Browsing by Author "Deckers, Jozef"

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Animal-powered tillage erosion assessment in the southern Andes region of Ecuador
(2007-06-01) Dercon, Gerd; Govers, Gerard; Poesen, Jean; Sánchez, Henrry; Loaiza, George; Vandenbroeck, E.; Rombaut, K.; Deckers, Jozef
While water erosion has been the focus of past research in the Andes, former studies show that soil erosion could also be related to the methods used in cultivating the fields. The main objective of the present study was to assess (i) tillage erosion caused by the traditional animal-powered “yunta” or ard plough in the Andes and the factors controlling the process and (ii) the implications for soil conservation. Erosion rates were experimentally measured on 27 sites, having slopes from ca. 0% to 60% and soils ranging from Andosols to Cambisols, in the Andes region of Ecuador (Gima, Azuay). Different tillage methods were assessed: (i) tillage parallel to the contour lines (‘Paralelo’) and (ii) tillage at an angle with the contour lines. Statistical analysis points out that erosion caused by animal-powered tillage is gravity-driven. A strong correlation exists between slope and downslope displacement: furthermore, tillage depth and initial soil condition are important. For the ‘Paralelo’ tillage method the tillage transportation coefficient (k) is below 100 kg m− 1 Tillage Pass− 1, for the combined ‘Arado’–‘Cruzado’ tillage method k may exceed 300 kg m− 1. Tillage erosion is responsible for the reduction of the slope between the contour strips over a relatively short time period of 20 years, resulting in the formation of terraces and therefore the reduction of the water erosion risk. However, at the same time it may negatively affect soil quality.
Clay mineralogy of the soils in the south ecuadorian páramo region
(2005-07) Buytaert, Wouter; Sevink, J.; Leeuw, B. De; Deckers, Jozef
The pa´ramo soils of the mountainous upper Andean region (N3300 m a. s. l.) of the Rio Paute basin in central Ecuador are characterized by a thick, dark, highly organic epipedon and are classified as Andosols and Histosols. Their high water retention and buffering capacity play a key role in the hydrology of the region, which is subject to land use changes and increased cultivation. In the west (Western Cordillera), the soils are largely formed in the late Miocene and Pliocene volcanoclastic Tarqui formation, while in the east (Central Cordillera) they are formed in an older, mostly intermediate low-grade metamorphic rocks. Ten soil profiles were sampled and studied, using extraction techniques (oxalate and pyrophosphate) and XRD-techniques. Major differences in composition of the clay fractions were found that allow for distinction of three main groups of pa´ramo soils. A first group consists of soils influenced by recent volcanic ashes and dominated by organometallic complexes and with minor but distinct amounts of degraded mica, most probably formed by weathering of primary mica, present in these ashes. The second group comprises soils formed in volcanoclastic material of various Tertiary and earlier formations, containing residual primary and secondary crystalline clay-size minerals, as well as organometallic complexes whose genesis can be linked to the abundant presence of easily weatherable materials in these formations. A third group consists of soils in relicts of Tertiary, highly weathered regolith, formed under humid tropical conditions before the Andean uplift and occurring in the Central Cordillera. These soils contain kaolinite and gibbsite and develop into Histosols in the absence of significant organometallic complexation.
Human impact on the hydrology of the Andean páramos
(2006) Buytaert, Wouter; Célleri, Rolando; De Bièvre, Bert; Cisneros, Felipe; Wyseure, Guido; Deckers, Jozef; Hofstede, Robert
This paper analyses the problems involved in the conservation and management of the hydrological system of the South American páramo. The páramo consists of a collection of neotropical alpine grassland ecosystems covering the upper region of the northern Andes. They play a key role in the hydrology of the continent. Many of the largest tributaries of the Amazon basin have their headwaters in the páramo. It is also the major water source for the Andean highlands and a vast area ofarid and semi-arid lowlands, where páramo water is used for domestic, agricultural and industrial consumption, and the generation of hydropower. Recently, the páramo is increasingly used for intensive cattle grazing, cultivation, and pine planting, among others. These activities, as well as global phenomena such as climate change, severely alter the hydrological regime. A review on the state of knowledge of its hydrology is given in a first part. In a second part, the impact of human activities and climate change on the hydrology of the páramo is discussed.
