Spatial variation and interaction of runoff generation and erosion within a semi-arid, complex terrain catchment: a hierarchical approach

Purpose

Closed erosion plots have been used extensively to investigate soil loss and its spatial variation within a watershed. However, erosion rates measured on closed plots at various locations within a watershed may not reflect the “real world” conditions due to plot boundary problems. The purpose of this study was to identify runoff and sediment sources in a semi-arid, complex terrain catchment by using the data collected from open plots, nested catchments, and tunnel systems.

Materials and methods

The study catchment, in the Loess Plateau of China, was partitioned into various-level geomorphic units. Runoff and sediment discharges were measured from 55 storm events between 1963 and 1968 on open plots and nested catchments. Storm flows were also monitored in 14 rainfall events from the tunnel systems between 1989 and 1990. This study combined the data collected from the two periods to investigate runoff and sediment sources from the different geomorphic units of the catchment.

Results and discussion

On the four open plots (S1, S2, S3, and S4) of the hill slope, total runoff depths of 128.5 mm (S1), 84.3 mm (S2), 101.92 mm (S3), and 141.73 mm (S4) were recorded from all the events over the first period, which correspondingly produced total sediment yields of 3.056 kg m^?2 (S1), 9.058 kg m^?2 (S1), 42.848 kg m^?2 (S3), and 97.256 kg m^?2 (S4). The number of runoff events also varied due to a non-uniformity in runoff generation among the different geomorphic units of the catchment. Tunnel flows generally had higher mean sediment concentrations than catchment outflows. Three nested catchments located from the headwaters (C1) to the mouth of the catchment (C3) generated total runoff depths of 120.02 mm (C1), 143.92 mm (C2), and 149.43 mm (C3), and correspondingly produced sediments yields of 62.01 kg m^?2 (C1), 144.02 kg m^?2 (C2), and 123.92 kg m^?2 (C3) for the first period.

Conclusions

Significant variations in runoff and erosion existed within the catchment. The spatial variation of runoff generation on the hill slopes resulted from the variation of soil infiltration. Sediment produced from the lower hill slope zone was disproportionally higher than that from the upper hill slope zone. Nevertheless, a significant portion of the sediment eroded on the lower slope zone was caused by runoff generated from the upper slope zone. Tunnel erosion also played a significant role in sediment production.     

Soil moisture variability along transects over a well-developed gully in the Loess Plateau,China

Knowledge of soil moisture distributions in gullies, which are highly variable spatially and temporally, is important for both restoring vegetation and controlling erosion in them, but little attention has been paid to this spatio-temporal variability to date. Therefore, we examined soil moisture profiles and their variability along three transects traversing sidewalls of a well-developed gully with steep slopes in a hilly area of the Chinese Loess Plateau. We took intensive measurements at 20-cm intervals from 0 to 160 cm depth, using a portable time domain reflectometer, from September 3 to October 20 2009 and from April 5 to July 20 2010. The results indicate that the mean, standard deviation and coefficient of variation of moisture content vary with time, their responses to precipitation vary at different depths, and moisture content is most variable when mean values are moderate (15–20%). Revised fitting functions developed and introduced by Famiglietti et al. (2008) captured with confidence the relationship between spatial variability (SD and CV) and spatial mean of moisture content (RMSE ranging from 0.0015 to 0.0293). Soil moisture clearly varied along the transects, the vertical distribution of soil moisture differed in different seasons, and correlation analysis showed that soil texture influenced the variability of surface soil moisture more strongly than terrain attributes (except during distinct rainfall events, when this pattern reversed). The results presented here should improve understanding of spatio-temporal variations in soil moisture profiles in well-developed gullies in the Loess Plateau, and potentially elsewhere.     

