Statistical assessment of seismicity patterns in Italy: Are they precursors of subsequent events?

The variations of seismicity rate in Central Apenninesprior to the sequence started in September, 1997 (at00:33 UTC, M _L5.6) has been analysedby statistical methods, with the purpose of pointingup eventual periods of quiescence. The analysis wascarried out on the instrumental catalogue of theIstituto Nazionale di Geofisica (ING), covering theperiod from January 1975 to March 1998. In apreliminary phase, the catalogue was declustered usingthe Reasenberg algorithm. After that, eventualmagnitude shifts due to variations in the modalitiesof observation have been individuated and corrected.The subsequent analysis, carried out making use of theZmap software package, has put in evidence thatthe sequence of September 1997 was preceded bya 2.5 year period characterised by absence of eventsof magnitude larger than 3.2, in an area approximately20 × 40 km wide, including the epicentre of themain shock. The statistical methodology shows thatonly 1/10³ of the space-time volumes analysed inthis study, exhibited quiescence of the same level.The study of seismicity rate change correlated toprevious main shocks in a larger area of CentralApennines shows that none of them were preceded by aseismic quiescence, specially close to the epicentreof the main shock, and lasting until the time ofoccurrence of the main shock as in the 1997 case.Actually, we found other patterns of precursoryquiescence with different time or space distribution.We conclude that precursory quiescence is a realfeature of Central Apennines seismicity, but it isdifficult to define a simple hypothesis, which appliesto the generality of cases and can be tested beforeimplementation in a system of earthquake riskmitigation.     

What compensates the topography of southern Norway? Insights from thermo-isostatic modeling

The origin of the high topography of the Norwegian Mountains is currently much debated. Several geophysical studies show that the uppermost mantle below southern Norway has anomalously low velocities as compared to other parts of the Baltic Shield. This study aims to shed lights on the structure of the lithospheric mantle below southern Norway by adapting and further refining a method based on isostatic and thermal equilibrium to compute temperature, temperature-related density and synthetic S-wave velocity in stable continental domains. The one-dimensional steady-state heat equation is used with topographic, Moho depth, crustal density and surface heat flow data. A condition of local isostasy is assumed and geoid undulations are used to constrain the range of possible lithosphere models.Results derived from this method suggest a thickening of the thermal lithosphere below southern Norway from west to east. The western part is found to have higher temperatures, lower densities and lower synthetic S-wave velocities than the eastern part, compatible with results from a recent P-wave travel time residual study. Comparison of the synthetic shear-velocity profiles beneath southwestern Norway with velocity profiles inverted from Rayleigh wave dispersion data suggests that the higher temperatures associated with a thinner lithosphere can explain parts of the seismic low-velocity anomaly.The inferred lithospheric structure is sensitive to uncertainties in the crustal input model, but the main features remain undisturbed by changes in the input data. The results show that the lithosphere of southwestern Norway can be in local isostatic equilibrium, if it is thinner and warmer than the lithosphere of eastern Norway. The present-day high topography may therefore be partially sustained by lower densities in the mantle lithosphere.     

What can we learn from the projections of changes of flow patterns? Results from Polish case studies

River flow projections for two future time horizons and RCP 8.5 scenario, generated by two projects (CHASE-PL and CHIHE) in the Polish-Norwegian Research Programme, were compared. The projects employed different hydrological models over different spatial domains. The semi-distributed, process-based, SWAT model was used in the CHASE-PL project for the entire Vistula and Odra basins area, whilst the lumped, conceptual, HBV model was used in the CHIHE project for eight Polish catchments, for which the comparison study was made. Climate projections in both studies originated from the common EURO-CORDEX dataset, but they were different, e.g. due to different bias correction approaches. Increases in mean annual and seasonal flows were projected in both studies, yet the magnitudes of changes were largely different, in particular for the lowland catchments in the far future. The HBV-based increases were significantly higher in the latter case than the SWAT-based increases in all seasons except winter. Uncertainty in projections is high and creates a problem for practitioners.     

How representative are local measurements of the surface shear stress for regional values?

