Lena Delta hydrology and geochemistry

Abstract

Abstract. The Lena River forms one of the largest deltas in the Arctic; studying this delta has raised many questions regarding processes that occur there that remain open today. Comparing long-term hydrometric observational data of Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) from the Khabarova polar station, located at the head of the delta not far from where the Lena River divides into its main branches, with field observations, which have been carried out since 2002 revealed new insights into the hydrological, hydrochemical, and geochemical processes within the delta. Three periods with various water volumes and intensity of fluvial processes were chosen from the long-term record of water and sediment discharge. The role of ice event (ice blockage and ice floating) during high water in reconfiguring branch channels and influencing the volume of sediment runoff was identified. Results were obtained quantifying the increase of water and sediment discharges in the middle part of the delta main branches. This increase is to a great extent connected with an additional influx of water, as well as an increase of suspended and dissolved material released from the ice complex. A range of major ion and biogenic element contents in the delta branches in summer is introduced, and differences specified between the hydrochemical composition of thawing ice complex waters, of small Lena River branches, and of estuarine areas. The conservative character of some dissolved substances was analyzed along the length of the river branches. The contents of carbon and geochemical substances in suspended and bottom sediments are reported.