Browsing by Author "Molina Verdugo, Armando"

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Análisis de la variabilidad espacial en el desarrollo del suelo y su relación con el almacenamiento de carbono en una microcuenca en el sur del Ecuador: Interacción de la cobertura vegetal y topografía
(Universidad de Cuenca, 2021-03-01) Contreras Arévalo, Tanya Augusta; Fernández Zhinín, René Fabricio; Ramírez Matamoros, Marco Tulio; Molina Verdugo, Armando; Vanacker, Veerle; Morales Matute, Óscar Patricio
The aim of this research was to analyze the influence of vegetation and topography on the storage of organic carbon and the thickness of the soil in a micro-basin of páramo in the south of Ecuador.A total of 135 sampling sites were selected, which were distributed within the study area. The sites were classified based on the vegetation cover (cushion plants, tussock grasses and native forest) and the topographic position (concave, convex and straight). Altered and unaltered soil samples were collected from the horizons (O, A, AC and AC) at each site. The organic carbon concentration (%C) and bulk density (DA) were determined for the collected soil samples in order to calculate the total carbon storage (TCS). Results showed average TCS values of 27.43 kg/m2 , 34.27 kg/m2 , 41.05 kg/m2 , for tussock grasses, cushion plants and forest vegetation respectively; while for the topographic position the average values varied from 31.06 kg/m2 , 35.16 kg/m2 and 36.53 kg/m2 , for concave, convex and straight, respectively. Forest soils have the greatest accumulation of organic carbon, followed by soils formed under cushion plants and tussok grass covers; although the latter two represent the most important soils for carbon reserves due to their extension on the territory. Furthermore, results revealed that the vegetation cover exerts a greater influence on the soil depth (soil thickness) compared to the effect of topography, especially at the valley bottoms and plain areas covered by cushions plants. Finally, this study has highlighted the importance of carbon storage in the subsoil as an important carbon source and it should be integrated in future research for modelling purposes.
Complex land cover change, water and sediment yield in a degraded Andean environment
(2012) Molina Verdugo, Armando; Vanacker, Veerle; Balthazar, Vincent; Mora Serrano, Diego Esteban; Govers, Gerard
Rapid land use/-cover change has increasingly transformed the hydrological functioning of tropical Andean ecosystems. The hydrological response to forest cover change strongly depends on the initial state of the ecosystem. Relatively little is known about human-disturbed ecosystems where forest plantations have been established on highly degraded land. In this paper, we analyze the impact of forest change on water and sediment fluxes for a highly degraded Andean catchment. Different pathways of land cover change (1963–2007) are observed in the Jadan catchment, with deforestation taking place in remote uplands and recovery and reforestation in the middle and lower parts where agricultural and bare lands are prevalent. Time series analyses of streamflow and rainfall data (1979/1982–2005/2007) show significant shifts in the distribution of rainfall and flow data. Changes in discharge are not resulting from changes in precipitation, as the direction of change is opposite. The removal of native forest for rangeland or croplands (by −20 km2) is likely to have contributed to the increase in total annual water yield, through an increase in annual baseflow by 25 mm. The observed changes in peakflow are important as the 1st percentile highest flow rates were 54% lower, while the 1st percentile rainfall amounts increased by 52%. The observed decrease in peakflow cannot be explained by clearcut of native forest, but is likely to be related to reforestation of degraded lands as well as spontaneous recovery of vegetation on remaining grazing lands. Over the same time period, a major decrease in specific sediment yields and suspended sediment loads was observed. Although deforestation in the upper parts led to increased landslide activity, this change is not reflected in an increased sediment yield. Small upland rivers are often nearly completely blocked by landslide material, thereby reducing their potential to transport sediment. In contrast, the reduction in estimated erosion is likely to be caused by the reduction of the degraded areas in areal extent as well as to the (partial) recovery of the vegetation in these areas
Distribución espacio-temporal de los deslizamientos y erosión hídrica en una cuenca andina tropical
(2020) Vanacker, Veerle; Guns, Marie; Clapuyt, Francois; Balthazar, Vincent; Tenorio, Gustavo; Molina Verdugo, Armando
