Low Concentrations Of Trace Elements Research Articles

Physico-Chemical Characterization of an Urban Rainwater (Zagreb, Croatia)

The characterization of organic matter (OM) and trace elements (TEs) was conducted in bulk precipitation samples collected in an urban area of Croatia (Zagreb center), from January 2009 to October 2011 (N = 31). Characterization of OM was performed by measurement of dissolved (DOC) and particulate forms of organic carbon (POC), as well as surface-active substances, copper complexing capacity and reduced sulfur species which were determined electrochemically. Concentrations of TEs (Al, Fe, Zn, Cr, Ba, Mn, Cu, Sr, Ti, Pb, V, Ni, Rb, Sb, As, Sn, Se, Co, Cd, Mo) were analyzed by HR ICP-MS. The most important outcome of this study is confirmed relatively low concentrations of DOC (0.69–4.86 mgC L−1) and TEs. Daily fluxes of Zn, Pb, Ni, As, and Cd were two to three times lower than that of those reported for an urban industrial site in Europe. Additionally, this study shows that the value and reactivity of rainwater DOC has not considerably changed if compared with the results from the 1998–1999 study (0.78–4.39 mgC L−1). High traffic density and thermal power plants are assumed to be the main local sources of pollutants in Zagreb. Using Al as a reference element, it was found that Cd, Sb, and Cu were associated with anthropogenic sources. The solubility of Sr, Zn, Cd, Ni, Cr, As, and Rb was higher than 70%. Another critical characteristic of precipitation composition is episodic variation in POC concentration because of Saharan dust transport. Obtained data can be valuable for environmental quality assessment, as well as for insight into atmospheric deposition processes.

Seasonal change in trace element concentrations of Paracentrotus lividus: Its use as a bioindicator

Abstract An assessment of classical and emerging trace element contamination was conducted on gonads of the sea urchin Paracentrotus lividus (Lamarck, 1819), in Corsica (Western Mediterranean). The aim of this study was to evaluate the contamination levels at different sites by following the seasonal variation of 22 trace elements. The sea urchins analyzed were taken in 2017 from reference and more impacted sites in four Corsican areas. The results obtained shown the importance of biotic factors such as gender, reproduction and the way of life. Variations have been highlighted with lower trace element concentrations during the summer season. This is mainly due to a dilution phenomenon resulting from gametogenesis. The pollution index (TEPI) was determined and highlighted differences in contamination levels at the various sites. This work could provide additional support for other tools for the diagnosis and monitoring of coastal water quality. It provides useful new data to enable managers to act at the source and reduce degradation in order to improve the ecological quality of marine waters.

Biomass quality index: Searching for suitable biomass as an energy source in Chile

A Biomass Quality Index (BQI) developed using a previously reported tool was shown to be a promising method to rank biomass suitable for solid biofuel production. The BQI was developed by selecting 12 chemical parameters to be analyzed among ten available biomasses produced in the north, central and south of Chile. Furthermore, a Parameter Quality Index (PQI) was calculated to estimate the contribution of each parameter in the BQI. The sum of all PQIs for each biomass allowed the BQI to be determined, and biomasses with lower BQIs were more highly ranked. The results showed that the first 3 ranks were dominated by biomasses collected in central Chile, hazelnut shell, cherry pits and corn cobs (BQI ≤ 16.1). Furthermore, a promising candidate that was ranked fourth place was wheat straw (BQI = 17.7), which may be able to be used the highly polluted southern zone. Meanwhile, grass and the microalgae N. gaditana were ranked last (BQI ≥ 69.5). The low BQI obtained for the studied biomasses were related to their low PQIs regarding moisture content, low trace element content, low ash percentage and high carbon content and HHV. By contrast, high BQI values were related to high PQIs for moisture, Cl, Na and K content. K had a high contribution and Cu had a low contribution in the index. Due to the difficulty of milling the top ranked biomass, further studies should include a grindability analysis or other physical parameters to complete the BQI methodology.

