Soil erosion dynamics response to landscape pattern

Simulating soil erosion variation with a temporal land use database reveals long-term fluctuations in landscape patterns, as well as priority needs for soil erosion conservation. The application of a multi-year land use database in support of a Soil Water Assessment Tool (SWAT) led to an accurate assessment, from 1977 to 2006, of erosion in the upper watershed of the Yellow River. At same time, the impacts of land use and landscape service features on soil erosion load were assessed. A series of supervised land use classifications of Landsat images characterized variations in land use and landscape patterns over three decades. The SWAT database was constructed with soil properties, climate and elevation data. Using water flow and sand density data as parameters, regional soil erosion load was simulated. A numerical statistical model was used to relate soil erosion to land use and landscape. The results indicated that decadal decrease of grassland areas did not pose a significant threat to soil erosion, while the continual increase of bare land, water area and farmland increased soil erosion. Regional landscape variation also had a strong relationship with erosion. Patch level landscape analyses demonstrated that larger water area led to more soil erosion. The patch correlation indicated that contagious grassland patches reduced soil erosion yield. The increased grassland patches led to more patch edges, in turn increasing the sediment transportation from the patch edges. The findings increase understanding of the temporal variation in soil erosion processes, which is the basis for preventing local pollution.     

Soil erosion susceptibility of Johor River basin

Malaysia is undergoing tremendous environmental changes due to population growth, economic development and urbanization. This has stimulated a rapid land use changes which in turn has increased the rate of soil erosion and river sedimentation. In this study, Universal Soil Loss Equation (USLE) and the Modified Universal Soil Loss Equation (MUSLE) are applied within a geographical information system (GIS) to assess the spatial pattern of soil erosion susceptibility of Johor River basin, Malaysia. Geomorphological, landuse and soil information along with other hydrological data such as, annual peak flow and runoff volumes are used to estimate the parameters required for the calculation of soil erosion susceptibility. The results show that annual erosion rate varies between 0.2 and 248.2 t/ha/year according to USLE, and between 19.2 and 2179.9 thousand tons per event according to MUSLE. The land cover management is found as the major factor responsible for soil erosion in the basin.     

Spatial and inter-annual variability of specific sediment yield: case of hillside reservoirs in Central Tunisia

Water erosion is the major process responsible for soil loss in Central Tunisia. It represents a main risk of sedimentation which threatens the lifetime of water and soil conservation works in the region, such as hillside reservoirs. This paper focuses on the study of spatial and inter-annual variability of specific sediment yield (SSY) estimated from sediment yield (SY) of 23 small watersheds of hill reservoirs located in the Tunisian Dorsal and the Cap Bon regions. The calculated values of mean inter-annual specific sediment yield varied from 180 to 3298 t/km²/year, over a period of 12 years (from 1994 to 2006). The selected catchments were classified into three groups according to their SSY data. The SSY map, elaborated with a geographical information system (GIS), showed an important spatial variability between watersheds of the same group. Moreover, analyses of the coefficient of variation (CV) showed that 70% of the considered sites demonstrate a tendency to moderate and high inter-annual variability of SSY. In order to identify the principal factors governing variability of erosion and sedimentation, a multiple regression analysis was carried out using nine parameters characterizing morphology, topography, land cover, climate and protection works of the 23 considered sites. The generated model revealed that 85% of SSY variability is correlated to seven principal factors, which are drainage area (A), rainfall intensity recorded in 30 min (I ₃₀), percentage of water and soil conservation works, percentage of clay and carbonate in soils, vegetation land cover, overall slope index (I _G) and rainfall amount (R _a). The obtained SSY results were compared to others cited in a large bibliographical synthesis of studies carried out at the planet scale. We deduced that the SSY values obtained in this study are among the relatively high series in the world. The high variability of specific erosion rates in Central Tunisia is believed to be related to the semi-arid climate, characterized by the irregularity and the severity of storms and the spatial and temporal variability of other multiple factors affecting erosion processes.     

