Spectral light absorption by yellow substance and its dynamics in the surface layers of thermokarst lakes of the Central Yamal

Abstract

The article presents the experimental data on dynamics of light absorption by yellow substance in the surface layer of 52 thermokarst lakes of the Middle Yamal obtained during hydrological, hydrobiological and hydrochemical field investigations in September 2018. In the study period, light absorption by yellow substance in the spectral range 400–700 nm was calculated as 0.7–0.9 m^–1. We measured concentrations of yellow substance С_ys and chlorophyll a Chl_a. The latter had its maximum equal to 12.5 mg/m³. Thirty-seven out of fifty-two samples showed 10.0–14.5 mg/m³ thus corresponding to oligo-and mesotrophic reservoirs. Eutrophic samples (Chl_a >30 mg/m³) were not registered. Maximum chlorophyll (18.8 mg/m³) was detected in site 52. Concentrations of yellow substance in lakes (2.3–19.3 g/m³) were defined with the use of the optical method due to the measured coefficient of light absorption by yellow substance at a wavelength of λ=450 nm. The correlation between Chl_a and С_ys concentrations in all samples indicated that a low content of chlorophyll (Chl_a <10 mg/m³) was randomly accompanied by a wide range of attenuation С_ys (from 0.5 to 3.0 g/m³), whereas its high concentrations – similarly, by random but significantly less variation of С_ys (from 1.1 to 1.9 g/m³).