首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
A method for collecting suspended sediment samples has been developed that pumps a discharge-weighted volume of water from fixed depths at four to 40 locations across a river and separates the suspended sediment in the sample using a continuous-flow centrifuge. The efficacy of the method is evaluated by comparing the particle size distributions of sediment collected by the discharge-weighted pumping method with the particle size distributions of sediment collected by depth integration and separated by gravitational settling. The pumping method was found to undersample the suspended sand sized particles (> 63 μm) but to collect a representative sample of the suspended silt and clay sized particles (< 63 μm). The centrifuge separated the silt and clay sized particles (< 63 μm) into three fractions. Based on the average results of processing 17 samples from the Mississippi River and several of its large tributaries in 1990, about 10% of the silt and clay sized material was trapped in a centrifuge bowl-bottom sealing unit containing the nozzle and consisted of mostly medium and coarse silt from 16 to 63 μm. About 74% was retained on a Teflon liner in the centrifuge bowl and consisted of sizes from 0–1 to 63 μm. About 9% was discharged from the centrifuge in the effluent and was finer than 0–1 μm. About 7% was lost during the processes of removing the wet sediment fractions from the centrifuge, drying and weighing. The success of the discharge-weighted pumping method depends on how homogeneously the silt and clay sized particles (< 63 μm) are distributed in the vertical direction in the river. The degree of homogeneity depends on the composition and degree of aggregation of the suspended sediment particles.  相似文献   

2.
Dynamic simulation on hydraulic characteristic values of overland flow   总被引：1，自引：0，他引：1  
The economic forest management is one of the main land use models on low hill gentle slope. In order to investigate the soil erosion properties of bare slope under economic forest, dynamic simulation on hydraulic characteristic values of overland flow was carried out under 0.5 mm min?1, 1.2 mm min?1 and 1.8 mm min?1 rainfall intensities. Results indicated that runoff shear stress increased with increasing of slope length and their relationship can be described by quadratic equation. There were abnormal points at the length of 4 m and 5.5 m under rainfall intensity of 1.8 mm min?1. The shallow flow was pseudo-laminar flow under 0.5 mm min?1, 1.2 mm min?1 and 1.8 mm min?1 rainfall intensities, and the runoff at upslope was sluggish flow then changed to torrential flow at downslope with increasing of slope length. Critical Reynolds number varied from sluggish flow to torrential flow with 1.8 mm min?1 rainfall intensity and was more than that under 0.5 mm min?1. Reynolds number can be estimated by power function of slope length. And there was a positive correlation between runoff shear stress and both Froude number Fr and Reynolds number Re. We hope this study can provide scientific gist for soil erosion control under economic forest.  相似文献   

3.
Production rates of22Na (T1/2 = 2.6years) from aluminium by the action of cosmic rays are measured at the Mont Blanc (altitude 4600 m), the Aiguille du Midi (3840 m), and the Col du Lautaret (2070 m). They are2.3 ± 0.5,1.8 ± 0.3,and0.77 ± 0.18 atoms min?1 kg?1, respectively, in good agreement with the calculated production rates, 2.4, 1.7 and 0.6 atoms min?1 kg?1, respectively, at the three stations.Production rates of24Na (T1/2 = 15hours) from aluminium and magnesium are also measured at the Aiguille du Midi; the observed rates of3.4 ± 0.4and6.0 ± 1.7 atoms min?1 kg?1, respectively, agree well with the theoretically expected rates of 3.7 and 5.6 atoms min?1 kg?1.The production rates of3H,7Be,10Be,14C,22Na,26Al,36Cl,37Ar,39Ar,53Mn,54Mn, and55Fe in terrestrial rocks by the action of cosmic rays are calculated in order to show the possibility of applying the measurements of these cosmogenic radionuclides to the earth science.  相似文献   