Assessing the impact of land cover changes on water balance components of White Volta Basin in West Africa

Land use and land cover (LULC) have been and still changing, through human activities, creating variability in hydrological cycle. This paper investigates the hydrological impacts of LULC changes on water balance in the White Volta Basin located in the West of Africa using the Soil and Water Assessment Tool (SWAT). Two LULC data for 1990 and 2006 and two plausible scenarios of land use change were evaluated. Results show a link between land cover and the hydrologic response with a decrease in land cover corresponding to decrease in surface water and base flow and increase evapotranspiration (ET). The results indicated that different LULC contributed to various effects in annual water yield and ET. The results also indicate the capability of the SWAT model to be used in the West African subregion even though there are data limitations associated with the model in West Africa. Overall, the model results support the existing efforts of Volta Basin water resource managers to protect the area along the Volta river against farming and indicate that additional emphasis should be placed on improving land management practices.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

Soil erosion by rainfall and runoff—state of the art

The processes of soil detachment and sediment transport by rainfall and overland flow and resulting sediment transport are described. The results of past research on the role of raindrop impact in detaching soil, experimental studies of erosion, and erosion modelling are presented. Studies of soil loss from experimental field plots led to the development of the Universal Soil Loss Equation and to its subsequent modification for use in quantifying erosion by individual storms. Systems to produce rainfall for erosion studies in the laboratory are described. A system which is currently being calibrated and used for erosion control system testing at Drexel University's Geosynthetic Research Institute (GRI) is described. Preliminary spatial rainfall distributions and runoff measurements are presented. Experimental results obtained by others on the performance of natural and geosynthetic erosion control systems are discussed along with a proposed experimental program for the GRI system.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

地表温度与植被指数相关性的空间尺度特征——以重庆市为例

为了揭示植被改善城市热岛的量化关系,以重庆市主城区为例,在不同的尺度上分析了地表温度与归一化植被指数之间的相关性,分别从全局和局部出发分析了两者之间的线性关系.结果发现,在120m尺度上两者之间的相关性最强,空间相关场表明相关性在空间上呈现较强的异质性;全局普通线性回归和地理加权回归分析发现,两者之间没有显著的线性关系,这说明可能还存在其他多种因素的复杂影响.     

Estimating sediment yield from a forest road network by using a sediment prediction model and GIS techniques

In forest lands, the stream channels receive the highest amount of sediment during road construction activities due to removal of vegetation cover from road surface, cut-slope, fill-slope, and ditch areas. Sediment delivered from a road section to streams causes serious damages on water resources and aquatic life. Performing revegetation in cut-slope and fill-slope reduce sediment yield from a road section; however, road surface and ditch continue to deliver considerable amount of sediment to the streams. Therefore, accurate prediction of sediment yield from existing road network can be very critical. In order to estimate average sediment yield, several sediment prediction models have been developed based on empirical relationships between various road erosion factors. In this study, average annual sediment yield from a road network to streams in a forest watershed was estimated by using the methodology of a GIS-based sediment prediction model, the SEDMODL model. GIS techniques were used to provide required data layers such as topography, streams, roads, geology, and average precipitation. The results indicated that the SEDMODL model integrated with GIS techniques can assist road managers to estimate total sediment yield quickly and effectively. Besides, critical road sections with high sediment yield potential can be identified and the efficiencies of various sediment control measures can be evaluated for these sections.     

Effect of different land use on soil erosion in the pre-alpine fringe (North-East Italy): Ion budget and sediment yield

