Phytoplankton dynamics in two tropical rivers with different degrees of human impact (southeast Brazil)

Abstract

Potamoplankton attracts little research attention worldwide and this also holds true in Brazil, despite its numerous river systems. The origin and maintenance of phytoplankton populations in these systems have not been well studied. We analysed biological, physical and chemical parameters of the Paraibuna and Pomba rivers to identify the main driving forces behind temporal and spatial phytoplankton patterns. Both systems are located in the southeast, the most populated region. These rivers are similar in climate and geomorphology, and have become eutrophic due to the increase in the human population of the region, especially in Paraibuna River catchments. Twelve and eleven stations were, respectively, sampled during the dry and rainy seasons in the Paraibuna and Pomba rivers. The seasonal pattern of abiotic and biotic variables was related to the increase in the discharge and dilution caused by the rainy period. However, human influences such as the presence of a reservoir and sewage inflow were important to distinguish the rivers. The phytoplankton community of Paraibuna River was influenced by Chapéu D'Uvas Reservoir, which was dominated by a toxic population of Cylindrospermopsis raciborskii. Pomba River phytoplankton was typical of the lotic tropical systems. Phytoplankton functional groups in both rivers were those commonly found in turbid and turbulent shallow lakes. Although the functional group approach was originally described for lentic environments, our data support this approach for lotic community patterns. PHYTOPLANKTON DYNAMICS IN TROPICAL RIVERS Figure 5. Principal Component Analysis based on data from the Paraibuna and Pomba rivers during the dry and rainy periods. WT ¼water temperature, Cond: electrical conductivity, Turb ¼ turbidity, DO: dissolved oxygen, TP: total phosphorus, SRP: soluble reactive phosphorus, SRSi: soluble reactive silica, DIN: dissolved inorganic nitrogen, Chlo: chlorophyll -a, Bact: bacterioplankton. Numbers indicate sample sites

Structure of potamoplankton along a gradient of preservation of riparian vegetation in subtropical streams

“…Other conditions for the development of phytoplankton in the summer have been reported, such as increased temperature and luminosity (Salmaso and Zignin 2010). In general, the low values of algal biomass recorded in the studied streams are in agreement with the mean values observed in other stream ecosystems (Soares et al 2007, Borges and Train 2009, Kireta et al 2012.…”

“…Considering the responses of potamoplankton community in the studied areas, the three major taxonomic classes identified (Bacillariophyceae, Chlorophyceae and Cyanobacteria) followed the results found in other temperate and tropical stream ecosystems (Padisák et al 1991, O'Farrel et al 2002, Soares et al 2007, Rodrigues et al 2009, Tavernini et al 2011, Wu et al 2012). According to Descy et al (2012), most taxons of Bacillariophyceae are not truly planktonic, but benthic taxons in suspension, as observed in the present study (Table II) Although found in the plankton in the studied streams, Cocconeis placentula var.…”

“…Similarly, Gomphonema parvulum already had its best development associated with nutrient-rich waters, especially in waters that contain domestic or agricultural wastewater (Patrick and Reimer 1975). In Brazil, this species was identified in the Pomba River (Paraná) (Soares et al 2007) being associated with high levels of flow, temperature and alkalinity found in the rainy season. According to the classification performed by the Software Omnidia (The Diatoms Software) (Lecointe et al 1993), Aulacoseira granulata, Cocconeis placentula var.…”

“…Historically, the phytoplankton from lotic ecosystems have received less attention in limnological studies (Rodrigues et al 2007). In Brazil, most of them refer to the taxonomical (Bittencourt-Oliveira and Castro 1993, BittencourtOliveira 1993a, b, Mendes-Câmara et al 2002, Soares et al 2007 and to the ecological approaches, focusing on diversity (Bittencourt-Oliveira 2002, Borges et al 2003), structure and the dynamics of phytoplankton (Train and Rodrigues 1998, Silva et al 2001, Soares et al 2007). Nevertheless, studies addressing the relations between the preservation of the riparian vegetation and its consequences on the potamoplankton structure are incipient in Brazilian limnology.…”

Comunidade fitoplanctônica no monitoramento de rios do estado de São Paulo

“…São diversos os estudos que relacionam a estrutura e a dinâmica da comunidade fitoplânctonica com as variáveis ambientais (SOUZA, 2008;GENTIL et al 2008;SOARES et al, 2007;DIAS-LOPES, 2007;PADISÁK et. al.…”