Influence of water volume reduction on the phytoplankton dynamics in a semi-arid man-made lake: A comparison of two morphofunctional approaches

Abstract

Signifi cant reductions in the water levels of lakes are infl uenced by droughts and freshwater demands, especially in semi-arid regions, where hydric stress is greater.The aim of this study was to investigate the dynamics of phytoplankton during two different water volume periods resulting from an extended drought in a semi-arid lake. Another objective was to compare two functional approaches to test which one of these best captures phytoplankton variability as a function of environmental variability. Multivariate analyses performed using the Reynolds Functional Groups (RFG) and Morphology-Based Functional Groups (MBFG) classifi cation schemes indicated two periods, high and a low water volume. The results demonstrated the importance of light availability on phytoplankton assemblages as these two periods showed signifi cant differences in water transparency and phytoplankton composition. During extended droughts the reduction in water volume enhances the development of bloom-forming cyanobacteria through the limitation of light in a eutrophic man-made lake. Moreover, both functional traits approaches demonstrated the effect of light availability on phytoplankton assemblage composition and can be applied in similar systems. However, the RFG classifi cation provides more information and allows a more detailed description of the algal assemblages.

Environmental conditions are more effective than nutrient availability and spatial processes on explaining microphytoplankton functional structure in a subtropical hypereutrophic reservoir

“…The variability of purely ENV component explained 45% of the variance in MBFG's biovolume and this component was mainly composed of abiotic predictors showing high seasonal variation (insolation, precipitation, water The key role of seasonal variability of environmental factors in structuring microphytoplankton community in the It a reservoir remains more evident when we observed the relative biovolume and the seasonal distribution of the most abundant MBFGs (MBFG III and V). Rising temperatures and increased organic and nutrient loading, for instance, were pointed as key drivers determining bloom events of the most large filamentous cyanobacteria that represent the MBFG III (Tucci and Sant'Anna, 2003;Viney et al 2007;Okello & Kurmayer 2011;Kosten et al 2012;O'Neil et al 2012;Paerl & Otten 2013;Lv et al 2014;Dao et al 2016;Haakonsson et al 2017;Simi c et al 2017;Bel o et al 2018;Braga & Becker 2020;Ribeiro et al 2020). This support our results that showed an important relative biomass of the MBFG III in the spring and summer samples, when high water temperatures were combined to increased precipitation, which possibly increase the load of allochthonous resources in these seasons.…”

“…Trait-based approaches started to be used mainly in the studies of plant ecology (Lavorel et al 1997;Lavorel & Garnier 2002). For phytoplankton, trait-based approaches have been applied to describe the structure and dynamics of communities and their response to environmental conditions in different freshwater ecosystems (Salmaso et al 2014;Beamud et al 2015;Rangel et al 2016;Souza et al 2016;Weithoff & Gaedke 2017;Rodrigues et al 2018;Bortolini et al 2019;Cupertino et al 2019;Braga and Becker, 2020). These functional classifications are based especially on: (i) physiological traits, established from relationships between species requirements and specific environmental conditions (Reynolds et al 2002;Padis ak et al 2009); and (ii) morphological traits, based mainly on individual continuous (e.g.…”

“…The morphology-based functional groups (MBFG) classification captures many of the functional differences among organisms, independent of their phylogenetic affiliation. This classification allows evaluation of specific functional features of the organisms, as well as the response of phytoplankton communities to spatial and temporal variability of environmental conditions (Kruk et al 2011;Kruk & Segura 2012;Reynolds et al 2014;Cardoso et al 2017;Bortolini et al 2019;Cupertino et al 2019;Braga & Becker 2020).…”

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

“…The most recent drought lasted from 2012 until mid-2018, and represented one of the longest droughts in the Brazilian semiarid region in the last decades (Marengo et al, 2018). This prolonged drought varied from moderately to extremely dry before our sampling, according to the Standard Precipitation Index (SPI) (Figueiredo & Becker, 2018;Braga & Becker, 2020;Marengo et al, 2020), with rainfall anomalies between 20 and 60% below the 1981-2000 mean. During this period, 2012 and 2016 were the driest years with rainfall 300-400 mm year -1 below the expected amount (Marengo et al, 2018).…”

The influence of trophic status and seasonal environmental variability on morpho-functional traits in tropical man-made shallow lakes

“…In tropical regions, the annual cycle of precipitation (i.e., rainy and dry seasons) promotes changes in chemical and physical water parameters leading to seasonal differences in phytoplankton assemblage composition (Azevedo et al, 2020;Bortolini & Bueno, 2017;Braga & Becker, 2020;Rangel et al, 2016). Dry periods reduce the water level and have been generally associated with increased eutrophication, water residence time, phytoplankton biomass, mainly cyanobacteria, and decreased water transparency (Aldridge, 2014;Braga et al, 2015;Brasil et al, 2016;Havens et al, 2016Havens et al, , 2019Medeiros et al, 2015;Mosley, 2015;Naselli-Flores, 2003;Padisák et al, 1999;Rocha Junior et al, 2018).…”