Impact of land use changes on the hydrological properties of volcanic ash soils in South Ecuador
(2002-06) Buytaert, Wouter; Deckers, Jozef; Dercon, Gerd; Bievre, Bert De; Poesen, Jean; Govers, Gerard
The effect of land use on the water retention capacity of Umbric Andosols in south Ecuador was studied. The objective was to acquire a better insight into the hydrological processes of the ecosystem and the role of the soil, in order to assess the impact of changing soil properties due to land use change on the hydrology of the high Andes region. Field data on the water retention capacity at wilting point of Umbric Andosols were collected for both cultivated field conditions and original bush vegetation. The pH in water and in NaF, texture, organic matter content and dry bulk density were measured to show which physicochemical soil characteristics are responsible for the water retention of the Umbric Andosols and for the irreversible loss in water retention due to air drying. Organic matter content appears to be very important and certainly more important than allophane clay content. Water retention of the organic litter layer was calculated to be 16 mm, this would be lost when vegetation was cleared and the land cultivated.
Linking hydrological, infinite slope stability and land-use change models through GIS for assessing the impact of deforestation on slope stability in high Andean watersheds
(2003-06-16) Vanacker, Veerle; Vanderschaeghe, Michiel; Govers, Gerard; Willems, Edith; Poesen, Jean; Deckers, Jozef; Bievre, Bert De
In the Ecuadorian Andes, episodic slope movements comprising shallow rotational and translational slides and rapid flows of debris and soil material are common. Consequently, not only considerable financial costs are experienced, but also major ecological and environmental problems arise in a larger geographical area. Sediment production by slope movement on hillslopes directly affects sediment transport and deposition in downstream rivers and dams and morphological changes in the stream channels. In developing countries world-wide, slope movement hazards are growing: increasing population pressure and economic development force more people to move to potentially hazardous areas, which are less suitable for agriculture and rangelands. This paper describes the methods used to determine the controlling factors of slope failure and to build upon the results of the statistical analysis a process-based slope stability model, which includes a dynamic soil wetness index using a simple subsurface flow model. The model provides a time-varying estimate of slope movement susceptibility, by linking land-use data with spatially varying hydrologic (soil conductivity, evapotranspiration, soil wetness) and soil strength properties. The slope stability model was applied to a high Andean watershed (Gordeleg Catchment, 250 ha, southern Ecuadorian Andes) and was validated by calculating the association coefficients between the slope movement susceptibility map of 2000 and the spatial pattern of active slope movements, as measured in the field with GPS. The proposed methodology allows assessment of the effects of past and future land-use change on slope stability. A realistic deforestation scenario was presented: past land-use change includes a gradual fragmentation and clear cut of the secondary forests, as observed over the last four decades (1963–2000), future land-use change is simulated based on a binary logistic deforestation model, whereby it was assumed that future land-use change would continue at the same rate and style as over the last 37 years (1963–2000).
Regional variability of volcanic ash soils in south Ecuador: the relation with parent material, climate and land use
(2007) Buytaert, Wouter; Deckers, Jozef; Wyseure, Guido
The high Andes region of south Ecuador is characterised by intense land use changes. These changes affect particularly the páramo, which is a collection of high altitudinal grassland ecosystems. In this region, the interaction between airborne volcanic ashes and the cold and wet climate results in very typical soils, with an elevated organic C contents. The physical soil properties are closely related to the high and reliable base flow in rivers descending from the páramo, which makes them important for the socio-economic development of the region. In this study, we analyse the regional variability of the soils in the south Ecuadorian rio Paute basin. In a first part of the study, data from soil profiles along north–south transects are used to determine the soil properties, and to relate the spatial variability of these properties to the major trends in parent material, volcanic ash deposits and climate. The profiles are Histic Andosols and Dystric Histosols devoid of allophane, with very high amounts of organic matter. Significant differences between the western and central mountain range are observed, as well as a general decrease in Andic properties from north to south, coinciding with the decrease in volcanic influence. Finally, the impact of human activities on the soil properties is assessed in a case study in the Machangara valley. Data from 5 profiles, located in an area with natural grass vegetation and a low degree of human impact are compared with 4 profiles in a heavily disturbed, intensively drained cultivated area. Despite the intensity of the land use, very few significant differences are found.