Local values of surface shear stress measured by eddy correlation devices were compared to regional ones generated by Monin–Obukhov similarity (MOS) theory in the atmospheric surface layer over the cooperative atmosphere–surface exchange study (CASES) area in eastern Kansas. For this comparison, minisodar average wind speed profiles were used to implement MOS. The local surface shear stress values were found to be representative of the regional ones only under free convective conditions. For weak to strongly neutral atmospheric conditions, regional values of the surface shear stress were underpredicted by a factor of two by the locally measured ones. Empirical interpolation equations are proposed to describe the relationship in the intermediate range. The surface roughness values of 0.12 and 0.40 m, respectively, were determined for the two locations of the minisodar sounders by regional analysis of their mean wind speed measurements under neutral atmospheric conditions. The roughness values found in this present study compared well to past investigations conducted in this region. Minisodar roughness values were found in this present study to be a good alternative to radiosonde determined ones.     

Seasonal–latitudinal variations of PMC particle size from SME measurements for the northern 1983 season and SNOE measurements for the northern 2000 and southern 2000/2001 seasons

The ultraviolet spectrometers (UVS) on the solar mesosphere explorer (SME) and student nitric oxide explorer (SNOE) measured scattered limb radiance at small and large scattering angles from polar mesospheric clouds (PMCs). The SME data are for the northern summer hemisphere (NH) in 1983 and 1984. The SNOE measurements are for the NH in 2000 and for the southern hemisphere (SH) in the 2000/2001 season. From this database, we deduce the modal particle size from the measured scattering angle asymmetry in radiance. This quantity is determined as a function of time within the PMC season, and latitude, assuming several scattering models depending on the adopted size distribution and particle shape. For assumed spherical particles with a Gaussian distribution of width of 14 nm, the results for SME show mode particle sizes that vary from about 35 to 60 nm throughout the season. The results for SNOE under the same assumption show that for high latitudes in the NH the particle size grows systematically from the seasonal onset, from about 25 nm to a maximum of about 45 nm at 30 days after solstice. Lower latitudes show a similar time dependence, but with smaller particle sizes. SH PMC particle sizes display a more complicated seasonal variability. Generally, variability in measured cloud height is anti-correlated with particle size for the seasons analyzed here. Particle sizes in the SH are generally smaller than those in the NH, consistent with the northern bias in PMC brightness, and with previous satellite studies. These results are interpreted in terms of our understanding of PMC microphysics and inter-hemispheric differences in temperature and dynamics. Our quantitative results for mode radius depend on the assumption of a constant distribution width. If the width varies with latitude or time, our calculated gradients of mode radius would be different.     

Is correlation dimension a reliable proxy for the number of dominant influencing variables for modeling risk of arsenic contamination in groundwater?

The correlation dimension (CD) of a time series provides information on the number of dominant variables present in the evolution of the underlying system dynamics. In this study, we explore, using logistic regression (LR), possible physical connections between the CD and the mathematical modeling of risk of arsenic contamination in groundwater. Our database comprises a large-scale arsenic survey conducted in Bangladesh. Following the recommendation by Hossain and Sivakumar (Stoch Environ Res Risk Assess 20(1–2):66–76, 2006), who reported CD values ranging from 8 to 11 for this database, 11 variables are considered herein as indicators of the aquifer’s geochemical regime with potential influence on the arsenic concentration in groundwater. A total of 2,048 possible combinations of influencing variables are considered as candidate LR risk models to delineate the impact of the number of variables on the prediction accuracy of the model. We find that the uncertainty associated with prediction of wells as safe and unsafe by LR risk model declines systematically as the total number of influencing variables increases from 7 to 11. The sensitivity of the mean predictive performance also increases noticeably for this range. The consistent reduction in predictive uncertainty coupled with the increased sensitivity of the mean predictive behavior within the universal sample space exemplify the ability of CD to function as a proxy for the number of dominant influencing variables. Such a rapid proxy, based on non-linear dynamic concepts, appears to have considerable merit for application in current management strategies on arsenic contamination in developing countries, where both time and resources are very limited.     

