RESUMO
The present study aimed to propose a water quality index (WQI) for the Federal District, Brazil, as a management tool for water resources used in irrigation. Irrigated agriculture is a sector that has been growing in the region, with a consequent demand for quality water. One strategy for assessing water quality in rural areas is to adopt monitoring programs, which generate a large amount of data that often needs to be synthesized. The use of indexes is a way of organizing data in a synthetic and easy to understand format. Although initially formulated to assess the quality of drinking water, it is believed that a similar logic can easily be applied to assess the quality of irrigation water. Studies that evaluate the quality of water for irrigation are very common in arid or semi-arid regions, due to the problems of saline water in the soil and crops. On the other hand, the microbiological approach to water is poorly investigated, since contamination of crops can pose a risk to food security. In this work, three water bodies were selected in rural areas due to their preponderant use: irrigation. The monitoring occurred between May 2012 and April 2013 in 9 sampling points. For each sample collected, 22 physical, chemical, and biological parameters were established. Principal component analysis (PCA) was used in the evaluation and selection of water quality variables to compose the WQI. From PCA, it was possible to reduce the number of parameters from 16 to 6 main ones that reflect the water resources characteristics in the region, which were pH, electrical conductivity, total hardness, sodium absorption ratio, nitrate, and Escherichia coli. Of the five classes proposed for WQI, two points were classified as "very good." The other sample points were classified as "good" and "average" for the irrigation practice. The adapted WQI proved to be a good tool in the management of the water quality of the three rivers, and it can be easily used to assess the quality of water for irrigation in the region.
Assuntos
Poluentes Químicos da Água/análise , Qualidade da Água , Irrigação Agrícola , Brasil , Monitoramento Ambiental , Abastecimento de ÁguaRESUMO
The intense use of water for both public supply and agricultural production causes societal conflicts and environmental problems in the Brazilian Federal District. A serious consequence of this is nonpoint source pollution which leads to increasing water treatment costs. Hence, this study investigates in how far agricultural Best Management Practices (BMPs) might contribute to sustainable water resources management and soil protection in the region. The Soil and Water Assessment Tool (SWAT) was used to study the impact of those practices on streamflow and sediment load in the intensively cropped catchment of the Pipiripau River. The model was calibrated and validated against measured streamflow and turbidity-derived sediment loads. By means of scenario simulations, it was found that structural BMPs such as parallel terraces and small sediment basins ('Barraginhas') can lead to sediment load reductions of up to 40%. The implementation of these measures did not adversely affect the water yield. In contrast, multi-diverse crop rotations including irrigated dry season crops were found to be disadvantageous in terms of water availability by significantly reducing streamflow during low flow periods. The study considers rainfall uncertainty by using a precipitation data ensemble, but nevertheless highlights the importance of well established monitoring systems due to related shortcomings in model calibration. Despite the existing uncertainties, the model results are useful for water resource managers to develop water and soil protection strategies for the Pipiripau River Basin and for watersheds with similar characteristics.