Browsing by Autor "Gerd Dercon"

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Distribution of nutrient pools in recently formed soils of Andean high wetlands (Huayna-Potos&#237;, Bolivia)
(2020) Michele Nuñez-Quiroga; Edson Ramírez; Gerd Dercon; Ana Navas
&lt;p&gt;The Andean glaciers are experiencing since 1980 an accelerated decline associated with an increase in air temperature across the region. Encompassing the shrinking of mountain glaciers new soils are formed as deglaciation facilitates biogeochemical processes and the subsequent development of vegetation. Under extreme environmental conditions high-altitude soils are constrained by climate, substrate and geomorphological characteristics of recently deglaciated surfaces that control soil features in high mountains. At the foot of Huayna-Potos&amp;#237;, the glacier retreat is gradually exposing mineral substrate, which is being colonised by soil biota and plants. The subsequent accumulation of organic matter is progressing rapidly especially in wetlands developed in the proglacial area thus accelerating the processes of soil formation. The characterization of soil organic carbon (SOC) pools is necessary to understand SOC dynamics in soils and a relative measure of C stability in soils.&lt;/p&gt;&lt;p&gt;In this study we attempt to evaluate the distribution of SOC, C fractions and nitrogen in glacial deposits and high altitude wetlands to relate it with that of &lt;sup&gt;137&lt;/sup&gt;Cs as indicator of soil stability. To this purpose topsoil sampling of moraines, colluvium and peat soil in wetlands was undertaken during a two weeks expedition to Huayna-Potos&amp;#237; Glacier area in the frame of IAEA INT5153 project in May 2017 and contents of SOC and its fractions (i.e. active and stable carbon fractions), nitrogen and &lt;sup&gt;137&lt;/sup&gt;Cs activity (Bq kg&lt;sup&gt;-1&lt;/sup&gt;) were determined.&lt;/p&gt;&lt;p&gt;The high wetlands both at favourable flat topographic positions and slopes have high organic rich soils showing large carbon sink capacity. More abundant depleted values of &lt;sup&gt;137&lt;/sup&gt;Cs in moraines and colluvium indicate greater impact of soil erosion processes in comparison to wetlands, whereas a higher &lt;sup&gt;137&lt;/sup&gt;Cs content is related to higher carbon contents and more abundant vegetation that would preserve soil from erosion. The size of the nutrient pool such as carbon and nitrogen is much higher in wetlands than in glacial deposits. In the carbon pool, the active fraction is more abundant than the stable fraction but in wetlands the ratio active/stable is much higher (mean: 31) than in glacial deposits (mean: 5). The contribution of the active fraction to SOC is also higher in wetlands (c.a. 1), while the opposite was found for the stable fraction contribution to SOC with almost a ratio of 0 in wetlands compared to 0.24 in glacial deposits. Paralleling the evolution of vegetation the enrichment in soil nutrients affects carbon (C) dynamics in the new soils that all are in the early forming stages with low C stability. Despite wetlands soils having the largest SOC content, the imbalance in the proportions of the C fractions with almost negligible stable C evidence the risk of interrupting the C cycle by loosing the more labile fraction. Therefore, focus should be directed to preserve the fragile new forming soils but specially wetlands because their key role in regulating the hydrological system and maintaining high altitude ecosystems.&lt;/p&gt;
Signals of an increasing drought condition in the Central Andes
(2025) Juliana Nogueira; Heitor Evangelista; Edson Ramírez; Newton de Magalhães Neto; Patricia Piacsek; Osama Mustafa; Ana Laura Navas Romero; Tim Stott; Bulat Mavlyudov; Gerd Dercon
<title>Abstract</title> The tropical glaciers of the Central Andes, particularly those in the Cordillera Real and surroundings, have been experiencing accelerated retreat since 1980. Dendrochronology based studies reach the same conclusions. These facts may profoundly impact communities living in the Andean high mountains and even in big cities like La Paz. This study examines the environmental changes in the Lake Tuni catchment and its associated glaciers (Condoriri, Jist'aña and Huayna-Potosí), located in the Cordillera Real Mountain range, 20-50 km northeast of La Paz. We employed a multi-proxy analysis based on the glacier´s dynamics, historical regional meteorological data, climate indices, and the geochemistry retrieved from a well-dated sedimentary record from Lake Tuni. The remote sensing data reveals a significant acceleration in glacier retreat beginning in the 1990s, with a pronounced worsening observed in the early 2000s while the sedimentary record shows a decline in runoff since 2000, characterized by a reduction in the terrigenous composition and magnetic susceptibility of sediments and a dominance of pollens of plants typical of drier conditions. Additionally, since the 1980s, increasing microcharcoal, dust, and wind-blown minerals from ice-free proglacial areas have darkened glacier surfaces, potentially accelerating melt. These indicators suggest a reduced availability of meltwater, which is critical for local water resources. Our findings imply that since the 1990s, the timing of glacier retreat has coincided with significant reductions in precipitation and changes in regional hydrology. We attribute these changes to altered Southern Amazon basin hydrology where vast areas of deforestation were created in the same period. This study highlights the extreme vulnerability of the Central Andes ecosystem, where the interplay and timing of climate change and land use by humans create unprecedented challenges. The continued retreat of these glaciers poses significant risks to water security for Andean communities, underscoring the urgent need for integrated, multidisciplinary approaches to enhance climate resilience in the region.
