Concentrations of major elements and their outflow into the Laptev Sea by the Lena River

Abstract The Lena River is the eighth largest river in the world in terms of water discharge (525 km 3 year −1 ) and the second largest after the Yenisei of the rivers discharging to the Russian Arctic. The sediment discharge of the Lena River is 17.6 × 10 6 tons year −1 (i.e. an average suspended sediment load of 34 mg l −1 ). The observations on the major element content in the lower reaches of the river started in 1935. In this work, chemical composition data are generalized for the Lena River waters in different parts of its drainage basin including some of its tributaries. Average dissolved solids change during the year from 60–70 mg l −1 during the flood (June-July) up to 300–330 mg l −1 in low discharge (March-April). Along with dissolved solid the class or type of waters also changes. During the greater part of the year bicarbonates and calcium ions predominate in the lower reaches of the river. During winter time, when the concentration of dissolved solid exceeds 250 mg l −1 , Lena waters are transformed to a chloride class with sodium and potassium predominating over calcium. The reason is the increasing role of groundwater input. The chemical composition of groundwaters is mainly controlled by the widespread limestone and dolomite deposits in the upper and middle reaches of the river. The plot of variations of major ion concentrations against total dissolved solid shows that the hydrochemical boundary between river and sea waters is located at 2‰. The Lena River system transports about 49.2 × 10 6 t year −1 of dissolved salts to the Laptev Sea, corresponding to an average chemical denudation of 19 t km −2 year −1 , which is half the global average.