Comparison of the Suspended Sediment Dynamics in Two Loess Plateau Catchments,China

Changes in runoff and sediment loads are of great importance for the management of river basins and the implementation of soil and water conservation measures. This study compared the suspended sediment dynamics in the Huangfuchuan and Yanhe catchments on the Loess Plateau. Both annual runoff and sediment load displayed significant reductions from 1955 to 2012. The decreasing rates were −0·88 mm a⁻¹ and −2·72 Mg ha⁻¹ a⁻¹ in the Huangfuchuan catchment, respectively, and ‐0.31 mm a⁻¹ and −1·20 Mg ha⁻¹ a⁻¹ in the Yanhe catchment. A total of 183 and 195 events, respectively, were selected to assess the suspended sediment dynamics in both catchments during the periods of 1971–1989 and 2006–2012. The results showed a good linear relationship between the sediment yield and runoff depth in both catchments from 1971 to 1989 and a relatively worse relationship in the Yanhe catchment from 2006 to 2012. The magnitude and frequency of the hyper‐concentrated sediment flow obviously decreased in the 2000s compared with that between 1971 and 1989. A hysteresis analysis suggested that complex and counter‐clockwise loops were the dominant patterns. Various soil and water conservation measures (e.g., afforestation, grassing, terraces, and check dams) played a critical role in runoff and sediment load changes in both catchments. The two catchments showed obvious heterogeneities in runoff and sediment yield because of different lithologies, soil types, and vegetation. The results of this study provide valuable information on suspended sediment dynamics and could be used to improve soil erosion control measures on the Loess Plateau. Copyright © 2016 John Wiley & Sons, Ltd.     

Reducing Sediment Connectivity Through man‐Made and Natural Sediment Sinks in the Minizr Catchment,Northwest Ethiopia

Man‐made and natural sediment sinks provide a practical means for reducing downstream reservoir sedimentation by decreasing soil erosion and enhancing the rate of sedimentation within a catchment. The Minizr catchment (20 km²) in the northwest Ethiopian highlands contains numerous man‐made soil and water conservation (SWC) structures such as soil bunds (Erken), fanya juu ridge (Cab) and micro‐trenches and natural sediment sinks such as wetlands, floodplains and grassed waterways. These sediment sinks reduce downstream sedimentation into the Koga reservoir, located at the catchment outlet, however, a large quantity of sediment is still reaching the reservoir. This study evaluates the function and effectiveness of both man‐made SWC structures and natural sediment sinks in reducing sediment export from the Minizr catchment. SWC structures and natural sediment sinks were digitized using Google Earth Imagery. Sediment pins and vertical sampling through the deposit were used to quantify the amount of deposited sediment. In addition, inflow and outflow of suspended sediment data were used to calculate the sediment‐trapping efficacies (STE) of man‐made SWC structures (soil bunds and fanya juu ridges) and natural sediment sinks. Results reveal that 144 km soil bunds and fanya juu ridges trapped 7,920 Mg y⁻¹ (55 kg m⁻¹ y⁻¹) and micro‐trenches trapped 13·26 Mg y⁻¹, each micro‐trench on average trapped 23 kg y⁻¹. The 17 ha floodplain located in the centre of the catchment trapped 9,970 Mg y⁻¹ (59 kg m⁻² y⁻¹), while a wetland with a surface area of 24 ha, located near the outlet of the catchment, trapped 8,715 Mg y⁻¹ (36 kg m⁻² y⁻¹). The STEs of soil bunds and fanya juu ridges, wetlands and floodplains were 54%, 85% and 77%, respectively. Substantial differences were observed between the STE of grassed and un‐grassed waterways at 75% and 21%, respectively. Existing man‐made and natural sediment sinks played an important role in trapping sediment, with 38% (26,600 Mg y⁻¹) of transported sediment being trapped, while 62% (43,000 Mg y⁻¹) is exported from the catchment and thus enters the Koga reservoir. Therefore, additional catchment treatment measures are required as an integrated catchment scale sediment trapping approach to help reduce sediment loads entering Koga reservoir. Moreover, to maximize the effectiveness of sediment trapping measures, avoid structural failure and ensure their sustainability, regular maintenance is needed. Copyright © 2016 John Wiley & Sons, Ltd.     