Groundwater trace elements change induced by M5.0 earthquake in Yunnan

Geochemical compositions changes in groundwater in response to earthquakes have been documented for decades, and most such studies have documented the changes in major ions or geochemical gases (e.g., Radon). Changes in trace elements, however, have received less attention. In this paper, we collected groundwater samples from a wellbore in Yunnan Province weekly and analyzed both the major and trace chemical compositions from February 2018 to September 2018. Combined with well water level records, we found that the August 2018 Tonghai M5.0 earthquake caused changes in both water levels and trace elements but caused no significant changes in the stable isotope and major ions. Such a response indicates that trace elements are more sensitive to crustal strain than are the major elements and isotopes. And We considered that earthquake-induced shaking caused a breach in the hydraulic barrier of the isolated reservoir that led to the mixing of water with low concentrations of trace elements as the mechanism to explain the coseismic response. This study demonstrate that some trace elements are more sensitive to earthquake strain than the commonly used chemical constitutents and that trace element monitoring should considered to be a priority in the future to provide a complete assessment of the sensitivity of different chemical constitutents to earthquake stresses.

New lunar meteorite NWA 10986: A mingled impact melt breccia from the highlands—A complete cross section of the lunar crust

AbstractNorthwest Africa (NWA) 10986 is a new mingled lunar meteorite found in 2015 in Western Sahara. This impact melt breccia contains abundant impact melt glass and clasts as large as 0.75 mm. Clasts are predominantly plagioclase and pyroxene‐rich and represent both highland and basalt lithologies. Highland lithologies include troctolites, gabbronorites, anorthositic norites, and troctolitic anorthosites. Basalt lithologies include crystalline clasts with large zoned pyroxenes representing very low titanium to low titanium basalts. In situ geochemical analysis of minerals within clasts indicates that they represent ferroan anorthosite, Mg‐suite, and gabbronorite lithologies as defined by the Apollo sample collection. Clasts representing magnesian anorthosite, or “gap” lithologies, are prevalent in this meteorite. Whole rock and in situ impact glass measurements indicate low incompatible trace element concentrations. Basalt clasts also have low incompatible trace element concentrations and lack evolved KREEP mineralogy although pyroxferroite grains are present. The juxtaposition of evolved, basaltic clasts without KREEP signatures and highland lithologies suggests that these basaltic clasts may represent cryptomare. The lithologies found in NWA 10986 offer a unique and possibly a complete cross section view of the Moon sourced outside of the Procellarum KREEP Terrane.

Trace elements of naftides of oil- and gas-bearing basin

The parameters of the concentration distribution of trace elements in the oil fields of oil and gas basins of the world, their physic-chemical properties, as well as the geological and geochemical features of oil formation in these basins were studied. It is shown that the ontogenesis of hydrocarbons associated with deep tectonic transformations (geodynamic factor) controls not only the placement of naphtides in the sedimentary cover, but also the diversity of their metallogenic specialization. The classification of oils of various ontogenesis zones is given in accordance to the degree of their enrichment of mineral elements and their belonging to the vanadium or nickel metallogenic type. The oil, characterized by primary rich concentrations of trace elements of the main zone of oil formation, and oil with initially low concentrations of trace elements in the zones of early generation are presented. The processes of transformation of the composition of oils in the areas of hypergenesis lead to their enrichment, whereas the oil of the catagenesis zone is depleted in trace elements.

Trace Elements in Naphthides in Oil and Gas Basins

The distribution of trace elements, physical and chemical properties of the oil, and geological and geochemical features of oil formation in world oil and gas basins were studied. It was shown that hydrocarbon ontogenesis associated with deep tectonic transformations (geodynamic factor) controls not just the distribution of naphthides in the sedimentary cover, but also the diversity of their metallogenic specialization. The classification of oils from various ontogenesis zones is given in accordance with their enrichment in trace elements and with the metallogenic (vanadium or nickel) type. Oil characterized by large primary concentrations of trace elements of the main zone of oil formation and oil with low initial concentrations of trace elements in the zones of early generation are presented. Transformation of the oil composition in the areas of hypergenesis leads to their enrichment, whereas the oil of the catagenesis zone is depleted in trace elements.

