Pesticide residues in ground water of the San Joaquin Valley, California

A regional assessment of non-point-source contamination of pesticide residues in ground water was made of the San Joaquin Valley, an intensively farmed and irrigated structural trough in central California. About 10% of the total pesticide use in the USA is in the San Joaquin Valley. Pesticides detected include atrazine, bromacil, 2.4-DP, diazinon, dibromochloropropane, 1,2-dibromoethane, dicamba, 1,2-dichloropropane, diuron, prometon, prometryn, propazine and simazine. All are soil applied except diazinon.

Pesticide leaching is dependent on use patterns, soil texture, total organic carbon in soil, pesticide half-life and depth to water table. Leaching is enhanced by flood-irrigation methods except where the pesticide is foliar applied such as diazinon. Soils in the western San Joaquin Valley are fine grained and are derived primarily from marine shales of the Coast Ranges. Although shallow ground water is present, the fewest number of pesticides were detected in this region. The fine-grained soil inhibits pesticide leaching because of either low vertical permeability or high surface area; both enhance adsorption on to solid phases. Soils of the valley floor tend to be fine grained and have low vertical permeability. Soils in the eastern part of the valley are coarse grained with low total organic carbon and are derived from Sierra Nevada granites. Most pesticide leaching is in these alluvial soils, particularly in areas where depth to ground water is less than 30m. The areas currently most susceptible to pesticide leaching are eastern Fresno and Tulare Counties.

Tritium in water molecules is an indicator of aquifer recharge with water of recent origin. Pesticide residues transported as dissolved species were not detected in non-tritiated water. Although pesticides were not detected in all samples containing high tritium, these samples are indicative of the presence of recharge water that interacted with agricultural soils.     

Linear spatial interpolation: Analysis with an application to San Joaquin Valley

The properties of linear spatial interpolators of single realizations and trend components of regionalized variables are examined in this work. In the case of the single realization estimator explicit and exact expressions for the weighting vector and the variances of estimator and estimation error were obtained from a closed-form expression for the inverse of the Lagrangian matrix. The properties of the trend estimator followed directly from the Gauss-Markoff theorem. It was shown that the single realization estimator can be decomposed into two mutually orthogonal random functions of the data, one of which is the trend estimator. The implementation of liear spatial estimation was illustrated with three different methods, i.e., full information maximum likelihood (FIML), restricted maximum likelihood (RML), and Rao's minimum norm invariant quadratic unbiased estimation (MINQUE) for the single realization case and via generalized least squares (GLS) for the trend. The case study involved large correlation length-scale in the covariance of specific yield producing a nested covariance structure that was nearly positive semidefinite. The sensitivity of model parameters, i.e., drift and variance components (local and structured) to the correlation length-scale, choice of covariance model (i.e., exponential and spherical), and estimation method was examined. the same type of sensitivity analysis was conducted for the spatial interpolators. It is interesting that for this case study, characterized by a large correlation length-scale of about 50 mi (80 km), both parameter estimates and linear spatial interpolators were rather insensitive to the choice of covariance model and estimation method within the range of credible values obtained for the correlation length-scale, i.e., 40–60 mi (64–96 km), with alternative estimates falling within ±5% of each other.     

Using hydrochemical,stable isotope,and river water recharge data to identify groundwater flow paths in a deeply buried karst system

The deeply buried river‐connected Xishan karst aquifer (XKA) in western Beijing, China, has been suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, the hydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km². Results show that (a) the river water is characterized by high Na contents; (b) the δ²H and δ¹⁸O values in the river water are distinctively higher than those of groundwater samples, after experiencing the long‐time evaporative enrichment in the upstream reservoir; (c) the Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals but excluded the water–silicate interaction; and (d) the groundwater samples in the direct recharge area of the XKA have the lowest Na concentrations and the δ²H and δ¹⁸O values. Based on the large differences in the Na contents and ¹⁸O values of groundwater and surface water, a simple two‐component mixing model is developed for the study area and the fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwater from its source zone to the discharge area. Overall, our results suggest that the recharged surface water can be a useful evidence for delineating the groundwater flow path in river‐connected karst aquifer. This study improves our understanding of the heterogeneity in karst groundwater systems.     

