Ritmos nictemerais e distribuição espaço-temporal de variáveis limnológicas e sanitárias em dois açudes do trópico semiárido (PB).

Abstract

Space/temporal and daily/vertical studies were fulfilled in two different dams with different typologies. Located at Paraiba State (Epitacio Pessoa and Bodocongo). The goals were to study the physical, chemical, biological and microbiological variations, in the surface and in the backwater during annual and daily cycles (24 hours): to identify the months, times and the most critical depths related to the water quality in the dams; to evaluate the efficiency in the hydraulic basin areas including water macrophyte, in the reduction of organic, inorganic and fecal pollutions during the long period and to analyze the patterns of stratification and the mix in the distribution of studied parameters. The quality of water showed variability on time and space, under influence of climate, morphological and anthropogenic factors. In the Epitacio Pessoa dam occurred variations in the quality on the shores were they were no more accentuated during the rains. In the Bodocongo dam, the tributary drains had a big influence in the water quality, helping the water homogeneity into the central point and in the shores. The grouping analysis in the both dams was followed by an associated instruction to the pollution/contamination levels. In the Epitacio Pessoa dam was formed three groups with dissimilar characteristics of point's quality where a group joined three points in the limnetic region of better water quality. Paraiba River with intermediate quality and a third represented by the point of flowing from Taperoa river, with the highest level of pollution, reflecting the human activities on its drainage basin. In Bodocongo was formed two groupings: one who joined the points from the shores and from the central and other that formed by the point of biggest impact atrophic, next to the continuing flushers of drains. In the Epitacio Pessoa dam the PCA extracted two main components, that accumulated 54% (rains) and 42% (drought) form the system variant. In the rains the components who standed out where: nutritious and suspended/cloudy solid and in the drought, the nutritious and salty components. In the Bodocongo dam the PCA showed in the rains the solid components associated with the cloudy and nutritious/sanitary state (40%) and in the dry spell, the following components: salty and algal nutritious/biomass (37%). The two dams showed daily patterns of stratification and mix that gave characteristics like hot polimitcs influenced by win and depth. The thermos stratification occurred during the illuminated times during the day and the mix predominated at night. The thermos homogeneity during the night favored the mix of released nutrients from the sediment increasing the amount in the water. The oxygen dissolved was more sensitive to the thermos stratification and showed a clinograd profile on the two water objects. The PCA applicated like nictemeral had like a source of more variability as temporal variations (day/night). The typology, based in the Carlson Modified Index classified the Epitacio Pessoa and Bodocongo dams as hipereutrophic. The water macrophytes showed themselves efficient in the reduction of the polluted loads in the Bodocongo dam, and with the appropriate handling, they can be ecological solutions in the improvement of the water quality during the stratification process.