Preferential Water Flow Paths Research Articles

Quantification of soil textural and hydraulic properties in a complex conductivity imaging framework: Results from the Wolfsegg slope

We present an approach that permits to predict hydraulic conductivity from extensive, multi-methodical geophysical data collected on a hillslope affected by landslides in Austria. The objective of the investigation is the spatial characterization of a slope affected by mass movements to derive hydrogeological structures and preferential flow paths. The geophysical data sets presented in this study consists of 24 densely distributed complex conductivity (CC) imaging profiles, collocated to these profiles we also collected 517 transient electromagnetic (TEM) soundings and 10 refraction seismic tomography (RST) profiles. Additionally, we also present well-logging data (namely electrical resistivity, natural gamma logs) collected in five boreholes. Cores recovered during the drilling of the boreholes are used to aid in the interpretation of the geophysical units, while analysis of the sediments was conducted to obtain grain size distributions, cation exchange capacity and mineralogy of the subsurface materials. While all geophysical data was processed initially independently, the final complex conductivity imaging results are based on the incorporation of structural constraints about the electrical units obtained from the TEM soundings. The interpretation of the resolved CC units is then sustained by the RST images and the lithological information from the boreholes. We estimate then the hydraulic conductivity of the subsurface derived from the CC images using a two-step approach. In a first step, we investigated the link between the complex conductivity and the different soil volume fractions of gravel, sand, silt and clay. In a second step, we applied a pedo-transfer function, namely the well-known Rosetta model, that permits to predict the hydraulic conductivity from the estimated grain size volumes. This approach allowed a quantitative interpretation of the geophysical data and thus a 3-dimensional (3D) representation of the grain size distribution and hydraulic conductivity in the investigated slope section. Thereby, we observed well-determined site-specific relationships (R2 > 0.7) from the comparison of the complex resistivity images and grain size analysis. The obtained hydrogeophysical 3D model permits to delineate the geometry of an aquiclude, and, thus, the analysis of preferential water-flow paths. In particular, we can identify a spatial correlation between the aquiclude interface and morphological features.

Effects of grazing exclusion on soil infiltrability and preferential flow in savannah livestock grazing systems

AbstractAlthough the establishment of grazing exclosures is often considered an important strategy of reducing soil degradation, their effect on hydrological functions is still poorly understood, particularly in dry‐hot savanna systems with heavy livestock grazing. In addition, the different roles played by the herb roots and the niche differentiation of woody plant roots induced by the grazing and exclosure in soil hydrological functions are still unclear. This study aimed to evaluate the effect of exclosure management on hydrological functions and services and assess the role of different functional vegetation types in improving these functions and services. The experiments were conducted in the continuous grazing areas and exclosure areas in a savanna ecosystem in Yuanjiang, southwest China. The root biomass of herb and woody plants, soil physical properties, water infiltration, and preferential water flow were measured in each study site. The results showed a significant improvement in soil physical properties with more termite holes, lower soil bulk density, and higher total and non‐capillary soil porosity in exclosure areas compared with grazing ones. As a result, the initial and average water infiltration, and preferential flow significantly increased by 132.76%, 185.31%, and 30.29%, respectively, in exclosure areas compared with the grazing ones. The results also showed that the exclosure significantly improved the soil surface water content by increasing the root biomass of herb and woody plants in the shallow soil layers. Herb plants probably improved water infiltration and insulated evaporation, while woody plants improved lateral preferential water flow paths and accelerated the water exchange between vertical and horizontal soil layers, thereby improving the water availability for different plants. This study demonstrated that the exclosure‐induced restoration and niche differentiation of herb and woody plants, coupled with improved soil structure in exclosures, could promote hydrological function and services and improve water management in savanna systems. Therefore, the grazing exclosures could be expanded periodically and cautiously to prevent soil degradation in the present savanna systems.

