Challenges and Advances in Soil and Groundwater Quality and Resources Assessment

1. Introduction

Groundwater and soil systems represent indispensable yet vulnerable components of the Earth’s critical zone, underpinning drinking water supply, agricultural production, ecosystem stability, and sustainable socio-economic development [1,2,3,4,5,6,7]. However, these vital resources face unprecedented pressures from the synergistic effects of climate change and intensive anthropogenic activities, including agricultural expansion, industrial discharge, rapid urbanization, and unsustainable resource extraction [6,8,9,10,11]. These compound stressors have significantly altered hydrological cycles and biogeochemical processes, leading to widespread contamination, resource depletion, and ecological degradation [7,8,12,13]. Consequently, the accurate assessment and sustainable management of soil-groundwater systems have emerged as a paramount challenge for both scientific research and environmental governance.

The complexity of pollutant behavior within the interconnected soil-groundwater continuum is a central concern [14,15,16]. Contaminants, encompassing both legacy and emerging inorganic (e.g., heavy metals, nutrients, and geogenic arsenic/fluoride) and organic (e.g., pesticides, industrial solvents, pharmaceuticals, perfluorinated compounds (PFCs), and microplastics) compounds, originate from diverse point and non-point sources [17,18,19,20,21,22,23,24]. Their mobilization, speciation, and ultimate fate are governed by a complex interplay of physical transport (advection, dispersion), geochemical reactions (adsorption–desorption, dissolution-precipitation, and redox transformations), and microbiological processes [20,25]. These dynamics are further modulated by site-specific factors such as lithology, hydraulic properties, and the frequency of surface water-groundwater exchange. Climate change intensifies these challenges by altering precipitation patterns and freeze–thaw cycles, which can accelerate contaminant leaching and remobilize stored pollutants. Moreover, elemental biogeochemical cycling has been shown to be critical factors controlling the transformation and fate of materials in these belowground environments [26].

Conventional assessment frameworks exhibit significant limitations in characterizing the spatial heterogeneity of contaminants and quantifying uncertainties in long-term risks under compound stress. This limitation arises primarily from inadequate representation of coupled multi-scale processes and oversimplified descriptions of complex transport-transformation behaviors in heterogeneous media. Therefore, developing an interdisciplinary framework integrating high-resolution in situ monitoring, process-based mechanistic modeling, multi-isotopic tracing (e.g., stable and non-traditional isotopes), and data-driven analytics is imperative [5,6,12,27,28,29,30,31,32,33,34,35]. Synthesizing these complementary approaches enables systematic elucidation of contaminant dynamics in multiphase media, reduces predictive uncertainty, and establishes a scientific foundation for precise environmental risk assessment and sustainable management strategies.

This Special Issue, entitled “Soil and Groundwater Quality and Resources Assessment,” brings together nine research articles that address these challenges through innovative methodologies and case studies across diverse geographical and climatic settings. Collectively, these contributions advance our understanding of contaminant transport mechanisms, groundwater dynamics, hydrogeochemical evolution, and integrated assessment frameworks under varying natural and anthropogenic stressors. This editorial synthesizes key findings from the published studies, highlights methodological innovations, and identifies emerging research directions for the scientific and managerial communities.

2. Modeling Transport Processes and Environmental Geological Effects

Several studies emphasize the power of numerical modeling in disentangling complex subsurface processes. An integrated numerical framework combining the Richards equation and advection–dispersion modeling was developed to simulate glyphosate mobility in agricultural soils (Contribution 1). Through inverse calibration, they revealed that the governing role of soil texture and clay content in contaminant mobility, providing a predictive tool for assessing groundwater vulnerability under long-term agrochemical practices. At the urban and engineering scale, Li et al. (Contribution 2) investigated the mechanical response of buildings to dynamically rising groundwater levels using FLAC3D simulations. Their findings identified phased settlement patterns and tensile stress concentrations at slab-wall junctions, which heighten cracking and seepage risks. The findings underscore the necessity of integrating dynamic groundwater monitoring and differentiated foundation design into structural risk management. Additionally, Zheng et al. (Contribution 3) integrated MIKE URBAN modeling with a genetic algorithm to optimize drainage network layout for annual cost minimization. By linking hydraulic performance with an annual cost system, their approach demonstrates how simulation-based optimization can enhance drainage efficiency while achieving substantial economic savings, providing a practical pathway for climate-resilient agricultural water management.

