The geochemistry of tungsten (W) in the environment is poorly studied. Tungsten usually occurs in low concentrations in natural waters and is not very mobile. For this study, we analyzed W together ...with molybdenum (Mo) in the dissolved and particulate fractions of two boreal estuaries during different seasons. Additionally, we sampled first-order streams that drain different landscape types and the receiving northern Baltic Sea. Furthermore, surface sediment from the estuaries was analyzed to obtain a comprehensive overview of the distribution of W and Mo in a boreal environment.
Both elements showed different distribution patterns during different seasons. While they decreased in the dissolved fraction during spring discharge, in winter, their concentrations were elevated. Molybdenum exhibited non-conservative behavior along the salinity gradient in winter, which was probably caused by its release from underlying sediments. In the particulate fraction, we found opposite behaviors for Mo and W, with higher particulate W and lower particulate Mo during spring discharge.
Molybdenum and W underwent fractionation from land to sea, indicating the different mobilities of these oxyanions. The Mo/W ratio in the dissolved fraction was mainly determined by the Mo concentration, as the W concentration varied only in a narrow range from first-order streams to the Bothnian Bay. In the particulate fraction, the Mo/W ratio appeared to be affected by scavenging processes and showed only small variations.
•We studied dissolved and particulate W and Mo in boreal estuaries and first-order streams during different seasons.•Particulate W and Mo showed contrasting behavior during spring discharge in the estuaries.•No removal of W occurred during transport from first-order streams to the recipient Bothnian Bay.•Molybdenum and W exhibited non-conservative behavior in the estuaries during low flow in winter.
Various stages of an analytical method for high-precision cadmium (Cd) isotope ratio measurements by MC-ICP-MS (sample preparation, matrix separation, instrumental analysis and data evaluation) were ...critically evaluated and optimized for the processing of carbon-rich environmental samples. Overall reproducibility of the method was assessed by replicate preparation and Cd isotope ratio measurements in various environmental matrices (soil, sediment, Fe-Mn nodules, sludge, kidney, liver, leaves) and was found to be better than 0.1‰ (2
σ
for
δ
114
Cd/
110
Cd) for the majority of samples. Cd isotope ratio data for several commercially-available reference materials are presented and compared with previously published results where available. The method was used in a pilot study focusing on the assessment of factors affecting Cd isotope composition in tree leaves. A summary of results obtained for a large number (
n
> 80) of birch (
Betula pubescenes
) leaves collected from different locations in Sweden and through the entire growing season is presented and potential reasons for observed variability in Cd isotope composition are discussed. Seasonal dynamics of element concentrations and isotope compositions in leaves were also compared for Os, Pb, Zn and Cd.
Various stages of an analytical method for high-precision cadmium (Cd) isotope ratio measurements by MC-ICP-MS (sample preparation, matrix separation, instrumental analysis and data evaluation) were critically evaluated and optimized for carbon-rich environmental samples. The method was used in a pilot study focusing on the assessment of factors affecting Cd isotope composition in birch leaves.
Holocene freshening has turned the Bothnian Bay, northern Baltic Sea into an oligotrophic basin. Sequestering of trace elements has changed significantly during the oligotrophication process. In ...principle, trace metals have been transferred from permanently buried sulfides to Fe–Mn-oxyhydroxides in the top layers of the sediment. The oxyhydroxide layers restrict the flux of trace metals from the sediment to the oxic bottom water. Hence, Fe–Mn cycling in the suboxic sediment enriches a number of trace metals in the surface sediment. Arsenic, Sn, Ge and Bi show enrichment in the Fe-oxyhydroxide layer, whereas Mo, Cd, Ni, Co, Cu, and Sb are enriched in the uppermost Mn-oxyhydroxide layer. This natural redox cycling in the sediment obscures pollution effects.
