The assessment of lake environments is crucial in tropical regions to ensure clean water access, while local lake sediments may serve as indicators of the local geology and environmental hazards. In this study, a multivariate approach was used to explore the sediment geochemistry of ten small lakes in Dak Lak province in Vietnam, which are characterized by contrasting elemental abundances. Specifically, multivariate analyses (CA and PCA) were applied to three datasets (bulk content, EFAl, and EFFe) of 57 elements and further combined with geochemical indicators and normalized rare earth element distribution patterns. The results enabled the identification of different groups of lakes with distinct geochemical fingerprints related to the major geochemical formations. The applied method can be effectively utilized to discriminate the provenance of surface sediment in water reservoirs, maintaining good coherence even with limited geochemical data. This study provides a foundation for sustainable land use and optimized irrigation in the Dak Lak region, which is under climate change stresses, such as longer and harder droughts.

This study provides baseline concentrations of major, trace (TE), and rare-earth elements (REEs) in the tropical lake bottom sediments and links the spatial variability of the elements to the controlling geochemical factors. The surface bottom sediment samples were collected in 10 water reservoirs in the Dak Lak Province of Central Vietnam. The concentrations of 57 elements were determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The potential contamination of bottom sediments was evaluated by calculating the geo-accumulation index (Igeo) and enrichment factor (EFAl and EFFe). The special goal of this study was the calculation of the local enrichment factor (LEF). Cluster analysis (CA) and principal component analysis (PCA) were applied to the enrichment factor distribution in order to indicate the element associations and their geochemical sources in various lakes. The values of the geochemical indices suggest low pollution of the lake bottom sediments. The found LEF values may be used as a background for long-term monitoring of potential hazardous elements in the region. Multivariate analysis shows that high spatial variability of element concentrations in lake bottom sediments is related to mineralogical provenance rather than to the age of the water reservoir, organic matter, and granulometric fraction content. The results suggest that application of the selected multivariate analyses (CA and PCA) to enrichment factor (EFFe) distribution has potential as a tool for identifying risk-elements and fingerprinting geochemical provenance even if applied to the limited geochemical data set.

This study provides baseline chemical composition of a tropical lake bottom sediments collected in previously unstudied ten water reservoirs in the Dak Lak province of Central Vietnam. The concentrations of 57 major, trace (TE) and rare-earth (REE) elements were determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). To link the spatial variability of the elements to the controlling geochemical factors, a multivariate approach was implemented. The environmental status of bottom sediments was evaluated by calculating the local geochemical background (LGB), geoaccumulation index (I-geo), enrichment factor (EFAl and EFFe), and local enrichment factor (LEF). The selected multivariate analysis tools (cluster analysis (CA) and principal component analysis (PCA)) were used to indicate the multi-element associations and their geochemical sources in various lakes. The bulk and LGB results can serve as a baseline for further environmental analyses in the region. The average values of geochemical indices suggested low pollution (I-geo < 0; EFAl, EFFe, and LEF < 2). The LEF distribution highlighted pronounced spatial variability in the chemical composition of the lake bottom sediments. However, the elevated LEF values (> 2.5) of some potentially hazardous TEs (Sn, Sb, Cs, As, Ag, Hg, W, Pb, Bi, and U) in the individual lakes might indicate the possible anthropogenic point source that should be further monitored. The multivariate analysis allowed the identification of three multi-element signatures that were linked to three main geological structures of the Dak Lak province. Therefore, the main process controlling spatial element distribution is the grain size and mineralogical fractionation of the catchment sedimentary material. An approach combining geochemical background concept (LGB and LEF) with multivariate analysis (CA and PCA) has proved to be an efficient tool for fingerprinting geochemical provenance, even if applied to limited geochemical data.

