Nunzio Romano

Prediction of soil water retention using soil physical data and terrain attributes

Characterization of soil hydraulic behavior at large scales using traditional methods is time-consuming and very costly. Efficient and cheap means of providing hydrological models with such information are procedures based on pedotransfer functions (PTFs) that estimate soil hydraulic parameters from easily measurable or already available soil physical data. Major objectives of this study are to compare the prediction performance of some published PTFs and to improve their predictive capability by accounting for certain landscape variables, such as slope, aspect, and wetness index, for example. This additional information can be easily extracted from a digital elevation model of the area under study. While topographic attributes have shown potential for mapping soil properties over a region with higher precision and simplifying estimation of some model parameters, the challenge is also to examine whether, and to what extent, ancillary data of this kind can specifically contribute to improve the predictions of soil hydraulic characteristics. Since the most recent distributed hydrological models rely even more on an accurate representation of landscape features, improving PTFs with the inclusion of topographic variables is in line with this tendency. Statistical indices of goodness-of-fit are calculated to evaluate the effectiveness of the proposed methodology. It is shown, for example, that systematic biases in water retention predictions from an original PTF can be conveniently corrected by adding some primary or compound terrain attributes. The results confirm the role of terrain variables in assessing the spatial patterns of soil hydraulic characteristics.

Numerical analysis of one-dimensional unsaturated flow in layered soils

Abstract The paper deals with numerical solutions to the Richards equation to simulate one-dimensional flow processes in the unsaturated zone of layered soil profiles. The equation is expressed in the pressure-based form and a finite-difference algorithm is developed for accurately estimating the values of the hydraulic conductivity between two neighboring nodes positioned in different soil layers, often referred to as the interlayer hydraulic conductivity. The algorithm is based upon flux conservation and continuity of pressure potential at the interface between two consecutive layers, and does not add significantly to simulation run time. The validity of the model is established for a number of test problems by comparing numerical results with the analytical solutions developed by Srivastava and Yeh29 which hold for vertical infiltration towards the water table in a two-layer soil profile. The results show a significant reduction in relative mass balance errors when using the proposed model. Some specific insights into its numerical performance are also gained by comparisons with a numerical model in which the more common geometric averaging operator acts on the interlayer conductivities.

Determining soil hydraulic functions from evaporation experiments by a parameter estimation Approach: Experimental verifications and numerical studies

A parameter estimation method is developed for the determination of unsaturated soil hydraulic properties from evaporation experiments under laboratory conditions. Variables used in the inversion procedure are soil water pressure heads at various positions and total soil weights, both measured as a function of time during the experiment. Unknown parameters of different analytical expressions used to describe the soil hydraulic properties are estimated by coupling a finite difference solution of the Richards equation with a nonlinear optimization problem. This problem is formulated by minimizing the deviations between the numerical solution of the transient flow process and the real system response measured during the experiment. Minimization of the objective function is performed using a version of the Levenberg-Marquardts method; the procedure also provides information about the uncertainty in parameter estimates. The performance of the selected parametric relationships is evaluated, and the applicability and accuracy of the proposed inverse method are shown by comparing estimated water retention and hydraulic conductivity functions with experimental results obtained via the instantaneous profile method. Parameter sensitivity analyses and stability of the inverse solutions are discussed with reference to the originally designed evaporation experiment and to an evaporation method that is developed with a view to reducing experimental efforts. Further insights into the properties of existence and uniqueness of inverse solutions are gained by examining contour plots of the objective functions under varying experimental conditions. The results confirm the reliability and flexibility of the proposed method and suggest that the evaporation flux imposed at the upper soil surface may determine the well posedness of the optimization problem.

Use of an inverse method and geostatistics to estimate soil hydraulic conductivity for spatial variability analysis

Abstract A field method for determining the soil hydraulic properties using a parameter estimation technique is presented. Input data for the inverse problem are soil-water potentials and soil-water contents measured at different soil depths and different times during a field transient drainage experiment. For the water retention function the parametric relation suggested by Van Genuchten was adopted. For the hydraulic conductivity function the relation proposed by Van Genuchten and the exponential relation were adopted. With the proposed method soil hydraulic properties along a transect of a volcanic Vesuvian soil were determined using as boundary condition the unit gradient of total potential at the bottom of the soil profile. Geostatistics were used to describe the spatial variability of hydraulic conductivity characteristics of the soil here considered. Finally, results obtained using this method were compared with those of the simplified method suggested by Sisson and Van Genuchten based on a unit gradient water flow model.

Spatial structure of PTF estimates

Publisher Summary This chapter focuses on soil-hydraulic characterization at relatively large spatial scale via pedotransfer functions (PTFs). The chapter describes the methods to determine the soil hydraulic properties for field- and large-scale modeling, which are more practical and also prove to be effective in detecting the spatial correlation structure of these properties. The chapter proposes some predictive methods that estimate the soil hydraulic conductivity characteristic from the measured water retention. There are various environmental and management problems that require the characterization of unsaturated soil hydraulic behavior with a trade-off between reasonable burdens and good accuracy and precision. Through the analysis of the results from differently developed PTFs, the chapter highlights the potential offered by this technique together with some limitations in assessing an average portrayal of soil hydraulic behavior at a field scale. An indirect method for soil hydraulic characterization is successful if it enables the relevant spatial patterns to be identified adequately. The chapter describes some general statements on quantitatively soil spatial variability and explains the way a spatial structure is determined using hydraulic data estimated from existing PTFs.

