Impacts of drying and reflooding on water quality of a tropical semi-arid reservoir during an extended drought event

Impactos do esgotamento hídrico e reinundação na qualidade da água de um reservatório da região tropical semiárida durante evento de seca prolongada

Abstract

Aim  The aim of this study was to analyze the water quality of a tropical, semi-arid reservoir after a reflooding. In terms of impact on water quality after a drought event, it is expected that there will be improvements with the reflooding. Less algal biomass, increased water transparency, decreased turbidity and low nutrient concentration.

Methods  This study was performed in a tropical, semi-arid man-made lake (Dourado Reservoir), during an extended drought period. This study consisted of a comparison of three distinct periods determined by water accumulation. The limnological variables, including water transparency, turbidity, electrical conductivity, pH, total phosphorus, soluble reactive phosphorus, and chlorophyll-a were analyzed. A principal component analysis (PCA) was also performed to verify the patterns of the variables in relation to the sample units in the studied periods.

Results  After water renewal, there was an expressive reduction in chlorophyll-a. Electrical conductivity, pH, and turbidity variables also reduced after the reflooding, indicating an improvement in water quality. There was no reduction in total phosphorus and soluble reactive phosphorus after the reflooding compared to the previous periods.

Conclusions  The significant reduction in algal biomass after reflooding in Dourado indicates water quality improvement in terms of eutrophication due to the change of the trophic state from eutrophic to mesotrophic.

Keywords:  man-made lakes; shallow; drylands; eutrophication