Groundwater Recharge Research Articles

Impacts of Wildfires on Groundwater Recharge: A Comprehensive Analysis of Processes, Methodological Challenges, and Research Opportunities

Increasing wildfire activity has led to complex ecosystem consequences, with direct effects on the subsystems that affect the presence and movement of water. Although studies have investigated the cascading effects of wildfires on the water balance, our understanding of broad-scale groundwater modifications post fire remains unclear. This review aims to elucidate fire-induced shifts in the water balance, their causal factors, and their potential effects on groundwater recharge. By scrutinizing prior research examples that modeled post-fire recharge scenarios, the review highlights persistent knowledge gaps. The challenge of quantifying and integrating fire-induced alterations in precipitation, wind, and land temperature patterns into recharge projection models is specifically addressed. Despite these gaps, post-fire values of hydrologically meaningful parameters such as leaf area index (LAI), curve number (CN), and near-surface saturated hydraulic conductivity (KST) have been identified. Simulating post-fire recharge via the extrapolation of these values requires the consideration of site-specific conditions, vegetation recovery, and ash removal. It frequently results in a reduced interception and increased surface runoff, while evapotranspiration remains dependent on site-specific factors and often dictates groundwater recharge estimates. Although post-fire recharge simulations are inherently complex and imprecise, their growing application can guide land-use alterations and support policy implementation that considers fire-induced water availability changes.

Identification and quantitative estimates of groundwater transfers to formerly charophyte dominated marl lakes with radon-222

Interaction with groundwater determines many processes in marl lakes. Net transfer of inorganic carbon helps define their chemical characteristics and determines their unique benthic flora. Nutrient enrichment weakens the biogeochemical buffering mechanisms which help maintain a clear-water state and many small, shallow marl lakes are prone to siltation. Despite hydrological processes being recognised as important for the complex interactions between plants, nutrient availability and physical sediment properties which shape marl lake ecology, groundwater discharge to many of these lakes has never been quantified. The aim of this study was to locate and quantify groundwater transfers to degraded marl lakes in a Special Area of Conservation on the island of Ireland. A RAD7 radon detector identified and measured elevated concentrations of 222Rn in three lakes for quantifying their groundwater influx with a 222Rn mass-balance equation. Conservative estimates of mean daily groundwater discharge to Kilroosky Lough, Drumacrittin Lough, and Dummy's Lough were 143 m3, 502 m3, and 269 m3 respectively. With extrapolation to the entire hydrological year, annual groundwater recharge contributed approximately 47 %, 155 %, and 50 % of the respective lake volumes. The areas within the lakes which were found to have the highest groundwater influence also closely matched the locations where substantial charophyte communities persist suggesting that the two are linked. These findings underline the importance of groundwater transfers for the water budget in small marl lakes and will inform management efforts to mitigate their eutrophication.

Dynamic interactions between groundwater level and discharge by phreatophytes

Many traditional models that predict plant–groundwater use based on groundwater level variations, such as the White method, make various simplifying assumptions. For example, these models often neglect the role of plant hydraulic redistribution, a process that can contribute up to 80% of transpiration. Thus, this work aims to avoid such assumptions and subsequently explore the dynamic interactions between groundwater levels and phreatophytic vegetation, including plant nocturnal transpiration, hydraulic redistribution, and response to atmospheric conditions, in shallow-groundwater ecosystems using Loblolly pine (Pinus taeda) as a model species. The model scenarios are formulated using a stomatal-optimization model coupled to the soil–plant–atmosphere continuum. Flow through soil and groundwater are described using the Richards equation and a linear reservoir approximation, respectively, with groundwater in contact with an external water body of fixed elevation. Results show that nocturnal transpiration, mediated by plant residual conductance, and hydraulic redistribution, are able to reduce groundwater levels at night and alter the groundwater recharge rate. Projected atmospheric conditions of increased carbon dioxide and elevated temperature have opposing effects on groundwater levels, which tend to roughly cancel each other under a projected scenario of 500 ppm carbon dioxide and 1.5 oC warming. Such detailed modeling can be used to provide further insights into coupled interactions between vegetation, climate and groundwater levels in phreatophyte-dominated ecosystems.