The oligotrophication process started approximately 3500years ago, reflected in decreasing deposition of Zn, a proxy for phytoplankton production, and formation of Mn oxyhydroxide layers. Similarly, Ba/Al data indicate a decrease in the pelagic input of plankton. Barium data also suggest that dissolved sulfide in the sediment never reached high concentrations. Germanium is closely related to Ba, suggesting that Ge can be used as a proxy for phytoplankton production. Vanadium, U, Re, and Mo all indicate that the bottom water never has been significantly sulfidic during the last 5500years. Rhenium data indicate that the organic carbon oxidation rate has decreased during the last 5500years. Cadmium follows the organic matter distribution, but started to increase 1000YBP (years before present). The reason for this enhanced input of Cd is unclear.
•Freshening transfer trace metals from sulfides to Mn–Fe oxyhydroxides.•The importance of Mn-redox cycling increases during freshening.•The sediment in the Bothnian Bay shows many similarities with sediments in the Arctic basin.•Germanium and zinc can both be used as sediment proxies for plankton production.
Surface sediments were collected during the 2000 TransArctic Expedition along the Siberian Arctic coastline, including the Ob, Yenisey, Khatanga, Lena, and Indigirka estuaries. Sediments were ...characterized for elemental composition (total organic carbon, TOC, black carbon, BC, and total N, as well as major and trace elements), isotopic signature (δ13C, δ15N, Δ14C, εNd, 87Sr/86Sr), and organic molecular composition to better understand river export variations over the large spatial scale of the Siberian Arctic. On average, 79 ± 9% of the total C in sediments was organic while 21 ± 9% was inorganic. BC made up 9 ± 4% of the TOC pool, with a general increasing trend from west to east along the Siberian coast. The combined Nd‐ and Sr‐isotopes (εNd and 87Sr/86Sr) were used to define two distinct sediment sources between east and west Siberian regions with the Khatanga River as a boundary. Data from pyrolysis‐GC/MS of the sedimentary organic carbon (SOC) indicated an increase in the freshness of the organic matter from west to east on the Siberian Arctic coast, with increasing relative abundance of furfurals (polysaccharides) with respect to nitriles. Values for the δ13C of SOC ranged from −27.1‰ (mostly terrigenous) to −23.8‰, while δ15N increased from east to west (3.1 to 5.2‰) with a significant correlation with C/N ratio. Values for the Δ14C of SOC ranged from −805 to −279‰, with a consistent trend increasing from the east (Indigirka River) to the west (Ob River). These Δ14C values corresponded to a 14C age of 2570 ± 30 yBP in the Ob estuary and 13,050 ± 50 yBP in the Indigirka estuary. Most importantly, Δ14C values were significantly correlated with the ratio of BC/TOC (R2 = 0.91, n = 6), consistent with the distribution pattern of increasing permafrost zone from the west to the east along the Siberian coast. Together, our results suggest that older OC was derived from the release of recalcitrant BC during permafrost thawing and riverbank and coastal erosion, likely enhanced by ongoing environmental changes in the northern ecosystem.
Temporal variations in the iron isotopic composition, δ56Fe between − 0.13‰ and 0.31‰, have been measured in the suspended fraction in a Boreal river. The major mechanism behind these variations is ...temporal mixing between two types of particles–colloids, Fe-oxyhydroxides and Fe–C colloids. Data in this study indicate that these two types of colloids have different Fe-isotope composition. The Fe–C colloid has a negative δ56Fe value whereas the Fe-oxyhydroxide colloid is enriched in 56Fe.
These two types of colloidal matter have different hydrogeochemical origin. The Fe–C colloid reaches the river during storm events when the upper sections of the soil profile (O and E horizons) are flooded by a rising water table. Colloidal Fe-oxyhydroxides reach the river via inflow and subsequent oxidation of groundwater enriched in dissolved Fe(II).
In natural waters, dissolved oxyanions often dominate over the particle-bound element fraction. Still, the scavenging of oxyanions by suspended particles might contribute significantly to their ...dynamic cycling and distribution. To investigate how oxyanions are affected by manganese (Mn) redox cycling, detailed depth profiles across the pelagic redox zone at the Landsort Deep, Baltic Sea, were collected for molybdenum (Mo), vanadium (V), and tungsten (W), for both dissolved (<0.22μm) and suspended particulate (>0.22μm) fractions.
