Diet of Cnesterodon decemmaculatus (Poeciliidae) and Jenynsia multidentata (Anablepidae) in a hypertrophic shallow lake of Uruguay

Diet of Cnesterodon decemmaculatus (Jenyns, 1842) and Jenynsia multidentata (Jenyns, 1842) were analysed in Lake Rodó, an urban hypertrophic lake from Montevideo, Uruguay. Both species displayed omnivory. The most consumed items for C. decemmaculatus were zooplankton, periphyton, phytoplankton and detritus; the diet of J. multidentata included zooplankton, insects, crustaceans and juvenile fish. Our results suggest that both species could be acting as facultative planktivores. The fish community of this lake is characterised by the dominance of C. decemmaculatus and J. multidentata. Under this condition, predation on large-bodied zooplankton could indirectly be contributing to maintain a high phytoplankton abundance and a low water transparency.

Occurrence of agrochemicals in surface waters of shallow soils and steep slopes cropped to tobacco

Tobacco cultivation in shallow soils and steep landscape under intense use of agrochemicals contributes to environment degradation. In this study, we assessed the concentration of agrochemicals in draw wells used for human consumption and a creek in a small catchment predominantly cropped to tobacco. Chlorpyrifos, flumetralin, and iprodione were determined by gas chromatography with electron capture detection, while imidalcloprid, atrazine, simazine, and clomazone were quantified by high-performance liquid chromatography with UV detection. Considering all sampling sites, all agrochemicals were detected at least once, except for flumetralin. The occurrence of agrochemicals in tobacco crops is a consequence of their fast transfer to surface water.

Turbulent shallow-water model for orographic subgrid-scale perturbations

A parallel pseudo-spectral method for the simulation in distributed memory computers of the shallow-water equations in primitive form was developed and used on the study of turbulent shallow-waters LES models for orographic subgrid-scale perturbations. The main characteristics of the code are: momentum equations integrated in time using an accurate pseudo-spectral technique; Eulerian treatment of advective terms; and parallelization of the code based on a domain decomposition technique. The parallel pseudo-spectral code is efficient on various architectures. It gives high performance onvector computers and good speedup on distributed memory systems. The code is being used for the study of the interaction mechanisms in shallow-water ows with regular as well as random orography with a prescribed spectrum of elevations. Simulations show the evolution of small scale vortical motions from the interaction of the large scale flow and the small-scale orographic perturbations. These interactions transfer energy from the large-scale motions to the small (usually unresolved) scales. The possibility of including the parametrization of this effects in turbulent LES subgrid-stress models for the shallow-water equations is addressed.

Numerical study of Petrov-Galerkin formulations for the shallow water wave equations

The behavior of Petrov-Galerkin formulations for shallow water wave equations is evaluated numerically considering typical one-dimensional propagation problems. The formulations considered here use stabilizing operators to improve classical Galerkin approaches. Their advantages and disadvantages are pointed out according to the intrinsic time scale (free parameter) which has a particular importance in this kind of problem. The influence of the Courant number and the performance of the formulation in dealing with spurious oscillations are adressed.

Effects of nutrient impoverishment on phytoplankton biomass: a mesocosms experimental approach in a shallow eutrophic reservoir (Garças Pond), São Paulo, southeast Brazil

Nutrient impoverishment in mesocosms was carried out in a shallow eutrophic reservoir aiming to evaluate the nutrient removal technique as a method for eutrophication reduction. Garças Pond is located in the Parque Estadual das Fontes do Ipiranga Biological Reserve situated in the southeast region of the municipality of São Paulo. Three different treatments were designed, each consisting of two enclosures containing 360 liters of water each. Mesocosms were made of polyethylene bags and PVC pipes, and were attached to the lake bottom. Treatment dilutions followed Carlson's trophic state index modified by Toledo and collaborators, constituting the oligotrophic, mesotrophic, and eutrophic treatments. Ten abiotic and 9 biological samplings were carried out simultaneously. Trophic states previously calculated for the treatments were kept unaltered during the entire experiment period, except for the mesotrophic mesocosms in which TP reached oligotrophic concentrations on the 31st day of the experiment. In all three treatments a reduction of DO was observed during the study period. At the same time, NH4+ and free CO2 rose, indicating decomposition within the enclosures. Nutrient impoverishment caused P limitation in all three treatments during most of the experiment period. Reduction of algal density, chlorophyll a, and phaeophytin was observed in all treatments. Competition for nutrients led to changes in phytoplankton composition. Once isolated and diluted, the mesocosms' trophic state did not change. This led to the conclusion that isolation of the allochthonous sources of nutrients is the first step for the recovery of the Garças Pond.

Pigmented Euglenophytes in a natural and shallow lake in the semiarid region of Paraíba State, Brazil

A floristic survey of the class Euglenophyceae in Panati Lake (7º11'14" S and 36º49'52" W) is presented. The samples were collected between November 2005 and April 2007 along the margins of the lake, and a total of 29 taxa were collected, described, and illustrated, comprising 11 specifics and 18 infraspecifics, with five typical and 13 non-typical varieties. The genus Trachelomonas showed the greatest richness (13 taxa), followed by the genus Lepocinclis (seven taxa). All of the 29 taxa cataloged had been previously reported for Brazil, most with wide geographical distributions, but all were new records for Paraíba State, and 25 new for northeastern Brazil - reflecting the need for more taxonomic studies of the Euglenophyceae in these locations.