Landscape, Soil, Lithology, Climate and Permafrost Control on Dissolved Carbon, Major and Trace Elements in the Ob River, Western Siberia

Abstract

In order to foresee possible changes in the elementary composition of Arctic river waters, complex studies with extensive spatial coverage, including gradients in climate and landscape parameters, are needed. Here, we used the unique position of the Ob River, draining through the vast partially frozen peatlands of the western Siberia Lowland and encompassing a sizable gradient of climate, permafrost, vegetation, soils and Quaternary deposits, to assess a snap-shot (8–23 July 2016) concentration of all major and trace elements in the main stem (~3000 km transect from the Tom River confluence in the south to Salekhard in the north) and its 11 tributaries. During the studied period, corresponding to the end of the spring flood-summer baseflow, there was a systematic decrease, from the south to the north, of Dissolved Inorganic Carbon (DIC), Specific Conductivity, Ca and some labile trace elements (Mo, W and U). In contrast, Dissolved Organic Carbon (DOC), Fe, P, divalent metals (Mn, Ni, Cu, Co and Pb) and low mobile trace elements (Y, Nb, REEs, Ti, Zr, Hf and Th) sizably increased their concentration northward. The observed latitudinal pattern in element concentrations can be explained by progressive disconnection of groundwaters from the main river and its tributaries due to a northward increase in the permafrost coverage. A northward increase in bog versus forest coverage and an increase in DOC and Fe export enhanced the mobilization of insoluble, low mobile elements which were present in organo-ferric colloids (1 kDa—0.45 µm), as confirmed by an in-situ dialysis size fractionation procedure. The chemical composition of the sampled mainstream and tributaries demonstrated significant (p < 0.01) control of latitude of the sampling point; permafrost coverage; proportion of bogs, lakes and floodplain coverage and lacustrine and fluvio-glacial Quaternary deposits of the watershed. This impact was mostly pronounced on DOC, Fe, P, divalent metals (Mn, Co, Ni, Cu and Pb), Rb and low mobile lithogenic trace elements (Al, Ti, Cr, Y, Zr, Nb, REEs, Hf and Th). The pH and concentrations of soluble, highly mobile elements (DIC, SO4, Ca, Sr, Ba, Mo, Sb, W and U) positively correlated with the proportion of forest, loesses, eluvial, eolian, and fluvial Quaternary deposits on the watershed. Consistent with these correlations, a Principal Component Analysis demonstrated two main factors explaining the variability of major and trace element concentration in the Ob River main stem and tributaries. The DOC, Fe, divalent metals and trivalent and tetravalent trace elements were presumably controlled by a northward increase in permafrost, floodplain, bogs, lakes and lacustrine deposits on the watersheds. The DIC and labile alkaline-earth metals, oxyanions (Mo, Sb and W) and U were impacted by southward-dominating forest coverage, loesses and eluvial and fertile soils. Assuming that climate warming in the WSL will lead to a northward shift of the forest and permafrost boundaries, a “substituting space for time” approach predicts a future increase in the concentration of DIC and labile major and trace elements and a decrease of the transport of DOC and low soluble trace metals in the form of colloids in the main stem of the Ob River. Overall, seasonally-resolved transect studies of large riverine systems of western Siberia are needed to assess the hydrochemical response of this environmentally-important territory to on-going climate change.

Hydrochemistry of Medium-size Pristine Rivers in Boreal and Subarctic Zone: Disentangling Effect of Landscape Parameters across A Permafrost, Climate and Vegetation Gradient

“…4). However, these correlations do not necessarily indicate a direct control but may be the consequence of the fact that carbonate-bearing loesses are most favorable substrate for productive forests compared to clay, sand and peat -rich soils [20]. The carbonate minerals of these substrates are known to act as sizable sources of alkaline-earth metals and uranium [the latter is carried in the form of highly labile uranyl-carbonate complexes] in shallow subsurface and groundwater feeding the river during summer baseflow [16,17].…”

“…These elements are essentially present in the river water in the form of Al-organic colloids or organic complexes [15,54,[56][57][58]. These two main groups of solutes were evidenced not only in large and small rivers and streams [14,16,17,20,59] but in lentic waters of the region, such as lakes and ponds [60,61], supra-permafrost waters [23], peat porewaters [22] and peat ice [21].…”

“…The interest of the WSL is that it contains huge peat resources and presents rather shallow, essentially discontinuous to sporadic/isolated permafrost, highly vulnerable to thawing [5][6][7][8][9][10]. For this relatively large territory (2 million km²), extensive studies of small [11][12][13][14][15][16][17][18][19] and large [20] river dissolved, colloidal and particulate load, chemical composition of soil ice and suprapermafrost waters [21][22][23][24] and gaseous regime of rivers and lakes [25][26][27] have been performed. However, the majority of these studies except that of the Ob River [20] dealt with single site sampling of a given river, without addressing the spatial variability of riverine solutes within a watershed.…”

“…For this relatively large territory (2 million km²), extensive studies of small [11][12][13][14][15][16][17][18][19] and large [20] river dissolved, colloidal and particulate load, chemical composition of soil ice and suprapermafrost waters [21][22][23][24] and gaseous regime of rivers and lakes [25][26][27] have been performed. However, the majority of these studies except that of the Ob River [20] dealt with single site sampling of a given river, without addressing the spatial variability of riverine solutes within a watershed. This is a clear shortcomings of current state of knowledge of western Siberian rivers, because without sufficient spatial coverage, one cannot test the impact of various landscape factors on water hydrochemistry within the same river basin.…”

Hydrochemistry of Medium-Size Pristine Rivers in Boreal and Subarctic Zone: Disentangling Effect of Landscape Parameters across a Permafrost, Climate, and Vegetation Gradient

“…The interest of the WSL is that it contains huge peat resources and presents rather shallow, essentially discontinuous to sporadic/isolated permafrost, highly vulnerable to thawing [7][8][9][10]. For this relatively large territory (2 million km 2 ), extensive studies of small [11][12][13][14][15][16][17][18][19] and large [20] river dissolved, colloidal and particulate load, chemical composition of soil ice and suprapermafrost waters [21][22][23][24], and gaseous regime of rivers and lakes [25][26][27] have been performed. However, the majority of these studies except that of the Ob River [20] dealt with single site sampling of a given river, without addressing the spatial variability of riverine solutes within a watershed.…”