Héctor Ulloa

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...

Reach scale ecologic influence of in-stream large wood in a Coastal Mountain range channel, Southern Chile

The ecologic infl uence of in-stream large wood (LW) was evaluated at reach scale in a third-order channel located in the Coastal Mountain Range, southern Chile. The tested hypotheses were that Coarse Particle Organic Matter (CPOM) retention is higher and benthic macro-invertebrates are more diverse in channel reaches storing higher volumes of LW. Three LW-low-volume reaches (mean LW volume of 8 m 3 100m -1 of reach channel length; plane bed morphology) and three LW-high-volume reaches (mean volume 262 m 3 100m -1 ; forced pool riffl e bed morphology) were selected within a 1557 m-long segment of the study channel. CPOM retention was inferred from the difference between the number of leaves collected in the downstream end of each reach and the leaves introduced in the upstream end. Mean CPOM retention was 72 and 90% among LW-low and high volume reaches, and showed a positive correlation (R = 0.61) with LW volume. Macro-invertebrates were more diverse and abundant in LW-high-volume reaches and the richness was twice than in LW-low-volume reaches. Bray-Curtis similarity index was low (40%) between LW-high and low volume reaches, while it was high (> 60%) among LW-low-volume reaches. Results confi rm the hypothesis that OM retention and benthic macro-invertebrate diversity and abundance were higher in high LW volume reaches. The higher diversity and abundance of macro-invertebrates associated with LW accumulations confi rm that logjams constitute a biotope that offers shelter and food. These results can guide the assessment of environmental impacts of stream intervention and restoration projects. The study was undertaken within the framework of Project Fondecyt 1110609.

Analysis of Channel Morphology and Large Wood Characteristics Through Remote Images in the Blanco River After the Eruption of the Chaitén Volcano (Southern Chile)

Volcanic eruptions drastically affect fluvial systems, modifying channel morphology and processes of supply and transport of sediment and wood material, destroying vegetation and reducing infiltration rates on hillsides. This work aims to study the morphological changes and the distribution of large wood (LW) material along the Blanco River after the eruption of the Chaiten volcano in May 2008 using aerial and satellite images. Four different images from pre and post-eruption conditions were used: a satellite image from 2005, an aerial one from 2009, and two satellite images from 2012 and 2013. To assess river morphology, the active channel was digitized in all the images; and LW assessment was carried out by digitizing every individual element as polyline and wood jams as polygons. Results showed a general increase in the channel width, being the most notable change between 2005 and 2009. The same occurred in the case of LW supply, both individual elements and wood jams within the active channel increased significantly between 2005 and 2009 but there were no statistically significant differences comparing 2009, 2012 and 2013 images. This drastic event provided an opportunity to study post-eruption situation in the Blanco River, and with the results obtained it was possible to verify that the shape of the channel and presence of LW were strongly affected by the volcanic eruption.

Toward participatory decision-making in river corridor management: two case studies from the European Alps

River managers are aware that river restoration entails addressing and effectively solving wicked social-ecological problems. Contemporary river corridor management is characterized by a variety of actors with different perspectives and interests, and by complex institutional settings and legal landscapes. Additionally, at the intersection between litho-, hydro-, and biological fields, new research suggests that river restoration should reactivate matter and energy fluxes, re-establish spatial connections with the floodplains, and enhance aquatic and terrestrial habitats without exacerbating flood risk. First, we outline a general structure of participatory river corridor management that addresses the following key requirements: (1) unambiguous, participatory spatial delineation of the river corridor; (2) comprehensive assessment of the river corridors hydro-geomorphological, ecological, socio-economic and cultural processes; (3) transparency and consistency of the decision-making process; as well as (4) a coherent envisioning process. Subsequently, we present an overview of two river corridor management processes, conducted in South Tyrol, Italy. Specifically, we analysed the Etsch/Adige River corridor between Laas/Lasa and Glurns/Glorenza in the Upper Vinschgau/Venosta valley characterized by intense agricultural land use and the densely populated Eisack/Isarco River corridor in Brixen/Bressanone. Based on structured interviews with project managers, we highlight strengths and shortcomings of the proposed participatory management and envisage procedural improvements.

Pyroclastic Eruption Boosts Organic Carbon Fluxes Into Patagonian Fjords

Fjords and old-growth forests store large amounts of organic carbon. Yet the role of episodic disturbances, particularly volcanic eruptions, in mobilizing organic carbon in fjord landscapes covered by temperate rainforests remains poorly quantified. To this end, we estimated how much wood and soils were flushed to nearby fjords following the 2008 eruption of Chaiten volcano in south-central Chile, where pyroclastic sediments covered >12 km2 of pristine temperate rainforest. Field-based surveys of forest biomass, soil organic content, and dead wood transport reveal that the reworking of pyroclastic sediments delivered ~66,500+14,600/-14,500 tC of large wood to two rivers entering the nearby Patagonian fjords in less than a decade. A similar volume of wood remains in dead tree stands and buried beneath pyroclastic deposits (~79,900+21,100/-16,900 tC), or stored in active river channels (5,900-10,600 tC). We estimate that bank erosion mobilized ~132,300+21,700/-30,600 tC of floodplain forest soil. Eroded and reworked forest soils have been accreting on coastal river deltas at >5 mm yr-1 since the eruption. While much of the large wood is transported out of the fjord by long-shore drift, the finer fraction from eroded forest soils is likely to be buried in the fjords. We conclude that the organic carbon fluxes boosted by rivers adjusting to high pyroclastic sediment loads may remain elevated for up to a decade, and that Patagonian temperate rainforests disturbed by excessive loads of pyroclastic debris can be episodic short-lived carbon sources.

Large Wood Mobility in Mountain Rivers, Chile

Previous research on large wood (LW) entrainment and mobility has shown that in small rivers most mobile pieces are shorter and thinner than bankfull width and depth, and are deposited perpendicular or oblique to the flow as individual pieces. LW size, quantity and position were investigated over several years in channel segments of four mountain experimental catchments in southern Chile. Every wood piece found within the bankfull channel with more than 10 cm in diameter and 1 m in length was measured, its position was referenced and several of these elements were tagged. The channel segments were re-surveyed after consecutive winter seasons and every tagged wood piece that had moved downstream from its initial position was re-referenced to investigate log mobility and calculate travel distance. LW mobility (the percentage of tagged wood pieces that had moved) was higher in periods where maximum water level exceeded channel bankfull depth, although the difference was not statistically significant, but there was no difference in LW diameter, length or travel distance in periods with maximum during which water levels did or did not exceed bankfull stage. A significant (R = 0.603) linear regression relationship was found between LW mobility (in %) as dependent variable and the ratio Hmax/HBk (Hmax the maximum water level registered during each winter period and HBk the bankfull stage). The ratio between LW travel distance and LW piece diameter decreased with an increase in the ratio between LW piece length and the mean channel bankfull width, although this relationship was not statistically significant.