4.
The drastic growth of population in highly industrialized urban areas, as well as fossil fuel use, is increasing levels of airborne pollutants and enhancing acid rain. In rapidly developing countries such as Iran, the occurrence of acid rain has also increased. Acid rain is a driving factor of erosion due to the destructive effects on biota and aggregate stability; however, little is known about its impact on specific rates of erosion at the pedon scale. Thus, the present study aimed to investigate the effect of acid rain at pH levels of 5.25, 4.25, and 3.75 for rainfall intensities of 40, 60, and 80 mm h?1 on initial soil erosion processes under dry and saturated soil conditions using rainfall simulations. The results were compared using a two‐way ANOVA and Duncan tests and showed that initial soil erosion rates with acidic rain and non‐acidic rain under dry soil conditions were significantly different. The highest levels of soil particle loss due to splash effects in all rainfall intensities were observed with the most acidic rain (pH = 3.75), reaching maximum values of 16 g m?2 min?1. The lowest levels of particle losses were observed in the control plot where non‐acidic rain was used, with values ranging from 3.8 to 8.1 g m?2 min?1. Similarly, under saturated soil conditions, the lowest level of soil particle loss was observed in the control plot, and the highest peaks of soil loss were observed for the most acidic rains (pH = 3.75 and pH = 4.25), reaching maximum average values of 40 g m?2 min?1. However, for saturated soils with acidic water but with non‐acidic rain, the highest soil particle loss was observed for the control plot for all the rainfall intensities. In conclusion, acidic rain has a negative impact on soils, which can be more intense with a concomitant increase in rainfall intensity. Rapid solutions, therefore, need to be found to reduce the emission of pollutants into the air, otherwise, rainfall erosivity may drastically increase.  相似文献   

5.
Measurement of excess 234Th (t1/2 = 24.1 days) in surface sediment from 12 stations throughout Long Island Sound, U.S.A., demonstrates: (1) a mean (summer) sediment inventory of 3.6 dpm/cm2 consistent with complete, nearly instantaneous removal of 234Th from the overlying water and capture within the estuary, and (2) preferential association of excess 234Th with small particles and inventory build-ups in muddy bottom areas. There may also be a tendency for higher inventories in areas of high physical or biogenic reworking of surface sediments. A range of particle reworking rates (0–5 cm) from <0.01 × 10?6 to 1.6 × 10?6 cm2/s is found in the Sound with most values ～0.2?0.5 × 10?6 cm2/s. The inventory and reworking patterns demonstrate the high mobility, both horizontal and vertical, of particles in the estuary on 234Th decay time scales and are unequivocal evidence for control of reactive element distribution in the water column by the muddy regions of the basin.  相似文献   

6.
Continuous flow centrifugation (CFC) is a well‐established technique used in natural surface water studies to collect large amounts of suspended solids, thus allowing a broad spectrum of measurements. However, a potential contamination or changes in the particle size distribution during the centrifugation may restrain the use of CFC effluents for element analysis in the colloidal and dissolved fractions. In this paper we evaluate the possibility of using the effluent of a Westfalia centrifuge (type KA2‐06‐075, 9700 rpm) for such analysis. This evaluation is based on two laboratory experiments with deionized and tap water and two field experiments in rivers. Elemental concentration changes across the CFC were assessed from the CFC influent and effluent after a filtration at 0·45 µm. Significant increases were found, mainly in the field experiments at a high suspended solids level and a slightly acid pH. A hypothesis was made on the origin of these increases as a superposition of a centrifuge intrinsic contamination and a particle fragmentation effect. A numerical model based on elemental concentration measurements (inductively coupled plasma mass spectrometry) gave a particle fragmentation level of 0·55% (mass percentage of particles broken up into smaller fragments during centrifugation). In another experiment, a direct particle counting (single particle counter) shows an excess of particles smaller than 500 nm in the CFC effluent, corresponding to a fragmentation level of 0·11%. In consequence, the use of CFC effluent for element analysis is possible in low‐turbidity river or lake waters, but should be carefully considered in waters with high suspended matter contents. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