Hydrological and isotopic characterization of river water,groundwater, and groundwater recharge in the Heihe River basin,northwestern China

We used hydrochemistry and environmental isotope data (δ¹⁸O, δD, tritium, and ¹⁴C) to investigate the characteristics of river water, groundwater, and groundwater recharge in China's Heihe River basin. The river water and groundwater could be characterized as Ca²⁺? Mg²⁺? HCO₃^?? SO₄^2? and Na⁺? Mg²⁺? SO₄^2?? Cl^? types, respectively. Hydrogeochemical modelling using PHREEQC software revealed that the main hydrogeochemical processes are dissolution (except for gypsum and anhydrite) along groundwater flow paths from the upper to middle Heihe reaches. Towards the lower reaches, dolomite and calcite tend to precipitate. The isotopic data for most of the river water and groundwater lie on the global meteoric water line (GMWL) or between the GMWL and the meteoric water line in northwestern China, indicating weak evaporation. No direct relationship existed between recharge and discharge of groundwater in the middle and lower reaches based on the isotope ratios, d‐excess, and ¹⁴C values. On the basis of tritium in precipitation and by adopting an exponential piston‐flow model, we evaluated the mean residence time of shallow groundwater with high tritium activities, which was around 50 years (a). Furthermore, based on the several popular models, it is calculated that the deep groundwaters in piedmont alluvial fan zone of the middle reaches and in southern part of the lower reaches are modern water, whereas the deep groundwaters in the edge of the middle reaches and around Juyan Lake in the lower reaches of Heihe river basin are old water. Copyright © 2010 John Wiley & Sons, Ltd.     

Estimation of groundwater recharge using water balance model

The main purpose of this paper is to apply a water balance concept with two models in the Ching-Shui watershed to describe the groundwater recharge. First of all, a soil moisture budget model is established to estimate the infiltration, runoff, evapotranspiration, and groundwater recharge in the watershed, where the moisture content of the soil is tracked through time. Secondly, the groundwater recharge was also estimated by the model of the base-flow-record estimation, with the assumption that groundwater evaporation is negligible. In addition, since the analyzed base-flow trends are high, when executing model analysis, the depths of infiltration estimated by stable-base-flow analysis is used to obtain more reasonable groundwater recharge value. The coefficients of groundwater recharge by the precipitation in the Ching-Shui watershed estimated from the established soil moisture budget model and the base-flow model were 12.40% and 9.92%, respectively. Comparison show the result of both models to be close.     

Multi-method groundwater recharge estimation at Eshito micro-watershed,Rift Valley Basin in Ethiopia

ABSTRACT

Understanding recharge processes is fundamental to improve sustainable groundwater resource management. Shallow groundwater (SGW) is being developed for multiple purposes in Ethiopia without consideration of monitoring. We established a citizen science-based hydro-meteorological monitoring network, with a focus on SGW recharge estimation, in Eshito micro-watershed, Ethiopia. Citizen scientists collected rainfall, groundwater-level and stream water-level data. We characterized the shallow aquifer using pumping tests. The data were used to estimate SGW recharge using three methods: chloride mass balance, water-level fluctuation (WLF) and baseflow separation. Approximately 20% and 35% of annual rainfall amount contributes to recharge based on the chloride mass balance and WLF results, respectively. Baseflow separation showed recharge values for the watershed vary from 38% to 28% of annual rainfall at the upstream and downstream gauging stations, respectively. This study shows that the recharge in previously unmonitored micro-watersheds can be studied if citizens are involved in data generation.     

Multiple-indicator study of the response of groundwater recharge sources to highly turbid river water after a landslide in the Tedori River alluvial fan,Japan

The large volume of groundwater stored in the Tedori River alluvial fan, Ishikawa Prefecture, Japan, is an important source of local drinking and industrial water. The Tedori River was observed to be highly turbid from the beginning of May 2015 to at least November 2017 due to a landslide in the upper reach of the river. After the landslide, the groundwater level was drawn down by several to 10 m near the middle river section during paddy irrigation periods in 2015 and 2016. This study addresses the impacts of the highly turbid water on groundwater recharge from the river and paddy fields. In 2016, we sampled groundwater, river water, paddy irrigation water, paddy ponding water, and precipitation five times at 2-month intervals. We analysed the H, O, and Sr stable isotopic compositions and major dissolved ion (and Sr) concentrations and compared our data to previous data obtained in June 2011. Ca, Sr, Cl, SO₄, and TN concentrations and δ¹⁸O values were higher in June 2016 than in June 2011; these increases were more extreme along the left bank of the Tedori River than along the right bank. We explored the mixing of Tedori River water with groundwater using a two-endmember mixing model based on their Sr concentrations and isotopic compositions. Compared to June 2011, mixing ratios were decreased near the Tedori River in 2016, and larger decreases were observed along the left bank and in the middle stream area. These results confirm that the contribution to groundwater recharge from the river decreased during the turbidity event, particularly along the left bank.     