This study focused on heavy metals (HM) (Cr, Ni, Zn, Cu and Pb) along with Fe and Mn detected in surface sediments from the River Cai—Nha Trang Bay estuarine system (South China Sea). The Adverse Effect Index (AEI) together with Toxic Units (TUs) were used to assess the potential heavy metal toxicity in the sediments. The selective single-step extraction procedure was applied to determine the chemical forms of HM in order to assess their potential bioavailability. Among HM, only Ni and Pb may be associated with considerable adverse effects on biota (AEI > 1) and high potential toxicity (contributing up to 30–40

This data article refers to the paper entitled “Multi-element signatures in solid and solution phases in a tropical mixing zone: A case study in the Cai River estuary, Vietnam” (Koukina et al., 2021), which considers the fate of major, trace, and rare-earth elements transported through the estuarine geochemical filter of the typical tropical estuary. The present work contributes to the local geochemical baselines as a background for long-term monitoring of potential hazardous elements. Therefore, the dataset covers the abundance, enrichment, and partitioning parameters of 53 chemical elements in the water, suspended particulate matter, and bottom sediment samples collected in the Cai River estuary and the adjacent part of the Nha Trang Bay (South China Sea) between July and August 2013. The total filtered, particulate, and sedimentary elements were determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The environmental indices (the enrichment factor and geoaccumulation index) and partition coefficients were calculated from the total element contents. The data provided is essential for the comprehensive environmental assessment of the anthropogenic impact on the coastal ecosystem as well as for the evaluation and modelling of element fractionation and mobility at the estuarine gradients.

This study provides baseline concentrations of major, trace, and rare earth elements (REEs) in the solid and solution phases of the tropical Cai River estuary under influence of multiple stresses. The application of the selected multivariate analysis tools (principal component analysis and redundancy analysis) to the enrichment factor and partitioning coefficients (K-SPM/Water and K-SPM/Sed) calculated from the bulk element contents highlighted the strongest relationships (considered as multi-element signatures) according to the efficiency of the transfer across the estuarine gradients (considered as a selective geochemical filter). Thus, most of the major and trace elements, and REEs studied mainly settle within the mixing zone due to the association with terrigenous aluminosilicate clay minerals, whereas Co, Ni, Cu, As, and Mo are transferred seaward because of their association with the most labile fraction of the fluvial particulate load (such as clays, organic colloids, and carbonates). The major and trace elements, and REEs investigated in this study are mainly introduced in the Cai River and its estuary via basement rock weathering under enhanced monsoonal precipitation, whereas Bi showed the most severe enrichment in the non-weathering distribution pattern. The fractionation of the fluvial element load within the estuarine geochemical filter is mainly controlled by the differential settling of fluvial mineral element-bearing phases along with estuarine colloid dynamics - a topic that must warrants further investigation.

This study focuses on heavy metals (HMs) (Cr, Co, Ni, Cu, Zn, and Pb) along with Al, Fe, Mn, organic carbon (TOC), and carbonates (TIC) detected in surface sediments from the River Cai-Nha Trang Bay estuarine system (South China Sea). The enrichment factors (EFAl and EFFe), Geoaccumulation Index (Igeo), Adverse Effect Index (AEI), and toxic units (TUs) were used to assess the HM enrichment and toxicity in the sediments. The selective single-step extraction procedure was applied to determine the chemical forms of HMs in order to assess their potential bioavailability. The EF and Igeo calculations suggest that sedimentary Fe, Mn, Cr, Co, Ni, and Cu are derived mainly from natural sources (EFAl and EFFe < 1.5 and Igeo < 0 at all sampling sites), while the moderate Pb enrichment (EFAl and EFFe ≥ 2 and Igeo ≥ 1 at all sampling sites) may indicate a moderate contamination. Cr, Cu, and Zn suggest low potential toxicity, while both Ni and Pb show above threshold AEI levels (AEI ≥ 1) and contribute up to 30–40% to the sum of toxic units (∑TUs) at all sampling sites. According to their comparative ability to mobilize metals from the sediments, the single extractants applied were arranged in descending order: acetic acid > ammonium oxalate >> sodium pyrophosphate. All single-step extractants mobilized substantive amounts of Pb (7–30% of total content, on average) from sediments, indicating considerable potential bioavailability. Among HMs studied, the percentage of acid-soluble Pb (23–35%) significantly exceeded the respective ranges in the sediments of other coastal regions. Pearson’s correlation and PCA analyses revealed that among HMs studied, Cr, Ni, and Co enrichment is positively associated with the salinity gradient due to the accumulation of the most fine-grained Fe-rich aluminosilicate host minerals in the bay zone, while sediments in the transitional zone are mainly enriched in Cu, Zn, and Pb due to the local accumulation of metal-rich detrital heavy minerals. The percentages of bioavailable forms of most of the HMs are negatively associated with the salinity gradient due to the preferential accumulation with fluvial Fe/Mn oxyhydroxides in the frontal and transitional zones. Generally, distribution of the enrichment indices of most of the HMs is not associated or even negatively associated with the percentage of the bioavailable forms. The intensity of monsoonal precipitation is shown to be an essential factor in the natural enrichment of estuarine sediments with bioavailable metals. Determining the local geochemical background of HMs and Pb, in particular, is a major goal for future study.

