Morphofunctional changes of phytoplankton community during pluvial anomaly in a tropical reservoir

Abstract

The present study focuses on the structure and function of phytoplankton community during periods of marked changes in hydrological traits, influenced by an atypical climatic event (La Niña) and its impact on Armando Ribeiro Gonçalves Reservoir of Rio Grande do Norte, situated in the Caatinga biome of northeastern Brazil. The main questions addressed were: What are the effects of environmental factors on the temporal variation of Morphologically Based Functional Group (MBFG) of phytoplankton community? How does the composition of cyanobacterial species shift in relation to high and low trends of phytoplankton diversity? The samples were collected monthly during 2008-2009 and analyzed for pH, temperature, electrical conductivity, dissolved oxygen content and the nutrients, such as, nitrate-nitrogen, ammoniacal nitrogen, total nitrogen and orthophosphate. Phytoplankton samples were collected for both qualitative and quantitative analyses to evaluate species richness index and species diversity index. The data was divided into two distinct hydrodynamic periods of instability and stability. The results demonstrate considerable changes in dissolved oxygen content, water transparency and nitrogen nutrients, which directly influenced the MBFG of phytoplankton community in space and time. The instability of reservoir water was caused by heavy rainfall, which exerts atypical external disturbances. The seasonal variation of MBFG demonstrates a change in cyanobacterial composition and their diversity during instability and stability periods. MBFG VII, composed by colonial cyanobacteria with mucilage, was associated with reduced values of electrical conductance and alterations in pH. The predominance of filamentous species with heterocyst (MBFG III) occurs only during the hydrodynamic stability period and did not show significant association with analyzed parameters. The co-dominance of MBGFs III, V and VII along with high species diversity of phytoplankton community occurred during the second hydrodynamic instability period which was associated with the reduction in water temperature. It is concluded that the decrease in cyanobacterial species dominance and the general increase in the diversity of phytoplankton community are influenced by pluvial anomaly. The higher water level during the period of pluvial anomaly resulted in nutrient pulse and the mixing of water column in the reservoir, which determined the MBPG phytoplankton community distribution.Keywords: hydrodynamism, environmental factors, phytoplankton community, morphofunctional groups. Alterações morfofuncionais da comunidade fitoplanctônica durante anomalia pluvial em um reservatório tropicalResumo O presente estudo centra-se na estrutura e função da comunidade fitoplanctônica nos períodos de alterações marcantes nas características hidrológicas, influenciado por um evento climático atípico (La Niña) e seu impacto sobre o Reservatório: Armando Ribeiro Gonçalves, no Rio Grande do Norte, situado no bioma Caatinga, localizado na Região Nordeste do Brasil. ...

Assessing temporal and spatial variability of phytoplankton composition in a large reservoir in the Brazilian northeastern region under intense drought conditions

“…These changes, in turn, lead to shifts in phytoplankton attributes (Chellappa et al, 2009;Câmara et al, 2015), which reinforce the use of this community to evaluate the environmental status of these aquatic ecosystems. For example, high concentrations of nutrients, high conductivity and increased phytoplankton biomass could be expected in reservoirs and lakes located in semi-arid regions with reduced water volume (Naselli-Flores, 2003;Bouvy et al, 2003;Mosley et al, 2012;Jirsa et al, 2013).…”

Cyanobacterial blooms in freshwaters bodies in a semiarid region, northeastern Brazil: A review

“…Extreme climatic events are already being observed in Northeast Brazil, causing changes in the phytoplankton community, especially in the dominance of cyanobacteria (e.g., Lira et al, 2014;Câmara et al, 2015;Brasil et al, 2016;Costa et al, 2016). Bouvy et al (2000) made one of the most important reports on cyanoHABs (in almost 40 reservoirs in the Northeast) associated with climate change, when the severe drought of 1998 (a consequence of the El Niño in 1997) made the environment favourable for cyanobacteria proliferation, specially Cylindrospermopsis raciborskii.…”

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

“…In tropical regions where rainfall is concentrated into just a few months of every year, reservoir volumes can change drastically, disturbing the water column and aquatic communities. These disturbances have a large influence on phytoplankton composition and biomass (Figueredo & Giani, 2005;Câmara et al, 2015).…”

“…There have been numerous studies on the environmental impact of tropical reservoirs on phytoplankton. Nevertheless, they usually focused on anthropogenic disturbances; few studies examined the impacts associated with natural disturbances (Chellappa, Chellappa, Câmara, Rocha, & Chellappa, 2009a;Câmara, Rocha, Pessoa, Chellappa, & Chellappa, 2015).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).…”

“…There have been numerous studies on the environmental impact of tropical reservoirs on phytoplankton. Nevertheless, they usually focused on anthropogenic disturbances; few studies examined the impacts associated with natural disturbances (Chellappa, Chellappa, Câmara, Rocha, & Chellappa, 2009a;Câmara, Rocha, Pessoa, Chellappa, & Chellappa, 2015).…”