A complex watershed‐scale water quality simulation model, the Hydrological Simulation Program‐FORTRAN (HSPF) model, was calibrated for a 16 km2 catchment. The simulation step size was 0.33 hours with predicted and recorded hydrologic flows compared on an annual and monthly basis during a total calibration period of four years. Unguided numerical optimization when applied alone did not yield a model parameter set with acceptable predictive capability; instead, it was necessary to apply a critical process that included sensitivity analysis, numerical optimization, and testing of derived model parameter sets to evaluate their performance for periods other than those for which they were determined. Using this critical calibration process, the model was proven to have significant predictive capability. Numerical optimization is an aid for model calibration, but it must not be used blindly.
A simulation analysis of contaminated sediment transport involves model selection, data collection, model calibration and verification, and evaluation of uncertainty in the results. Sensitivity analyses provide information to address these issues at several stages of the investigation. A sensitivity analysis of simulated contaminated sediment transport is used to identify the most sensitive output variables and the parameters most responsible for the output variable sensitivity. The output variables included are streamflow and the flux of sediment and Cs137. The sensitivities of these variables are measured at the field and intermediate scales, for flood and normal flow conditions, using the HSPF computer model. A sensitivity index was used to summarize and compare the results of a large number of output variables and parameters. An extensive database was developed to calibrate the model and conduct the sensitivity analysis on a 6.2 mi2 catchment in eastern Tennessee. The fluxes of sediment and Cs137 were more sensitive than streamflow to changes in parameters for both flood and normal flow conditions. The relative significance of specific parameters on output variable sensitivity varied according to the type of flow condition and the location in the catchment. An implications section illustrates how sensitivity analysis results can help with model selection, planning data collection, calibration, and uncertainty analysis.
Recebido em 14/5/08; aceito em 13/4/09; publicado na web em 30/9/09 EVALUATION OF SEDIMENT QUALITY -CASE STUDY: SUB-WATERSHED OF ESPÍRITO SANTO STREAM, AFFLUENT OF THE SÃO FRANCISCO RIVER. This study evaluated the environmental impact resulting from surface water and sediment contamination by metals in a watershed affected by a tailing basin that controls effluents coming from a zinc-ore beneficiation plant. The studies combined assessments of sediment chemistry (exceedances of sediment quality guidelines), benthic assemblage structure and acute and chronic ecotoxicity. The results showed that the levels of metal contamination in sediments are not yet enough to cause deleterious effects to the biota. However, the ecotoxicity tests indicated the occurrence of chronic effects, demonstrating that other factors, as the use of fertilizers, could also be a source of contamination.Keywords: sediments; acid volatile sulfite; benthos. INTRODUÇÃOO crescimento da população mundial estimula o aumento das atividades industriais, comerciais e agropecuárias. O desenvolvimento dessas atividades, de forma não sustentável, contribui para a contaminação dos recursos hídricos superficiais e subterrâneos em decorrência do lançamento de rejeitos contendo metais, matérias orgânicas, fertilizantes, pesticidas, óleos, percolados tóxicos de lixões, entre outros. Consequentemente, além da escassez, a sociedade mundial está se deparando com a queda da qualidade das águas em taxas muito acentuadas. Para combater esta ameaça é necessário avaliar a magnitude e a natureza dos problemas envolvidos e, portanto, estudos que contribuam para um melhor entendimento da relação causa-efeito, entre os processos produtivos e seu impacto ambiental em ecossistemas aquáticos são cada vez mais importantes e indispensáveis. Como resultados destes processos, os estudos de avaliação da qualidade da água têm passado por mudanças substanciais que incluem a avaliação da qualidade dos sedimentos, um compartimento que era, até bem pouco tempo, apenas considerado como um acumulador de nutrientes e de uma variedade de contaminantes.2 Pesquisas relacionadas à troca de espécies químicas dissolvidas entre o sedimento e a coluna d'água têm demonstrado que esse compartimento deve ser considerado como um ambiente de trocas e/ou interações dessas espécies com a coluna d'água e a biota residente. Uma variedade de fatores físicos, químicos e biológicos controla a mobilidade dos contaminantes presentes nos sedimentos, tais como ressuspensão pelo revolvimento, sorção, alterações de pH e potencial redox, entre outros. 4 Dependendo da estabilidade físico-química do ambiente esses contaminantes podem permanecer ligados por longo tempo aos suportes sedimentares, como os metais em ambientes anó-xicos ou, então, sofrer degradação como a maior parte dos compostos orgânicos (hidrocarbonetos e organoclorados). Uma vez depositados nos sedimentos, os contaminantes podem sofrer modificações quí-micas e biológicas que os disponibilizam à biota (micro-organismos, flora e fauna de um ecossist...
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