Al, Fe, Ti, Li, Zn, Pb, U, Sc, Sn, Bi, Zr, Ba, As, Sr, W, V, Co, Cu, Ni, Mo, Cr, Mn, Ba, Sn, Sb, Ag, organic (TOC) and carbonate (TIC) carbon contents in suspended particulate matter (SPM) and sediments were measured along the salinity gradient in the Cay River–Nha Trang Bay estuarine system in dry season. Most trace element contents were at natural levels. Particulate metals were characterized by the most significant loss in the frontal zone of the estuary with the highest horizontal gradients within the salinity interval of 0–8–20‰. Sedimentary metals were largely controlled by the accumulation of their most fine-grained host minerals in the sea floor depression. The calculation of the enrichment coefficient (KSPM/Sed) revealed associations of elements with a similar geochemical behaviour. Ti, Ca, Zr, Sb and W (KSPM/Sed ≪ 1) are primarily accumulated in estuarine sediments. Co, Cu, Ni, and Mo (KSPM/Sed ≫ 1) are removed out of the estuarine zone with surface water layer SPM. Al, Fe, Mn, Li, V, Zn, Sr, Sn, Cs, Bi, Pb and U (KSPM/Sed ≅ 1) are most likely controlled by their clay host minerals abundant in both sediments and SPM.

The distribution of particulate form of organic carbon (POC), Al, Fe, Ti, Li, Zn, Pb, U, Sc, Sn, Bi, Zr, Ba, As, Sr, W, V, Co, Cu, Ni, Mo, Cr, Mn, Ba, Sn, Sb, Hg, and Ag in the Cai river and Nha Trang Bay generally followed the distribution of total suspended matter (SPM) and was characterized by the most significant loss in the frontal zone of the estuary with highest horizontal gradients within the salinity interval of 8–20‰. The most part of these elements are supplied to the estuary with the Cai river discharge. Sedimentary Al, Fe, Ti, Li, Sc, Co, Cs, Zr, Cr, Zn, Co, Ni, Cu, Pb, Sn, and V are most likely controlled by the accumulation of their most fine-grained host minerals in sea floor depression of the bay. Sedimentary Bi, W, As, U, and Mo are mainly deposited with the coarse river material near the river mouth. The distribution of Ca, Sr, Mn, and Ba is largely controlled by the total inorganic carbon (TIC) content in the sediments. Metal form study revealed the highest percent contents of the labile forms for Mn, Co, and Pb in the sediments. The high levels of weak acid-soluble Pb and Co (30% and 43% of the total content in sediment, on average, respectively) contributes to a contamination problem in the Nha Trang Bay which arises from the Cai River discharge.

