Are water tables a subdued replica of the topography?

The water table in unconfined aquifers is often believed to be a subdued replica of the topography or land surface. However, this assumption has not been widely tested and in some cases has been found to be in error. An analysis of ground water rise in regional unconfined aquifers, using both a two-dimensional boundary element model and a one-dimensional Dupuit-Forchheimer model, reveals the conditions under which the water table does or does not closely follow the topography. A simple decision criterion is presented to estimate in advance under which conditions the water table is expected to be largely unrelated to the topography and under which conditions the topography controls the position of the water table.     

The Elbe flood 2002--toxic effects of transported contaminants in flatfish and mussels of the Wadden Sea

Cellular changes in livers from flounder (Platichthys flesus L.) and digestive glands of blue mussels (Mytilus edulis) were studied to analyze whether the Elbe flood catastrophe in August 2002 had any deleterious effects on animal health. Flatfish and mussels were sampled at different locations in the Elbe estuary and the Wadden Sea after the flood wave had reached the German Bight. Internationally used core biomarkers (lysosomal membrane stability, biotransformation enzymes) were applied to assess the toxic effects of putatively increased pollution levels. In comparison to earlier data from long-term studies at the same stations, we found a significant impairment in the function of cell organelles (lysosomes) involved in the detoxification and elimination of pollutants in fish liver. Concentrations of relevant contaminants (organochlorines, polychlorinated biphenyls) were analyzed in parallel with cellular biomarkers, and conspicuously raised concentrations of insecticides metabolites were detected. Cell recovery and a clear reduction in contaminant concentrations were observed in fish livers five months after the flood at all sampling sites except the Helgolander Tiefe Rinne.     

Fate of DDT-related compounds in Bohai Bay and its adjacent Haihe Basin, North China

Concentrations of ten DDTs (2,2-bis-(chlorophenyl)-1,1,1-trichloroethane) of which p,p'-DDA (2,2-bis(chlorophenyl)acetic acid), p,p'-DDM (bis(chlorophenyl)methane) and p,p'-DBP (dichlorobenzophenone) are often neglected, were measured in 25 water and 25 sedimentary samples from Bohai Bay and its adjacent Haihe Basin. The ratio of o,p'-DDX/p,p'-DDX in the upper reaches of Yongdingxin River ranged from 0.71 to 2.44, suggesting that the potential source of pollution would be the manufacturing or use of dicofol near this river. While DDA accounted for 52-93% of the SigmaDDT concentration in water, DDA was only detected in three sedimentary samples. And DDM was found to be an important degradation product of DDT in water following DDA. It should be noted that DBP (0.60-3.30 ng/g) is a major metabolite comparable with DDE (2,2-bis(chlorophenyl)-1,1-dichloroethylene, nondetectable-1.80 ng/g) and DDD (2,2-bis-(chlorophenyl)-1,1-dichloroethane, nondetectable-2.86 ng/g) in sediment in Bohai Bay. Finally, the SigmaDDT concentration in sedimentary sample from Bohai Bay was found to be dependent on the TOC (total organic carbon) value.     

Herbicide contamination and the potential impact to seagrass meadows in Hervey Bay, Queensland, Australia

Low concentrations of herbicides (up to 70 ng l(-1)), chiefly diuron (up to 50 ng l(-1)) were detected in surface waters associated with inter-tidal seagrass meadows of Zostera muelleri in Hervey Bay, south-east Queensland, Australia. Diuron and atrazine (up to 1.1 ng g(-1) dry weight of sediment) were detected in the sediments of these seagrass meadows. Concentration of the herbicides diuron, simazine and atrazine increased in surface waters associated with seagrass meadows during moderate river flow events indicating herbicides were washed from the catchment to the marine environment. Maximum herbicide concentration (sum of eight herbicides) in the Mary River during a moderate river flow event was 4260 ng l(-1). No photosynthetic stress was detected in seagrass in this study during low river flow. However, with moderate river flow events, nearshore seagrasses are at risk of being exposed to concentrations of herbicides that are known to inhibit photosynthesis.     