7.
Changes of soil surface roughness under water erosion process   总被引：5，自引：0，他引：5       下载免费PDF全文
The objective of this study was to determine the changing characteristics of soil surface roughness under different rainfall intensities and examine the interaction between soil surface roughness and different water erosion processes. Four artificial management practices (raking cropland, artificial hoeing, artificial digging, and contour tillage) were used according to the local agriculture customs of the Loess Plateau of China to simulate different types of soil surface roughness, using an additional smooth slope for comparison purposes. A total of 20 rainfall simulation experiments were conducted in five 1 m by 2 m boxes under two rainfall intensities (0.68 and 1.50 mm min?1) on a 15° slope. During splash erosion, soil surface roughness decreased in all treatments except raking cropland and smooth baseline under rainfall intensity of 0.68 mm min?1, while increasing for all treatments except smooth baseline under rainfall intensity of 1.50 mm min?1. During sheet erosion, soil surface roughness decreased for all treatments except hoeing cropland under rainfall intensity of 0.68 mm min?1. However, soil surface roughness increased for the artificial hoeing and raking cropland under rainfall intensity of 1.50 mm min?1. Soil surface roughness has a control effect on sheet erosion for different treatments under two rainfall intensities. For rill erosion, soil surface roughness increased for raking cropland and artificial hoeing treatments, and soil surface roughness decreased for artificial digging and the contour tillage treatments under two rainfall intensities. Under rainfall intensity of 0.68 mm min?1, the critical soil surface roughness was 0.706 cm for the resistance control of runoff and sediment yield. Under rainfall intensity of 1.50 mm min?1, the critical soil surface roughness was 1.633 cm for the resistance control of runoff, while the critical soil surface roughness was 0.706 cm for the resistance control of sediment yield. These findings have important implications for clarifying the erosive nature of soil surface roughness and harnessing sloped farmland. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Tropical rainforest canopy trees that have large projected areas of upwardly inclined branches are capable of funnelling large volumes of rainwater down their trunks. During periods of prolonged heavy rainfall on Mount Bellenden Ker in northeast Queensland, Australia, stemflow volumes were found to be as much as two orders of magnitude greater than the volume of incident rainfall expected in a rain gauge occupying an area equal to the trunk basal area. Stemflow totals ranging from 6000 to 70000 litres were generated by individual trees from 7800 mm of rainfall over two successive wet seasons. The combination of high intensity rainfall and the funnelling effect results in significant quantities of infiltration-excess at the ground surface. Stemflow fluxes as high as 31.4 cm3 min?1 per cm2 of basal area (i.e. the equivalent of 314 mm min?1) were recorded when rainfall intensity was only 2 mm min?1. The mean infiltration capacity of the topsoil was determined to be 6.2 mm min?1. The areas over which the stemflow would have had to spread in order to infiltrate were computed to be as much as 3 m2 around the bases of individual canopy trees. Approximations of the distances that the infiltration-excess would have travelled away from the tree bases were calculated by assuming that the infiltration area either expands radially outward in the form of an annulus or extends straight downslope from the tree base.  相似文献   

9.
The concentration of rock-forming elements, the static magnetic susceptibility κ, spectra of electron paramagnetic resonance, and their relative intensities I are studied in samples from a borehole drilled in Cenozoic sedimentary deposits of southern Western Siberia. All measured values experience appreciable irregular variations with depth. A linear dependence exists between κ and I within the range of their medium and large values; κ and I have maximum values in the same sample, and κmax = 1920 × 10?6SI, κmin = 210 × 10?6 SI, and κav = 630 × 10?6 SI. The magnetic properties of the samples are controlled by Fe2+ ions present in clastic material and by microphases (clusters) with Fe3+ ions of the goethite and lepidocrocite type present in the cement. The theoretically possible magnetic susceptibility of the Fe2+ ion system (provided that all iron exists in this form) is quite comparable with κmin but, even with very high concentrations of Fe2+, does not reach half of κav: (154 < κ(Fe2+) < 254) × 10?6 SI. Anomalously high values of κ are due to a large number of clusters with Fe3+ ions if structural units FeOOH do not dissociate and the interaction of the clusters with hydroxides of aluminum and precipitation medium impedes the process of their coagulation. Otherwise, the cluster sizes gradually increase, an antiferromagnetic structure develops in clusters, and the magnetic susceptibility decreases.  相似文献   

