Water Recharge Research Articles

Application of Geochemical and Isotopic Tools to Investigate Water Recharge and Salinization in a Coastal Phreatic Aquifer Suffering Severe Natural and Anthropogenic Constraints: Case of the Mornag Aquifer, NE Tunisia

Application of Geochemical and Isotopic Tools to Investigate Water Recharge and Salinization in a Coastal Phreatic Aquifer Suffering Severe Natural and Anthropogenic Constraints: Case of the Mornag Aquifer, NE Tunisia

Reconstruction of Past Water Levels in Data-Deficient Karst Springs

Karst aquifers are crucial for providing fresh water worldwide but are also incredibly sensitive to human impact and climate change. This study aims to reconstruct the historical water levels of karst springs, despite the lack of data. By combining collected data, we have created a detailed numerical model to understand the complex behavior of karst aquifers. Our research reveals significant drops in the water levels at Longtan Spring, mainly due to the overuse of groundwater and inadequate water recharge, which is critical for the success of the Springs Resurgence project. We have also mapped out historical groundwater levels and identified the necessary conditions to get the spring flowing again. The model proved to be reliable during its calibration from 2000 to 2007, with an average Nash–Sutcliffe efficiency coefficient of 0.52 for the monitoring wells. For the period from 1960 to 2019, our model showed a strong correlation coefficient of over 0.97 when compared with data from the GRACE satellite mission, demonstrating its high accuracy. The approach we have taken in this study provides a feasible way to figure out historical water levels in karst springs, which is vital for protecting these essential fresh water sources. This work will provide a strong basis for policies to restore the spring.

Assessing Recharge Sources and Seawater Intrusion in Coastal Groundwater: A Hydrogeological and Multi-Isotopic Approach

One of the crucial challenges of our time is climate change. The consequences of rising sea levels and drought greatly impact water resources, potentially worsening seawater intrusion. Characterizing coastal aquifers is an essential step in devising strategies to address these phenomena. Seawater intrusion poses a critical socio-economic and environmental issue in the coastal plain of Muravera, southeastern Sardinia (Italy). This coastal plain is an important agricultural area in Sardinia, and the health of the crops is compromised by the increasing salinization of shallow groundwater. To enhance our understanding of the hydrogeological conceptual model, which is essential for a sustainable resource management system, hydrogeological investigations were conducted and complemented by the chemical and multi-isotopic analyses of groundwater. The main objectives of this study were to identify groundwater recharge areas, understand salinization mechanisms and trace the evolution of water chemistry. Within this framework, a monthly survey monitoring piezometric level and electrical conductivity was carried out for one year. This survey was integrated with chemical and isotope analyses, including δ18OH2O and δ2HH2O, δ11B, δ18OSO4, δ34SSO4, and 87Sr/86Sr. Hydrochemistry analysis results revealed the occurrence of seawater–freshwater mixing, extending up to 4 km inland. H2O isotope analysis confirmed the mixing processes and indicated the meteoric origin of recharge waters for both shallow and semi-confined aquifers. The strontium isotopes ratio facilitated the identification of four main groundwater flow paths, confirmed by the SIAR model. The results of this combined hydrogeological–geochemical–isotopic survey provide essential elements for the future implementation of an integrated and sustainable management system. These findings enable interventions to slow the process of seawater intrusion and meet the economic needs for the development of local communities.

Spatio-temporal distribution of groundwater recharge under climate change in the Namngum++ river basin in lower Mekong region

