SSS11.1

Sediment source fingerprinting using a variety of soil tracers has been widely adopted for obtaining reliable sediment source information, which enables efficient catchment soil conservation and sediment management campaigns. But increasing challenges are rising towards the implementation of this technique against the context of complex landscape configurations and diverse human practices. Recent studies have examined and confirmed the within-source and temporal variability of tracer signatures, herein highlighting the “non-conservative” nature of traditional well-recognized tracers. In China, the landscape fragmentation under the household-base land use system, especially in hilly and mountainous regions, has exaggerate this issue. For example, the complex spatial configuration of mosaic land use patches and dynamic inter-season cropping transitions may significantly complicate soil imprinting processes, leading to highly variability of tracer signatures in a single source group even across a relatively small spatial scale, as well as the season changes of tracer signature for a given sampling unit. In response to this potential uncertainty, improvement of sampling strategies (e.g., increase sample number by enhance sample representativeness, repeated sampling to cover different cropping season) could be an potential option for technique refinement.

How to cite: Tang, Q. and He, X.: Spatial and Temporal variability of fingerprint signatures for sediment source apportionment: implications for technique refinement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4152, https://doi.org/10.5194/egusphere-egu22-4152, 2022.

The riverine derived particles play significant roles in sedimentological and geomorphological processes as well as biogeochemical cycles in estuaries. We collected a suite of water and sediment samples from the Changjiang (Yangtze) Estuary and adjacent East China Sea during to observe variations in the particulate ²³⁴Th, ⁷Be, ²¹⁰Pb, and ¹³⁷Cs activities as well as in particle transport, deposition, and resuspension. In the Changjiang Estuary, sedimentary particles in the North Passage experienced net deposition during neap tides whereas those in more seaward areas of the North Passage exhibited net resuspension during spring tides. based on a two-dimensional model of ⁷Be, ²³⁴Th, and ²¹⁰Pb. Using ⁷Be/²¹⁰Pb_ex and ¹³⁷Cs/²¹⁰Pb_ex activity ratios as tracers, we deduced that most of particles in the North Passage were not derived from the direct deposition of Changjiang input particles but were transported there from sediment deposited offshore. These riverine particles would undergo 3-6 years multiple cycles of deposition-resuspension-transport-deposition-resuspension before eventually buried in the shelf or export from inner shelf. The ⁷Be/²¹⁰Pb_ex ratio indicates a southward transport pathway in spring and northeastward transport pathway in summer. Besides, ²¹⁰Pb budget in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge in 2011) of particles could be transported offshore. The ratio of the mobile mud inventory of ²³⁴Th_ex/production in the overlying water column of > 2.5 in south inshore indicates that the sediment focusing resulted in the increased mass flux.

How to cite: Wang, J.: Changjiang sediment discharge to the East China Sea at the time scale of months to years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10802, https://doi.org/10.5194/egusphere-egu22-10802, 2022.

    It is well-known that ¹³⁷Cs has been widely applied as a powerful tracer for soil erosion and sediment dating studies since the 1960s. However, due to its relatively short half-life (30.2 year), the concentrations of global fallout ¹³⁷Cs in the environment have decreased by a factor of more than 2 comparing to the levels in the 1960s due to its radioactive decay, and this declined trend will continue. This makes the applications of ¹³⁷Cs for investigations of soil erosion, transportation and sedimentation less sensitive at present and will become difficult in the future. ²³⁹Pu and ²⁴⁰Pu, because of the long half-lives (T_1/2=24100 year for ²³⁹Pu and T_1/2=6561 year for ²⁴⁰Pu), their dominating source of nuclear weapons testing fallout worldwide, as well as their high retention and low mobility in soil, they were suggested as an ideal substitute of ¹³⁷Cs for environmental tracing studies. In recent years, with the rapid development of sensitive measurement techniques using mass spectrometry especially the inductively coupled plasma mass spectrometry (ICP-MS), the application of Pu isotopes in environmental studies becomes more attractive and competitive. Here we presented some preliminary studies regarding Pu isotopes as tracers for soil erosion studies and lake sediment dating in China. Our results indicated that Pu isotopes are powerful and promising tracers in future environmental studies.

