The relationship between the dominance of Cyanobacteria species and environmental variables in different seasons and after extreme precipitation

Abstract

© 2017 E. Schweizerbart'sche Verlagsbuchhandlung. The impact of climate change in Serbia, as found throughout the world, is reflected in the rapid changes in drought and heavy rain periods. We show the influence of high rainfall levels on the water quality, composition and seasonal succession of Cyanobacteria in the Šumarice reservoir, Serbia (44°01'49''N, 20°52'28''E). The changes in physical and chemical parameters of water, Chl-a, Cyanobacteria biomass, abundance of phytoplankton and Cyanobacteria along a temporal gradient are visualized using a self-organizing map (SOM). Data was collected monthly during 2013 and 2014. During 2013, the reservoir was characterized as mesotrophic and eutrophic, with a low level of nutrients (the maximum value of total phosphorus was 0.068 mg L-1 and total nitrogen was 0.764 mg L-1 in August), while the maximum values of Cyanobacteria biomass (12.7 mg L-1) and abundance (1.36 × 106 ind L-1) were in September, when Cyanobacteria represented 21 % of the whole phytoplankton. In the following year (2014), after the extreme precipitation (227 L m-2 in May and 138 L m-2 in July), the concentration of nutrients in the reservoir increased. In September, the maximum value of total phosphorus was 0.310 mg L-1, and the maximum value of total nitrogen was 6.828 mg L-1. In October, the maximum values of Cyanobacteria biomass (1567.28 mg L-1) and abundance (2.36 × 108 ind L-1) were recorded when the bloom of Aphanizomenon flos-aquae was observed, representing 98 % of the whole phytoplankton. This blooming is strongly positively correlated with the increase of total phosphorus and nitrogen. The extreme and long-term precipitation was significant enough to change the state of the reservoir from eutrophic to hypereutrophic.