Investigating the spatial distribution of soil erosion and deposition in a small catchment on the Loess Plateau of China, using Cs

An understanding of the spatial distribution of soil erosion and deposition in a catchment is important for designing soil and water conservation measures. Traditional monitoring techniques provide limited information on the spatial patterns of erosion and deposition. The fallout radionuclide ¹³⁷Cs was used to document rates and patterns of soil redistribution within a small (0.17 km²) gully catchment located near An'sai in Shaanxi Province, representative of the Loess Plateau of China. The local reference inventory was estimated to be 2266 Bq m⁻² and the ¹³⁷Cs inventories of 198 soil cores collected from the catchment, ranged from 0 to 3849 Bq m⁻². The coefficient of variation of the inventories of the individual cores was 0.85, reflecting the complex pattern of ¹³⁷Cs redistribution by soil erosion and deposition. Estimates of erosion rates derived from ¹³⁷Cs measurement ranged from less than 25 to 150 Mg ha⁻¹ year⁻¹, with about 70% of the net soil loss from the catchment coming from the gully area. The ¹³⁷Cs technique was shown to provide an effective means of documenting the spatial distribution of soil erosion and deposition within the small catchment.     

137Cs在黄土高原地区土壤侵蚀示踪中的应用研究

利用137Cs示踪法详细研究了黄土高原地区南沟小流域的土壤侵蚀状况。结果表明: 黄土高原地区不同利用方式下的土壤侵蚀速率都较大,耕作土壤与非耕作土壤相比由于大部分是坡地种植而具有较高的侵蚀速率。土壤侵蚀速率的空间变异较大且较为复杂。通过对土壤侵蚀类型分类可知,研究区域大部分属于极强度侵蚀。     

Soil erosion evaluation in a small basin through the use of Cs technique

Soil erosion significantly affects the most productive lands in Argentina, particularly the region called “Pampa Ondulada”. Quantification of the actual rates and patterns of soil loss is necessary for designing efficient degradation control strategies. The aim of this investigation was to gather using the ¹³⁷Cs technique a reliable set of data of erosion and sedimentation rates, in order to describe the long-term erosive landscape dynamic in a 300 ha basin representative for the “Pampa Ondulada” region of Argentina. The general topography of the basin is undulated with slopes gradients between 0 and 2.5% and slope lengths up to 800 m long. The main land use consisted in annual cropping under conventional tillage.For the soil erosion study in the basin the ¹³⁷Cs technique was used, which is based on the comparison between the ¹³⁷Cs inventories surveyed with a local reference ¹³⁷Cs profile. The sampling strategy was based on a multiple transect approach.The estimated mean soil erosion rates obtained applying Mass Balance Model 2 for the studied hillslopes ranged between −11.5 and −36 t ha⁻¹ per year and fitted the low and moderate erosion classes according to FAO. These values ranged beyond the admitted tolerance. Sedimentation was observed at the lower landscape positions probably related to changes from convex to concave slopes. The application of the ¹³⁷Cs technique in the studied basin proved to be a useful and sensible tool for assessing erosion/deposition rates. In areas with low topographic gradients like the Pampa Ondulada region, the slope length appears to be an important property for predicting spatial patterns of erosion rates.     

利用137Cs估算土壤侵蚀速率的定量模型

A quantitative model was developed to relate the amount of ^137Cs loss from the soil profile to the rate of soil erosion,According th mass balance model,the depth distribution pattern of ^137Cs in the soil profile ,the radioactive decay of ^137Cs,sampling year and the difference of ^137Cs fallout amount among years were taken into consideration.By introducing typical depth distribution functions of ^137Cs into the model ,detailed equations for the model were got for different soil,The model shows that the rate of soil erosion is mainly controlled by the depth distrbution pattern of ^137Cs ,the year of sampling,and the percentage reduction in total ^137Cs,The relationship between the rate of soil loss and ^137Cs depletion i neither linear nor logarithmic,The depth distribution pattern of ^137Cs is a major factor for estimating the rate of soil loss,Soil erosion rate is directly related with the fraction of ^137Cs content near the soil surface. The influences of the radioactive decay of ^137Cs,sampling year and ^137Cs input fraction are not large compared with others.     