Are flat‐field snow depth measurements representative? A comparison of selected index sites with areal snow depth measurements at the small catchment scale

Single or a limited number of point observations, such as from index stations, are commonly assumed to be representative for the snow cover of larger areas in many applications. This study presents a systematic investigation of the relationship between point observations and areal mean snow depths ranging from the scale of tens of metres to entire catchments. We analyse aerial snow depth information from four mountain regions in the European Alps, one in the Spanish Pyrenees and one in the Canadian Rocky Mountains, obtained from airborne laser scanning surveys. This rich data set allowed to compare point values with snow cover statistics, reflecting the real snow depth distribution of the investigation areas. We present two contrasting approaches in order to assess the representativeness of typical flat‐field snow depth measurements. In the first approach, we define potential index stations based on topographic characteristics as commonly applied for snow cover monitoring stations. The point observations of these index stations are then compared with the mean values in their vicinities. We show that most of the index stations strongly overestimate the snow depth of the catchment and of their surrounding area at distances of several hundreds of metres. Results confirm the expectation that the larger the support area, the smaller the difference to the mean of the complete catchment. The second approach was to analyse topographic characteristics of all cells with snow depths that deviated less than 10% from the catchment mean. It appears that these representative cells are rather randomly distributed and cannot be identified a priori. In summary, our results show large potential biases of index stations with respect to snow distribution and therefore also snow water equivalent. Copyright © 2014 John Wiley & Sons, Ltd.     

Degassing patterns of Tungurahua volcano (Ecuador) during the 1999–2006 eruptive period,inferred from remote spectroscopic measurements of SO2 emissions

This paper presents the results of 7 years (Aug. 1999–Oct. 2006) of SO₂ gas measurements during the ongoing eruption of Tungurahua volcano, Ecuador. From 2004 onwards, the operation of scanning spectrometers has furnished high temporal resolution measurements of SO₂ flux, enabling this dataset to be correlated with other datasets, including seismicity. The emission rate of SO₂ during this period ranges from less than 100 to 35,000 tonnes/day (t d^− 1) with a mean daily emission rate of 1458 t d^− 1 and a standard deviation of ± 2026 t d^− 1. Average daily emissions during inferred explosive phases are about 1.75 times greater than during passive degassing intervals. The total amount of sulfur emitted since 1999 is estimated as at least 1.91 Mt, mostly injected into the troposphere and carried westwards from the volcano. Our observations suggest that the rate of passive degassing at Tungurahua requires SO₂ exsolution of an andesitic magma volume that is two orders of magnitude larger than expected for the amount of erupted magma. Two possible, and not mutually exclusive, mechanisms are considered here to explain this excess degassing: gas flow through a permeable stagnant-magma-filled conduit and gas escape from convective magma overturning in the conduit. We have found that real-time gas monitoring contributes significantly to better eruption forecasting at Tungurahua, because it has provided improved understanding of underlying physical mechanisms of magma ascent and eruption.     

Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence

The cause(s) of primary outbreaks of the coral-eating crown-of-thorns starfish (Acanthaster planci) are still subject to scientific controversy. The possibility of primary outbreaks being linked to terrestrial runoff has been postulated a number of times, suggesting that enhanced nutrient supply is critical for enhanced A. planci larval development. This paper examines the evidence for such a cause, focussing particularly on the Great Barrier Reef (GBR). Nutrient discharges from rivers have increased at least four-fold in the central GBR over the last century, and concentrations of large phyto-plankton (>2 microm) of the inshore central GBR shelf in the wet season when A. planci larvae develop, is double that of other places and times. Larval development, growth and survival increase almost ten-fold with doubled concentrations of large phyto-plankton. This and other lines of evidence suggest that frequent A. planci outbreaks on the GBR may indeed be a result of increased nutrient delivery from the land.     

