Increasy eutrophication symptoms during a prolonged drought event in tropical semi-arid reservoirs, Brazil

Abstract

Eutrophication is a global problem and an important cause of the ecological health degradation of aquatic ecosystems. The aim was to evaluate the effect of prolonged drought period (2012 to 2019) on the trophic state of two Brazilian semi-arid reservoirs, Boqueirão de Parelhas (BOQ) and Passagem das Traíras (TRA). The work was carried out according to a drought classification system, based on the Standardized Precipitation Index (SPI), with an aggregated timescale of 36 months, defining three periods. In the Period I, higher values of Secchi and lower values of turbidity, solids, nutrients and chlorophyll-a were registered, when compared to the other periods, mainly in BOQ. The principal component analyses of both reservoirs reveled a showed a temporal trend of the sample units according to the consequences of the prolonged drought. The results indicated changes in limnological variables due to the reduction of accumulated water volume, and they demonstrated that prolonged droughts impact the intensification of eutrophication in both systems. The trophic state of the BOQ reservoir was changed from mesotrophic to eutrophic as a consequence of the drought, while in TRA the eutrophic state remained, but with more intensified symptoms, with higher concentration values of nutrients, solids and algal biomass.

Trophic state in Brazilian semiarid reservoirs after reflooding

“…Extreme events such as severe droughts and heavy rains directly impact the vulnerability of water bodies by altering their physical, chemical, and biological characteristics through fluctuations in water levels (Jeppesen et al, 2015;Moss, 2011;Santos et al, 2021;Wiegand et al, 2021;Moreira et al, 2023). These impacts have been observed in semiarid environments, leading to changes in the trophic state of water bodies (Brasil et al, 2016;Rocha Junior et al, 2018).…”

“…The prolonged drought event had a direct impact on the volume of the Cruzeta reservoir, which was very low in both periods. The decrease in rainfall, associated with high temperatures and the long water residence time in such systems contributes to the concentration of nutrients which in turn will maintain high algal biomass and higher values of electrical conductivity (Figueiredo & Becker, 2018;Santos et al, 2021). With the drought the reservoirs become highly susceptible to eutrophication and sedimentation, primarily due to the retention of nutrients (Barbosa et al, 2012;Jeppesen et al, 2015).…”

“…This process is exacerbated in the semi-arid region due to factors such as the presence of shallow soils and sparse vegetation, facilitating erosion processes and promoting diffuse pollution (Oliveira et al, 2021). The positive correlation between TP and turbidity, total suspended solids (OSS), and SRP can be attributed to the association of phosphorus with sediment particles that enter the reservoir through precipitation, thereby increasing turbidity levels (Medeiros et al, 2015;Santos et al, 2021).…”

Impacts of extreme precipitation events in water quality: a scientometric analysis in global scale

“…during severe droughts (Rocha Junior et al, 2018;Santos et al, 2021;Cortez et al, 2022). The drastic changes in water volume trigger alterations in various physical and chemical parameters, such as suspended solids and nutrient concentrations, turbidity, transparency, temperature, and pH (Stockwell et al, 2020;Mosley, 2015;Marengo et al, 2018;Santos et al, 2021).…”

“…during severe droughts (Rocha Junior et al, 2018;Santos et al, 2021;Cortez et al, 2022). The drastic changes in water volume trigger alterations in various physical and chemical parameters, such as suspended solids and nutrient concentrations, turbidity, transparency, temperature, and pH (Stockwell et al, 2020;Mosley, 2015;Marengo et al, 2018;Santos et al, 2021). These changes in light and nutrient conditions directly impact the phytoplankton community, thereby influencing trophic dynamics and overall ecosystem functioning (Guo et al, 2018;Ji & Havens, 2019;Lisboa et al, 2020).…”