Navegando por Assunto "Limnology"

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Acesso aberto (Open Access)
Aspectos limnoquímicos do reservatório da Usina Hidrelétrica de Tucuruí (PA): uma avaliação temporal entre 1986 e 2001
(Universidade Federal do Pará, 2003) SANTOS, Márcio José Moura dos; RAMOS, José Francisco da Fonseca; http://lattes.cnpq.br/8189651755374537
The reservoir of the Tucuruí UHE, whose quota is around 72 m, holds a volume of about 50.8 million cubical meters and floods an area of 2.850 of Km2 . It has about 170 km length along its major axis (Main River) and maximum 40 km width. The average time of water residence in the reservoir is approximately 50 days, with a volume of only 3 % of non renewable water. The present work deals with the hydrochemistry of the following water systems: The Tocantins River (up- and downstream the dam) and the reservoir itself. They have been characterized during the year 2001 through horizontal and vertical distribution of the diverse physical, physico-chemical and chemical parameters analyzed, besides time-series evaluation in the period 1986 up to 2001, since the lake formation up to now. The study was carried after analysis of the following parameters: Temperature, Transparency and Total Suspended Solids – TTS, pH, Conductivity, Dissolved Oxygen, free CO2, Ca2+, Mg2+, Na+ , K+ , HCO3 - , Fe-total, P-Total, Ammonia and Nitrate. Studies of the trophic levels of the systems during the year 2001 have also been carried out following the Carlson´s Index of trophic state. It is based on three variables: transparency, a-chlorophyl and P-Total, in order to classify the water body in terms of its trophic level. The data used in this work were gently yielded by Eletronorte Company (Center for Environmental Research - CPA), besides our proper data collected in a fild work in November, 2001. Sampling stations have been established in the reservoir, either in the central body (M1 and M3 – old channel; MJV, MP and MR – outer zone) as in the Caraipé compartment (C1 and C2). In the Tocantins river, samples were collected upstream (M5) and downstream the dam (JT, NP, IT, MJ and cm). The results have shown that the system, as a whole, exhibit quite different hydrochemical characteristics (the central and outer part of the reservoir and up and downstream parts of the Tocantins river. According to studies conducted by Eletronorte, such difference is due to diverse hydrodynamic conditions of the reservoir. For instance, in the central body, the outer parts (MJV, MP and MR) have a hydraulic retention time ned for the rainy and dry seasons. It is also important to notice the role of the Tocantins river as supplier of micronutrients, mainly iron and P-total that will further get into the reservoir. Time-series analysis of the variables Total Suspended Solids, pH, Dissolved Oxygen, free CO2, P-Total and Ammonia did not show significant increasing or decreasing contents. pH and DO have also shown a narrow range of variation while the other parameters exhibited strong variations in the period studied. Finally, in 2001, it is possible to classify the study area a mesotrophic and oligotrophic in the dry and rainny seasons, respectivelly. The results have also shown that inside the reservoir, trophic levels are lower than those found in the Tocantins river (up and downstrean). Regarding only the reservoir, one finds that the Caraipé compartment has a greater trophic level than the central body.
Acesso aberto (Open Access)
Modelagem tridimensional da hidrodinâmica e transporte sedimentar de um lago amazônico urbano
(Universidade Federal do Pará, 2025-04-17) CALLADO, Marco Antônio Vieira; ROLLNIC, Marcelo; http://lattes.cnpq.br/6585442266149471; https://orcid.org/0000-0002-8601-1514
Lakes are critical environments for sustaining human well-being, as they regulate local climate conditions, supply potable water, and underpin a wide range of ecosystem services. The continuous monitoring of these systems is essential for elucidating their metabolic processes and for informing effective management strategies for natural resources. This study aims to develop an environmental diagnosis and prognosis for a shallow Amazonian lake located in an urban area—Lago Água Preta—through the application of a three-dimensional numerical model of hydrodynamics and sediment transport. Numerical simulations were performed using the Delft3D-FLOW model, encompassing the region’s seasonal periods: wet and dry seasons. The simulations were driven meteorological variables and physical parameters of the lake, such as air temperature, humidity, cloud cover, solar radiation, bathymetry, water temperature, current velocity, and the inflow/outflow rates. This comprehensive dataset allowed for the construction of a computational environment capable of accurately representing the hydro-sedimentary processes within the lake Model calibration was performed using a one-month time series of water temperature from February (wet season), while validation was carried out with current data and vertical temperature profiles over four months (December, February, April, and June). The simulations presented good statistical indicators, demonstrating the model's reliability. The greatest discrepancies between simulation and observation occurred at points closer to the urban center. These differences are associated with the influence of anthropogenic activities, such as the discharge of domestic effluents, or with the narrow morphology of the lake in these areas, which can generate thermal shadow zones. The analysis of circulation and temperature patterns between seasonal periods revealed relatively small differences. Notably, there was an average increase of up to 2 °C in water temperature and approximately 0.02 m/s in current velocity during the warmer period. The most significant differences in average temperature occurred in the lake's daily cycle, varying by about 3°C, with a maximum variation of up to 10°C. Since the lake is fed by an artificial water inflow, this inflow is characterized by an intense discharge with a high sediment load. As it is a shallow lake with a maximum depth of up to 4 meters, this discharge is capable of influencing the lake’s entire metabolism by promoting the resuspension of bottom sediments and redistributing nutrients into the water column. Upon entering the lake, the inflow currents are rapidly decelerated, intensifying sedimentation near the inflow point. This process increases water turbidity and alters the local biotic dynamics, resulting in an environment dominated by phytoplankton and prone to eutrophication processes, which consequently reduce water quality. Therefore, based on the diagnosis provided by the modeling of Lago Água Preta, this study highlights the need for ongoing monitoring and control of anthropogenic influences to prevent the progressive degradation of the lake's metabolism. It also underscores the importance of lakes in general, especially when located in urban contexts.