10.
In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0·375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2°C min?1 increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137°C min?1 and the average percentage time spent above 2°C min?1 was ～70 ± 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2°C min?1. Simultaneous measurements of two thermocouples 5·5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, ～10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.  相似文献   

11.
Surface infiltration and internal drainage properties of five soil types from arid drylands of South Africa were studied under double ring infiltrometer, rainfall simulation plots (1 m2) and instantaneous drainage plots (9 m2). Changes in soil water content during 40 minute rainfall simulation for a rainstorm with average intensity of 1.61 mm min?1 and 30 day drainage period were measured at various depths by 1.5 m long capacitance soil water measuring (DFM) probe. Different (P < 0.05) mean surface steady infiltration rate ranged from 0.05 to 4.47 mm min?1 and had a negative power relationship (R 2 = 0.65) with horizon clay plus fine silt content. Power regression (R 2 ≥ 86%) described rainstorm infiltration and obtained steady rates within an average time of 15 minutes. Mean total infiltrated soil water content was lowest (P < 0.05) from surface horizons with either 47.7% clay plus fine silt content or bulk density of 1.91 g cm?3 and exchangeable sodium of not less than 44 mg kg?1. Surface horizons with lower surface bulk density and total sand fraction of more than 72% had infiltrated depth and mean total infiltrated soil water content up to 40 cm deeper and 0.55 mm mm?1 greater, respectively. Drainage rate at drained upper limit calculated from the Wilcox drainage model (R 2 ≤ 0.97%) was 0.2 mm day?1 or less were from underlying horizons with either clay plus fine silt of 45% or soft calcium carbonate. Higher drainage rate with accumulative drainage amount greater than 60 mm were from soil profile horizons with clay plus fine silt content of less than 20% and above unity steady infiltration rates. Rainstorm infiltration and drainage rates was shown to depend on permeability and coarseness of the respective soil surface and subsurface horizons; a phenomenon critical for harnessing rain and flood water to recharge groundwater. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
Abstract

Evapotranspiration rates determined from meteorological data by the Bowen ratio method were tested against rates obtained from weighing lysimeters. The tests were conducted on an irrigated field (73 by 92 meters), where the minimum fetch was 27 m. Air-temperature and vapor-pressure differences obtained as 15-minute averages at heights of from 5 to 40 cm above the crop surface were used to calculate evapotranspiration. The results indicate that the Bowen ratio method can be used successfully to determine the evaporative flux for short periods, which can be summed for longer periods. During daylight periods, the absolute errors were less that. 0.02 cal cm?2 min?1 (or ly min?1), while the relative errors were less than 5 percent.  相似文献   

13.
The water exchange between the subpolar and subtropical gyres of the North Pacific is demonstrated by the simulation of chlorofluorocarbon (CFC) using an ocean general circulation model. The simulated CFC concentration in the North Pacific is in good agreement with observations. The water exchange is clearly illustrated by the tongues of CFC concentration. The subpolar waters with high CFC are transported southward into the eastern subtropical gyre, whereas the subtropical waters with low CFC are transported northward into the western subpolar gyre. The simulated exchange transport along 42°N in the layer of σθ< 26.8 indicates that the northward mass transport is about 15 Sv (1 Sv = 106 m3·s-1) west of 165°E, and about 5 Sv between 175°W and 150°W. The southward mass transport is about 5 Sv between 165°E and 175°W, and about 2 Sv east of 150°W.  相似文献   

