Influence of ionic strength and conductivity on benthic diatom communities in a tropical river (Monjolinho), S?o Carlos-SP, Brazil

Benthic diatoms are important indicators of ecological conditions in lotic systems. The objective of this study was to elucidate the confounding effects of eutrophication, organic pollution and ionic strength and conductivity on benthic diatom communities. Benthic diatoms and water quality sampling was done at 10 sites during summer base flow period (2008 and 2009). Detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) were used to determine environmental gradients along which species vary with respect to ionic strength and conductivity and other environmental variables. Using variance partitioning, we assessed the individual importance of a set of environmental variables (eutrophication and organic pollution) versus ionic strength and conductivity on diatom community structure. The effects of ionic strength and conductivity and organic pollution, eutrophication and other environmental variables were integrated into overall resultant benthic diatom communities. Through partial CCA, we partitioned the variance in diatom data between two sets of exploratory variables, i.e. ionic strength and conductivity (26.9%); other variables, particularly eutrophication and organic pollution (23.0%); shared variance (11.3%) and unexplained variance (38.8%). Due to the interaction of the effects of ionic strength and conductivity and other variables in this study, laboratory experiments must be performed to confirm the observed effects of ionic strength and conductivity.     

Influence of humic acid on growth and tolerance to cupric ions in Melosira italica (subsp. subartica)

An optimum medium for culturing Melosira italica (subsp. subartica) is described. The optimum concentration of humic acid for growth of this species in culture was found to be 46 μg/ml. Tolerance to cupric ions also increased by addition of humic acid. Cultures tended to maintain a pH of about 6.0. Some ecological implications are discussed. Partially supported by CNPq (Conselho Nacional de Desenvolvintento Ceintifico e Technolǵica Brasil). Partially supported by CNPq (Conselho Nacional de Desenvolvintento Ceintifico e Technolǵica Brasil).     

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l⁻¹ Cd and 0.033 and 0.1 mg l⁻¹ Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l⁻¹) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l⁻¹) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems.     

Spatial variation of zooplankton groups in a tropical reservoir (Broa Reservoir, São Paulo State-Brazil)

In this paper the spatial variation of zooplanktonic groups(cladocerans, rotifers, nauplii and adults of copepods) in the Broareservoir was studied using geostatistical tools. The variation inthe density of cladocerans and nauplii and adults of copepods isstructured along the geographic space in the form of gradients, whichimplies the rejection of the hypothesis of spatial homogeneity andrandomness. In other words, the variation in the density of thesegroups is not distributed randomly over the geographic space. Thepatterns of spatial variation observed can be attributed to differentfactors (advection, behavioral mechanisms and limnological factors).The last conclusion is congruent with the multiple forces hypothesis(Pinel-Alloul, 1995; Pinel-Alloul et al., 1995). Implications tosampling methodology are also discussed.     

Calanoida (Copepoda) species composition changes in the reservoirs of São Paulo State (Brazil) in the last twenty years

A sampling programme was undertaken to monitor the total carbon (C) and total nitrogen (N) content of suspended matter in a small undisturbed upland drainage basin in the New Territories of Hong Kong. Mean C and N contents were 12.9% and 1.0%, respectively, for 132 samples. Samples collected under stable flow conditions had mean C and N contents of 12.8% and 1.1%, respectively. Stormflow samples had mean C and N values of 12.9% and 1.0%, respectively, which were very similar to the levels observed under stable flow conditions. The mean C: N ratios of 12.5 and 13.4 for stable flow and stormflow also reveal little variation with hydrologic conditions. When all the data is considered, little seasonal variation was observed in C and N. However, in winter there is a significant difference in C and N content between stable and stormflow samples. When C and N are plotted against water level, the scattergraphs suggest that as stage increases the percentage of C and N in the suspended matter declines. Scattergraphs of C and N against suspended sediment concentration reveal a negative association. This may reflect the dominance of inorganic sediments produced by erosion processes during rainfall.     

The response of Carlos Botelho (Lobo, Broa) Reservoir to the passage of cold fronts as reflected by physical, chemical, and biological variables.

This paper describes and discusses the impacts of the passage of cold fronts on the vertical structure of the Carlos Botelho (Lobo-Broa) Reservoir as demonstrated by changes in physical, chemical, and biological variables. The data were obtained with a continuous system measuring 9 variables in vertical profiles in the deepest point of the reservoir (12 m) coupled with climatological information and satellite images, during a 32-day period in July and August, 2003. During periods of incidence of cold fronts the reservoir presented vertical mixing. After the dissipation of the cold fronts a period of stability followed with thermal, chemical, and biological (chlorophyll-a) stratification. Climatological data obtained during the cold front passage showed lower air temperature, higher wind speed and lower solar radiation. The response of this reservoir can exemplify a generalized process in all shallow reservoirs in the Southeast Brazil and could have several implications for management, particularly in relation to the phytoplankton population dynamics and development of cyanobacterial blooms. Using this as a basis, a predictive model will be developed with the aim of advancing management strategies specially for the drinking water reservoirs of the Metropolitan Region of S?o Paulo.     

Size and dry weight of main zooplankton species in Bariri reservoir (SP, Brazil).

In order to generate a database for secondary production studies in the S?o Paulo State (Brazil) reservoirs, the size and dry weight of 13 sooplankton species from Bariri reservoir (middle Tietê River) were determined. Diameter and dry weight of eggs from some cladoceran and copepod species were also determined. Sizes varied from 108.6 microm (Keratella tropica) to 2488.6 microm (females of Argyrodiaptomus azevedoi), while dry weights varied between 0.025 microg (K. tropica) and 51.250 microg (females of A. azevedoi). Egg diameters varied between 75.0 microm (Mesocyclops ogunnus) and 171.8 microm (Ceriodaphnia silvestrii), while egg dry-weights varied between 0.074 microg (Acanthocyclops robustus) and 0.865 microg (Bosmina hagmanni). Size and dry weight distribution of the zooplanktonic organisms was not linear in the bariri reservoir.     

Predation on and by pelagic Turbellaria in some lakes in Brazil

Planktonic Turbellaria are of common occurrence in both natural and man-made lakes in Brazil. Experiments were performed in 1987 and 1989 to determine which zooplankton species are consumed by predatory Mesostoma sp. from three natural lakes in the Rio Doce Valley. Experiments were also performed in 1989 with a yet unidentified flatworm from Barra Bonita reservoir. Both predators consumed Daphnia and Ceriodaphnia at a high rate: 4 individuals per day in the case of Mesostoma sp., a large species and 1.5 ind day^–1 in the case of the smaller species from Barra Bonita reservoir. Consumption of copepod nauplii, copepodids and adults was much lower, and Ostracoda were not consumed at all. Experiments on food selectivity showed a clear preference by the flatworms for cladocerans.In the lakes studied, flatworms are heavily preyed upon by larvae of Chaoborus and by Mesocyclops species.Turbellaria densities in the natural lakes were around 300 individuals per cubic meter, whereas in Barra Bonita reservoir, 1000 individuals per cubic meter was a mean value in a fifteen days study.Federal University of São Carlos - Laboratory of LimnologyUniversity of São Paulo - Canter of Water Resource and Applied EcologyPost-graduate student - University of São Paulo