Using Cs measurements to validate the application of the AGNPS and ANSWERS erosion and sediment yield models in two small Devon catchments

Distributed erosion and sediment yield models are being increasingly used for predicting soil erosion and sediment yields in agricultural catchments. In most applications, validation of such models has commonly been restricted to comparison of the predicted and measured sediment output from a catchment, because spatially distributed information on rates and patterns of soil redistribution within the catchment has been lacking. However, such spatially distributed data are needed for rigorous model testing, in order to validate the internal functioning of a model and its applicability at different spatial scales. The study reported in this paper uses two approaches to test the performance of the agricultural non-point source pollution (AGNPS) and areal non-point source watershed environmental response simulation (ANSWERS) erosion and sediment yield models in two small catchments in Devon, UK. These involve, firstly, comparison of observed and predicted runoff and sediment output data for individual storm events monitored at the basin outlets and, secondly, information on the spatial pattern of soil redistribution within the catchments derived from ¹³⁷Cs measurements. The results obtained indicate that catchment outputs simulated by both models are reasonably consistent with the recorded values, although the AGNPS model appears to provide closer agreement between observed and predicted values. However, the spatial patterns of soil redistribution and the sediment delivery ratios predicted for the two catchments by the AGNPS and ANSWERS models differ significantly. Comparison of the catchment sediment delivery ratios and the pattern of soil redistribution in individual fields predicted by the models with equivalent information derived from ¹³⁷Cs measurements indicates that the AGNPS model provides more meaningful predictions of erosion and sediment yield under UK conditions than the ANSWERS model and emphasises the importance of using information on both catchment output and sediment redistribution within the catchment for model validation.     

贵州省西南部麦岗水库沉积物的137Cs和210Pb测年与沉积速率研究

对贵州省西南部麦岗水库沉积物柱芯MG4-2,采用210Pb和137Cs法进行了测年与现代沉积速率研究.结果表明,该柱芯中存在这3个明显的137Cs蓄积峰,对应1964,1975,1986年3个计年时标.运用210Pb的恒定补给速率(CRS)模式计算得到的年代,总体上与137Cs法的结果吻合较好,但存在一定的偏差,特别是与1964年的计年时标的偏差较大,这可能是因为沉积物柱芯受到了一些人为扰动所致.两种核素测定的平均沉积速率在数值上有一定的偏差,但都反映了麦岗水库沉积物近几十年以来经历了从慢到快再到慢的沉积过程,初步推测,沉积速率的这种变化与人类活动有一定的关系.两种计年方法结合,相互印证,使计年和沉积速率的研究更为准确.     

Assessment of erosion in the Boyer River watershed (Canada) using a GIS oriented sampling strategy and Cs measurements

Starting in the 1980's, the Rainbow Smelt (Osmerus mordax) population of the Boyer River (Canada) gradually declined due to water eutrophication and excessive siltation in the spawning area. Sediments and agricultural nutrients reach hydrosystems through runoff and soil erosion. The objectives of the study were to quantify the soil and sediment loss from agricultural fields and to identify the areas at risk, using ¹³⁷Cs measurements. Using a Geographical Information Systems (GIS), the watershed was subdivided into 6 isosectors presenting specific soil/slope combinations. Representative fields from each isosector were sampled for ¹³⁷Cs. Using GIS, the data for individual fields were extrapolated to isosectors and the whole cultivated area of the watershed. Based on this approach, it was estimated that around 30% of the arable lands of the watershed show erosion rates higher than 6 t ha^− 1 yr^− 1, which is considered as a tolerable level for Canadian soils, and that 45% of the residual area presents an erosion rate close to that limit. The average sediment production at the edge of fields was estimated at 2.8 t ha^− 1 yr^− 1, for an annual production of more than 60 000 t of material. Loamy soils with a slope higher than 2% were estimated to generate the highest sediment rate (6.9 t ha^− 1 yr^− 1) and nearly 40% of the overall sediment production.     

