Study And Evaluation On Heavy Metal Content In Liaohe Estuary Wetland Irrigated By Papermaking Wastewater

The LiaoheRiver estuary wetland is the second largest reed wetland in Asia.As the last barrier of Liaohe River,in recent years,the water supply condition of the Liaohe estuary wetland is poor and the natural precipitation is insufficient.There are some paper mills along the river,which discharge the wastewater to the wetland.The papermaking wastewater can supply a lot of water and nutrients,but also cause heavy soil accumulation in the soil.Therefore,a comprehensive and objective evaluation of wastewater irrigation to the impact on wetlands is of great significance.At present,many experts and scholars had been extensively discussed and research for the wetland heavy metal pollution comprehensive evaluation methods,and made a good results.But each method had its own advantages and disadvantages.This paper attempts to construct a comprehensive evaluation model based on set pair analysis to evaluate the heavy metal pollution in LiaoheRiver estuary wetland under wastewater irrigation,it can provide a new idea for the follow-up research.In this study,the four representative metals of Pb,Cd,Cu and Zn had been selected.And the effects on soil-reed system under papermaking wastewater irrigation with different concentrations had been studied by experimental device schemes which simulated the natural LiaoheRiver estuarywetland.The main conclusions were as follows:(1)The content of heavy metals in the soil-reed system was significantly increased under the irrigation by wastewater.The difference of heavy metals content between soil and reed was significant irrigated with different concentrations of wastewater.The content of Pb,Cu,Cd and Zn in soil and reed increased with the growth period.The general vertical distribution characteristics of soil heavy metals were as follows:The contents of Pb and Cu were the highest in 0-5cmsoil layer,while the lowest in 40-60cm The content of Cd was the highest in 0-5cm soil layer,20-40cm soil.The content of Zn in soil was the highest in 20-40cm soil layer,and the lowest in 10-20cm soil layer.The heavy metals mainly accumulated at the roots of reeds.(2)The study of heavy metals' enrichment and migration in soil-reed system showed that:the enrichment ability and migration ability of four metals in a decreased order were Cd>Zn>Cu>Pb.This result indicated that:wastewater irrigation promoted the enrichment of Cd,Cu and Pb in reed,the low concentration of wastewater could promote the enrichment of Zn in reed and inhibit with the high concentration.The effect of wastewater irrigation on the transport of Pb and Zn in reed was inhibited.The low concentration of wastewater was promoted to the migration of Cd in reed,but the high concentration was inhibited.The migration ability of Cu in reed was the strongest in CK,higher than the irrigated group,but with the increase of wastewater concentration,it gradually increased.The migration model of heavy metals in soil and reed roots showed that the content migration of Pb and Cd met the quadratic polynomial migration model,Cu met the exponential migration model,Zn met the logarithmic migration model.The migration model of four metals in reed roots and aboveground showed that,Pb and Cd met the exponential migration models,Cu and Zn met the quadratic polynomial migration models.(3)The comprehensive weights of Cd,Cu,Pb and Zn in soil surface were 0.539,0.150,0.106 and 0.205 by constructing a generalized set pair analysis and analytic hierarchy process.Cd was the main pollution contributor The ecological pollution of metals in soil was evaluated by the comprehensive evaluation model of set pair analysis and triangular fuzzy number coupling.It was found that the order of pollution degree of wetland caused by different concentrations of papermaking wastewater was CK<50mg· L-1<175mg·L-1<300mg·L-1,the pollution level is clean to mild pollution.(4)The metal pollution degree order in LiaoheRiver estuary wetland with different methods of the potential ecological pollution index and the cumulative index were consistent with the comprehensive evaluation based on set pair analysis.The evaluation result of potential ecological pollution index indicated that the integrated pollution level was a slight potential ecological pollution.The cumulative index evaluation result showed that the heavy metals were clean in the pollution level Comparison of the three methods showed that:the comprehensive evaluation model of the pairwise analysis,the analytic hierarchy process and the triangular fuzzy number can effectively solve the problem of independence and uncertainty and fuzziness of the index weight in the pairwise analysis,thus improved the soil heavy metal pollution Evaluation accuracy.