Tropical mountain regions are prone to high erosion rates, due to the occurrence of heavy rainfall events and intensely weathered steep terrain. Landslides are a recurrent phenomenon, and often considered as the dominant erosion process on the hillslopes and the main source of sediment. Quantifying the contribution of landslide-derived sediment to the overall sediment load remains a challenge. In this study, we derived catchment-average erosion rates from sediment gauging data and cosmogenic radionuclides (CRN), and examined their reliability and validity for constraining sediment yields in tectonically active regions. Then, we analysed the relationship between catchment-average erosion rates and landslide-derived sediment fluxes. The Pangor catchment, located in the western Andean mountain front, was selected for this study given its exceptionally long time series of hydrometeorological data (1974-2009). When including magnitude-frequency analyses of the sediment yields at the measurement site, the corrected gauging-based sediment yields remain one order of magnitude lower than the CRN-derived erosion rates. The underestimation of catchment-average erosion rates from gauging data points to the difficulty o f e xtrapolating fl ow fr equency an d se diment ra ting da ta in no n-stationary hy drological regimes, and severe undersampling of extreme events. In such conditions, erosion rates derived from cosmogenic radionuclides are a reliable alternative method for the quantification of catchment-average sediment yield. Landslide inventories from remote sensing data (1963-2010) and field measurements of landslide geometries are the input data for the derivation of landslide-derived sediment fluxes. The landslide-related erosion rates of 1688−+326901 and 630−+108300 t.km2.y-1 are similar to the CRN-derived erosion rates, likely indicating that landslides are the main source of sediment in this mountainous catchment. Copyright: © 2020 CSIC This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) L icense.
Impacto de la cobertura vegetal y las actividades antrópicas sobre la formación del suelo en una microcuenca de páramo en la cuenca del Río Yanuncay-Quebrada Cuevas
(2015) Asanza Cajamarca, Juan Carlos; Barahona Méndez, Juan Andrés; Molina Verdugo, Armando
This thesis aims to study the effect of vegetation cover and anthropogenic activities on soil formation in a páramo micro-catchment in the upper part of the Yanuncay basin (Cuevas stream). Non-allophonic Andosols are the main soils in the study area where the overgrazing and burnings are the common agricultural practices. Three types of vegetation were identified, grass páramo (Pj), cushion páramo (PHA), and Polylepis (BP) forest. 6 soil catenas were made and 18 soil profiles were studied for the distinct types of vegetation. Results of the statistical analyses show that the availability of cations and Si is low, whereas the availability of Al and Fe is high and these elements are strongly correlated to organic carbon. The upper horizons present values of pH lower to 5, bulk density is lower to 0.9gr/cm³, and the values of the ratio of Alp/Alo are between 0.5 and 1. These findings indicate that the páramo soils of the southern Ecuador are non-allophonic Andosols and the alumínic-organic complexes prevail, while the formation of allophones is limited, therefore these soils are well developed. Our analysis show that there are two patterns between vegetation groups, apparently the grass páramo and Polylepis forest have the same behavior, as they do not show significative differences. On the other hand, the results for the cushion páramo show a distinct behavior in comparison to the other two groups. Land use plays an indirect role but important in soil development, particularly the Pj and Pha are subjected to overgrazing of animals and burnings, these agricultural practices contribute further to disturb the biogeochemical cycle of páramo ecosystems
Levantamiento y evaluación de aptitudes de suelo para irrigación en la Zona de Bulán- San Cristobal
(1996) Minchala S., Germán; Molina Verdugo, Armando; Alvarado Moncayo, Darío
Long-term effects of climate and land cover change on freshwater provision in the tropical Andes
(2015) Mora Serrano, Diego Esteban
Andean headwater catchments play a pivotal role to supply fresh water for downstream water users. However, few long-term studies exist on the relative importance of climate change and direct anthropogenic perturbations on flow regimes. In this paper, we assess multi-decadal change in freshwater provision based on long time series (1974–2008) of hydrometeorological data and land cover reconstructions for a 282 km2 catchment located in the tropical Andes. Three main land cover change trajectories can be distinguished: (1) rapid decline of native vegetation in montane forest and páramo ecosystems in ∼ 1/5 or 20 % of the catchment area, (2) expansion of agricultural land 10 by 14 % of the catchment area, (3) afforestation of 12 % of native páramo grasslands with exotic tree species in recent years. Given the strong temporal variability of precipitation and streamflow data related to El Niño–Southern Oscillation, we use empirical mode decomposition techniques to detrend the time series. The long-term increasing trend in rainfall is remarkably different from the observed changes in streamflow that exhibit a decreasing trend. Hence, observed changes in streamflow are not the result of long-term climate change but very likely result from direct anthropogenic disturbances after land cover change. Partial water budgets for montane cloud forest and páramo ecosystems suggest that the strongest changes in evaporative water losses are observed in páramo ecosystems, where progressive colonization and afforestation of high alpine grasslands leads to a strong increase in transpiration losses.
