Vertical Water Movement Research Articles

Water and nitrogen distribution in uncropped ridge-tilled soil under different ridge width

Nitrate leaching to ground and surface water is an increasing concern in agriculture. A ridge-tillage configuration, with placement of nitrate nitrogen (NO 3 - -N) or its source in the elevated portion of the ridge, can potentially isolate fertilizer from downward water flow and minimize nitrate leaching. In the experiment, the simultaneous distribution of water, nitrate, and ammonium under three ridge widths was measured using the gravimetric method. Monitoring of the water movement revealed that vertical water movement was much greater than horizontal movement. Compared with 30 and 90 cm ridge width, soil water content at 60 cm ridge width could better meet crop water requirement and relatively decreased irrigation volume. The distribution of NO 3 - -N in the soil was similar to distribution patterns of water, while ammonium distribution measurements indicated that there existed an extremely high ammonium concentration in the furrow for ridge-furrow system. These results support the conclusion that water infiltrated in furrows and primarily moved laterally to ridge positions, minimizing downward water movement under the ridge. In this experiment, we recommend that the suitable ridge width for ridge tillage management should be within the range of 60 to 75 cm. Key words : Ridge tillage, ridge width, wetted front, soil water content, nitrate-nitrogen distribution, ammonium distribution.

Frequency dispersion of losses during acoustic sounding of water in Lake Baikal

The processes of horizontal and vertical water exchange play the most important role in the ecosys� tem of Lake Baikal providing the transport of organic and inorganic matter including oxygen in the entire volume of water up to the limiting depths. The investi� gation of the main processes of water transport in Lake Baikal based on the traditional methods of episodic profiling from research ships does not supply sufficient information about many inhomogeneous and nonsta� tionary processes. The difficulties are also related to the insufficient sensitivity of the existing instruments for measuring the vertical motion of water whose velocity usually does not exceed a few fractions of a millimeter per second. An infrastructure was created within the project of the Baikal neutrino telescope (1), and new technolo� gies were developed that make it possible to set up sys� tems of longterm multiparameter monitoring of dif� ferent processes in the lake including precise acoustic measurements. The initial goal of the investigations presented in this paper was to develop the methods of acoustic tomography (2) as a tool for investigation of the hydrophysical processes in Lake Baikal. It is possi� ble to study multiscale processes using acoustic path� ways with a length from tens of meters to tens of kilo� meters. The preliminary results of acoustic sounding in the water under ice over basic lengths on the order of hun� dreds of meters based on pulse signals were published in (3, 4). The key idea of the method is to measure the intrapulse phase distortions, which allows us not only to increase the sensitivity (as during typical phase measurements) but also to take into account the dis� persion distortions of the signals related to the depen� dence of attenuation on frequency. The amplitude, delay, and phase of the pulse signal and also the addi� tional phase modulation that results from the fre� quency dependence of attenuation in the signal band were recorded in the experiments. This dependence is manifested in the slope of the amplitudefrequency characteristic of the channel. In this case, the spec� trum of the amplitudemodulated pulse no longer remains symmetric with respect to the carrier fre� quency, which is manifested as additional intrapulse phase modulation. We note that this effect for the pulse narrow band signals is the effect of the first order of magnitude with respect to the bandwidth, while the usual dispersion (the dependence of the signal propa� gation velocity on frequency) leads to the effects of the second order with respect to the bandwidth. The appearance of additional phase modulation is not manifested on the envelope curve of the received sig� nal, but an additional quadrature component propor� tional to the derivative of the inphase component whose amplitude is proportional to the slope of the amplitudefrequency characteristic appears during detection by a synchronous phase detector.

Downwelling then upwelling again of the upwelled Kuroshio water in the southern East China Sea

As has been well known for several decades, the subsurface Kuroshio waters upwell onto the East China Sea when the Kuroshio impinges on the continental shelf northeast of Taiwan. Based on hydrological and geochemical data, our previous study demonstrated that the upwelled Kuroshio waters downwell then upwell again northwest of Taiwan in August. A subsequent effort attributed this complex phenomenon to varying vorticity or the Rossby number at the study area, which encompasses two strong currents, i.e., the Kuroshio and the Taiwan Warm Current. Moreover, downwelling‐favorable winds coincided with the observation period. This study demonstrates that the above phenomenon does not occur in the northern Taiwan Strait, but appears to surface outside of the strait during all seasons. In general, downwelling of previously upwelled Kuroshio waters from the east brings down waters from the surface, explaining why the recipient bottom waters show a horizontal maximum temperature but a minimum salinity, σt and NO3 + NO2. The downwelled waters subsequently upwell again. Since the recipient near‐surface waters arise from the depth, there exists a horizontal minimum in temperature but a maximum salinity, σt and NO3 + NO2 is found. However, whether wind patterns play a critical role in generating these vertical water movements remains unclear.

