Abstract: The rare earth elements (REE) of 65 samples have been analyzed, which were taken from mangrove wetland sediments in Dongzhai Harbor, Hainan Island. The results showed that the total amount of ΣREE ranged from 141.28~269.20 mg/kg, with an average value of 221.88 mg/kg. We found that the lowest value appeared in the S1 region, and the highest value in the S3 region. The mean values of ∑REE in S2, S3 and S5 were all higher than that of the whole study area, but the mean values of ∑REE in S1, S4 and S6 were lower than that of the whole study area. The distribution regularity was as follows: S3 >S5 >S2 >S4 >S6 >S1. In general, in the study area, the mean value of the LREE was 205.88 mg/kg, which was relatively enriched, accounting for 93% of the ∑REE content. The mean value of HREE was 16.00 mg/kg, accounting for 7% of the REE content, which was significantly lower than that of LREE, showing that LREE was the major contribution of ∑REE. The chondrite-normalized pattern of rare earth elements in the sediments of the study area showed that LREE was rich and HREE had relatively loss. LREE/HREE varied from 7.96 to 15.20, with an average value of 12.87, and the (La/Yb)CN varied from 7.99 to 13.11, with an average value of 10.12, fractionation between light and heavy REEs was obvious, indicating that REE in the sediments obviously had a differentiation and the main material sources of sediments were of matter coming from the mainland, as compared to the chondrite-normalized pattern . In addition, δEu ranged from 0.44 to 0.77, with an average of 0.58, showing an obviously negative anomaly. The distribution regularity was: barren shoal (0.56) > edge of forest (0.59)> inside of forest (0.65); but it showed a moderate positive Ce anomalies, δCe ranged from 1.48 to 2.46, with an average of 1.98. The sediments of different wetland showed that: inside of forest (225.38 mg/kg) >edge of forest (218.23 mg/kg)>barren shoal (212.91 mg/kg), ∑REE decreased gradually with the increase of the distance from the shore. The correlation showed that for the barren shoal R2=0.168, the edge forest R2=0.246 and inside of forest R2=0.295. There was no obvious correlation between ΣREE and grain size, the distribution of ΣREE was not controlled by grain size in the study area. As the forest, forest edge and barren shoal were in the same study area with the same material source, the material sources didn’t have influences on the REE differentiation among them. Regional chemical weathering, the scouring effect of seawater and the salinity of ocean waters resulted in the difference of REE composition among barren shoal, forest edge and inside of forest.

Key words: mangrove sediment, rare earth element, the Dongzhai Harbor