ISMC2021-6

As important soil and water conservation engineering measures, there are more than 100,000 check dams constructed on the Loess Plateau; these dams play a vital role in reducing floods and sediment in watersheds. However, the effects of check dams on hydrologic process are still unclear, particularly when they are deployed as a system for watershed soil and water management. This study examined the watershed hydrologic process modulated by the check dam system in a typical Loess Plateau catchment. By simulating scenarios with various numbers of check dams using a distributed physical-based hydrological model, the effects of the number of check dams on runoff generation and concentration were analyzed for the study catchment. The results showed that the presence of check dams reduced the peak discharge and the flood volume and extended the flood duration; the reduction effect on peak discharge was most significant among the three factors. The system of check dams substantially decreased the runoff coefficient, and the runoff coefficient reduction rate was greater for rainstorms with shorter return periods than for rainstorms with longer return periods. The check dams increased the capacity of the catchment regulating and storing floods and extended the average runoff concentration time in the catchment that flattened the instantaneous unit hydrograph. This study reveals the influencing mechanism of check dams on the hydrological process of a watershed under heavy rainstorm conditions and provides a theoretical basis for evaluating the effects of numerous check dams on regional hydrology and water resources on the Loess Plateau.

How to cite: Yuan, S., Li, C., Li, Z., and Zhang, Z.: Effects of a check dam system on the runoff generation and concentration processes of a catchment on the Loess Plateau, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-64, https://doi.org/10.5194/ismc2021-64, 2021.

The impact of climate change on soil erosion is pronounced in high mountain area. In this study, the revised universal soil loss equation (RUSLE) model was improved for better calculation of soil erosion during snowmelt period by integrating a distributed hydrological model in upper Heihe river basin (UHRB). The results showed that the annual average soil erosion rate from 1982 to 2015 in the study area was 8.1 t ha^-1 yr^-1, belonging to the light grade. To evaluate the influence of climate change on soil erosion, detrended analysis of precipitation, temperature and NDVI was conducted. It was found that in detrended analysis of precipitation and temperature, the soil erosion of UHRB would decrease 26.5% and 3.0%, respectively. While in detrended analysis of NDVI, soil erosion would increase 9.9%. Compared with precipitation, the effect of temperature on total soil erosion was not significant, but the detrended analysis of temperature showed that the effect of temperature on soil erosion during snowmelt period can reach 70%. These finding were helpful for better understanding of the impact of climate change on soil erosion and provide a scientific basis for soil management in high mountain area under climate change in the future.

How to cite: Wang, L., Zhang, F., and Wang, G.: Influence of climate change on soil erosion in high mountain area: a case study of upper Heihe river basin, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-71, https://doi.org/10.5194/ismc2021-71, 2021.

Unpaved roads are common man-made features that distributed in agricultural or forest watersheds. Road construction will change the underlying topography and alter the surface hydrology, in turn would enhance runoff generation and result in high soil loss risk. Therefore road erosion should be considered as one of the main sediment sources and should be properly evaluated. Process-based erosion models provide efficient tools to precisely evaluate soil loss along unpaved roads. This study was performed using the hillslope version of the Water Erosion Prediction Project (WEPP) to estimate soil loss from 20 typical road segments in the red soil region of South China. The terrestrial laser scanning (TLS)-measured soil losses were used to validate the model simulations. The results showed that the WEPP model could reasonably predict the total soil loss in relatively short (less than 100m) and gentle (slope gradient lower than 10%) road segments. On the contrary, the WEPP simulated soil loss would result in underestimation for long or steep road segments. Detailed WEPP plot outputs along roads revealed that most of the peak soil loss rates cannot be adequately calculated as comparing with the TLS-measured values. The linear critical shear stress theory in WEPP model for soil detachment simulation might responsible for the underestimation of non-linear peaked soil losses in long or steep road segments. Meanwhile, the lack of upslope flow and the curved road tortuosity were also found to be connected to the relatively low efficiency of the model outputs. Nevertheless, the WEPP simulation could accurately fit the detailed trend of soil loss variation along road segment despite the underestimation. Furthermore, the simulated results could provide a reliable prediction of the maximum soil loss positions. Therefore, the WEPP model could be adopted to evaluate erosion risk of unpaved roads in red soil region of China.