Modeling nitrogen loadings from agricultural soils in southwest China with modified DNDC

Degradation of water quality has been widely observed in China, and loadings of nitrogen (N) and other nutrients from agricultural systems play a key role in the water contamination. Process-based biogeochemical models have been applied to quantify nutrient loading from nonpoint sources at the watershed scale. However, this effort is often hindered by the fact that few existing biogeochemical models of nutrient cycling are able to simulate the two-dimensional soil hydrology. To overcome this challenge, we launched a new attempt to incorporate two fundamental hydrologic features, the Soil Conservation Service curve and the Modified Universal Soil Loss Equation functions, into a biogeochemistry model, Denitrification-Decomposition (DNDC). These two features have been widely utilized to quantify surface runoff and soil erosion in a suite of hydrologic models. We incorporated these features in the DNDC model to allow the biogeochemical and hydrologic processes to exchange data at a daily time step. By including the new features, DNDC gained the additional ability to simulate both horizontal and vertical movements of water and nutrients. The revised DNDC was tested against data sets observed in a small watershed dominated by farmlands in a mountainous area of southwest China. The modeled surface runoff flow, subsurface drainage flow, sediment yield, and N loading were in agreement with observations. To further observe the behaviors of the new model, we conducted a sensitivity test with varied climate, soil, and management conditions. The results indicated that precipitation was the most sensitive factor determining the rate of N loading from the tested site. A Monte Carlo test was conducted to quantify the potential uncertainty derived by variations in four selected input parameters. This study demonstrates that it is feasible and effective to use enhanced biogeochemical models such as DNDC for quantifying N loadings by incorporating basic hydrological features into the model framework.

Measurement of Net Nitrogen and Phosphorus Mineralization in Wetland Soils Using a Modification of the Resin‐Core Technique

A modification of the resin‐core method was developed and tested for measuring in situ soil N and P net mineralization rates in wetland soils where temporal variation in bidirectional vertical water movement and saturation can complicate measurement. The modified design includes three mixed‐bed ion‐exchange resin bags located above and three resin bags located below soil incubating inside a core tube. The two inner resin bags adjacent to the soil capture NH4+, NO3−, and soluble reactive phosphorus (SRP) transported out of the soil during incubation; the two outer resin bags remove inorganic nutrients transported into the modified resin core; and the two middle resin bags serve as quality‐control checks on the function of the inner and outer resin bags. Modified resin cores were incubated monthly for a year along the hydrogeomorphic gradient through a floodplain wetland. Only small amounts of NH4+, NO3−, and SRP were found in the two middle resin bags, indicating that the modified resin‐core design was effective. Soil moisture and pH inside the modified resin cores typically tracked changes in the surrounding soil abiotic environment. In contrast, use of the closed polyethylene bag method provided substantially different net P and N mineralization rates than modified resin cores and did not track changes in soil moisture or pH. Net ammonification, nitrification, N mineralization, and P mineralization rates measured using modified resin cores varied through space and time associated with hydrologic, geomorphic, and climatic gradients in the floodplain wetland. The modified resin‐core technique successfully characterized spatiotemporal variation of net mineralization fluxes in situ and is a viable technique for assessing soil nutrient availability and developing ecosystem budgets.

Alternative Employment of Crushed Shell Particles in Capillary Barrier of Soil

Capillary barrier is a tilting soil layer system which is composed of a finer soil layer underlain by a coarser soil layer. Water which infiltrates into the soil is suspended just above an interface between the soil layers and diverted downward along the interface, with the result that a vertical movement of water into deeper soil layers below the interface stops within some length along the interface. As the water diversion in the capillary barrier is caused by a sharp contrast in water retention capacity between the finer and coarser soils, any material which can provide the sharp contrast in water retention capacity can be alternatively employed in the capillary barrier system. In the study a coarse-grained material of crushed shell particles is selected as an alternative candidate for the lower layer soil of the capillary barrier, and its water retention capacity is measured to examine a practical effectiveness of the crushed shell particles in the capillary barrier system.

