28 research outputs found
Element transport in the Taz River, western Siberia
The riverine export fluxes of dissolved carbon, nutrient and metals from the land to the Arctic Ocean are fairly well quantified for five large Arctic rivers but remain virtually unknown for mid-sized Eurasian rivers, notably those draining through the permafrost zone. Because such rivers can most rapidly respond to on-going climate warming and permafrost thaw in the Arctic, their current hydrochemical composition and elemental yields are badly needed for judging the level of changes in the very near future. Towards quantifying the annual export fluxes and assessing the mechanisms of seasonal variability of river solutes, we monitored the pristine subarctic Taz River (Swatershed = 150,000 km2), which drains through boreal forest and peatlands in the discontinuous and continuous permafrost zone, on a weekly to monthly basis over a 3 year period. Based on seasonal pattern of riverine solutes (70% of annual Mn flux occurred in winter. A number of elements present in the snowpack exhibited sizable (> 45%) export during spring flood (Zn, Cu, Pb, Cd, Sb and Cs). The 3 years mean export fluxes (yields) of dissolved components were comparable to or 30–50% lower than those of other large and medium sized Arctic rivers. This was due mostly to a lack of fresh unaltered rocks and a dominance of peatlands within the Taz River watershed. Elevated concentrations of redox-sensitive micro-nutrients (such as Fe and Mn) occurring during winter baseflow can be linked to disproportionally large floodplain zone of this river which can act, especially in the river's lower reaches, as a stratified lake thereby releasing high amounts of redox-sensitive elements from the sediments. The role of suboxic zones in the Arctic boreal riverine landscape may be more important than previously thought, and may allow explaining anomalously high concentrations of some metals (i.e., Mn) reported in Arctic Ocean surface waters. It is anticipated that climate warming in the region may increase the contribution of winter flow and enhance the export of soluble elements and some nutrients (such as Si, Mn and Co)
Carbon emission and export from the Ket River, western Siberia
Despite recent progress in the understanding of the carbon (C) cycle of Siberian permafrost-affected rivers, spatial and seasonal dynamics of C export and emission from medium-sized rivers (50 000–300 000 km2 watershed area) remain poorly known. Here we studied one of the largest tributaries of the Ob River, the Ket River (watershed = 94 000 km2), which drains through pristine taiga forest of the boreal zone in the West Siberian Lowland (WSL). We combined continuous and discrete measurements of carbon dioxide (CO2) concentration using submersible CO2 sensor and floating chamber flux (FCO2), with methane (CH4), dissolved organic and inorganic C (DOC and DIC, respectively), particulate organic C and total bacterial concentrations over an 800 km transect of the Ket River main stem and its 26 tributaries during spring flood (May 2019) and 12 tributaries during summer baseflow (end of August–beginning of September 2019). The partial pressure of CO2 (pCO2) was lower and less variable in the main stem (2000 to 2500 µatm) compared to that in the tributaries (2000 to 5000 µatm). In the tributaries, the pCO2 was 40 % higher during baseflow compared to spring flood, whereas in the main stem, it did not vary significantly across the seasons. The methane concentration in the main stem and tributaries was a factor of 300 to 1900 (flood period) and 100 to 150 times lower than that of CO2 and ranged from 0.05 to 2.0 µmol L−1. The FCO2 ranged from 0.4 to 2.4 g C m−2 d−1 in the main channel and from 0.5 to 5.0 g C m−2 d−1 in the tributaries, being highest during August in the tributaries and weakly dependent on the season in the main channel. During summer baseflow, the DOC aromaticity, bacterial number, and needleleaf forest coverage of the watershed positively affected CO2 concentrations and fluxes. We hypothesize that relatively low spatial and seasonal variability in FCO2 of the Ket River is due to a flat homogeneous landscape (bogs and taiga forest) that results in long water residence times and stable input of allochthonous dissolved organic matter (DOM), which dominate the FCO2. The open water period (May to October) C emission from the fluvial network (main stem and tributaries) of the Ket River was estimated to 127 ± 11 Gg C yr−1, which is lower than the downstream dissolved and particulate C export during the same period. The estimated fluvial C emissions are highly conservative and contain uncertainties linked to ignoring hotspots and hot moments of emissions, notably in the floodplain zone. This stresses the need to improve the temporal resolution of FCO2 and water coverage across seasons and emphasizes the important role of WSL rivers in the release of CO2 into the atmosphere.</p
High riverine CO2 emissions at the permafrost boundary of Western Siberia
Acknowledgements: The study was part of the JPI Climate initiative, financially supported by VR (the Swedish Research Council) grant no. 325-2014-6898 to J.K. Additional funding from RNF (RSCF) grant no. 18-17-00237, RFBR grant no. 17-55-16008 and RF Federal Target Program RFMEFI58717X0036 ‘Kolmogorov’ to O.S.P. and S.N.K. as well as NERC grant no. NE/M019896/1 to C.S. is acknowledged. The authors thank A. Sorochinskiy and A. Lim for assistance in the field, as well as M. Myrstener, M. Klaus and S. Monteux for advice on data analysis. L. Kovaleva is acknowledged for artwork.Peer reviewedPostprin
Permafrost coverage, watershed area and season control of dissolved carbon and major elements in western Siberian rivers
Analysis of organic and inorganic carbon (DOC and DIC, respectively), pH, Na,
K, Ca, Mg, Cl, SO<sub>4</sub> and Si in ~ 100 large and small rivers
(< 10 to ≤ 150 000 km<sup>2</sup>) of western Siberia sampled
in winter, spring, and summer over a more than 1500 km latitudinal gradient
allowed establishing main environmental factors controlling the transport of
river dissolved components in this environmentally important region,
comprising continuous, discontinuous, sporadic and permafrost-free zones.
