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The water table fluctuation (WTF) method is popular for groundwater recharge (GR) estimation, but its accuracy is challenged when applied in areas with thick vadose zones because of the signal lag and attenuation with depth and uncertainties from barometric pressure effect and lateral flow. Improvement of the WTF method used the linear regression method and Darcy's law, and has been assessed to give satisfactory results. In particular, the improved method presented lower GR (20–34%) relative to the conventional method. GR decreased from the centre to the edge of the tableland. The regional average GR was 63–81 mm year−1, equivalent to 11–14% of annual average rainfall. Lag times between recharge and rainfall ranged from 1 to 9 months. Rainfall and vegetation dominated the spatiotemporal variability of GR. Our study provides reference and technical support for GR estimation with the WTF method in regions with a thick vadose zone. [ABSTRACT FROM AUTHOR]

Over exploitation of Ground Water (GW) has resulted in lowering of water table in the Jedeb watershed. In this study, water storage changes with GRACE satellite data and total annual precipitation with CHIRPS data in the Google Earth Engine system were investigated for the Jedeb watershed during 2003–2017. The groundwater recharge is estimated from a time series of groundwater storage using the water table fluctuation method. According to the results obtained from the GRACE satellite data on the fluctuations of annual water storage between 2003 and 2017, it was found that the biggest annual increase in water levels (15 cm) occurred in 2008, 2013, and 2015, and the biggest annual decrease (12.5 cm) occurred in 2012. The obtained net recharge rate varied from 18 to 25 cm/year for a 14-year period, and the average was 21 cm/year. This study indicates that the GRACE-based estimation of groundwater storage changes is skilled enough to provide monthly updates on the trend of groundwater storage changes for resource managers and policymakers in the Jedeb watershed. [ABSTRACT FROM AUTHOR]

Rainfall is a common trigger for landslide reactivation, as it raises groundwater levels and reduces bedrock or soil shear resistance. This study focuses on the Kualiangzi landslide in the southern region of Sichuan Province, China. Real-time monitoring of groundwater levels and rainfall from July 2013 to September 2016 is analyzed. Groundwater table increments, considering groundwater drainage rate, were calculated using the water-table fluctuation and master recession curve method and the response time of the groundwater table to rainfall events was estimated using the cross-correlation function. Results reveal that groundwater level declines from tension troughs to landslide fronts in the rainy season, with a significant positive correlation between the groundwater level in the tension trough and landslide surface displacement. Evaluated spring elevations for groundwater discharge range from 410 m to 440 m, which is in agreement with the actual spring elevations (390–423 m). Lag times of groundwater response to rainfall decreases with cumulative rainfall of the rainy periods. In the middle part of the landslide, two responses between rainfall and groundwater levels indicate two water movement pathways: Vertical cracks or fractures resulting from the slow landslide movement, and matrix pore space in unconsolidated sediment. Variations in peak values of the cross-correlation function suggest early dominance of the uniform matrix flow and later dominance of preferential flow during the rainy period.

Conservation of groundwater quality is of paramount importance for sustainable agricultural management. Hydrological factors such as rainfall patterns and water table (WT) management, including drainage practices, play a crucial role in groundwater recharge. This in turn has a significant impact on WT fluctuations, nutrient losses in the soil, and the leaching of fertilizers into groundwater which leads to groundwater pollution. Consequently, this study evaluates the long-term influence of seasonal rainfall and WT fluctuations on groundwater nutrient dynamics in tropical peatlands from an oil palm plantation (OPP). Linear regression analyses and Pearson correlation matrices were adopted to evaluate the relationships between seasonal rainfall, WT, and groundwater chemical parameters. The results showed that there was a significant increase in mean pH, NO3−, Na+, Ca2+, and PO43- values during the wet season compared to the dry season which could be attributed to the leaching of nutrients into groundwater due to rainfall, nutrient runoff from drainage systems and increased nitrification rate. A significant positive correlation (p

Groundwater management and sustainability are seriously threatened by the spatiotemporal decline in groundwater level. In India's Indo-Gangetic Plains (IGP), intensive agricultural and quick industrial growth has increased the stress on groundwater. In this study, we will examine the variability of underground water and how it relates to physiographic and non-physiographic variables in the Yamunanagar district from 2010 to 2020. The dataset has been used to analyse the spatial, and temporal variations of groundwater levels and their relationship with physiographic and non-physiographic aspects. The results of the study revealed that the northern and centre regions of the district exhibit favourable groundwater conditions. The analysis revealed a notable linear relationship between rainfall variability and fluctuations in the groundwater table. The water demand and groundwater levels show a strong relationship because they are directly related to groundwater extraction. It indicates that the increasing trend of groundwater depth or groundwater stress in the southeastern part of the study region is due to the excess use of water in industrial and domestic practices during the study period. Excessive use of groundwater for agriculture has led to groundwater depletion between 2010 and 2020. To enhance the current fixed irrigation system, it is recommended to advocate for an alternative irrigation system. The findings emphasize the need for adaptation and mitigation methods, standardization of groundwater management regulations, and the need for adequate supervision of well drilling practices. Climate change also plays a significant role in groundwater dynamics. [ABSTRACT FROM AUTHOR]

Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive, phloem-feeding beetle native to Asia, has killed millions of ash (Fraxinus spp.) trees in North America since it was detected in southeast Michigan in 2002. Consistently high mortality of black ash (Fraxinus nigra) and green ash (F. pennsylvanica) which often occur in riparian forests is a concern given their role in regulating soil moisture and shallow groundwater levels. We monitored and compared hydrologic processes in a riparian forest impacted by EAB invasion and an adjacent unimpacted riparian forest site in southwest Michigan. From 2018 to 2022, we recorded soil moisture, depth to groundwater and meteorological variables at 15-min intervals throughout the growing season in a canopy gap following EAB-caused ash mortality and in adjacent, unaffected forest in the Augusta Creek riparian zone. Groundwater contributions to evapotranspiration (ETG) were estimated using a groundwater level fluctuation (WLF) method. Significant differences in volumetric soil moisture content (16%--26% higher in the gap than forest), average depth to water (10 cm in the gap vs. 70 cm below land surface in the forest) and mean daily ETG (0.6 in the gap vs. 3.0 mm per day in the forest) persisted across four growing seasons. Within the gap, prolonged saturation of the near surface may be contributing to a shift from a forested riparian ecosystem to herb and sedge-dominated wetland. These differences have implications for an array of riparian zone ecosystem services, a concern given the extent of ash mortality already sustained in much of eastern North America. [ABSTRACT FROM AUTHOR]

