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- Ingri, Johan, et al.
(författare)
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Temporal variations in the fractionation of the rare earth elements in a boreal river; the role of colloidal particles.
- 2000
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 166:1-2, s. 23-45
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Land, Magnus, et al.
(författare)
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Ba/Sr, Ca/Sr and 87Sr/86Sr ratios in soil water and groundwater: implications for relative contributions to stream water discharge
- 2000
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Ingår i: Applied Geochemistry. - 0883-2927 .- 1872-9134. ; 15:3, s. 311-325
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Tidskriftsartikel (refereegranskat)abstract
- Barium/Sr and Ca/Sr ratios have been used to model the relative importance of different sources of stream water. Major and trace element concentrations together with 87Sr/86Sr ratios were measured in precipitation, soil water, groundwater and stream water in a small (9.4 km2) catchment in northern Sweden. The study catchment is drained by a first order stream and mainly covered with podzolized Quaternary till of granitic composition. It is underlain by a 1.8 Ga granite. A model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components: soil water, shallow groundwater, and deep groundwater. Contributions from precipitation are thus not included in the model. This source may be significant for the stream water generation, but it does not interfere with the calculations of the relative contributions from the subsurface components. The results show that the deep groundwater constitutes between 5 and 20% of the subsurface water discharge into the stream water. The highest values of the deep groundwater fraction occur during base flow. Soil water dominates during snowmelt seasons, whereas during base flow it is the least important fraction. Soil water accounts for 10–100% of the subsurface water discharge into the stream water. Shallow groundwater accounts for up to 80% of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow. The validity of the model was tested by comparing the measured 87Sr/86Sr ratios in the stream water with the 87Sr/86Sr ratios predicted by the model. There was a systematic difference between the measured and modelled 87Sr/86Sr ratios which suggests that the fraction of soil water is overestimated by the model, especially during spring flood. As a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period. However, it is concluded that the differences between measured and predicted values are relatively small, and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments.
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- Land, Magnus, et al.
(författare)
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Chemical weathering rates, erosion rates and mobility of major and trace elements in a boreal granitic till
- 2000
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Ingår i: Aquatic geochemistry. - 1380-6165 .- 1573-1421. ; 6:4, s. 435-460
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Tidskriftsartikel (refereegranskat)abstract
- Chemical weathering rates and erosionrates of granitic till in northern Sweden have beenestimated. The present-day chemical weathering rate iscompared with the long-term average weathering ratesince the last deglaciation approximately 8,700 yearsago. Also, the present-day release rates of major andtrace elements due to chemical weathering are comparedwith the mobility of these elements in a spodosolprofile as shown by soil water samples from the vadozezone. The estimation of the past weathering rate isbased on elemental depletion trends in a soil profile(typic haplocryod), whereas the present weatheringrate is based on elemental input/output budgets in asmall catchment ...
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- Land, Magnus, et al.
(författare)
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Past and present weathering rates in northern Sweden
- 1999
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Ingår i: Applied Geochemistry. - 0883-2927 .- 1872-9134. ; 14:6, s. 761-774
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Tidskriftsartikel (refereegranskat)abstract
- Past and present chemical weathering rates in granitic till have been estimated. The Kalix River watershed in northern Sweden was used as a study area in which 17 evenly distributed soil profiles were investigated. The two estimations are based on elemental depletion trends in soil profiles and input/output budgets for the elements in the watershed, respectively. In the calculations of the past weathering rate it was assumed that zircon is resistant, and thus Zr was considered to be immobile during weathering. The long-term average chemical erosion rate since the area was deglaciated 8700 a ago, expressed as the sum of major element oxides (SiO2, Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O), was estimated to be 5.8 g·m−2·a−1. In terms of base cation (Ca2+, Mg2+, Na+, K+) depletion this corresponds to 0.36 keq·ha−2·a−1. All elements analysed have been depleted from the E-horizon, and the most affected elements are P with an average mass loss of 86% (as P2O5), La 81%, Co 78%, Cu 77% and Ni 76%. The present-day weathering rate was calculated as the difference between outputs and inputs in the Kalix River watershed. The input was considered as the contribution from precipitation, while the output was calculated as the sum of (1) the river-transported dissolved fraction, (2) the river-transported suspended non-detrital fraction (chemically precipitated Fe- and Mn-oxy-hydroxides and matter sorbed on these particles), and (3) the biotic nutrient net uptake. River-transported outputs were measured for an annual cycle starting in September 1991 and ending in August 1992. The present-day chemical erosion rate of the till was estimated to be 6.3 g·m−2·a−1 (sum of major element oxides), or a base cation flux of 1.42 keq·ha−2·a−1. Part of this present-day rate is related to carbonate weathering in the Caledonian mountain range which makes it difficult to compare the present weathering rate with the historical weathering rate. After correction for carbonate weathering the resulting present-day weathering rate of granitic till in terms of base cation flux was estimated to be 0.65–0.75 keq·ha−2·a−1. This result indicates that the present cation flux has increased by a factor of 1.8–2.1 compared to the long-term average. However, given the uncertainties introduced by the carbonates in the Caledonian mountain range it is not possible to prove any significant difference between the mean post-glacial and the present-day weathering rate with the methods used in this study.
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- Land, Magnus, et al.
(författare)
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Seasonal variations in the geochemistry of shallow groundwater hosted in granitic till
- 1997
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 143:3-4, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- The groundwater chemistry in a small catchment in northern Sweden has been studied for a period of 15 months, including two snowmelt events. The groundwater was sampled from two wells in a slope facing a small stream. One well was placed at the top of the slope (28 m from the stream), and the other was placed closer to the stream (13 m from the stream). Both wells were completed to approximately the same elevation (1.5 m below the stream bed). In addition to groundwater compositions, the chemical composition of precipitation, soil water and stream water was investigated. The chemical composition of the groundwater in the well farther from the stream was fairly constant during the studied period. In the closer well the concentrations of Ca, Mg, Na, Sr, Si, and alkalinity decreased by approximately 10% during snowmelt in May. In contrast, the concentrations of Fe, Al, Ce and Cu increased. After the snowmelt, during June and July, the concentrations of Ca, Mg, Na, Sr, Si, and alkalinity in the closer well increased by a factor of 2–5 compared with the concentrations prior to the snowmelt. By August, the concentrations had decreased to the same levels as before the snowmelt and remained constant until next snowmelt. To explain these variations the Ca/Sr ratio was used as a natural chemical tracer for different water masses. It was found that the increased concentrations of Ca, Mg, Na, Sr, Si, and alkalinity during summer was caused by changes in the groundwater flow direction, which resulted in upwelling of deeper groundwater. At this time the area at the closer well acted as an unsaturated discharge area. The concentrations of Fe, Al, Ce and Cu decreased rapidly after the snowmelt and then remained constant except for two peaks in July and August. These variations were due to mixing with rapidly percolating soil water from the E-horizon and melt water or rain water, which is supported by increased content of dissolved oxygen.
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