Provenancing Central African copper croisettes: A first chemical and lead isotope characterisation of currencies in Central and Southern Africa

The Copperbelt is one of the richest copper deposits in the world and has been an important primary metal source for Central African cultures for over a millennium. The technology underlying this exploitation and the trade networks through which copper was exchanged, however, have not yet received much attention in archaeological research. This paper presents the first geochemical dataset for archaeological copper currencies in Central and Southern Africa: croisette ingots. Chemical and lead isotope analysis have been carried out for 45 precolonial copper artefacts with the aim of illuminating their provenance and production technology. The results show that highly pure copper with very low trace element content was produced, indicating the selection, beneficiation and smelting of specific Copperbelt ores. The variable croisette compositions and shapes reflected in burial assemblages support their suggested use as currencies over a large area. This study offers a highly novel contribution to provenance research in Central and Southern Africa, shedding new light on the broader trade networks associated with copper provisioning in these regions. The exploitation of a range of ore sources throughout the 2nd millennium CE has been identified, with a marked shift around the mid-15th century CE largely correlating to croisette typologies. Furthermore, these different geochemical copper signatures can be tentatively related to different Copperbelt zones. Combining these results with archaeological and historical evidence for regional copper production and consumption, this study provides a framework for the future study of copper production and exchange systems in the wider Central and Southern African region.

Petrogenesis of Early Cretaceous granites and associated microgranular enclaves in the Xiabie Co area, central Tibet: Crust-derived magma mixing and melt extraction

Multiple petrogenesis models have been proposed for granitic rocks and the mafic microgranular enclaves (MMEs) hosted in them. The mantle and crust-derived magma mixing/mingling process was widely suggested for the formation of MMEs or the host granitoids. However, whether the mixing between magmas derived from different crustal sources may also form microgranular enclaves (MEs, not restricted to mafic) or the host granites remain unclear. Here, we report petrological, geochemical, and zircon in situ Hf-O isotopic data for MEs and their host granites in the northern Nyima area, southern Qiangtang terrane (SQT), central Tibet. The host granitic rocks consist of amphibole-bearing biotite granites and syenogranite, minor granodiorite and aplite veins, and MEs comprising diorite and granodiorite. Host rocks and MEs are contemporaneous and were generated in the Early Cretaceous (∼120 Ma). Host granitoid samples are high-K calc-alkaline rocks and have high SiO2 (66–78 wt%) and low MgO (<1.14 wt%). They have enriched whole-rock εNd(t) (−1.82 to −3.06), and variable zircon εHf(t) (+0.64 to +5.12) and δ18O (7.35 to 9.61‰) values. The host granodiorites contain some mafic mineral-rich clots and lower silica contents than the biotite granites. They exhibit distinctive geochemical patterns (such as high K2O > 5 wt%, high Zr >500 ppm with Zr/Hf ratios >45, and high Ba >400 ppm), implying biotite and zircon concentrations. Combining this information with embayed feldspars, curved biotites, and closely spaced feldspar grains, we suggest that liquid loss resulted from crystal compaction or filter pressing. Both the fine-grained syenogranites and aplite veins exhibit high SiO2 and Rb/Sr ratios in addition to low Zr/Hf ratios and Zr and Ba concentrations with remarkably negative Eu anomalies, indicating that they are highly differentiated melts extracted from felsic crystal mush. Such a crystal mush is possibly represented by the biotite granites. Gradual contact relationships between variable granitic phases indicate that melt extraction and crystal concentration were coeval. Residual melt extraction from the crystal mush was facilitated by mush remobilization resulting from magma replenishment. We suggest that for the host rocks, the biotite granites were mainly derived by partial melting of ancient crust, and the granodiorites most likely resulted from the magma mixing/mingling that might be accompanied with the loss of melts, the fine-grained syenogranites and aplites represent highly evolved residual melts. MEs are geochemically characterized by intermediate to felsic compositions (SiO2 = 56.3–67.8 wt%), with low MgO (<4 wt%) and Mg# (< 53) and low mantle compatible trace element (Cr and Ni) contents. They exhibit enriched whole-rock Nd (εNd(t) = −0.36 to −2.71), depleted zircon εHf(t) (+0.51 to +5.68) and high δ18O values (7.45 to 9.57‰), except for one sample with comparable whole-rock εNd(t) (−1.32), relatively high zircon εHf(t) (+5.05 to +7.11) and δ18O (6.09 to 7.10‰) values. MEs exhibit evidence for quenched magma crystallization, chemical exchange, mineral disequilibrium and mass transfer, indicating inefficient magma mixing/mingling. Mafic minerals from MEs were in equilibrium with evolved melts rather than mantle-derived primitive melts. Given the substantial absence of contemporaneous basaltic rocks from the SQT and the relatively high SiO2 and low MgO contents and crust-like zircon stable oxygen isotope of MEs, we propose that they most likely resulted from the mixing/mingling of diverse crust-derived magmas. Therefore, our study provides important evidence for crust-derived magma mixing and melt extraction from mush.

