Dolichospermum lemmermannii (Nostocales) bloom in world s deepest Lake Baikal (East Siberia): abundance, toxicity and factors influencing growth

Abstract. Mass development of the cyanobacteria Dolichospermum (D. lemmermannii as dominant species) was reported in coastal zone Bol shye Koty Bay (western coast southern basin), towards end July to beginning August 2019. Blooms were observed 1 1.5-m wide bands adjoining shoreline and stretched uninterrupted over 2 km. Abundance blooms varied within 7.2 71.9 thousand cell mL-1, with 0.73 7.20 g m-3 biomass attained. Maximal concentration opposite biological station Irkutsk State University, a frequently visited place that hosting participants several conferences at time. Hydrochemical analysis samples collected four days after continuous heavy rains showed much higher concentrations nutrients contrast data obtained week before (24 July), which is normal for season. Nutrient elevated relative long term averages by 3 30 fold: phosphate up 0.200 mg L-1, ammonium ions 0.29 nitrates 0.31 L-1. Possible reasons harmful freshwater cyanobacterial bloom unusual this part lake are discussed. Excessive proliferation common D. open areas affected factors: long-lasting rains, zero wind, high air (from 13 15 night 29 daytime) water temperatures 19.2 ); absence isolated septic tanks nearshore zone.