Combining the digital filtering method with the SWAT model to simulate spatiotemporal variations of baseflow in a mountainous river basin

Study regionGanjiang River Basin, a typical mountainous river basin which located on the south bank of the middle-lower Yangtze River. The Ganjiang River is the seventh largest tributary of the Yangtze River. Study focusBaseflow, a key recharge source for the river streamflow. This study combined the digital filtering method with the SWAT model to examine the temporal and spatial patterns of baseflow across the Ganjiang River Basin, and quantitatively assessed land use change impact on baseflow. New hydrological insights for the regionBaseflow in the Ganjiang River Basin shows a "single peak" intra-annual distribution. Monthly variations of streamflow and baseflow across the basin are different. The variation of baseflow index is generally opposite to that of streamflow. A positive correlation has been noted between the annual baseflow and streamflow, while a negative correlation was found between the annual baseflow index and precipitation. Due to the potential influence of basin topography, river flow direction and rock layer distribution, baseflow and baseflow modulus showed a spatially increasing trend from south to north, with the northwest region having extremely strong groundwater recharge. In comparison to the basic scenario, under extreme land use scenarios of forest, grassland, and cropland, baseflow may experience an increase of 14.7 % and 2.9 %, while witness a decrease of 13.9 %. All results improve the understanding of baseflow spatiotemporal variations in river basins.

Characteristics and Indicative Significance of Groundwater Stable Isotopes in the Loess Plateau at the Regional Scale

Regional groundwater recharge is a critical scientific issue for sustainable groundwater resource development and management. However, spatial variations in groundwater recharge in the Loess Plateau （LP） remain poorly understood. To fill this knowledge gap, a systematic sampling campaign and stable isotope analysis were carried out for groundwater （shallow aquifer） in 13 major catchments during July 2019. The main objectives of this study were： ① to understandthe spatial distribution and influencing factors of stable isotopes in groundwater and ② to reveal the groundwater recharge sources and pathways and their spatial variations, combined with the precipitation stable isotope datasets. Stable isotopes in groundwater had poor spatial variations at the regional scale； however, they became isotopically depleted with the increase in annual average precipitation on the catchment scale （r = -0.87）. Compared with the stable isotope of precipitation, stable isotopes of groundwater were generally depleted and were similar to the precipitation of the rainy season （July-September）. These together indicated that there was pronounced seasonality of groundwater recharge, and the main recharge period was the rainy season. In particular, the recharge seasonality index （δP/G） was closely related to the catchment's average annual precipitation （r = -0.77） and leaf area index （r = -0.63）. In addition, groundwater lc-excess was generally negative, with the catchment-mean value ranging from -4.3‰ to -0.7‰. Hydrologically, this indicated that groundwater recharge pathways （ratio of matrix flow vs. preferential flow） were different among these catchments, which should be quantitatively determined by combining the saturated zone （groundwater） and the unsaturated zone （soil） in future work. Our findings can improve the understanding of groundwater recharge in LP and provide a scientific basis for sustainable management of groundwater resources at the regional scale.

Natural Water Sources and Small-Scale Non-Artisanal Andesite Mining: Scenario Analysis of Post-Mining Land Interventions Using System Dynamics

