Padrões limnológicos e do fitoplâncton nas fases de enchimento e estabilização dos reservatórios do APM Manso e AHE Jauru (Estado de Mato Grosso)

Abstract

This thesis was carried out during the filling and stabilization phases of the reservoirs of APM Manso (Dec/99-Apr/03) and AHE Jauru (Oct/02-Apr/04), in the state of Mato Grosso. It mostly aimed to identify limnological patterns similar to both reservoirs; analyze the influences of river basin, residence time and decomposition process on these patterns; verify the succession of functional groups in the phytoplankton community; and provide a limnological characterization of the tributaries of these hydroelectric reservoirs. In the APM Manso, the flooded area is about 427 km², the residence time (RT) is 429 days; while in the AHE Jauru, the flooded area is about 3 km², and the RT is 4 days. In the former, 11 samplings were conducted during the filling phase (Dec/99- Dezc/00), and 13 during the stabilization phase (Feb/01-Apr/03); the samplings were obtained from seven stations: two in the river, two in the intermediary zone and three in the limnetic zone of the reservoir. In the AHE Jauru, seven samplings were conducted, and the first one was performed one month after the filling was completed, which took three days; the samplings were obtained from two stations: one in the river and one in the reservoir. In both reservoirs, samplings were performed in three different depths in the water column in order to calculate mean, standard deviation and ANOVA. Historic series of weather (precipitation, wind, air temperature) and hydrology (discharge) in the basins of the tributaries of both the APM Manso (Manso and Casca rivers) and the AHE Jauru (Jauru river) as well as the limnological data of these rivers in the period studied were presented and discussed. In the Manso and Casca rivers, rain seasonality was shown to exert strong influence on the major physico-chemical water conditions. In the Juru River, the control was mainly due to the presence or absence of rain close to the collection states. The river conditions were also influenced by their drainage area (geology, soils) and soil uses. In the transition zone of the APM Manso, the oscillations in Secchi disc visibility, turbidity and suspended material were similar to the rivers, with tendency to stabilize in the limnetic zone after March/00. Electrical conductivity, alkalinity and dissolved oxygen were the main indicators of the mineralization process of labile organic matter in the APM Manso (filling phase) and AHE Jauru (Oct-Dec/02), and their patterns were similar to both reservoirs, being mostly controlled by the decomposition velocity. The DO concentrations remained low in the hypolimnion of the reservoirs, which was more noticeable in the APM Manso. The potassium, sodium, magnesium and calcium ions in the APM Manso tended to stabilize after March/00 in this reservoir. In the AHE Jauru, the concentrations of these ions were higher in October/02, with few oscillations and low concentrations in the following months. The mineralization processes of refractory matter, which is abundant in the flooded cerrado vegetation, led to an increment of the nitrogen nutrients (Kjeldahl nitrogen, ammonia, and nitrate) in the APM Manso during the stabilization phase as well as in the AHE Jauru from April to June/03. The residence time was one of the forces which controlled the sedimentation and stabilization processes. The phytoplankton showed functional groups which were generally good describers of the predominant limnological conditions in these reservoirs and their tributaries. In the AHE Jauru, the dominancy among these groups depended on the influence of the Jauru River, which was more perceptible in the rainy period. In the APM Manso, the chlorophyceae were predominant in both filling and stabilization phases; however, the cyanobacteria were also predominant in the latter, possibly due to the increment of nutrients and the decrease in alkalinity. The major limnological patterns identified in the reservoirs were: i) increase in electrical conductivity and alkalinity in the reservoirs (arm of the Casca river in the APM Manso and AHE Jauru); ii) decrease in mean concentrations of DO in relation to the tributaries; iii) increase of Zds and decrease in turbidity and MS (only during drought in the AHE Jauru); iv) increase of phytoplankton density (only during drought in the AHE Jauru). The results suggest that variation patterns in the APM Manso and AHE Jauru continue to occur today and that these environments were stabilized after Dec/00 and Dec/02, respectively