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

Groundwater is the primary water resource used for domestic, industrial, and agricultural needs for the community in the Yogyakarta-Sleman Groundwater Basin area. The urbanization rate has increased since the 1970s and has made massive use of groundwater, causing environmental problems, including the quality and quantity of groundwater. Therefore, this study aimed to investigate the spatiotemporal groundwater fluctuation trends based on the non-parametric Mann-Kendall test and recharge rate estimation using the water table fluctuation (WTF) method. The groundwater level data were collected from monitoring wells across the study area during 2018-2022, particularly emphasizing 8 wells representing recharge, transition, and discharge areas. The results showed that the groundwater fluctuation pattern generally followed the season. During the rainy season from January to April, groundwater reached the shallowest level and began to decline gradually when it entered the dry season from May to October. Groundwater recharge rate was estimated to vary from 171.49 to 1,505.56 mm/year. Meanwhile, the Mann-Kendall test showed that most of the Yogyakarta-Sleman Groundwater Basin area did not experience significant fluctuation trends, except for two monitoring wells in the center of Yogyakarta City which had increasing groundwater level trends. The rising groundwater levels were expected to be caused by urban wastewater recharge. This study has provided a new description and insights into spatiotemporal changes in the groundwater table and the quantification of groundwater recharge.

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

Groundwater is the primary water resource used for domestic, industrial, and agricultural needs for the community in the Yogyakarta-Sleman Groundwater Basin area. The urbanization rate has increased since the 1970s and has made massive use of groundwater, causing environmental problems, including the quality and quantity of groundwater. Therefore, this study aimed to investigate the spatiotemporal groundwater fluctuation trends based on the non-parametric Mann-Kendall test and recharge rate estimation using the water table fluctuation (WTF) method. The groundwater level data were collected from monitoring wells across the study area during 2018-2022, particularly emphasizing 8 wells representing recharge, transition, and discharge areas. The results showed that the groundwater fluctuation pattern generally followed the season. During the rainy season from January to April, groundwater reached the shallowest level and began to decline gradually when it entered the dry season from May to October. Groundwater recharge rate was estimated to vary from 171.49 to 1,505.56 mm/year. Meanwhile, the Mann-Kendall test showed that most of the Yogyakarta-Sleman Groundwater Basin area did not experience significant fluctuation trends, except for two monitoring wells in the center of Yogyakarta City which had increasing groundwater level trends. The rising groundwater levels were expected to be caused by urban wastewater recharge. This study has provided a new description and insights into spatiotemporal changes in the groundwater table and the quantification of groundwater recharge. [ABSTRACT FROM AUTHOR]

Shallow unconfined aquifer in hard rock terrain generally have complicated and heterogeneous hydrogeological setup. Present study incorporates dynamics of the static groundwater levels in the Chargarh river basin, Central India, during pre-monsoon and postmonsoon season, with special reference to lithological variation. The geological formations exposed in the basin are Deccan basalt and alluvium. The average pre-monsoon and postmonsoon static water levels in the basalt formation are 12.21 mbgl to 6.14 mbgl respectively, with 6.07-meter seasonal water table fluctuation. On the other hand, average pre-monsoon and post-monsoon static water levels (SWL) in the alluvial formation are 16.84 mbgl to 4.64 mbgl respectively, with 12.20 m the water table fluctuation (WTF). The pre-monsoon SWL in alluvium is deeper as compared to the pre-monsoon SWL in basalt. Similarly, WTF in alluvium is higher than WTF in basalt. These observations are reversed to that of the general assumption, that the WTF in soft rock formations are lower as compared to WTF in hard rock terrain. This can be attributed to the excessive withdrawal of groundwater for orange cultivation and sporadic artificial recharge structures in the alluvial formation. [ABSTRACT FROM AUTHOR]

The assessment of recharge is one of the most important issues in management and planning of the groundwater resources. In this study, the amount of recharge to the Semnan alluvial aquifer was investigated using methods of water table fluctuations (WTF), chloride mass balance (CMB), water budget and stable isotopes. The parameter is highly important for managing this vital aquifer as overexploitations for drinking, agricultural and industrial uses occurred, resulting in water table decline with an average rate of about 80 cm annually. Based on the results, the values of recharge into the Semnan alluvial aquifer are estimated about 4.4, 2.5 and 2.1 MCM/year by WTF, CMB and water budget methods, respectively. The isotopic data (18O and ²H) do not show any significant effects of evaporation on recharge process, confirming the main role of highland recharge in this arid-land aquifer. Combining results of the recharge studies in saturated zone of Semnan aquifer, yields annual rainfall recharge of about 3 MCM, which is about 5% of the annual precipitations. [ABSTRACT FROM AUTHOR]

Depression focused recharge (DFR) may be a hydrologically important process that impacts the vulnerability of public supply wells, specifically related to pathogenic contaminants. The nature of DFR in glacial moraine environments, such as those located in northern latitudes within North America and Europe, is less well established than in other regions such as the Prairie Pothole Region (Northern United States, Western Canada) and the High Plains Aquifer (Central United States). The objectives of this study were to quantify seasonal infiltration flux beneath a topographically‐closed depression within 50 m of a public supply well and to interpret the impact of this DFR process on well vulnerability. Field instruments including groundwater monitoring wells, pressure transducers, soil moisture sensors and temperature sensors were installed in vertical clusters to capture the dynamics of infiltration, drainage and recharge within the depression feature. Continuous weather data were recorded by a meteorological station at the site. Transient infiltration was quantified during two contrasting hydrological events. The first event (~2 days) was an intense rainfall (>50 mm) on a melting snowpack during the fall season when the soils were unfrozen. The second was a longer (35 day) period during the spring freshet when the surficial soils were initially frozen and subject to diurnal freezing and thawing and occasional precipitation events. The water table fluctuation method augmented by Darcy flux contributions, in addition to numerical modelling using the HYDRUS‐1D model, were used to quantify recharge rates beneath the depression. Numerical DFR estimates and analytical results differed by ±8%. Results indicate that recharge rates on the order of the annual regional average can occur beneath localized features in response to extreme events associated with snowmelt and intense rainfall. Such events may represent a microbial threat to groundwater quality if public supply wells are located nearby. [ABSTRACT FROM AUTHOR]

