A Simple Analytical Formula for the Leakage Flux Through a Perforated Aquitard

In this methods note, we present a simple analytical formula to quantify the steady‐state leakage flux (Q) over a perforated aquitard. The flux depends on the aquitard thickness (D), the radius of the perforation (R), the hydraulic conductivity of the material inside the perforation (k_fill), the conductivities of the overlying and underlying aquifers (k₁ and k₂, respectively), and the head difference between the two aquifers (ΔH): This equation assumes an aquitard separating two homogeneous and infinite aquifers (R ? aquifer thickness) in which radial flow to and from the perforation occurs, with no other recharge or discharge boundaries near the perforation. The flux through a perforation in a hypothetical case study with D = 10 m, k₁ = 10 m/d, k₂ = 20 m/d, R = 0.072 m, and ΔH = 1 m ranges between less than 1 mL/d if the hole is backfilled with bentonite (k_fill = 10^?4 m/d), to several liters per day if the perforation is backfilled with sand from the overlying aquifer (k_fill = 10 m/d), to several m³/d if the perforation forms an open conduit (k_fill = 10⁵ m/d). The leakage fluxes calculated with this model agree well with those calculated using a numerical model (MODFLOW).     

A textural analysis of Wellington Harbour sediments

Grain‐size and carbonate analyses have been carried out on bottom sediment samples of Wellington Harbour. From grain‐size parameters it was possible to establish a number of facies types and to outline sediment sources and directions of transport.     

Predicting reach‐specific properties of fluvial terraces to guide future fieldwork. A case study for the Late Quaternary River Allier (France) with the FLUVER2 model

Numerical models have not yet systematically been used to predict properties of fluvial terrace records in order to guide fieldwork and sampling. This paper explores the potential of the longitudinal profile model FLUVER2 to predict testable field properties of the relatively well‐studied, Late Quaternary Allier system in France. For the Allier terraces an overlapping ¹⁴C and U‐series chronology as well as a record of ¹⁰Be erosion rates exist. The FLUVER2 modelling exercise is focused on the last 50 ka of the upper Allier reach because for this location and period the constraints of the available dating techniques are tightest. A systematic calibration based on terrace occurrence and thicknesses was done using three internal parameters related to (1) the sediment erodibility; (2) the sediment transport distance; and (3) the sediment supply derived from the surrounding landscape. As external model inputs, the best available, reconstructed, tectonic, climatic and base‐level data were used. Calibrated model outputs demonstrate a plausible match with the existing fluvial record. Validation of model output was done by comparing the modelled and measured timing of aggradation and incision phases for the three locations. The modelled range of landscape erosion rates showed a reasonably good match with existing erosion rate estimates derived from ¹⁰Be measurements of fluvial sands. The quasi‐validated model simulation was subsequently used to make new testable predictions about the timing and location of aggradation and erosion phases for three locations along the Allier river. The validated simulations predict that along the Allier, reach‐specific dynamics of incision and aggradation, related to the variations in sediment supply by major tributaries, cause relevant differences in the local fluvial terrace stratigraphy. Copyright © 2016 John Wiley & Sons, Ltd.     

The contribution of organic and mineral colloidal nanoparticles to element transport in a podzol soil

The aim of this work is to analyze the size-distribution and composition of nanoparticles in a water-extract of a podzol B horizon. AsFlowFFF coupled to ICP–MS and a UV/VIS detector was used for particle fractionation and simultaneous measurement of the composition of the nanoparticles. Detected nanoparticles were organic and mineral particles; the mineral particles were dominated by clay and Fe-(hydr)oxides. Both organic- and inorganic particles contributed to the mobility of Fe, Al, trace metals and P. For Zn, Pb and P respectively 73%, 92% and 72% of the colloidal concentrations were associated with clay minerals. The large contribution of clay particles to the mobility of trace metals and P can be partly explained by the high amount of dispersed clay due to drying, sieving and rewetting of the soil. Inorganic nanoparticles can contribute significantly to the mobility of metals and P in soils.     

Identification of potential sites for aquifer storage and recovery (ASR) in coastal areas using ASR performance estimation methods

Performance of freshwater aquifer storage and recovery (ASR) systems in brackish or saline aquifers is negatively affected by lateral flow, density effects, and/or dispersive mixing, causing ambient groundwater to enter ASR wells during recovery. Two recently published ASR performance estimation methods are applied in a Dutch coastal area, characterized by brackish-to-saline groundwater and locally high lateral-flow velocities. ASR performance of existing systems in the study area show good agreement with the predicted performance using the two methods, provided that local vertical anisotropy ratios are limited (<3). Deviations between actual and predicted ASR performance may originate from simplifications in the conceptual model and uncertainties in the hydrogeological and hydrochemical input. As the estimation methods prove suitable to predict ASR performance, feasibility maps are generated for different scales of ASR to identify favorable ASR sites. Successful small-to-medium-scale ASR varies spatially in the study area, emphasizing the relevance of reliable a priori spatial mapping.     