How to cite: Xu, Y.: Plutonium isotopes as a good tracer for environmental studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6732, https://doi.org/10.5194/egusphere-egu22-6732, 2022.

Quantitative assessment of soil erosion and deposition rates using fallout radionuclides, including Beryllium-7 (⁷Be), requires reliable reference inventory, a crucial parameter in the conversion models. However, little information is currently available on the microscale spatial variabilities of ⁷Be inventory at reference locations, producing less confidence in the accuracy of the estimated soil redistribution rates with ⁷Be measurements.

To address this need, 44 soil cores were sampled extensively at 1 m intervals on a 5×12 m² bare flat reference plot in each year of 2019 and 2021 in Southwestern China. Surface soil samples were collected using a stainless steel cylinder with an internal diameter of 10 cm and a height of 3 cm. The soils are purple soils characterised by a silt loam texture. ⁷Be activity concentrations in <2 mm particles were measured to explore potential variability of fallout inventory at the microscale within the reference area. To determine possible causes of ⁷Be variation in soils, physicochemical characteristics including organic matter content (OM), pH, cation exchange capacity (CEC) and grain size compositions were also analysed. 

In the case of 2019, ⁷Be mass activities in soil samples ranged from 2.5 to 10.9 Bq kg^-1 and the areal activities ranged from 82.7 to 417.6 Bq m^-2. The deposition of ⁷Be was higher in 2021, with mass activities ranged between 5.6 and 22.1 Bq kg^-1 and the areal activities between 213.9 and 775.6 Bq m^-2. The higher inventory of ⁷Be in 2021 (211.1 ± 66.2 Bq m^-2, mean ± 1SD) than that of 2019 (456.1 ± 145.5 Bq m^-2) can be explained by higher rainfall amounts of 384.0 mm in 2021 (January 1 - May 18) 2021, compared with 225.4 mm for 2019 (January 1 - May 15). The coefficient of variation (CV) analysis indicated that soil pH and CEC were the most stable properties at the study site with CVs ranged from 1.3 to 5.1%. In contrast, ⁷Be contents in soils, in terms of both mass and areal activities, exhibited almost the strongest variation with CVs around 30%. No significant correlations were noted between ⁷Be activities and the measured soil properties. The high degree of spatial viability in ⁷Be areal activities at the reference site indicates that the simple assumption of uniform distribution of ⁷Be across the reference site needs detailed examination. A spatially-integrated sampling design is recommended to improve the accuracy of reference inventory estimates and thus soil erosion assessment with ⁷Be technique.

How to cite: Shi, Z., Long, Y., and Wen, A.: Microscale spatial variability of 7Be inventory at a reference site and its implications for soil erosion estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3270, https://doi.org/10.5194/egusphere-egu22-3270, 2022.

The Grain for Green Project is one of the important projects implemented by the Chinese government to control soil erosion on the Loess Plateau, and its successful implementation has brought remarkable ecological benefits to relevant regions in China. The land use change is the most intuitive representation. Meanwhile, the soil erosion and soil nutrient distribution has also been influenced to produce significant changes. In this research, the characteristics of soil erosion and nutrient loss characteristics of soils from different land utilization types including apple, shrub, forest, grass and gully land, and their relationship were quantitative evaluated with ¹³⁷Cs tracer technique in a typical watershed, which is located in Yan'an city of northern Shaanxi province in China. Results showed that soil erosion was observed in the all-land use types but shrub land, however, the degree of soil erosion was slight (the maximum value of soil erosion rate for 151.27 t/km²•a). The soil erosion of forest was significant differences with apple, shrub and gully but not with grassland. As will as there were significant differences in among shrub, apple orchard and gully. The soil nutrient loss, soil nutrient status and soil erosion degree showed a very similar pattern of spatial variation, with the difference that the correlation coefficients were different. In addition, there was highly significantly positive correlation between three indicators. However, Soil total nitrogen, total phosphorus, organic matter, N/P and C/P significantly affected the total nitrogen loss, total phosphorus loss and organic matter loss, but C/N ratio and nutrient loss were not significant. Soil nutrient loss in small watershed was more closely related to the soil carbon and nitrogen and soil erosion. The basic contents of different nutrients affected their nutrients loss laws, by and large, soil erosion affected soil nutrient loss and results in differences in nutrient distribution in the small watershed. 

