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1.
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.  相似文献   

2.
Periodic paddy field flooding is a major source of groundwater recharge. Many paddy fields thus are used as groundwater recharge ponds after harvesting the first crop of the summer. Following rice harvesting, paddy field surfaces may crack into fissures as a result of drainage and exposure to sunlight. Field observation indicates that applying precipitation to the paddy field can increase the rate of infiltration. To quantitatively evaluate the amount of infiltration in a cracked paddy field, this study sets up a simple soil crack model to simulate the field infiltration process. A three‐dimensional groundwater model FEMWATER is adopted to simulate water movement in the paddy field subjected to various crack conditions. Using the field and laboratory data of irrigation water requirements, soil physical properties, hydraulic conductivities and soil profiles obtained from Ten‐Chung, FEMWATER simulates the water movement in the dry cracked paddy. Simulation results show that if the cracks develop extensively and penetrate the ploughed soil, the infiltration rate may increase significantly. The infiltration fluxes of crack with depths of 80, 60 and 27·5 cm are 18·77, 14·50 and 8·06 times higher than that of 20 cm, respectively. The simulation results of cracks with 80 cm depth correlated closely with field observations. The results of the study elucidate the processes of unsaturated water movement in a dry cracked paddy field. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

3.
Water content and movement in soil profile and hydrogen isotope composition (δD) of soil water, rainwater, and groundwater were examined in a subalpine dark coniferous forest in the Wolong National Nature Reserve in Sichuan, China, following rainfall events in 2003–2004. Light rainfall increased water content in the litter and at soil depth of 0–80 cm, but the increased soil water was lost in several days. Heavy rainfall increased soil water content up to 85% at depths of 0–40 cm. Following the light rainfall in early spring, the δD of water from the litter, humus, illuvial, and material layers decreased first and then gradually reached the pre‐rainfall level. In summer, light rainfall reached the litter humus, and illuvial layer, but did not hit the material layer. Heavy rainfall affected δD of water in all layers. The δD of soil interflow slightly fluctuated with rainfall events. The δD of shallow groundwater did not differ significantly among all rainfall events. Light rainfall altered the shape of δD profile curve of water in the upper layer of soil, whereas heavy rainfall greatly affected the shape of δD profile curve of water in all soil layers. Following the heavy rainfall, preferential flow initially occurred through macropores, decayed plant roots, and rocks at different depths of soil profile. With continuing rainfall, the litter and surface soil were nearly saturated or fully saturated, and infiltration became homogeneous and plug‐like. Forest soil water, particularly in deeper soil profile, was slightly affected by rainfall and, thus, can be a source of water supply for regional needs, particularly during dry seasons. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
Abstract

Many of the hydrological and ecological functions of alluvial flood plains within watersheds depend on the water flow exchanges between the vadoze soil zone and the shallow groundwater. The water balance of the soil in the flood plain is investigated, in order to evaluate the main hydrological processes that underlie the temporal dynamics of soil moisture and groundwater levels. The soil moisture and the groundwater level in the flood plain were monitored continuously for a three-year period. These data were integrated with the results derived from applying a physically-based numerical model which simulated the variably-saturated vertical water flow in the soil. The analysis indicated that the simultaneous processes of lateral groundwater flow and the vertical recharge from the unsaturated zone caused the observed water table fluctuations. The importance of these flows in determining the rises in the water table varied, depending on soil moisture and groundwater depth before precipitation. The monitoring period included two hydrological years (September 2009–September 2011). About 13% of the precipitation vertically recharged the groundwater in the first year and about 50% in the second. The difference in the two recharge coefficients was in part due to the lower groundwater levels in the recharge season of the first hydrological year, compared to those observed in the second. In the latter year, the shallow groundwater increased the soil moisture in the unsaturated zone due to capillary rise, and so the mean hydraulic conductivity of the unsaturated soil was high. This moisture state of soil favoured a more efficient conversion of infiltrated precipitation into vertical groundwater recharge. The results show that groundwater dynamics in the flood plain are an important source of temporal variability in soil moisture and vertical recharge processes, and this variability must be properly taken into account when the water balance is investigated in shallow groundwater environments.

