Banca de DEFESA: ADJUTO RANGEL JUNIOR

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : ADJUTO RANGEL JUNIOR
DATE: 27/10/2022
TIME: 14:00
LOCAL: Google Meet
TITLE:

Environmental Factors Driving the Phytoplankton Community and the Ecological Responses of Water Supply Reservoirs in a Brazilian Tropical Semiarid Region

KEY WORDS:

Eutrophication, cyanobacteria, functional approach, microcystins, climate change.

PAGES: 198
BIG AREA: Outra
AREA: Ciências Ambientais
SUMMARY:

The climatic conditions of the Brazilian Semiarid Region (BSR) promote a scenario of vulnerability to water scarcity, which throughout the century encouraged the creation of artificial reservoirs to ensure water security, especially during drought periods. However, the multiple use of water increases the load of nutrients in the reservoirs, which are concentrated due to the high evaporation rates and the high residence time, making these systems more susceptible to eutrophication and contributing to water quality deterioration. Consequently, excessive growth of the phytoplankton community occurs, causing significant risks to biodiversity and ecosystem functioning, mainly when there is a proliferation of toxic cyanobacteria. Thus, the composition and biomass of the phytoplankton community may vary over time, and thus can be investigated and used as a tool to evaluate environmental pressures. In this context a useful way to investigate the phytoplankton community is by grouping the organisms based on similarities in adaptive and functional strategies, such as morphophysiological characteristics that respond to light and nutrient availability. The functional approach may be helpful in establishing relationships between the species’ traits and ecological processes. The present study aims to evaluate the environmental factors that drive the water quality and the phytoplankton community in seven reservoirs with different trophic degrees, in the semi-arid region of Ceará State, Northeast Brazil. Surface water samples (n = 56) were collected quarterly over two years (February 2018 to November 2019) in the dam area, where the catchment for human supply is located. In each sampling, hydroclimatic variables, physicochemical water variables, and biological components were investigated. In general, limnological variables were strongly influenced by the seasonal effect (between rainy and dry seasons). However, the results were variable among the reservoirs, indicating that intrinsic responses should be considered. In addition to precipitation, morphometric characteristics (size and depth) and land use of the reservoirs were important factors determining water quality. Reduced water volume increased concentrations of nutrients (phosphorus and nitrogen) and algal biomass (chlorophyll-a) in the reservoirs regardless of the season. However, eutrophication was enhanced during the rainy season, probably due to the loading of allochthonous material from the basin. The relatively low nutrient concentrations associated with the conditions of good water quality in Tatajuba (TAT) and Cachoeira (CAC) and moderate in Prazeres (PRA), Olho D'Água (ODA), and Rosário (ROS) seem to be limiting phytoplankton growth and, consequently, primary production in these systems. On the other hand, Lima Campos (LIC) and Ubaldinho (UBA) reservoirs showed the highest concentrations of nutrients, chlorophyll-a, and turbidity regardless of climatic conditions, showing that the sources are continuous, and the water quality of these reservoirs is more threatened. A total of 159 phytoplankton taxa were identified in the investigated reservoirs, distributed mainly in green algae (77 spp.), cyanobacteria (52 spp.), and diatoms (15 spp.), but also Euglenophyceae (eight spp.), Cryptophyceae (three spp.), Xantophyceae (three spp.) and Dinophyceae (one spp.). The identified taxa were included in 23 functional groups (RFGs), of which 13 (F, H1, J, K, Lm, Lo, M, MP, N, P, S1, Sn and W1) were considered descriptors of the reservoirs and contributed > 70% of the total biovolume. In general, a decrease in richness and diversity was observed towards the higher trophic gradient (e.g., LIC and UBA), while the opposite occurred for phytoplankton biovolume. The RFGs were representative of the trophic state of the investigated reservoirs and showed signs of eutrophication under oligo- to mesotrophic conditions. Overall, light availability and nutrient concentration were the main xii factors that determined the environmental threshold for the dominance and abundance of RFGs. Thus, the functional RFGs approach proved to be a clear tool to distinguish water quality of reservoirs according to their trophic state. Also, the higher biomass and dominance of cyanobacteria in LIC and UBA were probably driven by the conditions of high turbidity, stable water column, and eutrophication. In these reservoirs, specific cyanobacterial taxa represented > 98% of the phytoplankton biomass and were influenced by different abiotic factors. For example, total nitrogen and phosphorus were positively related to Microcystis aeruginosa and nitrate to Dolichospermum solitarium, while pH and nitrite were positively associated with Raphidiopsis raciborskii and Planktolyngbya limnetica. Microcystins were detected throughout the study in both reservoirs, with 100% of the LIC samples above the limit established by the Brazilian legislation (1 µg L-1 ) and 50% of the UBA samples. Thus, our findings show the need for mitigation measures and better water management in the studied reservoirs, avoiding the deterioration of water quality and compromising multiple uses, especially considering climate change scenarios, since potential cyanotoxin producers are becoming more frequent due to adaptive capacities and global changes.

COMMITTEE MEMBERS:
Externo à Instituição - KAOLI PEREIRA CAVALCANTE - UVA
Externo à Instituição - GUSTAVO HENRIQUE GONZAGA DA SILVA - UFERSA
Presidente - 2218942 - IVANEIDE ALVES SOARES DA COSTA
Interno - ***.819.324-** - JULIO ALEJANDRO NAVONI - UFRN
Externa à Instituição - MARIA CRISTINA BASÍLIO CRISPIM DA SILVA - UFPB