Signals of an increasing drought condition in the Central Andes
(2025) Juliana Nogueira; Heitor Evangelista; Edson Ramírez; Newton de Magalhães Neto; Patricia Piacsek; Osama Mustafa; Ana Laura Navas Romero; Tim Stott; Bulat Mavlyudov; Gerd Dercon
<title>Abstract</title> The tropical glaciers of the Central Andes, particularly those in the Cordillera Real and surroundings, have been experiencing accelerated retreat since 1980. Dendrochronology based studies reach the same conclusions. These facts may profoundly impact communities living in the Andean high mountains and even in big cities like La Paz. This study examines the environmental changes in the Lake Tuni catchment and its associated glaciers (Condoriri, Jist'aña and Huayna-Potosí), located in the Cordillera Real Mountain range, 20-50 km northeast of La Paz. We employed a multi-proxy analysis based on the glacier´s dynamics, historical regional meteorological data, climate indices, and the geochemistry retrieved from a well-dated sedimentary record from Lake Tuni. The remote sensing data reveals a significant acceleration in glacier retreat beginning in the 1990s, with a pronounced worsening observed in the early 2000s while the sedimentary record shows a decline in runoff since 2000, characterized by a reduction in the terrigenous composition and magnetic susceptibility of sediments and a dominance of pollens of plants typical of drier conditions. Additionally, since the 1980s, increasing microcharcoal, dust, and wind-blown minerals from ice-free proglacial areas have darkened glacier surfaces, potentially accelerating melt. These indicators suggest a reduced availability of meltwater, which is critical for local water resources. Our findings imply that since the 1990s, the timing of glacier retreat has coincided with significant reductions in precipitation and changes in regional hydrology. We attribute these changes to altered Southern Amazon basin hydrology where vast areas of deforestation were created in the same period. This study highlights the extreme vulnerability of the Central Andes ecosystem, where the interplay and timing of climate change and land use by humans create unprecedented challenges. The continued retreat of these glaciers poses significant risks to water security for Andean communities, underscoring the urgent need for integrated, multidisciplinary approaches to enhance climate resilience in the region.
The impact of glacier retreat on Andean high wetlands: Assessing the geochemical transfer and sediment provenance in the proglacial area of Huayna-Potosí (Bolivia)
(Elsevier BV, 2024) Ana Navas; Edson Ramírez; Leticia Gaspar; Iván Lizaga; Tim Stott; Francisco Rojas; Borja Latorre; Gerd Dercon
The accelerated decline of tropical Andean glaciers is affecting the water cycle of mountains in the region. In the Cordillera Real (Bolivia) on the Huayna-Potosí peak (6088 m a.s.l.), the rapid retreat of the Oeste Glacier is exposing new rock outcrops and glacial materials. Changes in the hydrological regime by glacier retreat are likely to modify the supply of sediments and subsequently affect the geochemical transfer of particle-bound elements within proglacial and downstream ecosystems. To address this issue, a sampling campaign in the proglacial area of Huayna-Potosí aimed to identify and collect sediments from the primary active landforms. To characterise elemental transfer and identify sediment provenance using fingerprinting techniques, streambed sediments were collected along the main stream from the glacier tongue at 5002 m a.s.l. to a wetland shallow lake at 4700 m a.s.l.. Geomorphological features control the production of fine particles and the distribution of particle-bound geochemical elements. Complex processes of solubilization, mobilisation, and retention govern the elemental transfer. Significant increases in 238U, as well as some major elements, were observed in the surface lake sediments, while Pb, Cr, and Cu decreased, and 137Cs was not detected. The spatial distribution patterns of geochemical elements and the assessment of the sediment provenance indicate that deglaciation fosters geochemical processes and the elemental transfer dynamics in the wetlands. Moraines and colluvium were found to be the primary contributors to sediment yield (93 %) while the rich organic soils in swamps contributed the least (7 %). The enhanced supply of sediments to the shallow lake in parallel to glacier decline may affect water quality and bring about further changes in the wetlands. Identifying primary sediment sources is essential for water management. Our findings enhance understanding of the compositional characteristics of mobilised sediment and their variations, aiding in more effective resource management to preserve these high-altitude wetlands.