Sílvia Pedro

Mobility of metals in salt marsh sediments colonised by Spartina maritima (Tagus estuary, Portugal)

Chemical associations of Zn, Pb, Cu, Co and Cd were determined using a sequential extraction procedure in sediments colonised by S. maritima in three salt marshes within the Tagus estuary: Rosário, Corroios and Pancas. Concentrations of these metals were also analysed in above- and belowground parts of Spartina maritima, as well as in sediments colonised by the plant. The highest metal concentrations in sediments were found in the marshes near the industrial and urban areas, whereas metal concentrations in plants were not significantly different among sites. This was thought to be a consequence of differences observed in metal bioavailability: Metals in Pancas, the least polluted location, were largely associated to easily accessible fractions for plant uptake, probably as a result of low organic matter content and high sandy fraction in sediments. S. maritima was able to induce the concentration of metals between its roots in the three salt marshes. The results obtained in this study indicate that S. maritima could be useful to induce phytostabilisation of metals in sediments, although the effectiveness to modify chemical associations is highly dependent on existing sediment parameters, and thus different results could be obtained depending on site characteristics.

Sea lamprey ( Petromyzon marinus L.) spawning migration in the Vouga river basin (Portugal): poaching impact, preferential resting sites and spawning grounds

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were captured.

Tissue Localization and Distribution of As and Al in the Halophyte Tamarix gallica under Controlled Conditions

Information on localization of Al and As in Tamarix gallica is required in order to better understand the detoxification mechanisms that confer tolerance in this halophyte plant species. Plants were subjected to different Al and As concentrations with and without salt supplementation. High concentrations of As and Al have been found in Tamarix gallica leaves and roots without symptoms of toxicity to the plant, which may be related to the particular compartmentation. A sequential extraction was carried out on leaves and roots to determine and compare the metal compartmentation in the plant. In this study, subcellular localization of As and Al was determined for the first time in roots and leaves of T. gallica, and provided evidence of the detoxification mechanisms of high As and Al concentrations. These results suggest that the subcellular distribution of As and Al play important roles in avoidance of metal toxicity. The most part of Al (that has high toxicity to the plant when available forms are present) was immobilized in cell walls, potentially suppressing its transportation to other subcellular compartments more susceptible to Al toxicity. On the other hand, the greater sequestration of As in the vacuole reduces its toxicity to the remaining cell organelles in the roots, but cell wall confinement remains an important tolerant mechanism in the leaves.