Anion Exchange Capacity Explains Deep Soil Nitrate Accumulation in Brazilian Amazon Croplands

Deep tropical soils with net anion exchange capacity can adsorb nitrate and might delay the eutrophication of surface waters that is often associated with many temperate croplands. We investigated anion exchange capacity and soil nitrate pools in deep soils in the Southern Brazilian Amazon, where conversion of tropical forest and Cerrado to intensive fertilized soybean and soybean-maize cropping expanded rapidly in the 2000s. We found that mean soil nitrate pools in the top 8 m increased from 143 kg N ha−1 in forest to 1,052 in soybean and 1,161 kg N ha−1 in soybean-maize croplands. This nitrate accumulation in croplands aligned with the estimated N surpluses in the croplands. Soil anion exchange capacity explained the magnitude of nitrate accumulation. High nitrate retention in soils was consistent with current low levels of streamwater nitrate exported from croplands. Soil exchange sites were far from saturation, which suggests that nitrate accumulation can continue for longer under current cropping practices, although mechanisms such as competition with other anions and preferential water flowpaths that bypass exchange sites could reduce the time to saturation.

Properties of preferential water flow paths networks and background for their genesis in the slopes of small mountain valleys

Properties of preferential water flow paths networks and background for their genesis in the slopes of small mountain valleys

Investigating sweep efficiency improvement in oil-wet porous media by the application of functionalized nanoparticles

Nanoparticle stabilized emulsions have gained recent attention as mobility control agents in EOR processes. Some recent studies have shown in-situ formation of nanoparticle stabilized emulsions during displacement of a brine phase containing nanoparticles by another non-wetting phase such as n-octane under water-wet conditions. The objective of this research is to evaluate the hypothesis of nanoparticle stabilized emulsion formation by varying the system wettability toward oil-wet condition. Partially hydrophobic silica NPs with proper interface affinity are firstly synthesized and characterized in this study. A series of drainage displacement experiments are then conducted in the oil-wet sandpack embedded in a CT scanner, in the absence or presence of the functionalized NPs and a surfactant. CT-scans during waterflooding in the presence of NPs and surfactant has revealed a piston like displacement as a result of in-situ emulsion formation at the water invading front, which is associated with later water breakthrough, higher pressure drop, considerable pressure fluctuations, and higher oil recovery compared to the control experiment. The effect of nanofluid slug size and nanofluid viscosity is further investigated on sweep efficiency improvement during drainage displacement. The results have revealed that the presence of an oil-based nanofluid is effective in re-distributing the preferential water flow paths into a more stable front as a result of in-situ emulsification and the overall displacement efficiency depends on the nanofluid propagation in porous media. The oil-based nanofluid flooding followed by waterflooding utilized here is found to be a potential conformance control technique for oil recovery in oil-wet porous media.

Domestic Wastewater Depuration Using a Horizontal Subsurface Flow Constructed Wetland and Theoretical Surface Optimization: A Case Study under Dry Mediterranean Climate