Data concerning ion budget from rainfall, runoff and soil loss measurements from two experimental plots located in North-East Italy, under different land cover (beech forest and vineyard, respectively), are reported. The chemical composition of rainfall, soil solution and runoff was determined to study the solute cycle within the soil, and the relationships between water, soil and vegetation. The forest ecosystem is more prone to acidification than the agricultural one; the elemental concentration of runoff water is considerably lower than that of soil solution. Comparing the ion input (rainfall) and output (runoff) at the two sites, it was possible to estimate the ion budget in the two soil-vegetation systems. The runoff amount and the ion balance are related to rainfall volumes and composition; the measured runoff under vineyard is 59% in comparison to the one under beech. The soil loss at the two experimental sites (170 kg/ha and 132 kg/ha, respectively) is quite limited. The measured sediment yield of the two catchments (0.24-0.19 t/ha/year, respectively) is consistent with data reported for native forests of western Europe. Comparing rainfall and soil loss at the two sites proved that maintenance of some form of land cover is advisable if runoff and erosion are to be minimized. In the European context, where the most important consequences of erosion are sedimentation downstream and loss of productivity, this type of data will yield valuable information for the understanding of such processes occurring at catchment scale, and will help policy-makers develop appropriate programs for the territory safeguard.     

Relative influence of wildfire on soil properties and erosion processes in different Mediterranean environments in NE Spain

Abandonment of terraced soils and increased brushland cover has increased wildfire occurrence to almost an annual rate in the Cap de Creus Peninsula, NE Pyrenees Range, Province of Girona, Spain. A wildfire occurred in August 2000 and affected an area of 6760 ha of shrubs and cork trees, whereas still cultivated plots were only slightly affected. Five stations of erosion measurements, corresponding to five different environments (from present cultivation to late abandonment) were destroyed by the passage of fire, and were promptly replaced to allow to monitoring post-fire effects on soil erosion. Selected soil properties were determined monthly before the fire and during 6 months after the fire at a monthly rate. Runoff and sediment yield together with dissolved organic carbon (DOC) in runoff water and organic carbon losses in eroded sediments (EOC) were evaluated throughout 2000. The last stage of abandonment, stands of cork trees, had the highest soil stability. Nevertheless, evidence of unfavourable soil conditions was detected at the shrub stage, when Cistus monspeliensis cover was the dominant opportunistic plant. This stage was considered to be a critical threshold leading either to degradation or regeneration processes according to fire frequency. A drastic change in soil properties, erosion and nutrient depletion occurred after the fire in all the environments. Statistics enabled to state that environments differed significantly in main soil properties. By statistically comparing the measured variables between the environments before and after the fire, DOC was found to be the soil parameter showing the highest significance between environments. Absolute values of erosion were low with respect to other Mediterranean environments although the shallow nature of these soils might deserve special attention because of a comparatively higher risk of degradation.     

Total sediment transport by the rivers of Abruzzi (Central Italy): prediction with the RAIZAL model

As sediment transport is mainly correlated with accelerated soil erosion, the study attempted to quantify the sediment transport by relying on qualitative classes of soil erosion risk. The classes were obtained by applying a modified RAIZAL model (MICROLEIS software package) to the most representative catchment basins of the Abruzzi area (Central Italy). They are characterized by eight homogeneous lithological groups (terrigenous and carbonatic units). Each lithological group is related to specific types of morphology, soil and land use. The estimates of total sediment transport obtained using the modified RAIZAL Codex were in good agreement with those measured or estimated by other methods, suggesting that the use of this Codex would be a valid alternative. Electronic Publication     

Parameter uncertainty analysis of non-point source pollution from different land use types

Land use type is one of the most important factors that affect the uncertainty in non-point source (NPS) pollution simulation. In this study, seventeen sensitive parameters were screened from the Soil and Water Assessment Tool (SWAT) model for parameter uncertainty analysis for different land use types in the Daning River Watershed of the Three Gorges Reservoir area, China. First-Order Error Analysis (FOEA) method was adopted to analyze the effect of parameter uncertainty on model outputs under three types of land use, namely, plantation, forest and grassland. The model outputs selected in this study consisted of runoff, sediment yield, organic nitrogen (N), and total phosphorus (TP). The results indicated that the uncertainty conferred by the parameters differed among the three land use types. In forest and grassland, the parameter uncertainty in NPS pollution was primarily associated with runoff processes, but in plantation, the main uncertain parameters were related to runoff process and soil properties. Taken together, the study suggested that adjusting the structure of land use and controlling fertilizer use are helpful methods to control the NPS pollution in the Daning River Watershed.     