How to cite: Cao, L., Li, X., and Shi, M.: Modelling soil erosion on unpaved road surface with process-based model and terrestrial laser scanning, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-85, https://doi.org/10.5194/ismc2021-85, 2021.

  Topography, one of the main factors in hillslope rainfall-runoff processes, is related to many environment problems initiated by rainfall, such as flash flood, soil erosion, and landslides, and crucial in hillslope hydrological models and large-scale hydrological-hydrodynamic models. This research investigated the effects of topography abstracted by the combination of longitudinal profile curvature and plan shape on the Hortonian rainfall-runoff processes. The results show that different profile curvature and plan shape leads to more than 10% difference in cumulative runoff and runoff rate and more than 20% difference in ponding time. Similar infiltration and runoff processes can occur on different hillslopes because of the similar slope gradient distributions, and partial area runoff can also occur in these hillslopes. The run-on effect causes more infiltration on convex hillslope topography. The soil property and rainfall temporal variability do not change the trends but can alter the magnitudes of the hillslope geometry effect. The study provides insights into the rainfall runoff processes on natural hillslopes that could benefit studies related to hillslope hydrology and geomorphology.

How to cite: Wang, J. and Chen, L.: The Effect of Hillslope Geometry on Hortonian Rainfall-Infiltration-Runoff Processes, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-39, https://doi.org/10.5194/ismc2021-39, 2021.

Rocky desertification is a serious environmental issue in karst regions that restricts food production and hinders local economic development. Generally, soil loss is known as a dominant factor driving rocky desertification. However, it is difficult to couple rocky desertification with the soil loss rate based on a database from short-term field plot observations. Hence, it is imperative to reconstruct the history of soil loss over long-term periods and to correlate the rocky desertification process with the soil loss rate. In karst regions, the most common geomorphic landforms are closed peak-cluster depressions. Researchers have shown that estimating soil loss from hillslopes based on a sediment deposition rate in a peak-cluster depression is possible. In this study, two typical peak-cluster depressions with different degrees of rocky desertification were selected, and sediment cores with lengths of 2 m were sampled from the depressions to determine pollen taxa, soil properties and sediments dating at different depths.The results showed that the burial ages of the sediments in the depressions were different in the time series. During the past millennium, soil loss in the LJWD watershed showed an overall decreasing and then increasing trend. While the change in soil erosion was more complex in the DJT watershed, high and low rates appeared alternately in the 748±100 – 2018 period. The alluvial pollen analysis demonstrated that the soil erosion changes in both watersheds were closely related to human farming activities and vegetation landscape changes. The soil loss history over the past 1000 years was insufficient to reveal the evolution of rocky deserts in karst areas, indicating that the formation of rocky deserts should have occurred over a longer historical period. Overall, the optically stimulated luminescence (OSL) dating and palynological techniques were reliable in the investigation of local erosional history in karst regions.

How to cite: Cao, Z., Ke, Q., Zhang, K., and Zhang, Z.: A thousand-year erosional and sedimentation history in karst watersheds based on OSL dating and palynological techniques, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-34, https://doi.org/10.5194/ismc2021-34, 2021.

The Quaternary loess-paleosol deposits in the Chinese Loess Plateau (CLP) provide complete records of paleoclimates for better understanding differences in paleosol development. However, soil properties are overwritten due to climatic conditions in later periods; therefore the true paleosol development cannot easily be quantified. Only a calibrated soil model allows interglacial soil simulation in the CLP over long timescales. Therefore, our objective is to quantify the degree of paleosol development in three different paleosols in the CLP: S2, S4 and S5-1 using a calibrated process-based soil development model, SoilGen2.

The variations of paleosol development were compared by clay% and calcium carbonate content% and anorthite content (kg/m²) in the simulated paleosol.