The wastewater generated by isolated houses without access to public sewers can cause environmental problems, like the contamination of aquifers with nitrates and phosphates, as occurs in southeastern Spain. The effectiveness of a previously built horizontal subsurface flow constructed wetland (HF-CW) was studied over two years as a possible solution. This HF-CW measured 27 m2; it was planted with Phragmites australis(Cav.) Trin. Ex Steuds sp. Altissima and the parameters studied were those required by European Union (EU) legislation and adopted by Spain. Average abatement efficiency rates, for the first and the second year of study, were: biochemical oxygen demand over five days (BOD5) (96.4%, 92.0%), chemical oxygen demand (COD) (84.6%, 77.7%), total suspended solids(TSS) (94.8%,89.9%),total nitrogen(TN)(79.5%,66.0%),ammonium nitrogen(NH4+-N)(98.8%, 86.6%) and total phosphorous (TP) (83.7%, 82.8%). Average abatement efficiency for nitrate nitrogen (NO3−-N) (−1280.5%, −961.1%) and nitrite nitrogen (NO2−-N) (−5.8%, −40.0%) were negative because its content in influent wastewater was very low and they appear mainly from influent NH4+-N, as a result of purification processes carried out in the HF-CW bed. The abatement rates make the system suitable to produce discharges into the environment in accordance with Spanish law. It is noteworthy that the HF-CW patch suffered an episode of bed drying during the summer of 2013, whereby the causes were related to system oversizing and high evapotranspiration in the area. As a consequence, the decrease in the abatement of water pollutants during the second year can be attributed to the creation of preferential water flow paths and short circuits through the constructed wetland (CW) bed. As a result of the oversizing of the CW, a theoretical resizing based on BOD5, TSS, TN or TP is proposed. The calculated values for the redesign were: 5.22 m2 considering DBO5, 0.18 m2 considering TSS, 10.14 m2 considering TN and 23.83 m2 considering TP. Considering the area where the HF-CW was located and in accordance with Spanish law for non-sensitive areas (no TN or TP requirements for wastewater discharge), BOD5 is the most appropriate parameter for design; it is 5.2 times lower than the HF-CW initially built and without risk of bed drying.

Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Abstract. A dual stable water isotope (δ2H and δ18O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values. A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top- and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

Layer-by-Layer Assembly of Zeolite/Polyelectrolyte Nanocomposite Membranes with High Zeolite Loading

Incorporation of zeolite nanoparticles into nanocomposite membranes is advantageous with respect to enhancing membrane permeability by providing preferential water flow paths through the subnanometer porous structure of zeolite while maintaining excellent separation capability. We present a layer-by-layer assembly approach to effectively incorporate zeolite nanoparticles into nanocomposite membranes. Negatively charged Linde type A (LTA) zeolite nanoparticles were sandwiched between two different polyelectrolyte layers, negatively charged poly(acrylic acid) (PAA) and positively charged polyethylenimine (PEI), to form a PEI–LTA–PAA trilayer. The zeolite loading in the multitrilayer membranes was between 30 and 60 wt %, which is attributed to the drastically improved compatibility between zeolite and polymers, a direct result of electrostatic interactions. The performance of the trilayer membrane was compared with that of a control PEI–PAA bilayer membrane in a forward osmosis membrane system. The incorpora...

The Nubian Aquifer in Southwest Egypt

Synthetic Aperture Radar (SAR) images, and topographic and groundwater data are used to understand heterogeneities of the Nubian Aquifer between 20–24.5°N and 25–32°E in southwest Egypt. New fluvial and structural interpretations emphasize that the desert landscape was produced by fluvial action, including newly mapped alluvial fans. In central locations, braided channels are spatially aligned with a NE structural trend, suggesting preferential water flow paths that are consistent with the local direction of groundwater flow. The alluvial fans and structurally enclosed channels coincide with gentle slopes and optimal recharge conditions (1–5%) derived from the new Shuttle Radar Topographic Mission (SRTM) slope map, indicating that these areas have high groundwater potential. The SAR interpretations are correlated with anomalies observed in groundwater data from 383 wells. Results suggest a relationship between the spatial organization of fluvial and structural features and the occurrence of low-salinity groundwater. Low-salinity water exists adjacent to the alluvial fans and in SW reaches of the structurally enclosed channels. Wells in the vicinity of structures contain low-salinity water, emphasizing that knowledge of structural features is essential to understand groundwater flow paths. The new approach is cost effective and noninvasive and can be applied throughout the eastern Sahara to assist in resource management decisions and support the much needed agricultural expansion.

