Juliana Silva França

Composition and dynamics of allochthonous organic matter inputs and benthic stock in a Brazilian stream

Riparian vegetation provides the nutrient and energy input that maintains the metabolism and biodiversity in tropical headwater streams. In the present study, it was hypothesised that ∼30% of riparian plant species contribute over 70% of coarse particulate organic matter and, because tropical plants are perennial and semi-deciduous, it was expected that leaf fall would occur year round. The aims of the present study were to evaluate the composition and structure of the plant riparian zone and the input and associated benthic stock of organic matter. The riparian vegetation was composed of 99 taxa. The most abundant plant species were Tapirira obtusa, Sclerolobium rugosum, Croton urucurana, Byrsonima sp. and Inga sp. The input and benthic stock showed a seasonal pattern, with higher values recorded at the end of the dry season and at the beginning of tropical storms. The biomass contributed monthly by the vegetation ranged from 28 ± 6gm −2 to 38 ± 11 gm −2 , and the mean monthly benthic standing stock was 138 ± 57 gm −2 . The results illustrate the importance of riparian vegetation as an energy source to tropical streams and how individual plant species contribute to organic matter inputs in these ecosystems.

Invertebrate colonisation during leaf processing of native, exotic and artificial detritus in a tropical stream

The relationship between leaf breakdown and colonisation by invertebrates in tropical aquatic ecosystems is poorly understood, especially in regard to the added problem of the potential effects of exotic species. To assess the colonisation by invertebrates during leaf breakdown in a third-order headwater stream in south-eastern Brazil, we conducted an experiment using the native species Miconia chartacea, the exotic species Eucalyptus grandis and artificial leaves. We hypothesised that the quality of the detritus and the leaf shape influence invertebrate colonisation because of the quality of the food and refuge offered by leaf detritus. Invertebrate density and richness were higher on leaves of E. grandis than on those of M. chartacea. Taxon richness did not differ among M. chartacea and the two sizes of artificial leaves offered, probably as a function of the chemical composition of E. grandis. Total invertebrate density was significantly higher in the organic detritus, suggesting that detritus provides food for the organisms. Our results indicate that the colonisation of invertebrates is probably affected by the chemical composition of detritus. Contrary to expectations, the community of invertebrates had no difficulty in colonising E. grandis, although it is an exotic species. In addition, the shredder activity did not influence leaf breakdown. These results may indicate that the invertebrates in this stream tend to behave as generalist feeders.

Use of the BEAST model for biomonitoring water quality in a neotropical basin.

The use of predictive models in Neotropical basins is relatively new, and applying these models in large basins is hindered by the lack of ecological, geographical, and social-environmental knowledge. Despite these difficulties, we used data from the das Velhas River basin to apply the BEAST (Benthic Assessment of SedimenT) methodology to evaluate and classify the level of environmental degradation. Our two main objectives were to modify and implement the BEAST methodology for use in biomonitoring programs of Brazilian basins, and to test the hypothesis that a gradient of environmental degradation determines a gradient in the structure and composition of benthic macroinvertebrate assemblages. We evaluated 37 sites: 8 in the main river, 15 in the main tributaries with different impact levels, and 14 in tributaries with minimally disturbed conditions (MDC). The BEAST model allowed us to classify 16 test sites: two as natural, four as altered, three as highly altered, and seven as degraded. Our results indicated degradation of the das Velhas River basin near its urban areas. The BEAST model indicated that the pollution gradient found among the sites generated a gradient of the macroinvertebrate assemblages, corroborating the hypothesis.

Diversidade de habitats físicos e sua relação com macroinvertebrados bentônicos em reservatórios urbanos em Minas Gerais

We assessed the effects of physical habitat structure on benthic macroinvertebrate communities in 3 reservoirs: Serra Azul (SA), Vargem das Flores (VF) and Ibirite (IB). We sampled physical and chemical habitat and benthic macroinvertebrates at 30 systematic sites in each reservoir. In SA, the dominant taxa out of 12 were Melanoides tuberculatus Muller, 1774 (15.2%) and Chaoboridae (63.8%). In VF, the dominant taxa, out of 11 were M. tuberculatus (34.2%) and Oligochaeta (33.6%). In IB, M. tuberculatus (91.2%) and Chaoboridae (6.27%) dominated and we collected only 7 taxa. In SA, benthos were significantly influenced by the deciduous shrub understory and bank angle. In IB and VF, the significant physical habitat variables were: land cover, human influence, and aquatic macrophytes. We conclude that human disturbances reduced terrestrial vegetation cover and riparian and littoral physical habitat structural complexity, leading to worse water quality. Those changes, in turn, reduced the taxonomic richness of the benthic macroinvertebrate communities.