Validating the Use of 137Cs Measurements to Derive the Slope Component of the Sediment Budget of a Small Rangeland Catchment in Southern Italy

The sediment budget is a key concept and tool for characterizing the mobilization, transfer and storage of fine sediment within a catchment. Caesium‐137 measurements can provide valuable information on gross and net erosion rates associated with sheet and rill erosion that can be used to establish the slope component of a catchment sediment budget. However, there is a need to validate the use of ¹³⁷Cs measurements for this purpose, because their reliability has sometimes been questioned. The study reported focuses on a small (3·04 ha) steepland (mean slope 37%) catchment in Southern Italy. It exploits the availability of information on the medium‐term sediment output from the catchment provided by the construction of a reservoir at its outlet in 1978 and the existence of estimates of soil redistribution rates derived from ¹³⁷Cs measurements made on 68 replicate soil cores collected from the slopes of a substantial proportion of the catchment in 2001, to validate the use of ¹³⁷Cs measurements to construct the slope component of the catchment sediment budget. An additional 50 replicate soil cores were collected from the catchment slopes for ¹³⁷Cs analysis, to complement the data already available. Nine cores collected from the area occupied by the reservoir were used to estimate the mean annual sediment input to the reservoir. In the absence of evidence that the poorly developed channel system in the catchment was either a significant sediment source or sink, it was possible to directly compare the estimate of net soil loss from the catchment slopes (7·33 Mg ha⁻¹ y⁻¹) with the estimate of sediment output from the catchment provided by the reservoir deposits (7·52 Mg ha⁻¹ y⁻¹). Taking account of the uncertainties involved, the close agreement of the two values is seen as providing a convincing validation of the use of ¹³⁷Cs measurements to both estimate soil redistribution rates and as a basis for constructing the slope component of the sediment budget of a small catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil and Water Assessment Tool Soil Loss Simulation at the Sub‐Basin Scale in the Alt Penedès–Anoia Vineyard Region (Ne Spain) in the 2000s

This paper evaluates soil loss due to water erosion in an area of 32,362 ha with a predominant land use of vineyards (Alt Penedès–Anoia region, Catalonia, Spain). The Soil and Water Assessment Tool (SWAT) was used incorporating daily climatic data for the period 2000–2010 and also detailed soil and land use maps. Particular attention was given to the universal soil loss equation cover and management factor (C factor) of vineyards, with a minimum value of 0·15 being determined for this crop. The model was calibrated using daily flow data for the year 2010, which yielded satisfactory results. Even so, significant differences were obtained on days with high‐intensity rainfall events, when the model overestimated runoff and peak discharge. In these vineyards, the simulated average soil losses per sub‐basin ranged between 0·13 and 9·73 Mg ha⁻¹ y⁻¹, with maximum values of between 26·32 and 42·60 Mg ha⁻¹ y⁻¹ registered in fine‐loamy soils developed on unconsolidated Tertiary marls. Other findings were related to problems associated with SWAT calibration under Mediterranean conditions characterised by major climate variability and high‐intensity rainfall events. Copyright © 2013 John Wiley & Sons, Ltd.     

Soil Erosion in Steep Road Cut Slopes in Palencia (Spain)

Construction associated to land development, such as roads and railroads, promote severe land degradation. Cutslope sediment yield is one of the major pollutants on waters close to the road and railroad network. To estimate road impact, soil erosion (E), sediment yield (SY) and morphological evolution of a railroad cut in Palencia (Spain), were studied using erosion nails, during the periods 1998–1999, 1999–2000 and 2000–2010. Data from two sample plots were analyzed by an ANOVA for repeated measures. Slope morphological evolution was estimated using a cubic polynomial regression, while E and SY were calculated by integration. The top and the toe of the slope eroded and accumulated 0·5 m respectively, evolving into a concave/convex slope profile. The mean measured E was 220 Mg ha⁻¹ y⁻¹. SY was 31 Mg ha⁻¹ y⁻¹, ranging from 109 Mg ha⁻¹ y⁻¹ to 24 Mg ha⁻¹ y⁻¹. Sediment yield was 4·5 times higher during the first year, than in all subsequent years. Results showed a decreasing trend and a stabilization in E and SY rates. However, both rates remain high and critical over the analyzed time, with regards to soil formation, water protection, land degradation and infrastructure maintenance. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamics of Runoff and Suspended Sediment Transport in a Highly Erodible Catchment on the Chinese Loess Plateau

