The influence of hydrogeological properties,seawater intrusion and refreshening on the quality of groundwater used for irrigation in an agricultural coastal plain in North Sardinia,Italy     

Daniele Pittalis  Alberto Carletti  Giorgio Ghiglieri  Fulvio Celico 《Environmental Earth Sciences》2016,75(11):963

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The effects of discharge and slope on hyporheic flow in step‐pool morphologies          下载免费PDF全文

Marwan A. Hassan  Daniele Tonina  Roger D. Beckie  Matthew Kinnear 《水文研究》2015,29(3):419-433

This paper focuses on surface–subsurface water exchange in a steep coarse‐bedded stream with a step‐pool morphology. We use both flume experiments and numerical modelling to investigate the influence of stream discharge, channel slope and sediment hydraulic conductivity on hyporheic exchange. The model step‐pool reach, whose topography is scaled from a natural river, consists of three step‐pool units with 0.1‐m step heights, discharges ranging between base and over‐bankfull flows (scaled values of 0.3–4.5 l/s) and slopes of 4% and 8%. Results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges. In contrast to findings in a pool‐riffle morphology, those in this study show that steep slopes cause deeper surface–subsurface exchanges than gentle slopes. Numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity. These experiments and numerical simulations emphasize the importance of topography, sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange. Our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool‐riffle bed forms. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Early to mid‐Holocene climate change at Lago dell'Accesa (central Italy): climate signal or anthropogenic bias?     

Walter Finsinger  Daniele Colombaroli  Jacques‐Louis De Beaulieu  Verushka Valsecchi  Boris Vannière  Elisa Vescovi  Emmanuel Chapron  André F. Lotter  Michel Magny  Willy Tinner 《第四纪科学杂志》2010,25(8):1239-1247

Despite the high potential of pollen records for climate reconstruction, pollen–climate relationships may be biased due to past and present human activities on the landscape. We use (i) transfer functions based on modern pollen–climate relationships to infer seasonal temperature and summer precipitation for the period 11 500–4500 cal. a BP and (ii) lake‐level change records based on different sedimentary proxies in multiple cores that are mainly indicative for summer hydrology at Lago dell'Accesa (central Italy). Quantitative reconstructions indicate lowest summer precipitation during two phases (8500–7700 cal. a BP and after 6000 cal. a BP) and a gradual winter temperature increase from 11 500 to ca. 8000 cal. a BP. Lowest summer precipitation was reconstructed during these phases characterised by vegetation shifts from open forests dominated by summergreen oaks (Quercus) to forests dominated by evergreen oaks (Quercus ilex), which are at present most abundant where summer drought is stronger. Similarly, the lake‐level record indicates two long‐lasting low summer precipitation phases (8800–7700 and 6400–4400 cal. a BP) that were interrupted by short‐term high summer precipitation events. Based on the broad agreement between the pollen‐inferred summer precipitation and the low‐frequency lake‐level changes, we suggest that the duration of the high summer precipitation events may have been too short to maintain drought‐sensitive trees, which may have been affected by high mortality rates when summer dry conditions returned. Although past and modern pollen–climate relationships may very likely have been affected by human activities since the Neolithic (i.e. when exploitation of the landscape started), we reject the hypothesis of a significant anthropogenic bias in the pollen‐based climate reconstruction. In addition, we suggest that pollen‐based and lake‐level reconstructions may have different inherent abilities of capturing high‐ and low‐frequency precipitation signals. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Analysis of raw soils and their re-suspended PM10 fractions: Characterisation of source profiles and enrichment factors     

D. Cesari  D. Contini  A. Genga  M. Siciliano  C. Elefante  F. Baglivi  L. Daniele 《Applied Geochemistry》2012

In this work, the inorganic chemical profiles of soil samples collected at different sites in the Salentum peninsula (Italy, Apulia region) are discussed. The samples were re-suspended in the laboratory, for PM10 sampling, using a ventilated wooden chamber and were then chemically analysed measuring the abundances of 17 elements. Different land use categories of soils (olive grove, arable land, vineyards, sand, and urban dust) were included in the 50 samples analysed: 45 collected in background areas and five collected in the urban area of Lecce. The objectives were to compare the chemical profiles of raw soil and re-suspended PM10 for different crustal sources and to estimate the potential improvements in the calculation of the enrichment factors of atmospheric PM10. The variability of elemental abundances in samples of the same category of soil collected in different zones was of the same order of magnitude as the differences observed between the various categories of soil. This allows the calculation of a weighted average composition of soil and urban dust and the corresponding weighted average composition of re-suspended PM10. In re-suspended PM10 from average background soil, all of the elements except Ca, Na, K and V have larger abundances with respect to raw soil. In urban dust, this is limited to Ca, V and Mg. The crustal enrichment factors (EFs) of atmospheric PM10 were evaluated by considering different reference elements and different reference tables. Results indicated that it is possible to apply a two-threshold (S₁ and S₂) scheme for the interpretation of EF, with thresholds derived from uncertainty in soil categories and from the choice of the reference element. A specific element is likely of crustal origin if EF < S₁ and likely of anthropogenic origin if EF > S₂. Between the two thresholds, the element can be considered of mixed origin. The thresholds vary according to the geological composition used in the evaluation of EF. If the average composition of local re-suspended soils is used, the thresholds are S₁ = 2 and S₂ = 4. If raw soil is used, the thresholds become S₁ = 5 and S₂ = 10. If the average upper-crust composition from literature data is used, the thresholds further increase to S₁ = 10 and S₂ = 20.  相似文献   