Light rare earth element redistribution during hydrothermal alteration at the Okorusu carbonatite complex, Namibia

AbstractThe Cretaceous Okorusu carbonatite, Namibia, includes diopside-bearing and pegmatitic calcite carbonatites, both exhibiting hydrothermally altered mineral assemblages. In unaltered carbonatite, Sr, Ba and rare earth elements (REE) are hosted principally by calcite and fluorapatite. However, in hydrothermally altered carbonatites, small (&lt;50 µm) parisite-(Ce) grains are the dominantREEhost, while Ba and Sr are hosted in baryte, celestine, strontianite and witherite. Hydrothermal calcite has a much lower trace-element content than the original, magmatic calcite. Regardless of the lowREEcontents of the hydrothermal calcite, theREEpatterns are similar to those of parisite-(Ce), magmatic minerals and mafic rocks associated with the carbonatites. These similarities suggest that hydrothermal alteration remobilisedREEfrom magmatic minerals, predominantly calcite, without significant fractionation or addition from an external source. Barium and Sr released during alteration were mainly reprecipitated as sulfates. The breakdown of magmatic pyrite into iron hydroxide is inferred to be the main source of sulfate. The behaviour of sulfur suggests that the hydrothermal fluid was somewhat oxidising and it may have been part of a geothermal circulation system. Late hydrothermal massive fluorite replaced the calcite carbonatites at Okorusu and resulted in extensive chemical change, suggesting continued magmatic contributions to the fluid system.

Mineralogical and geochemical characterization of the unconsolidated sands from the Mefou River terrace, Yaoundé area, Southern Cameroon

Nine sediment core samples from the right terrace of the Mefou River in the Yaoundé area (southern Cameroon) were used to investigate the provenance and evolution of sediments. The mineralogical and geochemical data have been reported using XRD, XRF and ICP-MS instruments. The sediment core is 87 cm thick and is subdivided from the bottom to the top into sandy, clayey sandy and, silty sandy layers. The sandy layer is 70 cm thick with a decreasing grain size from the bottom to the top. The nine sediment core samples are mainly composed of quartz, and accessory feldspars, kaolinite, goethite, rutile and muscovite/illite. This mineral assemblage can be explained by the combined effect of metamorphic source rocks and surrounding soils. The sandy texture as well as the abundance of quartz were confirmed by the high SiO2 contents particularly at the bottom of the sequence (71–85 wt%). The high SiO2/Al2O3, low alkali (Na2O + K2O) values, low REE contents (~107–389 ppm; avg. = 247 ppm) and the negative correlation between SiO2 with most of major and trace elements confirm the siliciclastic nature of sediments. The SiO2/Al2O3 ratio justifies the high proportion of quartz relative to clay minerals and the coarse grain size of the sediments. The Mefou alluvial sediments are classified as Fe-shale and Fe-sand. The LREE/HREE ratio and (La/Yb)N values exhibit the light REE-abundance linked to the nature of REE mineral-bearers. The spider diagrams reveal the high depletion of K and Sr due to the high feldspar alteration and the quartz-abundance. The REE-normalization relative to chondrite portrays slightly positive Ce anomalies (Ce/Ce*~1.11–1.15) and negative Eu anomalies (Eu/Eu*~0.43–0.63).The mineralogical and geochemical features are in concordance with the textural parameters and portray the siliciclastic nature of sediments inherited from the gneiss basement. The predominance of sands and the low trace element contents in alluvial sequence from the Mefou River are linked to the intensity of the hydrodynamic forces. The rock sources have undergone high degree of weathering and there is no evidence of significant sediment recycling.

