Problems of soil and groundwater pollution in the disposal of “marble” slurries in NW Sicily

This work deals with disposal of slurries generated during the cutting and polishing processes of slabs of decorative sedimentary carbonate rocks in the north western Sicily. At present, they are used as fillers of dismantled quarries near the sawmills and, as a final step of reclamation, are covered with earth layers. In spite of such inexpensive solution, there is lack of knowledge about the composition of the waste. In order to assess if there is any threat for the environment and to suggest indications for alternative solutions, such as recycling or inactivation processes, the slurries were analysed by XR diffraction, simultaneous thermal analysis, ICP/MS, ionic chromatography, FTIR, UV-Vis, COD and TOC measurements, grain size analysis. Results indicate that the slurries can threaten the groundwater, because of the high chemical oxygen demand; furthermore they can modify the mechanism of groundwater recharge, because of their grain size distribution. Some laboratory tests show that, even in very aggressive conditions, the solid pollutants persist in the waste and slowly release into water the products of their degradation. The slurry therefore should be subjected to inactivation treatment before disposal or, alternatively, recycled as secondary raw material for a suitable process.     

Electromagnetic methods to characterize the Savoia di Lucania waste dump (Southern Italy)

The aim of this work is the joint application and integration of non-invasive geoelectrical methods for studying the landfill of Savoia di Lucania (Southern Italy). This landfill for its engineering features and small dimensions (70 m × 30 m × 6 m) represents an optimal test site to assess a geophysical survey protocol for municipal solid waste landfills investigation and monitoring. The landfill of Savoia di Lucania has been built with a reinforced concrete material and coated with a high-density polyethylene (HDPE) liner. Three electrical resistivity tomographies (ERT), two self-potential (SP) map surveys and one induced polarization (IP) section have been performed, both in the surrounding area and inside the waste landfill. The geophysical investigations have well defined some buried boundaries of the landfill basin and localized the leachate accumulation zones inside the dumpsite. Comparison of our results with other engineering and geological investigations could be the key for evaluating the integrity of the HDPE liner. Finally, the joint use of the ERT, IP and SP methods seems to be a promising tool for studying and designing new monitoring systems able to perform a time-lapse analysis of waste landfill geometry and integrity.     

Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web

We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa present inHalodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity ≥ 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers and piscivores. These trophic groups, corss-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups.     

Chemical and isotopic equilibrium between CO2 and CH4 in fumarolic gas discharges: Generation of CH4 in arc magmatic-hydrothermal systems

The chemical and isotopic composition of fumarolic gases emitted from Nisyros Volcano, Greece, and of a single gas sample from Vesuvio, Italy, was investigated in order to determine the origin of methane (CH₄) within two subduction-related magmatic-hydrothermal environments.Apparent temperatures derived from carbon isotope partitioning between CH₄ and CO₂ of around 340°C for Nisyros and 470°C for Vesuvio correlate well with aquifer temperatures as measured directly and/or inferred from compositional data using the H₂O-H₂-CO₂-CO-CH₄ geothermometer. Thermodynamic modeling reveals chemical equilibrium between CH₄, CO₂ and H₂O implying that carbon isotope partitioning between CO₂ and CH₄ in both systems is controlled by aquifer temperature.N₂/³He and CH₄/³He ratios of Nisyros fumarolic gases are unusually low for subduction zone gases and correspond to those of midoceanic ridge environments. Accordingly, CH₄ may have been primarily generated through the reduction of CO₂ by H₂ in the absence of any organic matter following a Fischer-Tropsch-type reaction. However, primary occurrence of minor amounts of thermogenic CH₄ and subsequent re-equilibration with co-existing CO₂ cannot be ruled out entirely. CO₂/³He ratios and δ¹³C_CO2 values imply that the evolved CO₂ either derives from a metasomatized mantle or is a mixture between two components, one outgassing from an unaltered mantle and the other released by thermal breakdown of marine carbonates. The latter may contain traces of organic matter possibly decomposing to CH₄ during thermometamorphism.     

