Reservoirs are used in Brazilian semiarid for human supply, power generation, irrigated agriculture and more recently, intensive fish farming, being Sobradinho reservoir the largest of this region. In the last decade the semiarid region suffered a strong drought, in opposite direction to the increasing demand of water multiple uses. The present work aims to study the spatial-temporal variation of water quality in two reservoirs in the Brazilian semiarid region (Sobradinho and Itaparica reservoirs). For this, samples were collected in the dry and wet periods between 2011 and 2014, and the results were analyzed through boxplot charts and Principal Component Analysis (PCA). For both reservoirs, our results showed that the PCAs did not evidenced a specific seasonal change in the water quality characteristics, distinguishing the wet and dry periods along the four years studied. A clear temporal pattern was detected on both reservoirs with higher values of turbidity, dissolved oxygen and total phosphorus in the wet period and higher values of pH and alkalinity in the dry period. An upstream reduction of nutrients and turbidity were not found in this study, as is reported in literature for consecutive reservoirs, probably due to the irrigation and aquaculture activities, mainly in Itaparica reservoir.

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