Recharge is a crucial section of water balance for both surface and subsurface models in water resource assessment. However, quantifying its spatiotemporal distribution at a regional scale poses a significant challenge. Empirical and numerical modeling are the most commonly used methods at the watershed scales. However, integrated models inherently contain a vast number of unknowns and uncertainties, which can limit their accuracy and reliability. In this work, we have proposed integrated SWAT-MODFLOW and Transient Water Table Fluctuation Method (TWTFM) to evaluate the spatiotemporal distribution of groundwater recharge in Anyang watershed, South Korea. Since TWTFM also uses SWAT model percolation output data, calibration was performed for individual models and a coupled model. The coupled model was calibrated using daily streamflow and hydraulic head. The SWAT-MODFLOW model performed well during the simulation of streamflow compared to the SWAT model. The study output showed that the study watershed had significant groundwater recharge variations during the simulated period. A significant amount of recharge happens in the wet season. It contributes a significant amount of the average annual precipitation of the region. The direct flow components (surface and lateral) showed significant contributions when the water balance components were evaluated in the region. TWTFM showed a glimpse to estimate recharge, which requires representative monitoring wells in the study region. Comprehensively, the SWAT-MODFLOW model estimated groundwater recharge with reasonable accuracy in the region. [ABSTRACT FROM AUTHOR]

Prioritization of groundwater recharge potentiality evaluation is critical for sustainable water resources management. Since recharge is a main source for enhancing groundwater availability. Water scarcity is extremely severe in the upper Blue Nile Basin (i.e., Gunabay watershed). Therefore, this study emphasizes groundwater recharge delineating and mapping 3920.25 km2 in the data-limited area of the upper Blue Basin using proxy modeling (i.e., WetSpass-M model and geodetector model) and tools. The driving/influencing factors are rainfall, temperature, wind speed, evapotranspiration, elevation, slope, land cover, soil, groundwater depth, drainage density, geomorphology, and geology that control the movement of groundwater recharge. However, the first nine factors were used as inputs in the WetSpass-M model to evaluate groundwater recharge. To validate the groundwater recharge availability, water table fluctuation was established based on recorded groundwater levels. Furthermore, the major influencing factors and their interaction have been quantified using geodetector model. Spatiotemporal recharge distribution (in mm) is classified as very low (0–6), low (6–30), moderate (30–51), high (51–83), and very high (83–508) comprising 21%, 20%, 20%, 20%, and 19% of the total area, respectively. Very high groundwater recharge zone has been found in the northwest part of the area. The geodetector results showed that soil (0.841) and temperature (0.287) had larger individual contributions, but the interaction between soil and temperature (0.962) was more significant. It indicates that the interaction between climate and soil has the largest influence on groundwater recharge variability. Generally, the overall approach of this study can be applied to water sectors, policymakers, and decision-makers to overcome future water scarcity. [ABSTRACT FROM AUTHOR]

Study region: Robit Bata and Dengeshita watersheds, Upper Blue Nile basin, Ethiopia Study focus: Sustainable development of groundwater in the Ethiopian Highlands requires recharge measurements. The Water Table Fluctuation (WTF) method has been used to measure recharge. Lateral flow in sloping hillside aquifers violates the assumptions on which the original WTF method is based. We modified the original WTF method to include lateral flow controlled by gravity. New hydrological insights: Previously it was shown that the sum of recharge over the travel time in a sloping aquifer is equal to the base flow. Since recharge cannot be measured directly, the recharge calculated with the modified WTF method was tested using baseflow measurement in two contrasting highland watersheds, Robit Bata and Dengeshita, where groundwater depth and streamflow data were monitored from 2015 to 2018. Baseflow was determined with the one-parameter digital filter technique. Predicted and observed monthly baseflow agreed well with R2 > 0.9 and RMSE

[Display omitted] • The biogeochemical dynamics of the capillary fringe were studied using a soil column. • Geochemical and microbial depth stratifications are internally consistent. • The alternating oxic/anoxic zone exhibits a more flexible microbial network. • More active, not more diverse, microbes enhance capillary fringe N and C cycles. The capillary fringe (CF) exhibits steep chemical and redox gradients, representing a critical reactive interface in the subsurface. The spatial extent of the CF is temporally dynamic because of water table and soil moisture fluctuations. To simulate the spatio-temporal responses of the CF's microbial community structure and activity, a 91 cm long sandy soil column experiment was conducted by imposing three different sequential hydrologic regimes: a stable water table separating the unsaturated and saturated zones (static regime), periodic pulse infiltration events with a constant water table position (infiltration regime), and water table fluctuations under three drainage-imbibition cycles of 6, 12, and 18 days (fluctuating regime). The investigation focused on the microbially-mediated turnover of nitrogen (N) and carbon (C). Geochemical profiles in the soil column were monitored continuously, while microbial DNA was extracted for 16S rDNA sequencing at the start, middle and end of the experiment. The observed microbial community compositions corresponded to five categories: (1) initial soil, (2) near-surface and (3) CF and saturated soil under the infiltration regime, (4) unsaturated and (5) saturated soil in the fluctuating regime. Based on co-occurrence network analysis, microbial physiologies matched the predominant geochemical conditions, and relatively stable community structures prevailed throughout the experiment. NO 3 - and NH 4 + were more available to the microbes in the fluctuating regime's alternating oxic/anoxic zone, leading to a more flexible network. The prevalent microbial metabolic pathways predicted using FAPROTAX were mainly associated with N and C metabolisms and significantly correlated with the taxonomic compositions. However, the dominant microbial groups were shared among all the soil samples. The limited spatial differences in microbial community structure under the fluctuating regime were likely due to a more pronounced role of microbial activity than microbial diversity, and similar drying-wetting conditions between the soil column and the filed site. Internally consistent geochemical and microbial depth stratifications were identified by (1) the redox potential and nitrogen species distributions, (2) spatial moment analysis of NO 3 - and NH 4 + concentrations, (3) microbial community composition and (4) function. The five imposed hydrologic regimes generated distinct and coupled geochemical and microbial signatures. These signatures resulted from variations in the soil microbial community's activity, rather than diversity or abundance. [ABSTRACT FROM AUTHOR]