14.
The degradation behaviour of a phenolic waste-water from coking containing easily utilizable carbon sources (volatile fatty acids), substances with toxic effects (phenols and phenolic compounds), and non-biodegradable organic substances (humic-like substances) by an adapted activated sludge is investigated depending on dissolved oxygen concentration (DO) and temperature. In addition, the degradation of an acetate model water with the same population was investigated. The investigations were carried out in a special respiration fermenter system by recording oxygen consumption in DO-static experiments. The oxygen consumption curves were subjected to linear regression analysis, and the maximum oxygen consumption rates were used for further calculations. Evaluation of the degradation kinetics was carried out with non-linear regression analysis via commercial software utilizing the Marquardt-Levenberg algorithm and which tested various kinetic models to obtain the best curve fit. It is shown that the dependence of growth on DO in acetate model water is well represented by Monod kinetics but by contrast can only be described in phenolic wastewater with acceptable goodness by Hill kinetics, modified by a maintenance term. The kinetic constants calculated for the mesophilic range (37 °C) are for the model water as follows: maximum specific growth rate = 0.218 h?1, half saturation constant with respect to oxygen = 0.297 g L?1, and for the waste-water: maximum specific growth rate = 0.387 h?1, half saturation constant with respect to oxygen = 0.013 gL?1 and maintenance coefficient for oxygen = 0.107 g g?1 h?1. For the thermophilic range (55 °C), a higher growth rate but a significant lower yield coefficient are to be observed. The kinetic constants calculated are: maximum specific growth rate = 0.8 h?1, half saturation constant with respect to oxygen = 0.14 gL?1 and maintenance coefficient for oxygen = 0.3 g g?1 h?1. Therefore, it can be concluded that the toxic effect of the biodegradable phenols causes a maintenance metabolism which leads to higher oxygen demand. The diminution of the limiting DO and the increased maintenance metabolism confirm the assumption that a higher maintenance metabolism leads to increased sensitivity with respect to the cosubstrate oxygen. It can be concluded that the experimental and mathematical methods used permit the maintenance metabolism with respect to oxygen caused by toxic substrates and milieu influences to be accurately determined.  相似文献   

15.
The study of thermal expansion by a dilatometer technique on a few granitic rocks from the Peninsular shield and Himalayan regions of India confirms that the linear coefficient of thermal expansion (α) is a function of heating rate, crack porosity, thermal cycling, mineral composition and grain orientation. Permanent set in the samples occurs at the limiting temperature (Tp) and restricts the validity of the apparent thermal-expansion coefficient with rise in temperature. Values of α are determined for a heating rate of ?2°C min?1 in order to calculate the volume coefficient of expansion (αv) and the temperature dependence of density (ρT).  相似文献   

16.
Limited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (Ks) with depth, but differences between lateral Ks of a concretion layer and the vertical Ks of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low‐flow (LF) seeps (flow rates typically less than 0·05 L min?1), persistent high‐flow (HF) seeps (average flow rate of 0·39 L min?1) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than ?5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min?1 and sediment concentrations commonly approached 100 g L?1. Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min?1) and sediment concentrations (989 g L?1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
Surface water–groundwater interaction in the hyporheic zone may enhance biogeochemical cycling in streams, and it has been hypothesized that streams exchanging more water with the hyporheic zone should have more rapid nitrate utilization. We used simultaneous conservative solute and nitrate addition tracer tests to measure transient storage (which includes hyporheic exchange and in‐stream storage) and the rate of nitrate uptake along three reaches within the Red Canyon Creek watershed, Wyoming. We calibrated a one‐dimensional transport model, incorporating transient storage (OTIS‐P), to the conservative solute breakthrough curves and used the results to determine the degree of transient storage in each reach. The nitrate uptake length was quantified from the exponential decrease in nitrate concentration with distance during the tracer tests. Nitrate uptake along the most downstream reach of Red Canyon Creek was rapid (turnover time K?1c = 32 min), compared with nitrate uptake reported in other studies (K?1c = 12 to 551 min), but other sites within the watershed showed little nitrate retention or loss. The uptake length Sw‐NO?3 for the most downstream reach was 500 m and the mass transfer coefficient Vf‐NO?3 was 6·3 m min?1. Results from 15 other nitrate‐addition tracer tests were used to create a regression model relating transient storage and measures of stream flow to nitrate uptake length. The model, which includes specific discharge and transient storage area, explains almost half the variability in nitrate uptake length (adjusted R2 = 0·44) and is most effective for comparing sites with very different stream characteristics. Although large differences in specific discharge and storage zone area explain inter‐site differences in nitrate uptake, other unmeasured variables, such as available organic carbon and microbial community composition, are likely important for predicting differences in nitrate uptake between sites with similar specific discharge rates and storage zone areas, such as when making intra‐site comparisons. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