Application of the water table fluctuation method to characterize groundwater recharge in the Pampa plain,Argentina

Abstract

The water table fluctuation (WTF) method is based on accepting that rises of a water table are due to recharge water reaching the groundwater. To apply the method, an estimate of the specific yield of the zone of fluctuation of the groundwater level is required. In this paper, a method for estimation of the specific yield (S_y) is proposed; it consists of a graphical procedure which relates rises in groundwater level to the precipitation from which they originated. The method presents more reliable S_y values as the number of events measured increases. Eighteen years of daily measurements were analysed to obtain a S_y value of 0.09, which was used to apply the WTF method. The obtained recharge values show consistency with values calculated by other authors for the same region.

Editor D. Koutsoyiannis

Citation Varni, M., Comas, R., Weinzettel, P., and Dietrich, S., 2013. Application of water table fluctuation method to characterize the groundwater recharge in the Pampa plain, Argentina. Hydrological Sciences Journal, 58 (7), 1445–1455.     

Significance of stemflow in groundwater recharge. 2: A cylindrical infiltration model for evaluating the stemflow contribution to groundwater recharge

A primary model for evaluating the effect of stemflow on groundwater recharge has been developed. The model, a cylindrical infiltration model (CI model), is based on the infiltration area of stemflow-induced water instead of canopy projected area for determining the stemflow inputs to the soil surface. The estimated ratio of recharge rate by stemflow to the total recharge rate determined with this model agrees closely with values obtained from the mass balance of chloride in subsurface waters. This primary model is considered to be useful for estimating the effect of stemflow on groundwater recharge.     

The application of electromagnetic techniques to groundwater recharge investigations

The use of electrical methods for estimating spatial patterns of groundwater recharge was evaluated at a field site in southeastern Australia. Here, recharge increased from less than 0.2 mm year⁻¹ under native Eucalyptus vegetation, to between 1 and 14 mm year⁻¹ under dryland agriculture. This increase in recharge results in progressive leaching of salts in the soil profile. Differences in recharge can be estimated from differences in depth of leaching. The estimated recharge rates are correlated with soil texture, with higher recharge rates generally occurring through sandier soils. The relationships of recharge to salt content and soil texture both contribute to lower apparent electrical conductivities for higher recharge rates.

The effect of recharge rate on measured apparent electrical conductivities was modelled for various geophysical devices (including frequency-domain (FEM) and time-domain (TEM) electromagnetic instruments and direct current resistivity). The soil-texture effect was shown to have a greater effect than the solute leaching effect in determining the correlation between recharge and apparent electrical conductivity. Analysis of sensitivity to geological noise showed that variations in soil type below 2 m could disguise any correlation.

Correlations between recharge rate, measured at core sites from chloride tracer techniques, and apparent electrical conductivity, measured with FEM electromagnetic devices, supported the conclusions of the model. For DC resistivity and TEM methods, correlations between recharge and apparent electrical conductivity were not significant, although for resistivity this may be due partly to the small number of measurements made. The FEM device most sensitive to variations in recharge had an operating frequency of 9.8 kHz. At lower frequencies the sensitivity is reduced, as the instruments are sensing too deeply. The poor correlations for TEM, as compared with FEM, are due probably to the relatively deeper penetration of the TEM instrument used in the study, rather than any inherent differences between the techniques.

Because the major reason for the correlation between recharge and apparent electrical conductivity is soil texture, in this area the geophysical devices are mostly mapping soil type.     

Identification and assessment of water safety risk for groundwater recharge with reclaimed water in China

Groundwater recharge using reclaimed water has developed rapidly around the world to relieve the groundwater resource shortage and declining of the water table. Traditional water treatment systems are inefficient to remove all the types of contaminants, so it is urgent to identify the priority chemical substances (CSs) that deserve our first concern. In this study, we developed a method (EER method) to identify priority CSs in groundwater recharge by surface spreading and direct aquifer injection. Three stages were processed which were exposure assessment, effect assessment and ranking for identification of priority CSs. Fourteen cities in China were selected for data collected and 90 pollutants in reclaimed water samples were analyzed as the target pollutants for a case study. According to three stages, the 90 CSs studied were divided into five groups (primary control CSs and high, moderate and low and no risk control CSs). In the primary control CSs and high, moderate and low and no risk control CSs group there were 14, 18, 21, 21 and 16 CSs, respectively when groundwater recharged by surface spreading, while there were 15, 18, 21, 21 and 15 CSs when recharged by direct injection. This method provided an indicator of prioritizing the risk of 90 compounds in the reclaimed water for groundwater recharge.     

