David Andrew Barry

Within subterranean estuaries (STEs), Fe ²⁺ from freshwater is oxidized by O ₂ (aq) from seawater to form Fe precipitates and low‐permeability zones (“Fe curtains”). Tidal fluctuations generate an upper saline plume (USP) above the saltwater wedge (SW), enhancing freshwater–seawater mixing and associated chemical reactions. However, existing studies did not resolve how tidal forcing influences Fe curtain formation or how the resulting precipitates alter groundwater flow. Here, TOUGHREACT was employed to numerically investigate abiotic Fe precipitation and its consequent impacts on groundwater flow in STEs under tidal forcing. The simulation results indicate that Fe oxidation and precipitation predominantly occur within the USP and SW mixing zones. Fe accumulation within the USP is approximately twice that within the SW, especially near the high and low tidal marks, due to the faster tide‐driven seawater circulation. The resulting Fe precipitates reduce sediment porosity and permeability, locally decrease porewater velocity, and alter porewater flow patterns and the freshwater–seawater interface. The horizontal and vertical porewater velocities are reduced by about 20%–40% and 40%–80%, and ∼20% and ∼40% within the USP and SW Fe‐precipitated zone, respectively. Variations in freshwater flux and tidal amplitude regulate Fe precipitation primarily by modifying the configuration of the freshwater–seawater interface, whereas the Fe ²⁺ and O ₂ (aq) concentrations impact Fe precipitation mainly by the supply of reactants. These insights improve understanding of abiotic Fe precipitation and its hydrological implications under tidal forcing in STEs.

This study compares implicit stochastic optimization (ISO) and explicit stochastic optimization (ESO) for deriving operational rules for conjunctive use of surface water and groundwater, and proposes an improved ISO formulation that accounts for capturing interdependence among sequential decisions. In the present formulation, previously determined decision variables are introduced as additional inputs to the rule model. The analysis is carried out using the example of the conjunctive use system of the Qazvin Plain, Iran. ESO-based operational rules are derived using stochastic dynamic programming (SDP), whereas ISO-based rules are extracted from the analysis of optimization results using the M5 decision tree algorithm. The derived rules are evaluated in a simulation model driven by the historical inflow record and 14 synthetic inflow series. Incorporating previously determined decisions substantially improves the accuracy of ISO-based rules, increasing the correlation coefficient by up to 40.5% relative to the conventional ISO formulation. Nevertheless, ESO-based rules provide better overall system performance across all inflow scenarios, producing lower agricultural water deficits and better groundwater control. Under ESO-based operation, groundwater storage remains close to the prescribed bounds (0–80 ± 10 MCM), whereas ISO-based rules produce substantial deviations. These results show that the proposed ISO modification improves rule accuracy, but ESO remains the more reliable framework for conjunctive operation when groundwater sustainability is a primary objective.

Turbidity currents are one of the largest sediment-moving processes across our planet, connecting terrestrial sources to deep sea sinks. They play an important part in the transport and burial of organic material, transport contaminants such as microplastics and can reach velocities of multiple meters per second, at which point they form a hazard to submarine infrastructure. In lacustrine environments, they influence water quality by delivering nutrients and oxygen along the water column. Understanding what triggers the formation of turbidity currents is therefore key. Recently, some works have shed a light on the role of transient storage of sediment in the triggering of turbidity currents in oceans. In this model, the near-shore sea bed is preconditioned by the delivery of fresh sediment, either by river inflow or alongshore transport, until it is remobilized by wave action, slope failure or otherwise, and a turbidity current forms. However, the role of transient sediment storage in lakes has received little attention. In this contribution, its potential to precondition the bed for turbidity current generation in the Rhône River-fed lacustrine channel in Lake Geneva will be investigated.A combination of repeat event-wise gridded boat-towed Acoustic Doppler Current Profiler (ADCP) measurements, years-long infrared timelapse camera imagery and months-long moored ADCP measurements were used to study the occurrence of turbidity currents and coinciding changes in the bed depth near the Rhône River mouth at Lake Geneva.The boat-towed ADCP measurements revealed an aggradation over three months and a subsequent degradation over two weeks of up to 11 m near the river mouth. The structure of the bed changes pointed out that they were caused by a progradation and transgression of the delta lip. Timelapse images of the Rhône River plume showed an abrupt plume retreat symptomatic of a sudden slope failure, rather than a gradual erosion of the bed. In fjord systems, such failures have been proven to cause strong turbidity current events. Indeed, in this work timelapse images of a similar abrupt plume retreat were linked to a strong turbidity current event in the Lake Geneva lacustrine channel, establishing a link between transient storage of sediment followed by slope failures, and strong turbidity current generation in lakes.