Citation Pirastru, M. and Niedda, M., 2013. Evaluation of the soil water balance in an alluvial flood plain with a shallow groundwater table. Hydrological Sciences Journal, 58 (4), 898–911.  相似文献   

5.
The contradiction between the freshwater shortage and the large demand of freshwater by irrigation was the key point in cultivated lowland area of North China Plain. Water transfer project brings fresh water from water resource‐rich area to water shortage area, which can in turn change the hydrological cycle in this region. Major ions and stable isotopes were used to study the temporal variations of interaction between surface water and groundwater in a hydrological year after a water transfer event in November 2014. Irrigation canal received transferred Yellow River, with 2.9% loss by evaporation during water transfer process. The effect of transferred water on shallow groundwater decreased with increasing distance from the irrigation canal. Pit pond without water transfer receives groundwater discharge. During dry season after water transfer event, shallow groundwater near the irrigation canal was recharged by lateral seepage and deep percolation of irrigation, whereas shallow groundwater far from irrigation canal was recharged by deep percolation of deep groundwater irrigation. Canal water lost by evaporation was 2.7–17.4%. Influence of water transfer gradually disappeared until March as the water usage of agricultural irrigation increased. In the dry season, groundwater discharged to irrigation canal and pond; 2.2–31.6% canal water and 11.3–20.0% pond water were lost by evaporation. In the rainy season (June to September), surface water was fed mainly by precipitation and surface run‐off, whereas groundwater was recharged by infiltration of precipitation. The two‐end member mix model showed that the mixing ratio of precipitation in pond and irrigation canal were 73–83.4% (except one pond with 28.1%) and 77.3–99.9%, respectively. Transferred water and precipitation were the important recharge sources for shallow groundwater, which decreased groundwater salinity in cultivated lowland area of North China Plain. With the temporary and spatial limitation of water transfer effects, increased water transfer amounts and frequency may be an effective way of mitigating regional water shortage. In addition, reducing the evaporation of surface water is also an important way to increase the utilization of transfer water.  相似文献   

6.
To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic‐rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

7.
Depletion and recharge dynamics of soil water were studied at two forest sites in Northern and Southern Sweden during three growing seasons. At each site, having a stand of Norway spruce (Picea abies (L.) Karst), soil water potential was measured with 90 gypsum blocks in 30 profiles at depths of 6, 20, and 50 cm from the soil surface. The size of the rectangular plots was 250 m2. The large variation in soil water potential during desiccation periods extended throughout the measuring range of the gypsum blocks. The soil water potentials, at different times and depths, were log-normally distributed during only parts of the desiccation periods. Due to the large variation and skewed distribution of soil water potentials the nonparametric Spearman rank correlation statistics was used to analyse the pattern of desiccation and rewetting of the soil. In the beginning of a dry period the topsoil was more efficiently desiccated than the subsoil at both sites. This difference lasted throughout all droughts at the southern site and was explained by a higher root density in the topsoil. At the northern site, however, there was no difference in the degree of desiccation at different soil depths during an extended desiccation period. While certain microsites tended to be more depleted than others during desiccation periods, this did not prove to be significantly correlated to the rewetting of the soil after the different droughts. There was a vertical relationship in soil water desiccation in which an accentuated water depletion at the 6 cm soil depth was followed by a similar strong depletion 14 cm lower in the same observation profile. Strongly desiccated observation profiles were not necessarily situated close to each other but seemed randomly spread over the site. There was no relationship between extracted water at any of the three soil depths in the different observation profiles and proximity to trees or tree size.  相似文献   

8.
Many researchers have studied the influence of rainfall patterns on soil water movement processes using rainfall simulation experiments. However, less attention has been paid to the influence under natural condition. In this paper, rainfall, soil water content (SWC), and soil temperature at 10‐, 20‐, 30‐, 40‐, and 50‐cm depths were simultaneously monitored at 1‐min intervals to measure the variation in SWC (SWCv) in response to rainfall under different rainfall patterns. First, we classified rainfall events into four patterns. During the study period, the main pattern was the advanced rainfall pattern (38% of all rainfall events), whereas the delayed, central, and uniform rainfall patterns had similar frequencies of about 20%. During natural rainfall, rainwater rapidly passed through the top soil layers (10–40 cm) and was accumulated in the bottom layer (50 cm). When a high rainfall pulse occurred, the water storage balance was disturbed, resulting in the drainage of initial soil water from the top layers into the deeper layers. Therefore, the critical function of the top layers and the bottom layers was infiltration and storage, respectively. The source of water stored in the bottom layer was not only rainfall but also the initial soil water in the upper soil layers. Changes in soil temperature at each soil depth were comonitored with SWCv to determine the movement characteristics of soil water under different rainfall patterns. Under the delayed rainfall pattern, preferential flows preferred to occur. Under the other rainfall patterns, matrix flow was the main form of soil water movement. Rainfall amount was a better indicator than rainfall intensity for SWCv in the bottom layer under the delayed rainfall pattern. These results provide insights into the responses of SWCv under different rainfall patterns in northern China.  相似文献   

