This study was conducted to evaluate the impact of riparian buffer zones on water quality in the Jinghe watershed, China. To evaluate the effectiveness of riparian buffers in reducing sediments and nutrients in surface runoff, we employed two validated models: the agricultural non-point source pollution model (AnnAGNPS) and the riparian ecosystem management model (REMM). The AnnAGNPS was used to divide the catchment into homogeneous drainage areas and generate upland loadings for the REMM. The REMM model was then utilized to assess the impact of different riparian buffer designs on sediments and nutrient reduction in surface runoff. We tested five designs, including the recommended standard design by the United States Department of Agriculture (USDA). This design with 20 m herbaceous perennials next to the field (Zone 3), followed by a 20 m wide harvestable deciduous forest in the middle (Zone 2), and a 10 m wide non-harvestable deciduous forest adjacent to the river (Zone 1). We also evaluated alternative designs, such as removing Zone 3, removing Zone 2, and reducing the widths of the buffer zones further. For the entire Jinghe watershed, we calculated, compared, and analyzed the annual totals of water inflow, sediment yields, and dissolved nitrogen in surface runoff into and out of Zone 1, 2, and 3 for all the designs. The analysis indicated that the removal efficiency of sediments ranged from 85.7% to 90.8%, and the removal efficiency of dissolved nitrogen in surface runoff ranged from 85.4% to 91.9% for all the designs. It is also indicated that riparian buffer zones are highly effective in reducing sediments and nutrients in agricultural runoff, even with reduced buffer widths. This finding underscores the importance of implementing riparian buffer zones as a valuable approach in the agricultural intensive watershed with constraints for allocating for the creation of standard riparian buffers.

Frequent soil erosion disasters in the middle reaches of the Yellow River (MRYR) have a profound effect on the sediment load of the river. This paper addresses the intertwined effects of human activities and climate change on river runoff and sediment load. Therefore, runoff and sediment loads from hydrological stations along the main and tributary rivers within the MRYR were used. The Mann–Kendall (M–K) trend test and the double mass curve analysis, among other analytical tools, were used to examine the erosion patterns of these rivers from 1950 to 2022, as well as the main factors driving these changes. The results showed that the runoff depth of the Yan River tended to decrease, and there was a significant decrease in the mainstream and nine other tributaries, with a significant decrease in the sediment transport modulus for both the mainstream and tributaries. In the main river, human activities contributed between 69.99% and 94.69% to the runoff and between 88.52% and 98.49% to the sediment load, while in the tributaries, the contribution of human activities was greater. The annual runoff and annual sediment load in the MRYR showed a decreasing trend, with a discernible impact of human activities. The results of this research are of great significance for erosion control and the restoration of the ecological balance in the Yellow River Basin.

To investigate changes in runoff and sediment load in the Wuding River basin under the combined influence of climate change and human activities, trends were analyzed from 1960 to 2020, and the contribution rate of climate change and human activities was calculated. It was observed that the runoff and sediment load Mann–Kendall test value ranges at eight gauging stations were −7.42 to −3.88 and −9.28 to −3.34, respectively, indicating a significant decreasing trend in both. During the period of 1970–2000, the contribution of human activities to the reduction in runoff and sediment load was 69.9% and 75.3%, respectively. However, the impact of human activities intensified after 2001 due to the implementation of the policy of returning farmland to forests in the Wuding River basin, which contributed to 118.4% and 114.5% of the reduction in runoff and sediment load, respectively. Check dam and reservoir construction, reforestation, water diversion, and other human activities were all important factors in runoff and sediment load reduction. In particular, the total sediment retention by reservoirs in the Wuding River basin was approximately 879 million tons until 2010, and the total sediment retention by check dams was approximately 2747 million t until 2017. This study can provide support for the utilization of water resources and the construction of ecological civilization in the Wuding River basin, and can also provide a reference for the study of water and sediment changes in other basins.

