Browsing by Author "Machado, W."
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- Influence of biological activity on 65Zn and 109Cd removal from tidal water by chronically-polluted mangrove sedimentsPublication . Sondermann, Melissa N.; Suzuki, K. N.; Machado, E. C.; Machado, W.; Bellido, L. F.; Lopes, R. T.; Bellido, A. V. B.The biological activity influence on the mangrove sediment capacity to remove 65Zn and 109Cd from tidal water was evaluated in a site chronically polluted. Benthic Activity Indexes (BAI), corresponding to relative estimates of biological impact on radiotracer accumulation, were higher for 109Cd (~ 38%) than for 65Zn (~ 10%) in the top centimetre of sediment. However, BAI exceeded 96% for deeper sediment layers. This apparent decrease in radiotracer diffusion into deep sediments through biological activity inhibition is stronger than reported for much less polluted mangrove nearby, suggesting that benthic organisms tolerant of chronic metal pollution may affect metal sorption mechanisms.
- Removal of Zn and Cd from Overlying Water by Mangrove Sediments: Testing the Effects of Sediment Resuspension/Redeposition EventsPublication . Suzuki, K. N.; Castro, R. J. M.; Sondermann, Melissa N.; Machado, E. C.; Bellido, A. B.; Lopes, R. T.; Machado, W.Coastal sediment redeposition after resuspension events may change the sediment capacity to sequester pollutants after the formation of new sediment-water interfaces. To test this hypothesis, radiotracer experiments were performed to evaluate zinc (65Zn) and cadmium (109Cd) removal kinetics by redeposited mangrove sediments. After 24-h experiments, average inventories within redeposited sediments were close to those from control sediments (~ 20% lower in redeposited sediments), while average decreases of 41% (109Cd) and 27% (65Zn) in the half-removal times (t1/2) from overlying water were promoted by redeposited sediments in comparison with control sediments. High variability in metal removal rates, however, implied in no statistically significant differences between t1/2 values, suggesting a low influence of sediment redeposition on the metal removal capacity of mangrove sediments. More limited depth diffusion of metals was observed within redeposited sediments, always within the uppermost centimeter. Possible benefits to water quality by a slightly faster metal diffusion into redeposited sediments may be less effective due to this trend since the metal retention very close to the sediment top can facilitate new remobilization to the overlying water.