Indicadores da qualidade da bacia hidrográfica para gestão integrada dos recursos hídricos. Estudo de caso: Bacia hidrográfica do Médio Tocantins (TO)
Abstract
In this thesis a diagnosis of the conditions the watershed of the Middle Tocantins river was
carried out with the objective to develop a management plan for the area of influence of the
reservoir of the hydroelectric power plant, Luiz Eduardo Magalhães.
The power plant started its operation in 2002. The diagnosis of the water quality of the reservoir
and its tributaries was made with the objective to understand the relationships quality of the
watershed / water quality as a response of impacts and conservation areas. The Middle Tocantins
watershed has 13 sub-basins. In this work 4 sub-basins were selected, two heavily impacted
(Ribeirão da Água Fria e Córrego São João) and two with low impacts (Rio Lajeado and Ribeirão
São João).
The quality of the sub-basins was obtained evaluating the condition and vulnerability of the
watershed.
To characterize the watershed condition the indicator used was the state of conservation
(percentage of original vegetation cover, agricultural areas, urbanization, wetlands preserved).
Limnological, physical, chemical and biological analysis of the reservoir, both in short periods of
time with real time monitoring and seasonally was performed in order to analyses the dynamics
of the system and its response to external and internal inputs.
Hydrodynamics of the reservoir was analyzed in order to understand processes of vertical and
horizontal circulation and their interaction with the eutrophication of the reservoir. Nutrient
enrichment due to agricultural and urban wastes is one of the main problems of the degradation
of water quality.
The results show that from the four sub-basins analyzed, the two heavily impacted, Ribeirão da
Água Fria and Córrego São João, have the greatest percentage of areas of human activity (56-
61%) with 36-41% of preserved original vegetation and wetlands.
The two less impacted watersheds, (Ribeirão do Lajeado e Ribeirão São João) presented another
percentage: 54-56% of preserved areas and 41-44% of impacted areas.
Demographic expansion, urbanization and intensive soil use is the main cause of the increase of
eutrophication of the reservoir. The trophic state index applied to the reservoir showed that its
trophic states ranges from oligotrophy to mesotrophy. This could be probably due to the short
retention time of the reservoir (25 days) and the less intensive use and occupation of the
watersheds.
A management plan was prepared considering the risk areas and the environmental zoning
altogether with the reservoir dynamics. The aim of this plan (risk analysis for eutrophication and
sediment transport and input) is to provide a tool for decision makers to develop a process of
integrated, predictive and the watershed level of management in order to optimize multiple uses.