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

Jéssica Nayara de Carvalho Leite,Vanessa Becker

doi:10.1590/s2179-975x6918

Jéssica Nayara de Carvalho Leite, Vanessa Becker

Open Access

https://doi.org/10.1590/s2179-975x6918

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Abstract

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.

Highlights

In dry regions, man-made lakes promote greater water security to meet the demands of human supply and agricultural irrigation, especially during periods of extended drought (Rebouças, 1997)
Dourado reservoir showed a decrease in chlorophyll-a (CHLA) concentrations when compared to periods I e II from Period III (Figure 4)
Extreme events promote a huge vulnerability for continental aquatic bodies due to the process of water level fluctuation, which is directly linked to quality in physical, chemical, and biological aspects, especially in the semi-arid region (Brasil et al, 2016; Figueiredo & Becker, 2018; Costa et al, 2019)

Summary

Introduction

In dry regions, man-made lakes promote greater water security to meet the demands of human supply and agricultural irrigation, especially during periods of extended drought (Rebouças, 1997). The climatic variables influencing the process of water level fluctuation and the use and occupation of drainage basins become factors that directly influence the water quality of a reservoir (Straškraba & Tundisi, 1999; Beklioglu et al, 2007; Jeppesen et al, 2015) Some reservoirs reach such low water volumes that they are no longer sufficient for supply, discontinuing the water intake, or even drying completely at a certain frequency, going through periods of prolonged drought, due to the high evaporation rate (Abbaspour et al, 2012). Due to the lower water depth, the phosphorus stored in the sediment can be resuspended by several processes, such as the action of the winds and benthivorous fish, intensifying internal fertilization and, eutrophication (Beklioglu et al, 2007; Araújo et al, 2016; Costa et al, 2016)

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