Evaluating gully erosion using Cs and Pb/Cs ratio in a reservoir catchment

Water erosion in the hilly areas of west China is the main process contributing to the overall sediment of the Yellow River and the Yangtze River. The impact of gully erosion in total sediment output has been mostly neglected. Our objective was to assess the sediment production and sediment sources at both the hillslope and catchment scales in the Yangjuangou reservoir catchment of the Chinese Loess Plateau, northwest China. Distribution patterns in sediment production caused by water erosion on hills and gully slopes under different land use types were assessed using the fallout ¹³⁷Cs technique. The total sediment production from the catchment was estimated by using the sediment record in a reservoir. Sediment sources and dominant water erosion processes were determined by comparing ¹³⁷Cs activities and ²¹⁰Pb/¹³⁷Cs ratios in surface soils and sub-surface soils with those of sediment deposits from the reservoir at the outlet of the catchment. Results indicated that landscape location had the most significant impact on sediment production for cultivated hillslopes, followed by the terraced hillslope, and the least for the vegetated hillslope. Sediment production increased in the following order: top>upper>lower>middle for the cultivated hillslope, and top>lower>upper>middle for the terraced hillslope. The mean value of sediment production declined by 49% for the terraced hillslope and by 80% for the vegetated hillslope compared with the cultivated hillslope. Vegetated gully slope reduced the sediment production by 38% compared with the cultivated gully slope. These data demonstrate the effectiveness of terracing and perennial vegetation cover in controlling sediment delivery at a hillslope scale. Averaged ¹³⁷Cs activities and ²¹⁰Pb/¹³⁷Cs ratios in the 0–5 cm surface soil (2.22–4.70 Bq kg⁻¹ and 20.70–22.07, respectively) and in the 5–30 cm subsoil (2.60 Bq kg⁻¹ and 28.57, respectively) on the cultivated hills and gully slopes were close to those of the deposited sediment in the reservoir (3.37 Bq kg⁻¹ and 29.08, respectively). These results suggest that the main sediment sources in the catchment were from the surface soil and subsoil on the cultivated slopes, and that gully erosion is the dominant water erosion process contributing sediment in the study area. Changes in land use types can greatly affect sediment production from gully erosion. An increase in grassland and forestland by 42%, and a corresponding decrease in farmland by 46%, reduced sediment production by 31% in the catchment.     

A multi-scale approach of runoff generation in a Sahelian gully catchment: a case study in Niger

Runoff production conditions in a small gully catchment are studied at four different scales: the point scale (0.001 m²), the local scale (1 m²), the field scale (of the order of 100 m²) and the catchment scale (0.2 km²). At the point scale, infiltration measurements were conducted using a tension infiltrometer. At the local and the field scale, runoff plots were setup on typical soil surface conditions of the catchment (plateau bare soil, hillslope bare soil and fallow grassland). At the catchment scale, stream discharges were measured at two gauging stations.The overland flow yield is significantly nonuniform in space, due to the high spatial variability of infiltration capacities and the depressional storage of the soil surface. The runoff and the infiltration data collected confirmed the major role played by soil crusting on runoff generation in that part of Sahel. At the point scale, hydraulic conductivity measurements have shown that infiltration and runoff were driven by the hydraulic properties of the crust. At the field scale, microtopography and heterogeneity in the soil surface crusting decreased discharge volumes. The influence of vegetation growth on runoff yield was evident in the case of the fallow sites. Analysis of discharge data at the catchment scale highlights that infiltration through the bottom of the gully between two gauging stations leads to considerable runoff water transmission losses.     

Study of ephemeral gully erosion in a small upland catchment on the Inner-Mongolian Plateau

