| The mudflats are located at the junction of land and sea, an area extremely rich in ecological resources and the most important spatial carrier for human survival and development, and are strongly influenced by human activities. With the rapid social and economic development of coastal areas, more and more pollutants are discharged into the coastal waters with the flow of water, which seriously affects the coastal aquatic ecological environment. Sediment is the sink of most pollutants, including nutrients, heavy metals and organic compounds. Pollutants can be enriched in sediments through a series of physical changes such as adsorption, accumulation and precipitation. When the water environment conditions change, the pollutants in sediments will be released into the overlying water, which will affect the health of the aquatic ecosystem. Biological activities will also destroy the physical structure of the sediment-water micro-interface, change the oxygen content at the interface, and induce the movement of sediment particles, bring the interstitial water out of the sediment interface, and promote the release of heavy metals in the sediments. Heavy metal pollutants are inherently toxic, persistent and difficult to degrade, leading to many serious environmental problems and posing significant health risks. Therefore, it is necessary to evaluate the risk of heavy metal pollution in surface sediments as an important reservoir of heavy metal pollutants, which will provide a scientific basis for the ecological management and restoration of mudflats.At present, most of the studies on heavy metal pollution in the sediments of Rudong mudflats focus on the source of heavy metal elements and the evaluation of biotoxicity. There is no report on the correlation analysis the distribution characteristics of heavy metals in Rudong mudflats and the distribution characteristics of benthic animals in Rudong mudflats.
In this study, the distribution characteristics of seven heavy metal elements in the sediments of the Rudong Meretrix meretrix aquaculture area were analyzed, and the potential ecological risk index method was used to evaluate the environmental risk of heavy metals in the sediments of the aquaculture area. Meanwhile, the correlation analysis between the distribution of zoobenthos and heavy metal pollution was carried out to provide reference for the ecological environment of the Meretrix meretrix mudflats in Rudong as well as for the sustainable development of the clam mudflat resources. Through four field surveys in September and December 2022, and April and July 2023 in Meretrix meretrix mudflat aquaculture area in Rudong, Jiangsu Province, the contents of Zn, Cr, Cu, Pb, As, Hg, and Cd in the surface sediments were determined, the characteristics of benthic communities were analysed. The pollution risk assessment of heavy metals in surface sediments was carried out by using the potential ecological index method, and the response relationship between heavy metal pollution in sediments and the distribution of benthic animals was analyzed.The results showed that the average contents of heavy metals in the surface sediments were in the order of Cr>Zn>Pb>Cu>As>Cd>Hg, and the contents of Zn, Cu, Pb, As, Hg and Cd were in accordance with the quality standard of one type of marine sediments.The highest value and summer average value of Cr element exceed the first class standard of marine sediment quality, and meet the second class standard of marine sediment quality.The annual comprehensive potential ecological risk index ranged from 90.49 to 145.78, with an average of110.68. With reference to the classification of potential ecological risk, the overall risk level of Meretrix meretrix aquaculture area was at the medium risk level, and the order of individual potential ecological risk of each heavy metal element was Cd>Hg>As>Pb>Cu>Cr>Zn.The ecological risks of each sampling stations were mainly from Cd, Hg and As. 4 times of the sampling, the heavy metal Cd is the main contribution element with the highest potential ecological risk in the sediments of Rudong mudflats, and it is also the main element of the sediment pollution in Rudong mudflats .Cd, Hg and Cu are the important components of the industrial sewage discharge, and the land-based inputs and other pathways are the main sources of them.As is very rare in the natural environment, and it is the main constituent of chemical fertilizers and pesticides, and the use of pesticides in the mudflat shellfish aquaculture area may be the main source of the As pollution.Most of the Pb in the sediments comes from atmospheric deposition, and the Pb is related to the pollution emission of fishing ports ships in the region. Zn is related to the zinc plating industry and the machinery manufacturing industry, while Cr is applied in large quantities in the chemical and chromium-plating industries.A total of 68 species of macrobenthos were collected in the four samplings. The richness index d ranged from 0.74 to 5.01 (SD=±1.19), the evenness index J' ranged from 0.25 to 0.92 (SD=±0.15), and the diversity index H' ranged from 0.99 to 3.79 (SD=±0.65) at each sampling station. The mean values of the diversity index H' for the four seasons of spring, summer, autumn and winter werebetween 2 and 3, respectively, Compared with the biodiversity index evaluation criteria, the biodiversity of the four seasons belonged to a relatively rich level, and the habitat level was at a ' general ' level. The density of polychaetes in the benthic animals had a significant negative correlation with Cu, Pb, Cr and Cd heavy metal element index and RI. There was a significant negative correlation between the benthic animal richness index d and the heavy metal element indexes of Pb, Cr and As. |