How many and from where? Assessing the sensitivity of exposure durations calculated from paired bedrock 14C/10Be measurements in glacial troughs

We present a sensitivity analysis of the isochron approach of Goehring et al. (2013) for paired measurements of in situ ¹⁴C/¹⁰Be from glacially sculpted bedrock surfaces. This analysis tests how sensitive the resulting exposure durations from this technique are to both the number of samples analyzed and their locations along a glacial trough transect, using a dataset from Goehring et al. (2011) as a test case. A simple equally weighted combinatorial approach was employed to (1) generate non-repetitive combinations of n subsets of samples arranged from the ten possible samples (where n < 10), and (2) estimate the exposure duration and uncertainty for each set of simulations. Results from the Goehring et al. (2011) data indicate that five samples evenly distributed along a transect parallel to the ice margin are the minimum number of samples required for this method, while eight or more samples provide an optimal combination of accuracy and precision at the 1σ level. These findings should be applicable to paired in situ ¹⁴C/¹⁰Be measurements from other polished bedrock troughs at glacial margins, but need further experimental confirmation.     

Are salinity tolerances of non-native macroinvertebrates in France an indicator of potential for their translocation in a new area?

Because of its geographic and economic position, the Western part of Europe and France is prone to biological invasions. Among the aquatic species non-native to France, a high proportion of these species are considered to be salt-tolerant. To verify this assumption, we compared the salinity tolerance of 18 native and non-native species in France in order to determine whether the introduced non-native species are more salt-tolerant than the native ones. Contrary to our expectations, our study shows that both native and non-native macroinvertebrate species from the same taxonomic group which had originated from within Eurasia had very similar salinity tolerance. Our results show that species originate from outside Eurasia (introduced by the ballast or drinking water on ships) were more salt tolerant than native from France and non-native species originated from Eurasia. Thus, derivation of the acute test of the salinity tolerance in native ranges may give good indications of their potential ability to survive during the translocation by shipping from the area of origin to another area. Our approach does provide empirical evidence for potential of non-native species to survive translocation in saline water using standard, quick and inexpensive protocols.     

How many measurements are required to construct an accurate sand budget in a large river? Insights from analyses of signal and noise

Morphological change in river channels is frequently evaluated in the context of mass balance sediment budgets. In a closed sediment budget, measurements of sediment influx and efflux are coupled with measured changes in channel topography to provide both spatial and temporal resolution, and independent estimates of the mass balance. For sediment budgets constructed over long river segments (~10² channel widths or greater) and long periods (~2 years or longer), spatial and temporal accumulation of measurement uncertainty, compounded by inadequate sampling frequency or spatial coverage, may produce indeterminate results. The degree of indeterminacy may be evaluated in the context of a signal-to-noise ratio (SNR), which is a function of the magnitude of the mass balance and the magnitudes of potential systematic uncertainties associated with measurements and incomplete sampling. We report on a closed sand budget consisting of measurements of flux and two morphological surveys for a 50-km segment of a large river over a 3-year period. Accurate reporting of the magnitude and sign of the change in sand storage was only possible by using state-of-the-art techniques with high temporal frequency and large spatial extent. Together, a sand flux and morphological mass balance revealed that sand evacuation was temporally concentrated (~100% of mass change occurred during 19% of the study period) and highly localized (70% of mass change occurred in 12% of the study segment). A SNR analysis revealed that uncertainty resulting from undersampling may approach or exceed that caused by measurement uncertainty and that daily sampling of suspended-sand concentration or repeat mapping of at least 50% of the river segment was required to determine the sand budget with SNR > 1. The approach used here to analyze sand budget uncertainty is especially applicable to other river systems with large temporal variability in sediment transport and large spatial variability in erosion and deposition. © 2018 John Wiley & Sons, Ltd.     

Are spatial patterns of soil moisture at plot scales generalisable across catchments,climates, and other characteristics? A synthesis of synoptic soil moisture across the Mid-Atlantic