Metals composition of the surface waters of the Southern Baikal region and its connection with landscape and geological conditions

The metal composition of water and bottom sediments of southern Lake Baikal tributaries was studied and the water migration coefficients for micro- and trace elements were calculated. The map showing the study area divided into zones according to their ability to provide the certain water quality was drawn. The significant differences in mineralization, macro- and trace element composition between Lake Baikal water and tributary waters were found out. It was shown that values of water migration coefficients calculated for macro elements are similar in southern and main tributaries whereas coefficient values calculated for trace elements are quite different. This is due to dissolved matter sources such as rocks and deep ground waters which chemical composition is not typical for landscapes of Lake Baikal basin. The contribution of southern tributaries to macro element composition of lake water is between 7 and 15%, whereas tributaries contribution to trace element composition can hardly be evaluated because of higher element concentrations in riverine waters. The lower trace element concentrations in lake water with respect to riverine one is due to trace element migration in the form of complex organic compounds: long water residence time in lake favors to organic compounds decay by means of microbial- and photo-degradation followed by metal precipitation.

Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France)

The threat of trace elements (TE) stored in sediments depends on total concentrations, their chemical form, and also on the type of TE–particle association and their resultant stability. The present study aimed at identifying the major TE-bearing phases in river sediments and quantifying their in situ concentrations once total concentrations of TE had been determined in order to understand potential TE mobility and ensuing environmental risk during early diagenesis mechanisms and the sediment cascade. Several TE-enriched layers of sediment cores were selected in a polymetallic-contaminated river basin (Loire basin, France). Selected samples were taken from up- and downstream areas far from sites of specific mining, or heavy industrial or urban activities. They thus represent non-site-dependent sediments which were not modulated or controlled by specific mineralogy or anthropogenic activities. Detailed microscale investigation techniques (SEM, EPMA, and μSXRD) were used to characterize directly the complex TE–solid phase association within river sediments. Despite Bi, Cd, and Hg representing the highest enrichment of the studied sediment layers, these elements were not detected at a microscale and only ubiquitous TE such as As, Cu, Pb, and Zn could be quantified on polished thin sections (EPMA quantification limit = 1000 mg kg−1, n = 111). Three mineralogical groups were evidenced by PCA, EPMA, and μSXRD data. (i) Fine-grained aggregates of aluminosilicates were frequently detected, appearing multiphased in organic matrices. They were mostly enriched with Zn and Pb without any As or Cu. (ii) (Mn, Ti)-rich Fe oxyhydroxides were predominantly SEM observed, either as isolated grains, silicate coatings, or included in aggregates. They represented the highest detected in situ concentrations for all the studied TE. And finally, (iii) Mn-rich particles were not frequently observed with SEM but when present were characterized by the highest TE concentrations. Phosphates, carbonates, and S-rich particles (sulfides and/or sulfates) were also determined by PCA as a potential mineralogical group. However, due to their very low TE concentrations and frequency, they could not be considered representative of a TE-bearing mineralogical group. This fine sorting classification, combining different techniques at the particle scale, was used to visualize and quantify complex mineralogy and particle associations of TE-bearing phases in river bed sediments under no specific mineralogical control. It represents an interesting approach to understand TE mobility during sediment cascade and post-depositional processes in sediments.

Metal Composition of Surface Waters of the Southern Baikal Region and the Connection with Landscape and Geological Conditions

The metal composition of water and bottom sediments of southern Lake Baikal tributaries was studied and the water migration coefficients for micro- and trace elements were calculated. The map showing the study area divided into zones according to their ability to provide the certain water quality was drawn. The significant differences in mineralization, macro- and trace element composition between Lake Baikal water and tributary waters were found out. It was shown that values of water migration coefficients calculated for macro elements are similar in southern and main tributaries whereas coefficient values calculated for trace elements are quite different. This is due to dissolved matter sources such as rocks and deep ground waters which chemical composition is not typical for landscapes of Lake Baikal basin. The contribution of southern tributaries to macro element composition of lake water is between 7 and 15%, whereas tributaries contribution to trace element composition can hardly be evaluated because of higher element concentrations in riverine waters. The lower trace element concentrations in lake water with respect to riverine one is due to trace element migration in the form of complex organic compounds: long water residence time in lake favors to organic compounds decay by means of microbial- and photo-degradation followed by metal precipitation.