Cold-water Density Currents (CDCs) resulting from winter differential cooling and flowing down lateral slopes of a lake (winter cascading) can entrain sediment and contribute to cross-shore transport to its deeper layers. Field investigations along Lake Geneva’s northern shore reveal how CDCs induce sediment resuspension. Acoustic backscattering demonstrated that sediment resuspension is absent at 10-m depth on the steep slope (~30°) just beyond the edge of the shallow coastal shelf where CDCs were initiated but occurred intermittently at 30-m depth where the flow reached higher velocities (slope reduced to ~4.5°). This suggests that CDCs resuspend sediment on the sloping bed (but not on the shelf edge) and potentially transport it to deeper layers, causing sediment focusing (i.e., thicker sedimentation in deeper zones). During CDCs, resuspension occurs in short bursts, often at the head of CDC impulses, creating plumes that can extend to ~1.5 m above the lakebed. Velocity profiles near the bed were well fitted by a logarithmic profile, from which the Shields parameter was determined and compared to the critical Shields stress. However, the strong time-variability of the downslope velocity prevents computation of a representative Shields parameter needed to determine sediment resuspension. The CDC velocity at 1 m above the bed (above ~9 cm s ⁻¹ ) correlated well with high backscattering echo level (indicating sediment resuspension) and was a better predictor for resuspension than the Shields parameter. Since CDCs were found to occur ~25% of the days in winter, CDC-induced resuspension potentially affects lake ecosystem dynamics.

Large-scale lake clusters serve as important freshwater resources in arid and semi-arid regions, but the groundwater recharge patterns sustaining these clusters remain poorly researched. The Songnen Basin, a semi-arid region in northeastern China, contains numerous shallow lakes most of which are not connected to rivers, showing complex interconnections with the groundwater recharge and storage. Here, this paper investigates the role of groundwater in sustaining the freshwater in the lake clusters of the Songnen Basin using remote sensing and isotope analysis, especially during the winter of Chagan Lake, the largest lake in this basin. Our results suggest that deep groundwater upwelling through fault zones is a significant recharge source for Chagan Lake, contributing to the frequent occurrence of stable ice-free areas. Isotopic tracers indicate that this deep groundwater does not originate from local precipitation but likely originates from external sources, potentially the Tibetan Plateau. A deep-circulation groundwater pattern is proposed, suggesting that water-conduiting channels exist under the deep lithosphere in arid and semi-arid regions. When these channels are destroyed by earthquakes, deep-circulating groundwater would rises through faults and recharges lake clusters.

Although vertical mode‐one (V1) Kelvin waves are known to play an important role in nearshore dynamics of large lakes, observations of vertical mode‐two (V2) Kelvin waves are scarce, and their characteristics and significance are largely unknown. Combining field observations, 3D hydrodynamic modeling, and particle tracking, we demonstrate that previously undetected V2 Kelvin waves are common in Lake Geneva (Switzerland/France) during summer. V2 Kelvin waves with a 5‐d period persisted for over one month in 2021 and 2022. Modeling revealed a complex, spatially heterogeneous vertical structure. Since the lower nodal line depth varied from ∼150 to 200 m near the shores to ∼75 m in the lake center, V2 Kelvin waves were restricted to the deep eastern basin (maximum depth 309 m), and nearshore current profiles observed at ∼110‐m depth did not show the typical V2 modal structure. The waves produced large vertical isotherm displacements (∼25 m) and strong currents (∼28 cm s ⁻¹ ) in the nearshore thermocline and induced alongshore transport over nearly half the basin length. Currents were strongest ∼1 km from shore and decreased exponentially toward the lake center. Our findings explain why previous studies in Lake Geneva's nearshore regions (out to ∼75‐m depth) only detected V1 Kelvin waves and no V2 Kelvin waves. Modeling revealed that V2 Kelvin waves are consistently excited under typical summer stratification and wind forcing conditions. Our results suggest that these waves occur in other large deep lakes having a Burger number , with important implications for the transport and dispersion of sediments, nutrients, and pollutants.