9.
This study investigates spatial patterns and temporal dynamics of aquifer–river exchange flow at a reach of the River Leith, UK. Observations of sub‐channel vertical hydraulic gradients at the field site indicate the dominance of groundwater up‐welling into the river and the absence of groundwater recharge from surface water. However, observed hydraulic heads do not provide information on potential surface water infiltration into the top 0–15 cm of the streambed as these depths are not covered by the existing experimental infrastructure. In order to evaluate whether surface water infiltration is likely to occur outside the ‘window of detection’, i.e. the shallow streambed, a numerical groundwater model is used to simulate hydrological exchanges between the aquifer and the river. Transient simulations of the successfully validated model (Nash and Sutcliff efficiency of 0·91) suggest that surface water infiltration is marginal and that the possibility of significant volumes of surface water infiltrating into non‐monitored shallow streambed sediments can be excluded for the simulation period. Furthermore, the simulation results show that with increasing head differences between river and aquifer towards the end of the simulation period, the impact of streambed topography and hydraulic conductivity on spatial patterns of exchange flow rates decreases. A set of peak flow scenarios with altered groundwater‐surface water head gradients is simulated in order to quantify the potential for surface water infiltration during characteristic winter flow conditions following the observation period. The results indicate that, particularly at the beginning of peak flow conditions, head gradients are likely to cause substantial increase in surface water infiltration into the streambed. The study highlights the potential for the improvement of process understanding of hyporheic exchange flow patterns at the stream reach scale by simulating aquifer‐river exchange fluxes with a standard numerical groundwater model and a simple but robust model structure and parameterization. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Accurate estimation of the soil water balance (SWB) is important for a number of applications (e.g. environmental, meteorological, agronomical and hydrological). The objective of this study was to develop and test techniques for the estimation of soil water fluxes and SWB components (particularly infiltration, evaporation and drainage below the root zone) from soil water records. The work presented here is based on profile soil moisture data measured using dielectric methods, at 30‐min resolution, at an experimental site with different vegetation covers (barley, sunflower and bare soil). Estimates of infiltration were derived by assuming that observed gains in the soil profile water content during rainfall were due to infiltration. Inaccuracies related to diurnal fluctuations present in the dielectric‐based soil water records are resolved by filtering the data with adequate threshold values. Inconsistencies caused by the redistribution of water after rain events were corrected by allowing for a redistribution period before computing water gains. Estimates of evaporation and drainage were derived from water losses above and below the deepest zero flux plane (ZFP), respectively. The evaporation estimates for the sunflower field were compared to evaporation data obtained with an eddy covariance (EC) system located elsewhere in the field. The EC estimate of total evaporation for the growing season was about 25% larger than that derived from the soil water records. This was consistent with differences in crop growth (based on direct measurements of biomass, and field mapping of vegetation using laser altimetry) between the EC footprint and the area of the field used for soil moisture monitoring. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
One-dimensional infiltration experiments were conducted using hydrophilic and water-repellent soils from the Guishui River Basin to study the effects of soil water repellency on cumulative infiltration (CI) and the infiltration rate (IR). The test results show that, for the hydrophilic soil (HS) sample, CI increases monotonously with time and IR decreases monotonously. For the water-repellent soil (W-RS), however, the following characteristics were observed: (a) There is an inflection point in CI and a sudden increase in IR. Larger values of the initial soil water content produce an earlier and more significant inflection point in CI, and a larger peak value of IR. (b) The post-peak stable IR is greater than the pre-peak value, ignoring the beginning of rapid infiltration, and the overall IR presents a single peak. The applicability of various water infiltration models was analysed for the two soil types. Numerical analysis suggests the following conclusions: (a) For both HS and W-RS, the Kostiakov function, Gamma function, and Beta function (BF) models exhibit good applicability. (b) For W-RS, the Gauss function model not only reflects the monotonous decrease in IR, but also produces a steady IR in the initial stage, a gradual increase before the peak value, and a gradual decrease after the peak value. Similarly, the BF model reflects the monotonous decrease in IR. A piecewise BF reproduces the U-shaped change in rapid infiltration before the inflection point, as well as the gradual increase and right-skewed distribution curve of W-RS infiltration before and after the inflection point. The BF model achieves the best simulation accuracy and has the widest applicability.  相似文献   

