Hydrological Processes最新文献

Subsurface sediment transport in tile-drained landscapes occurs through macropores; however, little is known regarding how heterogeneous preferential flows influence fluxes. We performed laboratory rainfall simulations on 10 intact core lysimeters from a tile-drained field in Indiana, USA to study the impacts of surface and subsurface erosion on sediment leachate in heterogeneous preferential flow paths. Seven rainfall simulations were conducted to assess the impact of rainfall intensity on the leachate of surface eroded sediments (three events), and the impact of antecedent conditions on subsurface eroded sediments (four events). Cumulative sediment yield, linear mixed effects modelling, and hysteresis analyses were performed for all events. Results were presented in a series of four case studies. Results showed that surface sediment leachate concentration and yield were tightly linked to the filtration capacity of lysimeters, with more than 2/3rd of sediment originating from a single lysimeter, despite similar flow leachate volumes from each. Rainfall intensity significantly impacted the transport of surface eroded sediment at the highest intensity. Subsurface sediment erosion from undisturbed macropores was low compared to surface soils, but we found contrasting controls on sediment concentrations at low and high antecedent moistures that were equally important to sediment leachate yields. Disturbed macropores produced comparable sediment yields to surface erosion and behaved similarly to soil pipes in terms of erosion mechanics. Hysteresis results generally highlighted contrasting results for surface and subsurface sources but suggest that the prominence of slow flow, low-concentration leachate sources can alter the interpretation of results in field-scale applications. Our findings underscore an array of processes and pathways for sediment transport in the shallow vadose zone, and results will be useful for evaluating new model formulations.

The Youngest Toba Tuff (YTT) supervolcanic eruption occurred 75000 years ago, and resulted in distinctive ash fall deposition in different locations encompassing marine, estuarine, lacustrine, and fluvial sedimentary basins. Of the different sedimentary basins, the YTT crypto-tephra horizon preserved in the South Kerala Sedimentary Basin (SKSB) of the western coast of India is hosted by a paleo-estuarine carbonaceous clay layer. Along the eastern margin of SKSB, confined aquifers hosting highly acidic groundwater is associated with this YTT ash and associated organic matter (OM)-rich carbonaceous clay layer, creating worse acid rock drainage (ARD), which eventually gets neutralised during summer, signalled by the crystallisation of halotrichite. Hydrogeological investigation gave insights on some of the unique geochemical processes, which facilitated the neutralisation of ARD. The main aquifers in the area include laterite and clayey-sand, which is separated by this impervious layer hosting YTT ash. Wells tapping the clayey-sand aquifer, beneath this layer, is affected by the ARD condition due to the interaction with pyrite, manifested as low pH of groundwater (3.7). Simultaneously, leaching from YTT ash, which constitutes 11.91% of Al₂O₃, facilitates Al content to reach groundwater in high concentration (2879.97 ppb). During dry season, when the surface of YTT-hosting OM-rich carbonaceous clay layer is exposed, the leached Al interacts with the acid derived from the YTT-hosting OM-rich carbonaceous clay layer and results in the precipitation of halotrichite. The two processes, one resulting in ARD condition and the other as formation of halotrichite, occur in succession. Thus, the crystallisation of halotrichite signals the neutralisation of water as well as heralding the potability of water.

Grassland on the Qinghai-Tibet Plateau is highly susceptible to climate change and human activities, and vegetation degradation can affect biodiversity and soil erosion. Soil infiltration is a crucial water flow process that determines the amount of runoff and water storage capacity, and it is of great importance in maintaining biodiversity. This research investigated the effects of vegetation degradation and soil rates on soil infiltration rate and processes using the electrolyte tracer method. This technique accurately calculated soil infiltration rate by tracking continuous changes in the solute concentration change process throughout the experimental period and did not require calibration. Findings indicate that vegetation type, root mass, soil water content and soil porosity significantly affect soil infiltration rate. In particular, root mass was found to have a negative effect on soil infiltration rate. Soil moisture content initially dominated soil infiltration, but subsequently, soil porosity became increasingly influential in affecting infiltration in degraded meadow. Soil infiltration capacity varied more with vegetation type than with surface runoff. Shrub meadows had the highest infiltration rate followed by normal alpine meadows and degraded meadows, indicating the importance of vegetation on soil infiltration. The research also shows that mixed shrub and meadow can improve the ecological environment by introducing a more complex root system and increasing the infiltration rate. The electrolyte tracer method was used as an alternative to other methods that can be used in different environments than the one studied in this research.