Major (Si, Al, Fe, Ti, Mg, Ca, Na, K, S, P), minor (Mn) and trace (Li, V, Cr, Co, Ni, Cu, Zn, As, Sr, Zr, Mo, Cd, Ag, Sn, Sb, Cs, Ba, Hg, Pb, Bi and U) elements, their chemical forms and the mineral composition, organic matter (TOC) and carbonates (TIC) in surface sediments from the Cai River estuary and Nha Trang Bay were first determined along the salinity gradient. The abundance and ratio of major and trace elements in surface sediments are discussed in relation to the mineralogy, grain size, depositional conditions, reference background and SQG values. Most trace-element contents are at natural levels and are derived from the composition of rocks and soils in the watershed. A severe enrichment of Ag is most likely derived from metal-rich detrital heavy minerals such as Ag-sulphosalts. Along the salinity gradient, several zones of metal enrichment occur in surface sediments because of the geochemical fractionation of the riverine material. The parts of actually and potentially bioavailable forms (isolated by four single chemical reagent extractions) are most elevated for Mn and Pb (up to 36% and 32% of the total content, respectively). The possible anthropogenic input of Pb in the region requires further study. Overall, the most bioavailable parts of trace elements are associated with easily soluble amorphous Fe and Mn oxyhydroxides. The sediments are primarily enriched with bioavailable metal forms in the riverine part of the estuary. Natural (such as turbidities) and human-generated (such as urban and industrial activities) pressures are shown to influence the abundance and speciation of potential contaminants and therefore change their bioavailability in this estuarine system.

Major (Si, Al, Fe, Ti, Mg, Ca, Na, K, S, P), minor (Mn) and trace (Li, V, Cr, Co, Ni, Cu, Zn, As, Sr, Zr, Mo, Cd, Ag, Sn, Sb, Cs, Ba, Hg, Pb, Bi and U) elements, their chemical forms and the mineral composition, organic matter (TOC) and carbonates (TIC) in surface sediments from the Cai River estuary and Nha Trang Bay were first determined along the salinity gradient. The abundance and ratio of major and trace elements in surface sediments are discussed in relation to the mineralogy, grain size, depositional conditions, reference background and SQG values. Most trace-element contents are at natural levels and are derived from the composition of rocks and soils in the watershed. A severe enrichment of Ag is most likely derived from metal-rich detrital heavy minerals such as Ag-sulfosalts. Along the salinity gradient, several zones of metal enrichment occur in surface sediments because of the geochemical fractionation of the riverine material. The parts of actually and potentially bioavailable forms (isolated by four single chemical reagent extractions) are most elevated for Mn and Pb (up to 36% and 32% of total content, respectively). The possible anthropogenic input of Pb in the region requires further study. Overall, the most bioavailable parts of trace elements are associated with easily soluble amorphous Fe and Mn oxyhydroxides. The sediments are primarily enriched with bioavailable metal forms in the riverine part of the estuary. Natural (such as turbidities) and human-generated (such as urban and industrial activities) pressures are shown to influence the abundance and speciation of potential contaminants and therefore change their bioavailability in this estuarine system.

This study focuses on sediments from small restricted exchange environments along the Karelian shore of Kandalaksha Bay (White Sea, Russian Arctic), which are known as separating basins and are characterised by contrasting oxidising conditions within the water column and the occurrence of anoxia. In the basins that were studied, no significant contamination by trace heavy metals (Pb, Cu, Zn and Cr, in particular) was detected. The comparative study of the two most bioavailable metal forms, namely, labile (acid soluble) and organically bound (alkali soluble) forms, indicated that acetic acid and sodium pyrophosphate released 3–11% and 2–12%, respectively, of the total metal content from sediments. The most bioavailable parts of metals are weakly bound to organic matter and, to a greater extent, associated with easily soluble amorphous Fe-oxides. Among the studied elements, most of the bioavailable Zn and Cu was most likely bound to organic substances, whereas bioavailable Cr and Mn were controlled to a greater extent by the formation of Fe-oxyhydroxide. The elements studied could be arranged in the following decreasing order of average potential bioavailability: Cu > Zn > Mn > Fe > Cr > Pb. In the separating basins, the relative proportion of labile bioavailable metals is enhanced in relation to the neighbouring open coastal sea.

