FACTORS AFFECTING THE CONDITIONS OF SULFATE REDUCTION AND MERCURY METHYLATION IN THE RIVER AMUR ICE

• Main Authors: L. M. Kondratyeva, D. V. Andreeva, E. M. Golubeva
• Format: Article
• Language: Russian
• Published: Nauka 2018-04-01
• Series: Lëd i Sneg
• Subjects: amur river; biogeochemical processes; ice; mercury; methylation; microorganism; organic matter; sulfate reduction
• Online Access: https://ice-snow.igras.ru/jour/article/view/439
• ISSN: 2076-6734; 2412-3765

Results of the layer-by-layer studies of distribution of organic matter (OM) and mercury in ice cores sampled from the Amur River near the Khabarovsk city: its mainstream and the Pemzenskaya and Amurskaya branches, are presented. Comprehensive investigation of ice performed at the end of the freeze-up period allows making a retrospective analysis of the river ecosystem pollution during winter. Analysis of the total content of dissolved organic substances and aromatic compounds, determining a level of humification of the aquatic environment, was carried out with a spectrophotometer Shimadzu UV-3600 at 254 and 275 nm. The mercury content was determined by inductively coupled plasmamass spectrometry (ICP-MS). The number of cultured heterotrophic bacteria, sulfate-reducing bacteria (SRB) and their resistance to mercury (0.0005 and 0.001 mg/L) were used as indicators of biogeochemical processes going on in vitro. The maximum resistance to mercury at concentration of 0.001 mg/l was revealed from the sulfate-reducing bacteria in cores taken from the upper ice layer (0-10 cm) near the right bank of the Amurskaya branch. Periodical high mercury contamination of ice (up to 0.71 mkg/L) is estimated as a risk factor. In Pemzenskoy branch, the main factors for the mercury methylation in the ice were fine detritus, coming at the reservoir discharges, and the SRB resistant to mercury. These microorganisms were found in upper layers of the ice (10-35 cm) near the left bank and in the middle of the water stream (60–80 cm). A layer of ice (70–117 cm) with conditions also favourable for the sulfate reduction and the mercury methylation had been revealed in the mainstream of the Amur River near its right bank that is the cross-boundary area in the zone of influence of the Songhua river runoff. Among these conditions are high levels of OM, the presence of heterotrophic bacteria, which are destructors of high-molecular compounds, the potential producers of metabolites with methyl radicals, and the activity of the SRB resistant to mercury.