Ephemeral gully erosion is an important soil erosion process on the Inner-Mongolia Plateau in North China, and although its damage is very intense, little research on the area has been published. In this paper, a global positioning system (GPS) is used to measure the morphology of ephemeral gullies in a small catchment, the Inner-Mongolia Autonomous Region. First, this paper presents the characteristics of ephemeral gullies and soil loss due to ephemeral gully erosion. The network of ephemeral gullies takes on the shapes of tree branches, and there are 16 hole-ephemeral gullies in the middle of the ephemeral gullies. An average gully length of about 19.6 m ha⁻¹ and an average soil loss of 8.8 m³ ha⁻¹ due to ephemeral gully erosion were measured. Second, soil erosion influences crop production in cropland and combinations of vegetation in fallow. The difference between vegetation in the middle of ephemeral gullies and in other places is very obvious. Third, this paper discusses hole-ephemeral gullies that are holes locating in the middle of ephemeral gullies whose widths and depths are more than 0.5 m (Fig. 6) for the first time. The relationship between local hill slope gradient S (m m⁻¹) and upslope contributing area A (ha) can be expressed as S = 0.064A^−0.375 and may be a key indicator for determining the position of existing hole-ephemeral gully heads and for predicting where hole-ephemeral gullies could form in the small watershed on the Inner-Mongolian Plateau.     

黄土丘陵小流域蒸散发和水分平衡对植被恢复的影响

Evapotranspiration, soil moisture balance and the dynamics in a gully catchment of the Loess Plateau in China were determined with 6 land use treatments including natural grassland, shrubs （Caragana rnicrophylla）, two woodlands （Prunus armeniaca var. ansu and Pinus tabulaeformis）, cultivated fallow, and farmland （Triticum aestiuum L.） in order to obtain a better understanding of soil moisture balance principles and to improve vegetation restoration efficiency for ecological rebuilding on the plateau. Average runoff from cultivated fallow was very high, reaching 10.3% of the seasonal rainfall. Evapotranspiration under T. aestivurn was not significantly different from natural grasslands. Compared with natural grass, evapotranspiration was significantly greater （P 〈 0.05） in 2002 and there was an increase in soil moisture depleted in the 1-3 m soil under P. armeniaca, P. tabulaeformis and C. microphylla. During the two years of the study the average soil moisture （0-100 cm soil profile） of T. aestivurn was generally the highest, with P. armeniaca, P. tabulaeformis and C. rnicrophylla usually the lowest. Thus, according to the soil moisture balance principle for this area the planned reforestation project was not ecologically reasonable. Reducing human disturbance and restoration with grass could be more effective.     

Labile carbon limits in-stream mineralization in a subtropical headwater catchment affected by gully and channel erosion

Journal of Soils and Sediments - Gully and channel erosion are known to export large quantities of soil organic matter (SOM) to stream ecosystems. However, the implications for in-stream processing...     

Relationships between rainfall characteristics and ephemeral gully erosion in a cultivated catchment in Sicily (Italy)

Recent research has shown a lack of long-term monitoring for detailed analysis of gully erosion response to climate characteristics. Measures carried out from 1995 to 2007 in a wheat-cultivated area in Raddusa (Sicily, Italy), represent one of the longest series of field data on ephemeral gully, EG, erosion. The data set collected in a surface area of almost 80 ha, permits analysis of the influence of rainfall on EG formation and development. Ephemeral gullies formed in the study area were measured on a yearly scale with a Post-Processing Differential GPS for length and with a steel tape for the width and depth of transversal sections. Ephemeral gully formation was observed for 8 years out of 12, which corresponds to a return period of 1.5 years. The measurements show strong temporal variability in EG erosion, in agreement with the rainfall characteristics. The total eroded volumes ranged between 0 and ca. 800 m³ year⁻¹, with a mean of ca. 420 m³ year⁻¹, corresponding to ca. 0.6 kg m⁻² year⁻¹. Ephemeral gully erosion in the study area is directly and mainly controlled by rainfall events. An antecedent rainfall index, the maximum value of 3-days rainfall (H_max3_d), is the rain parameter which best accounts for EG erosion. This index is used here as a simple surrogate for soil water content. An H_max3_d threshold of 51 mm was observed for EG formation. The return period of the H_max3_d threshold is almost the same as the return period for EG formation. Although a mean of seven erosive rain events were recorded in a year, EG formation and development generally occur during a single erosive event, similarly to other semiarid environments. The most critical period is that comprised between October and January, when the soil is wetter and the vegetation cover is scarce. Empirical models for EG eroded volume estimation were obtained using the data set collected at this site. A simple power-type equation is proposed to estimate the eroded volumes using H_max3_d as an independent variable. This equation shows an R² equal to 0.67 and a standard error of estimation of 0.79.     