How to cite: Zhang, N.: Assessment of soil erosion and nutrient loss characteristics using fallout 137Cs on the Loess Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4308, https://doi.org/10.5194/egusphere-egu22-4308, 2022.

Identification the effects of land use and vertical zone on soil erosion is vital to optimize land management in mountainous areas. In this study, the variation in soil erosion rate under typical land uses and vertical zones in a small agricultural catchment of the Daliangshan region (DLS), Southwest China, were evaluated using the cesium-137 tracer technique. Ten plots representing five land uses with four typical vertical zones (valley, low mountain, middle mountain and subalpine) were selected herein. Two parallel downslope transects were built in each plot, and soil samples were collected at 3-7 m intervals along these transects. The results showed that the sloping farmland (4.82 kg·m^-2·y^-1) and grassland (4.09 kg·m^-2·y^-1) soil erosion rates were significantly higher than those in abandoned farmlands (0.91 kg·m^-2·y^-1) and forest lands (0.80 kg·m^-2·y^-1), and horizontal terraces were dominated by net deposition (with erosion rate of -0.62 kg·m^-2·y^-1). The low mountain zone yielded the highest erosion rate (5.65 kg·m^-2·y^-1), followed by the middle mountain (2.96 kg·m^-2·y^-1) and subalpine (1.46 kg·m^-2·y^-1) zones, and the lowest erosion rate (1.28 kg·m^-2·y^-1) was observed in the valley zone. In addition, the soil erosion rate showed significant correlations (P<0.05) with sloping farmland proportion. The results indicate that land use controls soil erosion, and the vertical zone associated with land use patterns, topography, and human activities impact soil erosion variation. The low mountain zone near the catchment lower reaches has the highest erosion rate, largely because it is dominated by steep sloping farmlands and affected by immigration from high-altitude areas. Our findings highlight the importance of agricultural activities in sloping farmlands regarding soil erosion acceleration and the role of vertical zone in soil erosion rate impact. Appropriate management measures must be implemented to prevent soil erosion in the low mountain zone with increasing anthropogenic activities.

How to cite: Wu, H., Xiong, D., and Yuan, Y.: Variation in soil erosion rate under typical land uses and vertical zones in an agricultural catchment of the Daliangshan region, Southwest China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3375, https://doi.org/10.5194/egusphere-egu22-3375, 2022.

        Fallout radionuclides such as ¹³⁷Cs and ²¹⁰Pb_ex have been successfully used to quantify rates of soil and sediment redistribution in many areas of the world in recent years. However, little attention has been given to the assessment of soil erosion rate in the abandoned farmland using the ¹³⁷Cs and ²¹⁰Pb_ex tracer techniques. The artificial derived ¹³⁷Cs is still basically uniformly distributed in the soil after farmland abandonment, while the depth distribution of the natural derived ²¹⁰Pb_ex in the soil of the abandoned farmland will be continuously changed by the combined effects of its continuous atmospheric deposition, infiltration and radioactive decay within 100 years after farmland abandonment. At present, there is no model to represent this change of ²¹⁰Pb_ex distribution after the farmland abandonment, and the existing steady-state ²¹⁰Pb_ex model is not suitable for soil erosion assessment in the abandoned farmland. It is necessary to develop a model on the changes of ²¹⁰Pb_ex depth distribution in the soil of abandoned farmland. In this study, the redistribution process of ²¹⁰Pb_ex in the soil after farmland abandonment was decomposed and theoretically deduced on basis of analyzing the physical mechanisms of ²¹⁰Pb_ex infiltration and decay in soil. The expression of ²¹⁰Pb_ex decay in the plough layer on the initial abandoned farmland and the expression of infiltration of the new fallout ²¹⁰Pb_ex in soil after farmland abandonment were incorporated to develop the model on changes in ²¹⁰Pb_ex depth distribution for the abandoned farmland. The parameters such as the plow depth and the diffusion coefficient required for the model were obtained according to the measured ¹³⁷Cs and ²¹⁰Pb_ex depth distributions from the typical abandoned farmlands in Sichuan Province, southwest China. The result showed that the modeled curves of ²¹⁰Pb_ex depth distribution in the farmland abandoned for 19, 15 and 8 years matched each other with the measured curves. In addition, the Nash-Sutcliffe efficiency coefficient (E_NS) test showed that the E_NS of the three abandoned farmland were 0.975, 0.961 and 0.889, respectively, indicating the modeled results are reliable. The present study has an important theoretical significance for the development of the models for calculating the soil erosion amount from ²¹⁰Pb_ex measurements on the abandoned farmland, and further provides an effective method for the evaluation of the soil erosion response driven by abandonment.