Time and scale of gully erosion in the Jedliczny Dol gully system, south-east Poland

Key catchments of the Roztocze loess area in south-east Poland have a great potential of revealing the history of long-term soil erosion and changes in land use. The knowledge of how and when soil erosion took place in the past helps one understand the impact of land use changes on the landscapes [Bork, H.-R., 1989. Soil erosion during the past Millennium in Central Europe and its significance within the geomorphodynamics of the Holocene. Catena 15, 121–131]. The Jedliczny Dol gully system near the town Zwierzyniec in south-east Poland was investigated by using detailed field stratigraphy and radiocarbon dating of charcoal and wood.In connection with new settlements which were established between the 14th and 16th centuries, arable land was cultivated and forests were used much more intensively. As a consequence, the loess soils were strongly eroded during heavy rainfalls. Up to 4 m of colluvial sediments were deposited in the gully system during the 15th and/or 16th centuries. The thickness of the colluvial sediments indicate severe erosion which might be related to excessive timber exploitation for the local glass and iron production. With the foundation of the so-called Ordinariat Zamoyski at the end of the 16th century, some parts of the area were presumably reforested. High pressure on the land at the beginning of the 19th century enabled a second main phase of gulling before 1900.Since 1890 at the latest, almost the whole catchment is used as a forest, however, concentrated runoff on compacted forest roads can still be high after heavy rainfalls.In loess areas soil erosion caused by intensive land use, triggered by heavy rainfalls, can change the landscape drastically. These changes will continue to influence how catchments react, even if land use gets less intensive again. This knowledge should be considered regarding future, sustainable land use and recent changes in land use in the south-eastern Polish loess regions.     

紫色丘陵区小流域土壤侵蚀产沙空间分布的 137Cs法初步研究

该文通过紫色丘陵区响水滩小流域不同土地利用类型、不同坡度和坡长、不同地貌部位土壤剖面中 ¹³⁷Cs含量的测定与分析，对其侵蚀空间分布进行了估算。研究结果表明：该流域 ¹³⁷Cs含量的背景值为1870 Bq/m²；流域内坡耕地、林地的年平均侵蚀强度分别为4468、1759 t/(km²·a)；土壤侵蚀量与坡长、坡度均指数相关；丘顶、丘坡和鞍部的年平均侵蚀强度分别为2125、4676、3625 t/(km²·a)。结果表明土地利用类型、坡长和坡度、地貌部位对土壤侵蚀量影响很大，坡耕地是该流域泥沙的主要来源。     

The use of environmental radionuclides as tracers in soil erosion and sedimentation investigations: recent advances and future developments

Although much of the recent attention on the environmental problems has focused on climatic change, there is also increasing concern that accelerated soil erosion and associated land degradation represent a major problem for sustainable development and environmental protection. There is an urgent need to obtain reliable quantitative data on the extent and rates of soil erosion worldwide to provide a more comprehensive assessment of the magnitude of the problems and to underpin the selection of effective soil conservation measures. The use of environmental radionuclides, in particular ¹³⁷Cs, affords an effective and valuable means for studying erosion and deposition within the landscape. The key advantage of this approach is that it can provide retrospective information on medium-term (30–40 years) erosion/deposition rates and spatial patterns of soil redistribution, without the need for long-term monitoring programmes. Advantages and limitations of the technique are highlighted. The launching of two closely linked International Atomic Energy Agency (IAEA) research networked projects in 1996 involving some 25 research groups worldwide has made a major contribution to co-ordinating efforts to refine and to standardise the ¹³⁷Cs technique. The efficacy and value of the approach has been demonstrated by investigations in a number of environments. Significant developments that have been made to exploit its application in a wide range of studies are reported in this review paper. Other environmental radionuclides, such as unsupported ²¹⁰Pb and ⁷Be offer considerable potential for use in soil erosion investigations, both individually and complementary to ¹³⁷Cs. The IAEA through research networks and other mechanisms is promoting further development and applications of these radionuclides in soil erosion and sedimentation studies for a sustainable resource use and environmental protection.     