All three oxyanions show a non-conservative behavior in the stratified Landsort Deep. Strong linear correlations with Mn in the particulate fraction in the redox zone of the Landsort Deep suggest that Mn redox cycling influences their distribution. In the dissolved fraction, Mo, V, and W exhibited rather different behavior. Molybdenum was depleted below the redox zone, while V was depleted only within the redox zone. Tungsten concentrations increased within the redox zone, being three times higher in the sulfidic zone than in the surface water. Unlike Mo, W shows no tendency for adsorption or co-precipitation under the prevailing weak sulfidic conditions in the deep water of the Landsort Deep and is, therefore, not exported to the underlying sediment.
The Landsort Deep data were compared with data from the northern Baltic Sea (Bothnian Bay, Kalix River and Råne River estuaries), where particulate iron (Fe) occurs in high abundance. The particulate fractions of Mo, V, and W decreased during mixing in these estuaries. Vanadium showed the most drastic reduction, with a decrease in dissolved and particulate fractions, indicating that different processes influence the distribution of these oxyanions.
•Detailed profiles for Mo, V, and W across the oxic–anoxic interface in the water column of the Landsort Deep were obtained.•Particulate molybdenum, vanadium, and tungsten show a strong correlation with particulate manganese.•Dissolved tungsten is enriched in the sulfidic zone whereas molybdenum is removed.•Dissolved and suspended particulate vanadium is removed during early estuarine mixing in the northern Baltic Sea.
Rare earth element (REE) data from weekly sampling of the filtered (<0.45 μm) and suspended particulate phase during 18 months in the Kalix River, Northern Sweden, are presented together with data on ...colloidal particles and the solution fraction (<3 kDa). The filtered REE concentration show large seasonal and temporal variations in the river. Lanthanum varied between approximately 300 and 2100 pM. High REE concentration in the filter-passing fraction is related to increased water discharge and there is a strong correlation between the REE concentration, organic carbon, Al and Fe. Physical erosion of detrital particles plays a minor role for the yearly transport of particulate REE in this boreal river system. The suspended particulate fraction, which is dominated by non-detrital fractions, accounted for only 35% of the yearly total transport of La in the river. Approximately 10% of the REE were transported in detrital particles during winter. At spring-flood in May, about 30% of the LREE and up to 60% of the HREE where hosted in detrital particles. Ultrafiltration of river water during spring-flood shows that colloidal particles dominate the transport of filter-passing REE. Less than 5% of the filtered REE are found in the fraction smaller than 3 kDa. The colloidal fraction shows a flat to slightly LREE enriched pattern whereas the solution fraction (<3 kDa) show an HREE enriched pattern, compared with till in the catchment. Suspended particles show a LREE enriched pattern. Data indicate that the REE are associated with two phases in the colloidal (and particulate) fraction, an organic-rich phase (with associated Al–Fe) and an Fe-rich (Fe–oxyhydroxide) inorganic phase. The Ce-anomaly in the suspended particulate fraction in the river shows systematic variations, and can be used to interpret fractionation processes of the REE during weathering and transport. There was no anomaly at maximum spring-flood but during the ice-covered period the anomaly became more and more negative. The temporal and seasonal variations of the Ce-anomaly in the suspended particulate phase reflect transport of REE–C–Al–Fe-enriched colloids from the upper section of the till (and/or from mires) to the river at storm events.
Isotopic information may provide powerful insight into the elemental cycling processes which occur in natural compartments. Further implementation of isotopic techniques in natural sciences requires ...a better understanding of the range of elemental and isotopic compositional variability in environmental matrices. This study assesses the local-scale concentration and isotopic composition variability of nine elements: boron (B), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), strontium (Sr), thallium (Tl), and zinc (Zn) in lysimetric waters, mushrooms, litter, needles, leaves, and lichens. Sequential extractions were also performed on soil samples from 6 depth profiles providing more detailed information on the variability of elemental concentrations and isotope ratios between the elemental pools present in soil. For most of the sample types studied the range of isotopic variability between samples spans almost the entire ranges reported in the literature for natural samples. These results represent a starting point for discussing the role of natural variability in isotopic studies (for example, as a limiting factor in the use of isotopic mixing models) and a baseline for future in-depth studies examining the controls on isotope fraction in natural systems.