Small-scale open-pit, non-artisanal mining of low-value ores is an understudied practice despite its widespread occurrence and potential impact on freshwater resources due to mining-induced land-use/cover changes (LUCCs). This research investigates the long-term impacts of andesite mining in Pasuruan, Indonesia, on the Umbulan Spring’s water discharge within its watershed. System Dynamics (SD) modeling captures the systemic and systematic impact of mining-induced LUCCs on discharge volumes and groundwater recharge. Agricultural and reservoir-based land reclamation scenarios then reveal post-mining temporal dynamics. The no-mining scenario sees the spring’s discharge consistently decrease until an inflection point in 2032. With mining expansion, reductions accelerate by ~1.44 million tons over two decades, or 65.31 thousand tons annually. LUCCs also decrease groundwater recharge by ~2.48 million tons via increased surface runoff. Proposed post-mining land interventions over reclaimed mining areas influence water volumes differently. Reservoirs on reclaimed land lead to ~822.14 million extra tons of discharge, 2.75 times higher than the agricultural scenario. Moreover, reservoirs can restore original recharge levels by 2039, while agriculture only reduces the mining impact by 28.64% on average. These findings reveal that small-scale non-artisanal andesite mining can disrupt regional hydrology despite modest operating scales. Thus, evidence-based guidelines are needed for permitting such mines based on environmental risk and site water budgets. Policy options include discharge or aquifer recharge caps tailored to small-scale andesite mines. The varied outputs of rehabilitation scenarios also highlight evaluating combined land and water management interventions. With agriculture alone proving insufficient, optimized mixes of revegetation and water harvesting require further exploration.

Experimental and numerical study of cadmium fate and transport mechanisms during artificial recharge in agricultural regions

Agricultural Managed Aquifer Recharge (AgMAR) uses agricultural lands and floodwater to enhance groundwater recharge, but its effectiveness can be hindered by heavy metals like cadmium (Cd), which pose risks to groundwater quality. Cd is particularly concerning due to its high mobility and persistence in the environment. This study investigates Cd's fate and transport in agricultural regions during MAR, focusing on sandy loam soils through batch and column experiments. Equilibrium and kinetic batch studies were conducted under varying Cd concentrations and exposure times to quantify the adsorption capacity and rate. HYDRUS-2D was used to simulate Cd's transport in soil under various ponding depths and Cd concentrations. Results showed a maximum Cd adsorption capacity of 439.58 mg/kg, with the Freundlich isotherm providing a better fit (R2 = 0.98) and indicating heterogeneous adsorption sites (n = 0.389). The kinetic experiment indicated chemisorption as the predominant mechanism, with an equilibrium adsorption capacity of 236.49 mg/kg. The pseudo-second-order kinetic model (rate constant 0.0016 h⁻1, R2 = 0.99) suggested that adsorption kinetics are influenced by Cd concentration and available adsorption sites. The column experimental findings supported by HYDRUS-2D modeling successfully explained the fate and transport of Cd within the soil columns. The model fitted parameter values for Freundlich adsorption isotherm coefficient (KF), linearity factor (Nu), and kinetic rate coefficient are (α) 47.37 L/kg, 0.00389 cm³/ppm and 0.0029 min⁻1, respectively. Modeling scenarios further elucidated the transport dynamics of Cd under simulated AgMAR conditions. Modeling scenarios indicated that with constant ponding of 5 cm over a year, Cd at 20 and 40 ppb concentrations in floodwater could potentially migrate below root zone systems. This study highlights the critical role of understanding Cd fate and transport in optimizing AgMAR systems and reducing Cd pollution risks, providing valuable insights for developing effective monitoring and management strategies.

Application of coupled WetSpass-M and MODFLOW models to estimate spatial–temporal water balance components in the Chemoga watershed, Ethiopia

ABSTRACT The groundwater level in the Chemoga watershed has been declining due to an increase in water demand, anthropogenic activities, and climate change effects. This paper uses the WetSpass-MODFLOW coupling to evaluate the groundwater recharge in the Chemoga watershed. The MODFLOW groundwater flow simulation model is then used to simulate the hydraulic head distribution based on these findings. The input data of WetSpass models are soil, land cover, topography, slope, and groundwater depth, as well as monthly meteorological characteristics (such as temperature, wind speed, and rainfall). The long-term spatial and temporal average annual precipitation of 1,453 mm is distributed as 169 mm (11.63%) groundwater recharge and 879 mm (60.5%) surface runoff, while 405 mm (27.87%) is lost through evapotranspiration. In such seasonal variations, the groundwater head due to the wet/summer stress period varied from 4 to 41 m. While in the dry/winter stress period groundwater head varied from 3.5 to 39.8 m, and also the groundwater head due to the annual stress period varied from 3.7 to 40 m. The findings are extensive and can be applied to water resource management and groundwater resource development in a sustainable manner by safeguarding high groundwater recharge locations, and reevaluating allowable groundwater abstraction rates.