沂蒙山区土壤侵蚀的137Cs示踪法初步研究

沂蒙山区是我国北方典型的土石山区,当地土壤由片麻岩、砂岩发育而来,质地疏松易流失,缺乏对泥沙侵蚀监测的长期观测数据。本研究采集了山东省沂蒙山区某一小流域的48个土样共72个样品,利用137Cs示踪技术,确定该地区土壤中的137Cs背景值约为1 740 Bq m-2,并利用杨浩等人的土壤侵蚀定量模型,对该流域土壤侵蚀进行了初步估算。估算结果表明该地区非耕地土壤侵蚀的平均速率为2 531 t km-2a-1,坡耕地土壤侵蚀的平均速率为6 953 t km-2a-1。由于人类耕作活动以及地形的影响,坡耕地土壤侵蚀严重,土壤侵蚀速率在坡面上呈复杂变化。当地土壤流失严重,使得土壤涵蓄水能力下降,加剧了洪涝、干旱灾害的发生,影响当地农业的可持续发展和人们生活水平的提高。     

Soil erosion and deposition rates in a cultivated catchment area in central Greece, estimated using the Cs technique

The spatial variation of soil erosion and deposition rates was studied in a small catchment cultivated by rainfed agriculture, in the Mouriki area, Viotia Greece, using the ¹³⁷Cs technique. A 25 m grid was established parallel to the slope and the ¹³⁷Cs inventories were defined for the grid points. After establishing the local reference inventory, the soil erosion and deposition rates were estimated using the ¹³⁷Cs residuals for individual points on the grid in conjunction with the four conversion (calibration) models described by Walling and He (2001) [Models for converting ¹³⁷Cs measurements to estimates of soils redistribution rates on cultivated and uncultivated soils]. The conversion models were validated by means of sensitivity analysis and using local experimental data. The resulting estimates of soil redistribution rates were interpolated by means of kriging, using Surfer Golden software. The magnitude of the soil erosion rates depend on many factors, including the location of the sampling point, the local slope, and the soil properties. The mass balance model 2 (MBM2) and mass balance model incorporating soil movement by tillage (MBM3) conversion models predict soil redistribution rates of the same order of magnitude as the experimental data and are able to take account of Chernobyl fallout. Predicted soil erosion rates for catchment grid varied from 6.71 to 85.55 t ha⁻¹ per year using MBM2 and from 3.54 to 95.78 t ha⁻¹ per year using MBM3. Deposition rates varied from 1.23 to 168.19 t ha⁻¹ per year using MBM2 and from 3.24 to 189.18 t ha⁻¹ per year using MBM3. High correlation was apparent between erosion/deposition rates (MBM2) and soil P (P<0.001), soil K (P<0.001), soil organic matter % (P<0.05), point slope (P<0.05), clay % (P=0.053) and altitude (P=0.057). The total soil losses from the catchment have been estimated at 18.34 t ha⁻¹ per year using MBM2 and 22.12 t ha⁻¹ per year using MBM3.     

Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco

In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the ¹³⁷Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m^− 2). All the sampling sites were eroded and ¹³⁷Cs inventories varied widely (between 245 and 3670 Bq m^− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha^− 1 yr^− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha^− 1 yr^− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha^− 1 yr^− 1 and reaching a maximum of 48.8 t ha^− 1 yr^− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha^− 1 yr^− 1) to 25° (40. 8 t ha^− 1 yr^− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha^− 1 yr^− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha^− 1 yr^− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area.     

Soil Redistribution investigations by combined use of soil 137Cs and selected chemical properties

Abstract

To improve the methods of application of phosphorus or supply of soil P to Azolla (A. microphylld), basal application, split application, inoculation of P-enriched Azolla, and soil disturbance were compared. Soil disturbance did not increase the floodwater P content. Phosphorus was applied to inoculum production plots to enrich Azolla with P. Thus, phosphorus-enriched Azolla could multiply 5–7 times after inoculation until it became P deficient. Trials on the methods of enrichment of Azolla with P showed that the best method was to broadcast twice 4.33 kg P (10 kg P₂O₅/ha) at 2-day intervals and to harvest Azolla 3 days after P application. Addition of P once or twice 2 weeks after the inoculation of P-enriched Azolla further increased the biomass production. Efficiency of P application was analyzed in terms of N gain in relation to the amount of P applied. This ratio in the P-enriched Azolla treatment was higher than the economically sound ratio -5-, and higher than or equal to that in the standard split application.     