Petroleum hydrocarbons are hazardous to ecosystems and human health, commonly containing n-alkanes and polycyclic aromatic hydrocarbons. Previous researches have studied alkane degraders and degrading genes under aerobic or anaerobic conditions, but seldom discussed them in the intermittent saturation zone which is a connective area between the vadose zone and the groundwater aquifer with periodic alteration of oxygen and moisture. The present study investigated the difference in alkane degradation efficiency, bacterial community, and alkane degrading gene diversity in aerobic, anaerobic, and aerobic-anaerobic fluctuated treatments. All biotic treatments achieved over 90% of n-alkane removal after 120 days of incubation. The removal efficiencies of n-alkanes with a carbon chain length from 16 to 25 were much higher in anaerobic scenarios than those in aerobic scenarios, explained by different dominant microbes between aerobic and anaerobic conditions. The highest removal efficiency was found in fluctuation treatments, indicating an accelerated n-alkane biodegradation under aerobic-anaerobic alternation. In addition, the copy numbers of the 16S rRNA gene and two alkB genes (alkB-P and alkB-R) declined dramatically when switched from aerobic to anaerobic scenarios and oppositely from anaerobic to aerobic conditions. This suggested that water level fluctuation could notably change the presence of aerobic alkane degrading genes. Our results suggested that alkane degradation efficiency, soil microbial community, and alkane-degrading genes were all driven by water level fluctuation in the intermittent saturation zone, helping better understand the effects of seasonal water table fluctuation on the biodegradation of petroleum hydrocarbons in the subsurface environment. [ABSTRACT FROM AUTHOR]

The reliable quantification of Groundwater Recharge (GR) is essential for efficient and sustainable groundwater resource practices. In this study, the spatio-temporal GR over the Ganga River Basin (GRB) was calculated using six different methods during 2003–2016. The Gravity Recovery and Climate Experiment (GRACE) and water fluxes were utilized as inputs to the GR methods. The GR of individual methods were validated with in-situ measurements, indicating a higher correlation ranged from 0.64 to 0.77. Overall, the GR trend shows an insignificant declining trend with a mean of −0.09 cm yr−1 for all selected methods. The spatial distribution of GR indicates large heterogeneity in the GRB with a higher recharge in the eastern than the western part. The uncertainty of each method and sensitivity of water fluxes were analyzed. Further, the possible causes of GR change through hydro-climatic variables as well as anthropogenic activities related to irrigation and urbanization were evaluated. [ABSTRACT FROM AUTHOR]

Groundwater trends affect the domestic, agricultural, and industrial prospects of a region. The study area is Bogura, a northern region of Bangladesh, located on the Pleistocene terrace of the Bengal Basin. The aquifer consists of medium-to-coarse sand, located at a depth of 4.66–42.68 m; groundwater is scarce during dry seasons. The water table (WT) time-series data for 2007–2019 were used for forecasting and characterizing present and future groundwater conditions using existing numerical simulations. The annual groundwater budget for discharge and storage was 2,772 and 2,442 Mm3, respectively. Thus, the annual scarcity of groundwater was 330.4 Mm3 (13.5%), excluding the surface water contribution of 10 Mm3 (0.4%). The present spacing of deep tube wells (DTWs) and shallow tube wells (STWs) was 744 and 372 m, respectively. Currently, the DTW spacing ranged 744–800 m; however, the STW spacing of 250–372 m is higher than the set distance. Hence, further installations of STWs were strictly disallowed for irrigation. WT declined by 1.0 m in the last 13 years, i.e., 0.07 m or 1.2% decline rate per annum, causing water scarcity in the region during the peak period in the dry season (June–February), thus affecting irrigation and limiting agricultural production. HIGHLIGHTS In the study, highest priority was given on groundwater use for irrigation.; The study emphasized the recharge-discharge and storage phenomenon as hydrological components.; The study forecasts and predicts the present and future threats of groundwater resources.;

Recharge is a crucial section of water balance for both surface and subsurface models in water resource assessment. However, quantifying its spatiotemporal distribution at a regional scale poses a significant challenge. Empirical and numerical modeling are the most commonly used methods at the watershed scales. However, integrated models inherently contain a vast number of unknowns and uncertainties, which can limit their accuracy and reliability. In this work, we have proposed integrated SWAT-MODFLOW and Transient Water Table Fluctuation Method (TWTFM) to evaluate the spatiotemporal distribution of groundwater recharge in Anyang watershed, South Korea. Since TWTFM also uses SWAT model percolation output data, calibration was performed for individual models and a coupled model. The coupled model was calibrated using daily streamflow and hydraulic head. The SWAT-MODFLOW model performed well during the simulation of streamflow compared to the SWAT model. The study output showed that the study watershed had significant groundwater recharge variations during the simulated period. A significant amount of recharge happens in the wet season. It contributes a significant amount of the average annual precipitation of the region. The direct flow components (surface and lateral) showed significant contributions when the water balance components were evaluated in the region. TWTFM showed a glimpse to estimate recharge, which requires representative monitoring wells in the study region. Comprehensively, the SWAT-MODFLOW model estimated groundwater recharge with reasonable accuracy in the region.

Riparian ecosystems fundamentally depend on groundwater, and accurate estimations of groundwater evapotranspiration (ETG) are important for understanding ecosystem functionality and managing regional water resources. Over the past several decades, various methods have been proposed to estimate groundwater evapotranspiration based on water table fluctuations. However, the majority of methods cannot resolve sub-daily variations in ETG. In this study, we proposed a new hydraulic theory-based ETG estimation method at a sub-daily time scale. To evaluate its performance, we employed a variety of measurements (i.e., water table levels, latent heat flux and soil water contents) at a riparian forest (T. ramosissima) in Northwest China from 25 July to 10 October in 2017. The results indicated that the proposed method can successfully estimate ETG at both sub-daily (R2 = 0.75) and daily (R2 = 0.88) time scales, but the variations in the specific yield under different water table conditions should be carefully taken into account. In addition, we investigated the seasonal variations in water uptake source of the riparian plant, and found that it had strong plasticity in water usage during the study period. That is, it consumed approximately equal amounts of soil water and groundwater when soil moisture was available, and tended to consume more groundwater for survival as the soil moisture was depleted. To verify the seasonal patterns of the water uptake of the riparian forest, systematic isotope-based studies are needed in future study. [ABSTRACT FROM AUTHOR]

Study region: Four districts (Meinong, Qishan, Dashu, and Daliao) of Kaohsiung city, Southern Taiwan Study focus: The understanding of aquifer recharge in terms of water table response to rainfall is of critical importance to groundwater systems management and various endeavors have been made to estimate the amount of recharge using rainfall data. The purpose of this study is to evaluate the groundwater level response to rainfall and determine the recharge potential for shallow aquifers. We showed a simple approach to estimate specific yield (Sy) and hydraulic conductivity (k) as functions of rainfall and water level data. New hydrological insights for the region: Correlation method is applied to investigate groundwater level response to associated rainfall and it was found that the rise in water table linearly depends on the rainfall amount per event. Results show the annual recharge rates of 244–1472 mm year─1, which represent 12–43% of rainfall in the study area. The estimated k (order of 10─4 to 10─5 m s─1) and Sy (0.20–0.51) were used as prior values to setup groundwater numerical modeling using WASH123D. The real-time case scenario simulation using pumping and rainfall data indicated the reasonable hydrological response of groundwater levels to rainfall. The long-term simulations should be performed with WASH123D to deal with the subjectivity of sustained groundwater pumping and sustainability of aquifers for better groundwater resource planning and management.