How to cite: Yuan, Y., Donghong, X., Yunqi, Z., Baojun, Z., and Xinbao, Z.: A model on changes in 210Pbex depth distribution for abandoned farmland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4387, https://doi.org/10.5194/egusphere-egu22-4387, 2022.

Impoundment regulation of the Three Gorges Reservoir (TGR) has created a water-level fluctuation zone (WLFZ) with a vertical height of 30 m and a total area of 349 km². This special zone received approximately 7% of the total sediment captured by the TGR. The present study aims to reveal the history of sediments accumulation since the WLFZ was formed in 2006. A sedimentary core was retrieved from a representative floodplain at the lower part of the WLFZ and subsequently sectioned with an interval of 5 cm. Particle composition, ¹³⁷Cs and ²¹⁰Pb_ex activities of sediment were measured after pretreatment. The result shows that the ²¹⁰Pb_ex activity can be used as a proxy for the seasonal high-resolution dating of sediment in the WLFZ, due to the sediments deposited during the dry season have high ²¹⁰Pb_ex activity, while the opposite is true for sediments deposited in the wet season. Then, the annual sequence of the sedimentary profile has been established based on the distribution pattern of ²¹⁰Pb_ex activity. The inter-annual variation of the sedimentary rate is shown as ‘low-high-low-high’, and mutation years are 2008, 2014, and 2018, corresponding deposition rates in these four periods are 12.5, 45, 20, and 32.5 cm, respectively. In the early period of the formation of the WLFZ (2006-2007), the staged impoundment of the TGR was the key influencing factor of the sedimentary rate. Afterward, the annual sedimentary rate was consistent with the suspended sediment load supplied into the TGR. From 2014 to 2017, due to the interception of the cascade reservoirs in the lower reaches of the Jinsha River, the suspended sediment load dropped sharply, resulting in a decrease in the sedimentation rate. From 2018 to 2019, the sedimentation rate of the floodplain increased owing to the increase in the suspended sediment load caused by frequent extreme rains in the upper reaches of the Yangtze River basin.

How to cite: Li, J., He, X., Bao, Y., Zhang, X., Wei, J., and Tang, Q.: 210Pbex records the historical sediments accumulation in the water-level fluctuation zone of the Three Gorges Reservoir, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10909, https://doi.org/10.5194/egusphere-egu22-10909, 2022.

Studies on the soil erosion rate for aeolian grassland are crucial for accessing the effect of grassland restoration. Sandy land is widely distributed in the alpine grassland areas of Northern Tibet where the conflict between grass and livestock is severe. In order to effectively curb grassland degradation and reduce desertification, a series of protection projects have been implemented in that area. However, due to the lack of continuous observations in the field, the quantitative research on soil erosion process of alpine grassland has been relatively lagging behind, especially the impact of protection projects on soil erosion is difficult to evaluate. We compared soil erosion rates with and without fence protections through ¹³⁷Cs and ²¹⁰Pb_ex trace technique. We also combined soil erosion in sand source areas with vegetation and a near-source climbing dune to illustrate the effect of fence protection. The results showed that: (1) The area of fence protection reduced soil erosion, the soil erosion rates of ¹³⁷Cs and ²¹⁰Pb_ex in fenced protected area were 0.99 t·ha^-1·yr^-1 and -0.12 t·ha^-1·yr^-1, respectively, while those in free grazing areas were 3.68 t·ha^-1·yr^-1 and 0.46 t·ha^-1·yr^-1, respectively. (2) Fence protection significantly improved vegetation coverage, the average NDVI of fenced protected areas increased by 0.027 from 2011 to 2019, with a growth rate of 67.43%. The average NDVI in fenced protected areas in 2019 was 1.34 times that of free grazing areas. (3) After the implementation of the fence protection in the sand source area, the climbing dune had shown a development trend from mobile to semi-fixed dune from the foot of the climbing dune to the middle (about 100m distance). Therefore, our results highlighted that fence protection was the major reason for the mitigation of soil erosion in the alpine grasslands, which were the source of sand, and their climbing dunes. The results can be used as a reference for the evaluation of grassland restoration effectiveness on the Qinghai-Tibet Plateau.

