with 3.9 g/m~2.Based on the above data,the four types of emergent plants such as Reed,Cattail,Thalia dealbata and Cyperus alternifolius have larger biomass and more accumulation of nitrogen and phosphorus,indicating that the emergent plants have a stronger nitrogen and phosphorus nutrient enrichment.(5)In this paper,The AHP method was used to comprehensively evaluate thepurification function and ornamental value of the 7 kinds of aquatic plants in the plot.The evaluation model consists of 13 evaluation factors,such as plant total nitrogen,plant total phosphorus,sediment total nitrogen,sediment total phosphorus,plant type,agglomeration degree,leaf color,leaf type,leaf texture,flower color,flower phase,flowering period and flower diameter.Based on the field surveys and the experimental data,by calculating the weights of the evaluation factors and scoring the 13 evaluation factors.Finally,the following evaluation scores are:Thalia dealbata(2.777),Cattail(2.687),Reed(2.673),Water Lily(2.157),Cyperus alternifolius(1.88),Myriophyllum verticillatum L.(1.658),Eichhornia crassipes(1.642).The results showed that the purification function and ornamental value of these four aquatic plants such as Thalia dealbata,Cattail,Reed and Water Lily are better,that is,they have higher actual landscape value.