Solid Sampling in Analysis of Various Plants Using Two-Jet Plasma Atomic Emission Spectrometry.

The possibility of two-jet plasma atomic emission spectrometry for analysis of different plants using solid sample preparation and unified calibration samples was investigated. The certified reference materials of wheat, maize, rice, potato, grass mix, birch leaves, and Elodea canadensis were used for analysis. On the basis of the behavior of these plants in the plasma, they were divided into two groups: starch-containing materials (cereal and root crops) and leaves/grass. It was found that the previous sample carbonization should be used for analysis of starch-containing plants while leaves and grass could be analyzed by the direct technique. Carbonization was only applied for determining low concentrations of trace elements in leaves and grass. The calibration samples based on graphite powder and simple sample preparation, dilution of powdered sample with a spectroscopic buffer, were used for both direct analysis and analysis after carbonization. Such an approach allowed estimation of B, Ba, Be, Cd, Co, Cr, Cu, Ga, Fe, Mn, Ni, Pb, Si, Sr, V, and Zn in different plants. The limits of detection (LODs) provided by the direct technique were at the level of (µg·g-1): n × 0.1 for Cd, Cu, and Mn; n for B, Ba, Co, Cr, Fe, Ga, Ni, Pb, Sr, V, and Zn; n × 10 for Si. Carbonization allowed improving LODs of elements several times depending on the thermal stability and mineral composition of plants. The LODs of elements in plants obtained after carbonization are the following (µg·g-1): n × 0.01 for Be, Cd, Cu, and Mn; n × 0.1 for Co, Cr, Fe, Ga, Ni, Pb, Sr, V, Zn; and n for Si. The techniques suggested are fast, easily workable, and do not require harmful chemical reagents. In some cases, the influence of variable matrices and different element species on analytical signal of elements was not completely suppressed; the deviation of element concentrations from the true values was discussed.

Energy production potential of phytoremediation plant biomass: Helianthus annuus and Silybum marianum

The use of the biomass of two plant species (Helianthus annuus and Silybum marianum) generated during the phytoremediation of a trace element contaminated soil was studied for the production of clean and renewable energy in laboratory experiments. Biogas production potential, aerobic biodegradability and calorific values of the plants were determined and compared with the results of the plants grown in non-contaminated soil to evaluate the effect of trace elements contamination on their potential use as feedstock for bioenergy production. The biogas production potential of the aerial vegetative biomass of S. marianum (194 - 223 ml g−1) was found to be higher than that from H. annuus (134 - 154 ml g−1), with no significant differences between non-contaminated and contaminated soils (average CH4 concentration: 63.1% for S. marianum and 65.7% H. annuus, respectively). The greatest biogas production was obtained from the seeds of H. annuus (356 - 473 ml g−1; 70.7% of CH4) after 9 days of anaerobic digestion. Also, the aerial vegetative biomass of H. annuus had higher calorific values than that of S. marianum (17.1 and 14.3 MJ kg−1, respectively). Combustion was the most efficient method for energy production compared to anaerobic digestion, while the presence of low concentrations of trace elements in plant biomass did not limit the potential energy recovery. These findings show the suitability of bioenergy production as an added value alternative for the management of plant biomass coming from phytoremediation processes.

Geochemical investigations in bulk and clay size fractions from lower Krishna river sediments, southern India: implications of elemental fractionation during weathering, transportation and deposition

Major and trace elements, including rare earth elements (REEs) geochemistry of bed sediments from the lower reaches of Krishna river suggest their origin mainly from weathering of Deccan basalts and Precambrian rocks of the southern India. The elemental compositions indicate evidence of sedimentary sorting during weathering, transportation and deposition. Highly depleted Na2O and high values of Chemical Index of Alteration (CIA) are suggestive of moderate to strong chemical weathering environment in lower reaches of Krishna river. Major, trace and REE concentrations of bulk sediments suggest marginal variations in relative contribution from mafic and felsic minerals. The bed sediments contain significantly low concentrations of trace elements like Ba, Sr, La, Ce and Nd and moderately low concentrations of V, Zr, Rb, Zn, Ni and Cr relative to upper continental crust (UCC) composition. Most of the other trace elements and REEs are almost similar to UCC indicating their origin from weathering of mixed rock types in catchment areas of Krishna river. Strong relationships of ΣREEs with Ti and Zr in bed sediments suggest that REEs are mainly controlled by heavy minerals such as titanite and zircon. A marked increase in REEs in clay fractions of sediments indicates their adsorption and/or substitution on clay lattice.