There was a significant latitudinal trend consisting in a general decrease in
DOC, DIC, SO<sub>4</sub>, and major cation (Ca, Mg, Na, K) concentration northward,
reflecting the interplay between groundwater feeding (detectable mostly in
the permafrost-free zone, south of 60° N) and surface flux (in the
permafrost-bearing zone). The northward decrease in concentration of
inorganic components was strongly pronounced both in winter and spring,
whereas for DOC, the trend of concentration decrease with latitude was absent
in winter, and less pronounced in spring flood than in summer baseflow. The
most significant decrease in K concentration from the southern
(< 59° N) to the northern (61–67° N) watersheds occurs
in spring, during intense plant litter leaching. The latitudinal trends
persisted for all river watershed size, from < 100 to
> 10 000 km<sup>2</sup>. Environmental factors are ranked by their increasing
effect on DOC, DIC, δ<sup>13</sup>C<sub>DIC</sub>, and major elements in
western Siberian rivers as follows: watershed area < season < latitude. Because the degree of the groundwater feeding is different
between large and small rivers, we hypothesize that, in addition to
groundwater feeding of the river, there was a significant role of surface and
shallow subsurface flow linked to plant litter degradation and peat leaching.
We suggest that plant-litter- and topsoil-derived DOC adsorbs on clay mineral
horizons in the southern, permafrost-free and discontinuous/sporadic
permafrost zone but lacks the interaction with minerals in the continuous
permafrost zone. It can be anticipated that, under climate warming in western
Siberia, the maximal change will occur in small (< 1000 km<sup>2</sup>
watershed) rivers DOC, DIC and ionic composition and this change will be
mostly pronounced in summer
Tests of electron flavor conservation with the Sudbury Neutrino Observatory
We analyze tests of electron flavor conservation that can be performed at the
Sudbury Neutrino Observatory (SNO). These tests, which utilize B solar
neutrinos interacting with deuterium, measure: 1) the shape of the recoil
electron spectrum in charged-current (CC) interactions (the CC spectrum shape);
and 2) the ratio of the number of charged current to neutral current (NC)
events (the CC/NC ratio). We determine standard model predictions for the CC
spectral shape and for the CC/NC ratio, together with realistic estimates of
their errors and the correlations between errors. We consider systematic
uncertainties in the standard neutrino spectrum and in the charged-current and
neutral current cross-sections, the SNO energy resolution and absolute energy
scale, and the SNO detection efficiencies. Assuming that either matter-enhanced
or vacuum neutrino oscillations solve the solar neutrino problems, we calculate
the confidence levels with which electron flavor non-conservation can be
detected using either the CC spectrum shape or the CC/NC ratio, or both. If the
SNO detector works as expected, the neutrino oscillation solutions that
best-fit the results of the four operating solar neutrino experiments can be
distinguished unambiguously from the standard predictions of electron flavor
conservation.Comment: 31 pages (RevTeX) + 10 figures (postscript). Requires epsfig.sty.
Gzipped figures also available at ftp://ftp.sns.ias.edu/pub/lisi/snopaper .
To appear in Phys. Rev.