The Inner Mongolia section of the Yellow River is a primary alluvial segment of the main channel. The variations in water and sediment not only alter the cross-sectional morphology and flow capacity of the river but also impact the scheduling of upstream cascade reservoirs. Based on runoff and sediment load data and topographic information from typical hydrological stations, the characteristics of runoff and sediment load variations and the evolutionary pattern of siltation in the Inner Mongolia River section were analyzed via trend analysis methods, Mann–Kendall test methods, the sediment load transport rate method, and the water level–flow relationship. The results showed that the water and sediment loads at the hydrological stations in the Inner Mongolia River section significantly changed from the 1960s to after 2000, with runoff decreasing by approximately 22% to 32% and the sediment load decreasing by approximately 65% to 73%. Sedimentation in the river section generally increased, and the average annual siltation amount reached 0.144 billion t. The joint utilization of the Longyangxia and Liujiaxia reservoirs in 1987 was the main reason for the rapid increase in siltation, and siltation in the Inner Mongolia River section was slightly reduced after 2005. In addition, the critical sediment load coefficients of the Bayangaole–Sanhuhekou and Sanhuhekou–Toudaoguai River sections were 0.0073 and 0.0051 kg·s/m⁶, respectively, from 1952 to 1968, and 0.0053 and 0.0037 kg·s/m⁶, respectively, from 1969 to 2020. This study could provide technical support for river flood control and reservoir water sediment regulation in Inner Mongolia.

Sediment transport capacity in rills is an important parameter for erosion modeling on hillslopes. It is difficult to measure, especially at gentle slopes with limited rill length. In this study, a special flume with variable slope gradients in upper and lower sections was implemented to measure the sediment transport capacity. The upper flume section with a higher slope gradient generates faster water flow that could scout more sediment to feed the water flow in the rill. The rest of the flume is set at the designated slopes to measure the transport capacity in different slope and runoff conditions. A series of flume experiments were conducted with silt-loam soil to verify the method. The sediment transport capacity was measured under slope gradients of 5°, 10°, 15°, 20°, and 25° and a flow rate of 2, 4, 8, and 16 L min⁻¹. The measured sediment transport capacity values were compared with reference measurements from other rill erosion experiments with similar materials and setups. At high slope gradients of 15°, 20°, and 25°, the newly suggested method produced almost the same transport capacity values. Under the low slope gradients of 5° and 10°, the maximum sediment concentrations from the 8 m long flume with the uniform gradients in the previous experiments, rill erosion with an 8 m long flume produced were about 36% lower than the values measured with the new method, which is insufficient to make the flow reach sediment transport capacity. The sediment transport capacities at lower slopes measured with the new method followed the same trend as those at higher slopes. The new method can supply enough sediments to ensure the flow approach transport capacity measurement and, therefore, provides a feasible approach for estimating sediment transport capacity for conditions with relatively gentle slopes.

Sediment transport capacity is not only an important parameter for rill erosion modeling but also a critical parameter for estimating other rill erosion model parameters. Sediment capacity is difficult to be measured, especially at gentle slopes with limited rill length. In this study, a special flume with variable slope gradients in different sections was implemented to feed and to transport sediments. Silt loam soil materials, collected from Beijing, were used in the laboratory experiments to measure sediment transport capacity to verify the method,. The experiments were designed under slope gradients of 5, 10, 15, 20 and 25° and flow rate of 2, 4, 8 and 16 L/min. Measured sediment transport capacity values were compared with reference measurements from other rill erosion experiments with similar soil materials. At high slope gradients of 15, 20 and 25°, the newly-suggested method produced almost the same transport capacity values as measured through rill erosion process data. Under the low slope gradients of 5 and 10°, limited length of eroding rill used in the previous experiments was not capable of producing sufficient sediments to make the flow reach sediment transport capacity. Data analysis indicates that rill erosion with a 8 m long flume produced maximum sediment concentrations about 36% lower than the values measured with the new method under low slope gradients of 5 and 10°. The sediment transport capacities at lower slopes measured with the new method followed the same trend as those at higher slopes. The experimental results indicated that the new method is capable of supplying sufficient sediments to ensure the flow approach transport capacity measurement. The method proposed in this study can provide a feasible approach for estimating sediment transport capacity as an  important model parameter for soil erosion prediction.