Hydrochemical tracers of the hydrological ì processes at the tundra-­‐taiga frontier, lower Yenisei region Nikita I. Tananaev1, 2 1 P.I. Melnikov Permafrost Ins4tute, Yakutsk, Russia 2 Ins4tut Na4onal Politechnique (INP) Toulouse, France Field and lab work supported by NSF (ARC-­‐1204070), The European Union (FP7-­‐FRIEND-­‐277059) Materials and Methods ì  Samples were taken in July by the V.N. Sukachev Forest Ins4tute staff; 23 samples in total; ì  Samples (V = 0.25L) were filtered through 220 nm syringe filters in the field; ì  Lab analyses – Observatoire Midi-­‐Pyrenees, ICP-­‐MS, Elan 6000 (Perkin-­‐Elmer, U.S.); 1104 element defini4ons; ì  Dissolved organic carbon analyses – TOC 5000 (Shimadzu, Japan). July 2013: hydrological conditions Fox Creek Graviyka Daily Precip Colloids? ì  In the surface waters of the boreal regions, Fe and Al mobiliza4on is related to the presence of the organic/inorganic colloids [Ingri et al., 2005; Anderson et al., 2006; Dahlqvist et al., 2007] ì  Mobiliza4on of the insoluble elements, including REEs, occurs within the soil profile, in either its organic or mineral part [Pokrovsky et al., 2006; Bagard et al., 2011] ì  Strong and straight linkage between Fe, DOC and REE concentra4ons may serve as a proof of the colloidal par4cles’ influence on the chemical flux and its composi4on Dissolved vs colloidal state (U/Th, Sr/Gd) ì  In the Yenisei waters, most elements are present in the dissolved state (U/Th > 85, Sr/Gd > 8) ì  For smaller rivers, U/Th is not illustra4ve, poten4ally due to the U binding to colloidal par4cles ì  In Liile Graviyka and Fox Creek waters, most elements are present in the colloidal state (Sr/Gd < 1.5) ì  In the Graviyka waters, most elements are present in the dissolved state (Sr/Gd > 7) Fe-­‐ и С-­‐colloids (a guess) REE in the filtrate (< 220 nm) LREE (organic layer) vs HREE (mineral horizon); NASC-­‐referenced Liile Graviyka Fox Creek Runoff formation processes assessed using Nd/Yb ratio [Bagard et al., 2011] ì  Fox Creek: fast subsurface flow; confined to the organic layer (Nd/Yb > 7) ì  Graviyka: slow subsurface flow; confined mostly to the mineral part of the soil profile (Nd/Yb < 5.8) ì  Liile Graviyka: simultaneous input from two runoff-­‐genera4ng processes and soil layers; both the upper organic layer and (Nd/Yb ≈ 6.4); ì  The Yenisei R.: transi4on of the surficial snowmelt-­‐rain runoff to groundwater runoff (Nd/Yb < 4.9) Conclusions (1) ì  Tundra landscapes with organic soils (Graviyka): chemical composi4on assumes a decisive role of valley slopes in the areas where mineral soils are widely present; ì  Mixed forests on seasonally frozen mineral soils (Fox Creek, Liile Graviyka): fast subsurface runoff within the upper organic layer. Conclusions (2) Permafrost Conditions ì  Graviyka: a permafrost aquitard is ac4ve constantly in the landscape units underlain by mineral soils. It promotes the flow rerou4ng towards the hydrographical network (two-­‐layer permafrost [Bassinot et al., 2004]). ì  Fox Creek (and, to some extent, the Liile Graviyka): no permafrost early in summer, water is either travelling fast towards the streams via the organic layer (ac4ve layer) or is lost due to infiltra4on to the deeper aquifers. Temporal dynamics of the REE content (NASC-­‐referenced) Yenisei Graviyka Liile Graviyka Fox Creek July 2013: hydrological conditions Water Stage Sr/Gd pH 8.6…8.9 μ 70…80 mg/l О2 80…100% Conclusions (3) -­‐ final ì  Peatlands of the Igarka region are hydrologically intact and disjointed from the streams during the summer4me (especially true for the Graviyka R.) ì  Reten4on capacity of the mires in the valley boioms (adjacent to the channel) plays an important role in the surface flow forma4on. ì  Permafrost, while performing hydrological func4ons, is linking together the sedimentary history of the region, its geomorphological and lythological proper4es, and contemporary hydrological processes.