SOIL MOISTURE DISTRIBUTION IN SANDY SOIL UNDER DRIP IRRIGATION SYSTEM USING NEUTRON SCATTERING METHOD

This work aims to study soil moisture behavior in sandy soil under drip irrigation system in order to control the management in sandy soil using neutron scattering technique. Studying soil moisture distribution through the soil profile is important to management the irrigation water, to achieve the maximum benefit from irrigation water. To achieve this aim, an experiment was carried out at the farm of Soil and Water Department, Nuclear Research Center, Atomic Energy Authority, Inshas (latitude longitude 30˚19 N longitude 31˚27 E), during onion growing season (2008/2009). Drip irrigation system was used for applying irrigation water. The uniformity of emitters' water application was checked to judge the system. Data showed that it's possible to use the combination work between neutron scattering technique and soil moisture retention models to study the direction of soil water movement within sandy soil profile. As well as predicting some soil plant concepts (i.e., active rooting depth and depth of collective active roots for water absorption);these concepts used to determine evapotranspiration, drainage rate and active rooting zone. Detecting total hydraulic potential within the wet area around the dripper along dripper lines and between lateral lines helps to study the behavior of soil moisture values within soil profile. The obtained data show also that the actual evapotranspiration of onion plant differs from site to site in wet area according to soil moisture availability. Surfer computer program also shows soil profile can be classified into different areas after and before irrigation within the wet area around drippers. The combination work between neutron probe, soil moisture tension models and. Surfer computer program shows study the horizontal and vertical movement of soil water in the wet area around the dripper and obtaining couture lines of soil moisture within the wet area.

Selected Soil Physical Properties and Implications on Water Management System in Northeast Florida

Selected soil physical properties at varying depths in a cultivated Alfisol in northeast Florida were studied using classical and geostatistical techniques. The objective was to investigate the variation in the physical properties among and within the sampling depths and understand its implications to field water management in the area. Seventy soil core samples were collected in a grid sampling scheme from five depths: 22.5 cm, 45 cm, 67.5 cm, 90 cm, and 120 cm. Particle size distributions, bulk density (Db), and saturated hydraulic conductivity (Ks) of the soil samples from each depth were measured and statistically compared among depths, and the spatial variation of properties within each sampling depth was determined. Clay content and Db increased significantly with increasing depth, whereas the Ks decreased. The Ks exhibited the maximum variation in both vertical and horizontal direction, whereas Db was the least variable among the three properties. The semivariogram analysis showed a weak spatial autocorrelation in soil properties within the sampling depths. The results suggested that despite significantly low conductivity and high Db of the soil profile at 120 cm, it was not impermeable enough to restrict vertical water movement as opposed to the general perception of the occurrence of a shallow impermeable layer in the profile and consequent perched water table conditions. The results, therefore, provided a definitive insight into the water table management system in the area, which is important for understanding the irrigation system, its efficiency, and consequent water quality impacts on surface and/or groundwater.

Coupling groundwater and land surface processes: Idealized simulations to identify effects of terrain and subsurface heterogeneity on land surface energy fluxes

This work investigates the role of terrain and subsurface heterogeneity on the interactions between groundwater dynamics and land surface energy fluxes using idealized simulations. A three‐dimensional variably saturated groundwater code (ParFlow) coupled to a land surface model (Common Land Model) is used to account for both vertical and lateral water and pressure movement. This creates a fully integrated approach, coupling overland and subsurface flow while having an explicit representation of the water table and all land surface processes forced by atmospheric data. Because the water table is explicitly represented in these simulations, regions with stronger interaction between water table depth and the land surface energy balance (known as critical zones) can be identified. This study uses simple terrain and geologic configurations to demonstrate the importance of lateral surface and subsurface flows in determining land surface heat and moisture fluxes. Strong correlations are found between the land surface fluxes and water table depth across all cases, including terrain shape, subsurface heterogeneity, vegetation type, and climatological region. Results show that different land forms and subsurface heterogeneities produce very different water table dynamics and land surface flux responses to atmospheric forcing. Subsurface formation and properties have the greatest effect on the coupling between the water table and surface heat and moisture fluxes. Changes in landform and land surface slope also have an effect on these interactions by influencing the fraction of rainfall contributing to overland flow versus infiltration. This directly affects the extent of the critical zone with highest coupling strength along the hillside. Vegetative land cover, as seen in these simulations, has a large effect on the energy balance at the land surface but a small effect on streamflow and water table dynamics and thus a limited impact on the land surface‐subsurface interactions. Although climate forcing has a direct effect on water table dynamics and feedbacks to the land surface, in this study it does not overcome that of subsurface heterogeneity and terrain.