Modelación del flujo de agua y nitrato en el suelo de la microcuenca Cuevas en el sur de los Andes ecuatorianos empleando Hydrus 1D
(2018) Edison Fernando, Amay Izquierdo; Molina Verdugo, Armando; Mora Serrano, Diego Esteban
With the purpose of studying an integral dynamics between the soil and water factors in the high Andean ecosystems, this research focused on the modeling of water flow and nitrate transport through the sub surface soil solution of the Cuevas microbasin (4.2 km2), in the south of the Ecuadorian Andes. The Hydrus 1D model was used to model the water content and the transport of nitrate through the soil profile in thirty monitoring points distributed in the microbasin under the coverings of páramo, polylepis forest and cushion. The model has been shown to be capable of achieving acceptable adjustments, considering the PBIAS error index, using inverse modeling in the optimization of pedotransference parameters. The results obtained reveal that the soil under the forest cover would be storing a greater percentage of water, up to 10% more than that reached under the coverings of páramo and cushion; On the other hand, nitrate seems to be consumed more under the cushion coverage. The investigation supposes an important advance in the integral study of watersheds; the findings, methods and limitations found in this work could help in the planning of future research within the axis of hydrological and geochemical modeling.
Multidecadal change in streamflow associated with anthropogenic disturbances in the tropical Andes
(2015) Molina Verdugo, Armando; Vanacker, Veerle; Brisson, Erwan; Mora Serrano, Diego Esteban; Balthazar, Vincent
Andean headwater catchments are an important source of freshwater for downstream water users. However, few long-term studies exist on the relative importance of climate change and direct anthropogenic perturbations on flow regimes in these catchments. In this paper, we assess change in streamflow based on long time series of hydrometeorological data (1974–2008) and land cover reconstructions (1963–2009) in the Pangor catchment (282 km2) located in the tropical Andes. Three main land cover change trajectories can be distinguished during the period 1963–2009: (1) expansion of agricultural land by an area equal to 14 % of the catchment area (or 39 km2) in 46 years' time, (2) deforestation of native forests by 11 % (or −31 km2) corresponding to a mean rate of 67 ha yr−1, and (3) afforestation with exotic species in recent years by about 5 % (or 15 km2). Over the time period 1963–2009, about 50 % of the 64 km2 of native forests was cleared and converted to agricultural land. Given the strong temporal variability of precipitation and streamflow data related to El Niño–Southern Oscillation, we use empirical mode decomposition techniques to detrend the time series. The long-term increasing trend in rainfall is remarkably different from the observed changes in streamflow, which exhibit a decreasing trend. Hence, observed changes in streamflow are not the result of long-term change in precipitation but very likely result from anthropogenic disturbances associated with land cover change.
