CONCENTRATIONS OF MAJOR ELEMENTS AND THEIR OUTFLOW INTO THE LAPTEV SEA BY THE LENA RIVER

The Lena River is the eighth largest river in the world in terms of wa ter discharge (525 km3 year-1) and the second largest after the Yenise i of the rivers discharging to the Russian Arctic. The sediment discha rge of the Lena River is 17.6 x 10(6) tons year-1 (i.e. an average sus pended sediment load of 34 mg l-1). The observations on the major elem ent content in the lower reaches of the river started in 1935. In this work, chemical composition data are generalized for the Lena River wa ters in different parts of its drainage basin including some of its tr ibutaries. 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 discha rge (March-April). Along with dissolved solid the class or type of wat ers also changes. During the greater part of the year bicarbonates and calcium ions predominate in the lower reaches of the river. During wi nter time, when the concentration of dissolved solid exceeds 250 mg l- 1, Lena waters are transformed to a chloride class with sodium and pot assium predominating over calcium. The reason is the increasing role o f groundwater input. The chemical composition of groundwaters is mainl y 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 hydro chemical boundary between river and sea waters is located at 2 parts p er thousand. The Lena River system transports about 49.2 x 10(6) t yea r-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 aver age.