川中丘陵区人工刨地耕作方式下紫色土坡耕地侵蚀速率的137Cs和210Pbex双核素示踪法研究

Purple soils are widely distributed in the Sichuan Hilly Basin and are highly susceptible to erosion, especially on the cultivated slopes. Quantitative assessment of the erosion rates is, however, difficult due to small size of the plots of the manually-tilled land, the complex land use, and steep hillslopes. 137Cs and 210Pbex (excess 210Pb) tracing techniques were used to investigate the spatial pattern of soil erosion rates associated with slope-land under hoe tillage in Neijiang of the Sichuan Hilly Basin. The 137Cs and 210Pbex inventories at the top of the cultivated slope were extremely low, and the highest inventories were found at the bottom of the cultivated slope. By combining the erosion rates estimates provided by both 137Cs and 210Pbex measurements, the weighted mean net soil loss from the study slope was estimated to be 3100 t km-2 year-1, which was significantly less than 6930 t km-2 year-1 reported for runoff plots on a 10°cultivated slope at the Suining Station of soil Erosion. The spatial pattern of soil erosion rates on the steep agricultural land showed that hoe tillage played an important role in soil redistribution along the slope. Also, traditional farming practices had a significant role in reducing soil loss, leading to a lower net erosion rate for the field.     

Use of Cs to estimate tillage- and water-induced soil redistribution rates on agricultural land under different use and management in central-south Chile

The purpose of this research was to evaluate the applicability of conventional ¹³⁷Cs sampling and a simplified approach, for estimating medium-term tillage- and water-induced soil erosion and sedimentation rates on agricultural land in Chile. For this purpose, four study sites under contrasting land use and management were selected in central-south Chile. First, a conventional ¹³⁷Cs approach, based on grid sampling was applied, adapting a mass balance conversion model incorporating soil movement by tillage to the site specific conditions of the study region. Secondly, using the same conversion model, the feasibility of estimating soil redistribution rates from measurements of ¹³⁷Cs inventories based on composite soil samples taken along contour lines was also tested at all four sites. The redistribution rates associated with tillage and water and the total rates estimated using both methods correlated strongly at all four sites. The conventional method provides more detailed information concerning the redistribution processes operating over the landscape. The simplified method is suitable for assessing soil loss and sediment accumulation in areas exhibiting simple topography and almost similar slopes along the contour lines. Under these conditions, this method permits faster estimation of soil redistribution rates, providing the possibility of estimating soil redistribution rates over larger areas in a shorter time. In order to optimise the costs and benefits of the methods, the sampling and inventory quantification strategy must be selected according to the resolution of the required information, and the scale and complexity of the landscape relief. Higher tillage- and water-induced erosion rates were observed in the annually ploughed cropland sites than in the semi-permanent grassland sites. Subsistence managed crop and grassland sites also show greater erosion effects than the commercially managed sites. The ¹³⁷Cs methods used permit discrimination between redistribution rates observed on agricultural land under different land use and management. The ¹³⁷Cs technique must be seen as an efficient method for estimating medium-term soil redistribution rates, and for planning soil conservation and sustainable agricultural production under the climatic conditions and the soil type of the region of Chile investigated.     

Assessment of soil erosion on arable land using Cs measurements: a case study from Jaslovske Bohunice, Slovakia

