José Etham de Lucena Barbosa

Aquatic systems in semi-arid Brazil: limnology and management

Aquatic systems in semi-arid Brazil include natural shallow lakes, artificial reservoirs and intermittent streams and rivers. These systems are distinctive features in the semi-arid landscape and comprise a range of associated systems functioning as an ever-changing mosaic of dry/wet patches. Lakes and reservoirs in semi-arid Brazil are subject to important periods of water shortages, whereas rivers and streams are characterized as highly variable and driven by the extremes of water flow and its absence. Within this view a catchment-scale approach must be used to create a holistic model to conceptualize and comprehend these aquatic systems, since the aquatic environment types in the semi-arid region of Brazil incorporate broader aspects within the catchment scale such as geomorphology, vegetation, climate and land use. This paper summarizes some of the information on the aquatic systems of the Brazilian semi-arid region and shows the importance of limnological studies in this region. It also attempts to establish perspectives for future research considering the catchment as a scale for surveying biological processes and limnological characteristics of the various aquatic systems. It is presented information on their overall structure and functioning, as well as characteristics of some biological communities, such as phytoplankton, periphyton, aquatic macrophytes, benthic invertebrates and fish. The importance of the understanding of eutrophication in reservoirs and the role of the dry phase in streams is emphasized, and information on possible actions of planning and management to improve water quality of reservoirs are presented.

Application of a statistical model for the assessment of environmental quality in neotropical semi-arid reservoirs.

The aim of this study was to develop a statistical model to assess the environmental quality of reservoirs located in semi-arid region using metrics of anthropogenic disturbance, water quality variables, and benthic macroinvertebrate communities as indicators. The proposed model was applied to 60 sites located in three reservoirs in the Paraíba river basin, Brazilian semi-arid region. Collections were made in December 2011. In each site, we collected one sample of benthic macroinvertebrates and one water sample for the determination of physical and chemical parameters. Characterization of the landscape was made through application of 10 physical habitat protocols on each site for the collected information on disturbance and subsequent calculation of disturbance metrics. The results showed the formation of two groups: group 1, consisting of 16 minimally altered sites, and group 2, with 44 severely altered sites. The proposed statistical model was sensitive enough to detect changes. In the minimally altered group, the Chironomids Aedokritus and Fissimentum were dominant, indicating a higher environmental quality, while Coelotanypus and Chironomus were abundant in severely altered sites with lower environmental quality. The conservation and management of reservoirs in semi-arid regions should be intensified in view of the need to maintain the environmental quality of these ecosystems.

Influence of ecological filters on phytoplankton communities in semi-arid solar saltern environments

ObjectiveThis study analyzed the influence of ecological filters (abiotic variables) on the phytoplankton community in hypersaline ecosystems.MethodsThe abiotic variables measured herein were: pH, water temperature, salinity, ammonium ion, total nitrogen, nitrite, nitrate, total phosphorus, and soluble reactive phosphorus. The phytoplankton community was studied for density, richness and Shannon-Wiener diversity index. Data were analyzed using analysis of variance, linear regression and Canonical correspondence analysis (CCA).ResultsIn total, 110 taxa were identified in 3 solar salterns, distributed into 9 taxonomic classes, with the predominance of Cyanobacteria (41.8%) and Bacillariophyceae (22.7%). The species Pseudanabaena galeata was the only species sampled in all saline environments. Salinity significantly influenced the richness in the three salterns, Augusto Severo (F(1,22) = 23.2, p <0.001), Francisco Menescal (F(1,22) = 50.02, p <0.001) and Santa Clara (F(1,22) = 66.33, p <0.001). The first two CCA axes explained 41.6% of total data variability, with a negative relationship with soluble reactive phosphorus for axis 2.ConclusionThe study showed the influence of the dynamics of salterns ecosystems on the phytoplankton community structure. This is associated with filters developed by the environment, where the increasing salinity, temperature and precipitation of salts influence the composition of these organisms in the ecosystem.

Diversity partitioning of a phytoplankton community in semiarid salterns

Salterns consist of a series of interconnected evaporators that form sectors in the salterns. Their operation generates an increasing saline gradient, which influences species diversity. The present study was conducted in three salterns, with the goal of evaluating the diversity partitioning of phytoplankton along the saline gradient. We identified 65 taxa; the species richness was similar among the salterns, with higher values occurring in initial sectors and a downward trend with increasing salinity. In the partitioning analysis, the α diversity contributed 33.8% of the total diversity. The diversity variance showed a strong reduction from the α to β1 (33.8–6.3%). At higher scales, the highest species richness was found between salt marshes; however, there was lower diversity and a decrease in similarity from the lower to the higher scale. Therefore, we demonstrated that the greater variance in phytoplankton richness was at higher scales.

Biotic or abiotic factors: which has greater influence in determining the structure of rotifers in semi-arid reservoirs?