Quartz fabrics and recumbent folds in the Sierra de Los Filabres (SE-Spain)

Abstract

An important generation of recumbent folds can be recognized in the Nevado-Filabride nappe complex in the Sierra de los Filabres in SE Spain.

Folding post-dates an initial phase of flattening and is prior to the main phase of non-coaxial deformation and thrusting in the upper part of the complex, involved in a large-scale movement zone with dominant sense of shear to the northwest.

Axial planes and axes of these folds are aligned sub-parallel to the plastic flow plane in quartz and the shear direction respectively. Relict quartz fabrics can be found however, which strongly suggest that some fold axes originated in this position and did not rotate towards parallelism with the shear direction. This apparently contradicts the generally accepted model of development of folds in mylonite zones.

The redistribution of linear structures of the older flattening fase over the folds, confirms that the original orientation of fold axes was close to the present and indicates that an important component of flexural slip was involved in fold formation.     

Using a groundwater quality negotiation support system to change land-use management near a drinking-water abstraction in the Netherlands

A negotiation support system (NSS) was developed to solve groundwater conflicts that arose during land-use management. It was set up in cooperation with the stakeholders involved to provide information on the impact of land use, e.g., agriculture, nature (forested areas), recreation, and urban areas, on the quality of both infiltrating and abstracted groundwater. This NSS combined simulation programs that calculate (1) the concentrations of nitrate in shallow groundwater for each land-use area and (2) the transport of nitrate in the groundwater-saturated zone. The user interface of the NSS enabled scenario analyses. The NSS was validated at a drinking-water abstraction near Holten (the Netherlands) using a spatial planning process aimed at sustainable land-use and groundwater-resource management. Two land-use scenarios were considered: a base scenario reflecting the autonomous development and an adapted land-use scenario. The calculated results for shallow groundwater provided an explicit spatial overview of the impact of historical land use and N application on the quality of abstracted groundwater as well as insight into the impact of changes in land use and N application. Visualization of the conflicting interests of agriculture and the drinking-water abstraction helped all stakeholders accept the necessary changes in land use identified by the adapted land-use scenario of the NSS. These changes were included in the preferred land-use management option in the regional planning process, which has since been formalized. The NSS provided system insight, scoping analyses, and education, in addition to generating quantitative information on the impact of land-use functions on groundwater quality.     

Nanoparticles in natural systems II: The natural oxide fraction at interaction with natural organic matter and phosphate

Information on the particle size and reactive surface area of natural samples and its interaction with natural organic matter (NOM) is essential for the understanding bioavailability, toxicity, and transport of elements in the natural environment. In part I of this series (Hiemstra et al., 2010), a method is presented that allows the determination of the effective reactive surface area (A, m²/g soil) of the oxide particles of natural samples which uses a native probe ion (phosphate) and a model oxide (goethite) as proxy. In soils, the natural oxide particles are generally embedded in a matrix of natural organic matter (NOM) and this will affect the ion binding properties of the oxide fraction. A remarkably high variation in the natural phosphate loading of the oxide surfaces (Γ, μmol/m²) is observed in our soils and the present paper shows that it is due to surface complexation of NOM, acting as a competitor via site competition and electrostatic interaction. The competitive interaction of NOM can be described with the charge distribution (CD) model by defining a ≡NOM surface species. The interfacial charge distribution of this ≡NOM surface species can be rationalized based on calculations done with an evolved surface complexation model, known as the ligand and charge distribution (LCD) model. An adequate choice is the presence of a charge of −1 v.u. at the 1-plane and −0.5 v.u. at the 2-plane of the electrical double layer used (Extended Stern layer model).The effective interfacial NOM adsorption can be quantified by comparing the experimental phosphate concentration, measured under standardized field conditions (e.g. 0.01 M CaCl₂), with a prediction that uses the experimentally derived surface area (A) and the reversibly bound phosphate loading (Γ, μmol/m²) of the sample (part I) as input in the CD model. Ignoring the competitive action of adsorbed NOM leads to a severe under-prediction of the phosphate concentration by a factor ∼10 to 1000. The calculated effective loading of NOM is low at a high phosphate loading (Γ) and vice versa, showing the mutual competition of both constituents. Both constituents in combination usually dominate the surface loading of natural oxide fraction of samples and form the backbone in modeling the fate of other (minor) ions in the natural environment.Empirically, the effective NOM adsorption is found to correlate well to the organic carbon content (OC) of the samples. The effective NOM adsorption can also be linked to DOC. For this, a Non-Ideal Competitive adsorption (NICA) model is used. DOC is found to be a major explaining factor for the interfacial loading of NOM as well as phosphate. The empirical NOM-OC relation or the parameterized NICA model can be used as an alternative for estimating the effective NOM adsorption to be implemented in the CD model for calculation of the surface complexation of field samples. The biogeochemical impact of the NOM-PO₄ interaction is discussed.     

Towards bridging the gap between climate change projections and maize producers in South Africa

Theoretical and Applied Climatology - Multi-decadal regional projections of future climate change are introduced into a linear statistical model in order to produce an ensemble of austral...