Field-scale spatial variability of soil calcium in a semi-arid region: Implications for soil erosion and site-specific management

Excess calcium(Ca) in soils of semi-arid and arid regions has negative effects on soil structure and chemical properties, which limits the crop root growth as well as the availability of soil water and nutrients. Quantifying the spatial variability of soil Ca contents may reveal factors influencing soil erosion and provide a basis for site-specific soil and crop management in semi-arid regions. This study sought to assess the spatial variability of soil Ca in relation to topography, hydraulic attributes, and soil types for precision soil and crop management in a 194-ha production field in the Southern High Plains of Texas,USA. Soils at four depth increments(0–2, 0–15, 15–30, and 30–60 cm) were sampled at 232 points in the spring of 2017. The Ca content of each sample was determined with a DP-6000 Delta Premium portable X-ray fluorescence(PXRF) spectrometer. Elevation data was obtained using a real-time kinematic GPS receiver with centimeter-level accuracy. A digital elevation model(DEM) was derived from the elevation data, and topographic and hydraulic attributes were generated from this DEM. A generalized least-squares model was then developed to assess the relationship between soil Ca contents of the four layers and the topographic and hydraulic attributes. Results showed that topographic attributes, especially slope and elevation, had a significant effect on soil Ca content at different depths(P 0.01). In addition, hydraulic attributes, especially flow length and sediment transport index(STI), had a significant effect on the spatial distribution of soil Ca. Spatial variability of soil Ca and its relationships with topographic and hydraulic attributes and soil types indicated that surface soil loss may occur due to water or wind erosion, especially on susceptible soils with high slopes. Therefore, this study suggests that the application of PXRF in assessing soil Ca content can potentially facilitate a new method for soil erosion evaluation in semi-arid lands. The results of this study provide valuable information for site-specific soil conservation and crop management.     

集水区耕作对干热河谷冲沟沟头溯源侵蚀过程的影响

随着气候变化与人类活动的加剧,中国干旱频繁发生且影响不断加剧,探索干旱对植被生长的影响对研究生态系统如何应对干旱具有重要意义。基于中国1982-2015年改进帕尔默干旱指数（scPDSI）与归一化植被指数（NDVI）数据,分析植被对干旱的响应规律及敏感性。结果表明：1）在中国西北地区、内蒙古地区、东部地区及青藏高原南部地区,短滞时（1-3月）scPDSI与NDVI的相关性较大（Rmax>0.4）,南方湿润地区降水充沛,植被对干旱的响应不敏感（Rmax<0.3）,其生长主要受能量因素控制;2）年均水分盈亏量、降水量、日照时数和气温对植被与干旱的关系影响较大,其中年均水分盈亏量是主要控制因子;3）不同植被类型对干旱的敏感性有较大差异,敏感排序为草地>林地>耕地。研究结果可为中国不同区域干旱对植被生长影响评估提供科学依据。     

上方来水来沙对浅沟侵蚀产沙及水动力参数的影响

 浅沟侵蚀是黄土高原重要的侵蚀类型,上方汇水对坡面浅沟侵蚀具有重要的影响。采用野外放水冲刷试验,定量分析26°坡耕地在上方来水量为5、10和15L/min时对坡下方浅沟侵蚀产沙及其水动力参数的影响。结果表明：上方来水的汇入使浅沟水流流速明显增大,雷诺数、弗劳德数、水流功率和剪切力分别增大33%～76%、21%～47%、29%～72%和18%～42%,阻力系数减少11%～13%,导致浅沟侵蚀产沙量明显增大;除流速和弗劳德数外,其余水动力参数随放水时间的延长呈递增趋势;上方来水使浅沟侵蚀产沙量相对增量与水流功率和剪切力相对增量均呈幂函数关系。     

Assessment of land management practices on soil erosion using SWAT model in a Tunisian semi-arid catchment

Journal of Soils and Sediments - Soil erosion is a widespread problem that has threatened the majority of Mediterranean countries. Land management practices are widely used to minimize runoff and...     