12.
In shallow water table‐controlled environments, surface water management impacts groundwater table levels and soil water dynamics. The study goal was to simulate soil water dynamics in response to canal stage raises considering uncertainty in measured soil water content. Water and Agrochemicals in the soil, crop and Vadose Environment (WAVE) was applied to simulate unsaturated flow above a shallow aquifer. Global sensitivity analysis was performed to identify model input factors with the greatest influence on predicted soil water content. Nash–Sutcliffe increased and Root Mean Square Error reduced when uncertainties in measured data were considered in goodness‐of‐fit calculations using measurement probability distributions and probable asymmetric error boundaries, implying that appropriate model performance evaluation should be carried out using uncertainty ranges instead of single values. Although uncertainty in the experimental measured data limited evaluation of the absolute predictions by the model, WAVE was found a useful exploratory tool for estimating temporal variation in soil water content. Visual analysis of soil water content time series under proposed changes in canal stage management indicated that sites with land surface elevation of less than 2.0‐m NGVD29 were predicted to periodically experience saturated conditions in the root zone and shortening of the growing season if canal stage is raised more than 9 cm and maintained at this level. The models developed could be combined with high‐resolution digital elevation models in future studies to identify areas with the greatest risk of experiencing saturated root zone. The study also highlighted the need to incorporate measurement uncertainty when evaluating performance of unsaturated flow models. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
内蒙古呼伦湖水量平衡计算与分析   总被引：2，自引：2，他引：0  
根据呼伦湖的实际水文过程,计算1963-1980年月水量平衡,在此基础上,分析库容与径流、径流+降雨、径流+降雨-蒸发的相关性.利用累积和分析水位、径流、降雨、蒸发年均值的突变情况,进而重点论述了2000年后水位持续降低的原因.同时,探讨各水平衡项的年内分布规律及相互关系.结果表明,2000年后水位的急剧降低是气候变化(暖干化)造成的.河川径流对水位的影响程度最大,其次为湖面降雨.每年4、5月,冰封期积累的降雪融化渗入地下补给湖泊,其他时间则由湖泊补给地下水.  相似文献   

14.
The Chinese Loess Plateau (CLP) is a unique Critical Zone with deep loess deposits, where soil moisture is primarily replenished by seasonal monsoon rainfall. However, the role of vegetation, coupled with complex topography, on rainwater infiltration on the CLP, especially after long‐term revegetation for controlling erosion, is inadequately quantified. Over the growing season of 2016, we monitored soil moisture at the 30‐min interval at 5 depths (10, 20, 40, 60, and 100 cm) in an afforested catchment and a nearby catchment with natural regrowth of grasses. Two monitoring sites were established in each catchment, one in the downhill gully and the other in the uphill slope. We found that vegetation, topography, and rainfall attributes together determined rainwater infiltration and soil moisture replenishment. An accumulated rainfall amount of 9 mm was required to trigger soil moisture response at 10‐cm depth at the 2 grassland sites and the forestland uphill‐slope site whereas 14 mm of rainfall was required for the forestland gully site covered by dense undergrowth and trees. Rainfall events with larger sums and higher peak intensities permitted rainwater infiltration to deeper soil depths. However, no rain recharged soil moisture to 100‐cm depth during the monitoring period. The forestland uphill‐slope site showed the deepest wetting depth (up to 60‐cm depth), fastest wetting‐front velocity (up to 4 cm/hr below 10‐cm depth), and the most significant soil moisture increase (up to 15% cm 3 cm?3 increase at 10‐cm depth) after rainfall in the growing season. The grassland gully site had the highest soil water storage, whereas soil moisture was depleted the most at the forestland gully site. Findings of this study reveal the transient dynamics of soil moisture after rainfall on the CLP, which signifies the role of revegetation on rainwater infiltration in the loess Critical Zone.  相似文献   