Spatial variability in crop response under contour hedgerow systems in the Andes region of Ecuador
(2006-03) Dercon, Gerd; Deckers, Jozef; Sánchez, Henrry; Ramírez, Marco; Vanegas, Raúl; Tacuri Espinoza, Víctor Eduardo; Loaiza, George; Govers, Gerard; Poesen, Jean
Land management practices on tropical soils have been studied extensively during the past decades. However, assessments of their impact on field-scale spatial variability in crop performance are rare. A case of practices affecting spatial crop response at field level in a systematic way is the contour hedgerow system, a widespread soil conservation technique on steep lands in the tropics. The objectives of this study were to assess: (i) spatial variability in crop response under contour hedgerow systems in the Andes and (ii) implications for management of steep land alley farming. In order to measure spatial variability in crop response, Triticum aestivum was sown in rows following the contours, placed every 25 cm along the slope direction. Grain yield was monitored on eight alleys, having slopes from 15 to 30%, a length of 4–8 m and soils ranging from Dystri-Vertic Cambisols to Haplic Phaeozem, in the Andes region of Ecuador. In order to relate crop response with soil fertility, soil sampling was carried out in bands following the contour. Top soil properties, such as organic carbon, NTotal, NO3−, P, exchangeable Aluminium, P fixation, exchangeable bases, CEC and texture, were analysed. The barrier strips of the contour hedgerow systems were composed of: (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability in crop response was described by fourth-order polynomial equations, where position in the alley was the independent variable and plant characteristics were the dependent variables. Grain yield ranged from 0.8 to 4.0 t ha−1 (net area). Clear and significant patterns of spatial variability in crop response were found in all alleys, with R2 varying from 0.55 to 0.90. Crop response was strongly and positively correlated with NO3−, P, exchangeable bases or organic carbon, dependent on the management, age and soil conditions of the alleys. Tillage erosion and soil accumulation on respectively the upper and lower elevations of the alleys were the main causes for a tendency to a significantly increased crop response along the slope direction. However, according the type of grass used in the barrier strip, competition for soil fertility and soil moisture occurred and influenced in negative way crop productivity in the lower elevations of the alleys. An index is proposed to assess the effect of contour hedgerows on crop response. The present study shows that contour hedgerow systems cannot always be evaluated as completely positive. Soil fertility improvement on the upper part of the alleys and a better management of the barrier strip are suggested to enhance crop productivity of contour hedgerow systems.