GIS-Based Analytical Hierarchy Process for Identifying Groundwater Potential Zones in Punjab, Pakistan

The quality and level of groundwater tables have rapidly declined because of intensive pumping in Punjab (Pakistan). For sustainable groundwater supplies, there is a need for better management practices. So, the identification of potential groundwater recharge zones is crucial for developing effective management systems. The current research is based on integrating seven contributing factors, including geology, soil map, land cover/land use, lineament density, drainage density, slope, and rainfall to categorize the area into various groundwater recharge potential zones using remote sensing, geographic information system (GIS), and analytical hierarchical process (AHP) for Punjab, Pakistan. The weights (for various thematic layers) and rating values (for sub-classes) in the overlay analysis were assigned for thematic layers and then modified and normalized using the AHP. The result indicates that about 17.88% of the area falls under the category of very high groundwater potential zones (GWPZs). It was found that only 12.27% of the area falls under the category of very low GWPZs. The results showed that spatial technologies like remote sensing and geographic information system (GIS), when combined with AHP technique, provide a robust platform for studying GWPZs. This will help the public and government sectors to understand the potential zone for sustainable groundwater management.

Modeling the impact of long-term land use changes on deep soil hydrological processes in the Loess Plateau, China

Land use change can significantly affect soil hydrology in arid and semi-arid regions, making it crucial to understand the relationship between vegetation roots and soil moisture. Current models often fail to predict root growth and its impacts on water dynamics accurately. Our work presents a novel model that seamlessly integrates the Community Land Model (CLM) with the Soil & Water Assessment Tool (SWAT). Furthermore, it enhances the root module within the CLM, enabling more accurate simulations of dynamic root depth and distribution across varying tree ages. This improvement particularly considers the crucial processes of dormancy and plant maturity. Soil moisture and root patterns under apple trees of varying ages and in wheat fields on the Loess Plateau was analyzed. Our findings indicate that our dynamic root depth model outperforms traditional static models, and can accurately reflect soil moisture levels with high precision (R2 = 0.80–0.81; Nash-Sutcliffe efficiency (NSE) = 0.65–0.75). In contrast to methods that utilize fixed root depths, dynamic root simulation can provide new insights. As apple orchards mature, the roots of 22-year-old apple trees have been found to reach a depth of 21 m in the soil. Conversely, the maximum root depth of wheat is limited to 1.9 m. This latter finding aligns more closely with the measured root depths, highlighting the accuracy of dynamic simulations. This model reveals that older apple orchards show decreased soil moisture at greater depths (>20 m), contrasting with wheat fields that affect moisture mostly within the top 2 m. Our results underscore the crucial role of dynamic modeling in comprehending root-soil water interactions. Furthermore, they imply that extended orchard cultivation practices can lead to a substantial depletion of deep soil moisture. Specifically, over a period of 1 to 22 years, a water deficit of up to 85 mm yr−1 has been observed. For a 22-year-old forest, the D-D (dynamic distributions of coarse and fine roots) method calculates a significant cumulative deep Soil Water Storage loss. Over the course of 22 years, this loss amounts to 1664 mm, which is almost three times compare to the annual rainfall recorded. Such a large loss has the potential to significant impact on groundwater recharge. This highlights the need for careful consideration in future afforestation efforts to prevent increased soil aridity.