High resolution MC-ICP-MS is used for the precise measurement of variations in the isotopic composition of Fe in ferromanganese concretions and sediments relative to IRMM-014 standard. The ...sensitivity for 56Fe in high resolution mode was 3 V per mg lm1 Fe, a figure that is comparable to those from other MC-ICP-MS instruments operated at low resolution. Incorporation of a guard electrode and the efficient ion transmission capabilities of the Neptune MC-ICP-MS instrument are responsible for the high sensitivity. It was observed that the use of HCl resulted in the formation of ClOH+, causing interference with 54Fe in particular. This acid has been preferred in some cases over HNO3 to minimize formation of ArN+, the major interferent for 54Fe. Using the high resolution mode of the Neptune, the nature of spectral interferences is unimportant as all are completely resolved and will not affect the accuracy of the determined Fe isotope ratios. As the instrument also provides flat-topped peaks, high resolution operation does not necessarily result in impaired precision, providing that higher concentrations are used to compensate for the loss in sensitivity compared with the low resolution mode. In the present work, external reproducibilities of 56Fe/54Fe and 57Fe/54Fe isotope ratios were better than 50 ppm (one standard deviation) at a concentration of 5 mg lm1. The level of instrumental mass discrimination observed for raw ratios drifted by as much as 0.09% per mass unit over a measurement session, but could be corrected on-line by simultaneous monitoring of the 62Ni/60Ni isotope ratio. Variations in the Fe concentrations or the acid strength of measurement solutions were found to affect the apparent mass discrimination. Increasing the Fe concentration caused a relative decrease in the raw 56Fe/54Fe and 57Fe/54Fe isotope ratios, thus ruling out the space charge effect as the explanation for this phenomenon. Instead, it is suggested that the larger dry aerosol particles formed at higher Fe concentrations are not completely vaporized until later in the plasma, thus reducing the relative rate of diffusional losses of lighter 54Fe from the central channel. However, application of on-line correction using Ni could adequately account for this effect. From the results for a variety of sedimentary geological materials, analysis of three-isotope data revealed that equilibrium fractionation of Fe occurred during deposition. To be able to distinguish between equilibrium and kinetic fractionation processes, it is imperative to collect accurate and precise data for the 56Fe/54Fe and 57Fe/54Fe isotope ratios. These requirements are readily fulfilled by applying high resolution MC-ICP-MS and on-line correction for instrumental mass discrimination using Ni.
Stable Fe isotope compositions have been measured in water samples of the subarctic Kalix River, a first-order stream, and soil water samples from a riparian soil profile adjacent to the first-order ...stream (Northern Sweden). In the first-order stream, dominated by forest, both the particulate (>0.22 µm) and dissolved (<0.22 µm) phase showed negative δ56Fe values (relative to IRMM-014) during base flow and meltwater discharge in May (−0.97 to −0.09‰). The Fe isotope composition in the water from the riparian soil profile varied between −0.20 and +0.91‰ with sharp gradients near the groundwater table. A linear correlation between the δ56Fe values and the TOC/Febulk ratio was measured during snowmelt in the unfiltered river waters (δ56Fe from −0.02 to +0.54‰), suggesting mixing of two Fe components. Two groups of Fe aggregates, with different Fe isotope compositions, are formed in the boreal landscape. We propose that carbon-rich aggregates, Fe(II)(III)-OC, have negative δ56Fe values and Fe-oxyhydroxides have positive δ56Fe values. A mixture of these two components can explain temporal variations of the Fe isotope composition in the Kalix River. This study suggests that stable Fe isotopes can be used as a tool to track and characterize suspended Fe-organic carbon aggregates during transport from the soil, via first-order streams and rivers, to coastal sediment. Furthermore, the differences in Fe isotope values in the Kalix River and the first-order stream during base flow conditions suggest that the primary Fe sources for river water change throughout the year. This model is combining the Fe isotope composition of first-order streams and rivers to weathering and transport processes in the riparian soil.
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