INFLUENCE OF THE HYDROLOGICAL CYCLE ON PHYSICAL AND CHEMICAL VARIABLES OF WATER BODIES IN THE VÁRZEA AREAS OF THE MIDDLE SOLIMÕES RIVER REGION (AMAZONAS, BRAZIL)

Abstract

The variation in water level in the Amazon varzea promotes cyclical isolation or union of various bodies of water. Among these, lakes and channels are the most relevant. Due to their cyclical geographic isolation, and even due to the often distinct origin of their waters, these environments showed limnological features which also vary from those bodies of water located outside the varzea setting. The objective of this study is to demonstrate the differentiation of the types of water bodies present in the Middle Solimoes area, inside and outside of the floodplain areas, by segregating their main physical and chemical parameters. It also aims to evaluate the influence of the flood pulse on these parameters in these types of bodies of water. In order to do this, expeditions were conducted monthly from 2004 to 2011, at twelve sampling stations located in different types of water bodies, including canals and lakes within the Mamiraua Sustainable Development Reserve, the Solimoes River and the mouth of the Tefe River. The parameters monitored were electrical conductivity, temperature, dissolved oxygen, oxygen saturation, pH and transparency. To analyze the data obtained from this monitoring, descriptive statistics and clustering were used. The temperature of the bodies of water in the Mamiraua RDS showed mean values ranging between 27.1 and 30.8 ° C. Dissolved oxygen concentrations resulted in average concentrations of from 0.3 to 0.6 mg.L-1, with a high standard deviation. Transparency was between 0.4 and 1.6 m. Electrical conductivity ranged between 87 and 204 μS.cm-1 in white waters and 10 - 21 μS.cm-1 in black/mixed waters of the mouth of the Tefe River. From the groupings obtained, it was possible to state that the lakes behave like independent bodies of water in the daught season, and during the season of high water they form a large grouping, suggesting a greater homogenization. An analysis of principal components with the parameters confirmed their relevance in the structuring of groups or types of bodies of water identified in the region. The pH distinguished itself as the main differentiating factor between white and black waters, followed by water transparency. Electrical conductivity was the main parameter responsible for the differentiation of water in different periods of the hydrological cycle, followed by water transparency. The variation in water level during the hydrological cycles evaluated over seven years of monitoring influenced the water quality in the lakes and canals of Mamiraua Sustainable Development Reserve and the Solimoes and Tefe Rivers. The parameters transparency, dissolved oxygen, and conductivity varied more markedly between the periods of draught and high water.