Trees never rest: the multiple facets of hydraulic redistribution

AbstractThe upward movement of water due to transpiration stops when soil water potential (Ψs) drops below leaf water potential (ΨL). Under these circumstances, water can move in any direction in the plant‐soil continuum through the passive conduits of roots and stems towards the lowest Ψs. This is generally termed as hydraulic redistribution (HR), but the positioning and orientation of the driving water potential gradient may vary. Any experimental method that can measure bi‐directional and low flows in the sapwood of roots and stems will be suitable to detect HR. Using one approach for measuring sap flow (the heat field deformation technique, HFD) in several forest species and sites across Europe, we were able to provide evidence on different types of HR: vertical hydraulic redistribution (VHR), horizontal hydraulic redistribution (HHR), foliar uptake (FU) and tissue dehydration (TD). VHR is the vertical water movement through roots in response to water potential differences between deep and topsoil, either hydraulic lift or hydraulic descent. HHR is the lateral water movement through roots in response to horizontal water potential gradients, namely under localised irrigation. FU is the water movement from crown to soil through stems when the crown is wetted by foggy weather. TD is the downward movement of water in stems or roots from above‐ground tree tissues to soil under prolonged drought or frost. Results from direct sap flow measurements indicated the vectoral and widespread nature of HR, a phenomenon of paramount importance for overall physiology and ecohydrology. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of hydrostatic instability based on mechanical analogy

A simple method of estimating spatiotemporal scales of vertical water exchange caused by the instability of the temperature profile is described. The motion of a hypothetical liquid particle with preset temperature and volume is described by a one-dimensional equation which describes an approximate model for estimating the vertical water exchange scales. An exact nonlinear expression is used for a force which acts on an immersed particle. Based on the first integral of motion, rotation points and time of motion between them are determined. The distance between the rotation points and the corresponding time period are considered as physically substantiated estimates of spatial and temporal scales of vertical water motion. These estimates are based on the fundamental principles and do not provided detailed information; however, they have general character and can be used for a description of concrete cases. The developed method is applied to the temperature profiles obtained in hydrophysical investigations with the Baikal Neutrino Telescope located in Southern Baikal.

Prediction of water table depths under soil water-groundwater interaction and stream water conveyance

Water table over an arid region can be elevated to a critical level to sustain terrestrial ecosystem along the natural channel by the stream water conveyance. Estimation of water table depth and soil moisture on river channel profile may be reduced to a two-dimensional moving boundary problem with soil water-groundwater interaction. The two-dimensional soil water flow with stream water transferred is divided into an unsaturated vertical soil water flow and a horizontal groundwater flow. Therefore, a prediction model scheme for water table depths under the interaction between soil water and groundwater with stream water transferred is presented, which includes a vertical soil water movement model, a horizontal groundwater movement model, and an interface model. The synthetic experiments are conducted to test the sensitivities of the river elevation, horizontal conductivity, and surface flux, and the results from the experiments show the robustness of the proposed scheme under different conditions. The groundwater horizontal conductivity of the proposed scheme is also calibrated by SCE-UA method and validated by data collected at the Yingsu section in the lower reaches of the Tarim River, which shows that the model can reasonably simulate the water table depths.