The anomalous entrance of water into groundwater systems can affect storage throughout long periods and normally relies on infrequent and irregular pulses of groundwater recharge defined by the term episodic recharge. Recently there was a groundwater recharge of large magnitude with unknown circumstances in the Caiuá aquifer. This unique event was explored in detail here and allowed to better understand the occurrence of such events in humid subtropical climates in South America. For this study, groundwater monitoring daily data from the Integrated Groundwater Monitoring Network was used combined with a specific yield obtained from geophysical wireline logging to obtain groundwater recharge rates. To improve the investigation, we also used a baseflow separation method to obtain the groundwater contribution into local rivers. The groundwater storage variations were also assessed by remote sensing with the GRACE data. Results showed the importance of high soil moisture storage on the occurrence of large episodic recharge events. We estimated that the groundwater recharger volumes derived from 1 year that included the unique episodic recharge observed (total of 866 mm for April 2015–March 2016) were comparable with the sum of 7 years of groundwater recharge (total of 867 mm). Atypical rainfall in winter periods were responsible for the increase in soil moisture that explained that unique event. GRACE‐based GWS showed concordance detecting the occurrence of the unique episodic recharge. However, the variation in terms of volumes obtained by GRACE does not represent the behaviour observed in the aquifer by the WTF method. The results also indicated that changes in aquifer storage caused by episodic recharge events directly affect low flows in rivers over long periods. The main knowledge gap addressed here relates to exploring a unique episodic recharge event quite rare to observe with its long‐term impacts on hydroclimatic variability over a humid subtropical portion of the Caiuá aquifer. [ABSTRACT FROM AUTHOR]

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

Precipitation patterns are becoming increasingly extreme, particularly at northern latitudes. Current climate models predict that this trend will continue in the future. While droughts have been repeatedly studied in many ecosystems over the last decades, the consequences of increasingly intense, but less frequent rainfall events, on carbon (C) cycling are not well understood. At northern latitudes, peatlands store one third of the terrestrial carbon and their functioning is highly dependent on water. Shifts in rainfall regimes could disrupt peatland C dynamics and speed-up the rates of C loss. How will these immense stocks of C be able to withstand and recover from extreme rainfall? We tested the resistance and resilience effects of extreme precipitation regimes on peatland carbon dioxide (CO2) and methane (CH4) fluxes, pore water dissolved organic carbon (DOC) and litter decomposition rates by exposing intact peat cores to extreme, spring-time rainfall patterns in a controlled mesocosm experiment. We find that more intense but less frequent rainfall destabilized water table dynamics, with cascading effects on peatland C fluxes. Decomposition and respiration rates increased with a deeper mean water table depth (WTD) and larger WTD fluctuations. We observed similar patterns for CO2 uptake, which were likely mediated by improved vascular plant performance. After a three-week recovery period, CO2 fluxes still displayed responses to the earlier WTD dynamics, suggesting lagged effects of precipitation regime shifts. Furthermore, we found that CH4 emissions decreased with deeper mean WTD, but this showed a high resilience once WTD dynamics stabilised. Not only do our results illustrate that shifting rainfall patterns translate in altered WTD dynamics and, consequentially, influence C fluxes, they also demonstrate that exposure to altered rainfall early in the growing season can have lasting effects on CO2 exchange. Even though the increased CO2 assimilation under extreme precipitation patterns signals peatland resistance under changing climatic conditions, it may instead mark the onset of vascular plant encroachment and the associated C loss.

Spatially distributed potential and net recharge rates were assessed in the paddy dominated Hirakud command area (Eastern India) at 100 m grid resolution using surface water balance and Water Table Fluctuation (WTF) methods, respectively, for the period 2001–05. Net recharge estimated using the WTF method corresponding to observation well locations was further interpolated using kriging technique available in the ArcGIS software. Net recharge to potential recharge ratios (%) were also assessed spatially. Water balance components (i) runoff was estimated using the Natural Resources Conservation Service-Curve Number (NRCS-CN) method (ii) reference evapotranspiration by (Hargreaves and Samani, Applied Engineering Agriculture ASABE 1:96–99, 1985)), crop evapotranspiration by (Allen et al., Crop evapotranspiration: Guidelines for computing crop water requirements, FAO Irrigation and Drainage, Food and Agriculture Organization, Rome, Italy, 1998) and evaporation from uncultivated lands by Ritchie (1972) approaches, and (iii) canal seepage using simple canal flow model. Annual groundwater draft during Kharif and Rabi was found to be 144.41 and 112.49 ha-m, respectively. Nearly, 90% of the study area contributed runoff in the range of 200–400 mm during the years 2002–03, 2003–04, and 2004–05. The estimated seepage losses vary between 5 and 15% of irrigation depth for all distributaries. Potential groundwater recharge during wet, normal, and dry years ranges between 650 and 1033 mm, and equivalent to 67%, 78%, and 60% of annual rainfall, respectively. Net recharge ranges between 8 and 11% of the annual rainfall. Mean ratio between net recharge to potential recharge is nearly 30%, indicating that nearly 70% of potential recharge is accounted as outflow from the study area. Parmanpur distributary canal located at the centre of the study area that exhibited higher potential recharge can be scheduled at the end to avoid water logging problem. Further, extraction of groundwater during non-monsoon period for irrigation purpose not only helps in controlling waterlogging but also helps in maintaining stable groundwater level. Overall, spatio-temporal distribution of recharge in the command area indicated that the irrigation demands during non-monsoon season can be met through sustainable management of underexploited groundwater resources. Such an integrated management of surface and groundwater can help in improving water use efficiencies as well as agricultural productivity. [ABSTRACT FROM AUTHOR]

Northern peatlands are substantial carbon sinks because organic matter in peat is highly stable due to the low rate of decomposition. Waterlogged anaerobic conditions induce accumulation of Sphagnum-derived phenolic compounds that inhibit peat organic matter decomposition, a mechanism referred to as the “enzymic latch”. Recent studies have predicted that the water table in northern peatlands may become unstable. We observed that such unstable water table levels can impede the development of Sphagnum mosses. In this study, we determined the effects of low and high frequency water table fluctuation regimes on Sphagnum growth and peat organic matter decomposition, by conducting a year-long mesocosm experiment. In addition, we conducted a molecular analysis to examine changes in abundance of fungal community which may play a key role in the decomposition of organic matter in peatlands. We found that rapid water table fluctuation inhibited the growth of Sphagnum due to fungal infection but stimulated decomposition of organic matter that may dramatically destabilize peatland carbon storage. Increased pH, induced by the fluctuation, may contribute to the enhanced activity of hydrolases in peat. We demonstrated that the water table fluctuation in peatlands impeded Sphagnum growth and accelerates decomposition due to fungal proliferation. Thus, we suggested that understanding the microbial community in the northern peatlands is essential for elucidating the possible changes in carbon cycle of peatland under the changing world.

