Andrés Iroumé

Variability of annual rainfall partitioning for different sites and forest covers in Chile

Precipitation, throughfall, stemflow and interception losses were determined in Chile on 29 research plots grouped in nine research sites, covering a wide range of rainfall zones, forest types, species, ages and densities. All the data are presented and analyzed on a 12-month time base. Throughfall varied between 55 and 86% of precipitation (P) and although it was higher in coniferous stands than in broadleaved forests the differences were not statistically significant. Stemflow varied from 1 to 13% of P in coniferous stands and between 1 and 8% of P in broadleaved forests. Stemflow for individual trees was higher under high annual rainfall and in low dense forests, and decreased when annual precipitation reduced and forest density increased. In broadleaved stands interception losses (I) ranged from 204 to 1097 mm/year while in coniferous forests I showed a narrower range of variation from 199 to 579 mm/year. Because the final effect of the replacement of native forests by plantations upon water yield also depends on transpiration and other evaporation losses, it was not possible to conclude that this substitution will increase water availability. In a Monterey pine stand interception losses increased with the age of the forest because of the tendency for the branches of this conifer to become horizontal, thus increasing interception capacity and decreasing stemflow. In a native forest that had reached its climax state interception losses decreased during nine years of measurement associated with the continuous reduction of interception capacity of the dense bamboo understorey.

Extending the timescale for using beryllium 7 measurements to document soil redistribution by erosion

[1] The need for spatially distributed information on soil mobilization, transfer, and deposition within the landscape by erosion has focused attention on the potential for using fallout radionuclides (i.e., 137 Cs, excess 210 Pb, and 7 Be) to document soil redistribution rates. Whereas 137 Cs and excess 210 Pb are used to estimate medium- and longer-term erosion rates (i.e., approximately 45 years and 100 years, respectively), 7B e, by virtue of its short half-life (53 days), provides potential for estimating short-term soil redistribution on bare soils. However, the approach commonly used with this radionuclide means that it can only be applied to individual events or short periods of heavy rain. In addition, it is also frequently difficult to ensure that the requirement for spatially uniform 7 Be inventories across the study area immediately prior to the study period is met. If the existing approach is applied to longer periods with several rainfall events (e.g., several weeks or more) soil redistribution is likely to be substantially underestimated. These problems limit the potential for using the 7 Be approach, particularly in investigations where there is a need to assemble representative information on soil redistribution occurring during the entire wet season. This paper reports the development of a new or refined model for converting radionuclide measurements to estimates of soil redistribution (conversion model) for use with 7 Be measurements, which permits much longer periods to be studied. This refined model aims to retain much of the simplicity of the existing approach, but takes account of the temporal distribution of both Be fallout and erosion during the study period and of the evolution of the 7 Be depth distribution during this period. The approach was successfully tested using 7 Be measurements from a study of short-term soil redistribution undertaken within an area of recently harvested forest located near Valdivia in Southern Chile. The study period extended over about 3 months and included the main part of the winter wet season of 2006. The estimates of soil redistribution obtained using the new conversion model were consistent with those obtained from erosion pins deployed within the same study area and were two to three times greater than those obtained using the approach and conversion model employed in existing studies.

Efecto de plantaciones de Pinus radiata y Eucalyptus globulus sobre el recurso agua en la Cordillera de la Costa de la región del Biobío, Chile

Se estudio el efecto de plantaciones forestales sobre el recurso hidrico en cuencas de la vertiente este de la Cordillera de la Costa de la region del Biobio, en el centro sur de Chile. La redistribucion de las precipitaciones, la oscilacion temporal de los caudales, la fluctuacion del contenido de agua edafica, la evapotranspiracion y el transporte de sedimentos fueron determinados para dos cuencas forestadas con Pinus radiata y dos con Eucalyptus globulus. De los 2.149 mm de precipitacion registrada, las plantaciones de P. radiata interceptaron el 16 y 17 %, y las de E. globulus un 10 y 11 %, respectivamente. El caudal de los efluentes para las dos cuencas con P. radiata fue equivalente al 33 %, monto que supero a las con E. globulus que alcanzaron el 20 y 23 % de la precipitacion. Durante el verano, los suelos presentaron una fuerte disminucion de su contenido de agua, sobrepasando en los primeros 30 cm el punto de marchitez permanente. Las cuencas con E. globulus tuvieron una evapotranspiracion equivalente al 76 y 70 %, y las de P. radiata al 65 y 64 %, respectivamente, de la precipitacion. Estas diferencias pudieron ser superiores si la disponibilidad de agua, durante el estio, no hubiese sido una limitante para satisfacer los requerimientos maximos de agua de cada una de las especies. La exportacion total de sedimentos para el periodo fue de 237 y 615 kg/ha en las cuencas con P. radiata y 152 y 125 kg/ha con E. globulus. Los resultados obtenidos siguen una tendencia semejante a los de investigaciones en estudios con condiciones edafoclimaticas y plantaciones similares.