Effects of flow reduction and spillways on the composition and structure of benthic macroinvertebrate communities in a Brazilian river reach

Dams are a major threat to aquatic biological diversity. By altering the natural flow of rivers, dams modify fluvial habitats, making them unsuitable for the growth and reproduction of many aquatic species. The aim of this study was to evaluate the effects of a reduced flow reach (RFR) on benthic macroinvertebrate communities. Benthic macroinvertebrates were collected at six sites downstream of the Amador Aguiar Power Plant I before (lotic phase) and after (semi-lentic phase) Araguari River mean flow was reduced from 346 to 7 m³.s⁻¹. Changes in macroinvertebrates richness, diversity and total biomass were not observed. Ablabesmyia, Tanytarsus (Chironomidae, Diptera), Leptoceridae and Polycentropodidae (Trichoptera) densities significantly increased the first year after flow reduction and the construction of spillways (t-test; p < 0.05). An analysis of similarity (ANOSIM) showed statistical differences in taxonomical composition despite considerable overlap in communities between the lotic and semi-lentic phases (R = 0.3; p < 0.01). In both phases, the macroinvertebrates were characterised by the dominance of groups tolerant to human disturbance (e.g., Chironomidae, Ceratopogonidae and Oligochaeta) and by the presence of the alien bivalve species Corbicula fluminea (Veneroidae), suggesting that the river was already degraded before the hydraulic modifications. Since the 1980s, the Araguari River has been continuously subjected to human pressures (e.g., cascade dams, urbanization and replacement of native vegetation by pasture and crops). These activities have led to impoverishment of biological communities and have consequently altered the ecosystem.

Benthic macroinvertebrates collection: a tool for the knowledgement of freshwater biodiversity

Zoological collections can be considered important registries of freshwater biodiversity for academical and research activities. The objective of this study was to organize a database of the diversity of benthic indicators of water quality collected in many freshwater ecosystems. The Benthic Macroinvertebrates Reference Collection of the Laboratory Ecology of Benthos, Institute of Biological Sciences, Federal University of Minas Gerais was created in 1997. This collection comprises 16,500 registers from different lotic and lentic ecosystems in Brazil and other countries. The taxa (with one or more organisms) are preserved in tubes, glasses, and wardrobes. In the tomb notebooks are registered: the taxonomical identification, origin, collection method, number of individuals, sample number and field observations. Besides the maintenance of the Reference Collection, a database is being constructed with the benthic biodiversity information. Up to this moment, the database has almost 71,000 registers preserved in 6,000 tubes and in 174 glasses. The incorporation of new organisms to the Collection is of c. 7,100.00 (+ 7,471.67) organisms per year. The aquatic insects are the main abundant and taxonomic diverse in the Collection. Diptera, Ephemeroptera, and Trichoptera were the most numerical important groups, with respectively 37.9%, 16.7%, and 14.5%. Among the Dipterans, Chironomidae comprises 59 genera. This Reference Collection represents an important tool for knowledge of benthic biodiversity in lotic and lentic ecosystems, allowing later taxonomical identification, and the development of population dynamics and community structure studies, due to the increase deposit of knew material. Moreover, it is of paramount importance to guarantee future taxonomical, biogeographical, phylogenetical and ecological studies, using this material. Key words: benthic macroinvertebrates, scientific collection, database.

Factors determining the structure and distribution of benthic invertebrate assemblages in a tropical basin

We used the das Velhas River basin in southeastern Brazil as a study unit to evaluate the role of various physical and chemical variables and the state of conservation in determining the structure and distribution of benthic macroinvertebrate communities. The habitats were characterized through the use of a rapid evaluation protocol, the examination of the granulometric composition of the sediments, and the precipitation in the sub-basins of the segments studied. The taxonomic structure was determined, Shannon-Wiener and Simpson diversity indexes, taxonomic richness, % EPT and % Chironomidae for the benthic assemblages. The results corroborated the importance of habitats in spatial structuring, the importance of the hydrological regime in temporal structuring, and the state of conservation as the main structuring agents of benthic macroinvertebrate assemblages.

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.