Riparian ecosystems fundamentally depend on groundwater, and accurate estimations of groundwater evapotranspiration (ETG) are important for understanding ecosystem functionality and managing regional water resources. Over the past several decades, various methods have been proposed to estimate groundwater evapotranspiration based on water table fluctuations. However, the majority of methods cannot resolve sub-daily variations in ETG. In this study, we proposed a new hydraulic theory-based ETG estimation method at a sub-daily time scale. To evaluate its performance, we employed a variety of measurements (i.e., water table levels, latent heat flux and soil water contents) at a riparian forest (T. ramosissima) in Northwest China from 25 July to 10 October in 2017. The results indicated that the proposed method can successfully estimate ETG at both sub-daily (R2 = 0.75) and daily (R2 = 0.88) time scales, but the variations in the specific yield under different water table conditions should be carefully taken into account. In addition, we investigated the seasonal variations in water uptake source of the riparian plant, and found that it had strong plasticity in water usage during the study period. That is, it consumed approximately equal amounts of soil water and groundwater when soil moisture was available, and tended to consume more groundwater for survival as the soil moisture was depleted. To verify the seasonal patterns of the water uptake of the riparian forest, systematic isotope-based studies are needed in future study.

In the present study, a 42-year record of rainfall and temperature from Airport and a 43-year rainfall record from Kizimbani meteorological station were analyzed to understand how these climatic variables are affecting groundwater supply on the Island of Zanzibar, Tanzania. Water table fluctuation (WTF) and rainfall data were examined for estimating groundwater recharge. The abstraction volume and recharge rate were used to estimate the water balance. Also, the different physicochemical parameters, such as chlorinity, nitrate, electrical conductivity (EC) and total dissolved solids (TDS) were examined to assess the impact of groundwater pumpage on water quality on the island of Zanzibar. Through the use of WTF method, the present study estimated the recharge rates, local sustainable yield (SY) and integrated water balance (IWB). Rainfall records showed that Zanzibar Island receives a total mean annual rainfall of 1673 mm out of which 7% (equivalent to 1.79 × 106 m3/y) recharges the groundwater. Temperature variations indicated an incremental trend accompanied by low rainfall. The average estimated SY was 0.72%, while the IWB showed a deficit of 39%. Furthermore, the total groundwater abstraction rate in the studied area was 2.49 × 106 m3/y, which was higher than the rate of recharge. This means that the groundwater resources are currently over-exploited and, if immediate action is not taken, the groundwater aquifers may be subjected to pollution, collapse and seawater intrusion. The effects of over-pumping were manifested by high levels of EC, chloride, TDS, total hardness and nitrate that showed an increasing trend with time. [ABSTRACT FROM AUTHOR]

The pump-and-treat (P&T) method is a common remediation approach that is used to mitigate occurrences of hydrocarbon contamination. In a well-studied site that had been contaminated by a large volume of jet fuel, continuous monitoring of the water table and floating phase thickness revealed the most significant process governing the effectiveness of the site's active remediation system. The floating phase thickness recorded in the wells monitored varied greatly (> 0.50 m) and was negatively correlated with the water table level. Although the dependence of light non-aqueous phase liquid (LNAPL) thickness on water table fluctuations is widely recognized, LNAPL recovery, which is governed by alternating cycles of LNAPL release and entrapment in pore spaces, has been poorly described. Thus, we present a specific case in which LNAPL recovery is expected only episodically, when the water table falls sufficiently. In the period spanning from 2006 to 2008, LNAPL remediation recovered nearly 180 m3 of oil. In later years, the volume of recovered LNAPL declined and ceased between 2010 and 2014, when the water table rose. Importantly, our research demonstrates that the P&T remediation approach is solely effective during a period of 4 months in dry years. Thus, cleanup methods and contaminated site management strategies should be reconsidered. [ABSTRACT FROM AUTHOR]

We use cross correlation of the ambient seismic field to estimate seasonal variations of seismic velocity in the Mississippi Embayment and to determine the underlying physical mechanisms. Our main observation is that the δt/t variations correlate primarily with the water table fluctuation, with the largest positive value from May to July and the largest negative value in September/October relative to the annual mean. The δv/v residuals after water level fluctuation correction correlate with air pressure in the short term and follow the trend of temperature in the long term. The δv/v residuals after water level fluctuation and air pressure correction correlate inversely with the wind speed. The correlation coefficients between water table fluctuation and δt/t are independent of the interstation distance and frequency, but high coefficients are observed more often between 0.3 and 1 Hz than between 1 and 2 Hz because high‐frequency coherent signals attenuate faster than low‐frequency ones. The δt/t variations lag behind the water table fluctuation by about 20 days, which suggests that the velocity changes can be attributed to the pore pressure diffusion effect. The seasonal variations of δt/t are azimuthally independent, and a large increase of noise amplitude only introduces a small increase to the δt/t variation. At close distances, the maximum δt/t holds a wide range of values, which is likely related to local structure. At larger distances, velocity variations sample a larger region so that it stabilizes to a more uniform value. We find that the observed changes in wave speed can be explained by a poroelastic model. Key Points: We observe the minimum wave speed from May to July due to the increased pore pressure from the water table fluctuation and the maximum wave speed in September/OctoberThe δt/t correlates primarily with the water table fluctuationA poroelastic model can explain the velocity variations in the crust [ABSTRACT FROM AUTHOR]

