Dissolved organic matter and nutrients in the Lena River, Siberian Arctic: Characteristics and distribution

Dissolved organic carbon (DOC) and nitrogen (DON), amino acids, carbohydrates and inorganic nutrients were measured on samples taken in July 1994 at 18 stations between Yakutsk and the Lena delta, East Siberia. There were no obvious gradients or features along the river, except in the tributaries, the Aldan and Vilyuy rivers, where significantly higher concentrations of several parameters were measured. Concentrations of DOC varied between 300 and 1000 μ M C, with most values varying between 500 and 700 μ M C (mean 570 μ M C). DON concentrations ranged between 9 and 28 μ M N (mean 13 μ M N). The C/N ratios of bulk dissolved organic matter (DOM) varied from 30 to 58, with 75% of the values being between 45 and 55 (mean 48). Total dissolved amino acids (TDAA) ranged between 1.6 and 5.4 μ M, averaged about 3.5 μ M, mostly in the combined form, and represented about 28% of the DON. Free amino acids were only about 2% of TDAA. Glycine, aspartic acid and glutamic acid predominated, accounting for about 41% of TDAA. Total dissolved carbohydrates ranged from 190 to 470 μ g glucose equivalents l −1 and averaged 299 μ g l −1, forming only 1.2 to 2.5% of the DOC pool. The following ranges of inorganic nutrients were measured: nitrate, 0.01 to 1.4 μ M N (mean 0.6 μ M N); nitrite, 0.03 to 0.1 μ M N (mean 0.07 μ M N); ammonium, 0.01 to 0.3 μ M N (mean 0.13 μ M N); phosphate, 0.2 to 1 μ M P (mean 0.5 μ M P); silicate, 59 to 87 μ M Si (mean 66 μ M Si). Carbon isotope data of the suspended organic material suggest that the low inorganic nitrogen values are not due to algal uptake, but rather an inherent characteristic of the river and the catchment area. This, together with positive correlations between silicate, DOC and DON and high C/N values, suggests that the composition of DOM in the Lena River is mainly determined by the input of soil-derived, recalcitrant material and not by autochthonous sources.