wAbstract
@The chemical status of `40 major and trace elements (TE) and
organic carbon (OC) in pristine boreal rivers draining the basaltic
plateau of Central Siberia (Putorana) and interstitial solutions
of permafrost soils was investigated. Water samples were filtered
in the field through progressively decreasing pore size (5Κm¨0.22Κm¨0.025Κm¨10
kDa¨1 kDa) using cascade frontal filtration technique. Most rivers
and soil porewaters exhibit 2-5 times higher than the world average
concentration of dissolved (i.e., 0.22Κm) iron (0.03-0.4 mg/L),
aluminum (0.03-0.4 mg/L), OC (10-20 mg/L) and various trace elements
that are usually considered as immobile in weathering processes
(Ti, Zr, Ga, Y, REEs). Ultrafiltration revealed strong relationships
between concentration of TE and that of colloidal Fe and Al. According
to their partition during filtration and association with colloids,
two groups of elements can be distinguished: (i) those weakly
dependent on ultrafiltration and that are likely to be present
as truly dissolved inorganic species (Li, Na, K, Si, Mn, Mo, Rb,
Cs, As, Sb) or, partially (20-30) associated with small size
Fe- and Al-colloids (Ca, Mg, Sr, Ba) and to small (1-10 kDa)
organic complexes (Co, Ni, Cu, Zn), and (ii) elements strongly
associated with colloidal iron and aluminum in all ultrafiltrates
largely present in 1-100 kDa fraction (Ga, Y, REEs, Pb, V, Cr,
Ti, Ge, Zr, Th, U). TE concentrations and partition coefficients
did not show any detectable variations between different colloidal
fractions for soil porewaters, suprapermafrost flow and surface
streams. TE concentration measurements in river suspended particles
demonstrated significant contribution (i.e., 30) of conventionally
dissolved (0.22Κm) forms for usually gimmobileh elements such
as divalent transition metals, Cd, Pb, V, Sn, Y, REEs, Zr, Hf,
Th. The Al-normalized accumulation coefficients of TE in vegetation
litter compared to basalts achieve 10-100 for B, Mn, Zn, As, Sr,
Sn, Sb, and the larch litter degradation is able to provide the
major contribution to the annual dissolved flux of most trace
elements. It is hypothesized that the decomposition of plant litter
in the topsoil horizon leads to Fe(III)-, Al-organic colloids
formation and serves as an important source of elements in downward
percolating fluids.x
1. Introduction
2. Sampling and analyses
3. Results and discussion
@3.1. Concentration and size fractionation of chemical elements
@@3.1.1. Major elements
@@3.1.2. Elements exhibiting 30-50 differences between filtrates
@@3.1.3. Element exhibiting large differences (50) between filtrates
@@3.1.4. Thermodynamic considerations
@3.2. Dissolved and particulate fluxes of TE
@3.3. Sources of TE and mechanisms of their migration
4. Conclusions
Acknowledgements
Appendix A. Supplementary data
References