REVISING WETTED SOIL VOLUME UNDER TRICKLE SOURCE FOR IRRIGATION SCHEDULING

Wetted soil shape under trickle irrigation is an important parameter in irrigation scheduling and design in agricultural farms. Irrigation water should not be beyond crop root zone to avoid deep percolation. Moreover, irrigation water applied should adequate crop water use in irrigation interval. The purpose of this work is to figure out the suitable shape of wetted soil based on soil type, flow rate, and crop water use. A field experiment was conducted in sand, silt and clay soils under trickle source with varying flow rates as 2, 4, 8, 16, and 24 liter/h. Squash, corn, and grape crops were selected to represent different root zones for irrigation scheduling. Field results showed that horizontal and vertical water movements were related to both emitter flow rate and soil intake rates. Suitable flow rate and irrigation interval were found for selected soil and crop types. Soil moisture content was contoured directly after irrigation and soil-water redistribution. Optimal flow rates were 2 and 4 liter/h in clay soil, 8 and 16 liter/h in loam, 16 and 24 liter/h in sand. Adjusted method was recommended to calculate irrigation interval by revising wetted root zone volume, taking into account different soil, crops, crop stages, and seasons.

Field tracer investigation of unsaturated zone flow paths and mechanisms in agricultural soils of northwestern Mississippi, USA

In many farmed areas, intensive application of agricultural chemicals and withdrawal of groundwater for irrigation have led to water quality and supply issues. Unsaturated-zone processes, including preferential flow, play a major role in these effects but are not well understood. In the Bogue Phalia basin, an intensely agricultural area in the Delta region of northwestern Mississippi, the fine-textured soils often exhibit surface ponding and runoff after irrigation and rainfall as well as extensive surface cracking during prolonged dry periods. Fields are typically land-formed to promote surface flow into drainage ditches and streams that feed into larger river ecosystems. Downward flow of water below the root zone is considered minimal; regional groundwater models predict only 5% or less of precipitation recharges the heavily used alluvial aquifer. In this study transport mechanisms within and below the root zone of a fallow soybean field were assessed by performing a 2-m ring infiltration test with tracers and subsurface monitoring instruments. Seven months after tracer application, 48 continuous cores were collected for tracer extraction to define the extent of water movement and quantify preferential flow using a mass-balance approach. Vertical water movement was rapid below the pond indicating the importance of vertical preferential flow paths in the shallow unsaturated zone, especially to depths where agricultural disturbance occurs. Lateral flow of water at shallow depths was extensive and spatially non-uniform, reaching up to 10 m from the pond within 2 months. Within 1 month, the wetting front reached a textural boundary at 4–5 m between the fine-textured soil and sandy alluvium, now a potential capillary barrier which, prior to extensive irrigation withdrawals, was below the water table. Within 10 weeks, tracer was detectable at the water table which is presently about 12 m below land surface. Results indicate that 43% of percolation may be through preferential flow paths and that any water breaking through the capillary barrier (as potential recharge) likely does so in fingers which are difficult to detect with coring methods. In other areas where water levels have declined and soils have similar properties, the potential for transport of agricultural chemicals to the aquifer may be greater than previously assumed.

Pavement subsurface drainage: importance of appropriate subbase materials

Past and current research has clearly established the detrimental effects of inadequate subsurface drainage within a road environment. In response, pavement engineers have developed a number of theoretical models to establish the lateral drainage requirements of pavements. The intention of the present paper is to extend current drainage design by accounting for the presence of a pervious subbase layer. A parametric study of an extended form of the time to drain problem was performed while focusing on the effect of subbase material characteristics under saturated and unsaturated conditions. The numerical results established that the addition of a suitable subbase material can shift drainage time from days to minutes by combining the effects of gravity, seepage distance, and discharge area to enhance vertical water movement. Although increasing saturated hydraulic conductivity of the subbase material was generally shown to favour vertical drainage, it also created a capillary barrier effect that hindered downward flow. The results of this analysis emphasize the importance and relevance of subbase material selection for improving the drainage quality of dense-graded base materials, which display excellent bearing capacity and remain stable under repeated loading.