Soil management for Alfisols in the semiarid tropics: erosion, enrichment ratios and runoff

Abstract. Continuous cultivation of soils of the semiarid tropics has led to significant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Alfisol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sediment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha^–1, but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha^–1 and 178 kg C ha^–1 being lost in sediment. Up to an extra 250 mm of water per year infiltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms.     

Analysis of the influence of gully erosion in the flow pattern of catchment streams, Southeastern Brazil

The baseflow of tributaries to the Velhas River in the northwest region of Ouro Preto County (São Francisco Basin, Brazil) has been declining in the last years, without a simultaneous decrease in the water input. This can only be attributed to badly planned human activities, which result in soil crusting or compaction, erosion, among other types of impact, such as groundwater overexploitation and wetland drainage. Almost all of the study area has been eroded by hundreds of large-size gullies. In order to analyze the influence of erosion in the hydrological behavior of small streams, two similar and contiguous catchments were selected. The only remarkable difference between them is a gully that occupies circa 42% of one of the catchments (“eroded catchment”). Rainfall, flow rates and chemical data were obtained throughout a hydrological year and the results showed that the eroded catchment presented smaller baseflow rates and bigger but short-lived stormflows. This contrasting flow regime is attributed to the gully, which is causing the partial withdraw of the regolith and the exposure of weathered rock. As the regolith has smaller hydraulic conductivities and higher storage coefficients, the exposure of weathered rock on the gully floor explains the odd flow behavior of the eroded catchment. Other studies in the same region confirm the impact caused by the gullies. Thus, the superposition of many gullies can cause decrease of the baseflow and increase of the stormflow. As gullies are very common erosion features in Brazil, they should be much more studied in order to better understand this and other similar types of environmental impact.     

Soil erosion and runoff in different vegetation patches from semiarid Central Mexico

Vegetation patches in arid and semiarid areas are important in the regulation of surface hydrological processes. Canopy and ground covers developed in these fertility islands are a natural cushion against the impact energy of rainfall. Also, greater levels of organic matter improve the soil physicochemical properties, promoting infiltration and reducing runoff and soil erosion in comparison with the open spaces between them. During the 2006 rainy season, four USLE-type plots were installed around representative vegetation patches with predominant individual species of Huisache (Acacia sp), Mesquite (Prosopis sp), Prickly Pear or Nopal (Opuntia sp) and Cardon (Opuntia imbricata), to evaluate soil erosion and runoff, in semiarid Central Mexico. A comparative bare surface condition (Control) was also evaluated. Vegetative canopy and ground cover were computed using digital images. Selected soil parameters were determined. Soil erosion was different for the studied vegetation conditions, decreasing as canopy and ground cover increased. There were not significant differences in runoff and soil erosion between the Control and O.imbricata surfaces. Runoff was reduced by 87%, 87% and 98% and soil loss by 97%, 93%, and 99% for Acacia farnesiana, Prosopis laevigata and Opuntia sp, respectively, as compared to the Control. Soil surface physical conditions were different between the low vegetation cover conditions (Control and O.imbricata surfaces) and the greater vegetation cover conditions (A.farnesiana, P.laevigata and Opuntia sp), indicating a positive effect of vegetation patches on the regulation of surface hydrological processes.     

Soil erosion and runoff: The need to rethink mitigation strategies for sustainable agricultural landscapes in western Europe

Agricultural landscapes that are intensively farmed, as in western Europe, face the challenge of a transition to more sustainable systems. Although erosion rates are relatively low in western Europe, the agricultural landscape is confronted by the need to mitigate the off-site impacts of erosion. An important challenge is that of disrupting connectivity between runoff and sediment sources, often farmers' fields, and freshwater systems or local communities. Mitigation strategies should include monitoring of erosion rates and off-site impacts and a mix of engineered and alternative measures such as buffer strips and retention ponds. Also needed are supportive government policies and actions including awareness of institutional memory problems and the promotion of farmer education. For the future, the risk of climate change must be appreciated and built into the planning of comprehensive mitigation strategies. Our perspective is that the overall aim should be a ‘sustainable agricultural landscape’ and not simply a reduction of erosion and runoff on farmers' fields.     