The role of terrain analysis in using and developing pedotransfer functions

Publisher Summary This chapter discusses the way terrain features can be employed to efficiently parameterize the soil hydraulic behavior in land-surface models via pedotransfer functions (PTFs) and to improve the prediction performance of PTFs at various scales. The problems of better assessing the spatial variability of soil hydraulic properties and improving in the local estimation of these properties can be translated into two main issues: more efficient interpolations among available input predictor variables and the possibility to locally calibrate a PTF in a cost-effective way. Therefore, the chapter presents a framework in which terrain attributes can help resolve both these issues when a PTF is employed to estimate soil hydraulic properties. The chapter illustrates the techniques developed for computing terrain attributes and discusses the issue of interpolating spatially sparse data of soil properties using terrain attributes as ancillary data. The chapter also discusses the opportunities in the improvement of predictive capabilities of PTFs via incorporation of topographic information.

Use of a flux‐based field capacity criterion to identify effective hydraulic parameters of layered soil profiles subjected to synthetic drainage experiments

This study explores the feasibility of identifying the effective soil hydraulic parameterization of a layered soil profile by using a conventional unsteady drainage experiment leading to field capacity. The flux-based field capacity criterion is attained by subjecting the soil profile to a synthetic drainage process implemented numerically in the Soil-Water-Atmosphere-Plant (SWAP) model. The effective hydraulic parameterization is associated to either aggregated or equivalent parameters, the former being determined by the geometrical scaling theory while the latter is obtained through the inverse modeling approach. Outcomes from both these methods depend on information that is sometimes difficult to retrieve at local scale and rather challenging or virtually impossible at larger scales. The only knowledge of topsoil hydraulic properties, for example, as retrieved by a near-surface field campaign or a data assimilation technique, is often exploited as a proxy to determine effective soil hydraulic parameterization at the largest spatial scales. Comparisons of the effective soil hydraulic characterization provided by these three methods are conducted by discussing the implications for their use and accounting for the trade-offs between required input information and model output reliability. To better highlight the epistemic errors associated to the different effective soil hydraulic properties and to provide some more practical guidance, the layered soil profiles are then grouped by using the FAO textural classes. For the moderately heterogeneous soil profiles available, all three approaches guarantee a general good predictability of the actual field capacity values and provide adequate identification of the effective hydraulic parameters. Conversely, worse performances are encountered for the highly variable vertical heterogeneity, especially when resorting to the “topsoil-only” information. In general, the best performances are guaranteed by the equivalent parameters, which might be considered a reference for comparisons with other techniques. As might be expected, the information content of the soil hydraulic properties pertaining only to the uppermost soil horizon is rather inefficient and also not capable to map out the hydrologic behavior of the real vertical soil heterogeneity since the drainage process is significantly affected by profile layering in almost all cases.

Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale

Abstract Mapping soil hydraulic parameters with traditional scaling methods that use laboratory-determined hydraulic characteristics (the LAB method) is not always feasible as it involves expensive, time-consuming and sophisticated measurements on soil samples collected in several locations of the study area. An alternative scaling method (the AP method) has been recently proposed to indirectly retrieve the soil hydraulic properties following the Arya-Paris physico-empirical pedotransfer function, which makes use of particle-size distribution and bulk density values. In this synthetic study we verify the performance of the AP method from a functional perspective, by evaluating the differences in the simulated soil water budget through a Monte Carlo approach. Notwithstanding that the AP method can provide soil hydraulic property patterns with faster experimental procedures and minor costs, we observe significant bias in the predicted spatially-averaged soil water budget due to a poor parametric calibration of the AP method and an imprecise identification of the spatial correlation structure of the AP-estimated scaling factors. Citation Nasta, P., Romano, N., and Chirico, G.B., 2013. Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale. Hydrological Sciences Journal, 58 (5), 1059–1071.

An Integrated Approach for the Environmental Characterization of a Wide Potentially Contaminated Area in Southern Italy

This paper deals with the environmental characterization of a large and densely populated area, with a poor reputation for contamination, considering the contribution of environmental features (air, soil, soil hydraulic and groundwater) and the potential effects on human health. The use of Geographic Information System (GIS) has made possible a georeferenced inventory and, by overlaying environmental information, an operational synthesis of comprehensive environmental conditions. The cumulative effects on environmental features were evaluated, taking into account superposition effects, by means of the Spatial MultiCriteria Decision Analysis (S-MCDA). The application of the S-MCDA for converging the combination of heterogeneous factors, related to soil, land and water, deeply studied by heterogeneous groups of experts, constitutes the novelty of the paper. The results confirmed an overall higher potential of exposure to contaminants in the environment and higher mortality rates in the study area for some tumours, but hospital admissions for tumours were generally similar to the regional trend. Besides, mortality data may be strictly dependent on the poor socioeconomic conditions, quality of therapy and a lack of welfare in the area relative to the rest of Italy. Finally, as regards the possible relationship between presence of contaminants in the environment and health conditions of the population no definite conclusions can be drawn, although the present study encourages the use of the new proposed methods, that increase the possibilities for studying the combined effect of more environmental factors.

Elemental Composition of Natural Nanoparticles and Fine Colloids in European Forest Stream Waters and Their Role as Phosphorus Carriers

Biogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1-100 nm) and fine colloids (100-450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (~1-20 nm, >20-60 nm, and >60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2 ± 5% (Si) and 53 ± 21% (Fe; mean ± SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al, and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P, and Ca were not. The fine colloidal fractions >60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP <60 nm changed from North to South Europe from Fe- to Ca-dominated particles, along with associated changes in acidity, forest type, and dominant lithology. (Less)