Keywords: Soil erosion; Radionuclides; Fence protection; Alpine grassland; Climbing dune

How to cite: Liu, L., Yuan, Y., Xiong, D., and Zhang, X.: Preliminary evaluation on soil erosion of alpine grassland fence project based on 137Cs and 210Pbex trace technique in the Northern Tibet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4973, https://doi.org/10.5194/egusphere-egu22-4973, 2022.

Abstract: Geochemical fingerprinting was used to identify the sources of fine sediments derived from three types of contrasting lithological zones and deposited in a reservoir in a medium-sized catchment over the past 60 years. The impact of grain-size sorting on the source of fine sediments in the reservoir was investigated. Overall, the fine sediment sources identified in the sediment cores indicated changing trends in sediment contribution from the three types of lithological zones during the past 60 years. Although the granite zone covers half of the catchment, has thicker soils, is more prone to soil erosion, and has been subjected to more human disturbance than the limestone and shale zones, it only provided 25% of the fine sediment in the cores. The limestone and shale zones, on the other hand, account for 23% and 15% of the catchment, respectively, but produce 42% and 33% of the fine sediment in the cores. This is due to grain-size sorting in the reservoir system during downstream sediment transit and deposition. These data show that grain-size sorting has had a significant impact on the sediment source. This study provides new insight into the source of sediments deposited in a reservoir system from different lithological zones at the scale of a medium-sized catchment across multi-decadal periods.

Keywords: Sediment source; Composite fingerprinting techniques; Reservoir Contrasting lithologies

How to cite: Xu, M., Zhang, Y., Wu, T., Li, Z., and Wang, Y.: Use of composite fingerprinting technique to identify sources of fine-sediment deposited in a reservoir, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11139, https://doi.org/10.5194/egusphere-egu22-11139, 2022.

Understanding the influence of rainfall pattern on suspended sediment source on catchments and river basin scales is of great importance for reasonable implementing of soil conservation and sediment control measures. Such information, however, is unavailable or difficult to assemble. According, this study used the rainfall data from 2011 to 2013 recorded by pluviograph to analyze the effect of rainfall pattern on sediment source in the Qiaozi West catchment on the Chinese Loess Plateau. The suspended sediment in six erosive rainfall events were continuous collected at the outlet of the catchment and surface soil samples were collected from potential sediment sources  including, inter-gully (farmland, forest, grassland) and gully areas (gully slope and gully wall) of the watershed. A total of 54 rainfall events were divided into four patterns according to the variation of rainfall intensity in rainfall processes, which were advanced, intermediate, delayed, and uniform patterns. The rainfall was dominated by the advanced pattern in the studied catchment, which accounts for 43% of all observed rainfalls. There were six rainfall events had suspended sediment samples, two intermediate pattern erosive rainfall events generated the largest percentage of the total sediment yield of six events. The results based on the composite fingerprinting approach indicated that farmland and gully wall were the main sediment source in the catchment regardless of rainfall patterns. However, cultivated field having loose topsoil created in tillage has relatively high contribution to suspended sediment in runoff at the advanced pattern, while loose materials from collapsed gully walls has relatively high contribution to suspended sediment in runoff at the intermediate and delayed rainfall pattern. Further studies are necessary to gain better insight into erosion pattern variation under different rainfall pattern.

How to cite: Liu, Y., Yang, M., Zhang, F., and Zhang, J.: The effect of rainfall pattern on sediment source in a small catchment on the Chinese Loess Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3726, https://doi.org/10.5194/egusphere-egu22-3726, 2022.