Identification of a Holocene aquifer–lagoon system using hydrogeochemical data     

F. Sola  A. Vallejos  L. Daniele  A. Pulido-Bosch 《Quaternary Research》2014

The hydrogeochemical characteristics of the Cabo de Gata coastal aquifer (southeastern Spain) were studied in an attempt to explain the anomalous salinity of its groundwater. This detritic aquifer is characterised by the presence of waters with highly contrasting salinities; in some cases the salinity exceeds that of seawater. Multivariate analysis of water samples indicates two groups of water (G1 and G2). Group G1 is represented in the upper part of the aquifer, where the proportion of seawater varies between 10 and 60%, whilst G2 waters, taken from the lower part of the aquifer, contain 60−70% seawater. In addition, hydrogeochemical modelling was applied, which reveals that the waters have been subject to evaporation between 25 and 35%. There was a good agreement between the modelled results and the observed water chemistry. This evaporation would have occurred during the Holocene, in a coastal lagoon environment; the resulting brines would have infiltrated into the aquifer and, due to their greater density, sunk towards the impermeable base. The characteristics of this water enabled us to reconstruct the interactions that must have occurred between the coastal aquifer and the lagoon, and to identify the environmental conditions that prevailed in the study area during the Middle Holocene.  相似文献   

Experimental analysis of different software packages for orientation and digital surface modelling from UAV images   总被引：1，自引：0，他引：1  

Giovanna Sona  Livio Pinto  Diana Pagliari  Daniele Passoni  Rossana Gini 《Earth Science Informatics》2014,7(2):97-107

The use of UAVs finds application in a variety of fields, among which are the small scale surveys for environmental protection application. In this frame some experimental tests were carried out at Politecnico di Milano to assess metric accuracies of images acquired by UAVs and derived photogrammetric products. A block of 5 strips and 49 photos was taken by fixed wing system SenseFly, carrying a camera Canon Ixus 220HS on a rural area included in an Italian Park. Images are processed through bundle adjustment, automatic DEM extraction and orthoimages production steps with several software packages, with the aim to evaluate their characteristics, capabilities and weaknesses. The software packages tested were Erdas-LPS, EyeDEA (University of Parma), Agisoft Photoscan, Pix4UAV, PhotoModeler Scanner. For the georeferencing of the block 16 pre-signalized ground control points were surveyed in the area through GPS (NRTK survey). Comparison of results is given in terms of differences among orientation parameters and their accuracies. Moreover, comparisons among different digital surface models are evaluated. Furthermore, exterior orientation parameters, image points and ground points coordinates, obtained by the various software packages, were used as initial values in a comparative adjustment made by scientific in-house software. Paper confirms that computer vision software are faster in computation and, even if their main goal is not to pursue high accuracy in points coordinates determination, they seems to produce results comparable to those obtainable with standard photogrammetric approach. Agisoft Photoscan seems in this case to yield the best results in terms of quality of photogrammetric products.  相似文献   

Validation of theoretical footprint models using experimental measurements of turbulent fluxes over maize fields in Po Valley   总被引：1，自引：0，他引：1  

Daniele Masseroni  Chiara Corbari  Marco Mancini 《Environmental Earth Sciences》2014,72(4):1213-1225

Representative source area of turbulent fluxes measured by eddy covariance stations is an important issue which has not yet been fully investigated. In particular, the validation of the analytical footprint models is generally based on the comparison with Lagrangian model predictions, while experimental results are not largely diffused in literature. In this work, spatial distribution of carbon dioxide, latent and sensible heat fluxes across two different maize fields in Po Valley, is used to validate two theoretical footprint models. Experiments are performed in two totally different scenarios at bare and vegetated soils using two eddy covariance systems: one fixed station which is located about in the middle of the field and a mobile station which is placed at various distances from the field edge to investigate the horizontal variation of the vertical scalar fluxes. The first objective of this work is to provide detailed information about the spatial distribution of turbulent fluxes across Po Valley characteristic fields at bare and vegetated soils, highlighting peculiarities and uniqueness. The second objective consists in the comparison between mobile measurements of carbon dioxide, latent and sensible heat fluxes and the predictions of two analytical footprint models widely used in literature. Contemporaneously, the latter objective will permit to understand what is the best footprint model which, under typical Po Valley atmospheric turbulent conditions, describes a representative source area compatible with the field dimensions and the turbulent flux distributions. The results show that both models are in good agreement with experimental measurements. The results also show that the spatial distribution of turbulent fluxes is strongly influenced by the presence of vegetation in the field. Moreover, the representative source area is different for different scalar fluxes. Another result is about 10:1 fetch-to-height obtained for both field situations.  相似文献   