The spatial variation of soil moisture over very small areas (<100 m²) can have nonlinear impacts on cycling and flux rates resulting in bias if it is not considered, but measuring this variation is difficult over extensive temporal and spatial scales. Most studies examining spatial variation of soil moisture were conducted at hillslope (0.01 km²) to multi-catchment spatial scales (1000 km²). They found the greatest variation at mid wetness levels and the smallest variation at wet and dry wetness levels forming a concave down relationship. There is growing evidence that concave down relationships formed between spatial variation of soil moisture and average soil moisture are consistent across spatial scales spanning several orders of magnitude, but more research is needed at very small, plot scales (<100 m²). The goal of this study was to characterise spatial variation in shallow soil moisture at the plot scale by relating the mean of measurements collected in a plot to the standard deviation (SD). We combined data from a previous study with thousands of new soil moisture measurements from 212 plots in eight catchments distributed across the US Mid-Atlantic Region to (1) test for a generalisable mean–SD relationship at plot scales, (2) characterise how landcover, land use, season, and hillslope position contribute to differences in mean–SD relationships, and (3) use these generalised mean–SD relationships to quantify their impacts on catchment scale nitrification and denitrification potential. Our study found that 98% of all measurements formed a generalised mean–SD relationship like those observed at hillslope and catchment spatial scales. The remaining 2% of data comprised a mean–SD relationship with greater spatial variation that originated from two riparian plots reported in a previous study. Incorporating the generalised mean–SD relationship into estimates of nitrification and denitrification potential revealed strong bias that was even greater when incorporating mean–SD observations from the two riparian plots with significantly greater spatial variation.     

Are steroids really the cause for fish feminization? A mini-review of in vitro and in vivo guided TIEs

Feminization of fish has been reported throughout the world in freshwater and marine systems. While the population impacts are conflictive, enough negative effects warrant additional research into causation. In order to ascertain the identities of specific feminizing agents, variants of toxicity identification evaluations (TIEs) have been employed. The majority of these evaluations have utilized in vitro estrogen receptor-based cell-lines to identify chromatographic fractions that possess biological activity from predominately wastewater derived from municipal treatment facilities and have concluded that synthetic and natural estrogens are the primary cause for feminization of fish. This paper will focus on three aquatic systems impacted by wastewater originating from purely domestic, and industrial/domestic secondary treatment systems. Wastewater and sediment extracts were evaluated by in vitro and in vivo biological responses in a TIE fractionation design. While in vitro responses tended to mirror in vivo responses in purely domestic wastewater systems, in vitro responses tended to severely underestimate in vivo estrogenic activity when normalized to estradiol equivalents in more complex systems. TIE fractionation schemes using in vivo biological responses failed to indicate any relationship to steroids in either wastewater or sediment extractions. These data consistently support the view that mechanisms other than direct ER binding and activation by toxicants may be important in the feminization of fish particularly residing in habitats that receive complex wastewater or agricultural effluents.     

Are steroids really the cause for fish feminization? A mini-review of in vitro and in vivo guided TIEs

Feminization of fish has been reported throughout the world in freshwater and marine systems. While the population impacts are conflictive, enough negative effects warrant additional research into causation. In order to ascertain the identities of specific feminizing agents, variants of toxicity identification evaluations (TIEs) have been employed. The majority of these evaluations have utilized in vitro estrogen receptor-based cell-lines to identify chromatographic fractions that possess biological activity from predominately wastewater derived from municipal treatment facilities and have concluded that synthetic and natural estrogens are the primary cause for feminization of fish. This paper will focus on three aquatic systems impacted by wastewater originating from purely domestic, and industrial/domestic secondary treatment systems. Wastewater and sediment extracts were evaluated by in vitro and in vivo biological responses in a TIE fractionation design. While in vitro responses tended to mirror in vivo responses in purely domestic wastewater systems, in vitro responses tended to severely underestimate in vivo estrogenic activity when normalized to estradiol equivalents in more complex systems. TIE fractionation schemes using in vivo biological responses failed to indicate any relationship to steroids in either wastewater or sediment extractions. These data consistently support the view that mechanisms other than direct ER binding and activation by toxicants may be important in the feminization of fish particularly residing in habitats that receive complex wastewater or agricultural effluents.     