Delineating groundwater potential zones using integrated remote sensing and GIS in Lahore, Pakistan.

Groundwater depletion and water scarcity are pressing issues in water-limited regions worldwide, including Pakistan, where it ranks as the third-largest user of groundwater. Lahore, Pakistan, grapples with severe groundwater depletion due to factors like population growth and increased agricultural land use. This study aims to address the lack of comprehensive groundwater availability data in Lahore's semi-arid region by employing GIS techniques and remote sensing data. Various parameters, including Land Use and Land Cover (LULC), Rainfall, Drainage Density(DD), Water Depth, Soil Type, Slope, Population Density, Road Density, Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-Up Index (NDBI), Moisture Stress Index (MSI), Water Vegetation Water Index (WVWI), and Land Surface Temperature (LST), are considered. Thematic layers of these parameters are assigned different weights based on previous literature, reclassified, and superimposed in weighted overlay tool to develop a groundwater potential zones index map for Lahore. The groundwater recharge potential zones are categorized into five classes: Extremely Bad, Bad, Mediocre, Good, and Extremely Good. The groundwater potential zone index (GWPZI) map of Lahore reveals that the majority falls within the Bad to Mediocre recharge potential zones, covering 33% and 28% of the total land area in Lahore, respectively. Additionally, 14% of the total area falls under the category of Extremely Bad recharge potential zones, while Good to Extremely Good areas cover 19% and 6%, respectively. By providing policymakers and water supply authorities with valuable insights, this study underscores the significance of GIS techniques in groundwater management. Implementing the findings can aid in addressing Lahore's groundwater challenges and formulating sustainable water management strategies for the city's future.

Springs of the Arabian Desert: Hydrogeology and Hydrochemistry of Abu Jir Springs, Central Iraq

The Arabian Desert is characterised by very low rainfall and high evaporation, yet over 210 springs are on its northeastern edge in central Iraq along the Abu Jir lineament, which represents the western depositional margin of a foreland basin infilled by the floodplain sediments of the Tigris and Euphrates Rivers; there is little evidence of faulting. The springs discharge from gently east-dipping Paleocene–Eocene limestones, either where groundwater flowpaths intersect the ground surface or where groundwater flow is forced to the surface by confining aquitards. Calculated annual recharge to the aquifer system across the Arabian Desert plateau (130–500 million m3) is significant, largely due to rapid infiltration through karst dolines, such that karst porosity is the primary enabler of groundwater recharge. The recharge is enough to maintain flow at the Abu Jir springs, but active management of groundwater extraction for agriculture is required for their long-term sustainability. The hydrochemistry of the springs is determined by evaporation, rainfall composition (high SO4 concentrations are due to the dissolution of wind-blown gypsum in rainfall), and plant uptake of Ca and K (despite the sparse vegetation). Limestone dissolution has relatively little impact; many of the springs are undersaturated with respect to calcite and lack tufa/travertine deposits. The springs at Hit-Kubaysa contain tar and high levels of H2S that probably seeped upwards along subvertical faults from underlying oil reservoirs; this is the only location along the Abu Jir lineament where deep-seated faults penetrate to the surface. The presence of hydrocarbons reduces the Hit-Kubaysa spring water and converts the dissolved SO4 to H2S.

Water accounting of groundwater over exploited districts in Haryana and Punjab states to analyse impacts of water conservation measures on water availability

ABSTRACT Escalating water scarcity threatens to sustainable food production, necessitating enhanced water use efficiency through effective water management practices. The present study aims to conduct water accounting in the groundwater-depleted districts of Haryana and Punjab, India, analysing the potential irrigation water savings achievable through the implementation of efficient management techniques in these selected districts. The study area encompasses Kaithal and Karnal districts in Haryana and Patiala and Sangrur districts in Punjab with water availability assessment for 2015. Results showed that there is a mismatch between the annual groundwater pumped and replenishable groundwater recharge in all selected districts indicating a need for improved water management. Adjusting the timing of rice sowing to align with the onset of the rainy season can significantly save water and reduce groundwater extraction. For instance, delaying rice transplanting from May 21st to June 15th can reduce crop water demand by 10.89%. Similarly, transplanting rice on June 15th can reduce water demand by 9.03%, 6.23%, 4.31%, and 2.46% compared to transplanting on May 26th, May 31st, June 5th, and June 10th, respectively. Shifting of a rice-wheat cropping system to a maize-wheat system can substantially decrease crop water demand. Replacing rice with maize can result in a 54.66% reduction in crop water demand per hectare.