Runoff is the key factor to understand the land degradation causing high risk of soil erosion and can reduce the water available for human societies and ecosystems. The dynamics of runoff and suspended sediment transport are not completely understood. In this study, we examined the trends, breaking point and regime changes for the runoff and sediment load at different temporal scales using 50 years of continuous observational data from a highly erodible sub‐catchment with an area of 7,325 km² in the Beiluo River basin on the Loess Plateau, China. At the annual scale, the runoff and sediment load declined significantly (p < 0·05) with decreasing rates of −0·23 mm y⁻¹ and −164·9 Mg km⁻² y⁻¹, respectively. Abrupt changes in the runoff and sediment load series were detected between 1979 and 1999; thus, the data were divided into intervals of 1960–1979, 1980–1999 and 2000–2009. The flow duration curve analysis indicated increasing low‐flow values and decreasing daily runoff and sediment discharge peaks, which suggested that soil and water conservation measures reduced the volume of runoff and the sediment load. This led to a more uniform runoff regime. At the flood event scale, we investigated the relationship between runoff and the suspended sediment load based on 123 flood events, which showed clearly that the magnitude and frequency of hyper‐concentrated sediment flows decreased in 2000–2009 compared with 1960–1999. The annual erosive rainfall exhibited non‐significant changes throughout the entire study period. We conclude that soil and water conservation measures (e.g. afforestation, grassing, terraces and check dams) have played major roles in the changes in runoff and the sediment load in the Beiluo River catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil degradative effects of slope length and tillage methods on alfisols in Western Nigeria. I. Runoff,erosion and crop response

Field runoff plots were established in 1984 to evaluate the effects of slope length on runoff, soil erosion and crop yields on newly cleared land for four consecutive years (1984–1987) on an Alfisol at Ibadan, Nigeria. The experimental treatments involved six slope lengths (60 m to 10 m at 10-m increments) and two tillage methods (plough-based conventional tillage and a herbicide-based no-till method) of seedbed preparation. A uniform crop rotation of maize (Zea mays)/cowpeas (Vigna unguiculata) was adopted for all four years. An uncropped and ploughed plot of 25 m length was used as a control. The water runoff from the conventional tillage treatment was not significantly affected by slope length, but runoff from the no-till treatment significantly increased with a decrease in slope length. The average runoff from the no-till treatment was 1·85 per cent of rainfall for 60 m, 2·25 per cent for 40 m, 2·95 per cent for 30 m, 4·7 per cent for 20 m and 5·15 per cent for 10 m slope length. In contrast to runoff, soil erosion in the conventional tillage treatment decreased significantly with a decrease in slope length. For conventional tillage, the average soil erosion was 9·59 Mg ha⁻¹ for 60 m, 9·88 Mg ha⁻¹ for 50 m, 6·84 Mg ha⁻¹ for 40 m, 5·69 Mg ha⁻¹ for 30 m, 1·27 Mg ha⁻¹ for 20 m and 2·19 Mg ha⁻¹ for 10 m slope length. Because the no-till method was extremely effective in reducing soil erosion, there were no definite trends in erosion with regard to slope length. The average sediment load (erosion:runoff ratio) also decreased with a decrease in slope length from 66·3 kg ha⁻¹ mm⁻¹ for 60 m to 36·3 kg ha⁻¹ mm⁻¹ for 10 m slope length. The mean C factor (ratio of soil erosion from cropped land to uncropped control) also decreased with a decrease in slope length. Similarly, the erosion:crop yield ratio decreased with a decrease in slope length, and the relative decrease was more drastic in conventional tillage than in the no-till treatment. The slope length (L) and erosion relationship fits a polynomial function (Y=c+aL+bL²). Formulae are proposed for computing the optimum terrace spacing in relation to slope gradient and tillage method. © 1997 John Wiley & Sons, Ltd.     