Fate of heavy metals in a strongly acidic shooting‐range soil: small‐scale metal distribution and its relation to preferential water flow

AbstractTo assess the mobility of Pb and associated metals in a highly contaminated shooting range soil (Losone, Ticino, Switzerland), we investigated the spatial distribution of the metals and their relation to preferential water flow paths. A 2.2 m2 plot located 40 m behind the stop butt was irrigated with a solution containing bromide and Brilliant Blue, a slightly sorbing dye. A soil profile 50 cm in width was sampled down to 80 cm with a spatial resolution of 2.5 cm, resulting in 626 samples. Concentrations of elements (12 ≤ Z ≤ 92) were determined by energy‐dispersive Xray fluorescence spectrometry, and Brilliant Blue concentrations were determined with a chromameter. In the acidic (pH 3), organic matter‐rich, well drained Dystric Cambisol, maximum concentrations of 80.9 g kg‐1 Pb, 4.0 g kg‐1 Sb, and 0.55 g kg‐1 Cu were measured in the topsoil. Within 40 cm soil depth, however, Pb, Sb, and Cu approached background concentrations of 23 mg kg‐1, 0.4 mg kg‐1, and 9.4 mg kg‐1, respectively. The even horizontal distribution and the steep gradient along soil depth indicate tight metal binding in the topsoil, and a fairly homogeneous transport front. In contrast, water flow through the profile was highly heterogeneous. In the uppermost 20 cm, preferential flow was initiated by heterogeneous infiltration at the soil surface, but had no influence on metal distribution. Below 20 cm, however, preferential flow originated from larger tree roots, and metal concentrations were significantly elevated along these macropores. Spatial distributions of Pb, Sb, and Cu were similar, suggesting that all three metals are strongly retained in the topsoil and transported along preferential water flow paths in the subsoil.

Flow Velocity Effects on the Retardation of FD&C Blue no. 1 Food Dye in Soil

AbstractDyes are often used as tracers of water and solute flow in soil. However, there has been little published research on the effects of flow velocity on the relative movement of dye and wetting fronts. Recently, the FD&C Blue no. 1 dye has been used as a tracer of preferential water flow paths in soils, and has attractive properties suggesting it will be used increasingly in the future. The objective of this study was to characterize the effects of flow velocity on the adsorption characteristics of the FD&C Blue no. 1. We performed a series of laboratory experiments on the characterization of the equilibrium adsorption isotherm as well as the effect of flow velocity on adsorption characteristics of the FD&C Blue no. 1 in three horizons of Verndale sandy loam (coarse‐loamy over sandy, mixed, frigid Udic Argiboroll). Batch equilibration (24 h) measurements resulted in linearized Freundlich distribution coefficients (Kd) of 4.33, 23.95, and 4.59 L kg−1 for the Ap, Bt, and C horizons, respectively. Neither organic C nor clay content differences accounted for the variation between horizons. Leaching experiments with a 1 g L−1 dye solution and repacked soil columns containing either Ap, Bt, or C horizon material showed that the dye was retarded relative to the wetting front, and that the extent of retardation was inversely related to the time period during which dye solution was applied. Therefore, this dye (and perhaps others) should not be used to make inferences about the movement of water or other solutes until the effect of the application rate is evaluated for the flow conditions in the system(s) of interest.

Effect of root systems on preferential flow in swelling soil

Abstract Permeability problems on irrigated soils may be alleviated by root systems that increase water flow by creating macropores. Infiltration rates have been shown to increase where plant roots decay and serve as preferential flow paths. For low‐organic‐matter swelling soil, there is a question whether macropores are able to resist the lateral swelling forces of the soil. The objective of this study was to observe preferential water flow paths in a swelling soil under two cropping systems. A Holtville silty clay (clayey‐over‐loamy, montmorillonitic Typic Torrifluvent) was observed in situ. Two crops, alfalfa (Medicago sativa, L.) and wheat (Triticum turgidum, L.) provided sharply contrasting root systems, with wheat possessing fine, fibrous roots; alfalfa on the other hand, has a taproot system. Macropores were observed after applying soil‐adsorbing methylene blue dye to irrigation water. Shrinkage cracks failed to conduct dye after 10 minutes into a flood irrigation. Earthworm (Lubricus terrestris) c...