Poverty alleviation is a critical concern in developing countries. China launched the Targeted Poverty Alleviation (TPA) program and implemented a series of anti‐poverty initiatives, aiming to reduce poverty and enhance the well‐being of rural households. The TPA program has been recognized as significantly promoting rural development, but whether it can benefit all poor households equally has been underexplored. This study systematically examines the impact of the TPA program on poor households with different causes of poverty and empirically analyzes income differences across household and village types under different income groups using a linear quantile mixed model (LQMM), based on survey data from a high‐altitude deep‐poverty county in southwest China. The results indicate an income imbalance among poor households with different causes of poverty, whereas households in poor and non‐poor villages exhibit equivalent development. Differences are more pronounced at higher income quantiles, suggesting that the policy provides relatively uniform benefits to poorer households. Analysis of income sources reveals disparities between wage and transfer incomes, while benefits from business income remain consistent. These findings underscore the need for sustained policy support to enhance the stability and sustainability of poverty alleviation and income transformation among low‐income households. This study contributes to a deeper understanding of the TPA program, and the recommendations derived from the results can serve as references for poverty alleviation in rural areas of developing countries.

Shear layers and corresponding Kelvin Helmholtz‐type Coherent Structures (KHCS) can be generated by rivers discharging into laterally‐unconfined quiescent open water bodies (e.g., lakes). When the river discharge has a greater density than the receiving water due to temperature and/or suspended sediment, both the shear layers and KHCS will be influenced by the negative buoyancy of the plume and thus become highly three‐dimensional (3D). The present study uses a turbulence‐resolving Computational Fluid Dynamics model based on Large Eddy Simulation to simulate the nearshore flow fields of a hyperpycnal river plume entering an unconfined quiescent ambient. Shear layers are observed at both sides of the plume and their growth is suppressed by negative buoyancy arising from the greater density of the river plume. The plume‐ambient interface is tilted by the negative buoyancy and is transformed into a curved face. As a result, the shear layer is also tilted and shear‐induced vorticity progressively changes its direction from vertical near the water surface to transversal near the bottom. Tilted along with the shear layers, KHCS present unique 3D subsurface structures and create strongly mixed and curved “coherent structure regions” in transects. Quadrant analysis shows that the “Ejection” and “Sweep” events associated with KHCS dominate the local mass and momentum exchange between the plume and ambient water. At the plume‐ambient interface, the KHCS generate near‐periodic velocity fluctuations whose non‐dimensionalized frequency (Strouhal number) decreases with increasing local Richardson number.

Macrobenthic invertebrates are widely distributed on sediments, and the micro‐morphology such as burrows and sand mounds due to their bioturbation activities can cause substantial changes in hyporheic exchange (HE). This study explores the characteristics of HE induced by benthic burrows through flume experiments and numerical simulations, focusing on the influence of burrow depth, mound height, and inter‐burrow distance. Our findings reveal that burrows enhance HE by forming preferential flow conduits. With the increased interfacial pressure drop and the newly formed circulations, the pore water tends to outflow through burrow sidewalls along the preferential paths in greater velocity under the enhanced advection, and the “pumping” effects persist even below the burrow depth. The pore water flux increased by 10.76 times on the burrow sidewall at most. Eddies are induced by mounds above the streambed, changing the inflow/outflow patterns on the interface. The interfacial exchange rate below eddies is decreased while the solute can inflow within more distant ranges away from burrows. The effects of mound height carry out in the shallow streambed, and quickly decrease as penetration depth increases. Variations in inter‐burrow distance affect the transition process of HE from advection‐ to dispersion‐dominated. As the distance increases, the solute transport is promoted first due to the enhanced advection, and then decreased with the weakened advection and the larger proportion of the dispersion. This study provides important insights into the key mechanism of HE, highlighting the critical role of benthic burrows in aquatic ecosystems.