Byssal detachment underestimates tolerance of mussels to toxic compounds

Mussels are sedentary organisms attached to solid substrata by means of byssus threads. Mussels detached from their substratum tend to reattach by producing new byssus threads. Therefore, in bioassays using mussels, if the test animals are in an unattached status, increased byssogenic activity would expose their soft body parts to the toxic compound used. We test the tolerance of two mussel species (Mytilopsis leucophaeata and Mytilus edulis) to an oxidizing biocide (chlorine) and show that detached mussels are 24-28% less tolerant than byssally attached ones. Detached mussels also showed higher oxygen consumption, filtration rate, foot activity, byssus thread production and byssogenesis index, parameters which are associated with valve opening. A review of literature showed that most of the published data on toxicity against heavy metals and biocides are generated using unattached mussels. The data, therefore, represent an underestimation of the toxicity of the tested compound. Correction data are presented for chlorine tolerance of Dreissena polymorpha, Mytilopsis leucophaeata and Mytilus edulis. The present study suggests the importance of maintaining mussels in their attached status, while undertaking toxicity bioassays.     

Metal speciation and environmental impact on sandy beaches due to El Salvador copper mine, Chile

Several coastal rocky shores in northern Chile have been affected by the discharges of copper mine tailings. The present study aims to analyze the chemical speciation of heavy metals in relation to the diversity of sessile species in the rocky intertidal benthic community on the northern Chilean coast, which is influenced by the presence of copper mine tailings. In particular, the chemical forms of Cd, Cu, Fe, Mn, Ni, Pb and Zn in beach sediment samples collected in the area influenced by El Salvador mine tailings were studied using a sequential chemical extraction method. In general, all the elements present a maximum concentration in the area near the actual discharge point (Caleta Palito). With regard to Cu and Mn, the concentrations range between 7.2-985 and 746-22,739 microg/g respectively, being lower than background levels only in the control site of Caleta Zenteno. Moreover, the correlation coefficients highlight that Fe, Mn and Ni correlate significantly and positively in the studied area, showing a possible common, natural origin, whilst Cu shows a negative correlation with Fe, Mn and Ni. It could be possible that Cu has an anthropogenic origin, coming from mining activity in the area. Cd, Fe, Mn, Ni, Pb and Zn are mostly associated with the residual phase, whilst Cu presents a different speciation pattern, as resulted from selective extractions. In fact, Cu is highly associated with organic and exchangeable phases in contaminated localities, whilst it is mainly bound to the residual phase in control sites. Moreover, our results, compared to local biological diversity, showed that those sites characterized by the highest metal concentrations in bioavailable phase had the lowest biodiversity.     

Heavy metals accumulation in two syntopic sandhopper species: Talitrus saltator (Montagu) and Talorchestia ugolinii Bellan Santini and Ruffo

We assessed the capacity for heavy metals accumulation in Talorchestia ugolinii by standard methods of heavy metals analysis. To compare the bioaccumulation in syntopic sandhopper species, we collected samples of T. ugolinii and Talitrus saltator living on the same and on different beaches in Corsica. There was a marked difference in the zonal distribution of the two species along the sea-land axis of the beach: T. ugolinii was distributed nearer the water line than T. saltator. The bioaccumulation capacity of T. ugolinii only partly matched that of the Mediterranean T. saltator: while Hg, Zn, Cu, and Cd were accumulated by both species, Al and Fe were accumulated by T. saltator but not by T. ugolinii. Pb was accumulated only by T. ugolinii, while Cr did not seem to be accumulated by either species. The bioaccumulation in sympatric T. saltator and T. ugolinii specimens collected on the same beach reflected the general trend of the two species on the Tyrrhenian and Corsican coasts, respectively. Moreover, six of the eight heavy metals considered (Hg, Pb, Zn, Fe, Al, Cu) were present in higher quantities in T. ugolinii than in T. saltator, independently of whether the trace elements were accumulated by the two species. Thus, there are some differences between T. ugolinii and T. saltator, even when the two species live in the same locality. These differences involve their zonation within the damp belt of sand, the bioaccumulation of some heavy metals (Al, Pb, Fe), and the quantity of each heavy metal in the body, independent of the bioaccumulation capacity.