Potential of mine land reclamation for soil organic carbon sequestration in Ohio

Soils are an effective sink for carbon storage and immobilization through biomass productivity and enhancement of soil organic carbon (SOC) pool. The SOC sink capacity depends on land use and management. Degraded lands lose large amounts of C through SOC decomposition, erosion, and leaching. Thus, restoration of disturbed and degraded mine lands can lead to increase in biomass productivity, improved soil quality and SOC enhancement and sequestration. Reclamation of mined lands is an aggrading process and offers significant potential to sequester C. A chronosequence study consisting of 0‐, 5‐, 10‐, 15‐, 20‐ and 25‐year‐old reclaimed mine soils in Ohio was initiated to assess the rate of C sequestration by pasture and forest establishment. Undisturbed pasture and forest were used as controls. The SOC pool of reclaimed pasture sites increased from 15·3 Mg ha⁻¹ to 44·4 Mg ha⁻¹ for 0–15 cm depth and from 10·8 Mg ha⁻¹ to 18·3 Mg ha⁻¹ for 15–30 cm depth over the period of 25 years. The SOC pool of reclaimed forest sites increased from 12·7 Mg ha⁻¹ to 45·3 Mg ha⁻¹ for 0–15 cm depth and from 9·1 Mg ha⁻¹ to 13·6 Mg ha⁻¹ for 15–30 cm depth over the same time period. The SOC pool of the pasture site stabilized earlier than that of the forest site which had not yet attained equilibrium. The SOC sequestered in 0–30 cm depth over 25 years was 36·7 Mg ha⁻¹ for pasture and 37·1 Mg ha⁻¹ for forest. Copyright © 2000 John Wiley & Sons, Ltd.     

Combining Qualitative and Quantitative Methods for Soil Erosion Assessments: An Application in a Sloping Mediterranean Watershed,Cyprus

In arid and semi‐arid regions, water erosion is difficult to model because of highly irregular precipitation regimes and changes in vegetation cover. The application of quantitative, process‐based models at the catchment scale is often problematic because of large data requirements. Qualitative methods require less data and can be more easily performed in a relatively short time, but they are more subjective. The objective of this research is to develop an erosion assessment methodology that combines qualitative field surveys with quantitative model estimates. The qualitative World Overview of Conservation Approaches and Technologies (WOCAT) methodology is based on expert observations per mapping unit, while the Pan‐European Soil Erosion Risk Assessment (PESERA) model simulates hill slope soil loss based on land cover, soil texture, meteorological data and slope profile. This study was conducted in the 106·4‐km² Peristerona watershed in Cyprus with a mean local slope higher than 40% in the mountainous upstream area and less than 8% in the plain. Out of 68 units, PESERA and WOCAT results were in agreement in 40 units, while PESERA results were lower in 25 and higher in 3 units. Both methods identified burnt areas and complex cultivation patterns as the most degraded. The total PESERA‐based sediment yield for the watershed was 1·2 Mg ha⁻¹ y⁻¹, which fell within the range of the sediment yield measured at the check‐dam downstream (0·2–2 Mg ha⁻¹ y⁻¹). This study provides a linkage between qualitative and quantitative soil erosion methods and helps to translate the outcomes of the former into the latter, thus providing a good tool for local erosion assessment. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling Post‐Tree‐Harvesting Soil Erosion and Sediment Deposition Potential in the Turano River Basin (Italian Central Apennine)