Unexpected hydrologic response to ecosystem state change in tallgrass prairie

In grasslands around the world, climate change is occurring in tandem with woody encroachment (the spread of woody vegetation in grass-dominated ecosystems). State transitions from grassland to shrub/woodland have been identified aboveground via changes in species cover and composition, but the hydrological impact of these transitions is not well understood. Shifts from grass- to woody-dominance have the potential to impact evapotranspiration, soil moisture dynamics, and groundwater recharge. Therefore, it is possible that the consequences of aboveground vegetation change may be observable in the hydrological system. We leveraged long-term hydrological records from a tallgrass prairie site in northeastern Kansas, USA, to examine how concurrent changes in climate and land-cover have altered hydrological dynamics over the last century. Stream discharge has declined in recent decades despite > 100 years of climate wetting. The relationship between incoming precipitation and streamflow has weakened over the last 40 years, suggesting that shifts in the physical landscape are altering patterns of hydrological connectivity. Long-term isotope records show a divergence in the isotopic composition of precipitation (no change in δ18O) and stream/groundwater (decreasing δ18O) over the last decade. These results suggest that woody encroachment is accelerating the hydrological cycle, potentially by decreasing groundwater recharge (via increased evapotranspiration) and/or increasing infiltration rates (via creation of macropores). Holistically, these changes illustrate the interdependence of above- and below-ground processes in the local hydrological cycle, and the cascading long-term consequences (decades to centuries) for critical zone function once woody encroachment has occurred.

Measuring and monitoring tree cover and plant canopy height in Pune city, India

Global datasets often fall short in estimating tree cover areas outside the forest tracts, particularly in urban areas. This limitation poses a challenge for accurately estimating tree cover outside forests (ToF) and understanding their contribution to ecosystem services. In the context of increasing population pressure and unsustainable urbanization in Indian cities, regional-level tree cover and canopy height estimations are crucial for evaluating the impact of ToF on various ecosystem services, including carbon sequestration, climate change adaptation, biodiversity hotspots, groundwater recharge, soil conservation, flood control, urban heat mitigation, and psychological and emotional well-being. This technical note outlines a rapid and cost-effective methodology for assessing tree canopy cover and height, specifically tailored for ToF estimation, offering a valuable tool for addressing these socio-urban environmental challenges and enabling sustainable land use planning.

Estimation of Surface and Groundwater Interaction by Stable Isotopic Techniques – A Case Study of Chengalpattu District, OMR Region

Isotopes are atoms of an element having the same atomic number but different mass numbers. Isotopes in hydrology and water resources are used for identifying its occurrence, movement, residence times, recharge, and discharge process. Stable isotopes of hydrogen(δ2H) and oxygen(δ2O) are used for identifying the surface and groundwater interactions as they constitute hydrogen and oxygen. In this study oxygen and hydrogen stable isotopes are used to identify surface and groundwater interaction in Old Mahabalipuram Road (OMR) regions of Chengalpattu district. The precipitation, lake, surface, and groundwater were collected during pre-monsoon, monsoon, and post-monsoon seasons. The collected sample is analyzed for stable isotopic compositions of oxygen and hydrogen seasonal-wise. The measured stable isotopic compositions during pre-monsoon season of stable oxygen are -4.29 to -2.00 and stable hydrogen are -29.39 to -24.67. The isotopic compositions during monsoon season range from -4.72 to -4.00 and for hydrogen ranges from -29.39 to -23.50. During monsoon season the depletion of isotopic composition is seen and the enrichment of isotopic composition is observed during pre-monsoon season. The variation in stable isotopic composition of oxygen and hydrogen are observed. A Groundwater Water Meteoric Water Line (GMWL) is developed for the study area, and it is compared with a Local Meteoric Water Line (LMWL) for better interpretation of the results. A slight deviation is observed from that of GMWL to LMWL mostly due to isotopic depletion and evaporation effects. From the analysis, a good correlation exists between precipitation and surface water in the study area indicating about recharge mechanism existing in the study area. The groundwater recharge is observed during monsoon seasons and discharge is more towards the pre-monsoon seasons.