Groundwater meets the water needs of one third of global population. The erratic nature of rainfall, likely to be exacerbated by climate change further compounded by population growth and urbanization, underscore the crucial role of groundwater in water resources management in Namngum++ river basin in Lower Mekong. Climate change affects groundwater by altering different hydrological processes such as evapotranspiration, infiltration and most importantly the ground water recharge. This study attempts to quantify groundwater recharge in the basin and how climate change is likely to impact it in three stress periods (2030s, 2060s and 2090s) under socio-economic pathways (SSP 2-4.5 and SSP 5-8.5) scenarios. Precipitation, maximum temperature and minimun temperature datasets from four global climate models (GCMs) under coupled model inter comparison project phase 6 (CMIP6) were linearly bias corrected. The Soil and Water Assessment Tool (SWAT), a semi-distributed model, was then employed to assess climate change impact on groundwater recharge. The model performance was very good with coefficient of determination and Nash Sutcliffe Efficiency of 0.72 and 0.70 for calibration period (2000–2010) and 0.80 and 0.77 for validation period (2011–2015) respectively. The hydrological response unit (HRU) level groundwater recharge for four GCMs were individually computed then ensembled by averaging across stress periods. Precipitation, minimum temperature and maximum temperature are likely to increase by 8.20%, 1.40 °C and 1.60 °C for SSP2-4.5 and 11.15%, 1.85 °C and 1.96 °C for SSP5-8.5 respectively. Groundwater recharge is likely to increase for 2060s and 2090s by 9.31% and 8.31% respectively in SSP2-4.5 and decrease by −3.25% in 2030s while increase up to 2.23% in 2060s and finally decreasing by −1.10% in 2090s in SSP5-8.5. The differences in the direction of change for two scenarios are attributed to increase in evapotranspiration due to elevated temperature, as well as increased stream flow yielded by increased precipitation in SSP5-8.5 compared to SSP2-4.5. While this study acknowledges uncertainties that permeate every step, it still presents a potential future scenario for water management.

Impact of Concepts and Spatial Scales on Irrigation Efficiency for Sustainable Water Resources Management: A Review

This paper provides a review of different ‘irrigation efficiency’ concepts evolved over the time since the term was originally conceived, from an engineering perspective; the impact of scale, i.e., from field to basin, on savings in water demands through hightech irrigation—the efficiency paradox; the role of rice cultivation—water guzzler or recharge basin; and policies for transforming high-tech irrigation into water-conserving interventions. As these issues are interlinked, their synergetic resolution is necessary for establishing sustainable irrigated-agriculture at basin scale. There is a consensus on the utility of classical irrigation for designing the capacity of different components of an irrigation system; and also appreciation of the fact that it does not represent the true picture of water savings/losses at the basin scale. Consumed fraction-based water accounting makes a better representation of irrigation performance from field to basin scales. In literature, studies from different countries revealed the positive impact of hightech irrigation in improving land productivity and income at the field scale but without any significant water conservation for further use to other sectors/locations. Many studies also indicate that introduction of high-tech irrigation in water-scarce but abundant irrigable land regions led to increased water use, which resulted in further decline of water table and/or deterioration of groundwater quality. The increase in water demand on improving irrigation efficiency is known as the efficiency paradox or rebound effect. In water-scarce areas, high-tech irrigation should be promoted with caps on water withdrawals even if the water transfer to downstream areas or other uses is not required. High-tech irrigation is helpful in reducing transaction costs for achieving water conservation, but gold plating of irrigation infrastructure alone would not be sufficient. This study emphasizes on enactment and enforcement of policies for regulating total water withdrawal, limiting irrigated area, and adopting ecologically-compliant cropping patterns for establishing sustainable irrigated-agriculture without the rebound effect.

Investigating ground water recharge potential through various analytical methodologies: A case study at Babina block, Bundelkhand region

Investigating ground water recharge potential through various analytical methodologies: A case study at Babina block, Bundelkhand region

Оценка уязвимости карстовых подземных вод к загрязнению на основных массивах Горного Крыма с использованием региональной методики

