Appropriate temporal resolution of precipitation data for discharge modelling in pre-alpine catchments

Precipitation time series with high temporal resolution are desired for hydrological modelling and flood studies. Yet the choice of an appropriate resolution is not straightforward because the use of too high a temporal resolution increases the data requirements, computational costs and, presumably, associated uncertainty, while performance improvement may be indiscernible. In this study, the effect of averaging hourly precipitation on model performance and associated uncertainty is investigated using two data sources: station network precipitation (SNP) and radar-based precipitation (RBP). From these datasets, time series of different temporal resolutions were generated, and runoff was simulated for 13 pre-alpine catchments with a bucket-type model. Our results revealed that different temporal resolutions were required for an acceptable model performance depending on the catchment size and data source. These were 1–12 h for small (16–59 km²), 3-21 h for medium (60–200 km²), and 24 h for large (200–939 km²) catchments.     

Meso-scale variability of coastal suprabenthic communities in the southern Tyrrhenian Sea (western Mediterranean)

Meso-scale spatial variability of coastal suprabenthic communities inhabiting muddy bottoms at 50–80 m depth in three gulfs of northern Sicily (Western Mediterranean) was here investigated. Although similar as concerns the hydrological and oceanographic conditions, the three areas, that encompass a large portion of the continental shelf (135 km), are characterized by different geo-morphological features. In addition, they are subjected to different trawl fishery pressures. The Gulf of Castellammare is a semi-enclosed bay, where the trawling activity has been banned since 1990. The Gulf of Termini Imerese and the Gulf of Sant’Agata are open areas, subjected to high trawl fishing intensity. In terms of density, gammarid amphipods showed differences among the three gulfs; in terms of biomass, cumaceans and amphipods were more abundant in the Gulf of Castellammare than in the other two areas. Multivariate analyses provided evidence for separation of suprabenthic assemblages between the Gulf of Castellammare and the other two gulfs. The Gulf of Castellammare seemed to host the most diversified and stable community according to α- and β-diversity indices. In the same way the low value of δ¹³C vs. δ¹⁵N correlation found in the gulf of Castellammare, which evidences the occurrence of several food sources, supports the idea of a higher stability in the semi-enclosed, trawl-ban area. In the other two areas δ¹³C vs. δ¹⁵N correlations were high, suggesting the existence of a pelagic source sustaining the suprabenthic communities. This is also confirmed by the lower δ¹³C concentrations found in suprabenthic species. Taking into account the homogeneous oceanographic conditions among gulfs, other factors, such as geo-morphology and trawling pressure should be involved in the observed differences among the three areas in terms of assemblage structure, diversity, and trophodynamics of suprabenthic communities.     

四川盆地奥陶系岩相古地理与勘探潜力

在前人研究基础上,依托露头和钻井资料,以沉积相分析为核心,结合四川盆地构造演化,采用单因素分析多因素综合法,以"组"为单元编制了奥陶纪岩相古地理图。奥陶纪四川盆地及邻区总体呈现西高东低的古地理格局,自西向东发育滨岸相、混积潮坪相、局限台地相、开阔台地相和斜坡相—盆地相。从岩相古地理视角对成藏条件的分析表明:奥陶系五峰组沉积期四川盆地主体属于局限海环境,发育了一套优质烃源岩,此外,与奥陶系临近的上覆志留系龙马溪组和下伏寒武系筇竹寺组烃源岩在有断层沟通的情况下可提供有效气源;奥陶系碳酸盐岩总体致密,白云石化、表生溶蚀和裂缝的存在是储层形成的关键因素,对应发育了桐梓组—红花园组颗粒滩白云岩储层、岩溶储层和宝塔组裂缝储层等三类储层;奥陶系发育下部(下生上储)和上部(上生下储)两套成藏组合,具有较好的勘探潜力。     

Extinction versus backscatter relationships for lidar applications at 351 nm: maritime and desert aerosol simulations and comparison with observations

Functional relationships linking at λ₀=351 nm aerosol extinction α_λ0^aer and backscatter coefficient β_λ0^aer of maritime and desert type aerosols are determined to allow for inversion of the single-wavelength lidar signals. Such relationships are derived as mean behavior of 20,000 extinction versus backscatter computations, performed for aerosol size distributions and compositions whose describing parameters are randomly chosen within the naturally observed variability. For desert-type aerosols, the effect of the particle non-sphericity is considered and it is shown that the extinction to backscatter ratio of non-spherical dust particles can be up to 60% larger than the values obtained for spherical particles. Aerosol extinction and backscatter coefficient profiles obtained inverting the single-wavelength lidar signal with the modeled relationships are then compared to the same profiles measured by a combined elastic-Raman lidar operating at 351 nm. Analytical back trajectories and satellite images are used to characterize advection patterns during lidar measurements and to properly choose the modeled functional relationship. A good accordance between the two techniques is found for advection patterns over the lidar site typical of maritime and dust conditions. Maximum differences between the model-based α_λ0^aer and β_λ0^aer vertical profiles and the corresponding ones measured by the combined elastic-Raman lidar technique are of 30% and 40% in maritime and desert dust conditions, respectively. The comparison of elastic-Raman lidar measurements and model-based results also reveals that particle non-sphericity must be taken into account when mineral dust-type aerosols are directly advected over the measurement site.     