Valorization of treated wastewater from the soaking of baby alpaca skin fur

Baby alpaca fur industry generates considerable wastewater during the soaking process, which contains high levels of total suspended solids (TSSs), proteins, and salts, among other components. The valorization of wastewater after precipitation, coagulation–flocculation, and aeration treatments was evaluated for use in irrigation water, fertigation, groundwater recharge, concrete construction, and disposal. The precipitation treatment sludge and the coagulation–flocculation treatment were evaluated as a protein source, soil quality improvement, and disposal. The treatment system included evaluations of nine pH levels, seven coagulant doses, and seven aeration times. The contents of TSSs, chemical oxygen demand (COD), total Kjeldalh nitrogen (TKN), ammonia nitrogen (N–NH3), and oils and fats (O&G), among other parameters, were determined in the treated and untreated wastewater. Before entering the treatment system, the physicochemical characterization of the wastewater showed a high concentration of parameters related to organic matter and dust, such as O&G, five-day biological oxygen demand (BOD5), COD, TSSs, TKN, and N–NH3. The optimal removal parameters were pH 12 for the chemical precipitation of proteins, a dose of 480 mg/L FeCl3 as a coagulant for TSSs removal, and 150 min of aeration; removal efficiencies of 99.02 %, 77.49 %, 79.93 %, and 64.62 % for TSSs, Cod, TKN, and N–NH3, respectively, were obtained. The wastewater after treatment can be used for groundwater recharge and concrete construction, and the wastewater with 2 % dilution can be used for irrigation water and fertigation. The sludge after precipitation is rich in protein and can be used as a protein source or soil quality improver.

Understanding the Source and Evolution of Precipitation Stable Isotope Composition across O‘ahu, Hawai‘i

Abstract Pacific Islands present unique challenges for water resource management due to their environmental vulnerability, dynamic climates, and heavy reliance on groundwater. Quantifying connections between meteoric, ground, and surface waters is critical for effective water resource management. Analyses of the stable isotopes of oxygen and hydrogen in the hydrosphere can help illuminate such connections. This study investigates the stable isotope composition of rainfall on O‘ahu in the Hawaiian Islands, with a particular focus on how altitude impacts stable isotope composition. Rainfall was sampled at 20 locations from March 2018 to August 2021. The new precipitation stable isotope data were integrated with previously published data to create the most spatially and topographically diverse precipitation collector network on O‘ahu to date. Results show that δ18O and δ2H values in precipitation displayed distinct isotopic signatures influenced by geographical location, season, and precipitation source. Altitude and isotopic compositions were strongly correlated along certain elevation transects, but these relationships could not be extrapolated to larger regions due to microclimate influences. Altitude and deuterium excess were strongly correlated across the study region, suggesting that deuterium excess may be a reliable proxy for precipitation elevation in local water tracer studies. Analysis of spring, rainfall, and fog stable isotope composition from Mount Ka‘ala suggests that fog may contribute up to 45% of total groundwater recharge at the summit. These findings highlight the strong influence of microclimates on the stable isotope composition of rainfall, underscore the need for further investigation into fog’s role in the water budget, and demonstrate the importance of stable isotope analysis for comprehending hydrologic dynamics in environmentally sensitive regions.

