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The aim of this study was to investigate temporal trends and controlling factors of As and V in running waters throughout Sweden. For this purpose, data on stream water chemistry from 62 streams of varying catchment size and characteristics, included in the Swedish environmental monitoring programmes were evaluated. The geochemical software Visual MINTEQ was used to model the speciation and trend analyses were performed on total concentrations of As and V as well as modelled fractions (dissolved species as well as arsenate and vanadate adsorbed to ferrihydrite). The trend analyses showed increasing total concentrations of As and V in southern Sweden. Concentrations of As and V correlated significantly to Fe concentrations in 59 and 60 of the 62 streams respectively, indicating that Fe is an important determining factor for As and V concentrations in Swedish streams. This was confirmed by the geochemical modelling that indicated that the adsorbed fraction is the dominant form of As and V and that the concentrations of As and V in Swedish streams are thus highly determined by concentrations of colloidal or particulate Fe. It is therefore suggested that the increasing trends of As and V are to a large extent due to increasing concentrations of colloidal Fe, which is stabilised by increasing concentrations of DOC. Further the geochemical modelling indicates that the dissolved fraction of As and V generally is small, with the exception of a few streams with high pH and/or phosphate concentrations.

The concentrations of selenium in 10 catchments of a stream network in northern Sweden were monitored over two years, yielding almost 350 observations of selenium concentrations in streamwater. The export of selenium was found to be systematically greater from forests than from mires. Accounting for atmospheric deposition, which was monitored over four years, there was a net accumulation of selenium in mires, while the export from forest soils was approximately equal to the atmospheric deposition. In forest dominated catchments the concentrations of selenium oscillated rapidly back and forth from high to low levels during spring floods. High selenium concentrations coincided with rising groundwater tables in the riparian forest soils, while low selenium concentrations were associated with receding groundwater. Thermodynamic modeling indicated that precipitation of elemental selenium would occur under reducing conditions in the riparian soils. Since changes in the redox conditions are likely to occur near the transition from the unsaturated to the saturated zone, it is hypothesized that the transport of selenium from forest soils to streams is controlled by redox reactions in riparian soils.

The discharge of terrestrial dissolved organic matter (DOM) by streams is an important cross-system linkage that strongly influences downstream aquatic ecosystems. Isotopic tracers are important tools that can help to unravel the source of DOM from different terrestrial compartments in the landscape. Here we demonstrate the spatial and seasonal variation of delta34S of DOM in 10 boreal streams to test if the tracer could provide new insights into the origin of DOM. We found large spatial and seasonal variations in stream water delta34S-DOM values ranging from -5.2 per thousand to +9.6 per thousand with an average of +4.0 +/- 0.6 (N = 62; average and 95% confidence interval). Large seasonal variations were found in stream water delta34S-DOM values: for example, a shift of more than 10 per thousand during the spring snowmelt in a wetland-dominated stream. Spatial differences were also observed during the winter base flow with higher delta34S-DOM values in the fourth-order Krycklan stream at the outlet of the 68 km2 catchment compared to the small (< 1 km2) headwater streams. Our data clearly show that the delta34S-DOM values have the potential to be used as a tracer to identify and generate new insights about terrestrial DOM sources in the boreal landscape.

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With a halflife of 1.49 Myr, the 60 Fe-60 Ni decay scheme is ideally suited for dating meteorites and planetary processes that occurred in the first 10 Myr of the early Solar System (ESS). Ni has two neutron-rich isotopes, 62 Ni and 64 Ni, produced through nuclear statistical equilibrium processes occurring in neutron-rich supernova ejecta. Excesses and deficits have been documented for neutron-rich isotopes from iron group elements ( 48 Ca, 50 Ti, 54 Cr, 62 Ni, and 64 Ni) in normal and FUN calcium-aluminium-rich inclusions (CAIs) as well as primitive and differentiated meteorites, providing information on the scale and extent of isotopic heterogeneity in the ESS.We have developed analytical protocols for high-precision Ni isotope measurements in metal and silicate materials by MC-ICPMS, enabling typical external reproducibilities of 0.010& and 0.015& for d 60 Ni* and d 62 Ni values, respectively. Two terrestrial rock standards (BHVO-1 and DTS-2b) have d 60 Ni* and d 62 Ni identical within analytical uncertainty to the Ni standard solution, thus validating our approach. One enstatite chondrite (Qingzhen) and a martian dunite (NWA2737) yielded d 60 Ni* and d 62 Ni values identical to the terrestrial average. Three carbonaceous chondrites (Murchison, Orgueil and Renazzo) have average d 60 Ni* and d 62 Ni values of 0.0012 ± 0.0057& and 0.0341 ± 0.0025&, respectively. These results suggest that if 60 Fe was present in the ESS when these bodies formed, it was homogenously distributed (±20%) within the accretion region of the terrestrial planets and chondrites. Seven iron meteorites show resolvable uniform deficits in d 60 Ni* of 0.0233 ± 0.0071& and 0.0409 ± 0.0213&, respectively. Although d 60 Ni* deficits in irons are consistent with Fe/Ni fractionation during the lifespan of 60 Fe, a whole-rock fragment and olivine separate from the 4.566 Gyr old angrite SAH99555 as well as a chondrule and CAI from Allende with supracanonical 26 Al/ 27 Al yielded identical deficits in d 60 Ni*, not correlated with their Fe/Ni ratios. We suggest that irons, SAH99555 and the Allende chondrule and CAI analysed here formed in the absence of 60 Fe, at a time when 26 Al was widespread within ESS solids, reflecting a late injection of 60 Fe in the ESS. Injection of 60 Fe occurred after accretion of the angrite parent body, 600,000 yr after CAI-formation, but was homogeneously distributed within the ESS at the time of accretion of chondrite parent bodies. Observed excesses and deficits in 62 Ni are correlated with 54 Cr anomalies. These results provide important constraints regarding the origin of short-lived nuclides in the ESS, and demonstrate the presence of large-scale coupled Cr and Ni isotopic heterogeneity in ESS materials.