Soil hydraulic properties control the provision of hydrological services. Vegetation and topography influence these properties by altering soil structure and porosity. The underlying mechanisms are not yet fully understood for the high Andean region. In this study, we examined how vegetation and topographic attributes are related to soil hydraulic properties and soil pore structure in young volcanic ash soils, and further correlated them to soil texture, organic carbon, and root characteristics to explain these relationships. In a 0.7 km 2 study site located in the Andean páramo of northern Ecuador, we measured soil water retention, saturated hydraulic conductivity, bulk density (BD), and pore size distribution parameters on eight soil profiles with contrasting vegetation types (cushion-forming plants vs. tussock grasses) and topographic positions (summit vs. hillslope). We observed significant differences in soil hydraulic properties and soil pore structure in the uppermost horizons by vegetation type, whereas topography had a minor effect. In the A horizons, we found higher water retention at saturation and field capacity (10%-14%), higher total available water (8%-15%), and higher saturated hydraulic conductivity (4-12 times) under cushion-forming plants compared to tussock grasses. The elevated values under cushion plants were attributed to the presence of larger pores, lower soil BD, and higher soil organic carbon content as a result of coarser root systems. Total available water was generally high (0.34-0.40 cm 3 cm À3 ), and locally not associated with any soil property. The higher water retention in soils under cushion vegetation can enhance soil water storage for plants and the regulation of water flows during prolonged
Abstract. The Neotropical Andean grasslands above 3500 m a.s.l., known as páramo, offer remarkable ecological services for the Andean region. The most important of these is the water supply of excellent quality to many cities and villages in the inter-Andean valleys and along the coast. The páramo ecosystem and especially its soils are under constant and increased threat by human activities and climate change. In this study, the recovery speed of the páramo soils after drought periods are analysed. The observation period includes the droughts of 2009, 2010, 2011, and 2012 together with intermediate wet periods. Two experimental catchments – one with and one without páramo – were investigated. The Probability Distributed Moisture (PDM) model was calibrated and validated in both catchments. Drought periods and its characteristics were identified and quantified by a threshold level approach and complemented by means of a drought propagation analysis. At the plot scale in the páramo region, the soil water content measured by time domain reflectometry (TDR) probes dropped from a normal value of about 0.84 to ∼ 0.60 cm3 cm−3, while the recovery time was 2–3 months. This did not occur at lower altitudes (Cumbe) where the soils are mineral. Although the soil moisture depletion observed in these soils was similar to that of the Andosols (27 %), decreasing from a normal value of about 0.54 to ∼ 0.39 cm3 cm−3, the recovery was much slower and took about 8 months for the drought in 2010. At the catchment scale, however, the soil water storage simulated by the PDM model and the drought analysis was not as pronounced. Soil moisture droughts occurred mainly in the dry season in both catchments. The deficit for all cases is small and progressively reduced during the wet season. Vegetation stress periods correspond mainly to the months of September, October and November, which coincides with the dry season. The maximum number of consecutive dry days were reached during the drought of 2009 and 2010 (19 and 22 days), which can be considered to be a long period in the páramo. The main factor in the hydrological response of these experimental catchments is the precipitation relative to the potential evapotranspiration. As the soils never became extremely dry nor close to the wilting point, the soil water storage capacity had a secondary influence.
RESUMEN Se evaluó la calidad del agua de los ríos Tarqui, Yanuncay, Machángara y Tomebamba, afluentes del río Paute. En línea con la necesidad de incorporar nuevos enfoques en la vigilancia de la calidad del agua, este estudio aplicó el ampliamente conocido Water Quality Index (QWI) pero, en lugar de utilizar los nueve parámetros originalmente requeridos por el método, utilizamos 18 parámetros fisicoquímicos y microbiológicos. Para cada río, se llevaron a cabo nueve campañas de monitoreo, cubriendo períodos hidrológicos representativos y midiendo descargas de flujo. Los resultados muestran que, en general, en las áreas de captación de los ríos, el recurso hídrico es adecuado para casi todo tipo de uso, pero gradualmente, a medida que avanza aguas abajo, la calidad disminuye debido a las descargas de aguas residuales sanitarias, industriales y a factores naturales como escorrentía o sedimentos por erosión. La condición más crítica de calidad de las aguas evaluadas se presentó durante las condiciones de sequía, principalmente debido a la disminución del oxígeno disuelto y al aumento de la temperatura, la salinidad, la materia orgánica y las bacterias coliformes. Por otro lado, durante los períodos lluviosos, los parámetros indicadores de una disminución en la calidad del agua fueron el color, la turbidez, y el contenido de nutrientes como fósforo y nitrógeno. En general, los ríos tienen mejor calidad para condiciones de flujo medio, que prevalecen durante la mayor parte del año. Los presentes resultados se analizaron de acuerdo con los objetivos de calidad establecidos en estudios anteriores, permitiendo una evaluación cualitativa del sistema
<p>The high tropical Andes ecosystem, known as p&#225;ramo, provides important hydrological services to densely populated areas in the Andean region. In order to manage these services sustainably, it is crucial to understand the biotic and abiotic processes that control both water quality and fluxes. Recent research in the p&#225;ramo highlights a knowledge gap regarding the role played by soil-vegetation interactions in controlling soil-water processes and resulting water and solute fluxes.</p><p>Here, we determine the hydrological and geochemical fluxes in four soil profiles in the p&#225;ramo of the Antisana&#180;s water conservation area in northern Ecuador. Water fluxes were measured biweekly with field fluxmeters in the hydrological year Apr/2019- Mar/2020 under two contrasting vegetation types: tussock-like grass (TU) and cushion-forming plants (CU). Soil solution was collected in parallel with wick samplers and suction caps for assessing the concentrations of dissolved cations, anions and organic carbon (DOC). In addition, soil moisture was measured continuously in the upper meter of the soil profile, i.e. first three horizons (A, 2A and 2BC), using water content reflectometers. The vertical water flux in the upper meter of each soil profile was simulated using the 1D HYDRUS model. We carried out a Sobol analysis to identify sensitive soil hydraulic parameters. We then derived water fluxes by inverse modeling, based on the measured soil moisture. We validated the calculated water fluxes using the fluxmeter data. Solute fluxes were estimated by combining the water fluxes and the soil solution compositions.