Hydrological Processes最新文献

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.

Western U.S. land managers have been investigating the use of in-stream structures such as beaver dam analogues (BDAs) to help restore natural stream processes. There is a presumption that BDAs may modify groundwater hydrology, but there have been few studies that have documented such changes. In this study we combine well transect measurements, streamflow measurements and hydrologic modelling to evaluate changes in riparian water storage and groundwater flow paths brought about by the installation of 45 BDAs across a 1.5-km stretch of Red Canyon Creek in Lander, WY. Based on 3 years of observations, we found that when the majority of BDAs were retaining water, there was an increase in the riparian water table, even in wells 50 m from the stream. Much of the stream reach with BDAs was a losing stream prior to BDA installation. As measured using well transects, the installation of the BDAs led to enhanced hydraulic gradients away from the stream. Additionally, BDA installation induced a measurable but very small increase in the subsurface down valley flow. Watershed-scale modelling validated against weekly-averaged streamflow observations indicated that a disproportionate fraction of streamflow in summer is contributed from higher elevation areas with sufficient storage to detain late spring snowmelt. Increases in the valley bottom water table elevation due to the BDAs added less than 0.5% of the subsurface storage already present in the high elevation portion of the watershed.

The heterogeneity of solute transport is potentially the result of spatial variations in root morphological traits across different diameter classes. However, the mechanism of root systems on solute transport remains unclear. In this study, soil columns collected from Quercus acutissima-, Pinus taeda- and Phyllostachys edulis stands were used to investigate the relationship between solute transport and root systems. The results showed that solute transport parameters like the average pore water velocity (V), dispersion coefficient (D) and distribution coefficient (β) decreased with increasing soil depth, while the dimensionless mass transfer coefficient (ω) showed fluctuating changes. The V, D and β in topsoil (0–20 cm) were 1.39–57.41 times larger than those in subsoil (30–50 cm), while the ω in subsoil was 2.30–2.36 times larger than that in topsoil. The RLD of fine roots (diameter: 0–1 mm) and the total RSAD could significantly promote the V. There was a positive relationship between the D and RSAD of medium roots (diameter: 1–3 mm) and RLD of total roots. The RLD of medium roots and total roots could both have positive effects on β. Yet, the negative effects of the RSAD and RVD of medium roots on ω were observed. Quercus acutissima stands had strong soil and water conservation ability but increased the risk of retaining pollution. Pinus taeda stands could promote rapid infiltration and resist pollution retention. Although Phyllostachys edulis stands had weak soil and water conservation ability, they reduced the risk of pollution downward transport. This study advanced the understanding of the potential regulation on solute transport and provided suggestions for forest management.

Quantifying groundwater discharge into rivers is essential for understanding pollutant pathways and managing water quality. This study estimates groundwater discharge in a 10-km curved section of the lower Ganjiang River, a large meandering river linking Nanchang City to Poyang Lake, using a ²²²Rn mass balance model validated by a water balance approach. River reaches L1, L2, and L7 received groundwater discharge of (2.65 $��\pm �$ 0.22) × 10⁴ m³/d, (1.43 $��\pm �$ 0.17) × 10⁴ m³/d, and (0.82 $��\pm �$ 0.12) × 10⁴ m³/d, with groundwater discharge rates of (29.65 $��\pm �$ 2.50) mm/d, (32.63 $��\pm �$ 3.84) mm/d, and (32.89 $��\pm �$ 5.06) mm/d, respectively. Fluxes of groundwater-derived solutes, including nitrogen species, manganese, and organic carbon, varied by reach and reflected land use impacts. Upstream reaches near urban and industrial areas showed elevated NH₄⁺–N and TOC, while agricultural zones contributed high NO₃⁻–N and Mn. The study reveals that river curvature effects on groundwater discharge are scale-dependent. These findings offer new insights for groundwater discharge estimation and pollution control strategies in large curved river systems.

Cryogenic vacuum extraction (CVE) is widely used to extract water from plant stems for analysis of stable water isotopes, yet it is known to induce significant δ²H offsets. Whether δ¹⁸O is similarly biased has remained uncertain, especially in halophytes that often depend solely on δ¹⁸O as a tracer. Here, we conducted controlled rehydration experiments on Tamarix chinensis stems with two isotopically distinct spiking waters (groundwater and tap water) to evaluate the isotopic offsets (Δδ) in the CVE-extracted stem water relative to the spiking water. The CVE-extracted water showed significant δ¹⁸O offset (Δδ¹⁸O), in addition to δ²H offset (Δδ²H). For the groundwater treatment, the Δδ²H and Δδ¹⁸O averaged −10.88‰ and −0.62‰, respectively, while in the tap water treatment Δδ²H and Δδ¹⁸O averaged −10.61‰ and −0.80‰. Δδ¹⁸O and Δδ²H were positively correlated and both became less negative with increasing stem relative water content, enabling an offset-correction approach. Ignoring the δ¹⁸O offset led to approximately 9% underestimation of shallow soil water contribution and a corresponding overestimation of groundwater uptake in a mixing model. These results underscore the need to correct for CVE-induced δ¹⁸O biases in plant water source studies, especially for halophytes. The linear relationship between isotopic offsets and stem relative water content offers a promising basis for correcting these biases, improving the accuracy of plant water source apportionment and our understanding of plant water use strategies.