Roadmap on dynamics of molecules and clusters in the gas phase
This roadmap article highlights recent advances, challenges and future prospects in studies of the dynamics of molecules and clusters in the gas phase. It comprises nineteen contributions by scientists with leading expertise in complementary experimental and theoretical techniques to probe the dynamics on timescales spanning twenty order of magnitudes, from attoseconds to minutes and beyond, and for systems ranging in complexity from the smallest (diatomic) molecules to clusters and nanoparticles. Combining some of these techniques opens up new avenues to unravel hitherto unexplored reaction pathways and mechanisms, and to establish their significance in, e.g. radiotherapy and radiation damage on the nanoscale, astrophysics, astrochemistry and atmospheric science
Trace element transport in western Siberian rivers across a permafrost gradient
Towards a better understanding of trace element (TE) transport in
permafrost-affected Earth surface environments, we sampled ∼ 60 large and small rivers (< 100 to ≤ 150 000 km<sup>2</sup>
watershed area) of the Western Siberian Lowland (WSL) during
spring flood and summer and winter baseflow across a 1500 km latitudinal
gradient covering continuous, discontinuous, sporadic and permafrost-free
zones. Analysis of ∼ 40 major and TEs in the dissolved
(< 0.45 µm) fraction allowed establishing main environmental
factors controlling the transport of metals and TEs in rivers of
this environmentally important region. No statistically significant effect
of the basin size on most TE concentrations was evidenced.
Two groups of elements were distinguished: (1) elements that show the same
trend throughout the year and (2) elements that show seasonal differences.
The first group included elements decreasing northward during all seasons
(Sr, Mo, U, As, Sb) marking the underground water influence of river
feeding. The elements of the second group exhibited variable behavior in the
course of the year. A northward increase during spring period was mostly
pronounced for Fe, Al, Co, Zn and Ba and may stem from a combination of
enhanced leaching from the topsoil and vegetation and bottom waters of the
lakes (spring overturn). A springtime northward decrease was observed for
Ni, Cu, Zr and Rb. The increase in element concentration northward was observed for Ti, Ga, Zr and Th only in
winter, whereas Fe, Al, rare earth elements (REEs), Pb, Zr, and Hf
increased northward in both spring and winter, which could be linked to
leaching from peat and transport in the form of Fe-rich colloids. A
southward increase in summer was strongly visible for Fe, Ni, Ba, Rb and V,
probably due to peat/moss release (Ni, Ba, Rb) or groundwater feeding (Fe,
V). Finally, B, Li, Cr, V, Mn, Zn, Cd, and Cs did not show any distinct trend
from S to N.
<br><br>
The order of landscape component impact on TE concentration in rivers was
lakes > bogs > forest. The lakes decreased export of
Mn and Co in summer and Ni, Cu, and Rb in spring, presumably due to biotic
processes. The lakes enriched the rivers in insoluble lithogenic elements in
summer and winter, likely due to TE mobilization from unfrozen mineral
sediments. The rank of environmental factors on TE concentration in western
Siberian rivers was latitude (three permafrost zones) > season
> watershed size. The effect of the latitude was minimal in
spring for most TEs but highly visible for Sr, Mo, Sb and U. The main factors
controlling the shift of river feeding from surface and subsurface flow to
deep underground flow in the permafrost-bearing zone were the depth of the
active (unfrozen) seasonal layer and its position in organic or mineral
horizons of the soil profile. In the permafrost-free zone, the relative role
of carbonate mineral-bearing base rock feeding versus bog water feeding
determined the pattern of TE concentration and fluxes in rivers
of various sizes as a function of season.
<br><br>
Comparison of obtained TE fluxes in WSL rivers with those of other subarctic
rivers demonstrated reasonable agreement for most TEs; the
lithology of base rocks was the major factor controlling the magnitude of TE
fluxes. Climate change in western Siberia and permafrost boundary
migration will essentially affect the elements controlled by underground
water feeding (DIC, alkaline earth elements (Ca, Sr), oxyanions (Mo, Sb, As)
and U). The thickening of the active layer may increase the export of
trivalent and tetravalent hydrolysates in the form of organo-ferric
colloids. Plant litter-originated divalent metals present as organic
complexes may be retained via adsorption on mineral horizon. However, due to
various counterbalanced processes controlling element source and sinks in
plant–peat–mineral soil–river systems, the overall impact of the
permafrost thaw on TE export from the land to the ocean may be smaller than
that foreseen with merely active layer thickening and permafrost boundary
shift