</p><p>Our preliminary results suggest that water fluxes and DOC concentration vary under different vegetation types. The fluxmeter data from the 2A horizon indicates that the cumulative water flux under TU (2.8 - 5.7 l) was larger than under CU (0.8 &#8211; 1.1 l) during the dry season (Aug-Sep and Dec-Jan). However, the opposite trend was observed in the wet season for maximum water fluxes. Moreover, the DOC concentration in the uppermost horizon was higher under CU (47.3 &#177;2.2 mg l<sup>-1</sup>) than under TU (3.1 &#177;0.2 mg l<sup>-1</sup>) vegetation during the monitoring period. We associate the water and solute responses under different vegetation types to the contrasting soil hydro-physical and chemical properties (e.g., saturated hydraulic conductivity and organic carbon content) in the uppermost soil horizon. Our study illustrates the existence of a spatial association between vegetation types, water fluxes and solute concentrations in Antisana&#180;s water conservation area. By modelling the hydrological balance of the upper meter of the soil mantle, the water and solute fluxes will be estimated for soils with different vegetation cover.</p><p>&#160;</p>
The Neotropical Andean grasslands above 3500 m a.s.l., known as páramo, offer remarkable ecological services for the Andean region. The most important of these is the water supply of excellent quality to many cities and villages in the inter-Andean valleys and along the coast. The páramo ecosystem and especially its soils are under constant and increased threat by human activities and climate change. In this study, the recovery speed of the páramo soils after drought periods are analysed. The observation period includes the droughts of 2009, 2010, 2011, and 2012 together with intermediate wet periods. Two experimental catchments -one with and one without páramo -were investigated. The Probability Distributed Moisture (PDM) model was calibrated and validated in both catchments. Drought periods and its characteristics were identified and quantified by a threshold level approach and complemented by means of a drought propagation analysis. At the plot scale in the páramo region, the soil water content measured by time domain reflectometry (TDR) probes dropped from a normal value of about 0.84 to ∼ 0.60 cm 3 cm −3 , while the recovery time was 2-3 months. This did not occur at lower altitudes (Cumbe) where the soils are mineral. Although the soil moisture depletion observed in these soils was similar to that of the Andosols (27 %), decreasing from a normal value of about 0.54 to ∼ 0.39 cm 3 cm −3 , the recovery was much slower and took about 8 months for the drought in 2010. At the catchment scale, however, the soil water storage simulated by the PDM model and the drought analysis was not as pronounced. Soil moisture droughts occurred mainly in the dry season in both catchments. The deficit for all cases is small and progres-sively reduced during the wet season. Vegetation stress periods correspond mainly to the months of September, October and November, which coincides with the dry season. The maximum number of consecutive dry days were reached during the drought of 2009 and 2010 (19 and 22 days), which can be considered to be a long period in the páramo. The main factor in the hydrological response of these experimental catchments is the precipitation relative to the potential evapotranspiration. As the soils never became extremely dry nor close to the wilting point, the soil water storage capacity had a secondary influence.
<p>Soils play a key role in the provision of vital ecosystem services. Soil functions, that deliver these services, are governed by soil properties.&#160; Soil structure is a fundamental property of soils since it controls water, geochemical and biological processes.&#160; The soil pore system, one of the main components of soil structure, can be affected by different biological feedbacks. Vegetation can have an impact on soil pore system through changes in pore size distribution and porosity, causing differences in soil hydraulic properties as well as soil-water processes.</p><p>In high elevation tropical Andean ecosystems (p&#225;ramos) little is still known about vegetation feedbacks on soil properties. At high elevation p&#225;ramos (above 4100m), it is possible to find high diversity and co-dominance of plant species over short distances. In these landscapes, cushion plants and tussock grasses dominate alongside shrubs. These vegetation types, adapted to extreme local climatic conditions, are placed on young volcanic soils. We take advantage of this diverse setting, located within Antisana&#180;s water conservation area in the north of Ecuador, by studying soil hydraulic properties and soil pore system in eight soil profiles. We hypothesize that the effect caused by Calamagrostis intermedia (tussock) and Azorella pedunculata (cushion) species on soil pore system and soil hydraulic properties at different horizons will be statistically different. In addition, we explore these effects in relation to other soil's physical properties and root traits.</p><p>Soil hydraulic properties were determined on the basis of field observed saturated hydraulic conductivity as well as based on water retention contents at saturation (porosity), field capacity and permanent wilting point measured in the laboratory by the multi-step outflow method and the porous membrane pressure cell. Furthermore, water retention curves were fitted to measured data by the bimodal van Genuchten model. Based on these fittings the pore size distribution was determined. Equivalent pore diameters were derived from the soil water tension head via the capillary rise equation. Statistical analysis to determine differences was carried out by means of the Mann-Whitney U test.&#160; &#160;&#160;&#160;&#160;&#160;&#160;</p><p>The results show that measurable differences in soil hydraulic properties and soil pore system between vegetation species are present at the upper soil horizons, while they become negligible at greater depth. These differences are mainly related to bulk density and root traits. Based on this baseline study, further research could elucidate the effects of vegetation species on soil-water processes at high elevation p&#225;ramo landscapes and will contribute to enhancing water resources management.</p>
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