Effects of afforestation on groundwater recharge and water budgets in the western region of Uruguay

Uruguay has stimulated the development of its forest sector since the promulgation of Forest Law N° 15 939 in December of 1987. Nevertheless, the substitution of natural grasslands with forest plantations for industrial use has raised concerns regarding hydrological processes of groundwater recharge and water consumption involving evapotranspiration. The purpose of this study is to assess the effects of this substitution approach on water resources. Input data were collected from two small experimental watersheds of roughly 100–200 hectares located in western Uruguay. The watersheds are characterized by Eucalyptus Globulus ssp. Maidenni and natural grasslands for cattle use. Total rainfall, stream discharge, rainfall redistribution, soil water content and groundwater level data were collected. Groundwater recharge was estimated from water table fluctuations and from groundwater contributions to base flows. Seasonal and annual water budgets were computed from October of 2006 to September of 2014 to evaluate changes in the hydrological processes. The data show a decrease in annual specific discharge of roughly 17% for mean hydrological years and no conclusive effects on annual groundwater recharge in the forested watershed relative to the reference pasture watershed. Reduced annual specific discharge is equivalent to the mean annual interception. The computed actual annual evapotranspiration is consistent with international catchment measurements. Reduction rates vary seasonally and according to accumulated rainfall and its temporary distribution. The degree of specific discharge decline is particularly high for drier autumns and winters (32 to 28%) when the corresponding rainfall varies from 275 to 400 mm. These results are of relevance for water resources management efforts, as water uses downstream can be affected. These findings, based on a study period dominated by anomalous wet springs and summers and by dry autumns and winters, oppose earlier results based on 34 years of rainfall and discharge data drawn from Uruguayan large basins. Copyright © 2016 John Wiley & Sons, Ltd.     

Regularities in the formation of groundwater infiltration recharge

The effect of meteorological, landscape, geological-pedological, and hydrogeological factors on the formation of total water balance and infiltration recharge of groundwater. The results of analysis of calculated mean annual and within-year values of water balance elements on land surface and in the vadose zone were used to identify some regularities, governing the resulting input of moisture to groundwater table at different depth of its occurrence (infiltration).     

Spectral responses of water level in tidal river and groundwater

The water level of five river stages and seven groundwater wells in the Taipei Basin were analysed by spectral analysis in the frequency domain. The diurnal, semi‐diurnal and quarter‐diurnal tidal components of the Tanshui River appear to relate closely to astronomical tides as K₁, M₂ and M₄, respectively. It is also found that the diurnal component reveals a reversed phase angle in the middle section of the Tanshui River; the phase of the quarter‐diurnal component is also found to be reversed at stations upstream in the Tanshui River and Hsintien Stream. It is believed that these phenomena could be caused by local variation in the river channel topography. The autospectrum and cross‐spectrum between groundwater elevation and nearby river stage were observed to correlate highly with the frequency of the astronomical tides K₁, M₂ and M₄. From the study of the phase shift and time lag of water level fluctuations at river stages and groundwater wells, it was found that the tidal effects of diurnal, semi‐diurnal, and quarter‐diurnal components were significantly different. The relationships between phase and the fluctuated range of atmospheric pressure and water level imply that change in atmospheric pressure does not affect water level fluctuation in the river stage and groundwater well. Copyright © 1999 John Wiley & Sons, Ltd.     

Responses of soil water dynamic processes and groundwater recharge to irrigation intensity and antecedent moisture in the vadose zone