Nutrient exchanges between the water column and a subtidal benthic microalgal community

Exchanges of nutrients between a shallow (ca. 1 m) nodiment and the water column were measured in the York River, Virginia, during 1983, using transparent and opaque plexiglass hemispheres. Exchanges of nitrate and phosphate were not significantly different between dome treatments, but ammonium release was significantly reduced within the transparent domes. Within the dark domes, ranges of hourly rates of ammonium and phosphate exchange were 21 to 364 μmol N m² and 3 to 76 μmol P m² while those in the transparent domes were ?162 to 244 and 6 to 80, respectively. Negative values denote uptake by the sediment. Nitrate 1 nitrite exchanges averaged only 15% and 17% of the total dissolved luorganle nitrogen exchange in the dark and transparent domes, respectively.     

An electrochemical study of Ni2+, Co2+, and Zn2+ ions in melts of composition CaMgSi2O6

Cyclic voltammetry has been done for Ni²⁺, Co²⁺, and Zn²⁺ in melts of diopside composition in the temperature range 1425 to 1575°C. Voltammetric curves for all three ions excellently match theoretical curves for uncomplicated, reversible charge transfer at the Pt electrode. This implies that the neutral metal atoms remain dissolved in the melt. The reference electrode is a form of oxygen electrode. Relative to that reference assigned a reduction potential of 0.00 volt, the values of standard reduction potential for the ions are $\text{E}{}^1\text{(}\text{Ni}{}^{\mathrm{2+}}\text{Ni}{}^0\text{,}\text{diopside}\text{, 1500°C) = ?0.32 ± .01}\text{V}$, $\text{E}{}^1\text{(}\text{Co}{}^{\mathrm{2+}}\text{Co}{}^0\text{,}\text{diopside}\text{, 1500°C) = ?0.45 ± .02}\text{V}$, and $\text{E}{}^1\text{(}\text{Zn}{}^{\mathrm{2+}}\text{Zn}{}^0\text{,}\text{diopside}\text{, 1500°C) = ?0.53 ± .01}\text{V}$. The electrode reactions are rapid, with first order rate constants of the order of 10^?2 cm/sec. Diffusion coefficients were found to be 2.6 × 10^?6 cm²/sec for Ni²⁺, 3.4 × 10^?6 cm²/sec for Co²⁺, and 3.8 × 10^?6 cm²/sec for Zn²⁺ at 1500°C. The value of $\text{E1}$ ($\text{Ni}{}^{\mathrm{2+}}\text{Ni}{}^0$, diopside) is a linear function of temperature over the range studied, with values of ?0.35 V at 1425°C and ?0.29 V at 1575°C. At constant temperature the value of $\text{E}{}^1\text{(}\text{Ni}{}^{\mathrm{2+}}\text{Ni}{}^0\text{, 1525°C}$) was not observed to vary with composition over the range CaO · MgO · 2SiO₂ to CaO·MgO·3SiO₂ or from 1.67 CaO·0.33MgO·2SiO₂ to 0.5 CaO·1.5MgO·2SiO₂. The value for the diffusion coefficient for Ni²⁺ decreased by an order of magnitude at 1525°C over the compositional range CaO · MgO · 1.25SiO₂ to CaO · MgO · 3SiO₂. This is consistent with a mechanism by which Ni²⁺ ions diffuse by moving from one octahedral coordination site to another in the melt, with the same Ni²⁺ species discharging at the cathode regardless of the SiO₂ concentration in the melt.     