Spatial variability in soil properties on slow-forming terraces in the Andes region of Ecuador
(2003-07) Dercon, Gerd; Deckers, Jozef; Poesen, Jean; Sánchez, Henrry; Vanegas, Raúl; Ramírez, Marco
Due to severe land degradation problems, soil conservation is a matter of major concern in the Ecuadorian Andes. Slow-forming terraces, a variation of hedgerow agro-forestry systems composed by contour grass barrier strips, can be considered as the most frequently used technique in Andean rural communities of Ecuador. However, due to shallow soils, terrace development often has the disadvantage causing gradients in soil properties from the upper to the lower elevations within the terrace. The main objectives of this study were to assess (i) spatial variability in soil properties on slow-forming terraces in the Andes and (ii) implications of variability for the management of this soil conservation technique. In order to measure spatial variability, soil sampling (0–15 cm) was carried out in bands following the contour, which were located every 1 m beginning at the highest point of elevation and including the lowest point on the terrace. Soil properties, such as pH(H2O), pH(NaF), organic carbon, total nitrogen, NO3−, P, K, exchangeable aluminium, P fixation, exchangeable bases, cationic exchange capacity, base saturation and texture, were monitored on eight terraces, having slopes from 15 to 30%, a length of 4–8 m and soils ranging from Cambisols to Phaeozems, in the Ecuadorian Andes (Gima, Azuay). Terraces, which were 2–4 years, were managed in a traditional or more intensified way (i.e. without or with the application of organic manure). Bufferstrips were composed by (i) Pennisetum clandestinum and Lolium multiflorum or (ii) Phalaris tuberosa. Spatial variability was analysed by stepwise multiple regression analysis, where position on the terrace was the independent variable and soil property was the dependent variable. Factor analysis was carried out in order to compare spatial variability patterns of the terraces and formulate management strategies. High spatial variability in soil properties was found. Although spatial variation was site dependent, it was clear that soil fertility increased from the upper to the lower part of the terraces. The present study shows that management strategy could influence the pattern and magnitude of spatial variation. Site-specific soil fertility improvement is suggested as means to combat variation caused by tillage erosion in slow-forming terraces.
Spatial variation of suspended sediment concentrations in a tropical Andean river system: The Paute River, southern Ecuador
(2007-06-01) Vanacker, Veerle; Molina, Armando; Govers, Gerard; Poesen, Jean; Deckers, Jozef
Tropical mountain ecosystems are sensitive to environmental change brought about by natural and anthropogenic processes. The steep topography, shallow soils and unsustainable land use practices following forest conversion often lead to enhanced rates of geomorphic activity including soil erosion, landsliding and fluvial activity. Rapid demographic growth and socio-economic development have accelerated environmental change over the past few decades. During the last 50 years, water erosion on agricultural fields caused by inappropriate agricultural practices was perceived as the major source of stream sediment in tropical Andean catchments. However, because of sporadic data on sediment production, -transport and -export in tropical Andean catchments, it is unclear as to whether geomorphic activity is mainly controlled by natural or anthropogenic factors. A research program has been carried out in the 5176 km2 Paute River catchment located in southern Ecuador to examine the variability in sediment loads in rivers. A monitoring program was set up in the central part of the watershed to extract information on the spatial variability in river sediment load in relation to catchment variables describing climate, lithology, topography and land use. Twenty-nine river sections were sampled during two successive rainy seasons. At each visit, suspended sediment samples were taken and instantaneous river discharge was measured. Geographic data related to topography, landscape morphology, rainfall, land cover and geology were collected. Watersheds that were affected by intense landslide erosion in the upstream area have a significantly higher weighted suspended sediment concentration than the remaining watersheds. There is some evidence to suggest that occurrence of these large, infrequent landslides is mainly related to topographic steepness, rather than to actual land use practices or human activities.
