Importance of the Spatial Distribution of Rare Earth Elements in the Bottom Sediments of Reservoirs as a Potential Proxy for Tracing Sediments Sources. A Case Study in the Dominican Republic

Rita Fonseca,Catarina Gomes Pinho,Joana Fonseca Araújo

doi:10.3390/geosciences11120490

Rita Fonseca, Catarina Gomes Pinho + Show 1 more

Open Access

https://doi.org/10.3390/geosciences11120490

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Journal: Geosciences	Publication Date: Nov 30, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: University of Évora

Abstract

The geochemical composition of rare earth elements (REE) in the bottom sediments of two Dominican reservoirs and in soils from their catchments was studied to identify possible sources of the deposited materials. Knowledge of the origin of the sediments will serve to control the excessive rates of erosion and sedimentation that occur annually due to periodic extreme climatic events that promote excessive silting of the lakes, followed by loss of storage capacity and degradation of water quality. The REE contents of sediments and soils were normalized to the North American Shale Composite (NASC) and the ratio of light/heavy rare earths (LREE/HREE ratio), Ce and Eu anomalies, and some fractionation parameters were determined. The REE patterns are more homogeneous in the sediments, indicating uniform sedimentation in both deposits. The sediment data reflect depletion of REE from the sources, enrichment of light REE (LREE) and some middle REE (MREE), and positive Eu and Ce anomalies. All data were plotted in correlation diagrams between some fractionation parameters of light–middle–heavy REE and anomalies of Ce and Eu. The similarity of the ratios between these parameters in all samples and the overlap of data from soils and rocks on the sediment projection in the diagrams allowed a good discrimination of the main sources of the materials.

Highlights

Sediments are often reservoirs of many substances in aquatic environments, especially in lakes fed by rivers that receive water and sediments from upstream tributaries [1,2]
Their most common oxidation state is +3, europium and cerium are stable in tetravalent and divalent oxidation states under certain environmental conditions [11], which depend on temperature, pressure, composition, and redox conditions [12]. They can be classified into light rare elements (LREE, including La, Ce, Pr, Nd, Sm, and Eu) and heavy rare earth elements (REE) (HREE, including Gd, Tb, Dy, Ho, Er, Yb, and Lu). They can be considered as the members of the medium atomic number group (MREE), which includes the elements from Sm to Ho [9]
The aim of this study is to present the most comprehensive data on the study of rare earth elements in the sediments of two reservoirs in the Dominican Republic (Sabana Yegua and Tavera)

Summary

Introduction

Sediments are often reservoirs of many substances in aquatic environments, especially in lakes fed by rivers that receive water and sediments from upstream tributaries [1,2]. The most important contribution of the analysis of REE in clastic sediments is the analysis of their origin [9] This coherent group of elements occurs in very small amounts in natural waters, has a short hydraulic residence time in aquatic systems, and is little affected by the mixing and homogenization effects of erosion and sedimentation processes, resulting in uniform patterns of REE in sedimentary materials that reflect their content in source rocks [7,10]. This group occurs as trace elements in most rock types and is highly electropositive. They can be considered as the members of the medium atomic number group (MREE), which includes the elements from Sm to Ho [9]

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