Percorrer por autor "Cravo, A."
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- Using biochemical and isotope geochemistry to understand the environmental and public health implications of lead pollution in the lower Guadiana River, Iberia: A freshwater bivalve studyPublication . Company, Rui; Serafim, Angela; Lopes, Belisandra; Cravo, A.; Shepherd, T. J.; Pearson, G.; Bebianno, Maria João; Cravo, AlexandraLead is a natural component of aquatic ecosystems with no known biological role and is highly toxic. Its toxicity stems from its ability to mimic biologically important metals and to produce membrane damage through lipid peroxidation (LPO). Most lead poisoning symptoms are thought to occur by interfering with an essential enzyme, delta-aminolevulinic acid dehydratase (ALAD), the activity of which is markedly inhibited by lead. The purpose of this work was to study the levels and effects of lead pollution (responses of ALAD and oxidative stress biomarker LPO) in the freshwater bivalve Corbicula fluminea along the lower Guadiana River (Portugal and Spain); a major river system impacted by historic mining pollution and more recent anthropogenic inputs. The results show that the enzymatic activity of ALAD is negatively correlated with the total Pb concentration of the whole tissue suggesting that ALAD has considerable potential as a biomarker of lead exposure in C. fluminea. To identify the sources of lead to which bivalves have been exposed, high precision (206)Pb/(204)Pb, (207)Pb/(204)Pb, (208)Pb/(204)/Pb ratios for C. fluminea confirm that historical mining activities in the Iberian Pyrite Belt are the dominant source of lead pollution in the lower Guadiana River. The isotope patterns however exhibit marked seasonal and geographic variation in response to rainfall and river water management. Locally, other anthropogenic sources of lead have been detected in C. fluminea close to population centres, thus adding to its versatility as a freshwater bio-indicator. Overall, the study highlights the value of natural ecosystems as monitors of water quality and their importance for public health assessment and surveillance.
- Variability of nutrients and chlorophyll a in Ancao Inlet during a spring tidal cycle in April 2009Publication . Alcantara, P.; Cravo, A.; Jacob, J.; Cravo, AlexandraSao Luis or Ancao Inlet is the most western of the six inlets of the Ria Formosa lagoon, in southern Portugal. This inlet contributes relatively little to the water volume exchange over a tidal cycle (similar to 10%). Temperature, salinity, pH, dissolved oxygen, and chlorophyll a and nutrient concentrations were measured hourly at the surface, at an intermediate level, and near the bottom over a complete spring tidal cycle, at a sampling point in the middle of the inlet. Current velocity was also measured hourly over the entire cross-section of the inlet using an acoustic Doppler current meter. From these parameters, the flow rate and the transport of nutrients and chlorophyll a were calculated and integrated over the complete tidal cycle providing the net transport. The results show that this is a well-mixed dynamic inlet where, during spring tide, the tidal signal is evident particularly for the nutrient and chlorophyll a concentrations. The nutrient concentrations were low (almost depleted), while the chlorophyll a concentrations were high (4-6 mg m(-3)). The estimated transports through Ancao Inlet revealed that there was a net import of chlorophyll a, nitrate, and phosphate to the Ria Formosa lagoon, while silicate was exported to the adjacent coastal area.