Short-term thermal stratification and partial overturning events in a warm polymictic reservoir: effects on distribution of phytoplankton community

Abstract

In lentic freshwater ecosystems, patterns of thermal stratification play a considerable part in determining the population dynamics of phytoplankton. In this study we investigated how these thermal patterns and the associated hydrodynamic processes affect the vertical distribution of phytoplankton during two consecutive diel cycles in a warm polymictic urban reservoir in the metropolitan region of São Paulo, Brazil. Water samples were taken and physical, chemical and biological data collected at half-meter intervals of depth along a water column at a fixed site, every 3 hours throughout the 48-hour period. Two events of stratification, followed by deepening of the thermocline occurred during the study period and led to changes in the vertical distribution of phytoplankton populations. Aphanocapsa delicatissima Nägeli was the single dominant species throughout the 48-hour period. In the second diel cycle, the density gradient induced by temperature differences avoided the sedimentation of Mougeotia sp. C. Agardh to the deepest layers. On the other hand, Pseudanabaena galeata Böcher remained in the 4.0-5.5 m deep layer. The thermal structure of the water was directly affected by two meteorological factors: air temperature and wind speed. Changes in the cell density and vertical distribution of the phytoplankton were controlled by the thermal and hydrodynamic events.Keywords: phytoplankton, thermohydrodynamics, thermal stratification, diel variation, Guarapiranga reservoir. Estratificação térmica de curto prazo e eventos de desestratificação parcial em um reservatório polimítico quente: efeitos sobre a distribuição da comunidade fitoplanctônica ResumoEm ecossistemas de água doce, os padrões de estratificação térmica têm uma influência considerável sobre a dinâmica populacional do fitoplâncton. Neste estudo nós investigamos como os padrões de estratificação térmica e os processos hidrodinâmicos afetaram a distribuição vertical do fitoplâncton durante dois ciclos nictemerais consecutivos em um reservatório urbano na cidade de São Paulo. As amostragens e medidas das variáveis físicas e químicas foram realizadas a cada três horas durante um período de 48 horas, ao longo de um perfil vertical. Ocorreram dois eventos de estratificação e subsequente abaixamento da termoclina acarretando alterações na distribuição vertical do fitoplâncton. Aphanocapsa delicatissima Nägeli foi a principal espécie dominante durante todo o período avaliado. No segundo ciclo nictemeral o gradiente de densidade criado pelas diferenças de temperatura impediu o afundamento de Mougeotia sp. C. Agardh para as camadas mais profundas. Por outro lado Pseudoanabaena galeata Böcher se manteve nas camadas de 4.0 e 5.5 m. A estrutura térmica da água foi diretamente afetada pelos fatores meteorológicos temperatura do ar e velocidade do vento. As mudanças na densidade e na distribuição vertical do fitoplâncton foram controladas pelos eventos térmicos e hidrodinâmicos.Palavras-chave: fitoplâncton, termohidrodinâmica, estratificação térmica, variação ...

Roles of Nutrient Regime and N:P Ratios on Algal Growth in 182 Korean Agricultural Reservoirs

“…Algal biomass growth (chlorophyll-a) in a freshwater ecosystem is controlled by various chemical and physical factors that include water temperature [4,13], water column stability [14], ambient nutrient concentrations (particularly TN:TP ratio) [3,15], low silica [16], high pH [17][18], lower deepwater light penetration [19][20], and the top-down grazing process of zooplanktons and fish [11,[21][22]. Among these factors the ratio of TN:TP has been considered the fundamental indicator of phytoplankton growth [3][4]23].…”

Identification of Cyanobacteria in a Eutrophic Coastal Lagoon on the Southern Baltic Coast

“…The dominance of picocyanobacterial species is reported for other lagoons, e.g., Patos Lagoon, Brazil or Florida Bay, United States (Phlips et al, 1999), Chesapeake Bay, United States (Wang and Chen, 2004; Chen et al, 2006) and Laguna Chascomús, Argentina (Iachetti and Llames, 2015) ( Table 1 ). Similar phytoplankton communities are also found in freshwater lakes (e.g., Lake Santa Olalla, Spain (López-Archilla et al, 2004), Lake Baikal, Russia (Belykh et al, 2006), lakes in southern Sweden (Komárková-Legnerová and Cronberg, 1994), Guarapiranga Reservoir, Brazil (Santos et al, 2015), Vargem das Flores Reservoir, Brazil (Gomes et al, 2012), reservoirs along the Iguaçu River, Brazil (Silva et al, 2005) and in the Mount Cameroon region, Cameroon (Oben and Oben, 2006). Shallowness and a eutrophic state are common features of all these waters.…”

Phytoplankton, physical and chemical microscale variations in three brackish rock pools

“…peaked at the surface and correlated with temperature. The occurrence of this cyanobacteria genus was related to high temperatures (Santos et al 2015) and tolerance of high pH (Reynolds et al 2002).…”