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Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The infiltration medium and its formation mechanism. • Surface water infiltration processes on the Loess Plateau. • Human and tectonic activities govern the distribution patterns of groundwater. Terraces of the Yellow River are among the most crucial geomorphological landforms pertaining to human survival on the Loess Plateau. After more than half a century of surface flood irrigation, rapid rises in groundwater levels have led to frequent geological disasters, causing a rapid short-term evolution of Yellow River terraces, and an increasingly serious contradiction between this rapid evolution and human survival. However, the process by which water transfers through the thick loess vadose zone and causes a rapid groundwater response within months or years remains controversial. Using the Heitai platform of Yellow River terrace IV as an example, we found, on the basis of regional geological surveys, that at least 112 tectonically-induced cracks have developed in this area. We contend that the superimposed effects of earthquake ground motions from historical and ancient earthquakes since the Late Pleistocene have driven the development of such densely distributed cracks in the loess layer. These cracks, together with a series of fault planes generated by NE-directed extrusive stress at the regional scale, constitute a potential network of preferential channels for water transport within the Heitai platform. Combined with the results of a large-scale in situ ponding test and electrical resistivity tomography, we found that this network of cracks helps to establish catchment areas within the loess layer, thereby increasing soil saturation at a more extensive spatial scale, which may then increase the overall movement velocity of the wetting front. We semi-quantified the efficiency of the crack network in enhancing the recharge of surface water to groundwater, and suggested that the impact of human and tectonic activities substantially shortens the response time of groundwater to surface water, with the reduced time far exceeding one order of magnitude. The results of a field investigation of structural traces and terrace groundwater after the Ms 6.2 Jishishan earthquake on 18 December 2023 further emphasize that a causal mechanism of human and tectonic activities leading to the rapid short-term evolution of groundwater distribution patterns may be universally applicable to all Yellow River terraces on the Loess Plateau. This study mitigates the long-standing controversy concerning the mode of surface water infiltration, including piston flow and preferential flow, and the infiltration medium by which rapid surface water recharge to groundwater occurs in loess areas over short time periods. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Precipitation is the only source of groundwater recharge in the Chinese loess region. However, rainfall has been the main driver of geological disasters and engineering challenges in China, such as landslides, slope collapse and sinking of foundations. The roles of preferential flow and piston flow in moisture transfer in the thick loess vadose zone remain controversial. This study used a 100‐m thick loess shaft to monitor soil moisture content and soil temperature over 5 years, whereas climate indices were monitored on the Earth surface. The soil water characteristic curves and hydraulic conductivity function of the loess and the palaeosol collected in the profile were measured in a laboratory. The soil profile moisture transfer process was simulated based on the climatic boundary conditions and measured hydraulic parameters. The monitored and simulated results suggest that loess moisture transfer is dominated by piston flow. The thick loess vadose zone above the groundwater level could be divided into two sub‐zones, namely the active and steady zones. The active zone has a thickness of ~7 m and shows a direct response to climate change, with soil moisture content regulated by rainfall infiltration, evaporation and transpiration and soil moisture moving as transient flow. Although preferential flow can move in the active zone along joints, fissures and holes when water accumulates in the lower ground during heavy rainfall, piston flow remains the main mode of water movement. The steady zone has a thickness of <7 m and is above the groundwater level. Soil moisture content and soil temperature in the steady zone show temporal stability and soil moisture moves as a steady flow. Piston flow is the only mode of water movement in the steady zone. Since percolation velocity in the steady zone is estimated to be 73.3 mm/year, 1330 years of rainfall infiltration through the 97.5 m thick vadose zone would be required to recharge groundwater. [ABSTRACT FROM AUTHOR]

In 2001, a borehole was drilled to 400 m depth below the ground surface of a tableland in northern Japan, where horizontal porous sedimentary rock strata are deposited. Fresh drill-core and groundwater samples were collected from the borehole for estimating global fallout bomb pulses of 3H, which becomes tritiogenic 3He (tri3He) through β-decay, and 36Cl. In the northern hemisphere, the maximum fallout deposition of 36Cl from nuclear testing was observed during 1954–1957, and that of 3H in 1963. Most 3H (half-life 12.3 y) in the rock porewater had decayed to tri3He during the 38 years between 1963 and 2001. In the borehole, bomb pulses were observed in profiles of tri3He and 36Cl/Cl at 101 m and around 138 m depth below the ground surface, respectively. The downward groundwater velocity was estimated to be 2.9–3.1 m/y from the depth of the 36Cl/Cl bomb pulse and 2.7 m/y from the depth of the tri3He bomb pulse. Although the two velocity estimates differ by 10–15%, it is possible to model groundwater flow in the tableland as downward piston flow without diffusion. [ABSTRACT FROM AUTHOR]

