Flávia Bottino

Temporal and spatial variation of limnological variables and biomass of different macrophyte species in a Neotropical reservoir (São Paulo - Brazil)

AIM: This study reports an investigation of limnological characteristics and aquatic macrophyte occurrence in a neotropical reservoir in order to assess the spatio-temporal variation of water and sediment variables and their influence on plant distribution. METHODS: Macrophytes, water and sediment samples were collected from a Brazilian reservoir in different seasons from four main arms of the reservoir. In total sixteen water-sediment variables were analyzed including N:P ratio and Trophic State Index. The plants were collected using a quadrat sampling procedure and the dry weight per sample was measured. MANOVA was performed to evaluate spatial and temporal variation of environmental variables as well as seasonal biomass differences. To assess the relationship among environmental variables and macrophytes an ordination analysis (using Canonical Correspondence Analysis: CCA) was carried out. RESULTS: The spatial and temporal variation of limnological variables generated a heterogeneous system which supports the presence of different species of macrophyte. pH, dissolved oxygen and sediment composition were important predictors of Polygonum lapathifolium occurrence while nutrients were associated with Eichhornia crassipes and Pistia stratiotes. Inorganic substances were related to biomass variation of Eichhornia azurea and Myriophyllum aquaticum. CONCLUSIONS: The spatial variation of the environmental variables has caused heterogeneity in the reservoir and it may support the occurrence of different species of macrophyte. Limnological variables highlighted in CCA are important to predict the species occurrence and their control in the study area.

Structure and dynamics of the community of periphytic algae in a subtropical reservoir (state of São Paulo, Brazil)

Much remains to be learned about biological diversity, which constitutes a valuable natural resource. Due to the pressure that human activity has put on natural resources, biodiversity has been reduced, often unbeknownst to those responsible for that activity. Therefore, we aimed to perform a quantitative and qualitative analysis of periphytic algae in the Itupararanga reservoir, correlating the results with the physical and chemical characteristics of the water, as well as with climatic conditions. To that end, five samples were collected at four sampling stations in the Itupararanga reservoir during the year 2010. Aquatic macrophytes were collected with a 156-cm2 frame, and the periphytic algae were scraped free of the macrophytes with a brush. Samples were fixed in formaldehyde and Lugols solution for the qualitative and quantitative analyses, respectively. We identified 156 taxa belonging to eight classes, and the overall density was 10,200-171,800 individuals/mm2. The taxonomic composition and abundance of periphyton were found to be dependent on spatial and temporal factors, such as the type of substrate and the characteristics of the sampling site, as well as seasonal variations in the chemical and physical properties of the water.

Can free-floating and emerged macrophytes influence the density and diversity of phytoplankton in subtropical reservoirs?

Abstract Aquatic macrophytes and phytoplankton are important for primary production and metabolism in lentic systems. We investigated the influence of the macrophytes on the phytoplankton in a subtropical reservoir on a seasonal scale (2009–2010). Our study was one of the first to investigate the effects of free-floating and emerged macrophytes on phytoplankton assemblages in a subtropical reservoir. The concentrations of total phosphorus (25–92 μg/L) and the inflow discharge to the reservoir (6.4–54.3 m3/s) varied seasonally (p < 0.05, multivariate analysis of variance [MANOVA]) and were positively and negatively related with the macrophyte biomass, respectively (principal components analysis [PCA]). Light availability was significantly different within the sampling periods (p < 0.05) and influenced phytoplankton densities (0.6 × 103 to 21.0 × 103 ind/mL) and chlorophyll a (<0.5–51.3 μg/L). Abiotic environmental factors and macrophytes influenced the phytoplankton dynamics, and it was difficult to clearly separate these effects. Although the MANOVA did not show seasonal variation of the macrophyte biomass (p > 0.405), the PCA suggested that phytoplankton densities were inversely correlated with the biomass of most of the macrophyte species. Higher phytoplankton diversity and flagellate species were associated with greater plant biomass. Our study has management implications because (1) although not presenting significant seasonal variation, the macrophyte biomass was inversely correlated with phytoplankton densities, and (2) the presence of free-floating and emerged plants induced qualitative shifts in the phytoplankton, increasing the diversity of species. The removal of the macrophytes by management actions (e.g., mechanical removal) or natural forces (e.g., wind effect) might influence the phytoplankton community and the trophic state of subtropical reservoirs.