The effect of land-use changes on the hydrological behaviour of histic andosols in south Ecuador
(2005-12) Buytaert, Wouter; Wyseure, Guido; Bievre, Bert De; Deckers, Jozef
The south Ecuadorian Andean mountain belt between 3500 and 4500 m altitude is covered by a highly endemic and fragile ecosystem called paramo. The Histic Andosols covering this regi ´ on have highly developed hydric properties and exert a key function in the hydrological regulation of the paramo ecosystem. Unlike most Andosols, their extreme ´water retention capacity is not due to the presence of typical minerals such as allophane or imogolite. Although these minerals are virtually absent, the large organic carbon content, due to organometallic complexation, gives rise to similar properties. The water content at 1500 kPa can exceed 2000 g kg 1, and the high hydraulic conductivity at saturation (about 15 mm h 1) drops sharply when low suction is applied. The three methods applied, i.e. the inverted auger hole, the tension infiltrometer and the constant-head permeameter method, give very similar results. The paramo ´is characterized by a slow hydrological response and a good water regulation, caused by the combination of a high water storage capacity and high conductivity. The wide pore size distribution of the organometallic complexes results in a water retention curve that differs significantly from the classic Mualem–Van Genuchten description, but can better be described with a simple linear or semilogarithmic model. The soils investigated are very prone to irreversible structural changes caused by land-use changes. The conversion of natural land for cultivation has a large impact on the hydrological function of the region. The water storage capacity increases by 5 to 30%, and the hydraulic conductivity is 31% higher in cultivated catchments. These changes are related to a larger peak flow, a smaller base flow and generally a smaller discharge buffering capacity, despite the higher storage capacity. Copyright  2005 John Wiley & Sons, Ltd
The impact of environmental change on the intensity and spatial pattern of water erosion in a semi-arid mountainous Andean environment
(2003-04-01) Vanacker, Veerle; Govers, Gerard; Poesen, Jean; Deckers, Jozef; Loaiza, George
Aerial photographs taken in 1976 and 1989 and a field survey in 1999 showed that land use in a 900-ha catchment in the southern part of the Ecuadorian Andes is highly dynamic. Over 23 years, ca. 83 ha of arable land was abandoned and ca. 70 ha was taken into agricultural production. Changes in land use were not spatially homogeneous. Parcels on unstable geologic formations and close to village centres were preferably set-aside. Land taken into cultivation was preferably located on gently sloping areas close to newly built sites and arterial roads. The area with bush vegetation increased by regeneration of natural vegetation on fields set-aside in the late 1970s and early 1980s. There was a complex interaction between water erosion and environmental change in the study area. Land taken into production was levelled for furrow irrigation: this led to a net reduction in the area susceptible to water erosion. However, one quarter of the area affected only by sheet and rill erosion 23 years ago has since become incised by deep gullies. This increase in gully density was related to inadequate construction and management of irrigation infrastructure, rather than to change in vegetation cover and/or soil erodibility caused by agricultural practices. This factor is often overlooked in studies of the effects of environmental change on geomorphologic processes.
The use of the linear reservoir concept to quantify the impact of changes in land use on the hydrology of catchments in the Andes
(2004) Buytaert, Wouter; Wyseure, Guido; Deckers, Jozef; De Bièvre, Bert
The high Andes region of South Ecuador (The Paramo) is characterized by a cold and wet climate. Most soils of the Páramo region are Andosols and Histosols, with a very high water retention capacity that is affected irreversibly by drying. This key property of Páramo soils buffers catchment outflow, resulting in an almost uniform outflow pattern which, notwithsyanding the variability in rainfall, can be very variable in space and time. These soils serve as the most important reservoir of drinking and irrigation water for the densely populated inter-Andean depression region. The Páramo has long served only as an extensive grazing area but recent population pressure and land scarcity have increased cultivation. Two small Páramo catchments (about 2 km2) were monitored intensively for precipitation and discharge for over a year to assess the effect of such land-use changes on the hydrological properties. One catchment is in an undisturbed area and grazed intensively while in the other, local farmers started intensive drainage for cultivation of potatoes about five years ago. The linear reservoir concept has been used to assess the overall retention capacity of the catchment in terms of both peak response and base flow. In this model, every catchment is considered as a series if independent parallel reservoirs, each characterized by mean residence times (T). In every catchment, three major mean residence time can be distinguished. In the undisturbed catchment, an immediate response. characterized by a T of 5.4 hours, is followed by a slower response with a T of 44.3h. The base flow has mean T value of 360 h. The response of the cultivated catchment is similar with T values of 3.6 h., 27.2 h and 175 h, respectively. As a result, in the disturbed catchment, water release is about 40% faster than in the undisturbed catchment, so that the base flow falls rapidly to lower levels. The linear reservoir model is a simple way of quantifying the impact of land use changes on the water regulation capacity of Páramo catchments.