Banca de QUALIFICAÇÃO: ADJUTO RANGEL JUNIOR

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : ADJUTO RANGEL JUNIOR
DATE: 27/04/2022
TIME: 08:00
LOCAL: Google Meet
TITLE:

ENVIRONMENTAL FACTORS DRIVING WATER QUALITY AND PHYTOPLANKTON COMMUNITY IN TROPICAL SEMI-ARID RESERVOIRS.

KEY WORDS:

Eutrophication; nutrients; cyanobacteria; microcystins; climate change.

PAGES: 123
BIG AREA: Outra
AREA: Ciências Ambientais
SUMMARY:

The climatic conditions of the Brazilian Semiarid Region (BSR) promote a vulnerability scenario of water scarcity, which throughout the century encouraged reservoir creation to guarantee water security, especially in drought periods. However, the multiple uses of water increase the nutrient load in the reservoirs, which are concentrated due to the high evaporation rates in the region and the long residence time of the reservoirs, making these systems more susceptible to eutrophication and contributing to the deterioration of the stored water quality. Consequently, there is excessive growth of the phytoplankton community, leading to significant risks to biodiversity and ecosystem functioning, especially when there is toxic cyanobacteria proliferation. The composition and biomass of the phytoplankton community can change over time and, thus, can be investigated and used as a tool to assess environmental changes. The present work aims to evaluate the environmental factors driving water quality and the phytoplankton community in seven multiple-use reservoirs with different trophic statuses, in the semi-arid region of the state of Ceará, Northeastern 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 and water physicochemical variables were measured, and biological components were analyzed. In general, the limnological variables were strongly influenced by the seasonal effect (wet and dry seasons). However, the results were variable among the investigated reservoirs, indicating that intrinsic responses must be considered. In addition to precipitation, morphometric characteristics (size and depth) and land use of the reservoirs are important factors that determine water quality. The reduction in the water volume increased the total nutrient concentrations (phosphorus and nitrogen) and algal biomass (chlorophyll-a) in the reservoirs regardless of the season. However, eutrophication was potentiated during the rainy season, probably due to the loading of allochthonous material from the basin. The relatively low nutrient concentrations associated with the good water quality conditions in Tatajuba (TAT) and Cachoeira (CAC) reservoirs, and moderate in Prazeres (PRA), Olho D'Água (ODA), and Rosário (ROS) reservoirs seem to be limiting the phytoplankton growth and, consequently, primary production in these systems. On the other hand, the Lima Campos (LIC) and Ubaldinho (UBA) reservoirs showed the highest nutrient and chlorophyll-a concentrations, as well as turbidity values, regardless of climate conditions. This fact demonstrates the presence of continuous sources and, therefore, the water quality of these reservoirs is even more threatened. In these reservoirs, specific cyanobacteria taxa represented > 98% of the cyanobacteria biomass and were influenced by different abiotic factors. For example, total nitrogen and phosphorus were positively associated with Microcystis aeruginosa and nitrate with Dolichospermum solitarium, while pH and nitrite were positively associated with Raphidiopsis raciborskii and Planktolyngbya limnetica. Furthermore, microcystin was detected throughout the study in LIC and UBA reservoirs with concentrations ≥ 1 µg L^-1 in most samples, compromising the water quality for human consumption. Thus, our findings show the need for mitigation measures and better water management in the investigated reservoirs to avoid water quality deterioration and multiple uses compromising, especially considering climate change scenarios, since potentially toxin-producer cyanobacteria are becoming more frequent due to adaptive capabilities and global changes.

BANKING MEMBERS:
Externa à Instituição - BÁRBARA MEDEIROS FONSECA - null
Externa à Instituição - ANA CELIA MAIA MEIRELES - UFCA
Presidente - 2218942 - IVANEIDE ALVES SOARES DA COSTA
Externa ao Programa - 1516627 - JULIANA ESPADA LICHSTON
Interna - 1298966 - RAQUEL FRANCO DE SOUZA