A mathematical model of a highly heterogeneous functioning karst aquifer is described. The aquifer is in a high-relief karst massif and, as is common for such locations, data are scarce and there are no borehole, piezometer or pumping-test data. The scarcity of data in this case required a parsimonious approach to ensure that the level of complexity of the model was commensurate with the amount, type and quality of the available data. Parsimony also requires the model to include the minimum essential components that account adequately for the data, which in this and similar cases are the functional dualities of the karst system: duality in recharge, flow and discharge. The model is three-dimensional (3D) in the sense that the aquifer is discretized into 3D voxels, although the flow is one-dimensional (1D) and vertical in the vadose zone, and horizontal and two-dimensional (2D) in the saturated zone. The parsimonious model was designed by coupling a 1D unsaturated gravity-driven flow along the vertical (along each column of voxels that discretize the aquifer) and a 2D unconfined Darcy flow in the saturated zone. In the context of this type of aquifer, preferential recharge through the network of karst conduits implies a rapid rise in the water table, the location and extension of which are model parameters. The karst springs are simulated by drains. The methodology, which is completely general, is illustrated by application to the karst aquifer in the Sierra de las Nieves mountains in southern Spain. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil water is very important in hilly areas with thin soil layers and deep groundwater tables, such as the karst peak-cluster region of Southwest China. An investigation into soil water movement can provide insights into management of shallow water resources and soil nutrients, as well as prevention of groundwater pollution. In this study, 18O and 2H tracers were used to trace soil water movement in planar soil mass type microhabitats in the middle part of a steep hillslope covered by grasses in a karst peak-cluster region of China. From May 2008 to July 2009, samples of precipitation and two types of soil water, which had different integrated degrees of mobility and were of different depth intervals or depths, were collected. The hydrogeochemical characteristics were compared between precipitation and soil water, and these data were applied in convolution-based lumped parameter models. Our results indicated that vertical piston flow, rather than lateral flow along the soil-bedrock interface, played an important role in soil water percolation at least in the upper soil layer approximately 7 cm over the permeable bedrock. The mixing effect and preferential flow might also play a role in soil water percolation. In general, the evaporation effect on soil water was weak except for the uppermost 10 cm soil matrix water during winter. The lower limits of mean transit time of soil matrix flow passing through 5, 15, 25, 35, and 41.5 cm depths were 4.81, 7.70, 16.19, 21.85, and 27.44 days, respectively. Our study demonstrated the crucial functions of the soil reservoir in regulating the water cycle and could provide guidance on conservation of soil water and hydrological studies. The applied method was proved to be a suitable approach for investigating soil water movement on a monthly scale. [ABSTRACT FROM AUTHOR]

Numerous studies have been conducted to understand the mechanism of groundwater recharge for water resources management. But the roles of wide-spread village ponds on the Chinese Loess Plateau on groundwater recharge remains uncertain. Here, to evaluate the groundwater recharge under village ponds, we measured environmental tracers (2H, 18O, Cl-) in rainwater, groundwater, and pore waters of the deep unsaturated zone under three land-cover types (cropland, a village pond, and two apple orchards with stand ages of 10 and 27 years). The results show that shallow groundwater is recharged by both diffusive recharge and focused recharge. Specifically, diffusive recharge occurs beneath farmlands, grasslands, orchards and similar land-cover types, but diminishes in old orchards due to deep root water uptake. The diffusive recharge beneath crop field had an infiltration velocity of 10.3–12.5 cm yr−1; the resulting recharge rate was 30–33 mm yr−1, accounting for 5–6% of the annual precipitation. However, focused recharge occurs mainly beneath village ponds with low-lying terrain, and had an infiltration velocity of 26 cm d−1 during the rainy season; the resulting mean recharge rate was 134 mm yr−1 in the catchment of the pond, accounting for 23.1% of the annual precipitation. Given that the water table is generally more than 30 m below the soil surface, it takes hundreds of years for rainwater to reach the water table via the diffusive recharge but only days to months via the focused recharge. Diffusive recharge contributed 55–68% to the total recharge while focused recharge contributed 32–45%. However, the conversion of croplands to apple orchards and the decrease in the number of village ponds are occurring, which diminishes diffusive recharge, and reduces focused recharge, respectively. These findings are critical to understanding hydrological processes and protecting groundwater resources. We should preserve, reclaim, and construct village ponds to ensure groundwater recharge, in addition to optimizing areal ratio of large farmland to apple orchards in the region for the sustainable utilization of groundwater resources. • Diffusive recharge and focused recharge coexist as processes of groundwater recharge in the Loess Tableland. • Diffusive recharge occurs in farmland and natural area and has a slow, steady velocity (10.3–12.5 cm yr−1). • Focused recharge occurs beneath village ponds and has a relatively rapid velocity (26 cm d−1) during the rainy season. • Diffusive recharge contributed 55–68% of the total recharge while focused recharge contributed only 32–45%. [ABSTRACT FROM AUTHOR]

