The aquatic systems responsible for water supply in the Brazilian Federal District (FD) have been threatened by anthropogenic pressures, especially considering the expressive demographic increase in the region during the last decades. The purposes of this research were: (a) to assess the water quality in streams located in the FD by monitoring physical-chemical variables; (b) to define baselines for these variables among different ecological status categories. The 14 investigated streams were sampled between 2006 and 2009, in the dry (August-September, 2006, 2008, 2009) and rainy (March-April, 2008, 2009) seasons. All sampling sites were classified in four categories ("very impacted", "impacted", "in transition" and "natural") using an adaptation of a rapid habitat assessment protocol. Differences in water quality among sites were generally well predicted in the four ecological status categories defined by the protocol, which showed a gradient in nutrient concentrations from reference sites classified as "natural" (medians: electrical conductivity = 7.3 μS cm(-1); nitrate = 0.040 mg L(-1); ammonium = 0.039 mg L(-1); soluble reactive phosphorus (SRP) = <0.001 mg L(-1); total phosphorus (TP) = 0.006 mg L(-1); ) to those classified as "very impacted" (medians: electrical conductivity = 87.7 μS cm(-1); nitrate = 0.247 mg L(-1); ammonium = 0.219 mg L(-1); SRP = 0.010 mg L(-1); TP = 0.035 mg L(-1)). Point sources inputs were the main factor for water quality deterioration. The nutrient baselines reported were relatively low when compared to data collected from reference areas in Brazil (e.g., São Paulo State) or temperate regions, especially for TP.
Purpose While environmental risks associated with petroleum extraction such as oil spills or leaks are relatively well known, little attention has been given to the impacts of silt. The increase in petroleum exploitation in Amazonia has resulted in sediment input to aquatic systems, with impacts on their biodiversity. Here we use a combination of field measurements and statistical analyses to evaluate the impacts of anthropogenic silt derived from the construction of roads, borrow pits, and wells during the terrestrial development of gas and oil, on macroinvertebrate communities in streams of the Urucu Petroleum Province in the Central Brazilian Amazon. Material and methods Ten impacted and nine nonimpacted streams were sampled in January, April, and November of 2007. Macroinvertebrates were sampled along a 100-m continuous reach in each stream at 10-m intervals using a dip net. Abiotic variables including, a siltation index (SI), suspended inorganic sediment (SIS), sediment color index (SCI), suspend organic sediment (SOS), pH, electrical conductivity, dissolved oxygen, temperature, water velocity, channel width, and depth, were measured at three equidistant points in each stream (∼30-m intervals). Results and discussion SI did not differ between impacted and undisturbed streams. SIS was higher and SCI lower (more reddish) in impacted than in non-impacted streams. SCI had a positive and SIS a negative effect on both macroinvertebrate richness and density. SIS and SCI also influenced macrophyte taxonomic composition. In impacted streams, taxonomic richness and density were 1.5 times lower than in non-impacted streams. No taxon was significantly associated with impacted streams. SIS was positively correlated with SOS and electrical conductivity while SCI was negatively correlated with SOS, electrical conductivity, and pH. The lack of difference in SI between impacted and nonimpacted streams suggests that anthropogenic sediment does not accumulate on stream beds. The reddish color of SIS in impacted streams reflects terrestrial erosion and indicates the rapid flow of suspended sediments through these reaches, impacting macroinvertebrate richness, density, and species composition. Conclusions Anthropogenic suspended silt has had a significant negative impact on aquatic macroinvertebrate diversity and density in streams in the Urucu Petroleum Province. Soil conservation measures are needed to reduce silt inputs and restore these streams to their natural condition. Additional studies are also needed to investigate the dynamics of sediments in the impacted streams.