Modeling effectiveness of agricultural BMPs to reduce sediment load and organophosphate pesticides in surface runoff

Quantifying effectiveness of agricultural BMPs at the watershed scale is a challenging issue, requiring robust algorithms to simulate not only the agricultural production system but also pollutant transport and fate. This research addresses the challenge to simulate performances of BMPs in reducing organophosphates (OPs) runoff at the watershed scale. The SWAT model is calibrated and validated following a sensitivity analysis combining Latin Hypercube sampling and One-factor-At-a-Time simulation. The calibrated model is then applied in the Orestimba Creek Watershed to simulate BMPs including buffer strips, sediment ponds, vegetated ditches, use reduction, and their combinations. BMP simulation suggested that sediment ponds trap 54-85% of sediment from field runoff, but less than 10% of dissolved diazinon and chlorpyrifos. Use reduction can reduce pesticide load in a close-to-linear fashion. Effectiveness of vegetated ditches and buffers depends on their physical dimension and vegetation cover. Combining individual BMPs provides enhanced mitigation effects. The combination of vegetated ditches, buffer strips and use reduction decreases diazinon and chlorpyrifos load by over 94%. This study has suggested that the SWAT model reasonably predicts BMP effectiveness at the watershed scale. Results will assist decision making in implementing BMPs to reduce pesticide loads in surface runoff.     

GIS的嘉陵江流域吸附态氮磷污染负荷研究

以美国通用土壤流失方程为基础,根据研究流域的特征和已有的研究成果确定方程中的因子算式,在地理信息系统GIS支持下,估算了各单元的土壤流失量,应用吸附态非点源污染负荷模型,对嘉陵江流域吸附态氮磷污染负荷进行了数值模拟与定量分析。结果表明:嘉陵江流域近年平均输沙模数为161.94 t/(km2.a),北碚出口吸附态氮磷污染负荷分别为29620.8 t/a和1391.96 t/a,吸附态氮磷流失较严重的地区主要分布在白龙江和西汉水流域,各土地利用类型吸附态氮磷流失模数大小顺序依次为:荒地>灌木>草地>农田>城镇>林地。     

Sediment yield as a desertification risk indicator

Soil erosion is often regarded as one of the main processes of desertification. This has led to the use of various desertification indicators that are related to soil erosion. Most of these indicators focus, however, on small spatial units, while little attention has been given to the amount of sediment exported at the catchment scale. Such a small spatial unit approach neglects the transfer of sediment through catchments as well as the scale-dependency of erosion processes. Furthermore, this approach does not consider important off-site impacts of soil erosion, such as sediment deposition in reservoirs, flooding as well as ecological impacts.This study aims to illustrate the importance of also considering catchment sediment yield (SY, t km^− 2 y^− 1) in desertification assessment studies. Based on recently established databases of SY and soil loss rates in Europe and examples from previous studies, we illustrate that soil erosion rates at the plot scale are not representative for catchment SY, as they are often several orders of magnitude smaller. Also, the erosion response of catchments to changes in land use or climate often differs strongly from responses to those changes at the plot scale. We further discuss several of the impacts of SY and their link with desertification: i.e. the sedimentation of reservoirs, problems related to flooding, catchment hydrology, export of nutrients and ecological implications.Using earlier established criteria we evaluate the potential for using catchment SY as a desertification indicator and conclude that this could give an important added value to desertification studies. SY, used in combination with other indicators, allows the identification of other sediment sources than those considered at the plot scale and can reflect the results of desertification processes over longer time periods than periods over which assessments at the plot scale have been made. We argue therefore, that SY is a strong complementary indicator of desertification providing valuable information on the catchment response to changes in drivers of desertification.     