The overall aim of the paper is the assessment of human‐induced accelerated soil erosion processes due to forest harvesting in the Upper Turano River Basin. The spatio‐temporal pattern of soil erosion processes was investigated by means of a spatially distributed modelling approach. We used the Unit Stream Power Erosion and Deposition model. During the soil erosion‐modelling phase, the forest cover changes were mapped via remote sensing. According to this operation, the forest sectors exploited for timber production amounted to about 2781 ha or 9·9% of the wooded surface from March 2001 to August 2011. In this period, the average annual net soil erosion rate estimated by means of modelling operations totalled 0·83 Mg ha⁻¹ y⁻¹ for all the forest lands. The net soil erosion rate predicted for the disturbed forest lands is significantly higher than the average value for the entire forest (5·34 Mg ha⁻¹ y⁻¹). Estimates indicate a soil loss equal to 8521 Mg y⁻¹ (net soil erosion 0·34 Mg ha⁻¹ y⁻¹) in the undisturbed forest area (254 km²), whereas the 27·8 km² of disturbed forest area could potentially lose 14 846 Mg y⁻¹. The paper shows that a disturbed forest sector could produce about 74·2% more net erosion than a nine times larger, undisturbed forest sector. Copyright © 2013 John Wiley & Sons, Ltd.     

Sediment Yield Deduction from Check–dams Deposition in the Weathered Sandstone Watershed on the North Loess Plateau,China

As the basic unit of erosion and sediment yield, it was critical to determine the amount of soil erosion and sediment yield in the small watersheds for sustaining a reasonable water resource and sediment regulation system. In this study, we determined the sediment yield from the dams‐controlled watershed on the North Loess Plateau. Three check dams in the watershed were investigated by drilling ten‐hole sedimentation cores. The corresponding flood couplets were dated according to thickness of deposition layers, distribution of sediment particle size and historical erosive rainfall events. On the basis of the check dams capacity curve, the soil bulk density and the thickness of couplets, the deposit mass of check dams, and then the sediment yield of watershed at different temporal and spatial scale were deducted. In total of the 33, 60 and 55 couplets were corresponded to individual flood events in the dam MH1# from 1976 to 1984, the dam MH2# from 1985 to 2007, and the dam MH4# from 1981 to 2009, respectively. The specific sediment yield for flood events was 1,188.5–11,527.9 Mg km⁻², 1,278.6–17,136.7 Mg km⁻², and 3,395.9–33,698.5 Mg km⁻², and the annual average sediment yield was 10,728.6 Mg (km² · a)⁻¹, 12,662.9 Mg (km² · a)⁻¹, and 16,753.3 Mg (km² · a)⁻¹ in dam MH1#, MH2# and MH4# controlled watershed, respectively. The sediment yields were inversely proportional to the dams – controlled areas. For the whole watershed, the annual average sediment yield was 14,011.1 Mg (km² · a)⁻¹ from 1976 to 2009. There were large amounts of sediments (42.3–50.5%) were intercepted gradually along the way from small watersheds to the river channel. And the minimum rainfall for sediment deposited in the dams was greater than 20 mm in this watershed. The results of this study suggested that the sediments retained behind check dams were helpful to quantifying the amount of erosion sediment yield and understanding the soil erosion evolution in the small and ungauged watersheds. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface Disturbance and Erosion by Pigs: A Medium Term Assessment for the Monsoonal Tropics

Introduced pigs (Sus scrofa ) are recognised as having significant environmental impacts. Here, we quantify the effect of feral pigs in a catchment (undisturbed by Europeans) in the monsoonal tropics of northern Australia. Field data collected over a 5‐year period showed that the areal extent of pig disturbance ranged from 0·3 to 3·3% of the survey area (average 1·2%, σ = 0·9%). Mass of exhumed material was considerable and ranged from 4·3 to 36·0 Mg ha⁻¹ y⁻¹ (average 10·9 Mg ha⁻¹ y⁻¹). The excavations produce surface roughness which acts as sediment traps. Over the 5‐year study period, there was no evidence to suggest that pigs produce any rill or gully erosion. There does not appear to be any relationship between rainfall amount and area disturbed or volume of material exhumed. However, a significant positive relationship was observed between number of disturbances and rainfall. The location of any disturbance appears to be random and has no relationship with topography or geomorphic attributes such as slope, upslope contributing area or wetness indices derived from a high‐resolution digital elevation model of the site. While pigs are disturbingly relatively large volumes of soil, there is no clear evidence to support any increase in local erosion and soil structural change may be occurring slowly and only be observable over the long term. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel sediment source fingerprinting quantifying erosion-induced total nitrogen and total phosphorus outputs from an intensive agricultural catchment,North China

