Seasonal and spatial variations in the number of ammonifying and denitrifying bacteria in communities of plankton and epilithon from the littoral zone Lake Baikal
G. V. PODLESNAYA, M. YU. SUSLOVA, YU. R. SHTYKOVA, I. V. TOMBERG, E. V. ELETSKAYA, O. A. TIMOSHKIN, O. I. BELYKH
Limnological Institute of SB RAS, Irkutsk, Russia
Keywords: nitrogen cycle, ammonifying bacteria, denitrifying bacteria, most probable number (MPN) method, water quality, Lake Baikal
Abstract
We present the results of study on the number of indicator bacterial groups of the nitrogen cycle in plankton and epilithon of the littoral zone Lake Baikal in the spring and autumn periods from 2017 to 2019. The number of ammonifying bacteria (AB) in the lake waters varied from 25 to 6.0 × 105 cells/ml; in epilithic biofilms - from 3.5 × 103 to 9.5 × 106 cells/cm2. The stations subject to anthropogenic impact showed a high number of AB as evidence of active mineralization of nitrogen-containing organic compounds. The maximum number of AB in the water column and the biofilms from stony substrates was detected in June 2017 in the water area of the Severobaikalsk town. The average annual number of AB in the water column was (5.0 ± 2.8) × 102 cells/ml in June and (6.0 ± 1.3) × 102 cells/ml in September. In epilithic biofilms, it was an order of magnitude lower in June than in September, (3.4 ± 1.2) × 104 cells/cm2 and (2.6 ± 1.4) × 105 cells/cm2, respectively. The number of denitrifying bacteria (DB) in water varied from 0 to 60 cells/ml; in epilithic biofilms - from 6 to 2.5 × 103 cells/cm2. Throughout the study period, the highest number of DB in epilithon was detected in June at the station near Elokhin Cape. The average annual number of DB in the water column was 13 ± 4 cells/ml in June and 7 ± 6 cells/ml in September; in epilithic biofilms - (7.9 ± 2.4) × 102 cells/cm2 in June and (4.8 ± 0.5) × 102 cells/cm2 in September. The number of planktonic AMB positively correlates with the concentration of ammonium ions; the number of DB directly depends on the nitrate concentration and inversely depends on nitrites at some stations.
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