Rare-earth and trace elements and hydrogen and oxygen isotopic compositions of Cretaceous kaolinitic sediments from the Lower Benue Trough, Nigeria: provenance and paleoclimatic significance

This study evaluated the Cretaceous (Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rare-earth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments’ provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr (651–1352 ppm), Ba (56–157 ppm), V (38–90 ppm), and Sr (15.1–59.6 ppm). Average values of Co and Ni were 1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies, typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment. 18O values ranged from + 15.4 to + 21.2‰ for the investigated samples, consistent with a residual material derived from chemical weathering of felsic rock and redeposited in a sedimentary basin (typical values of + 19 to + 21.2‰). While in the basin, the sediments experienced extended interactions with meteoric water enriched in δD and δ16O. However, the variation in δD and δ16O values for the investigated samples is attributed to the high temperature of formation (54–91 °C). The δD and δ18O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot, tropical climatic conditions.

Deep groundwater quality in the southwestern United States

Groundwater demands are growing in many arid regions, and the use of non-traditional water resources, especially during extreme droughts, is increasingly common. One non-traditional resource is deep groundwater, which we define from ∼150 m to several kilometers or more deep. We analyze 41 081 data points from 17 basins in the southwestern United States (US) to estimate the distribution of fresh and usable deep groundwater for potential human consumption and irrigation. We find the Great Basin to have the largest percentages of fresh and usable deep groundwater with 88%, 96%, and 98% of the total dissolved solids (TDS) concentrations less than 1000 ppm, 3000 ppm and 10 000 ppm respectively. Seven out of the 17 southwestern basins indicate the presence of substantial quantities of usable deep groundwater (<10 000 ppm TDS). We also find that the Great Basin and the Central Valley of California have 64% and 36%, respectively, of deep groundwater with sufficiently low toxic (Na, Cl, and B) and trace element concentrations for irrigation use without treatment, with greater percentages available for more tolerant crops. Given the potentially large deep fresh and usable groundwater volumes across the southwestern US, it is important to characterize the resource and protect it for potential use in decades and centuries to come.

Response of phytoplankton from the metalimnetic chlorophyll maximum to macro- and micro-nutrients amendments in Lake Geneva

Despite re-oligotrophication and low trace elements concentrations, direct determination of limiting nutrient(s) of the phytoplankton community in Lake Geneva is still missing. Incubation experiments were carried out with either addition of phosphate (+P), nitrate (+N), reactive silica (+Si), iron (+Fe), nickel (+Ni) and molybdenum (+Mo) to surface water collected between 9 and 12 m, during seasonal fieldtrips in 2015. Macro- and micro-nutrients, dissolved concentrations, temperature and irradiance as well as chlorophyll a (Chl a) levels, Chl a:POC ratios, POP:POC ratios and Chl a variable fluorescence parameters were quantified. The rapid phosphorus consumption, elevated inorganic nitrogen to phosphorus ratios and increased Chl a, Chl a:POC and POP:POC, in response to P additions, all indicated a phosphorus limitation in phytoplankton. Moreover, none of the measured parameters differed significantly from the control in the other treatments. These results were also confirmed by the response of Chl a variable fluorescence. The effective photosystem II quantum yield in ambient light, the absolute electron transfer rate and the connectivity, under 53 μmol photons/m2/s illumination, significantly increased while the non-photochemical quenching decreased in the +P treatment. Phytoplankton cells supplemented with phosphate were thus more efficient to capture photons and to drive them into photochemistry at light levels close to in situ levels. This is the first study to demonstrate directly a phosphorus limitation in Lake Geneva, pointing towards the success of its re-oligotrophication process.