Banca de DEFESA: AMANDA MAGALHAES CONTIN

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : AMANDA MAGALHAES CONTIN
DATE: 31/03/2021
TIME: 14:00
LOCAL: Remoto (google meet ou plataforma zoom)
TITLE:

WATER LEVEL FLUCTUATIONS AFFECT ENVIRONMENTAL INTEGRITY OF A LARGE TROPICAL RESERVOIR

KEY WORDS:

Climate change; Severe droughts; Tropical power-plant reservoirs; Water quality; Phytoplankton.

PAGES: 80
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geografia Física
SPECIALTY: Hidrogeografia
SUMMARY:

Water level fluctuations occur naturally in reservoirs, as a result of seasonal climatic (pluviosity patterns) and hydrological conditions (losses through evaporation, artificial flow regulation). However, intensification of water level fluctuations caused by global warming and extreme climatic events (severe droughts and rain events) may adversely affect environmental integrity and compromise the sustainability of water systems. Changes in physical and chemical conditions, including in water temperature and stability of the water column, nutrient concentrations, spatial distribution and composition of primary producers and consumers are some of the expected effects of water level fluctuations in aquatic ecosystems. This study focused on the effects of water level fluctuation on physical (water temperature and transparency) and chemical (concentration of inorganic and organic nutrients) conditions, as well as on phytoplankton composition, biomass, as diversity, in the Furnas Hydroelectric-Powerplant Reservoir (UHE-Furnas). It has been hypothesized that severe reduction in water level would increase water temperature and reduce water transparency, as well as cause reduction in dissolved oxygen (DO) concentrations and increases in nutrient concentrations, besides altering pH values.  Moreover, such changes could result in environmental homogenization of water conditions between the two main tributaries of the reservoir (Grande and Sapucaí rivers). Furthermore, water level fluctuation is also expected to affect biomass and taxonomic composition of phytoplankton, stimulating biomass increases and benefiting some phytoplankton groups, such as Cyanobacteria and flagellated mixotrophic species, under increased nutrient and temperature and low water transparency conditions. We collected water samples from bays located in both tributaries of the reservoir during 2014, 2015 and 2016. In situ we measured water temperature, pH, DO concentrations and transparency. Water samples were collected for nutrient analyses, including organic dissolved nitrogen (DON), nitrate and nitrite (NO₃+NO₂–N), ammonium (NH₄-N), soluble reactive phosphorus (SRP) and total phosphorus (TP). For phytoplankton quantitative and qualitative analyses, water samples were collected and preserved with Lugol solution until microscopic analysis. Biovolume was calculated for biomass quantification and diversity was calculated based on biomasses using Shannon-Wiener index. Fatty acid analyses were carried out to identify single fatty acids which could indicate differences in phytoplankton and bacterial biomasses in seston among sampling stations and periods. Sampling stations located in the Sapucaí river had significantly higher ammonium and DON concentrations, as well as lower DO concentrations, than sampling stations from the Grande river. For all remaining physical and chemical variables there were no significant differences between sampling stations of both rivers. This result corroborates the hypothesis of homogenization in water quality conditions between both rivers, due to water level fluctuation. This is supported by the significant negative correlations detected between water level, NO₃+NO₂-N and TDN concentrations in Rio Grande sampling stations, meaning that reduced water level caused nutrient concentrations to increase in the water column. Water level was also negatively correlated to phytoplankton biomass and the concentrations of the saturated fatty acid 18:0 (octadecanoic acid), a very common fatty acid in phytoplankton cells. Under low water level conditions increased nutrient concentrations seems to promote phytoplanton growth, resulting in higher phytoplankton biomass and higher concentrations of 18:0 in the sestonic fraction. In Sapucaí sampling stations, NO₃-N, TDN and TP were positively correlated with water level, suggesting an important contribution of allochthonous input of nutrients from adjacent terrestrial systems during rain events.  As a result, high water levels also affected positively phytoplankton biomass and 18:0 concentrations in Sapucaí sampling stations. Water level manual regulation is an important tool for managing water quality conditions in hydroelectrical power-plans reservoirs. Moreover, water level changes caused by severe droughts or intense rain events are also expected to affect water quality conditions and the community structure of aquatic organisms. However, different responses of tributaries to water level fluctuations, for instance, due to differences in land use and nutrient exportation rates from the surrounding watershed, may modulate overall reservoir response to changes in water level. Understanding such differences in ecosystem responses and including land use analysis of the reservoir watershed is of paramount importance for the success of reservoir management during severe water level changes, not only to preserve water quality and ecosystems services, but also to keep environmental integrity and sustainability of the aquatic biological communities.

BANKING MEMBERS:
Presidente - 2566929 - IOLA GONCALVES BOECHAT
Interna - 007.170.909-65 - FRANCIELLE DA SILVA CARDOZO - UFSJ
Interno - 1375368 - LEONARDO CRISTIAN ROCHA
Interno - 1671307 - BJORN GUCKER
Externo à Instituição - CLEBER CUNHA FIGUEREDO - UFMG