Hydrological Processes最新文献

Splash erosion (SER) is a key stage of soil erosion, and bedrock fissures in the karst area makes the erosion situation complex. However, the effects of different bedrock fissure ratios (BFRs) on SER in karst area have not yet been reported. We investigated the effect of five BFRs (0%, 1%, 2%, 3% and 4%) changes on SER under three slope gradients (10°, 15° and 20°) and one rainfall intensity (1.5 mm min⁻¹) in the karst area using simulated rainfall experiments. Single simulated rainfall event lasted for 18 min. The outcomes confirm that as the BFRs increased, the upslope splash erosion (USER), downslope splash erosion (DSER) and total splash erosion (TSER) increased. Surface runoff showed no statistically significant variation across different BFRs and slope gradients, but fissure runoff at 4% BFR was highest for all slopes. BFR was significantly correlated with the fissure runoff, USER, DSER and TSER at 15° and 20° slopes. Our results underscore the greater the BFRs, the greater the SER in karst slope. This work contributes to advancing knowledge about how BFRs impact SER in thin karst soil layers.

Groundwater–surface water exchange plays a fundamental role in the transport of energy and solutes in coastal salt marshes, which are positioned at an intersection between terrestrial and marine hydrologic environments. Hydraulic gradients in shallow marsh sediments continuously change due to tidal water level variations that alternately flood and drain the marsh platform, often superimposed on terrestrial groundwater drainage. We use timeseries data from Vertical Temperature Profiler and Conductivity-Temperature-Depth instruments to investigate the space–time patterns of groundwater–surface water exchange at a hillslope-adjacent fringing salt marsh on the Herring River in Wellfleet, MA. Analyses of data acquired from September to December 2023 demonstrate that time-averaged exchange rates systematically vary from recharge near the tidal channel to saline groundwater discharge towards the upland fringe and systematically decrease during the transition from summer to winter conditions. Exchange rates were continuously modulated by tides, including high-frequency compound and harmonic components generated by non-linear interactions as the astronomical tide propagated into the estuary. The exchange rate sensitivity to tidal forcing decreased with both frequency and distance from the tidal channel, consistent with the lateral diffusion of pore pressure perturbations through the high permeability layer underlying the surficial, low permeability peat. We find that tidal loading of the marsh sediments is a two-stage process consisting of direct, instantaneous loading during inundation and indirect, time delayed loading via lateral diffusion of pore pressure variations in-between inundation intervals. The combination of terrestrial groundwater entering the marsh through the high permeability layer beneath the peat, seawater flooding the marsh platform during inundation, and tidally induced pore pressure variations diffusing into the marsh generates a complex space–time exchange pattern, including bi-directional exchange at tidal periods, with poorly understood but important implications for biogeochemical processes in the marsh sediments and constituent fluxes to the coastal ocean.

Measurement of sediment concentrations in runoff plots has previously lacked refined quantitative operational standards specifically targeting the stirring and sampling procedures within the collection tank, often leading to substantial representativeness issues in unevenly stirred samples. Consequently, sediment concentration measurements have frequently underestimated true values, incurring significant errors. In this study, we investigated how sampling parameters (stirring time, sampling interval and sample volume) affect the accuracy of sediment concentration measurements. For the experiment, we utilised topsoil from a quaternary red soil with sediment concentrations set at 5.07, 50.72 and 101.45 g/L, at a water depth of 60 cm. Relative measurement errors were compared for different stirring times, sampling intervals and sample volumes. Additionally, three sampling methods—manual, mechanical and mechanical plus depth profile—were evaluated for sediment concentrations of 1.05, 5.07, 10.49, 50.72, 101.45 and 439.1 g/L under identical water depth conditions (60 cm). In each method, water samples were collected from the surface, middle and bottom layers of the collection tanks, then thoroughly mixed and weighed in aluminium boxes to measure the sediment concentration. The findings indicate that the impacts of the assessed sampling parameters on measurement errors stabilise at a stirring time of 180 s, a sampling interval of 0 s, and a sample volume of 800 mL. Under these conditions, the average relative errors obtained using the manual, mechanical and mechanical plus depth profile methods were 37%, 24% and 14%, respectively, with the mechanical plus depth profile method thus demonstrating the highest measurement accuracy. Notably, this study was conducted using a single soil type (quaternary red soil), which may limit the generalizability of the findings to soils with different textures (e.g., sandy or clayey soils) or physicochemical properties. On the basis of these findings, we recommend the adoption of the mechanical plus depth profile method, coupled with a precise control of stirring time, sampling interval and sample volume, to enhance the accuracy of sediment concentration measurements in collection tanks. This approach promises to provide significant improvements in the reliability and precision of sediment concentration assessments, while future research could expand to investigate multiple soil types to further validate the conclusions.

Karst regions exhibit heterogeneous water distribution attributable to their unique topographical features. Research concerning water absorption, efficiency dynamics and the underlying mechanisms within commercial plantation forests remains limited, which constrains our understanding of ecohydrological processes. In this study, three typical commercial forests (Juglans regia, Prunus salicina and Prunus persica) were selected as research subjects. We investigated seasonal variations in water uptake patterns and water use efficiency (WUE) of each species by combining stable isotopes (δ²H, δ¹⁸O and δ¹³C) with the MixSIAR model. We hypothesise that these forests adjust their water absorption depth in response to seasonal variations in water availability, consequently influencing WUE. Our results showed that the most important water source for J. regia and P. salicina was 0–30 cm soil water, contributing 55% and 41.6%, respectively. Groundwater provided the next highest contributions, at 25.2% and 30.6%, respectively. In contrast, P. persica mainly used groundwater in spring and autumn (51.2% and 42.3%), 30–60 cm soil water and 0–30 cm soil water in summer (39.5% and 39.1%). Groundwater is an indispensable water source for commercial forests, with a minimum use proportion of 18.8% in summer and a maximum that can reach 51.2% in spring, highlighting the ‘stabiliser’ role groundwater provides during seasonal droughts in karst areas. The WUE of P. persica is significantly higher than that of J. regia during the spring and autumn seasons (p < 0.05). These results suggest groundwater is a crucial water source for commercial forests in humid subtropical zones, and vegetation with a greater dependence on groundwater exhibits a higher WUE. This study elucidates the ecological strategies employed by subtropical karst commercial forests to adapt to variations in soil moisture by flexibly adjusting their water absorption depth. The findings provide a scientific basis for the rational allocation of water resources within commercial forests in this region.

Flooding induced by landfalling tropical cyclones (TCs) poses significant hydrological and socio-economic challenges in Northern Vietnam, a region characterised by complex catchment topography, varying degrees of urbanisation, and frequent exposure to hydro-meteorological hazards. This region spans the Red River Delta (RRD), with its urban centres including Ha Noi, the capital of Vietnam. Using data covering 70 TC events from 1979 to 2023, we investigated interactions between TC characteristics, catchment properties, and observed flood responses, and further developed a systematic methodology for flood susceptibility mapping that incorporates aspects of flood severity covering affected area, duration, and magnitude. The severity metrics are shown to correlate with TC properties (particularly average daily precipitation and the proportion of area with total precipitation > 50 mm) and catchment-specific hydrological characteristics (particularly elevation, runoff coefficient, and antecedent soil saturation). These characteristics are merged via the analytic hierarchy process (AHP) combined with fuzzy comprehensive evaluation, to generate flood susceptibility maps that were benchmarked against provincial- and grid-level historical flood extent data. By identifying the underlying hydrological drivers that determine spatial variability in flood susceptibility, this study informs early warning system design and long-term flood management strategies for TC-affected catchments.