Intensive farming is a primary cause of increased sediment and associated nitrogen (N) and phosphorus (P) loads in surface water systems. Determining their contributing sources, pathways and loads present major challenges in the high-intensity agricultural catchments. Herein, we quantify the sediment sources and magnitude of sediment total N and total P from different sources using a novel application of compound-specific stable isotope (CSSI) and fallout radionuclides (FRNs) of ¹³⁷Cs and ²¹⁰Pbex in an intensive agricultural catchment in North China. Sediment sources from surface and sub-surface soils were estimated from FRNs fingerprint and accounted for 62 ± 7% and 38 ± 7% respectively, while surface soil from land uses that originated from hillslope were identified by CSSI fingerprint. Using a novel application of FRNs and CSSI sediment fingerprinting techniques, the dominant sediment source was derived from maize farmland (44 ± 0.1%), followed by channel bank (38 ± 7%). The sedimentation rate (13.55 ± 0.30 t ha⁻¹ yr⁻¹) was quantified by the ¹³⁷Cs cores (0–60 cm) at the outlet of this catchment. The total N and total P in sediment were both mostly derived from maize farmland and least from channel banks. The channel banks are significant sediment sources but contribute little to the input of sediment N and P for eutrophication. It implies that chemically-applied farmlands are the main hotspots for catchment erosion control and pollution prevention. The novel application of FRNs and CSSI techniques cost-effectively quantified sediment N and P loads from different sources with a single visit to the catchment, enabling rapid assessment for optimizing soil conservation strategies and land management practices. Keywords: Sediment sources, Land use, N and P loads, Compound-specific stable isotope, Fallout radionuclides.     

Effect of land management on runoff and soil losses from two small watersheds in St Lucia

The influence of land use on runoff and soil loss was assessed on two small watersheds in the Eastern Caribbean island of St Lucia, under contrasting land management regimes. The data generated from these watersheds revealed that the soil losses from an intensively cultivated agricultural watershed were 20‐times higher in magnitude than that of a forested watershed both for peak rainfall event and for total duration of analysis. This was due to higher surface runoff rates and exposure of soil to direct raindrop impact within cultivated areas. Whereas the forest canopy cover in combination with higher infiltration capacities of the forested land reduced the erosive runoff from the forest watershed and thus the soil loss. Moreover, the energy intensities of large storms in excess of 40 mm were estimated and found to range between 400 MJ mm ha⁻¹ h⁻¹ and 1834 MJ mm ha⁻¹ h⁻¹. 1

1 Megajoules‐millimeters per hectare‐hour.

Soil loss from the agricultural watershed was strongly correlated (R² = 0·85) to storm energy‐intensity (EI₃₀). However, the correlation of soil loss with the EI₃₀ (R² = 0·71) was poor for the forest watershed due to the effect of canopy vegetation, which significantly reduced the energy of raindrop impact. Over the study period, cumulative soil losses were 10·0 t ha⁻¹ for the agricultural site and 0·5 t ha⁻¹ for the forest site. 2

2 Metric tons per hectare.

The largest storm observed during the study period resulted in erosion losses of 3·78 t ha⁻¹ and 0·2 t ha⁻¹ from the agricultural and forest sites respectively. The regression models were developed using the measured data for prediction of runoff and soil loss over the watersheds of St Lucia under similar conditions. This study contributed towards efficient watershed management planning and implementation of suitable water conservation measures in St Lucia. Copyright © 2005 John Wiley & Sons, Ltd.     