Modeling aluminum–silicon chemistries and application to Australian acidic playa lakes as analogues for Mars

Recent Mars missions have stimulated considerable thinking about the surficial geochemical evolution of Mars. Among the major relevant findings are the presence in Meridiani Planum sediments of the mineral jarosite (a ferric sulfate salt) and related minerals that require formation from an acid–salt brine and oxidizing environment. Similar mineralogies have been observed in acidic saline lake sediments in Western Australia (WA), and these lakes have been proposed as analogues for acidic sedimentary environments on Mars. The prior version of the equilibrium chemical thermodynamic FREZCHEM model lacked Al and Si chemistries that are needed to appropriately model acidic aqueous geochemistries on Earth and Mars. The objectives of this work were to (1) add Al and Si chemistries to the FREZCHEM model, (2) extend these chemistries to low temperatures (<0 °C), if possible, and (3) use the reformulated model to investigate parallels in the mineral precipitation behavior of acidic Australian lakes and hypothetical Martian brines. FREZCHEM is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. Aluminum chloride and sulfate mineral parameterizations were based on experimental data. Aluminum hydroxide and silicon mineral parameterizations were based on Gibbs free energy and enthalpy data. New aluminum and silicon parameterizations added 12 new aluminum/silicon minerals to this Na–K–Mg–Ca–Fe(II)–Fe(III)–Al–H–Cl–Br–SO 4–NO 3–OH–HCO 3–CO 3–CO 2–O 2–CH 4–Si–H 2O system that now contain 95 solid phases. There were similarities, differences, and uncertainties between Australian acidic, saline playa lakes and waters that likely led to the Burns formation salt accumulations on Mars. Both systems are similar in that they are dominated by (1) acidic, saline ground waters and sediments, (2) Ca and/or Mg sulfates, and (3) iron precipitates such as jarosite and hematite. Differences include: (1) the dominance of NaCl in many WA lakes, versus the dominance of Fe–Mg–Ca–SO 4 in Meridiani Planum, (2) excessively low K + concentrations in Meridiani Planum due to jarosite precipitation, (3) higher acid production in the presence of high iron concentrations in Meridiani Planum, and probably lower rates of acid neutralization and hence, higher acidities on Mars owing to colder temperatures, and (4) lateral salt patterns in WA lakes. The WA playa lakes display significant lateral variations in mineralogy and water chemistry over short distances, reflecting the interaction of acid ground waters with neutral to alkaline lake waters derived from ponded surface runoff. Meridiani Planum observations indicate that such lateral variations are much less pronounced, pointing to the dominant influence of ground water chemistry, vertical ground water movements, and aeolian processes on the Martian surface mineralogy.

Infiltração da água no solo no sistema pedológico Campus do Arenito, cidade gaúcha, noroeste do estado do Paraná

Considerando a importância do conhecimento do comportamento hídrico das coberturas pedológicas para os estudos de prevenção e contenção dos processos erosivos, o presente trabalho foi realizado em uma vertente com sistema pedológico "Latossolo Vermelho eutrófico/Argissolo Vermelho eutrófico", oriundo do arenito Caiuá, localizado na fazenda experimental da Universidade Estadual de Maringá, município de Cidade Gaúcha, noroeste do Estado do Paraná. Após abordagem morfológica detalhada do sistema pedológico, realizaram-se ensaios de infiltrometria nos principais horizontes diagnósticos e suas respectivas transições em seis perfis de solos dispostos ao longo da vertente. A dinâmica hídrica da cobertura latossólica encontra-se marcada por um comportamento distinto entre a superfície e a subsuperfície. Os horizontes superficiais Ap, AB e, ou, BA exibem ao longo do tempo uma alternância de condições de umidade, ora mais úmidos, ora mais secos, devido à distribuição e intensidade das chuvas. Em profundidade, no horizonte Bw, as condições hídricas dependem da movimentação da água vertical e lateral, não respondendo, portanto, diretamente às variações atmosféricas como na superfície. Na cobertura argissólica, o bloqueio da drenagem vertical ocorre no topo do Bt, gerando acima (horizonte AE) uma zona mais constantemente úmida. De modo geral, os horizontes superficiais dos Argissolos não apresentam as alternâncias de umedecimento e secamento verificadas nos Latossolos; permanecem sempre mais úmidos do que aqueles, em razão dos fluxos hídricos laterais de montante.