Temperatures in the arctic and subarctic are rising at more than twice the rate of the global average, driving the accelerated thawing of permafrost across the region. The impacts of permafrost degradation have been studied in the discontinuous permafrost zone at Umiujaq, in northern Quebec, Canada, for over 30 years, but the effects of changing land cover on groundwater recharge are not well understood. The water table fluctuation method was used to compute groundwater recharge using 4 years of water level data and soil moisture readings from five field sites characteristic of different stages of permafrost degradation and vegetation invasion. Results indicate that as vegetation grows taller, groundwater recharge increases, likely due to increased snow thickness. Results were then combined with a preexisting conceptual model that describes the evolution from tundra to shrubland and forests to create a new model for describing how groundwater recharge is affected by landscape evolution. Plain language summary: Thawing permafrost (ground that is below 0°C for at least 2 years) allows for vegetation to grow in areas where growth was not previously possible. This paper examines how different types of vegetation affect the ability of water to infiltrate the soil and flow toward the water table, a process called groundwater recharge. Using field data from five typical types of vegetation in the discontinuous permafrost zone in northern Quebec, Canada, we estimated how much groundwater recharge occurred under these different types of vegetation: tundra/permafrost mound, lichens and herbs, lichens and low shrubs, medium shrubs, and trees. Based on the results, as the plants grow larger, more groundwater recharge is possible. This increase in recharge occurs because taller plants trap more snow in winter, resulting in the production of more meltwater in spring. We then combine our results with the findings from another study in the same area, which stated that the five types of land cover represent a model for how the landscape will change as the permafrost thaws. Our new combined model allows for the estimation of how groundwater recharge will change as a result of permafrost thaw and ecological change. Key Points: Increased landcover height appears positively correlated with increased rechargeAs land cover increases in height, the date of the first recharge event in a given hydrologic year moves later into the summerIncreased recharge is driven by greater snow thickness and prolonged snowmelt due to snow entrapment and shading under taller land cover [ABSTRACT FROM AUTHOR]

Laboratory-scale column experiments were conducted to investigate the influence of water table fluctuation on light non-aqueous phase liquid (LNAPL) migration and redistribution in porous media. A simplified image analysis method (SIAM) was used to evaluate the saturation distributions of the LNAPL and water in the entire domain under dynamic conditions. Two LNAPL volumes differentiated as low and high volumes were exposed to two patterns of water table fluctuations. High-resolution SIAM images of the soil column during LNAPL migration and subsequent water table fluctuations were collected and analyzed. Results show that when the water table was lowered in the experiment of low LNAPL volume by 10 cm (from 28 to 18 cm) and then raised back to its initial location (28 cm), the water saturation dropped from 100% initially to around 30% while the LNAPL saturation increased and remained at 7% to 25% at 36 cm. By doubling the LNAPL volume to 50 ml, the initial LNAPL saturation above the water table increased and the capillary fringe height increased from 36 to 38 cm. Comparison between the two LNAPL volumes showed that the LNAPL covered a larger area for the case of high LNAPL. The LNAPL saturation extended up to around 53 cm while for the case of low LNAPL, the LNAPL extended up to height of 50 cm. Moreover, water saturation below was lesser for the case of high LNAPL. This was due to the increasing volume of LNAPL which caused the water to be pushed downward. However, similar downward migration of water was observed in both sets of experiments. This indicates that doubling the volume of LNAPL while maintaining the same groundwater fluctuation pattern did not affect the general LNAPL behavior. Overall, this study demonstrates that the SIAM technique is an accurate and cost-effective tool for the visualization of the time-dependent NAPL/water movement in laboratory-scale experiments and dynamic changes in fluid saturation in porous media. [ABSTRACT FROM AUTHOR]

The Brazilian Savannah Biome is strategic for Brazilian agriculture and for maintaining Brazil's hydrological balance, contributing to river flows from eight of the twelve Brazilian hydrographic regions. In recent years, there has been a continuous growth of irrigated agriculture, the main activity that uses the water resource, and the emergence of conflicts over water use. Thus, to improve water resource management in the Brazilian Savannah, it is important to better understand groundwater recharge rates to determine the magnitude of the sustainable groundwater resource in the region. The study aimed to evaluate groundwater recharge estimation methods in a watershed located in the Brazilian Savannah region. For this, recharge rates were calculated for the period from October 2009 to September 2011 using the methods of baseflow separation, water table fluctuation, and a sequential water balance (BALSEQ). The recharge rates estimated by the baseflow separation, and water table fluctuation methods were, respectively, 23.7% and 26.6% of the total rainfall of 1753.8 mm in the watershed. Using the BALSEQ water balance method, the potential recharge for the period was estimated to be 31.5% of annual average precipitation. The recharge estimates calculated by the methods were consistent with those observed in other agricultural watersheds in the Brazilian Savannah Biome. Also, the evaluated methods can be used as a tool by water resource managers for the rational use of groundwater. [ABSTRACT FROM AUTHOR]

In recent decades, increasing population activities are a complex task throughout the world. The scarcity of water in southern India is high as compared to the global average. Progressive development of the aquifer system by artificial recharging can be considered as a tool for increasing groundwater resource. The water conservation techniques had been used for increasing groundwater storage in the hard rock. 'This research focuses on estimation of groundwater recharges using empirical model through artificial recharge structures, which plays a major role to enhance recharge. The groundwater recharge by water table fluctuation is estimated in context of recharge structures. It is an important role as sustainable development of groundwater resources. The normal groundwater renews by an annual rainfall varied from 11 to 16%. The total recharge is estimated 173.12 ha m in which the influence by conservation recharge structures varies from 0.34 to 26.33 which indicates the groundwater storage optimal maintained in the Pappireddipatti watershed (total number of structures is 22), whereas Vaniyar sub-basin groundwater recharge is estimated 530.30 ha m (total number of structures is 138). The performance of artificial recharge structures is to reduce extra surface runoff in the watershed. The optimal performances need to maintain for continuous withdrawal of groundwater through natural and artificial recharge structures. An empirical approach is used for the assessment of the recharge from rainfall with reasonable accuracy on the periodic groundwater recharge in the hard rock aquifer. The rainfall based on Thiessen polygon method was prepared by annual fall from three-gauge station in the watershed. The effective depth of precipitation of the rainfall is 915.31 mm. Hence, the recharge rate could be increased in close to suitable recharge site in the watershed. A GIS approach was utilized to incorporate six contributing variables: lithology, land use/land cover, soil types, geomorphology, drainage, and slope. The outcome of benefits showed that around 72% of the evaluation zone is assigned as good to moderate potential groundwater recharge whereas low bring down potential groundwater energize ranges with poor potential groundwater recharge covers 38% in the area. The outcomes demonstrate that the groundwater recharge potential zone is focusing on sustainable groundwater development. Further, there is improved in water level in low recharge area to moderate recharge with respect to rainfall influence at recharge structures. It confirms the interconnection of the aquifer. [ABSTRACT FROM AUTHOR]