A metabolism-based trophic index for comparing the ecological values of shallow-water sediment habitats

We determined fluxes of oxygen and nutrients between water and sediments at 21 sites primarily in Virginia and North Carolina estuaries, over the past 15 yr. These sites represented broad ranges in salinity, tidal amplitude, hydrology, nutrient availability, turbidity, light availability, depth, sediment grain size, and anthropogenic disturbance. In general, we found that heterotrophically dominated sediments had the potential to degrade water quality, whereas photoautotrophy in the sediments ameliorated this impact. We propose a benthic trophic state index as a management tool to make general assessments of the degree to which sediments support ecological processes related to photoautotrophy. The index can be based on simple measurements of metabolic parameters. We also evaluated the relative significance of variability in the index across a number of spatial and temporal scales. Reduced photoautotrophy and/or enhanced heterotrophy tended to be associated with finer-grained, organic-rich sediments. This sediment type was common in oligohaline areas at water depths exceeding 2 m. Temporally, autotrophy declined from winter to spring particularly at sandy sites, while interannual variability was more pronounced for mud sites. *** DIRECT SUPPORT *** A01BY074 00011     

Diet of Haplognathia ruberrima (Gnathostomulida) in a Caribbean marine mangrove

Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a δ¹³C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low δ¹³C value can not be due to specific ingestion of ¹³C‐depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by δ¹³C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electron microscope views revealed the absence of bacterial endosymbionts. Energy‐dispersive X‐ray spectroscopy analysis detected low levels of sulfur (0.32%±0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low δ¹³C value of H. ruberrima can not be due to the presence of sulfur‐oxidizing symbionts but more probably to the selective and exclusive consumption of free‐living, sulfur‐oxidizing bacteria.     

An inverse procedure to estimate transmissivity from heads and SP signals

Experimental hydraulic heads and electrical (self-potential) signals associated with a pumping test were used in an inverse model to estimate the transmissivity distribution of a real aquifer. Several works reported in the literature show that there is a relatively good linear relationship between the hydraulic heads in the aquifer and electrical signals measured at the ground surface. In this experimental test field, first, the current coupling coefficient was determined by the best fit between experimental and modeled self-potential signals at the end of the pumping phase. Soon afterward, with the hydraulic heads obtained from the self-potential signals, the transmissivity distribution of the aquifer was conditioned by means an inverse model based on the successive linear estimator (SLE). To further substantiate the estimated T field from the SLE analysis, we analyzed the drawdown rate, the derivative of the drawdown with respect to the ln(t), because the drawdown rate is highly sensitive to the variability in the transmissivity field. In our opinion, these results show that self-potential signals allow the monitoring of subsurface flow in the course of pumping experiments, and that electrical potentials serve as a good complement to piezometric observations to condition and characterize the transmissivity distribution of an aquifer.     

Riparian reforestation and channel change: A case study of two small tributaries to Sleepers River, northeastern Vermont, USA

Measurements of two small streams in northeastern Vermont, collected in 1966 and 2004–2005, document considerable change in channel width following a period of passive reforestation. Channel widths of several tributaries to Sleepers River in Danville, VT, USA, were previously measured in 1966 when the area had a diverse patchwork of forested and nonforested riparian vegetation. Nearly 40 years later, we remeasured bed widths and surveyed large woody debris (LWD) in two of these tributaries, along 500 m of upper Pope Brook and along nearly the entire length (3 km) of an unnamed tributary (W12). Following the longitudinal survey, we collected detailed channel and riparian information for nine reaches along the same two streams. Four reaches had reforested since 1966; two reaches remained nonforested. The other three reaches have been forested since at least the 1940s. Results show that reforested reaches were significantly wider than as measured in 1966, and they are more incised than all other forested and nonforested reaches. Visual observations, cross-sectional surveys, and LWD characteristics indicate that reforested reaches continue to change in response to riparian reforestation. The three reaches with the oldest forest were widest for a given drainage area, and the nonforested reaches were substantially narrower. Our observations culminated in a conceptual model that describes a multiphase process of incision, widening, and recovery following riparian reforestation of nonforested areas. Results from this case study may help inform stream restoration efforts by providing insight into potentially unanticipated changes in channel size associated with the replanting of forested riparian buffers adjacent to small streams.