FORMS OF TRACE ELEMENTS IN BOTTOM SEDIMENTS OF THE LOWER SHAGAN RIVER (FROM ATOMIC LAKE TO THE IRTYSH RIVER)

This article presents the gross contents and chemical fractionation of trace elements in bottom sediments of the lower Shagan River. Twenty samples were collected at ten cross-sections between the outlet of Atomic Lake and the confluence with the Irtysh River. The point-by-point profiles show element-specific spatial patterns rather than one common accumulation zone. Local maxima of Li, Al, Cr, La, Ce, and Mn occur mainly 66–96 km downstream from Atomic Lake; Ga and Ba are higher in the upper part of the surveyed reach, while U and Mo show multiple separated peaks. Six fractions were identified: water-soluble, exchangeable, weakly specifically sorbed, organic-bound, Fe–Mn oxide/hydroxide-bound, and residual. Most elements, except Ga, had gross contents below upper continental crust values. Less than 20% was extracted using H₂O, Ca (NO₃)₂, and NaOH combined, whereas more than 70% of many elements occurred in poorly soluble forms.

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