Groundwater systems are largely influenced by rainfall variability which is considered the principal source of recharge. The present study explores the relation between the long-term rainfall (1992–2014) and the corresponding water table variation over the Varanasi district. The temporal trends of both the water table and long-term rainfall were analyzed using non-parametric Mann-Kendall time-series trend test. The district experienced an annual rainfall average of 876 mm during the study period. In the recent decade (2003–2014), the amount of annual rainfall and rainy days declined by 42 mm and 8 days, respectively, were compared with previous decade (1992–2002). The water table fluctuation had also shown decreasing trend in the recent decade and were compared with the previous decade. The frequent fluctuations in rainfall anomaly and water table fluctuation had been related to El Nino and La Nina events to study the impact of these events at regional scale. The intense cultivation of water intensive crops as well as rainfall variation was found to be one of the major causes behind the water table fluctuation in the study area. Therefore, artificial water recharge and change in cropping pattern through cultivating less water consuming crops with efficient irrigation technologies of water management may help to overcome the upcoming adverse situations. [ABSTRACT FROM AUTHOR]

Purpose: Erhai Lake is the second-largest freshwater lake on the Yunnan–Guizhou Plateau in the southwest China. Water quality protection for the lake is necessary because it is a potable water supply for more than one million people. However, nitrogen exchanges between the soil profile (SP) and shallow groundwater (SW) accelerate nitrogen loss from the soil into groundwater in the nearshore vegetable fields of Erhai Lake due to excessive nitrogen accumulation in the SP and shallow and variable groundwater tables. More nitrogen enrichment in the groundwater increases the nitrogen input to lake water from groundwater migration and threatens the water safety of the water in Erhai Lake. However, there is a lack of information on the effect of fluctuations in the SW table on nitrogen concentrations in the SW and SP in this region. Materials and methods: Field monitoring of plots at different elevations was conducted to monitor the SW table and nitrogen concentrations in the SW and SP from June 2015 to May 2016. Results and discussion: With increasing SW depth, TN and NO3−–N concentrations in the SW decreased exponentially, and the NH4+–N concentration increased. The NO3−–N, DTN, and NH4+–N concentrations in the SP were positively linearly correlated with SW depth. With an increase in the NO3−–N, DTN, and NH4+–N concentrations in the soil of the groundwater level fluctuation zone, NO3−–N, TN, and NH4+–N concentrations in the SW showed exponential increases. Multiple factors, including nitrogen application rates, properties of the SP, rainfall, and topography, affected the SW table and the nitrogen distribution in the SP. Then, TN, NO3−–N, and NH4+–N concentrations in the SW presented temporal-spatial variations via nitrogen exchange between the SP and SW. Conclusions: The SW table fluctuations significantly affected the nitrogen concentrations in the SW and SP. These results provide a scientific basis for regulating seasonal SW tables and preventing nitrogen loss from the SP. [ABSTRACT FROM AUTHOR]

Climate change is expected to alter the hydrology and vascular plant communities in peatland ecosystems. These changes may have as yet unexplored impacts on peat mercury (Hg) concentrations and net methylmercury (MeHg) production. In this study, peat was collected from PEATcosm, an outdoor, controlled mesocosm experiment where peatland water table regimes and vascular plant functional groups were manipulated over several years to simulate potential climate change effects. Potential Hg(II) methylation and MeHg demethylation rate constants were assessed using enriched stable isotope incubations at the end of the study in 2015, and ambient peat total Hg (THg) and MeHg concentration depth profiles were tracked annually from 2011 to 2014. Peat THg and MeHg concentrations and the proportion of THg methylated (%MeHg) increased significantly within the zone of water table fluctuation when water tables were lowered, but potential Hg(II) methylation rate constants were similar regardless of water table treatment. When sedges dominate over ericaceous shrubs, MeHg concentrations and %MeHg became significantly elevated within the sedge rooting zone. Increased desorption of Hg(II) and MeHg from the solid phase peat into pore water occurred with a lowered water table and predominant sedge cover, likely due to greater aerobic peat decomposition. Deeper, more variable water tables and a transition to sedge-dominated communities coincided with increased MeHg accumulation within the zone of water table fluctuation. Sustained high water tables promoted the net downward migration of Hg(II) and MeHg. The simultaneous decrease in Hg(II) and MeHg concentrations in the near-surface peat and accumulation deeper in the peat profile, combined with the trends in Hg(II) and MeHg partitioning to mobile pore waters, suggest that changes to peatland hydrology and vascular plant functional groups redistribute peat Hg(II) and MeHg via vertical hydrochemical transport mechanisms. Unlabelled Image • Climate change anticipated to induce shift in peatland hydrology, plant communities. • Peat Hg(II), MeHg tracked annually over PEATcosm experiment. • Lowered water tables, sedges increase Hg(II), MeHg in water table fluctuation zone • High water tables promote net downward migration of Hg(II), MeHg in peat profile. • Changes to hydrology, ecology redistribute peat Hg(II), MeHg via vertical transport [ABSTRACT FROM AUTHOR]

Predicting specific yield for a given aquifer remains a great challenge due to its dynamic characteristics, especially under periodic (e.g., seasonal and diurnal) groundwater level fluctuations. In this study, a dimensionless period of groundwater level fluctuations, which depends on the saturated hydraulic conductivity, the length of the groundwater level fluctuation period, and the soil water retention properties, is first introduced. Then, the relationship between the predicted specific yield and the dimensionless period of groundwater level fluctuations is defined based on the theory of variably saturated flow. The proposed approximate formula is tested by series of simulations of variably saturated flow within homogeneous and isotropic porous media with the Hydrus‐1D program. The results of numerical experiments demonstrate an invariant relationship between the predicted specific yield and the dimensionless period for a wide range of changes in the dimensionless period of groundwater level oscillations. Furthermore, the sensitivity analysis of the dependence of the predicted specific yield on the van Genuchten parameters indicates the applicability of estimating the specific yield via van Genuchten parameters, which can be predicted by the soil texture classes for a given length of the oscillation period and a known saturated hydraulic conductivity in the zone of groundwater level fluctuations. The proposed model can be used for predicting the dynamics of the specific yield under seasonal or diurnal groundwater level fluctuations. Key Points: Specific yield (Sy) is a dynamic and time‐dependent parameterA model for predicting Sy under periodic water table oscillations is proposedThe proposed model is able to estimate Sy under diurnal and seasonal water level fluctuations [ABSTRACT FROM AUTHOR]

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