Introduction. Assessment of groundwater vulnerability to contamination is an effective tool for scientific substantiation of the sanitary protection zones for drinking water sources. Karst ground waters of the Mountain Crimea form the main resources for water supply in the Crimean Peninsula. This study has a purpose to perform the assessme nt and mapping of karst ground waters resource vulnerability to contamination on such representative massifs of the Crimean Mountains as Chatyrdag, Dolgorukovsky, Karabi and Ay-Petri . Materials and methods. Assessment of karst ground waters vulnerability is conducted by use of Mountain -Crimean method. It has been developed on the base of some wide-tested European methods (COP-method and Slovene approach) with methodological modification and adaptation to regional conditions of the Mountain Crimea. The input data for assessment is spatial information about ground waters vulnerability factors: protective layers in vadose zone, flow concentration by streams, sinkholes and caves, precipitation regime etc. The collected spatial information was converted into attributed geo data layers, which were subsequently subjected to overlay operations in Arc GIS 10 software according to assessment scheme. Results. According to the assessment results, approximately 34 and 14% of the Chatyrdag massif area gained the category of high and very high vulnerability, on the Karabi massif – 14 and 17%, on the Dolgorukovsky massif – 14 and 2%, on the Ay-Petri massif – 19 and 7% of total area respectively. The result ing vulnerability maps demonstrate significant mosaics and contrast, which is associated with discrete distribution of protective covers and high differentiation of ground water recharge conditions within the catchments of karst massifs. Discussion. Analysis of the resulting vulnerability maps have revealed that the leading factors determining areas of high and very high vulner ability of karst waters are runoff concentration factors, while the factors of protective cover mainly determine the areas with low vulnerability. The zones of high vulnerability on the Chatyrdag and Karabi massifs are mainly coincide with areas of high density of karst forms (sinkholes and caves), while high vulnerability zones of the Ay-Petri and Dolgorukovsky massifs are predominantly associated with areas near permanent and temporary watercourses. In general, the obtained maps of groundwater vulnerability are quite consistent with the known data on the hydro-geological conditions of the assessed massifs. Conclusions. The identified differences in the area ratio and spatial distribution of ground waters vulnerability categories between the assessed massifs are a consequence of local geological, geo-morphological and hydrological features. The obtained results confirm high applicability of the Mountain-Crimean regional method for groundwater vulnerability assessment, at least for the karst massifs of the Mountain Crimea. Suggestions for practical application and direction for future research. The produced groundwater vulnerability maps create a scientific basis for delineation of water protection zones, assessing the risks of groundwater pollution and developing the territorial planning schemes within studied areas. The next stage of study is an assessment of groundwater source vulnerability for individual karst springs used in water supply.

Precipitation Variations in the Central Qilian Mountains since the 7th Century and Regional Differences: Evidence from Tree-Ring Data

The Qilian Mountains, located in northwest China and serving as a crucial water recharge area, have exhibited significant regional differences in precipitation patterns in recent decades. However, the limited temporal coverage of instrumental data has hindered a deep understanding of hydroclimate variations and regional differences. Further investigation into their long-term spatial and temporal precipitation characteristics is urgently needed. In this study, a new tree-ring-width chronology spanning 1743 years was established in the central Qilian Mountains using Qilian juniper (Juniperus przewalskii Kom.) samples. Significant correlations were found between the tree-ring indices and precipitation during both the growing and pre-growing seasons. Based on these correlations, annual precipitation from August of the previous year to July of the current year was reconstructed. The reconstruction model successfully explains 34.5% of the variation in precipitation during the calibration period. The analysis of the reconstructed series reveals notable interannual to multi-decadal dry–wet variability during the period from 614 AD to 2016 AD. The mid- to late-15th century emerges as the longest-lasting dry period, while the last decade stands out as the wettest. Comparative analysis with other precipitation reconstructions in the eastern and western Qilian Mountains reveals that regional drought events tend to be more pronounced and enduring. Low-frequency fluctuations on decadal to century scales show distinct wet and dry periods in the 12th–18th centuries in both the eastern and western parts of the Qilian Mountains, with weaker fluctuations in subsequent centuries. However, the central part of the Qilian Mountains exhibits opposite trends, possibly due to the complex interactions of multiple circulation systems.

Groundwater potential zones delineation using GIS and AHP techniques in upper parts of Chemoga watershed, Ethiopia

Water is one of the most imperative needs and used for innumerable purpose. The needs of groundwater exploration have being increased due to the radical climatic changes, for continually increased population growth and a change of human lifestyle. GIS and AHP of multicriteria decision making are the most effective, applicable and logical approaches to delineate the groundwater potential zones in upper parts of Chemoga watershed. GIS and AHP are a 7 computer-based systems used to handle, store, manipulate, analyze and present geospatial data to resolve several complicated problems in the environment. Hence, the groundwater potential zone is delineated by overlaying the weights of ten influencing factors (lineament density, rainfall, geomorphology, Lithology, slope, drainage density, roughness, land use/land cover, depth to groundwater level and elevation) in ArcGIS platform under spatial analysis tool. All those influencing factors are selected on the bases of their contribution for the ground water recharge. Based on the findings of weighted overlay analysis, 11.1, 18.2, 47.1, 15.4 and 8.2% of the region depicted very good, good, moderately good, poor, very poor groundwater potential zones, respectively. The investigated groundwater potential sites have validated by seven existed borehole data and hence the study verified their close relationships. Out of seven boreholes, about 7–4 and 3–1 were found under very good to good and poor to very poor groundwater potential zones, respectively.

