Spectroscopic Investigation on Hydrophobic and Hydrophilic Fractions of Dissolved Organic Matter Extracted from Soils at Different Salinities

Organic matter can be considered one of the most important indicators of the extent of soil desertification processes. Among the causes of desertification, salinization induced by different factors is raising the greatest concern in the Mediterranean area. In the present research, hydrophilic (HI) and hydrophobic (HO) fractions of dissolved organic matter (DOM) extracted from soils at different degrees of salinization have been investigated by means of spectroscopic techniques such as tridimensional fluorescence spectroscopy in the mode of emission excitation matrix (EEM) and Fourier transform infrared spectroscopy (FT‐IR). The FT‐IR spectra were distinctive in differentiating HI from HO fractions and each DOM fraction as a function of soil salinity. The EEM spectra of HO fractions exhibited a shift toward longer emission wavelengths and higher fluorescence intensity (FI) values as compared to that of the HI fractions. These results could be ascribed to the different molecular complexities of HI and HO fractions. Further, a marked quenching effect was observed in the FI of both the DOM fractions with increasing soil salinity, which allowed to obtain immediate information on the soil salinity degree by comparing the fluorescence intensity.     

Cenomanian–Turonian transition in a shallow water sequence of the Sinai, Egypt

Environmental and depositional changes across the Late Cenomanian oceanic anoxic event (OAE2) in the Sinai, Egypt, are examined based on biostratigraphy, mineralogy, δ¹³C values and phosphorus analyses. Comparison with the Pueblo, Colorado, stratotype section reveals the Whadi El Ghaib section as stratigraphically complete across the late Cenomanian–early Turonian. Foraminifera are dominated by high-stress planktic and benthic assemblages characterized by low diversity, low-oxygen and low-salinity tolerant species, which mark shallow-water oceanic dysoxic conditions during OAE2. Oyster biostromes suggest deposition occurred in less than 50 m depths in low-oxygen, brackish, and nutrient-rich waters. Their demise prior to the peak δ¹³C excursion is likely due to a rising sea-level. Characteristic OAE2 anoxic conditions reached this coastal region only at the end of the δ¹³C plateau in deeper waters near the end of the Cenomanian. Increased phosphorus accumulations before and after the δ¹³C excursion suggest higher oxic conditions and increased detrital input. Bulk-rock and clay mineralogy indicate humid climate conditions, increased continental runoff and a rising sea up to the first δ¹³C peak. Above this interval, a dryer and seasonally well-contrasted climate with intermittently dry conditions prevailed. These results reveal the globally synchronous δ¹³C shift, but delayed effects of OAE2 dependent on water depth.     

Stability of streambanks formed in partially saturated soils and effects of negative pore water pressures: the Sieve River (Italy)

Streambanks of alluvial channels are usually composed of loose materials, which are unsaturated in ambient conditions. Unsaturated soils are subject to negative pore water pressures, which cause an apparent cohesion. The latter is the main factor in allowing the stability of near-vertical banks. Even during moderate in-bank flow events, the apparent cohesion can be strongly reduced as the material approaches full saturation; therefore, during the drawdown phase, as the confining pressure of the water in the channel disappears, a bank failure is likely to occur. Channel bed-level lowering along the Sieve River, Central Italy, has caused widespread bank instability. A geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks. Interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils, in order to obtain relations between bank angle and height in limit equilibrium conditions. A stability chart was obtained with curves for different apparent cohesion values, and a stability analysis was performed taking into account the effects of flow events. In order to investigate the pore pressure effects, a series of piezo-tensiometers were installed in a streambank of the Sieve River. Data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall, evapotranspiration, and water stage variations. A planar failure with a tension crack occurred in the upper cohesive part of the bank during December 1996. The safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material. Safety factor variations through time are therefore shown as a function of seasonal variations in matric suction.     

How to improve the representation of hydrological processes in SWAT for a lowland catchment – temporal analysis of parameter sensitivity and model performance

Model diagnostic analyses help to improve the understanding of hydrological processes and their representation in hydrological models. A detailed temporal analysis detects periods of poor model performance and model components with potential for model improvements, which cannot be found by analysing the whole discharge time series. In this study, we aim to improve the understanding of hydrological processes by investigating the temporal dynamics of parameter sensitivity and of model performance for the Soil and Water Assessment Tool model applied to the Treene lowland catchment in Northern Germany. The temporal analysis shows that the parameter sensitivity varies temporally with high sensitivity for three groundwater parameters (groundwater time delay, baseflow recession constant and aquifer fraction coefficient) and one evaporation parameter (soil evaporation compensation factor). Whereas the soil evaporation compensation factor dominates in baseflow and resaturation periods, groundwater time delay, baseflow recession constant and aquifer fraction coefficient are dominant in the peak and recession phases. The temporal analysis of model performance identifies three clusters with different model performances, which can be related to different phases of the hydrograph. The lowest performance, when comparing six performance measures, is detected for the baseflow cluster. A spatially distributed analysis for six hydrological stations within the Treene catchment shows similar results for all stations. The linkage of periods with poor model performance to the dominant model components in these phases and with the related hydrological processes shows that the groundwater module has the highest potential for improvement. This temporal diagnostic analysis enhances the understanding of the Soil and Water Assessment Tool model and of the dominant hydrological processes in the lowland catchment. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Pumice and Sand on the Sustainability of Granular Iron Beds for the Aqueous Removal of CuII,NiII, and ZnII

Current knowledge of the basic principles underlying the design of Fe⁰ beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe⁰ beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe⁰ in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe⁰). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of Cu^II, Ni^II, and Zn^II (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe⁰, (ii) additive admixture lengthened the service life of Fe⁰ beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe⁰/sand column was the most efficient for contaminant removal. The evolution of the permeability was well‐fitted by the approach that the inflowing solution contained dissolved O₂. The achieved results are regarded as starting point for a systematic research to optimize/support Fe⁰ filter design.     

Multilevel models for analyzing people’s daily movement behavior

A survey on the daily movement behavior of the people residing in the territory of the Municipality of Pisa, Italy, was carried out in October 2002. This work is aimed at modeling the distance covered and the number of trips taken in a day as functions of several individual characteristics. In order to take the potential intra-family and intra-area correlation of the observations into account, multilevel models are estimated. We use two and three level hierarchical linear and Poisson models to estimate the number of daily trips taken by an individual. Likelihood ratio tests indicate the movement behavior in 1 day is more alike for individuals within a family than for individuals from different families.