Dinámica y alternativas de manejo de material leñoso de gran tamaño en cuencas del sur de Los Andes

Los elementos lenosos tienen un efecto positivo en la morfodinamica de los canales y en la biodiversidad de los cauces de montana. Sin embargo, su presencia puede aumentar los riesgos asociados a las inundaciones extremas en las llanuras pobladas. Este estudio reporta acerca de la abundancia, la distribucion espacial, los mecanismos de incorporacion y deposicion de los elementos lenosos entre cuencas del sureste de los Andes (Tres Arroyos, Rio Toro, y Buena Esperanza). Los resultados muestran grandes diferencias entre las cantidades y los volumenes de elementos lenosos de las cuencas analizadas, debido a las diferentes perturbaciones historicas y a las distintas caracteristicas de cubierta del bosque. Para estimar la movilidad de las piezas lenosas, estas fueron marcadas en el Buena Esperanza y en el Tres Arroyos. Los eventos ordinarios (intervalo de recurrencia menores de dos anos) movieron solo elementos pequenos y aislados (diametro < 0,25 m, longitud < 3 m) y para distancias relativamente cortas. Las cuencas de estudio reportadas son tomadas como casos paradigmaticos para ilustrar una estrategia de gestion de elementos lenosos. La eliminacion de los elementos y los cortes de la vegetacion riberena, no son estrategias eficaces, porque los raros eventos de gran magnitud son capaces de movilizar los arboles de las laderas por remocion en masa. Areas propensas a inundaciones deben ser preservadas libres de asentamientos sensibles. Sin embargo, importantes infraestructuras presentes pueden ser protegidas con soluciones estructurales especificamente disenadas. Su potencial uso en el contexto de las tres cuencas andinas analizadas es presentado en este trabajo.

Interdisciplinary Studies of Eruption at Chaitén Volcano, Chile

High-silica rhyolite magma fuels Earths largest and most explosive eruptions. Recurrence intervals for such highly explosive eruptions are in the 100- to 100,000-year time range, and there have been few direct observations of such eruptions and their immediate impacts. Consequently, there was keen interest within the volcanology community when the first large eruption of high-silica rhyolite since that of Alaskas Novarupta volcano in 1912 began on 1 May 2008 at Chaiten volcano, southern Chile, a 3-kilometer-diameter caldera volcano with a prehistoric record of rhyolite eruptions [Naranjo and Stern, 2004semi; Servicio Nacional de Geologia y Mineria (SERNAGEOMIN), 2008semi; Carn et al., 2009; Castro and Dingwell, 2009; Lara, 2009; Munoz et al., 2009]. Vigorous explosions occurred through 8 May 2008, after which explosive activity waned and a new lava dome was extruded.

Material leñoso de gran tamaño en dos cuencas de la Cordillera de la Costa de Chile con diferente historia de uso del suelo

Resumen es: El material lenoso en los cauces de montana depende, principalmente, de las caracteristicas del bosque ribereno que los alimenta. Esta investigacion pres...

Use of Remote Imagery to Analyse Changes in Morphology and Longitudinal Large Wood Distribution in the Blanco River After the 2008 Chaiten Volcanic Eruption, Southern Chile

Abstract The 2008 haitén volcanic eruption generated significant changes in the channel morphology and large wood () abundance along the fluvial corridor of the lanco iver, southern hile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the lanco iver widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of were introduced to the study segment; individual per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km−1 were observed in the year 2009. Between 2009 and 2012 the quantity of was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.

Movilidad y reclutamiento de material leñoso de gran tamaño en dos cauces de la Cordillera de la Costa de Chile

Resumen es: Se estudio la movilidad de material lenoso de gran tamano (LW) en segmentos de los cauces principales de las cuencas Vuelta de Zorra y Pichun, ubicadas e...

Role and management of in-channel wood in relation to flood events in Southern Andes basins

This paper analyses the connection among wood dynamics, channel morphology and flood risk in mountain basins of the Southern Chilean Andes and of the Argentinean Tierra del Fuego. Guidelines for the management of in-channel wood and of the riparian buffer strip are suggested, along with considerations about possible input from landslides and debris flows. A selection of low-impact check dams specifically designed for the retention of floating LW elements is finally provided.

The need for a hydromorphological approach to Chilean river management

El manuscrito refleja la opinion de los autores acerca de la necesidad de aplicar un enfoque hidromorfologico para la gestion de los rios chilenos. Se presenta una breve resena de los ultimos avances cientificos sobre el enfoque hidromorfologico en la gestion de rios, asi como una vision general de las condiciones de los rios chilenos y sus mayores perturbaciones. Por otra parte, se hace enfasis en la necesidad de incluir en la toma de decisiones los servicios directos como los indirectos proporcionados por los rios. Se afirma que la hidromorfologia es un elemento fundamental a considerar al determinar el estado ecologico de los rios. La comprension de como las variables hidrologicas y morfologicas interactuan de forma dinamica es sin duda clave para evaluar la presencia o ausencia de un equilibrio dinamico, una condicion que, a su vez, fomenta tanto la diversidad de habitat como el desarrollo sostenible de los ecosistemas acuaticos y riberenos. Los autores concluyen que es necesario cambiar el paradigma actual de gestion aplicado en los rios chilenos desarrollando una estrategia que permita evaluar las condiciones hidromorfologicas y ecologicas de los rios. Ademas, sugieren implementar legislacion especifica orientada a promover estandares ecologicos y geomorfologicos en la practica de gestion, con el apoyo de un fortalecimiento y una ampliacion de la ensenanza academica de la geomorfologia y ecologia fluvial.