Dynamics of Dissolved Carbon in the Mainstem of the Lena River in July 2017

The dynamics of dissolved carbon forms in the waters of the mainstem of the Lena River from the middle reaches (the city of Yakutsk) to the nearshore zone of the Laptev Sea was investigated in July 2017. It is shown that, in the summer period, the river waters were a source of CO 2 to the atmosphere and the Arctic shelf. The rate of CO 2 outgassing into the atmosphere varied from 0.8 to 137.9 mmol m –2 day –1 at an average value of 31.3 mmol m –2 day –1 . The highest spatial variability of the hydrochemical and hydrooptical parameters was observed in the middle reaches of the river, which was determined by the river hydrograph and the influence of the tributaries. The observed differences in the average values of the parameters studied, calculated for the two sections of the river, were formed during the high rainfall flood in the middle reaches and the summer baseflow in the lower reaches. The analysis of the qualitative composition of dissolved organic matter (DOM), based on its optical characteristics, showed the presence of the more labile DOM in the middle reaches of the river as compared to the lower ones. A relationship is established between the optical characteristics and the composition of DOM with the concentrations of dissolved CO 2 in the mainstem of the Lena River. It is shown that the optical parameters of waters are a useful tool for understanding the dynamics and quality of river DOM and its relationship with the CO 2 fluxes in the Arctic rivers.