ObjectiveThe objective of this study is to evaluate whether the distribution of structural attributes of rotifers in reservoirs in the semiarid region is more strongly influenced by abiotic or biotic environmental factors (density of cyanobacteria).MethodSampling occurred in two reservoirs in the Paraiba Basin, northeastern Brazil (Pocoes and Camalau) during April and June 2012. Eight sampling points were distributed at two stations in each reservoir: the region near the entrance of the main tributary and region of the dam and collections were made in the limnetic and littoral zone in every season. To assess the abiotic influence and density of cyanobacteria in the distribution of the structural attributes of rotifers, environmental variables bivariate correlation was conducted in series.ResultsIn Pocoes reservoir, the distribution of rotifer biomass was negatively related to the density of cyanobacteria; among the environmental variables, chlorophyll-a and total nitrogen were negatively related to all of the tested structural attributes, while the concentrations of total phosphorus were strongly related to the abundance of rotifers. In the Camalau reservoir, the biomass was a structural attribute with a stronger correlation to the density of cyanobacteria; between the environmental variables and Egeria densa, nitrate was negatively related to all of the attributes tested, while transparency was moderately related to the abundance, biomass and richness as well as Chara sp. with abundance.ConclusionsAssemblages of rotifers are more clearly related to environmental conditions, especially those indicative of trophic conditions, despite the density of cyanobacteria having been a factor that was positively related to the structural characteristics of rotifers and thus indicative of such structural assemblies. This can be used for analysis of local environmental condition factors.

Spatial modeling of limnological parameters in a solar saltwork of northeastern Brazil

AimIn this research, we aimed to model limnological parameters in the Salina Unidos (Macau-Brazil) using GIS technology. We hypothesized that in solar saltworks, the geochemical characteristics of the brines (i.e. the strong solution of salts) vary considerably through the salt ponds circuit, in which drastic changes can damage the entire salt production.MethodsGeochemical parameters were monitored in seven sampling points distributed along the salt ponds circuit, during a complete cycle of salt production, i.e., from January to December 2007. The open source software Spring 5.1.6 was used to build, store, analyze and model the spatial distribution of the parameters.ResultsWe identified a spatial gradient of the salinity and temperature, with values increasing from evaporation ponds to concentration ponds, showing a relationship with the salt production. The parameters, depth, dissolved oxygen concentrations and total dissolved reactive phosphorus showed a decrease from the evaporation ponds towards the concentration ponds. Among the dissolved inorganic nitrogen forms analyzed (NH3-, NO2- and NO3-), nitrate was the predominant, namely in the concentration ponds, where it reached the highest concentrations. The concentration of chlorophyll awas higher in the initial and intermediate evaporation ponds, showing a distinct dynamics of in relation to other environmental variables.ConclusionsThe increased concentration of the analyzed limnological parameters, from the evaporation ponds towards the concentration ponds, evidenced a heterogeneous distribution varying significantly with season. The geochemical spatialization of brine, as illustrated by GIS approach, is very important for the conservation of these environments because this spatial heterogeneity can provide a high diversity of habitat types. This spatial analysis proved to be a practical tool for an adequate management of solar saltworks considering the environmental (ecosystem) and the socio-economic aspects.

Top-down and bottom-up control of epilithic periphyton in a tropical stream

Tropical forests are characterized by high tree biomass that forms a dense canopy, thereby reducing the amount of light that reaches forest streams. Forest streams are likely to receive large amounts of organic matter in the form of leaf litter and also have low primary production relative to more open forested systems. Forest clearing can, therefore, affect the in-stream carbon cycle by increasing carbon immobilization and decreasing mineralization. We addressed the question of whether heavily shaded streams are bottom-up limited by light and nutrients or top-down limited by grazers. To answer these questions, we experimentally manipulated nutrients and grazers in enclosures established in either a shaded or a partially open stretch of an Atlantic Forest stream in Brazil. Algal biomass in this stream was low (51.5 to 367.2 mg Chl a /m2). Prior tree removal resulted in a 58% increase in light in the semi-open stream area, and enclosures in this area had a 2.7× increase in algal biomass and a 4× increase in primary production (from 10–40 mg C m−2 d−1) relative to enclosures in shaded areas. Nutrient (P) addition had no effect on algal standing crop. Grazing by the caddisfly Helicopsyche caused a ∼50% reduction in algal biomass. The addition of the most abundant predator, the stonefly Anacroneuria, to the enclosures did not reduce feeding by Helicopsyche. Substrates in the shaded and semi-open stretches differed in the dominance of some algal taxa, and grazing appeared to favor the cyanobacteria Dolichospermum sp. over diatoms. We conclude that algae in forested, low-order streams in the Atlantic Forest are limited by both top-down (herbivory) and bottom-up (light) factors. These findings suggest that tree removal in riparian areas can cause small changes to light availability in streams, but that even small changes can have profound effects on primary producers and, therefore, energy supply for stream consumers.