Physical Modelling of Stress-dependent Permeability in Fractured Rocks

This paper presents the results of laboratory experiments conducted to study the impact of stress on fracture deformation and permeability of fractured rocks. The physical models (laboratory specimens) consisted of steel cubes simulating a rock mass containing three sets of orthogonal fractures. The laboratory specimens were subjected to two or three cycles of hydrostatic loading/unloading followed by the measurement of displacement and permeability. The results show a considerable difference in both deformation and permeability trends between the first loading and the subsequent loading/unloading cycles. However, the micrographs of the contact surfaces taken before and after the tests show that the standard deviation of asperity heights of measured surfaces are affected very little by the loadings. This implies that both deformation and permeability are rather controlled by the highest surface asperities which cannot be picked up by the conventional roughness characterization technique. We found that the dependence of flow rate on mechanical aperture follows a power law with the exponent n smaller or larger than three depending upon the loading stage. Initially, when the maximum height of the asperities is high, the exponent is slightly smaller than 3. The first loading, however, flattens these asperities. After that, the third loading and unloading yielded the exponent of around 4. Due to the roughness of contact surfaces, the flow route is no longer straight but tortuous resulting in flow length increase.     

The last Eurasian ice sheets – a chronological database and time‐slice reconstruction,DATED‐1

We present a new time‐slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time‐slice maps of ice‐sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice‐sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice‐margin lines for each time‐slice; a most‐credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice‐sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27–26 ka) than the eastern limit on the Russian Plain (at c. 20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm²) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continental‐scale approach highlights instances of conflicting evidence and gaps in the ice‐sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time‐slices (DATED‐1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA ( www.bcdc.no ; http://doi.pangaea.de/10.1594/PANGAEA.848117 ).     

Determining the extent of weathering of spilled fuel in contaminated soil using the diastereomers of pristane and phytane

A method is described for determining the relative extent of weathering in moderately biodegraded, hydrocarbon-contaminated soils from Antarctica. Plotting the pristane diastereomer ratio (PrDR) vs. pristane/phytane (Pr/Ph) allows the relative extent of weathering (primarily evaporation in this case) to be determined. PrDR is used to account for biodegradation as it is independent of evaporation. The method is straightforward and as robust as conventional ratios.     

“Galileo Galilei” (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein

“Galileo Galilei” (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle—which is at the basis of the General Theory of Relativity—to 1 part in 10¹⁷. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009.     

Land use change and anthropogenic driving forces: A case study in Yanhe River Basin

Human activities alter land use patterns and affect landscape sustainability. It is therefore very important to investigate the relationship between land use change and human activities. This study focuses on the detection of changing land use patterns in the Yanhe River Basin in northern Loess Plateau of China between 1995 and 2008. Landscape metrics were used to analyze the changing land use patterns and to explore the related anthropogenic driving forces. Results show that:1) Totally, 186 590 ha of cropl...     

Reduction of iodate in seawater during Arabian Sea shipboard incubations and in laboratory cultures of the marine bacterium Shewanella putrefaciens strain MR-4

Shipboard incubations from the US JGOFS cruise to the Arabian Sea (TN045) March, 1995 showed evidence of iodate reduction in 0.45 μ (Gelman Supor membrane) filtered seawater samples collected from intermediate depths (200–600 m) within the oxygen minimum zone (OMZ). Inorganic chemical reduction of iodate in these samples was ruled out as no free sulfide was measurable and concentrations of ammonia and nitrite were found to be less than 5 μM. To examine whether the reduction of iodate observed at sea could have been the result of bacterial metabolism, reduction of iodate (IO₃⁻) to iodide (I⁻) by Shewanella putrefaciens strain MR-4 was studied in artificial seawater using electrochemical methods. MR-4 is a ubiquitous marine bacterium which may be of considerable importance when considering redox zonation in the water column because it is a facultative anaerobe and may switch amongst a suite of electron acceptors to support metabolism. In all experiments MR-4 reduced all iodate to iodide. The rate of formation of [I⁻]in the culture followed pseudo-first order kinetics. This is the first report of the marine bacterial reduction of iodate where the concentrations of iodide and iodate were measured directly. Our results may help to explain the depth distribution of iodine speciation reported in productive waters like the Arabian Sea and for the first time couple iodine speciation with bacterial productivity in the ocean.