• A generic framework is presented for studying recharge processes at field scales. • Piston flow is dominant during soil water infiltration in loess tableland. • The tritium peak method can still be used in loess unsaturated zones. • The groundwater in Xifeng tableland is tritium-free. The corrected 14C age ranges from 220 to 19,220 years. Characterization of the rainfall infiltration mechanism, whether piston or preferential flow, through an unsaturated zone is necessary for groundwater resource assessment and for analysis of environmental geological hazards. However, several limitations and difficulties remain in determining the infiltration mechanism in arid and semiarid areas. This study combines the evaluations of soil water infiltration characteristics, recharge rate, and determination of groundwater age at a water table in a semiarid loess tableland to examine the recharge processes. The case study is the Xifeng loess tableland in the Loess Plateau of China, which has an unsaturated zone depth of 40–75 m and an obvious 1963-3H peak at a depth of 7.5 m. According to the piston flow, the soil water infiltration velocity is 0.12–0.14 m/yr, corresponding to a recharge rate of 37–41 mm/yr, based on the 1963-3H peak and chloride mass balance method. All of the groundwater from the water table and wells is old (tritium-free), with ages ranging from hundreds of years to 20,000 years, which suggests that no rapid modern recharge has occurred since the 1950s. The chloride content of soil water in the deep unsaturated zone, with an average value of 10.8 mg/L in the unsaturated zone below 30 m, overlaps with that in groundwater, at 4.0–10.9 mg/L. The comprehensive isotopic and chemical compositions for soil water and groundwater showed that piston flow was dominant during soil water infiltration at the field scale, resulting in the delay of modern water and related solutes entering the groundwater. Combined evaluations of the unsaturated zone with those of the saturated zone and the use of multiple environmental tracers, such as Cl, Br, 2H, 18O, 13C, 3H and 14C, can be regarded as a generic framework for studying the recharge processes in arid and semiarid areas with thick unsaturated zones at macroscopic and field scales. [ABSTRACT FROM AUTHOR]

The effects of land use change on the occurrence and frequency of preferential flow (fast water flow through a small fraction of the pore space) and piston flow (slower water flow through a large fraction of the pore space) are still not fully understood. In this study, we used a five year high resolution soil moisture monitoring dataset in combination with a response time analysis to identify factors that control preferential and piston flow before and after partial deforestation in a small headwater catchment. The sensor response times at 5, 20 and 50 cm depths were classified into one of four classes: (1) non-sequential preferential flow, (2) velocity based preferential flow, (3) sequential (piston) flow, and (4) no response. The results of this analysis showed that partial deforestation increased sequential flow occurrence and decreased the occurrence of no flow in the deforested area. Similar precipitation conditions (total precipitation) after deforestation caused more sequential flow in the deforested area, which was attributed to higher antecedent moisture conditions and the lack of interception. At the same time, an increase in preferential flow occurrence was also observed for events with identical total precipitation. However, as the events in the treatment period (after deforestation) generally had lower total, maximum, and mean precipitation, this effect was not observed in the overall occurrence of preferential flow. The results of this analysis demonstrate that the combination of a sensor response time analysis and a soil moisture dataset that includes pre- and post-deforestation conditions can offer new insights in preferential and sequential flow conditions after land use change. [ABSTRACT FROM AUTHOR]

Piston and preferential water flow are viewed as the two dominant water transport mechanisms regulating terrestrial water and solute cycles. However, it is difficult to accurately separate the two water flow patterns because preferential flow is not easy to capture directly in field environments. In this study, we take advantage of the afforestation induced desiccated deep soil, and directly quantify piston and preferential water flow using chloride ions (Cl−) and soil water profiles, in four deforested apple orchards on the Loess Plateau. The deforestation time ranged from 3 to 15 years. In each of the four selected orchards, there was a standing orchard that was planted at the same time as the deforested one, and therefore the standing orchard was used to benchmark the initial Cl− and soil water profiles of the deforested orchard. In the deforested orchards, piston flow was detected using the migration of the Cl− front, and preferential flow was measured via soil water increase below the Cl− front. Results showed that in the desiccated zone, Cl− migrated to deeper soil after deforestation, indicating that the desiccated soil layer formed by the water absorption of deep-rooted apple trees did not completely inhibit the movement of water. Moreover, there was an evident increase in soil water below the downward Cl− front, directly demonstrating the existence of preferential flow in deep soil under field conditions. Although pore water velocity was small in the deep loess, preferential water flow still accounted for 34–65% of total infiltrated water. This study presented the mechanisms that regulate movement of soil water following deforestation through field observations and advanced our understanding of the soil hydrologic process in deep soil. [ABSTRACT FROM AUTHOR]