Spearman rank order correlation coefficients for (n=10) Cu ac sol Cu alk sol Cu total Zn ac sol Zn alk sol Zn total Pb ac sol Pb alk sol Pb total Cr ac sol Cr alk sol Cr total Mn ac sol Mn alk sol Mn total Fe ac sol Fe alk sol

According to the results of the comparative study performed of the littoral sediments sampled in small inlets of Kandalaksha Bay (the White Sea in the Russian Arctic), the metals (Fe, Mn, Cu, Zn, Pb, Cr, and Li) occur mainly in a biogeochemical-stable mineral-incorporated form, which comprises 77–99% of the total metal content. The ratio of the liable form, which is easily extracted by a weak acid, is on average 3.2% for the total Fe, 2.0% for Mn, 1.7% for Cr, 5.6% for Pb, 5.8% for Zn, 6.5% for Cu, and is negligible for Li. The concentrations of the most studied trace metals are below the threshold level according to the environmental quality guidelines (the sediment analysis). The ratio of the metal forms evidences the natural origin of the elevated concentrations of both Zn and Cr in the sediments.

The White Sea of Russian Arctic is characterized by extreme diversity of enclosed estuarine systems that are often sites of unique biota. The present study focuses on surface sediments from representative restricted exchange environments of the inner part of Kandalaksha Bay, adjacent to the Karelian shore of the White Sea. The TOC and n-alkanes distribution study revealed the major input of terrestrial organic matter into the sediments from higher plants and minor presence of autochthonous microbial sources. Metal (Fe, Mn, Cu, Zn, Cr and Pb) forms study showed that metals in sediments occur mainly in a biogeochemically stable mineral-incorporated form, which comprises up to 98% of total metal content, while labile (acid soluble) and organically bound (alkali soluble) forms make up to 3–11% and 2–12% of total metal content, respectively. Presumably, the major part of both acid soluble and alkali soluble forms is comprised of metals associated with easily soluble amorphous Fe-oxides and bound to sediment organic matter. According to sediment quality guidelines, all trace-metal contents were below the threshold levels. Among sites studied, the heightened contents of bioavailable metal forms are related to sediments enriched in organic matter and/or located within the sea-fresh water barrier zones. The elements studied may be arranged in the following decreasing sequence according to their potential bioavailability: Cu > Zn > Mn > Fe > Cr > Pb. The present study can serve as a basis for comprehensive environmental assessment of the region and objective anoxia prognosis in Arctic ecosystems, while the role of microbial community in element speciation in sediments needs special attention.

Major (Al, Fe), minor (Mn), and trace (Li, Cu, Ni, Cr, Cd, Zn, Pb) metals along with nutrients (TOC, TON, TS, TP) and enzymatic activities were determined in 18 surface sediment and two soil samples collected in six small bays of the Karelian shore of Kandalaksha Bay, White Sea, Russian Arctic. The studied sediments tended to be marine, with a major input of organic matter from autochthonous sources. Marine organic material might be an important carrier of trace metals in the examined sediments. According to sediment quality guidelines, all trace-metal contents were below the threshold levels. The results of azocasein-trypsin tests also suggested no significant contamination of analysed sediments and soils. A comparison of the trace-metal contents in the sediments examined with those of the western Arctic shelf showed higher levels of Zn and Cr in the Karelian shore. Presumably these disparities were related to regional differences in sediment chemistries rather than to any enhanced pollution within the studied area. Both geochemical composition and enzymatic-activities patterns among sites studied are largely controlled by the sediment granulometry. The evolution of sediments in the restricted exchange environments under investigation is caused by depositional conditions, which are strongly affected by small-scale hydrodynamic processes specific for each particular area. The most vivid examples are separating basins, where the fine-grained sediments enriched in organic matter — and thus in nutrients and metals — are formed under calm hydrodynamic conditions enhanced by severely restricted water exchange.

AbstractA geochemical study of the Severnaya Dvina estuary was carried out during two oceanographic cruises to the White Sea. The amount and distribution of trace (Mn, Co, Cu, Ni, Pb, and Zn) and major (Al and Fe) elements in suspended particulate matter and sediments were determined. The main source of most metals studied was river discharge. A metal speciation study showed that the prevailing form is in the estuarine sediments, the minerals of which incorporated 60–99% of the total metal contents. Two zones of metal accumulation were found in sediments that were considered as local geochemical barriers within the major river–sea barrier.