Climate change, inter-annual precipitation variability, recurrent droughts and flash flooding, coupled with increasing water needs, are shaping the co-evolution of socioeconomic and cultural assemblages, water laws and regulations, and equitable drinking water access and allocation worldwide. Recognising the need for mitigation strategies for drinking water availability in urban areas, the Isotope Hydrology Section of the International Atomic Energy Agency (IAEA) coordinated a state-of-the-art global assessment to evaluate water sources and distribution of drinking water supply in urban centres, an initiative entitled ‘Use of Isotope Techniques for the Evaluation of Water Sources for Domestic Supply in Urban Areas (2018–2023)’. Here, we report on (a) current research trends for studying urban drinking water systems during the last two decades and (b) the development, testing and integration of new methodologies, aiming for a better assessment, mapping and management of water resources used for drinking water supply in urban settings. Selected examples of water isotope applications (Canada, USA, Costa Rica, Ecuador, Morocco, Botswana, Romania, Slovenia, India and Nepal) provide context to the insights and recommendations reported and highlight the versatility of water isotopes to underpin seasonal and temporal variations across various environmental and climate scenarios. The study revealed that urban areas depend on a large spectrum of water recharge across mountain ranges, extensive local groundwater extraction and water transfer from nearby or distant river basins. The latter is reflected in the spatial isotope snapshot variability. High-resolution monitoring (hourly and sub-hourly) isotope sampling revealed large diurnal variations in the wet tropics (Costa Rica) (up to 1.5‰ in δ¹⁸O) and more uniform diurnal variations in urban centres fed by groundwater sources (0.08‰ in δ¹⁸O) (Ljubljana, Slovenia). Similarly, while d-excess was fairly close to the global mean value (+10‰) across all urban centres (10‰–15‰), reservoir-based drinking water systems show lower values (up to ~ −20‰) (Arlington, TX, USA and Gaborone, Botswana), as a result of strong evapoconcentration processes. δ¹⁸O time series and depth-integrated sampling highlighted the influence of the catchment damping ratio in the ultimate intake water composition. By introducing new, traceable spatial and temporal tools that span from the water source to the end-user and are linked to the engineered and socio-economic structure of the water distribution system, governmental, regional or community-based water operators and practitioners could enhance drinking water treatment strategies (including more accurate surface water blending estimations) and improve urban water management and conservation plans in the light of global warming.

Stream–aquifer interactions (SAIs) play a critical role in effective groundwater management, yet their complex dynamics remain poorly understood in channelized lowland perennial streams. This study presents a multi-scale, multi-technique investigation of SAIs along two long-stream reaches in Tennessee, United States. The goal is to define a suitable methodology for characterising SAIs in this specific hydrological setting, serving as a starting point for developing a more standardised and replicable approach. The methodology includes an initial evaluation of various field techniques, followed by extensive surveys using potentiomanometers, electromagnetic induction (EMI), vertical temperature profilers (VTPs) and complementary methods such as seepage meters, bank tests and well-data analyses. Results reveal distinct hydrogeomorphic behaviours across and along the streams, challenging the SAI-homogeneity notions typically assumed in groundwater models. Nonconnah Creek exhibited streambed colmation and negligible hydraulic gradients, resulting in disconnection from the aquifer during low flows, except for a 300-m losing reach with high downward gradients. In contrast, the Loosahatchie River displayed relatively homogeneous streambed properties and small, upward hydraulic gradients, suggesting uniform SAIs along the surveyed reaches. EMI proved highly effective for mapping streambed sediments quickly, while potentiomanometers accurately measured small head differences critical for understanding SAI dynamics. VTPs were less practical due to the extended data-collection times required and their vulnerability to flooding. This study emphasises the importance of multi-scale investigations using diverse techniques to accurately characterise SAIs in lowland streams, highlighting the confounding influences of geological formations, anthropogenic alterations and depositional processes on groundwater–surface water interactions. The findings contribute to refining local water balances, informing groundwater management strategies and underscoring the need for incorporating local-scale field data into regional groundwater models. The proposed methodology serves as a foundation for developing a standardised approach for characterising SAIs in lowland channelized perennial streams, adaptable for similar stream systems worldwide.

The Northeast United States exhibits significant spatial heterogeneity in flood seasonality, with spring snowmelt-driven floods historically dominating northern areas, while other regions show more varied flood seasonality. While it is well documented that since 1996 there has been a marked increase in extreme precipitation across this region, the response of flood seasonality to these changes in extreme precipitation and the spatial distribution of these effects remain uncertain. Here we show that, historically, snowmelt-dominated northern regions were relatively insensitive to changes in extreme precipitation. However, with climate warming, the dominance of snowmelt floods is decreasing and thus the extreme flood regimes in northern regions are increasingly susceptible to changes in extreme precipitation. While extreme precipitation increased everywhere in the Northeastern United States in 1996, it has since returned to near pre-1996 levels in the coastal north while remaining elevated in the inland north. Thus, the inland north region has and continues to experience the greatest changes in extreme flooding seasonality, including a substantial rise in floods outside the historical spring flood season, particularly in smaller watersheds. Further analysis reveals that while early winter floods are increasingly common, the magnitude of cold season floods (Nov-May) have remained unchanged over time. In contrast, warm season floods (June-Oct), historically less significant, are now increasing in both frequency and magnitude in the inland north. Our results highlight that treating the entire Northeast as a uniform hydroclimatic region conceals significant regional variations in extreme discharge trends and, more generally, climate warming will likely increase the sensitivity of historically snowmelt dominated watersheds to extreme precipitation. Understanding this spatial variability in increased extreme precipitation and increased sensitivity to extreme precipitation is crucial for enhancing disaster preparedness and refining water management strategies in affected regions.