Heavy Metal Contamination of Soil Beneath a Waste Disposal Site at Dengkil, Selangor, Malaysia

Heavy metals leaching from solid waste facilities pose concerns because of the metal ions being distributed to surroundings through surface, subsurface, lateral and/or vertical movement of water. In view of this concern, heavy metals, namely Fe, Mn, Cu, Cr, Ni, Zn, Pb, and Co, in soil horizons beneath the Ampar Tenang waste disposal site at Dengkil, Selangor, were extensively studied through chemical analyses of 21 representative soil samples collected in triplicate. The soil samples were collected from nine augered boreholes. Three of the boreholes are located within the disposal site and three each up-slope and down-slope of the disposal site. Soils sampled from the soil-waste interface (ATI) within the dumping site show relatively high concentrations of most of the heavy metals analyzed as compared with samples collected from upslope area (ATU) of the dumping site. Soil samples from a downslope area (ATD) show a slightly elevated concentration of heavy metals. The results of chemical analyses also show that Cr, Zn and Pb have higher levels of concentration among all studied heavy metals. It was found that, in most cases, the heavy metal concentrations were generally high within the near surface soil layer and decreased in concentration with increasing depth. Site observations indicate that, in addition to the vertical infiltration of leachate from the solid waste, shallow groundwater level strongly influences contaminant dispersion in soils below the waste site. Properties of the soil indicate that the Ampar Tenang soil (ATS) is more permeable than the minimum limit of formation permeability required underlying a waste disposal site. The acidic-pH soil environment and groundwater fluctuations also influence the mobility of heavy metals spatially and vertically in the vicinity of the waste disposal site at Ampar Tenang.

Effect of subsurface drip irrigation on onion yield

Subsurface drip system is the latest method of irrigation. The design of subsurface drip system involves consideration of structure and texture of soil, and crop’s root development pattern. A 3-year experiment was conducted on onion (Allium Cepa L., cv. Creole Red) in a sandy loam soil from October to May in 2002–2003, 2003–2004 and 2004–2005 to study the effect of depth of placement of drip lateral and different levels of irrigation on yield. Tests for uniformity of water application through the system were carried out in December of each year. Three different irrigation levels of 60, 80 and 100% of the crop evapotranspiration and six placement depths of the drip laterals (surface (0), 5, 10, 15, 20 and 30 cm) were maintained in the study. Onion yield was significantly affected by the placement depth of the drip lateral. Maximum yield (25.7 t ha−1) was obtained by applying the 60.7 cm of irrigation water and by placing the drip lateral at 10 cm soil depth. Maximum irrigation water use efficiency (IWUE) (0.55 t ha−1 cm−1) was obtained by placing the drip lateral at 10 cm depth. The greater vertical movement of water in the sandy-loam soil took place because of the predominant role of gravity rather than that of the capillary forces. Therefore, placement of drip lateral at shallow depths is recommended in onion crop to get higher yield.

Chemical and isotopic ( δ18O‰, δ2H‰, δ13C‰, 222Rn) multi-tracing for groundwater conceptual model of carbonate aquifer (Gran Sasso INFN underground laboratory – central Italy)

Summary A hydrochemical and isotope study was conducted on the drainage waters of an underground laboratory, located inside the Gran Sasso massif (central Italy). The study was expected to improve the conceptual model of groundwater circulation at the base of an over 1000-thick unsaturated zone in the Gran Sasso partitioned karst aquifer. This lithostratigraphically and tectonically complex aquifer is typical of Africa–Europe thrust-and-fold collision belt in the Mediterranean area. In this case, investigations on water–rock interactions during recharge in complex aquifers, overlaid by a thick unsaturated zone, have been made thanks to the strategic location of the Gran Sasso underground laboratories, located in the core of a huge carbonate aquifer. Knowledge of the local basic hydrogeological setting was the starting point for a detailed hydrogeochemical and isotopic study, which was carried out at the aquifer scale and at the fine scale in the underground laboratories. The water–rock interaction processes were investigated both spatially and in temporal sequences, analysing recharge waters and groundwater in the underground laboratories by multitracing techniques, including major ions and δ18O‰, δ2H‰ and δ13C‰ stable isotopes. Use of 222Rn provides information on transit time in the aquifer. Processes proved to be typical of carbonate rocks, with clear influence of vertical movement of water on chemical–physical parameters through the unsaturated zone. Conversely, in the saturated zone, these processes proved to be dominantly affected by local geological–structural conditions. A conceptual model with dual flow velocity is proposed, directly related to the local geological-structural setting. 222Rn decay enables to calculate an effective velocity of around 10 m/day for the fracture network, through the sequence of less permeable dolomites and underlying limestone. Lag time between recharge and chemical changes in the saturated zone testifies to an effective velocity of about 35 m/day for fast flow through recent and active extensional faults.