| Microplastics are plastic fragments with particle size less than 5mm.Due to their widespread distribution in the environment and threats to the ecosystem and human health,microplastics have become a new type of pollution problem that is highly valued globally in recent year.It has been proved that the transport of microplastics from land to sea through rivers is the most important source and sink process of microplastics.Based on this,estuaries,as the most sensitive land-sea interaction area in coastal areas,become the key point in the whole transportation process of microplastics and are considered as the potential sink of microplastics.As a result,mangroves,the main ecosystems and buffers in estuarine areas,are likely to have been heavily contaminated by microplastics.In addition,mangroves,with their complex roots,act as filters and impeders to the flow of water,thereby fully capturing and retaining floaters,and have been shown to be collectors of Marine plastic floaters.Therefore,the mangroves have the potential to become important concentrations of microplastics.However,information about the distribution of microplastics in the mangrove ecosystem is limited.In order to promote the study of microplastics in the mangrove ecosystem,our studied the occurrence and distribution characteristics of microplastics in different mangrove sediments,water(pore water and tidal water)and typical mangrove benthic organisms(Ellobium chinense)in the north of Beibu gulf,a major mangrove distribution area in China.The main research results are as follows:(1)The water exchange flux is an important factor in determining the content of microplastics in the coastal zone,and the semi-closed Maowei Sea may have high content of microplastics due to its poor water exchange capacity.Thus,this study selected the Maowei Sea,a typical semi-enclosed sea,as its representative study site.The results show that the features of microplastics in mangrove sediment collected at the semi-enclosed Maowei Sea were relatively large quantities(ranging from520?±?8 to 2310?±?29 items/kg),variety types(PP,PE,PS and so on)and large percentages of particles with size less than 1?mm(>75%).And the analysis revealed that the microplastic abundances in the river estuaries were much lower than those at the oceanic entrance zones.Moreover,some other factors,including the rhizosphere/non-rhizosphere and the proportion of organic matter,codetermined the distribution and characteristics of microplastics.(2)Hydrodynamic factors have always been considered as the predominant factors determining the transportation of suspended particulate matter in tidal flats.In our study,the extent to which the two most critical hydrodynamic factors(tidal range and current velocity)impact the distribution of MPs in mangrove sediments was evaluated.In the different zones of the mangrove forest,strong linear relationships were observed between the tidal current velocity and MPs content during both the flood and ebb tide periods(p=0.002,R~2>0.837).And a general increasing trend was found from the seaward boundary to the landward boundary.The MPs growth rates showed obvious linear relationships with the tidal current velocity(p<0.005,R~2>0.905).(3)In this study,the typical benthic snail(Ellobium chinense)was selected as the representative biota species in mangrove ecosystems located on the river basin or estuary of Beibu Gulf of South China.A total microplastics content of 7±2 items/kg-53±6 items/kg was measured in snails.More importantly,other than industrial areas(such as QZG),the microplastics in snail organs were not related to microplastics in adjacent sediment/tidal water but were significantly affected by microplastics in pore water. |
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