Results of Bacterioplankton Studies in the Dnistrovskiy Estuary in 2003-2018

Abstract

Purpose. Determination of long-term changes in bacterioplankton number in the Dnistrovskiy Estuary in 2003-2018 and data usage for aquatic environment quality assessment. Methods. Bacterioplankton number determination was done using direct microscopy method under microscope with magnification of 1200. Ecological classification of surface waters quality adopted in Ukraine was used for water trophic status assessment. Results. Changes of bacterioplankton quantitative characteristics in summer periods of 2003-2018 have been analyzed. Tendency of increase in bacteria quantity has been revealed in the past eight years, as well as the waters’ trophic status increase from polytrophic in summer periods of 2003-2005, 2007-2009 and 2015-2016 to hypertrophic in 2011-2014 and 2017-2018. Maximal out of all the years bacterial number was identified in July 2012 that exceeded the peak value in the end of past century. Existence of statistical connections between bacterioplankton and water conductivity, transparency, chlorophyll a, pheophytin and total phosphorus were shown. Conclusions. It has been established that microbiological regime forming in the Dnistrovskiy Estuary took place under the influence of natural processes of organic matter production and pollution factors that revealed themselves the most in the middle and southern parts of the estuary. Among the aquatic environment parameters controlled bacterioplankton number, like chlorophyll a, reflected the changes of the Dnistrovskiy Estuary trophic state the most realistic way. At that, index of bacterioplankton is indispensible for indication of water pollution with organic matter of anthropogenic origin.