Water quality aspects from Spanish sites to support managed aquifer recharge (MAR) guidelines not based on maximum allowable concentration standards

Most countries that have technical guidelines or regulations for artificial recharge or managed aquifer recharge (MAR), that include water quality aspects are based on the establishment of standards or Maximum Allowable Concentrations (MACs) to regulate the quality of the water percolated or injected into an aquifer. The number of parameters in these guidelines vary considerably (from 6 in Spain to 156 in the USA) and often apply to all aquifers within administrative boundaries (e.g., national territory), regardless of the nature of the receiving medium, the depth of the water table, and other key factors. Eleven MAR systems in Spain have been studied (eight operational and three experimental, with limited number of data from three sites), characterising both, the recharge water quality and the water resulting from the interaction processes recharge water-soil-unsaturated zone-saturated zone of the aquifer. In all cases, an improved effect on groundwater quality is observed, even though some parameters in the recharge water don’t comply with the standards employed in some European countries, where this article focuses. The article suggests that regulating water quality for MAR through MACs at national level gives room for another alternative approach specific for each site. It might be recommendable to establish local standards at the regional or aquifer-wide level to better reflect the diversity of groundwater occurrence. As per the article, sectoral water authorities could receive more decision-making power on granting permits for MAR based on the quality of the hydrogeological and risk studies for each request. This would help reduce the application of the precautionary principle when in granting permission.

Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning

The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, “Clean Water and Sanitation”. However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4+), total nitrogen (TN), and phosphate (PO43−) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4+, and PO43−, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4–73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4+ removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO43− removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.

DECOMPOSITION OF RIVER HYDROGRAPHS TAKING INTO ACCOUNT DATA OF HYDROGEOLOGICAL OBSERVATIONS

In the case of absence of reliable information on fluctuations of levels and hydraulic parameters of aquifers within a large catchment, the method of river hydrograph decomposition can be used to assess groundwater component and other constituents of river water recharge. The difficulties and shortcomings of this method, which relies on specific schematizations and assumptions, are analysed and discussed. We propose to take into account the results of calculations of lateral groundwater inflow to the river accomplished using the numerical method based on observations at representative balance sites in order to improve the accuracy of the method of decomposition of the river hydrograph. A proper schematization should also be justified for river catchment (or its part), which describes the interaction of surface water, shallow groundwater, and artesian (deep) interlayer waters, which provides rationale for defining or neglecting groundwater inflow to river during the flood periods. The most disputable issue remains the allocation of the phase of “reverse water inflow to river banks” during flood periods. The groundwater level rise at the beginning of the flood results from the infiltration recharge to the aquifer and from inflow of water from the river. The contribution of inflow to river bank to groundwater level rise is dependent from the distance from the river to the observation well. To establish hydraulic head gradient from the river towards the adjacent groundwater aquifer at flood peak, at least two observation wells are needed, one of which should be located 3–4 m from the river water edge on the elevated part of the bank which is not flooded, and the other should be located 50–70 m from the bank towards the watershed. It is proposed that the phase of maximum groundwater inflow to the river should be adjusted based on the dates of the beginning and ending of the groundwater level decrease during the recession of the river flow during the flood period. The combined application of the described above methods showed that the use of only hydrograph decomposition method underestimates the share of groundwater recharge to the river by 2–5%. Based on the analysis of the Pivdennyi Buh River hydrographs during the 1980–2020 period, general tendencies of changes in the shallow groundwater and deep subsurface recharge of the Pivdennyi Buh River in its upper basin (upstream of the city of Khmilnyk) have been established: deep subsurface recharge prevailed over the shallow groundwater component (33.4 compared to 25.0% of the total). At the same time, the total subsurface runoff constituted on average 58%.