Patterns in soil chemical weathering related to topographic gradients and vegetation structure in a high andean tropical ecosystem
(2019) Molina Verdugo, Armando; Vanacker, Veerle; Corre, Marife D; Veldkamp, Edzo
Although climate exerts a major control on mineral weathering and soil formation processes, the combined effect of vegetation and topography can influence the rate and extent of chemical weathering at the hillslope scale. In this paper, we examined spatial patterns in volumetric strain and soil weathering extent associated with topographic gradients and vegetation patterns. In a high Andean catchment, we selected 10 soil toposequences on andesitic flows: 5 under tussock grasses, 3 under cushion forming plants, and 2 under native forest. Along each toposequence, one pit was excavated at the shoulder, backslope, and toeslope resulting in 30 soil profiles. Depth‐weighted total soil porosity of the 30 soil profiles averaged 64 ± 6%. The association between volumetric strain and soil organic C indicates that biotic agents can be effective in dilating the regolith during weathering. The young, postglacial volcanic soils were depleted in mono‐divalent and divalent cations, with total mass losses ranging between 793 and 1610 kg/m2 . The accumulation of Al‐humus complexes in the soil matrix plays an essential role in chemical transformation of the nonallophanic soils. Beyond the marginally significant topographic control on chemical weathering extent, our data show highly significant differences in chemical weathering extent between vegetation communities with total mass losses in forest soils being, respectively, 19% and 22% higher than in grasslands and cushion‐forming plants. The vegetation mosaic in alpine ecosystems might therefore provide essential clues to underst
Tracking spatial variation in river load from Andean highlands to inter-Andean valleys
(2018) Tenorio , Gustavo E.; Vanacker, Veerle; Campforts, Benjamin; Alvarez, Lenin; Zhiminaicela Saquinaula, Cesar Santiago; Vercruysse, Kim; Molina Verdugo, Armando; Govers, Gerard
Mountains play an important role in the denudation of continents and transfer erosion and weathering products to lowlands and oceans. The rates at which erosion and weathering processes take place in mountain regions have a substantial impact on the morphology and biogeochemistry of downstream reaches and lowlands. The controlling factors of physical erosion and chemical weathering and the coupling between the two processes are not yet fully understood. In this study, we report physical erosion and chemical weathering rates for five Andean catchments located in the southern Ecuadorian Andes and investigate their mutual interaction. During a 4-year monitoring period, we sampled river water at biweekly intervals, and we analyzed water samples for major ions and suspended solids. We derived the total annual dissolved, suspended sediment, and ionic loads from the flow frequency curves and adjusted rating curves and used the dissolved and suspended sediment yields as proxies for chemical weathering and erosion rates. In the 4-year period of monitoring, chemical weathering exceeds physical erosion in the high Andean catchments. Whereas physical erosion rates do not exceed 30 t km−2 y−1 in the relict glaciated morphology, chemical weathering rates range between 22 and 59 t km−2 y−1 . The variation in chemical weathering is primarily controlled by intrinsic differences in bedrock lithology. Land use has no discernible impact on the weathering rate but leads to a small increase in base cation concentrations because of fertilizer leaching in surface water. When extending our analysis with published data on dissolved and suspended sediment yields from the northern and central Andes, we observe that the river load composition strongly changes in the downstream direction, indicating large heterogeneity of weathering processes and rates within large Andean basins.
Vegetation effects on soil pore structure and hydraulic properties in volcanic ash soils of the high Andes
(2022) Vanacker, Veerle
Soil hydraulic properties control the provision of hydrological services. Vegetationand topography influence these properties by altering soil structure and porosity. Theunderlying mechanisms are not yet fully understood for the high Andean region. Inthis study, we examined how vegetation and topographic attributes are related to soilhydraulic properties and soil pore structure in young volcanic ash soils, and furthercorrelated them to soil texture, organic carbon, and root characteristics to explainthese relationships. In a 0.7 km2study site located in the Andean páramo of northernEcuador, we measured soil water retention, saturated hydraulic conductivity, bulkdensity (BD), and pore size distribution parameters on eight soil profiles with con-trasting vegetation types (cushion-forming plants vs. tussock grasses) and topo-graphic positions (summit vs. hillslope). We observed significant differences in soilhydraulic properties and soil pore structure in the uppermost horizons by vegetationtype, whereas topography had a minor effect. In the A horizons, we found higherwater retention at saturation and field capacity (10%–14%), higher total availablewater (8%–15%), and higher saturated hydraulic conductivity (4–12 times) undercushion-forming plants compared to tussock grasses. The elevated values under cush-ion plants were attributed to the presence of larger pores, lower soil BD, and highersoil organic carbon content as a result of coarser root systems. Total available waterwas generally high (0.34–0.40 cm3cm 3), and locally not associated with any soilproperty. The higher water retention in soils under cushion vegetation can enhancesoil water storage for plants and the regulation of water flows during prolonged rainfall events. The saturated hydraulic conductivity of the surface horizons is highcompared to rainfall intensities resulting in high infiltration capacity; whilst its declinewith depth reveals the potential for generation of subsurface stormflow, especiallybelow cushion-forming plants. Our findings highlight that soil hydraulic properties dif-fer among vegetation types, and show the significance of vegetation types for soilhydrology