Effect of visitors’ pressure on soil and vegetation in several different micro-environments in urban parks in Tel Aviv

The effect of the pressure imposed by visitors on urban soil and herbaceous vegetation was investigated in seven micro-environments in parks in Tel Aviv. Soil properties (organic matter content, soil moisture, soil surface compaction/penetration depth), litter biomass, and herbaceous vegetation characteristics (vegetation cover, number of species, height) were determined in seven micro-environments: oak and pine trees, each under high and under low visitors’ pressure; a herbaceous area without visitors’ pressure; paths; and a resting area. Soil samples were collected from the upper 0–5 cm soil depth. In addition, in the tree micro-environments soil samples were taken at 0.5, 1, 2, and 3 m from the tree trunk. Averages and variances of soil properties and the vegetation characteristics varied among the various micro-environments and according to visitors’ pressure. Soil organic matter and soil moisture contents were significantly higher under oak trees with low visitors’ pressure than in other micro-environments. Litter biomass and penetration depth significantly decreased with increasing visitors’ pressure under pine and, especially, oak. The vegetation cover, number of species, and height of herbaceous vegetation were greatest in the herbaceous area, lower under with the trees where there was high visitors’ pressure and lowest in paths and resting areas. Thus, the soil properties in the oak micro-environment and the vegetation characteristics in the herbaceous area were the most sensitive to visitors’ pressure. For each tree and open area, increasing visitors’ pressure was accompanied by increasing spatial homogeneity of soil and vegetation. A radial spatial pattern of soil properties developed under oak with low visitors’ pressure.     

Research progress on the watershed sediment delivery ratio

The watershed sediment delivery ratio (SDR) reflects the transport status of eroded soil in a watershed, and it is an important parameter in studying the relationship between basin erosion and sediment yield of rivers. This review study mainly focuses on China. Based on existing studies of the SDR, this study reviews and summarizes the definition, functions, influencing factors, and estimation methods, research suggestions and prospects of SDR. Results indicate that there are some differences in understanding the connotation of SDR. Influencing factors are extremely complex and can be attributed to both natural and anthropogenic factors. Estimation methods are various and can be summarized as one-factor, two-factor and multi-factor types. Most estimation methods are empirical regression equations based on hydrological data from specific watersheds and far from universal. Regional SDR modelling is still an important research tool for understanding watershed sediment transport in the future.     

Changes in land cover and vegetation carbon stocks in Andalusia, Southern Spain (1956-2007)

Land use has significantly changed during the recent decades at global and local scale, while the importance of ecosystems as sources/sinks of C has been highlighted, emphasizing the global impact of land use changes. Land use changes can increase C loss rates which are extremely difficult to reverse, in the short term, opposite to organic carbon (OC) which accumulates in soil in the long-term. The aim of this research is to improve and test methodologies to assess land cover change (LCC) dynamics and temporal and spatial variability in C stored in vegetation at a wide scale. LCCs between 1956 and 2007 in Andalusia (Southern Spain) were selected for this pilot study, assessed by comparison of spatial data from 1956 to 2007 and were reclassified following land cover flows (LCFs) reported in major areas in Europe. Carbon vegetation densities were related to land cover, and C vegetation stocks for 1956 and 2007 were calculated by multiplying C density for each land cover class with land cover areas. The study area has supported important changes during the studied period with significant consequences for vegetation C stocks, mainly due to afforestation and intensification of agriculture, resulting in a total vegetation C stock of 156.08 Tg in 2007, with an increase of 17.24 Tg since 1956. This study demonstrates the importance of LCC for C sequestration in vegetation from Mediterranean areas, highlighting possible directions for management policies in order to mitigate climate change as well as promoting land conservation. The methodologies and information generated in this project will be a useful basis for designing land management strategies helpful for decision makers.     

汾河水库上游流域产沙分析

根据汾河水库上游流域的地形地貌和土壤类型,从三个方面分析了汾河上游流域的土壤侵蚀情况,认为黄土丘陵沟壑是主要的产沙区,并提出了雨洪过程相应的含沙量过程的计算方法,为含沙量资料缺乏地区提供了参考依据。