The dynamics of nocturnal sap flow components of a typical revegetation shrub species on the semiarid Loess Plateau, China.

The components of nighttime sap flux (En), which include transpiration (Qn) and stem water recharge (Rn), play important roles in water balance and drought adaptation in plant communities in water-limited regions. However, the quantitative and controlling factors of En components are unclear. This study used the heat balance method to measure sap flow density in Vitex negundo on the Loess Plateau for a normal precipitation year (2021) and a wetter year (2022). The results showed that the mean values were 1.04 and 2.34g h-1 cm-2 for Qn, 0.19 and 0.45g h-1 cm-2 for Rn in 2021 and 2022, respectively, and both variables were greater in the wetter year. The mean contributions of Qn to En were 79.76% and 83.91% in 2021 and 2022, respectively, indicating that the En was mostly used for Qn. Although the vapor pressure deficit (VPD), air temperature (Ta) and soil water content (SWC) were significantly correlated with Qn and Rn on an hourly time scale, they explained a small fraction of the variance in Qn on a daily time scale. The main driving factor was SWC between 40-200cm on a monthly time scale for the Qn and Rn variations. Rn was little affected by meteorological and SWC factors on a daily scale. During the diurnal course, Qn and Rn initially both declined after sundown because of decreasing VPD and Ta, and Qn was significantly greater than Rn, whereas the two variables increased when VPD was nearly zero and Ta decreased, and Rn was greater than Qn. These results provided a new understanding of ecophysiological responses and adaptation of V. negundo plantations to increasing drought severity and duration under climate changes.

Assessing the Economic Value of Water Environmental Services in Mount Merbabu National Park

Mount Merbabu National Park (MMNP) is a conservation area that provides environmental services (water) to surrounding villages spread across its area; however, the community has not realized its essential role. The study aims to calculate the economic benefits of water environmental services in MMNP, which the surrounding community utilizes for household needs. Primary data collection was conducted by interviews using structured questionnaires. Samples were determined using the purposive sampling method on 39 MMNP water sources. Data analysis was carried out by calculating public perceptions of water use and assessing willingness to pay for water use for household needs. The study results showed that the economic value of household water is IDR 10,700,681,768 per year, with the value of the willingness to pay the community for water utilization and conservation IDR 4,360,408,000 per year. The total economic benefit of water in the MMNP area is IDR 15,061,089,768 per year. The views and dynamics of water source management on Mount Merbabu are diverse. The water on Mount Merbabu has been a blessing, a source of conflict, a source of life, and can be a tool of political intimidation. It is necessary to make the public aware of water sources, recharge areas, and better water utilization because water has economic value. Keywords: economic value, environmental services, Mount Merbabu National Park, water, willingness to pay

Contributions of homestead agroforestry during the war in Tigray, Ethiopia

Rapid population growth and unplanned settlement and resettlement has increased agricultural development in Ethiopia's Tigray Region, causing forest and land degradation. Governmental and non-governmental organisations have responded to this by establishing exclosures and communal grazing lands to foster natural regeneration. Their efforts have significantly enhanced environmental recovery, reduced soil erosion and increased water recharge, but challenges remain. Transplanted seedlings have low growth and survival rates, and economic gain is hampered by biased benefit sharing and ownership. Additionally, the war that began in Tigray in 2020 has made it difficult to implement watershed-level communal plantations. Farmers and their families have, therefore, adopted homestead agroforestry, an integrated tree-crop-animal production system. The Relief Society of Tigray (REST) assessed farmers' experiences with homestead agroforestry practices and found that, in addition to providing beneficial ecosystem services, homestead agroforestry had contributed significantly towards income generation, food production and energy supply, which proved especially vital in times of war and extreme poverty. The tree species Ziziphus spina-christi was even named "the tree that saved lives" as its fruit became a staple food for those affected by the war. Homestead agroforestry also reduced pressure on forests by meeting people's increasing need for biomass energy, helping to curb deforestation. Despite its many benefits, there remain challenges to developing homestead agroforestry, but available remedies and recent advancements have led district leaders to commit to making homestead agroforestry their priority agenda. Regional strategic documents, technical and financial support, and capacity strengthening are now needed to propel homestead agroforestry to improve more people’s livelihoods and further mitigate forest degradation and land loss.

