Heavy metals in Hediste diversicolor (polychaeta: nereididae) and salt marsh sediments from the lagoon of Venice (Italy)

The nereid polychaete Hediste diversicolor was frequently used as biomonitor of heavy metals contamination in estuaries. In the present work, the bioaccumulation of five heavy metals (Cd, Cr, Cu, Mn, Pb) in tissues of H. diversicolor collected from six salt marshes in the lagoon of Venice is studied by analysing the relationships between concentrations of the operationally-defined reactive fraction of trace metals in sediments and total concentrations in tissues. The characterisation of sediment samples shows a clear distinction between sites near and far from the Industrial Zone; no analogous pattern is observed for tissue concentrations suggesting that metal bioaccumulation is controlled by complex interactions between metal bioavailability and physiological factors. Considering relationships between metals, strong inverse correlations are observed in polychaetes and sediments for Cu and Cr concentrations suggesting a possible interaction between these two metals. The role played by organic matter (OM) in the availability of metal is highlighted considering inverse relationships found between bioaccumulation factors for Cu, Cr, Cd and OM.     

Sediment toxicity assessment in the Lagoon of Venice (Italy) using Paracentrotus lividus (Echinodermata: Echinoidea) fertilization and embryo bioassays

The capacity of two toxicity bioassays (fertilization and embryo toxicity tests) to discriminate sediment toxicity using the sea urchin Paracentrotus lividus was tested in five stations with different levels of pollution in the Lagoon of Venice. Two stations were located in estuarine sites, two in the industrial zone, and one in a site at the top of our quality gradient (reference). Elutriate was chosen as sediment matrix to assess the potential effects of bioavailable pollutants in the water column as a consequence of sediment resuspension (dredging and dumping, fishing gear, etc.). An experimental design based on Quality Assurance/Quality Control procedures (QA/QC) was adopted in order to set the methodological basis for an effective use of these bioassays in monitoring programs. Results revealed both higher embriotoxicity than spermiotoxicity in all stations and the efficacy of combined use of both toxicity bioassays in discriminating differing pollution/bioavailability between stations and periods. The good representativeness of the integrated sampling scheme and the standardization of all experimental phases yielded high precision of results. Clear Toxicity Fingerprints were evidenced for the investigated sites through the combined use of both bioassays. A good fit between ecotoxicological data and chemical contamination levels was found, except for unnatural sediment texture.     

Monitoring transitional waters using reduced benthic assemblages

In this study, the use of reduced assemblages of benthic invertebrate taxa is proposed to describe similarity relationships between samples from transitional environments. A data set from four different studies, made up of 641 samples for a total 203 species, was analysed using permutation randomisation tests in order to extract a pool of taxa able to approximate the full set of species. The identified "operational set", comprising 19 taxa, was capable of adequately reproduce similarity relationships between samples (Rho>0.90, p<0.001). All selected taxa were easily extractable from the samples and easy identifiable by non-specialised technicians; these characteristics were considered appropriate for the development of rapid and cost-effective monitoring procedures based on benthic invertebrate assemblages.     

Localized deer absence leads to tick amplification

Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tickborne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots.     

Venice and its lagoon fin de siecle

Regional Environmental Change - This study presents a reconstruction of basin scale long-term annual surface mass balance (SMB) estimates for 91 glaciers (≥ 1 km2) of Chandra basin in...