18.
Fine suspended materials in the particle-size range1 < r < 6 μm (r, equivalent sphere radius) from the equatorial North Atlantic, between the ocean surface and greater depths (30–5100 m), can be consistently described by a size-distribution relationshipdN/dr = Ar?b, where the parametersA andb are independent ofr. The shape of the particle-size distribution is essentially constant and independent of depth, as reflected in the values of the logarithmic slope of the size distributionb = 4.0 ± 0.3. The particle-number and mass concentration, however, decrease strongly with depth, most of the decrease taking place in the surface layer 200 m deep. In the surface layer, mass concentration decreases exponentially with the half-concentration depthz1/2 ? 60m; in the deep layer (200–5000 m),z1/2 ? 1000m. The computed removal half-lives of the particulate material are0.8 ± 0.6yr in the surface layer, and60 ± 20yr in the deep layer, both half-lives being considerably shorter than Stokes settling residence times. The fast turnover or removal rate in the surface layer is compatible with the rates of zooplankton growth and carbon assimilation.  相似文献   

19.
Oxygen isotope exchange between anhydrite and water was studied from 100 to 550°C, using the partial equilibrium method. The exchange rate was extremely low in NaCl solution. In the lower-temperature range, acid solutions were used to produce sufficient reaction to determine the oxygen isotope fractionation factors. The fractionation factors obtained in the present study are definitely different from those given by Lloyd [8]. They are similar to those for the HSO4?-water system studied by Mizutani and Rafter [19], and are consistently 2‰ higher than those of the barite-water system by Kusakabe and Robinson [5]. The temperature dependence of the oxygen isotope fractionation factors was calculated by the least squares method in which the weight was taken to be inversely proportional to the experimental error. The fractionation is given by:103lnαanhydrite-water=3.21×(103/T)2?4.72Available δ18O values of natural anhydrite were used to test the validity of this expression. It is shown that this newly revised geothermometer can be successfully applied to natural hydrothermal anhydrite.  相似文献   

20.
Some conceptual models suggest that baseflow in agriculturally fragmented watersheds may contain little, if any, groundwater. This has critical implications for stream quality and ecosystem functioning. Here, we (a) identify the sources and flowpaths contributing to baseflow using 222Rn and 87Sr/86Sr and (b) quantify mean apparent ages of groundwater and baseflow using multiple isotopic tracers (CFC, SF6, 36Cl, and 3H) in 4 small (0.08 to 0.64 km2) tributary catchments to the Wabash River in Indiana, USA. 222Rn activities and 87Sr/86Sr ratios indicate that baseflow in 3 catchments is sourced primarily from groundwater; baseflow in the fourth is dominated by a source similar to agricultural run‐off. CFC‐12 data indicate that springs in 1 catchment are discharging significant proportions of water that recharged between 1974 (42 ± 2 years) and 1961 (55 ± 2 years). Those same springs have 36Cl/Cl ratios between 1,381.08 ± 29.37 (×10?15) and 1,530.64 ± 27.65 (×10?15) indicating that a substantial proportion of the discharge likely recharged between 1975 (41 years) and 1950 (66 years). Groundwater samples collected from streambed mini‐piezometers in a separate catchment have CFC‐12 concentrations indicating that a large proportion of the recharge occurred between 1948 (68 ± 2 years) and 1950 (66 ± 2 years). Repeat sampling conducted in September 2015 after above‐average summer rainfall did not show significant decreases in mean apparent age. The relatively old ages observed in 3 of the catchments can be explained by geological complexities that are likely present in all 4 catchments, but overwhelmed by flow from the shallow phreatic aquifer in the fourth catchment.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号