Combining physical-based models and satellite images for the spatio-temporal assessment of soil infiltration capacity   总被引：1，自引：1，他引：0  

Daniele Pedretti  Daniel Fern��ndez-Garcia  Xavier Sanchez-Vila  Marco Barahona-Palomo  Diogo Bolster 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1065-1075

The performance of managed artificial recharge (MAR) facilities by means of surface ponds (SP) is controlled by the temporal evolution of the global infiltration capacity I _c of topsoils. Cost-effective maintenance operations that aim to maintain controlled infiltration values during the activity of the SP require the full knowledge of the spatio-temporal variability of I _c . This task is deemed uncertain. The natural reduction in time of I _c depends on complex physical, biological and chemical reactions that clog the soil pores and has been observed to decay exponentially to an asymptotic non-zero value. Moreover, the relative influence of single clogging processes depend on some initial parameters of the soil, such as the initial infiltration capacity (I _c,0). This property is also uncertain, as aquifers are typically heterogeneous and scarcely characterized in practical situations. We suggest a method to obtain maps of I _c using a geostatistical approach, which is suitable to be extended to engineering risk assessment concerning management of SP facilities. We propose to combine geostatistical inference and a temporally-lumped physical model to reproduce non-uniform clogging in topsoils of a SP, using field campaigns of local and large scale tests and additionally by means of satellite images as secondary information. We then postulate a power-law relationship between the parameter of the exponential law, λ, and I _c,0. It is found that calibrating the two parameters of the power law model it is possible to fit the temporal evolution of total infiltration rate at the pond scale in a MAR test facility. The results can be used to design appropriate measures to selectively limit clogging during operation, extending the life of the infiltration pond.  相似文献   

Optical satellite imagery for quantifying spatio-temporal dimension of physical exposure in disaster risk assessments     

Daniele Ehrlich  Patrizia Tenerelli 《Natural Hazards》2013,68(3):1271-1289

This work addresses the use of remote sensing imagery to quantify the built environment and its spatial and temporal changes. It identifies building footprint map, building location map and built-up area map as information products that can be used to quantify physical exposure, one of the variables required in disaster risk assessments. The paper also reviews urban land use maps and urban classes in land cover maps as potential source for deriving exposure information. The paper focuses on the latest generation of satellite-borne remote sensing imaging systems that deliver high-resolution optical imagery able to resolve buildings and other three-dimensional man-made constructions. This work also reviews the semantics, the spatial unit used to define physical exposure, image processing procedures and change techniques.  相似文献   

Seasonal snow cover decreases young water fractions in high Alpine catchments     

Natalie Ceperley  Giulia Zuecco  Harsh Beria  Luca Carturan  Anthony Michelon  Daniele Penna  Joshua Larsen  Bettina Schaefli 《水文研究》2020,34(25):4794-4813

Estimation of young water fractions (F_yw), defined as the fraction of water in a stream younger than approximately 2–3 months, provides key information for water resource management in catchments where runoff is dominated by snowmelt. Knowing the average dependence of summer flow on winter precipitation is an essential context for comparing regional drought severity and provides the hydrological template for downstream water users and ecosystems. However, F_yw estimation based on seasonal signals of stable isotopes of oxygen and hydrogen has not yet explicitly addressed how to parsimoniously include the seasonal shift of water input from snow. Using experimental data from three high-elevation, Alpine catchments (one dominated by glacier and two by snow), we propose a framework to explicitly include the delays induced by snow storage into estimates of F_yw. Scrutinizing the key methodological choices when estimating F_yw from isotope data, we find that the methods used to construct precipitation input signals from sparse isotope samples can significantly impact F_yw. Given this sensitivity, our revised procedure estimates a distribution of F_yw values that incorporates a wide range of possible methodological choices and their uncertainties; it furthermore compares the commonly used amplitude ratio approach to a direct convolution approach, which circumvents the assumption that the isotopic signals have a sine curve shape, an assumption that is generally violated in snow-dominated environments. Our new estimates confirm that high-elevation Alpine catchments have low F_yw values, spanning from 8 to 11%. Such low values have previously been interpreted as the impact of seasonal snow storage alone, but our comparison of different F_yw estimation methods suggests that these low F_yw values result from a combination of both snow cover effects and longer storage in the subsurface. In contrast, in the highest elevation, glacier dominated catchment, F_yw is 3–4 times greater compared to the other two catchments, due to the lower storage and faster drainage processes. A future challenge, capturing spatio-temporal snowmelt isotope signals during winter baseflow and the snowmelt period, remains to improve constraints on the F_yw estimation technique.  相似文献