This study assessed the results of anthropogenic sediment input on macroinvertebrate trophic structure in streams located in an area of oil and natural gas exploitation in Brazil's Amazon forest. The results indicate that macroinvertebrate communities both in streams impacted by anthropogenic sediments and in non-impacted streams are composed mainly of taxa in the following functional feeding groups: predators, gathering-collectors, scrapers, shredders and filtering-collectors.The highest densities were observed for collector-gatherers, followed by scrapers, predators, shredders and filtering-collectors. However, both the richness and the density of all groups were reduced in impacted streams. The reductions were significantly related to suspended inorganic sediment load and to the colour of suspended sediments. The relative proportion of shredders in streams impacted by anthropogenic sediments was significantly reduced as compared with the proportion observed in non-impacted streams. This resulted from lower availability of coarse particulate organic matter in these streams owing to burial of leaves and other plant material. These results indicate changes in the functioning and productivity of streams owing to anthropogenic siltation. This is because the benthic macroinvertebrate communities, sampled during this study, were dependent on the degradation of leaves, which are the primary energy source sustaining the benthic foodweb.
The zooplanktonic community of Lake Paranoá has been studied for more than thirty years. Until 1998, when it was considered eutrophic, only three cladoceran species were known from the reservoir. Since 1999, when Lake Paranoá underwent intentional flushing, definite changes in species diversity and composition were identified. At the same time, exploratory studies on littoral cladoceran species were being done. The present study aims to provide additional information on the cladoceran species composition of Lake Paranoá. Seven new species records are presented, four of them also representing the first record from the Federal District (Brasília). The population previously considered as belonging to Bosmina longirostris was reconsidered and re-identified as Bosmina freyi. Figures and comments on species taxonomy and distribution are also provided.
Short-term fluctuations and structure of phytoplankton were examined for two months in the dry season (August-September/1997) in a eutrophic reservoir of central Brazil. Algicide treatment for the control of Microcystis aeruginosa bloom influenced the short-term variation pattern of the phytoplankton community. Algicide treatment was effective in controlling M. aeruginosa bloom, but it also influenced the Cylindrospermopsis raciborskii population. These species retained low densities, showing small colonies and trichomes, respectively. Drops in Cyanobacteria populations following algicide treatment were succeeded by progressive increase in Chlorophyta. The shifts in environmental conditions may have allowed the development of this group. In this study correspondence analysis of abundance data for phytoplankton assemblage in lake Paranoá revealed that available light, rather than chlorophyll-a, total suspended material, and water temperature, accounted for most of the short-term fluctuation in phytoplankton structure during algicide application. Canonical correspondance analysis (CCA) showed the primary importance of water transparency changes in abundance of taxa in the community. Algicide treatment for the control of nuisance blooms is discussed as a contribution to improved efficiency in reservoir management.Key words: Cyanobacteria, Chlorophyta, reservoir, Brazil. RESUMO Efeitos da aplicação de algicida (sulfato de cobre) sobre flutuações de curta duração do fitoplâncton no lago Paranoá, Brasil centralFlutuações de curta duração e a estrutura do fitoplâncton foram analisadas ao longo de dois meses na estação seca (agosto-setembro de 1997) em reservatório eutrófico do Brasil central. A aplicação de algicida para o controle de florescimentos de Microcystis aeruginosa exerceu influência sobre a variação temporal da comunidade fitoplanctônica, sendo efetiva também no controle do florescimento de M. aeruginosa e sobre a população de Cylindrospermopsis raciborskii. Ambas permaneceram em baixas densidades numéricas, com pequenas colônias e tricomas, respectivamente. Quedas bruscas de populações de Cyanobacteria após o tratamento de algicida foram seguidas por progressivo aumento de Chlorophyta. Mudanças de condições ambientais podem ter permitido o desenvolvimento deste último grupo. Análise de correspondência de dados de abundância do fitoplâncton no lago Paranoá revelou que a variável luz disponível se relacionou mais à flutuação de curta duração em estrutura do fitoplâncton do que a clorofila-a, o material suspenso total e a temperatura da água. A ACC constatou que as mudanças de transparência de água foram de primordial importância na abundância dos taxa fitoplanctônicos. O tratamento de algicida no controle de florescimentos algais é discutido aqui em relação ao gerenciamento eficiente de reservatórios.Palavras-chave: Cyanobacteria, Chlorophyta, reservatório, Brasil.
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