Phytoplankton functional groups in a tropical reservoir in the Brazilian semiarid region

Ruceline Paiva Melo Lins,Beatriz Susana Ovruski De Ceballos,Luciana Gomes Barbosa,Luiz Carlos Serramo Lopez

doi:10.15517/rbt.v65i3.29446

Abstract

Phytoplankton functional groups structure and species abundance vary according to environmental conditions. The present study investigated the natural and anthropogenic stressors that affect phytoplankton functional group biomass in a Brazilian semiarid region reservoir (Argemiro de Figueiredo reservoir). Sampling occurred between August 2007 and July 2009 on a bi-monthly basis for the first year, and in a monthly basis for the last two years. There were three collection points (PC: river confluence; PNC: near the cages; PD: dam site). The water environment analysis of abiotic variables included: temperature, transparency, coefficient of vertical light attenuation, dissolved oxygen, pH, electrical conductivity, alkalinity, dissolved inorganic nitrogen, and reactive soluble phosphorus. Phytoplankton samples were collected into a Van Dorn bottle, and were then preserved in acetic lugol and were quantified using an inverted microscope to determine phytoplankton density and biomass; the identified species were assembled in functional groups. The data were explored by canonical correspondence analysis. Individual analyses were made to test the temporal and spatial variability of the data and the factors that interfered most with the biotic and abiotic variables. Functional groups S1, SN, and K, consisting of filamentous Planktothrix agardhii (Gomont) Anagnostidis & Komárek, Cylindrospermopsis raciborskii (Woloszynska) Seenaya & Subba Raju, and the coccoid Aphanocapsa incerta (Lemmermann) Cronberg & Komárek, respectively, dominated the dry months when the water was warm, turbid, and alkaline. The overflow reservoir served as a natural disturbance reducing the phytoplankton biomass to less than 50 % and the dominance of cyanobacteria, promoting the domain of functional groups F, M, MP, Lo, and X2. The nutrient inputs from intensive fish farming, associated with a low local depth (Zmax = 7.7 m) close to the cages (PNC), resulted in a significant human disturbance that increased the prevalence of functional groups S1, SN, and K, which are composed primarily of cyanobacteria. We concluded that, in reservoirs, overflow events are natural disturbances that have the ability to reduce phytoplankton biomass and alter the structure of local communities, and that intensive fish farming is an anthropogenic disturbance that increases the availability of nutrients and stimulates an increase in biomass of the functional groups that include cyanobacteria. Furthermore, the functional groups of phytoplankton were reliable control of environmental conditions in the reservoirs of tropical semiarid regions.

Highlights

Cycles of both drought and extreme rainfall occur at intervals ranging from a few years to decades
Two questions were raised: (i) Is reservoir overflow a natural disturbance that can disrupt or alter phytoplankton biomass? (ii) Do the nutrients derived from pisciculture in the reservoir cause an anthropogenic disturbance that increases the biomass of cyanobacterial phytoplankton functional groups? To answer these questions, we analyzed the reservoir’s phytoplankton population using the functional group
The highest values for both were measured near the net cages. pH and dissolved oxygen (DO) in the vertical profiles were highest in the euphotic zone, while alkalinity, Soluble reactive phosphorus (SRP), and Dissolved inorganic nitrogen (DIN) were highest in the aphotic zone (Table 2)

Summary

Introduction

Cycles of both drought and extreme rainfall occur at intervals ranging from a few years to decades. Reservoirs in the semiarid region of Brazil are usually very hydrologically stable (Bouvy et al, 2000) This factor is critical for sustaining the long-term dominance of certain phytoplankton species (Huszar, Silva, Marinho, Domingos, & Sant’Anna, 2000). We analyzed the reservoir’s phytoplankton population using the functional group This approach has been widely employed in ecological studies and is an effective tool for explaining community structures and their responses to alterations in environmental conditions (Kruk, Mazzeo, Lacerot, & Reynolds, 2002; Kruk et al, 2011; Brasil & Huszar, 2011; Reynolds, 2014; Török et al, 2016)

Methods

Results

Conclusion