Distribution of selected heavy metals in sediments of the Agueda river (Central Portugal)

The state of river water deterioration in the Agueda hydrographic basin, mostly in the western part, partly reflects the high rate of housing and industrial development in this area in recent years. The streams have acted as a sink for organic and inorganic loads from several origins: domestic and industrial sewage and agricultural waste. The contents of the heavy metals Cr, Cd, Ni, Cu, Pb, and Zn were studied by sequential chemical extraction of the principal geochemical phases of streambed sediments, in the <63 mum fraction, in order to assess their potential availability to the environment, investigating, the metal concentrations, assemblages, and trends. The granulometric and mineralogical characteristics of this sediment fraction were also studied. This study revealed clear pollution by Cr, Cd, Ni, Cu, Zn, and Pb, as a result from both natural and anthropogenic origins. The chemical transport of metals appears to be essentially by the following geochemical phases, in decreasing order of significance: (exchangeable + carbonates) much greater than (organics) much greater than (Mn and Fe oxides and hydroxides). The (exchangeable + carbonate) phase plays an important part in the fixation of Cu, Ni, Zn, and Cd. The organic phase is important in the fixation of Cr, Pb, and also Cu and Ni. Analyzing the metal contents in the residual fraction, we conclude that Zn and Cd are the most mobile, and Cr and Pb are less mobile than Cu and Ni. The proximity of the pollutant sources and the timing of the influx of contaminated material control the distribution of the contaminant-related sediments locally and on the network scale.

Transport of the smoke plume from Chiado’s fire in Lisbon (Portugal) sensed by atmospheric electric field measurements

The Chiado’s fire that affected the city centre of Lisbon (Portugal) occurred on 25th August 1988 and had a significant human and environmental impact. This fire was considered the most significant hazard to have occurred in Lisbon city centre after the major earthquake of 1755. A clear signature of this fire is found in the atmospheric electric field data recorded at Portela meteorological station about 8 km NE from the site where the fire started at Chiado. Measurements were made using a Benndorf electrograph with a probe at 1 m height. The atmospheric electric field reached 510 V/m when the wind direction was coming from SW to NE, favourable to the transport of the smoke plume from Chiado to Portela. Such observations agree with predictions using Hysplit air mass trajectory modelling and have been used to estimate the smoke concentration to be ~0.4 mg/m3. It is demonstrated that atmospheric electric field measurements were therefore extremely sensitive to Chiado’s fire. This result is of particular current interest in using networks of atmospheric electric field sensors to complement existing optical and meteorological observations for fire monitoring.