Mulching effects on soil physical quality of an alfisol in western Nigeria

Degradation of soil physical quality, following deforestation and cultivation, is a major soil‐related constraint to an intensive use of soil for crop production in subhumid regions of subSaharan Africa. Use of crop residue mulch is an important strategy to minimize the risks of soil degradation. Therefore, a three‐year experiment was conducted to study the effects of five rates of mulch application (0, 2, 4, 6 and 8 Mg ha⁻¹ season⁻¹) on soil physical properties and growth and yield of maize (Zea mays). Mulch rate of rice straw significantly increased maize grain and stover yields during the first season, and the stover yield during the second season. In comparison with the control, the grain yield increased by 20 per cent at 2 Mg ha⁻¹ of mulch rate and by 33 per cent at 8 Mg ha⁻¹ of mulch rate. The rate of increase was 0·16 Mg ha⁻¹ for grain yield and 0·38 Mg ha⁻¹ for stover yield for every Mg of mulch applied. The increase in stover yield during the second season was 67 per cent for 8 Mg ha⁻¹ mulch rate compared with the unmulched control. Effects of mulch rate on soil physical properties were confined mostly to the surface 0–5 cm depth. For this depth, mulching decreased bulk density from 1·17 Mg m⁻³ for control to 0·98 Mg m⁻³, and penetration resistance from 1·54 kg cm⁻² to 1·07 kg cm⁻² for 8 Mg ha⁻¹ of mulch rate. Application of mulch up to 16 Mg ha⁻¹ yr⁻¹ for three consecutive years had no effect on soil physical properties below 5 cm depth. Experiments were probably not conducted for a long enough period. For mulch farming to be adopted by farmers of West Africa, it must be an integral part of the improved farming system. Copyright © 2000 John Wiley & Sons, Ltd.     

Assessment of soil erosion hazard in Kilie catchment,East Shoa,Ethiopia

This paper reports on a field study conducted in Kilie catchment, East Shoa Zone, Ethiopia to assess the rate of soil erosion by employing a soil loss prediction model (Universal Soil Loss Equation) integrated with in remote sensing and geographical information systems (RS/GIS), environment and gully measurement techniques. The final soil erosion risk map was produced after multiplication of the six factors involved in the USLE and RS/GIS. Gully measurement showed that the erosion rate is higher for the upland areas than the lowlands due to inappropriate soil and water conservation measures, free grazing by animals and conversion of hillside areas into farmlands. About 97·04 per cent of the study catchment falls within a range of 0–10 t ha⁻¹ yr⁻¹ sheet/rill erosion rate. We found that 2·17 per cent of the study area in the uplands has a soil erosion rate falling between 10 and 20 t ha⁻¹ yr⁻¹. About 0·8 per cent of the study area in the uplands is hit by severe sheet/rill erosion rate within the range of 20–60 t ha⁻¹ yr⁻¹. Gully erosion extent in the study area was evaluated through gully measurement and quantification methods. Gully density of 67 m ha⁻¹ was recorded in the catchment. The gully to plot area ratio was found to be 0·14 on average. Hence, in the upland areas, sustainable land management practices are required in order to reduce the rate of soil erosion. Copyright © 2011 John Wiley & Sons, Ltd.     

Soil erosion assessment of Lake Alemaya catchment,Ethiopia

Land degradation due to soil erosion is the major problem facing Ethiopia today. In the Lake Alemaya catchment soil erosion is caused by the intense rainfall, steep topography, and poor vegetation cover coupled with cultivation of steep lands, and inadequate conservation practices. Sediment from the catchment has affected the storage capacity of Lake Alemaya. This study has integrated the Agricultural Non‐point Source Pollution Model (AGNPS) and the technique of the Gographic Information System (GIS) to quantify soil erosion in the Lake Alemaya catchment. After application of the AGNPS, it appears that 66 per cent of the catchment has a soil erosion rate of 10 to more than 80 t ha⁻¹ y⁻¹. The annual soil loss is estimated at 31 t ha⁻¹, which is more than the permissible value of 1–16 t ha⁻¹ for different agro‐ecological zones of Ethiopia. The sediment yield of the catchment is about 10 148 ton with a delivery ratio of 6·82 per cent. Therefore, an effective management plan is needed for the conservation and rehabilitation of the catchment and to maintain the storage capacity of Lake Alemaya. Copyright © 2006 John Wiley & Sons, Ltd.     