Seasonal and isotopic precipitation patterns in the semi-arid and high mountain areas

Precipitation plays a crucial role in the natural hydrological cycle. Understanding the spatial and temporal variations of precipitation isotopes is essential for identifying hydrological, meteorological, and ecological processes. In high mountain areas with arid and semi-arid conditions, especially in regions with endorheic basins, the portion of precipitation that infiltrates the groundwater as the primary source of water recharge. However, estimating this recharge is challenging and prone to high uncertainty.The main objective of this study was to implement a robust and detailed methodology to analyze the influence of meteorological variables and the origin of moisture sources on the stable isotopic composition (δ18O and δ2H) of precipitation. As an illustrative case, we focused on the Los Pozuelos Basin, an endorheic basin in the Altiplano-Puna region of the Andes. The analysis incorporated precipitation samples collected over a 3-year period (January 2020 to April 2023) along with comprehensive monitoring of local atmospheric variables, satellite imagery, and HYSPLIT backward trajectory models.The examination involved a multivariate analysis of meteorological and stable isotope data and atmospheric transport pattern. Precipitation characteristics exhibited seasonal variability, with summer precipitation being depleted in heavy isotopes due to its extended continental journey and the recycling it undergoes while crossing the Amazon basin with convective activity. Another moisture path from the Atlantic Ocean, via the Río de la Plata or Gran Chaco basin, represented an intermediate isotopic stage. La Niña events intensified westerly winds, drawing moist air masses from the Pacific Ocean and causing rainfall in the study area. In winter, precipitation comes from the Pacific Ocean and isotopically enriched due to the low amount of precipitation and lower convective activity.By employing a meticulous methodology and multivariate statistical analysis, the study contributes positively to the broader discourse on water resource management and conservation in arid and semi-arid environments.

Vietnamese farmers’ perception of climate change effects on water resources and determinants of climate change

ABSTRACT This study investigates crop farmers’ perception on climate change effects on water resources and factors that influence their perceptions of it in Vietnam. A sample of 253 was randomly selected from a total population of 685 crop farmers and a structured questionnaire was created to gather data. Descriptive and inferential statistics were used. The research results showed that climate change effects on water resources varied by landform. A majority of farmers perceived that: shifts in rainfall amount and variability affect the operation of runoff water and groundwater recharge; shifts in temperature level and variability considerably influence evapotranspiration; and changes in runoff amount and runoff variability greatly influence soil water storage and groundwater. Mixed cropping systems, use of soil conservation, extension contacts, farming practices, non-agricultural activities, credit programme participation, information and communication technology (ICT) owned, and education level are the important determinants of farmers’ perceptions on climate change.

Multiple isotopes reveal the impact of land use change on nitrate transport and transformation in deep loess deposits

The deep-rooted economic trees decrease water storage but increase nitrate-nitrogen (NO3–N) accumulation in the soil due to the root water uptake and excessive use of fertilizers. Knowing how the NO3 accumulates in the soil and to what extent it can be flushed out or transformed can provide insights on the processes controlling N flux to waterways. We sampled cultivated farmland and orchards with varying ages of apple and peach trees in the loess deposits to > 15 m depth to measure the contents and isotopes of water and NO3 in soils. The novelty of this study is that the water isotopes are used to analyze water and NO3 transport, while the NO3 isotopes are further employed for NO3 source and transformation analysis. The parabolic NO3–N profiles (258–3579 kg N ha−1) were mainly observed within 0–5 m under different land use types. The surface-aggregated NO3 reservoirs under old apple orchard were about six times of farmland due to the overuse of chemical fertilizers, while those of peach orchard were only half of farmland because of less fertilizer inputs and possible root absorption effects. Piston flow resulted in the overall slow water movement and low NO3 flux under different land use types in deep loess deposits. Despite the soil water recharge by precipitation and low surface evaporation, the strong transpiration effects further resulted in no water and NO3 fluxes in the deep layers under old apple orchard. Nitrate reservoirs were mainly contributed by soil organic N (44 % ± 26 %) and ammonium N fertilizer (36 % ± 20 %), but their transformation was dominated by nitrification under old apple orchard and by mineralization in deep layers. The risks of NO3 bombs are temporarily weakened by lower dried soil layers under deep rooted plants; however, with lower water movement rates and limited denitrification potential, NO3 would eventually reach the aquifers in a few hundred years or more. This study provides new insights for clarifying NO3 transport and transformation processes by combing multiple isotopes, and the NO3 bombs would chronically endanger the sustainable development of terrestrial ecosystems and the environment in arid regions.

