Many hypotheses have been raised about the controls of the distribution and fractionation of the rare earth elements (REE) in coastal ecosystems. Here, REE were measured in estuarine sediments and in six mangrove soil profiles along the estuarine salinity gradient of the Jaguaripe estuary, northeastern Brazil. The aim of this study was to evaluate the fractionation, distribution, remobilization, and possible sources of these elements. The ΣREE and Y in oxic estuarine sediments ranged from 202 to 220 mg kg⁻¹ and from 12 to 15 mg kg⁻¹, respectively. The normalized abundances to the Post Archean Australian Shale (PAAS) showed that light REE (LREE; La, Ce, Pr, and Nd) were consistently enriched over heavy REE (HREE; Er, Tm, Yb, and Lu). Among the REE, only LREE showed significant correlation with Al (r = 0.85) and Fe (r = 0.96) indicating that Al and Fe oxy-hydroxides are the main host phases of the LREE in estuarine sediments. The average ΣREE for mangrove soils throughout the salinity gradient ranged from 161 ± 18 mg kg⁻¹ (lower estuary) to 183 ± 16 mg kg⁻¹ (upper estuary). Al-normalized Mn and Fe concentrations showed small peaks down-core, indicating diagenetic remobilization. Vertical REE profiles have shown that post-deposition processes might contribute to the patterns in the abundances of the ΣREE and their fractionation at the surface and subsurface mangrove soils. Below the top 15 cm, diagenetic alteration after burial is not leading to substantial variation in the LREE/HREE profiles. The coincidence of peaks in individual REE/Al down core along with Fe and Mn peaks reflects the participation of the REE in early diagenesis. The REE abundances observed here corroborate to the characterization of the Jaguaripe estuary as a pristine system and can be used as a background for the region.

关于控制沿海生态系统中稀土元素（REE）的分布和分级的许多假设已经提出。在这里，在巴西东北部Jaguaripe河口的河口盐度梯度上，在河口沉积物和六个红树林土壤剖面中测量了REE。这项研究的目的是评估这些元素的分离，分布，迁移和可能来源。含氧河口沉积物中的ΣREE和Y范围为202至220 mg kg ^-1和12至15 mg kg ^-1， 分别。原始澳大利亚后页岩（PAAS）的归一化丰度表明，轻质稀土元素（LREE； La，Ce，Pr和Nd）始终比重质稀土元素（HREE； Er，Tm，Yb和Lu）富集。在REE中，只有LREE与Al（r = 0.85）和Fe（r = 0.96）表现出显着相关性，表明Al和Fe的氢氧根是LREE在河口沉积物中的主要宿主相。在整个盐度梯度中，红树林土壤的平均ΣREE从161±18 mg kg ^-1（河口下部）到183±16 mg kg ^-1（河口上方）。Al归一化的Mn和Fe浓度在核的下游显示出小峰，表明成岩作用固定。垂直REE剖面表明，沉积后的过程可能有助于ΣREE的分布及其在表层和地下红树林土壤中的分馏。在顶部15厘米以下，埋葬后的成岩作用变化不会导致LREE / HREE剖面发生实质性变化。单个REE / Al下部核中的峰与Fe和Mn峰的重合反映了REE在早期成岩作用中的参与。在此观察到的REE丰度证实了Jaguaripe河口为原始系统的特征，可以用作该地区的背景。