In this study, a field experiment was conducted to investigate the soil water dynamics and water percolation through the deep vadose zone. A calibrated HYDRUS‐1D model was used to simulate the process of soil water movement and the water budget. Based on the measured volumetric soil water contents, the model was well calibrated and validated. Then, we conducted scenario analyses to determine the combined effects of irrigation amount (IA), antecedent soil moisture (AM), crop evapotranspiration, and deep percolation (DP) in an irrigation event. Four IAs (5, 10, 15, and 20 cm) and three AM conditions (AM‐1, AM‐2, and AM‐3) were controlled in the scenario analyses. The results indicate that according to the S_e's (effective saturation) values status and the observed or simulated depth, there could be different conclusions on the influence of DP. Under different IAs in dry (AM‐1) and medium (AM‐2) AM status, DP changed slightly; it was 0.39 and 2.47 cm in AM‐1 and 0.40 and 2.48 cm in AM‐2 for the summer maize and winter wheat crop, respectively; the AM had a crucial contribution to DP. While under the condition of wet AM (AM‐3) or small observation depth, the water inputs could have a significant effect on DP. According to increasing irrigation intensity, the higher values of S_e (>0.6) in the whole profile were only displayed between 70 and 300 cm at AM‐1, 70–500 cm at AM‐2, and 70‐below 600 cm at AM‐3, which were gradually extended and moved down with increasing AM. Hence, the IA significantly affected the water percolation at a depth of 200 cm, whereas there was a weak influence at 600 cm except in AM‐3. Furthermore, in the higher values of the S_e (>0.65) domain, the correlation between IA and DP was an exponential function and significantly under P < 0.05. In addition, DP began to occur when the soil water content was equal to or greater than 0.75 times that of the field water capacity or the S_e > 0.65. When the coarse silt layer became embedded in the silt clay soil profile, it lagged the process of water transport but did not affect permeability in the end.     

Using atmospheric tracers to reduce uncertainty in groundwater recharge areas

A Monte Carlo-based approach to assess uncertainty in recharge areas shows that incorporation of atmospheric tracer observations (in this case, tritium concentration) and prior information on model parameters leads to more precise predictions of recharge areas. Variance-covariance matrices, from model calibration and calculation of sensitivities, were used to generate parameter sets that account for parameter correlation and uncertainty. Constraining parameter sets to those that met acceptance criteria, which included a standard error criterion, did not appear to bias model results. Although the addition of atmospheric tracer observations and prior information produced similar changes in the extent of predicted recharge areas, prior information had the effect of increasing probabilities within the recharge area to a greater extent than atmospheric tracer observations. Uncertainty in the recharge area propagates into predictions that directly affect water quality, such as land cover in the recharge area associated with a well and the residence time associated with the well. Assessments of well vulnerability that depend on these factors should include an assessment of model parameter uncertainty. A formal simulation of parameter uncertainty can be used to delineate probabilistic recharge areas, and the results can be expressed in ways that can be useful to water-resource managers. Although no one model is the correct model, the results of multiple models can be evaluated in terms of the decision being made and the probability of a given outcome from each model.     

A water balance model to estimate climate change impact on groundwater recharge in Yucatan Peninsula,Mexico

ABSTRACT

The aim of this paper is to estimate the effect that climate change will have on groundwater recharge at the Yucatan Peninsula, Mexico. The groundwater recharge is calculated from a monthly water balance model considering eight methods of potential and actual evapotranspiration. Historical data from 1961–2000 and climate model outputs from five downscaled general circulation models in the near horizon (2015–2039), with representative concentration pathway (RCP) 4.5 and 8.5 are used. The results estimate a recharge of 118 ± 33 mm·year^–1 (around 10% of precipitation) in the historical period. Considering the uncertainty from GCMs under different RCP and evapotranspiration scenarios, our monthly water balance model estimates a groundwater recharge of 92 ± 40 mm·year^–1 (RCP4.5) and 94 ± 38 mm·year^–1 (RCP8.5) which represent a reduction of 23% and 20%, respectively, a result that threatens the socio-ecological balance of the region.     

Application of grey correlation method to evaluate potential groundwater recharge sites

Artificial recharge is a practical tool available for increasing the groundwater storage capacity. The efficiency of artificial recharge is related to various hydrogeological factors of the target area. In this study, a variable saturated groundwater flow model, FEMWATER, was used to evaluate the arrival times of recharged water that infiltrates from an artificial recharge pond to the groundwater table under various hydrogeological conditions. Forty-five arrival times were generated by FEMWATER. The relationships between the arrival times and hydrogeological factors used in the simulation of FEMWATER were analyzed by the grey correlation method. The results show the order of importance of the factors as they influence the arrival time. In order from high to low importance, they are α, D _g, θ _e, D _p, K _S and β. D _g and D _p are interpreted as the potential for movement of the recharge water; θ_e is the water storage capacity of soil, and K _S represents the ability of soil to transport water. α and β describe the characteristic curve of the unsaturated soil. The method was applied to evaluate a suitable site for artificial recharge in the Yun-Lin area. Grey correlation analysis was performed to obtain the grey correlation grade using the minimum arrival time as a reference sequence. An index is proposed herein to determine the recharge efficiency of 20 sampling sites. A contour mapping of index values at the 20 sampling sites identified three areas for artificial aquifer recharge in Yun-Lin. Area A in the upper plain is considered more appropriate for groundwater recharge than areas B and C in the coast.