Soil penetrometer resistance spatial variability in a Ferralsol at several soil moisture conditions

The penetrometer resistance (PR) spatial variability in a Ferralsol under different soil moisture conditions was characterized through statistical and geostatistical methods. PR measurements were made in a 10-row, 10-columns, 3-m spacing grid at 20–30 cm depth using a hand-pushing penetrometer. Measurements were made for dry soil conditions (before irrigation) as well as 2 and 24 h after irrigation. The soil bulk density (BD) and the relative topographical altitudes (RT) were measured at the same locations. The PR spatial variability is normally distributed for dry soil conditions and after irrigation-water redistribution. A normal distribution fits also to the BD spatial variability. PR mean and coefficients of variations are lower for wet soil conditions and vary notably according to the soil moisture condition. The PR semivariance values are much higher for dry soil conditions than those found for wet soil conditions. However, the semivariogram of PR before irrigation shows almost a pure nugget effect. Irrigation yields a spatial structure in PR measurements. Despite the differences in the shown spatial structure, the range of the PR semivariograms before and 24 h after irrigation is about 8–10 m, which is very similar to the range of the BD semivariogram. The correlation coefficients between PR and the other measured variables are very small before and after irrigation, which could lead to the conclusion that those variables are not related at all. However, according to the co-dispersion coefficients plotted as a function of the separation lag, the correlation between those variables changes according to the separation distance. Particularly, PR and the RT show correlation 24 h after irrigation only for lags between 5 and 12 m. The results pointed out that PR spatial variability depends on soil moisture condition, soil BD and on several local features as microtopography.     

黄土高原风蚀水蚀交错带沟岸对柠条林地土壤水分的影响

The most serious erosion on the Loess Plateau of China exists in the wind-water erosion crisscross region where the annual precipitation is about 400 mm, the ecological environment is very fragile, and water is the key limiting factor for improving the environment. In this study, changes of soil moisture content for Caragana korshinskii Kom. shrubland in the gully bank of the Loess Plateau were studied using the methods of soil sampling and neutron probe. A typical gully （75 m long, 28 m wide, and 10 m deep） was selected, and six neutron probe access tubes （6 m long） were installed at points 50, 100, 200, 300, 400, and 500 cm from the gully border for obtaining soil moisture data from July to October 2004 at approximately 10 d intervals. Soil samplings were simultaneously carried out for moisture determination at the six points. Results showed that the soil moisture of the shrubland in the gully bank significantly varied between 300 and 400 cm in the horizontal direction and up to 600 cm in vertical direction of the gully. Seasonal changes in soil moisture revealed a curve with a single peak that occurred at the end of August or early September. A linear regression equation was fit for soil water storage and the distance from the gully border, with coefficients depending on rainfall characteristics, sampling point, and time of measurement.     

黄土丘陵沟壑区鱼鳞坑雨季土壤水分状况

在黄土高原半干旱地区,降水是限制植被生长的主要限制因子。鱼鳞坑作为一种集水措施在人工造林中被普及推广。为研究鱼鳞坑雨季的集水功能,对样地鱼鳞坑内部、上部及侧面坡面典型部位的土壤水分进行了连续性监测,结果显示：7—8月,鱼鳞坑内的平均土壤含水量维持在低于鱼鳞坑外部坡面的水平;鱼鳞坑内20～40 cm土层是土壤水分的主要利用层,鱼鳞坑的集雨效果表现在40～60 cm土层上;单个鱼鳞坑的集雨效果存在差异性,这种差异性主要表现在有径流产生的降雨期。单个鱼鳞坑的集雨效果受鱼鳞坑的布置模式、施工工艺等因素的影响。