Abiotic factors driving cyanobacterial biomass and composition under perennial bloom conditions in tropical latitudes

Abstract

While warming and eutrophication have increased the frequency and magnitude of harmful cyanobacterial blooms globally, the scenario for many eutrophic tropical freshwaters is a perennial year-round bloom. Yet, the drivers of persistent blooms are less understood when conditions such as light, temperature, and nutrients favor cyanobacteria growth year-round, and especially in regions facing recurrent periods of drought. In order to understand the drivers of cyanobacteria dominance, we assessed the abiotic conditions related to the abundance and dominance of the two dominant bloom-forming genera Raphidiopsis and Microcystis, in six shallow, man-made lakes located in the semiarid Northeastern region of Brazil during a prolonged regional drought. Lower water level corresponded to increased phosphorous and nitrogen concentration and, consequently, phytoplankton biomass. Cyanobacterial biomass was also proportional to phosphorus concentrations during year-round blooms. Yet, the two dominant cyanobacterial genera, Raphidiopsis and Microcystis, seldom co-occurred temporally and the switch between them was driven by water transparency. Our results illustrate the effects of drought induced water level reductions on the biomass and composition of cyanobacterial blooms in tropical shallow man-made lakes. Given the ideal year-round conditions (i.e., high light and temperature), droughts may be expected to intensify the risk and multitude of problems associated with eutrophication.

Permanent occurrence of Raphidiopsis raciborskii and cyanotoxins in a subtropical reservoir polluted by domestic effluents (Itupararanga reservoir, São Paulo, Brazil)

“…It has been reported that environmental factors such as light, temperature, and nutrients have an important in uence on the production of cyanotoxins, and that the consequences may be aggravated by climatic changes (Piccini et al 2011;Paerl & Paul 2012;Antunes et al 2015;Huisman et al 2018;Pham et al 2020,Vanderley et al 2021. Melo et al (2019) identi ed high concentrations of TN (484.66 ± 215.16 µg L -1 ) in the Itupararanga reservoir during the same period as this study, reporting that the primary productivity of the reservoir was limited by phosphorus.…”

“…In the present study, although the cyanobacteria biomass decreased at points where thermal strati cation occurred, R. raciborskii and other species that also have aerotopes (D. solitarium, P. isothrix, and A. gracile) were abundant. Furthermore, changes related to the availability of light, due to reduced water transparency, can have a signi cant in uence on regulation of the dominance of cyanobacteria genera throughout the year (Vanderley et al 2021).…”

“…Furthermore, its sensitivity is related to strati cation of the water column and ushing (Reynolds et al, 2002;Padisák et al, 2009). However, the many ecophysiological adaptations re ect the high genetic variability of this species, accounting for its wide occurrence in different regions of the world (Piccini et al 2011;Antunes et al 2015;Vanderley et al 2021).…”

Permanent occurrence of Raphidiopsis raciborskii and cyanotoxins in a subtropical reservoir polluted by domestic effluents (Itupararanga reservoir, São Paulo, Brazil)

“…It has been reported that environmental factors such as light, temperature, and nutrients have an important in uence on the production of cyanotoxins, and that the consequences may be aggravated by climatic changes (Piccini et al 2011;Paerl & Paul 2012;Antunes et al 2015;Huisman et al 2018;Pham et al 2020,Vanderley et al 2021. Melo et al (2019) identi ed high concentrations of ) in the Itupararanga reservoir during the same period as this study, reporting that the primary productivity of the reservoir was limited by phosphorus.…”

Increasy eutrophication symptoms during a prolonged drought event in tropical semi-arid reservoirs, Brazil

“…In this sense, studies indicate that the semiarid region has already shown symptoms of intensification of eutrophication due to these extreme drought events, increasing the concentration of nutrients, conductivity, solids and algal biomass (Brasil et al, 2016;Costa et al, 2016;Figueiredo & Becker, 2018;Rocha et al, 2018). Furthermore, the decrease in water volume in these dry periods favors the blooms of potentially toxic cyanobacteria (Bouvy et al, 1999;Costa et al, 2019, Medeiros et al, 2015, Vanderley et al, 2021.…”