15.
The main objective of this research was to analyse the effect of soil management on soil sealing and on soil water content under contrasting tillage practices and its influence on corn yield. The experimental research was carried out in a field cultivated with irrigated corn differentiated into three zones representing a gradient of soil texture (Z1, Z2, and Z3, i.e., increasingly coarser). Two plots under different soil management practices (conventional intensive tillage, CT, and no‐tillage, NT) were selected in each zone. The susceptibility to sealing of each soil and the steady infiltration rates were evaluated in the laboratory subjecting the soils to rainfall simulation applied at an intensity of 25 mm h?1. In addition, soil porosity under each treatment was quantified. Soil water content (0–90 cm depth) was determined gravimetrically at the beginning and the end of the growing cycle and at the surface (0–5 cm) during three growing seasons and continuously at two depths (5–15 and 50–60 cm) during the last growing cycle. Soil water content was simulated using the SIMPEL model, which was calibrated for the experimental conditions. Corn yield and above‐ground biomass were also analysed. Significant differences in soil sealing among zones, with decreasing soil sealing for coarser textures, and treatments were observed with infiltration rates that were near twice in NT than in CT, being the effect of soil cover significant in the reduction of soil detachment and soil losses. NT showed higher soil water content than CT, especially in the surface layers. Above‐ground biomass production was smaller in CT than in NT, and in the areas with higher sealing susceptibility was 30% to 45% smaller than in other zones, reaching the smallest values in Z1. A similar reduction in corn yield was observed between treatments being smaller in CT than in NT. No‐tillage has been confirmed as an effective technique that benefits soil physical properties as well as crop yields in relation to CT, being its impact greater in soils susceptible to sealing.  相似文献   

16.
Dry saline soils are common in the arid and hyper‐arid basins located in the Chilean Altiplano, where evaporation from shallow groundwater is typically the major component of the water balance. Thus, a good understanding of evaporation processes is necessary for improving water resource planning and management in these regions. In this study, we conducted laboratory experiments with a natural saline soil column to estimate evaporation rates and assess the liquid and water vapor fluxes under different water table levels. Water content, electrical conductivity and temperature at different depths were utilized to assess the liquid and water vapor fluxes in the soil column. We observed movement of water that dissolves salts from the soil and transports them to areas in the column where they accumulate. Isothermal liquid flux was predominant, while thermal and isothermal liquid and thermal water vapor fluxes were negligible, except for deep water table levels where isothermal and thermal water vapor fluxes had similar magnitude but opposite directions. Differences observed in total fluxes for all water table levels were due to different upward and downward fluxes, which depend on changes in water content and temperature within the soil profile. Both the vapor flux magnitude and direction were found to be very sensitive to the choice of empirical parameters used in flux quantification, such as tortuosity and the enhancement factor for local temperature gradients in the air phase within the column. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

17.
Soil water content is a key variable for biogeochemical and atmospheric coupled processes. Its small‐scale heterogeneity impacts the partitioning of precipitation (e.g., deep percolation or transpiration) by triggering threshold processes and connecting flow paths. Forest hydrologists frequently hypothesized that throughfall and stemflow patterns induce soil water content heterogeneity, yet experimental validation is limited. Here, we pursued a pattern‐oriented approach to explore the relationship between net precipitation and soil water content. Both were measured in independent high‐resolution stratified random designs on a 1‐ha temperate mixed beech forest plot in Germany. We recorded throughfall (350 locations) and stemflow (65 trees) for 16 precipitation events in 2015. Soil water content was measured continuously in topsoil and subsoil (210 profiles). Soil wetting was only weakly related to net precipitation patterns. The precipitation‐induced pattern quickly dissipates and returns to a basic pattern, which is temporally stable. Instead, soil hydraulic properties (by the proxy of field capacity) were significantly correlated with this stable soil water content pattern, indicating that soil structure more than net precipitation drives soil water content heterogeneity. Also, both field capacity and soil water content were lower in the immediate vicinity of tree stems compared to further away at all times, including winter, despite stemflow occurrence. Thus, soil structure varies systematically according to vegetation in our site. We conclude that enhanced macroporosity increases gravity‐driven flow in stem proximal areas. Therefore, although soil water content patterns are little affected by net precipitation, the resulting soil water fluxes may strongly be affected. Specifically, this may further enhance the channelling of stemflow to greater depth and beyond the rooting zone.  相似文献   

