Study On Teh Role Of Sediments,Leaves And Benthos In Typical Mangrove Ecosystems In The Beibu Gulf During The Migration Of Microplastics

Microplastics（MPs）have attracted worldwide attention due to their small size and self-toxicity.Studies confirm that both terrestrial and marine sources transport large amounts of plastic debris to the coast by river or tide.Mangrove forests are the most common coastal ecosystems in the tropics and are generally considered to be efficient in conserving MPs due to their abundant plant biomass.For mangroves,however,the ability to retain MPs remains at an empirical level.In addition,the investigation of the occurrence and distribution of MPs in mangroves is limited to the environmental matrix（sediment,pore water and tidal water）,which limits our understanding of mangrove ecosystems.In order to explore the impacts of mangrove ecosystems on the migration of MPs,this study was the first to explore the dynamic changes of MPs content in mangrove sediments and adjacent rivers,as well as the occurrence and distribution characteristics of MPs on mangrove leaves and in mangrove benthos（Phascolosoma esculenta）.The Beibu Gulf was the main distribution area of mangrove in China and thus was selected as the target area for this study..The main research results are as follows:（1）This study explored the impacts of estuarine mangrove ecosystems on the transport of MPs in rivers.Except for the Nan Du river with the absence of mangrove forest,the abundance of MPs in the upstream of mangrove was significantly higher than that in the downstream of mangrove（p<0.05）.The abundance of MPs in mangrove sediments was significantly higher than that in upstream and downstream rivers（p<0.05）,suggesting that mangrove sediments played an important role in intercepting and retaining the river MPs.Denser,larger,more regular-shaped MPs was more likely to be intercepted by mangrove plants.Furthermore,the combined effects of ecological indicators,the properties of mangrove and the hydrodynamic factors jointly determined the interception rates of MPs.（2）The results showed that MPs was detected in both non-flooded and flooded parts of mangrove leaves,and the MPs abundance in the flooded part was significantly higher than that in the non-flooded part.In the same mangrove,the MPs on the leaves of the flooded and non-flooded parts was not different among different tree species,but the abundance of MPs on the flooded leaves was related to the distance from the mangrove to the land.For the first time in this report,a more statistically significant classification method was used to classify MPs on leaves,and it was confirmed that water and air were both sources of MPs on leaves,and water contributed more to MPs on leaves than air.Furthermore,we estimate that mangrove leaves host a total of approximately 2.55-3.41×10¹⁴MPs around the world,indicating that mangrove leaves are a potential MPs reservoir.（3）The abundance of MPs in the digestive tract of Phascolosoma esculenta,a typical benthic organism,was within the range of 0.18-2.00 items/individual in mangrove forests and adjacent tidal flat areas in the Beibu Gulf,China.In addition,there was no significant difference in the MPs in the digestive tract between mangrove and non-mangrove areas.The results showed that there was no significant difference in the MPs of the digestive tract between mangrove and non-mangrove areas.The regression analysis showed that the MPs in the digestive tract of Phascolosoma esculenta had no correlation with those in the adjacent tidal flat and pore water,but had a strong correlation with those in mangrove sediments.PP/PE,fiber,white/clear,less than 1mm was the most common feature detected for MPs.