Institute of Hydroecology

Research on the dynamics and driving mechanisms of submerged macrophytes communities during the natural restoration period of lakes with different trophic level remains relatively scarce. This study aims to investigate the structural characteristics of submerged macrophytes communities and their coupling relationships with environmental factors in urban lakes of varying trophic states in Wuhan during a natural restoration phase. Six lakes in Wuhan (comprising two mesotrophic, two light-eutrophic, and two medium-eutrophic lakes) were selected as study areas. Simultaneous monitoring of submerged macrophytes and aquatic environmental factors was conducted from August 2023 to April 2024. The results showed that a total of eight submerged macrophytes species were recorded, with Vallisneria natans, Myriophyllum spicatum, and Hydrilla verticillata identified as dominant species. As trophic levels decreased, the species richness, biomass, and diversity indices of submerged macrophytes significantly increased, whereas community structure became more stable. PCoA analysis revealed distinct community differentiation among lakes with different trophic states. The trophic levels of the lakes determined the key environmental factors influencing submerged macrophytes: biomass in mesotrophic lakes was primarily associated with water temperature (WT) and turbidity (Turb); in light-eutrophic lakes, the dominant factors shifted to chemical oxygen demand and nitrate; in medium-eutrophic lakes, Turb and dissolved oxygen exerted strong constraints. Plant co-occurrence network analysis indicated that interspecific interactions within the community appeared to be dominated by competition, which may result in a relatively loose network structure. Random forest models identified nitrogen as the core driver. Structural equation modeling further confirms that nutrients exert a direct negative effect on submerged macrophytes biomass by increasing Turb and chlorophyll a (path coefficient = -0.629), while WT exhibits a positive effect (0.454). This study enhances our understanding of the response patterns of submerged macrophyte communities in urban lakes during natural recovery to trophic levels and environmental factors, highlighting the key roles of nitrogen control and improved physico-hydrological conditions in promoting the recovery of submerged macrophytes. These findings provide theoretical support for adaptive management strategies in the ecological restoration of eutrophic lakes.

<title>Abstract</title> The structurally complex Cangdong fault zone primarily controls the medium-low temperature geothermal potential of the Dongli Lake field in Tianjin, China. However, the accurate numerical characterization of such fault-controlled reservoirs remains challenging, as regional models often oversimplify fault zones as equivalent porous media, obscuring critical permeability anisotropy. To address this gap, this study established a high-resolution conceptual and numerical model of the western reservoir by integrating seismic profiles, drilling data, and dynamic monitoring. The core of our approach was a meticulous natural-state calibration process, which quantitatively constrained the reservoir's properties. The calibrated model achieved an exceptional match with observed data, with mean relative errors of 3.33% for temperature and 9.73% for pressure. Crucially, this process revealed a pronounced permeability anisotropy in the primary Jixian System Wumishan Formation (Jxw) reservoir, with horizontal permeability (3.00×10⁻¹³ m²) an order of magnitude higher than its vertical component (3.00×10⁻¹⁴ m²), directly quantifying the fault zone's dominant control on fluid flow. Subsequent dynamic sensitivity analysis, grounded in this validated model, demonstrates that optimal well placement must target these high-permeability zones proximal to the main fault. Furthermore, we propose adaptive reinjection protocols to manage reservoir pressure and mitigate thermal drawdown. This research provides a robust, calibrated framework and delivers scientifically-grounded strategies to ensure the long-term sustainability of the Dongli Lake geothermal resource, with methodological implications for modeling other fault-controlled sedimentary basin systems.

ABSTRACT The lower Yellow River is a key watershed between the Haihe and Huaihe Rivers. The Kaifeng section, as a key river segment, holds significant geographical and ecological importance, and studying its shallow groundwater hydrochemistry is crucial for sustainable groundwater use. This study systematically analyzes the hydrochemical characteristics of shallow groundwater in the region using methods like Piper diagrams, Gibbs plots, ion ratios, and mathematical analysis to elucidate groundwater formation mechanisms, thereby filling a critical gap in systematic research on the influence of the Yellow River on adjacent groundwater systems. The findings show that shallow groundwater in the Kaifeng section is weakly alkaline, dominated by , Ca 2+ , Na + , and Mg 2+ , with HCO 3 ‐Ca (Mg, Na) type water accounting for 88.7%. The main hydrochemical mechanism is water‐rock interaction, with silicate and carbonate minerals as the primary sources. Moreover, groundwater composition is significantly influenced by lateral seepage from the Yellow River, especially on , Na + , and Ca 2+ concentrations. accounts for &gt; 65.0% of anions, and Na + + Ca 2+ exceed 75.0% of cations. Groundwater recharge mainly comes from precipitation and river inflow. The ratios of , Na + , and Ca 2+ indicate that Yellow River seepage influence diminishes with distance, while rainfall impact increases.