3. Hydrochemical Processes and Source Identification

Understanding groundwater chemistry evolution under natural and anthropogenic forcing is a recurrent theme across this Special Issue. For example, Ouedraogo et al. (Contribution 4) combined hydrochemistry, stable isotopes (δ18O, δ2H), GIS and multivariate statistics to elucidate surface water–groundwater interactions, the key hydrogeochemical processes and anthropogenic pollution in the Kou basin. Their findings confirm strong hydraulic connectivity between aquifer layers and nitrate contamination from anthropogenic activities, providing a baseline for integrated water resource management in water-scarce regions. In arid endorheic systems, Guo et al. (Contribution 5) integrated inverse hydrochemical modeling with isotopic evidence to quantify mineral dissolution, evaporation concentration, and cation exchange processes along groundwater flow paths in the Qaidam Basin. The work provides a mechanistic understanding of salinity evolution and highlights hydrochemical processes as key drivers of mineral transport and enrichment in arid basins. Zhang et al. (Contribution 6) further advanced the analysis of groundwater dynamics by developing a GIS-based multi-factor weighted comprehensive evaluation system to classify groundwater response types under compound stress. Their results demonstrate how precipitation variability, groundwater extraction, and land use jointly shape spatial heterogeneity in groundwater behavior, offering a framework for differentiated groundwater management strategies.

4. Risk, Eco-Environmental Assessment and Sustainable Management

Several studies address groundwater quality degradation and its implications for human health and ecosystem security. Li Jiani et al. (Contribution 7) proposed an improved DRASTICL model and a kernel density estimation–trapezoidal fuzzy number–Monte Carlo simulation (KDE-TFN-MCSS) model to assess the vulnerability index and health risk in the Songnen Plain, respectively. Furthermore, groundwater quality index (E-GQI) and self-organizing maps (SOM) were employed for water quality assessment and contaminant source apportionment. Applied to a cold-region aquifer system, this method reduces uncertainty in risk estimation and reveals persistent non-carcinogenic and carcinogenic risks associated with NH4+ and As, particularly under freeze–thaw and urbanization influences. Focusing on industrial regions, Du et al. (Contribution 8) applied spatial autocorrelation analysis and SOM coupled with K-means clustering to investigate the spatial distribution and key influencing factors of nine heavy metals (Cr, Fe, Mn, Ni, Cu, Zn, As, Ba, and Pb) in southern China. Their results highlight the intertwined impacts of industrial pollution, domestic sewage, agricultural activities, and natural mineral dissolution, demonstrating the necessity of integrated source-oriented management in industrialized landscapes. At the watershed scale, Hao et al. (Contribution 9) constructed an ecological–environmental geological quality evaluation system for the Kundulun River Basin, emphasizing the dominant role of land use, precipitation, and groundwater depth in shaping ecological risk patterns. Their zonal management recommendations provide actionable guidance for balancing resource exploitation and ecological protection in arid and semi-arid regions.

5. Synthesis and Future Perspectives

Collectively, the studies in this Special Issue underscore several key insights. First, groundwater systems respond nonlinearly to environmental stresses, with physical, chemical, and anthropogenic processes interacting across scales. Second, integrating numerical models with hydrochemical, isotopic, and data-driven approaches is essential for capturing system complexity and reducing uncertainty. Third, management-oriented frameworks, linking scientific understanding with engineering design and policy needs, are increasingly critical under accelerating climate change and human pressure.

Future research should prioritize (1) coupling groundwater models with climate projections and land-use change scenarios, (2) advancing uncertainty-aware risk assessment tools for vulnerable populations and ecosystems, (3) strengthening cross-scale integration from pore-scale processes to basin-scale management, and (4) integrating the hydro-biogeochemical processes. By doing so, groundwater science can more effectively support sustainable water governance and resilience under compound environmental stress.

The contributions assembled in this Special Issue provide both methodological innovations and practical insights, collectively advancing the frontiers of groundwater and soil-water system research. We hope that this collection will stimulate further interdisciplinary collaboration and inform adaptive management strategies in diverse hydrogeological settings worldwide.