Evolution characteristics and attribution analysis of runoff in the coal mining area in northwest China: A case study of the Kuye River Basin

ABSTRACT The Kuye River Basin is the main coal-producing area in northwest China, and it is also a typical arid and semi-arid area. Under the combined influence of climate change and human activities, the runoff of the basin decreases noticeably. The Mann–Kendall trend test, the Hurst index, cumulative anomaly, and wavelet analysis were used to analyze the runoff evolution characteristics of the Kuye River, and the contributions of climate change and human activities to the runoff reduction were quantitatively separated by the slope-changing ratio of the cumulative quantity. The results showed that the runoff decreased significantly from 1970 to 2020, and there was an obvious abrupt change in 1996, while the change trends in precipitation and evaporation were not significant. The contributions of climate change and human activities to runoff reduction were 22.71 and 77.29%, respectively, and human activities have become the dominant factor in runoff variations. Coal mining and the implementation of soil and water conservation measures are considered to be the main human activities contributing to the reduction in runoff. In particular, mining activities reduce groundwater recharge to rivers, which provides a profound understanding of the effect of human activities in mining areas on runoff variation.

Assessment of urbanization impacts on soil erosion and groundwater recharge in Enugu, Southeastern Nigeria

The study of Land Use and Land Cover (LULC) in Enugu, southeastern Nigeria, is crucial for understanding its effects on erosion and groundwater recharge. Different LULC types, coupled with varying slope gradients and soil types, create a complex interaction that influences soil stability and water infiltration in the region. This research aims to assess the distribution of LULC types, slope gradients, and soil types in Enugu, and to evaluate their impacts on erosion rates and groundwater recharge potential. Data for LULC, slope gradients, and soil types were collected and analyzed to determine their spatial distribution and characteristics. The study employed GIS techniques to map these variables and assess their interactions. Erosion potential and groundwater recharge capacity were evaluated based on the characteristics of the LULC types, slopes, and soils. The analysis revealed that trees cover the largest area (3709.74 km²), playing a significant role in stabilizing the soil and reducing erosion through their extensive root systems and canopy cover. Rangeland (2631.81 km²) also contributes to soil stability, although less effectively than forested areas. Crops (192.40 km²) have mixed impacts on erosion depending on agricultural practices. Built areas (1162.69 km²) present challenges due to impervious surfaces, which increase surface runoff and reduce groundwater recharge. Slope gradients were found to correlate with erosion processes and groundwater dynamics. Gentle slopes (0 - 1.81 degrees) cover 1870.15 km² and facilitate infiltration, enhancing groundwater recharge. Moderate slopes (1.81 - 4.06 degrees), covering 3275.46 km², are more prone to erosion, while steeper slopes (4.06 - 11.73 degrees) covering 2176.54 km² experience accelerated runoff and increased erosion rates. The steepest slopes (11.73 - 44.06 degrees) are the most erosion-prone areas, requiring significant intervention. The soil analysis showed that Dystric Nitosols (4052.80 km²) with the lowest K-factor (0.0178) are least prone to erosion and have high infiltration capacity, making them beneficial for groundwater recharge. Plinthic Acrisols (2732.53 km²) and Ferric Acrisols (102.36 km²) exhibit moderate erosion susceptibility. Dystric Fluvisols (793.92 km²) with the highest K-factor (0.0223) are highly erosion-prone. Gleysols (20.69 km²) have low to moderate erosion susceptibility. The interplay between LULC types, slope gradients, and soil types significantly influences erosion and groundwater recharge in Enugu. The study highlights the need for targeted land management practices, such as afforestation, contour farming, terracing, and the use of cover crops to mitigate erosion and enhance groundwater recharge. This research provides a comprehensive analysis of the relationships between LULC, slope gradients, and soil types in Enugu, offering valuable insights for developing effective land management strategies to address erosion and groundwater recharge challenges.