Riparian vegetation plays a vital role in inhibiting soil and water loss, but few studies have quantified the relationships between vegetation spatial pattern and the hydraulic characteristics of upslope runoff. This study investigated how hydraulic characteristics (e.g., runoff coefficient, flow regime, flow resistance, and flow shear stress of overland flow) responded to differences in vegetation cover (15% and 30%), slope gradient (5°, 10°, 15°, and 20°), and vegetation pattern in the riparian zone along the lower Yellow River, China, based on landscape pattern analysis and a runoff scouring experiment with flow rates of 9 and 15 L/min and an experimental plot size of 1 m × 3 m. We found that runoff generation on shallow slopes was moderated by increasing vegetation cover, but that this moderating effect decreased on steeper slopes. The regime of overland flow switched from laminar and subcritical on the 5° slope (Fr = 0.56–0.87) to laminar and critical on the 10°, 15°, and 20° slopes (Fr = 1.02–2.18). Flow resistance increased with vegetation cover and flow rate and decreased with slope gradients, and it was larger on shallow slopes with high vegetation cover. Flow shear stress had a range of 1.42–3.55 N m⁻², and it increased with increasing slope gradient, vegetation cover, and flow rate. The hydraulic characteristics of upslope runoff, especially flow resistance, were significantly related to vegetation pattern at both the landscape and class levels. Flow resistance was negatively related to patch density, and positively related to perimeter–area fractal dimension and connectance index. The influencing mechanism of landscape patterns on soil erosion processes is dependent on the landscape scale, since the relationships between flow resistance and some landscape pattern indices (aggregation index, effective mesh size, and splitting index) were opposite at the landscape level compared to the class level. We conclude that fragmented vegetation distributions reduce flow resistance, and that riparian vegetation could be managed to inhibit slope erosion by increasing flow resistance.

Climate variation and land use changes have been widely recognized as two major factors that impact hydrological processes. However, it is difficult to distinguish their contributions to changes in streamflow. Quantifying their contributions to alteration of streamflow is especially important for the sustainable management of water resources. In this study, the changes in streamflow for the period of 1960–2008 at two stations (Dongwan and Luhun) were analyzed in the Yihe watershed in China based on hydrological data series and climate parameters. Using a non-parametric Mann–Kendall (MK) and Pettitt’s test, as well as Budyko analysis, we first examined the trends of hydroclimatic variables and the breakpoint of annual streamflow over the past 50 years. Subsequently, we evaluated the contributions of annual precipitation (P), potential evapotranspiration (PET), and land use condition (represented by w), respectively, to streamflow variation. We observed a decreasing trend for P, as well as increasing trends for PET and w. Annual streamflow showed a significant downward trend with an abrupt change occurring in 1985 during the period of 1960–2008. Accordingly, we divided the studied period into two sub-periods: period I (1960–1985) and period II (1986–2008). The sensitivity of the streamflow to the different environmental factors concerned in this study differed. Streamflow was more sensitive to P than to PET and w. The decrease in P was the greatest contributor to the decline in streamflow, which accounted for 50.01% for Dongwan and 55.36% for Luhun, followed by PET, which accounted for 24.25% for Dongwan and 24.45% for Luhun, and land use change was responsible for 25.25% for Dongwan and 20.19% for Luhun. Although land use change plays a smaller role in streamflow reduction, land use optimization and adjustment still have great significance for future water resource management, since climate variation is difficult to control; however, the pattern optimization of land use can be achieved subjectively.

Soil erosion inflicts multiple and severe damage throughout the world. The importance of vegetation spatial patterns in conserving soil and water has been widely acknowledged. In this study, by using the leakiness index (LI), which indicates the soil and water conservation function of the landscape by integrating landscape patterns closely with hydrological processes, we analyzed the changes in this function of riparian vegetation under different patterns with the aim of identifying the optimal pattern for improving soil and water conservation in severely eroded riparian buffer zones. Prior to this, the relationship between the erosion modulus and LI was discussed to provide certain evidence for the potential application of LI to the study area given the limited empirical works. Results showed that LI illustrated a significantly linear correlation with the erosion modulus (R² = 0.636, p < 0.01), thereby suggesting a promising application of LI in the Beijiang riparian vegetation buffer zone. A comparison of the LI values regarding four different vegetation patterns indicated that under the premise of the same coverage (40%), the aggregation degree and patch orientation with low LI values exerted improved performance for soil and water conservation, so we selected the horizontal distribution and compact aggregation as the optimal pattern for vegetation regulation. The spatial variations of LI values in the study area showed that five regions were suffering from severe erosion, thus becoming the targeted area for regulation. The final regulation with the optimal vegetation pattern in severely eroded areas performed well given that the soil and water conservation was improved to a high level with a LI value less than or equal to 0.2. The results described in this study provide an alternative screening method to figure out the severe erosion areas needing improvement, a further understanding of the effect of vegetation pattern on soil and water conservation and a theoretical basis for the extended application of LI.

Riparian woodlands play a significant role in hosting plant diversity and maintaining soil and water resources. However, riparian woodlands are highly sensitive to fluvial and human disturbances, and most are now degraded as a result. In this study, we analyze variation in soil nutrients and plant diversity and their relationships in riparian woodlands along the middle and lower reaches of the Yellow River in China, based on field investigation. Our results indicate that soil nutrient content and plant diversity were lowest in plots located closest to the river. Specifically, we found a hump-shaped relationship with increasing distance from river. This result can be attributed to the intermediate disturbance hypothesis,which explains that species diversity increase at intermediate disturbance levels. However, total species richness within each subzone was greatest close to the river, due primarily to the high level of species turnover observed among plots located closest to the river. Soil nutrients in the riparian woodlands were positively correlated with plant diversity across all distances. Specifically, soil TC, NO3 --N, and A-P contents were significantly correlated with plant species richness and diversity. This relationship also conformed to a hump-shaped response curve between species richness and soil nutrients, though species richness increases with increasing nutrient levels. Results from this study can provide a basis for sustainable management of riparian ecosystems.