Cold fronts and reservoir limnology: an integrated approach towards the ecological dynamics of freshwater ecosystems

Abstract

In this paper the authors discuss the effects of cold fronts on the dynamics of freshwater ecosystems of southeast South America. Cold fronts originating from the Antarctic show a monthly frequency that promotes turbulence and vertical mixing in reservoirs with a consequence to homogenize nutrient distribution, dissolved oxygen and temperature. Weak thermoclines and the athelomixis process immediately before, during and after the passage of cold fronts interfere with phytoplankton succession in reservoirs. Cyanobacteria blooms in eutrophic reservoirs are frequently connected with periods of stratification and stability of the water column. Cold fronts in the Amazon and Pantanal lakes may produce fish killings during the process of "friagem" associated mixing events. Further studies will try to implement a model to predict the impact of cold fronts and prepare management procedures in order to cope with cyanobacteria blooms during warm and stable water column periods. Changes in water quality of reservoirs are expected during circulation periods caused by cold fronts.Keywords: cold fronts, ecological dynamics, reservoirs, stability, turbulence, cyanobacteria blooms, water quality.Frentes frias e limnologia de reservatórios: uma abordagem integrada para a dinâmica ecológica dos ecossistemas de águas interiores ResumoNeste trabalho, os autores discutem o impacto das frentes frias na dinâmica dos ecossistemas de água doce da região sudeste da América do Sul e com repercussões no Centro Oeste e Amazônia. Frentes frias com origem no continente Antártico mostram uma frequência mensal que tem como consequência o aumento da turbulência e a mistura vertical em represas, homogeneizando a distribuição de nutrientes, de oxigênio dissolvido e a temperatura da água. Termoclinas fracamente estabilizadas e o processo de atelomixia imediatamente antes, durante e após a passagem das frentes frias intervêm na sucessão fitoplanctônica em represas. Frentes frias na Amazônia e Pantanal podem ser a causa da mortalidade em massa de peixes devido à remoção das camadas anóxicas do fundo dos lagos de várzea (friagem). Florescimentos de cianobactérias em reservatórios eutróficos são frequentemente relacionados com períodos de estratificação e estabilidade vertical da coluna de água. Futuros estudos deverão implementar um modelo preditivo que poderá ser fundamental no gerenciamento de reservatórios de abastecimento de água. Estes modelos terão a capacidade de prever frequência de florescimentos de cianobactérias e gerenciar melhor a qualidade da água desses reservatórios.Palavras-chave: frentes frias, dinâmica ecológica, reservatórios, estabilidade, turbulência, florações de cianobactérias, qualidade da água.

The climatic rhythm and blooms of cyanobacteria in a tropical reservoir in São Paulo, Brazil

“…The most critical events, with a density of cyanobacteria of more than 30000 cel/mL, were related to the Instability Line (34324.5 cel/mL) and to the Stationary Polar Atlantic Front (37761.9 cel/mL). These results demonstrate that the mechanism of mixing and stratification proposed by Tundisi et al (2010) could occur both with the front enters and also with other weather types that disturb the water column. Within this context, the successions of weather types which cause the increase in the cyanobacterial density are mainly related to a meeting of a Tropical Equatorial mass or Equatorial Continental mass with a Tropical Instability Line or Polar Atlantic Front and its derivations.…”

“…The vertical structure of tropical reservoirs is susceptible to stratification and the mixing process originating from weather events, as documented in Tundisi et al (2004Tundisi et al ( , 2010 and Moraes et al (2010). These studies showed that, according to the variability of wind stress and regimes, aquatic ecosystems present several responses in their physical, chemical, and biological variables.…”

“…To understand the influence of the weather on cyanobacterial blooms, Tundisi et al (2010) propose a mechanism of the functioning of reservoirs and lakes of southeastern Brazil that is related to the patterns of instability during cold fronts and stability in the absence of cold fronts as an alternative to a model of phytoplankton succession for lakes and reservoirs that is based on the instability of the water column. However, this approach only uses one type of weather, and for a model, it is important to analyse the succession of the weather types over the course of a long period of time.…”

Drought can cause phytoplankton growth intensification in Barra Bonita reservoir

“…Weather conditions such as precipitation, wind and cold front play important roles over the water column mixing (Curtarelli et al 2014) and, consequently, underwater light climate (Tundisi et al 2010). The water column mixing and retention time are pointed as the main responsible for phytoplankton species richness in the reservoir (Calijuri et al 1996;Matsumura-Tundisi and Tundisi 2005;Dellamano-Oliveira et al 2008).…”

“…The water column mixing and retention time are pointed as the main responsible for phytoplankton species richness in the reservoir (Calijuri et al 1996;Matsumura-Tundisi and Tundisi 2005;Dellamano-Oliveira et al 2008). On the other hand, predominance for determined specie is frequently associated with thermal stratification and stability of the water column (Tundisi et al 2010). Therefore, blooms of cyanobacteria occur in the fall when retention time is longer, while chlorophyta and diatom are more common during the spring and summer when the retention time is shorter (Perry et al 1990;Lepš et al 1990).…”