ABSTRACT Accurate identification of groundwater contamination sources is crucial for effective water pollution prevention, yet precise quantitative methods remain limited. This study investigates the sources of groundwater contamination in the Hutuo River area, a region heavily influenced by human activities, using hydrochemical analysis, the positive matrix factorization (PMF) model, and geostatistical methods. The findings reveal that the groundwater is slightly alkaline, with total hardness (TH) and nitrate (NO 3 − ) concentrations exceeding standards at rates of 81.5%–85.2% and 44.4%–59.3%, respectively, indicating significant human impact. Based on hydrochemical methods, it has been identified that SO 4 2− in groundwater primarily originates from the dissolution of gypsum, while Ca 2+ and Mg 2+ mainly come from the dissolution of carbonates. NO 3 − is predominantly sourced from fertilizers and sewage. The PMF model identifies industrial wastewater, domestic sewage, water−rock interactions, and nonpoint source pollution as the primary sources. Domestic and industrial sewage contribute 44.1%, 34.9%, and 28.3% to groundwater pollution during the dry, flood, and normal water seasons, respectively, while industrial sewage contributes 24.1%, 19.2%, and 20.9%. Our research findings provided a scientific basis for preventing the deterioration of groundwater quality and protecting the ecological environment in areas strongly affected by human activities.

<strong class="journal-contentHeaderColor">Abstract.</strong> The growing demand for high-quality water requires sustainable strategies to promote reuse and recycling. Managed Aquifer Recharge systems, particularly Soil-Aquifer Treatment (SAT) systems, have demonstrated effectiveness in improving water quality by reducing contaminants through biodegradation, retention, and sorption. The coexistence of solid, liquid, and gas phases in the unsaturated zone (USZ) enhances adsorption, and retention of pathogens and colloids, while the availability of organic carbon and terminal electron acceptors sustains this zone as critical for biodegradation processes. During recharge, the hydration-drainage front in the USZ follows a depth-dependent pattern. However, soil heterogeneity causes water to infiltrate through preferential pathways, gradually hydrating the surrounding medium. This behavior is further influenced by system management (recharge strategy, applied flow rate, and/or installation of reactive barriers), which also promotes the development of biofilms. These biofilms facilitate water retention and act as localized microreactors for contaminant biodegradation. We investigate the influence of recharge strategies (pulsed versus continuous) and the presence of a reactive barrier on the hydration-drainage front in the USZ and biofilm development in two SAT systems. This was achieved using cross-hole electrical resistivity tomography and assessing biofilm formation through extracellular polymeric substances quantification in solid samples collected from the USZ during the recharge episodes. The study compared two SAT systems: one consisting of fine sand and another with a reactive barrier incorporating of sand, woodchips, compost, biochar, zeolites, and clay. Two recharge episodes were analyzed: one with a continuous flow rate and the other using a pulsed flow rate (while maintaining the same average flow rate across both episodes). Resistivity measurements, associated with the properties of the porous medium and the fluids circulating through it, were collected in the initial dry state and during the recharge, revealing the 3D distribution of the USZ volume during hydration (at the start of recharge) and drainage (when recharge ceased). Over time, these measurements also indicated the potential formation of biofilms in the SAT system. Measurements at the beginning and end of each recharge period capture the 3D evolution of water content. Results showed that water infiltration occurred through preferential pathways or fingers, creating significant heterogeneity in water content in both SAT systems. The reactive barrier enhanced water retention during dry periods, supporting biofilms development. Furthermore, the pulsed recharge strategy promoted biofilm growth more effectively than the continuous recharge strategy. These findings provide insight into optimizing recharge strategies and media composition to manage system dynamics and, consequently, enhance contaminant removal in SAT systems.

The influence of foundation pit excavation on the bearing behavior of concrete tubular piles at the pit bottom remains unclear. Based on the Vesic cavity expansion theory, this paper proposes a method for calculating pile driving resistance, which takes into account the residual effect of vertical pressure changes on earth pressure during excavation. Furthermore, relying on the statistical regularity between Qu/Pu (ratio of ultimate bearing capacity to ultimate cavity expansion pressure) and L/d (length-to-diameter ratio), theoretical formulas for calculating the ultimate bearing capacity of tubular piles before and after foundation pit excavation are established, with their reliability and influencing factors analyzed. This method only requires determining the L/d of the tubular piles and the theoretical value of pile driving resistance. With its simple parameter requirements, it is suitable for estimating the ultimate bearing capacity of tubular piles affected by excavation. By comparing the computed penetration resistance, earth pressure, and driving resistance of tubular piles with field measurements, the computed results show good agreement with field measurements, and the accuracy of the proposed method meets the requirements of engineering design, verifying its feasibility as an empirical method. The fitting results of the Qu/Pu ratios indicate that the deviations between the measured and computed values are 4.17% and 5.64% before and after excavation, respectively. Additionally, L/d and L/H (ratio of pile length to excavation depth) significantly affect the earth pressure, driving resistance, and vertical bearing capacity of monopoles. Smaller L/d and L/H ratios lead to greater earth pressure on the pile and more pronounced effects on driving resistance and vertical bearing capacity. The development of this method offers an approach for estimating the ultimate bearing capacity of tubular piles before and after foundation pit excavation during preliminary design, thereby holding substantial engineering significance.