Our results show that paleosol development is stronger in S5-1, S4, S2 in the studied paleosols in decreasing order of intensity. Each paleosol showed distinct variations in clay migration and decalcification processes under varying climate and dust deposition at the time of development. The model correctly simulated the two-sub paleosol units in paleosol S2. In conclusion, the results indicate that the (calibrated) SoilGen2 model combined with modeled climate can quantify and describe the paleosol development in the CLP fairly.

How to cite: Ranathunga, K. N., Finke, P., Yin, Q., and Yu, Y.: Quantifying paleosol development during three interglacial periods in the Chinese Loess Plateau by soil-climate modeling., 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-66, https://doi.org/10.5194/ismc2021-66, 2021.

Quantifying the relative contributions of climate and human activities to changes in sediment discharge is closely related to regional water resources, soil management and even the healthy operation of ecosystems. However, few studies used different methods to decompose influences of climatic variability and human activities on sediment discharge change, especially in karst regions of southwest China where experiencing severe soil erosion. This study systematically reviewed four different methods including simple linear regression method, double mass curve method, sediment identify factor analysis, and elastic coefficient method to separate the contribution of climate change and human activities to sediment discharge variation in four karst watersheds of southwest during 1955 to 2015. The trend and abrupt change year of sediment discharge in four watersheds were obtained by nonparametric Mann-Kendall test. Result showed that the sediment discharge in four watersheds all decreased significantly (P<0.05), and the abrupt change years were 2003, 2003, 2004 and 2004 for Wujiang, Yujiang, Hongshui, and Xijiang watersheds, respectively. The simple linear regression method, double mass curve method and elastic coefficient method all indicated that the sediment discharge was mainly influenced by human activities, with the contribution rate ranging from 73% to 101%. For the sediment identify factor analysis method, the sediment concentration is the principal factor influencing sediment discharge variation, and the contribution rate of sediment discharge varied from 100% to 154%. The results can provide good reference value for evaluating the influence of the climate and human activities on sediment discharge, and is significance for proper formulation of regional soil conservation policy in karst watersheds.

How to cite: Si, C., Xingxiu, Y., Zhenwei, L., Xianli, X., and Mingming, D.: Using four different approaches to separate the effects of climate change and human activities on sediment discharge in karst watersheds, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-89, https://doi.org/10.5194/ismc2021-89, 2021.

Soil erosion is a severe issue in Southwest China due to complex karst geomorphology and excessive farming activities. It is also difficult to observe and evaluate using traditional research methods. Fortunately, as a supplement to traditional methods, the ¹³⁷Cs tracing technique has strong potential to monitor and evaluate soil loss in karst regions. However, ¹³⁷Cs might move downward with tiny particles under adequate rainfall conditions. This is critical because it directly affects accuracy of using the ¹³⁷Cs conversion model to evaluate soil erosion. Thus, in our study, in order to explore whether tracers actually moved vertically and to evaluate the movement distance and the factors influencing the movement, magnetic powder (Fe₃O₄) and rare earth oxides (CeO₂ and La₂O₃) were used as the substitute tracers under different conditions (rainfall and leaching area) of a simulated leaching experiment, which possess similar properties as ¹³⁷Cs and have no toxicity problems in humans and the environment. The results showed that tracers moved downward 6 cm when water was added to simulate 1-10-year rainfall conditions and 8 cm when water was added to simulate 15-20-year rainfall conditions. The movement distance of tracers increased slowly with increasing water input, and the concentration of the tracers that moved related indirectly to the leaching area. Tracer movement at the edge of the simulated profile was affected by tracer type and concentration since there was no transition layer between soil and plastic column. Our field observations in two karst watersheds showed that ignoring the vertical movement of tracer can cause the overestimation of soil loss amount by 6.90% and 22.22% respectively. This study proved that in the karst area of Southwest China with abundant rainfall, ¹³⁷Cs would move vertically, and the soil loss will be overestimated if the vertical movement distance of the tracer is ignored.

How to cite: He, J., Zhang, K., Cao, Z., and Ke, Q.: Tracer vertical movement and its affecting factors in karst soil profiles using the simulated leaching method, 3rd ISMC Conference ─ Advances in Modeling Soil Systems, online, 18–22 May 2021, ISMC2021-33, https://doi.org/10.5194/ismc2021-33, 2021.