CARBON BUDGET AND SEQUESTRATION POTENTIAL IN A SANDY SOIL TREATED WITH COMPOST

The effects of compost application on soil carbon sequestration potential and carbon budget of a tropical sandy soil was studied. Greenhouse gas emissions from soil surface and agricultural inputs (fertiliser and fossil fuel uses) were evaluated. The origin of soil organic carbon was identified by using stable carbon isotope. The CO₂, CH₄ and N₂O emissions from soil were estimated in hill evergreen forest (NF) plot as reference, and in the corn cultivation plots with compost application rate at 30 Mg ha⁻¹ y⁻¹ (LC), and at 50 Mg ha⁻¹ y⁻¹ (HC). The total C emissions from soil surface were 8·54, 10·14 and 9·86 Mg C ha⁻¹ y⁻¹ for NF, HC and LC soils, respectively. Total N₂O emissions from HC and LC plots (2·56 and 3·47 kg N₂O ha⁻¹ y⁻¹) were significantly higher than from the NF plot (1·47 kg N₂O ha⁻¹ y⁻¹). Total CO₂ emissions from fuel uses of fertiliser, irrigation and machinery were about 10 per cent of total CO₂ emissions. For soil carbon storage, since 1983, it has been increased significantly (12 Mg ha⁻¹) under the application of 50 Mg ha⁻¹ y⁻¹ of compost but not with 30 Mg ha⁻¹ y⁻¹. The net C budget when balancing out carbon inputs and outputs from soil for NF, HC and LC soils were +3·24, −2·50 and +2·07 Mg C ha⁻¹ y⁻¹, respectively. Stable isotope of carbon (δ¹³C value) indicates that most of the increased soil carbon is derived from the compost inputs and/or corn biomass. Copyright © 2011 John Wiley & Sons, Ltd.     

Establishing a Holocene sediment budget for the river Dijle

A Holocene sediment budget was constructed for the 758 km² Dijle catchment in the Belgian loess belt, in order to understand long-term sediment dynamics. Hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings, which was extrapolated to the entire catchment using morphometric classes. As large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times, a correction was applied for the presence of forests. Total Holocene erosion amounts 817 ± 66 Mt for the catchment, of which 327 ± 34 Mt was deposited as colluvium. This corresponds with a net Holocene soil erosion rate of 10.8 ± 0.8 × 10³ Mg ha^− 1 for the entire Dijle catchment. Alluvial deposits were studied through 187 augerings spread over 17 cross-valley transects. The total alluvial sediment deposition equals 352 ± 11 Mt or 42% of total eroded sediment mass. Results indicate that at the scale of a medium-sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected. As a result the estimation of erosion through alluvial storage and sediment export would yield large errors. Dating of sediment units show an important increase in alluvial deposition from medieval times onwards, indicating the important influence of agricultural activities that developed from that period. Mean sediment export rates from the catchment for the last 1000–1200 years range between 0.8 and 1.3 Mg ha^− 1 a^− 1 and are consistent with present suspended sediment measurements in the Dijle. Erosion for agricultural land for this period is 9.2 ± 2.2 Mg ha^− 1 a^− 1. Sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment.     

Sediment and Phosphorus Loads from a Stream Draining Agricultural and Forest Lands in Northwest Spain

ABSTRACT

Transport of suspended sediment (SS) and phosphorus (P) via surface runoff from soils to surface waters is a major problem of water quality degradation in many European rivers and in other parts of the world. This problem is especially serious during wet periods, which can produce twice the P loads of dry periods. In this study, the SS load and particulate phosphorus (PP) exported from a small catchment located in NW Spain (in which cultivated soils had different degrees of vegetation cover) were analyzed during two rainy periods of February 2006 and February 2007. The SS and PP loads were calculated from the data of discharge, and SS and PP concentrations were measured in water samples collected at the catchment outlet. SS and PP loads were higher in 2006 than in 2007, while there was higher rainfall and stream flow in 2007. Differences in the degree of vegetation cover in the cultivated fields with good connectivity with the stream, which was the main source area of sediment in this catchment, explain the differences in SS and PP loads between the two periods. Soil losses caused during both rainy periods were low (0.02 Mg ha^?1); however, they may be detrimental to quality of the stream water due to the P linked to soil particles. PP concentrations were above the critical values of P for eutrophication during the study periods, highlighting the need to take conservation measures to reduce soil erosion and sediment delivery to watercourse.