This study was carried out to obtain a representative set of data on long-term erosion rates from a pilot area located close to the Jaslovske Bohunice village, in western Slovakia using the ¹³⁷Cs-method. The study area chosen was representative of the hilly loess cultivated areas of Slovakia. The sampling strategy was based on a multiple transect approach. Analyses of the samples for ¹³⁷Cs activity were made at the Nuclear Power Plant Research Institute, Jaslovske Bohunice. The ¹³⁷Cs-method was used to obtain long-term estimates of soil erosion in the Jaslovske Bohunice site, a representative hilly loess cultivated area of Slovakia. The estimated reference ¹³⁷Cs inventory was 2910 Bq m⁻², with a coefficient of variation of 4.3%.Examination of the ¹³⁷Cs redistribution in relation to the topography of the study area revealed that, within individual transects the ¹³⁷Cs inventories were closely related to major landforms. The ¹³⁷Cs inventories were considerably lower on the slopes than on the plateau and they were highest in the valley. However, when plotted against a selection of individual quantitative slope parameters, i.e. the S and the LS factors of the USLE or slope inclination, the correlations obtained were weak.Three conversion models, i.e. the proportional model (PM), the simplified mass balance model (MBM1) and the standard mass balance model (MBM2), from the set of models developed at Exeter University, Great Britain were selected to interpret the resulting ¹³⁷Cs measurements into soil erosion/deposition rates. The mean erosion rates estimated with the PM were 22.4, 35.6 with MBM1 and 17.3 t ha⁻¹ per year with MBM2. There was a good agreement between the average of these mean erosion rates (25.1 t ha⁻¹ per year) for the Jaslovske Bohunice site and the estimated mean soil erosion rate obtained for small erosion plots (15 t ha⁻¹ per year) for conditions similar to the study site. Nevertheless, further research on the application of the ¹³⁷Cs-method, in particular the independent validation of the results obtained, is needed. Several issues requiring further study have been highlighted.     

Soil and phosphorus redistribution along a steep tea plantation in the Feitsui reservoir catchment of northern Taiwan

Abstract

Feitsui reservoir, the major water supply of Taipei city, has shown declining water quality in recent years. The reservoir is located in an area famous for tea cultivation, and the question arises as to whether the hillside tea plantations have contributed to increased sediment and nutrient discharge into the reservoir. In this study, soil and phosphorus redistribution were examined along a steep tea plantation in the reservoir's catchment and the provenance of reservoir sediment was assessed. Fallout radionuclides were used as soil erosion/deposition tracers and as markers of sediment sources. Continuous fertilizer application has raised (inorganic) phosphorus levels in the studied tea plantation. The plantation's narrow bench terraces trap eroded material and slow down soil and nutrient translocation. Nevertheless, eroded soil and phosphorus have accumulated on a vegetated toeslope below the tea plantation. The reservoir sediment contained significant amounts of inorganic phosphorus and cesium-137, and application of a mixing model resulted in a surface soil contribution of approximately 30%. This points towards tea plantations as possible sediment and pollutant sources and underlines the necessity of soil conservation strategies, such as the maintenance of vegetated riparian buffer zones. However, other sources, such as landslide debris and urban wastewaters, cannot be entirely ruled out. Further research is needed to better characterize the catchment's soils and sediments and to improve sediment fingerprinting efforts. Potential point and non-point pollution sources need to be examined in detail to better understand how phosphorus enters the reservoir.     

Soil and phosphorus redistribution along a steep tea plantation in the Feitsui reservoir catchment of northern Taiwan

Feitsui reservoir, the major water supply of Taipei city, has shown declining water quality in recent years. The reservoir is located in an area famous for tea cultivation, and the question arises as to whether the hillside tea plantations have contributed to increased sediment and nutrient discharge into the reservoir. In this study, soil and phosphorus redistribution were examined along a steep tea plantation in the reservoir's catchment and the provenance of reservoir sediment was assessed. Fallout radionuclides were used as soil erosion/deposition tracers and as markers of sediment sources. Continuous fertilizer application has raised (inorganic) phosphorus levels in the studied tea plantation. The plantation's narrow bench terraces trap eroded material and slow down soil and nutrient translocation. Nevertheless, eroded soil and phosphorus have accumulated on a vegetated toeslope below the tea plantation. The reservoir sediment contained significant amounts of inorganic phosphorus and cesium-137, and application of a mixing model resulted in a surface soil contribution of approximately 30%. This points towards tea plantations as possible sediment and pollutant sources and underlines the necessity of soil conservation strategies, such as the maintenance of vegetated riparian buffer zones. However, other sources, such as landslide debris and urban wastewaters, cannot be entirely ruled out. Further research is needed to better characterize the catchment's soils and sediments and to improve sediment fingerprinting efforts. Potential point and non-point pollution sources need to be examined in detail to better understand how phosphorus enters the reservoir.