Shrinkage and desiccation: evaluating the streambed bacterial responses to intermittent water deficit

Hydrological drought, characterized by a significant deficiency in rainfall events, promotes natural desiccation processes. The reduction in water recharge and the loss of freshwater ecosystems pose urgent challenges in the face of increasing global population and the escalating demand for water resources. The variability in the duration of no-flow periods can have profound implications for ecosystem functioning, specifically impacting the microbiota residing in streambed sediments and the vital processes they perform. The streambed serves as an ecotone where microorganisms form biofilms, playing critical roles in in-stream biogeochemical cycles and greenhouse gas emissions. Consequently, prolonged desiccation periods and subsequent rewetting episodes can disrupt, limit, or alter the functions and structure of microbial communities, thereby compromising the overall functioning of aquatic ecosystems. Understanding how streambed microbial communities respond to prolonged desiccation events is crucial. This revision manuscript provides a synthesis of recent empirical and experimental studies that have explored various aspects of streambed microbial communities in the context of diverse drying-rewetting periods. A special focus is placed on highlighting key microbial community structural and functional responses that could be used as endpoints of responses to desiccation. In particular, we showed the greater expression of the phenol-oxidase activity among the intermittent streambeds submitted to long-term drought. This result suggested a potential begin of transition from freshwater to terrestrial systems. Additionally, we observed a tendency of decreasing bacterial diversity in the dry conditions together with a change in the relative abundance of certain microbial taxa and a general shift from Gram-negative to Gram-positive bacteria. All of these evidences strengthened the similarity between the dry streambed systems studied and a (dry)-soil environment, suggesting that prolonged and unusual dry periods could boost the terrestrial transition of the aquatic intermittent ecosystem. By summarizing these findings, we aim to enhance our understanding of the responses exhibited by streambed microbiota in the face of desiccation events. The synthesized results may further provide potential diagnosis and/or management tools for intermittent freshwater ecosystems functioning.

Influence of Spring Water Residence Time on the Irrigation Water Stability in the Hani Rice Terraces

The stability of irrigation water is critical for the sustainability of alpine agriculture. Based on monthly precipitation and terraced field water and spring water samples obtained between 2015 and 2016, the study used the mean residence time and isotope mixing model to analyze the influence of spring water residence time on irrigation water stability in the Hani Rice Terraces. The results indicate that: (1) The mean residence time of precipitation and terraced field water in spring water was 2.46 years and 1.55 years, respectively, implying that the terraced field’s irrigation water source could be refilled by spring water recharged 1.5–2.5 years ago. (2) The mean residence time of precipitation in ascending and descending springs was 2.73 years and 1.95 years, respectively. The mean residence time of terraced field water in ascending and descending springs was 1.54 years and 1.04 years, respectively. The ascending spring’s recharge water residence time is 0.5–0.8 years longer than that of the descending spring, indicating that the spring water exhibits intra-seasonal and inter-seasonal staggered peak recharging. At the same time, the total recharge period of the ascending–descending spring is extended to 1–3 years, which means the terraced fields have a drought resistance of three years. (3) The mean residence time of precipitation and terraced field water at higher altitudes in the ascending spring is 2.52 times and 3.73 times, respectively, while in the descending spring, it is 3.36 times and 6.49 times to the lower altitude region. This means that the mean residence time of the recharge water source in the lower terraced fields was shorter, and the elevation difference between ascending and descending springs was smaller, thereby regulating the spatial homogeneous distribution of recharge water sources in the terraced fields.