Research On The Characteristics Of Rare Earth Elements In Sediments And Their Source Tracers In The Mangrove Areas Of Northern Hainan Island

Mangrove wetland of Hainan Island is the most complete and distributed in China.However,the mangrove area was reduced year by year due to the destruction of man-made activities such as early neglect,reclamation and pollutant discharge.In recent years,because people's awareness of ecological and environmental protection is enhanced,the mangrove wetlands have been again to restore and protect,and at the same time people began to strengthen the research of mangrove ecological environment,such as the morphological characteristics,accumulation and distribution of heavy metals,organic matter,morphological and biological effectiveness of heavy metals and related research.However,it should be noted that there has no research about the rare earth elements composition and source tracers of sediment,this paper selects the Dongzhai Harbor ? Bamenwan Bay and Xinying Harbor mangrove wetland as the research area in the northern of Hainan Island,it analyzes the sediment rare earth elements compositions,spatial changes and differentiation characteristics,comparing the distribution pattern and characteristic parameter of rare earth elements in the surrounding areas,and uses the discriminant function to discriminate the source of sediments,to provide reference for the restoration and management of mangrove in Hainan.It is found that the rare earth elements in sediments have the following characteristics of study area:(1)The total amount of rare earth elements in sediments of northern Hainan Island mangrove wetlands ranged from 191.35 mg.kg-1to 400.90 mg.kg-1,the coefficient of variation was 24.4%,the spatial content changes greatly;the average content is 261.14 mg.kg-1,compared to other areas of China,it was at a medium high level.The average content of LREE is 242.48 mg.kg-1,the average content of HREE is 18.66 mg.kg-1,the average value of ?LREE/?HREE is 13.04,indicating that LREE was the main content of the ?REE contribution in mangrove sediments in northern Hainan Island.The value of ?Eu ranged from0.50 to 0.82,with an average value of 0.66 and a negative anomaly.The ?Ce value ranged from 1.55 to 2.28,with an average value of 1.9 and apparent positive anomaly.(2)The content of rare earth elements in different sediments of mangrove wetland area was as follows: Xinying mangrove Harbor Mangrove Wetland > Eight Bay Mangrove Wetland > Dongzhaigang wetland,the content distribution of ?LREE??HREE and ?REE reached an agreement.It is obviously that the negative anomalies of Eu was discovered in Dongzhaigang Mangrove Wetland,showing that the sedimentary environment in this area was bebeficial to the reduction;the positive anomalies of Ce was also discovered in this area,showing that this area was greatly influenced by ocean effect;The maximum of?LREE/?HREE was discovered in Xinyingmangrove Harbor Mangrove Wetland,it showed that the REE fractionation is very obvious in this area.(3)The ?REE content showed difference in different tidal sediments: forest sediments >forest edge sediments > light beach sediments,the distribution of ?REE was mainly controlled by the sediment content of TOC instead of the grain size composition of the sediment,and the erosion by the sea and other physical and chemical factors together control the content of ?REE.The negative anomaly of Eu,positive anomaly of Ce and the difference of ?LREE/?HREE didn't have a significant difference in the three regions,indicating that the environment of the three tide level does' t exist much difference.(4)In the vertical direction,the overall performance of ?REE conten in sediment was as follows: B layer(10 ~ 15cm)>C layer(20 ~ 30cm)>D layer(30 ~ 40cm)>A layer(0 ~ 5cm), the distribution of ?REE was controlled by size components in sediment,at the same time the strong water leaching lead to the mass loss of rare earth elements in the A layer.The smallest negative anomaly of Eu in existed in the A layer,the largest positive anomaly of Ce also existed in the A layer,it can be found that the A layer is often disturbed by the marine environment so that the oxygen content of the A layer is increased,and the Ce in the seawater is precipitated to the surface sediments.The differentiation of LREE and HREE in A layer is the most serious.(5)Further analysis of rare earth elements source,the Chondrite-Normalized REE patterns show that relatively enriched in light REE,with flat HREES patterns and obvious negative Eu anomalies,which is diagnostic of a terrigenous sediment source,the curve is tilted with a negative slope of the distribution pattern;Upper continental curst-normalized rare earth elements pattern shows that have litter significant fractionation,overall performance are relatively flat,the(La/Yb)N with an average of 1.18,which is diagnostic of a terrigenous sediment source.Comparing characteristics and distribution patterns with the soils and sediment form different kinds of surrounding,it is found that the sediments in the area are basically consistent with others,it is shown that sediments in the study area are dominated by terrigenous debris.Using Sm/Nd as contrasting elements for FD discriminant analysis,it demonstrated that sediments in the study area were mainly Hainan Island,and correlative with the soils of Hainan Island.Simultaneously,affected by coastal erosion and ocean circulation.