18.
Seasonal signals of stable isotopes in precipitation, combined with measurements of isotope ratios in soil water, can be used for quantitative estimation of groundwater recharge rates. This study investigates the applicability of using the piston flow principle and the peak shift displacement method to estimate actual groundwater recharge rates in a humid Nordic region located in the province of Quebec, Canada. Two different sites with and without vegetation (C1 and C2) in an unconfined aquifer were tested by measuring soil water isotope ratios (18O/16O and 2H/1H) and volumetric pore water content. Core samples were obtained along the vadose zone down to the groundwater table at the two sites (2.45 m for Site C1 and 4.15 m for Site C2). The peak shift method to estimate groundwater recharge rates was shown to be accurate only in certain specific conditions inherent to the soil properties and the topographical situation of the investigated sites. Indeed, at Site C2, recharge from the snowmelt could not be estimated because of heterogeneity in the lower part of the vadose zone. At this same site the later recharge after the snowmelt (in the period from late spring to early autumn) could be estimated accurately because the upper part of the vadose zone was homogeneous. Furthermore, at site C1, runoff/runon phenomena hampered calculations of actual infiltration and thus produced inaccurate results for recharge. These two different site effects (heterogeneity in the first site and runoff/runon in the other site) were identified as being limiting factors in the accurate assessment of actual recharge. This study therefore recommends the use of the peak shift method for (1) humid Nordic regions, (2) homogeneous and thick vadose zones, and (3) areas with few or limited site effects (runoff/runon).  相似文献   

19.
High‐elevation mountain catchments are often subject to large climatic and topographic gradients. Therefore, high‐density hydrogeochemical observations are needed to understand water sources to streamflow and the temporal and spatial behaviour of flow paths. These sources and flow paths vary seasonally, which dictates short‐term storage and the flux of water in the critical zone (CZ) and affect long‐term CZ evolution. This study utilizes multiyear observations of chemical compositions and water residence times from the Santa Catalina Mountains Critical Zone Observatory, Tucson, Arizona to develop and evaluate competing conceptual models of seasonal streamflow generation. These models were tested using endmember mixing analysis, baseflow recession analysis, and tritium model “ages” of various catchment water sources. A conceptual model involving four endmembers (precipitation, soil water, shallow, and deep groundwater) provided the best match to observations. On average, precipitation contributes 39–69% (55 ± 16%), soil water contributes 25–56% (41 ± 16%), shallow groundwater contributes 1–5% (3 ± 2%), and deep groundwater contributes ~0–3% (1 ± 1%) towards annual streamflow. The mixing space comprised two principal planes formed by (a) precipitation‐soil water‐deep groundwater (dry and summer monsoon season samples) and (b) precipitation‐soil water‐shallow groundwater (winter season samples). Groundwater contribution was most important during the wet winter season. During periods of high dynamic groundwater storage and increased hydrologic connectivity (i.e., spring snowmelt), stream water was more geochemically heterogeneous, that is, geochemical heterogeneity of stream water is storage‐dependent. Endmember mixing analysis and 3H model age results indicate that only 1.4 ± 0.3% of the long‐term annual precipitation becomes deep CZ groundwater flux that influences long‐term deep CZ development through both intercatchment and intracatchment deep groundwater flows.  相似文献   

20.
The groundwater in shallow loess aquifers in high mountain–hills in the western Loess Plateau in China is almost the sole water resource for local residents. However, the question about how the loess groundwater naturally circulates in these high mountain–hills, characterized by low precipitation and high potential evaporation, remains unclear. The objectives of this study are to evaluate the application of hydrogen and oxygen isotopes to (1) examine temporal variations of the isotopic composition of precipitation and shallow groundwater and (2) uncover the mechanism of groundwater recharge in high mountain–hills. Results from 2 years of monitoring data show a difference in the stable isotopes for groundwater and local precipitation between the winter and summer periods. Similar to precipitation, stable isotopes in groundwater are observed to be depleted in winter and enriched in summer, particularly in oxygen isotope. A prominent characteristic is that H and O isotopes of groundwater show a very clear response to strong precipitation in the rainy season in 2013. The results highlight that local precipitation is the likely recharge source for groundwater in shallow loess aquifers. Annual recharge from local precipitation maintains the groundwater resource in the shallower loess aquifer. The mechanisms governing shallow loess groundwater recharge in high mountain–hills were evaluated. In addition to possible vertical slow percolation of soil water through the unsaturated zone, rapid groundwater recharge mechanisms have been identified as temporal preferential infiltration through sinkholes, slip surface or landslide surface and through the interface of loess layer and palaeo‐soils. Most groundwater can be recharged after a heavy rainy season. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

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