Analysis Of Environmental Investagetion And Evaluation Of Pollution In The Lahlu Wetland

As an alpine wetland in Tibet,Lahlu wetland has more special economic,social and protection functions than ordinary wetlands.In this paper,based on the needs of the third-stage restoration project of Lalu wetland,Lahlu wetland is taken as the object,and the water body and sediment are collected from the wetland in the dry season,the flood season and the normal season,so as to analyze its pollutant content and evaluate its pollution status.In addition,through quadrat method,it counts biodiversity and important values as well as analyze changes in plant diversity and influencing factors.The main conclusions are as follows.(1)The combined nitrogen and phosphorus pollution indices for bottom sediments in the Lalu wetland are ranked as the water period of dryness(3.645)> the water period of flatness(3.034)> the water period of abundance(2.678).The organic pollution index is ranked as the water period of dryness(1.294)> the water period of flatness(1.218)> the water period of abundance(0.558).Overall,the pollution index in the north and west is relatively low and classified as light-medium pollution,while the rest of the region is relatively severe and mostly moderate-heavy.(2)Six common heavy metals were examined in the sediment,of which three were detected,Cr,Pb and Cu.Both the cumulative index method and the potential ecological risk index indicated some degree of heavy metal contamination in the sediment,with the contamination and potential ecological risk being Cu>Pb>Cr,and the water period of dryness >the water period of abundance > the water period of flatness.Pb and Cu are higher in bottom sediment near the western settlements of the Lalu Wetlands and Cr and Cu are higher in bottom sediment near the southern lookout.(3)The improved Neymaro index shows that the water evaluation of water quality in the Lalu wetlands during the water period of dryness ranking is Class V(57.2%)> Class III(22.4%)> Class IV(10.2%)> Class I(6.1%)> Class II(4.1%).The water quality evaluation during the period of abundance ranking is Class I(46.9%)> Class III(38.7%)> Class II(10.2%)> Class IV(2.1%)= Class V(2.1%);The water quality evaluation during the period of flatness ranking is Class I(50%)> Class III(18.8%)> Class II(14.5%)> Class V(10.4%)>Class IV(6.3%).The overall water quality during the period of dryness is poor than the water period of abundance and the period of flatness,where the greater pollution of Class IV and Class V water quality areas are concentrated in the north east.(4)Improved evaluation of the Nemero index shows that the water body heavy metals in the Lalu wetlands during the water period of dryness ranking is Class I(91.7%)> Class II(4.15%)= Class III(4.15%);Water quality evaluation grade ranking during the period of abundance is Class III(44.6%)> Class II(28.3%)> Class I(14.6%)> Class IV(10.4%)> Class V(2.1%);Water quality evaluation grade ranking during the period of flatness Class I(98%)>Class II(2%).Heavy metals in wetland waters during the period of dryness are mainly distributed in the western region,with the pollution trend gradually improving from west to east.The period of abundance Phase IV,V water bodies are mainly distributed in the north of Luting North Road near the residential area,the wetland pollution trend from the northwest to southeast gradually become well,the water period of flatness basically has no heavy metal pollution of water bodies.(5)Plant communities are more variable in different regions of the Lalu Wetlands,with greater plant richness in the western and mid-western regions(R=1.27 and R=1.36 than in other regions)and uneven distribution(H=1.89 and 1.90),and lower plant richness in the southern and northern regions((R=0.66 and R=0.80)and uneven distribution of plant communities(H=1.63 and 1.18).The eastern region is a community with water onions as the dominant species and less abundant plants.Environmental factors such as dissolved oxygen,p H,nitrogen,phosphorus and heavy metals affect the plant diversity in the Lalu wetlands.(6)The nitrogen and phosphorus content of plants in Lalu wetland during the flood season is relatively high in flood season,among which the azolla filiculoides and myriophyllum are relatively high prominent and cattails have lower nitrogen and phosphorus content.The nitrogen and phosphorus absorption of the calamus,scirpus validus,polygonum hydropiper,typha orientalis presl and reed are ahead of other plants in both periods,which can be taken as the most preferred choice to harvest.(7)The results of the study reveal that the major risk areas for pollution prevention and control in Lahlu wetland are the observation platform in the south,the residential area in the west,the Party School in the north,and the northeast corner of the wetland.The restoration and management of this area should be strengthened in the future.