The effect of river damming on vegetation: is it always unfavourable? A case study from the River Tiber (Italy)

River damming leads to strong hydromorphological alterations of the watercourse, consequently affecting river vegetation pattern. A multitemporal and spatial analysis of the dam effect on composition, structure and dynamic of the upstream vegetation was performed on Tiber River at Nazzano-dam (Rome). The main research questions were as follows: How does plant landscape vary over time and along the river? Where does the dam effect on vegetation end? How does naturalistic importance of the vegetation affected by damming change over time? Data collection was performed mapping the vegetation in aerial photos related to the period before (1944), during (1954) and after dam construction (1984, 2000). The plant landscape has significantly changed over time and along the river, particularly as a result of the dam construction (1953). The major vegetation changes have involved riparian forests and macrophytes. Dam effect on vegetation is evident up to 3 km, and gradually decreases along an attenuation zone for about another 3 km. Despite the fact that the damming has caused strong local hydromorphological modification of the river ecosystem transforming it into a sub-lacustrine habitat, it has also led to the formation of wetlands of considerable naturalistic importance. Indeed, in these man-made wetlands, optimal hydrological conditions have been created by favouring both the expansion of pre-existing riparian communities and the rooting of new aquatic communities, albeit typical of lacustrine ecosystems. Some of these plant communities have become an important food resource, refuge or nesting habitats for aquatic fauna, while others fall into category of Natura 2000 habitats. Therefore, river damming seems to have indirectly had a “favourable” effect for habitat conservation and local biodiversity.     

Atmospheric Volatile Organic Compound Monitoring. Ozone Induced Artefact Formation

Assessment of population exposure to VOC in ambient atmospheres is receiving heightened interest as the adverse health effects of chronic exposure to certain of these compounds are identified. Active (pumped) and passive samplers are the most commonly used devices for this type of monitoring. It has been shown, however, that these devices, along with all other preconcentration techniques, are susceptible to ozone interference. It is demonstrated that this interference occurs even at low ozone concentrations and that it may result in the under-estimation of population exposure. A convenient and effective ozone scrubbing method is identified and successfully applied and validated for both active and passive samplers for a range of VOC.     

Speciation of inorganic arsenic in coastal seawater from Ionian and Tyrrhenian Seas (Sicily, Italy) using derivative anodic stripping chronopotentiometry

The purpose of this paper was to use derivative anodic stripping chronopotentiometry (dASCP) as a sensitive and accurate technique, to determine the concentrations of dissolved As (III) and As (V) in coastal seawater samples from the Straits of Messina, the Ionian and the Tyrrhenian seas, and to investigate the relationship between the anthropogenic activities on the coastal areas and the concentration of dissolved inorganic arsenic in seawaters. The obtained data indicated that As (V) was the most abundant species, with concentration ranging from 26.7 to 307 nM, whereas As (III) levels were lower than 48 nM in all the samples. In particular, As (III) and As (V) levels significantly decreased from high to low anthropogenic activities zones (p < 0.00001, ANOVA), with the reference samples, from a wildlife reserve, showing the lowest values. Furthermore it was observed that human activities influenced inorganic arsenic speciation, since the zones that received high human input presented the highest As(V)/As (III) ratio.     

Application of photocatalysis as a post treatment method of a heterotrophic-autotrophic denitrification reactor effluent

The aim of this study is the application of photocatalysis as an effective post treatment scheme for the removal of the organic matter and bacteria released by an innovative biological denitrification process referred to as heterotrophic-autotrophic denitrification, which combines heterotrophic and autotrophic denitrification processes. Photocatalytic treatment was applied using TiO2 as a photocatalyst in the loading range of 0.25-2.00 g l(-1) for irradiation periods up to 60 min using a black light fluorescent lamp with an intensity of I(0)=1309 microW cm(-2). The photocatalytic inactivation data were modelled to pseudo first order kinetics as well as by the areal rates to evaluate the photocatalyst loading effect. Chlorination was used as a final disinfection step to attain an overall inactivation of total coliforms as well as to the formation of very low level of trihalomethanes.     

Degrees of vacuolation of the absorptive intestinal cells of five Sagitta (Chaetognatha) species: possible ecophysiological implications

The cell organization and ultrastructure of the intestine have been studied in five species of Sagitta, one epiplanktonic (S. bipunctata Quoy and Gaimard, 1827), four mesoplanktonic (S. megalophthalma Dallot and Ducret, 1969, S. decipiens Fowler, 1905, S. minima Grassi, 1881, S. zetesios Fowler, 1905). The intestinal epithelium is composed of two ciliated cell types. The first (S-cell) principally occurs in the anterior intestine and represents typical secretory cells. The second (A-cell) occurs in the median and posterior intestine and displays ultrastructural features involved in absorption and intracellular digestion, that is, coated pits, endocytotic vesicles, cytoplasmic tubules, and two distinct types of digestive vacuoles. Whereas S-cells exhibit few ultrastructural differences among the five species, the vacuolar volume of the A-cells located in the mid portion of the intestine is higher in the mesoplanktonic species. In S. zetesios and S. megalophthalma, each side of the median intestine comprises several hypervacuolated A-cells visible in transverse section; their degree of vacuolation is inversely proportional to their number. The increased volume of the intestinal vacuoles is most marked in S. decipiens and S. minima; in both these species, each lateral side of the median intestine displays a single ultravacuolated A-cell. The possible ecophysiological implications of intestinal vacuoles are discussed in relation to patterns of the vertical distribution of several Sagitta species. The vacuoles are presumed to regulate buoyancy, enabling the mesoplanktonic species to make vertical diel migrations. Received: 22 January 2000 / Accepted: 28 July 2000     

A Numerical Study of the Dynamics of the Riverine Thermal Bar in a Deep Lake

A numerical model based on a Finite Volume formulation of the Navier–Stokes equations is used to simulate a range of scenarios leading to a thermal bar formed by a river inflow to an idealised deep lake. The results presented here show that small riverine salinity increases have a profound effect on the dynamics of the thermal bar, suppressing horizontal propagation of the plume and raising the possibility of a thermal bar which is capable of sinking to great depths. This finding is particularly relevant to Lake Baikal in Siberia, where the vigorous deep-water renewal is still not fully understood. An analysis of the buoyancy forces governing the depth of penetration of the thermal bar plume shows that realistic salinity gradients are an important factor in determining the circulation of Baikal waters. Observations of the saline curtailment of the thermal bar's horizontal propagation also reveal a potential for reduced productivity in the ecosystem of any temperate river delta during the Spring renewal period.     

Arsenic biomonitoring using a hyperaccumulator fern (Pteris vittata)

Samples of Pteris vittata L. (brake fern or ladder brake) collected in Genova and in areas outside urban centres, have been analysed for arsenic content in order to assess if hyper accumulating plants are suitable for monitoring purposes. Hyper accumulation ability of the Ligurian fern populations was evaluated by analysing specimens grown with hydroponic media added with As(v). Arsenic concentrations in the range 2-310 microg g(-1) dry weight have been measured in samples collected in different sites along the Ligurian coast. Arsenic concentrations in fern fronds correlate with the estimated arsenic emission in the area, verifying the applicability of P. vittata as an arsenic biomonitor.