Can Nassarius reticulatus be used as a bioindicator for Hg contamination? Results from a longitudinal study of the Portuguese coastline

The focus of this work is to explore the use of the netted whelk, Nassarius reticulatus (L.), as an indicator of mercury (Hg) contamination, by assessing the concentration of Hg in the sediments and in the whelk along the entire Portuguese coast. Total Hg concentrations ranged from below the detection limit (0.01 ng absolute mercury) up to 0.87 mg kg(-1) dry weight (dwt) in sediments and between 0.06 and 1.02 mg kg(-1) (dwt) for organisms, with no significant differences between males and females. Although organic mercury was not detected in the sediments, it represented, on average, 52% of the total Hg in the whelk tissues, and as high as 88% in some cases, suggesting mercury accumulation from dietary intake. Significant negative correlations were found between the total Hg concentrations in the sediments and the log(10) of Hg concentrations in whelk tissues males (r=-0.64; P<0.01) and females (r=-0.52; P<0.01) indicating that the species is a poor indicator of Hg contamination. Nevertheless, since the highest concentrations of organic mercury in the whelk tissues were found in the least contaminated areas, this species must be highly relevant in the trophic web, namely on the possible biomagnification of mercury. The high dietary mercury accumulation from feeding on carrion and the low bioavailability of mercury to whelks in estuarine sediments may be the basis of the mercury accumulation pattern in N. reticulatus.     

The hydrogen and oxygen isotopic compositions of hydroxyl in clay mineral from a weathering profile: New proxies for paleo-climate change?

Recent studies suggest that the hydrogen and oxygen isotopic compositions of clay minerals can indicate paleoclimate.Here,we report mineralogy and stable isotopic records(d D and δ~(18)O_(OH))of a weathering profile located in the Fujian Province,aiming to validate whether hydroxyl stable isotopes can indicate paleo-precipitation and paleo-temperature.Our results indicate that the d D and δ~(18)O_(OH)changes in the kaolinite hydroxyl of the weathering profile are basically determined by the isotopic composition of paleo-meteoric water and paleotemperature,respectively.Nevertheless,whether the d D and δ~(18)O_(OH)of kaolinite can quantitatively indicate paleo-precipitation and paleo-temperature needs to be verified further,and especially,the structural oxygen isotopic composition that is the essential element for the kaolinite formation temperature calculation has to be constrained in future work.     

Significance of an In Vivo Genotoxicity Test for Surface Waters Is Increased when the Physiological Characteristics of the Test Organism (Bivalvia: Mollusca) Are Taken into Account?

The alkaline filter elution assay using the gills of the freshwater clam species Corbicula fluminea detects breaks in single‐stranded DNA and is thus a good method for determining the genotoxic potential of surface waters. In attempting to standardize the procedure, a wide range of factors which could have an influence on the uptake of genotoxic substances by the exposed clams were studied. The most important parameters of the static exposure in relation to the rate of filtration by the animals turned out to be the temperature, the volume of the water, and the exposure time. Differences in body size and in the amount of suspended particles in surface waters did not play a significant role. The results demonstrate that the in vivo test system can be quite sensitive and its results reproducible when the relevant species‐specific characteristics of the test organisms are brought into consideration, even if the test organism belongs to a biologically more advanced group. A clear dose‐response relationship to the reference substances 4‐nitroquinoline‐1‐oxide (NQO) and N‐methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG) can be observed even after a short exposure time of between four and twenty hours. No genotoxic effects were observed when using this method on surface waters from the area of Cologne (including water from the Rhine River and within the protection zone 2 of the Cologne waterworks).     

Are artificial neural network techniques relevant for the estimation of longitudinal dispersion coefficient in rivers? / Les techniques de réseaux de neurones artificiels sont-elles pertinentes pour estimer le coefficient de dispersion longitudinale en rivières?

Abstract

Abstract Accurate application of the longitudinal dispersion model requires that specially designed experimental studies are performed in the river reach under consideration. Such studies are usually very expensive, so in order to quantify the longitudinal dispersion coefficient, as an alternative approach, various researchers have proposed numerous empirical formulae based on hydraulic and morphometric characteristics. The results are presented of the application of artificial neural networks as a parameter estimation technique. Five different cases were considered with the network trained for different arrangements of input nodes, such as channel depth, channel width, cross-sectionally averaged water velocity, shear velocity and sinuosity index. In the case where the sinuosity index is included as an input node, the results turned out to be better than those presented by other authors.