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See detailCambios ambientales del último milenio en sedimentos lacustres del Lago Thompson, Patagonia Chilena Norte
Sacré, Vincent ULg; Fagel, Nathalie ULg; Leclercq, Louis ULg et al

Poster (2012, October 25)

Este estudio se enfoca en un análisis multiproxy de un testigo sedimentario del Lago Thompson (area 1 km2; 751 masl ; 45°38’S 72°47’W) obtenido en 2008 (LT08-E, 130 cm), con el objetivo de documentar la ... [more ▼]

Este estudio se enfoca en un análisis multiproxy de un testigo sedimentario del Lago Thompson (area 1 km2; 751 masl ; 45°38’S 72°47’W) obtenido en 2008 (LT08-E, 130 cm), con el objetivo de documentar la variabilidad climática durante el último milenio en la Patagonia Chilena Norte y su impacto sobre el ambiente. El modelo de datación se basó en cinco fechados de 14C. Los resultados de 210Pb y 137 Cs no permitieron estimar la tasa de sedimentación para la parte superficial del núcleo. El lago Thompson esta caracterizado por una pequeña cuenca de suaves pendientes y sus sedimentos están dominados por limo arcilloso y partículas amorfas (principalmente diatomeas). Esto último es sustentado por la relación atómica de carbono/nitrógeno (C/N) que indica el origen fitoplanctónico del sedimento (8-10). Los perfiles de rayos –X, susceptibilidad magnética y LOI 550ºC evidencian dos depósitos volcánicos en 1410-1440 y 1780-1790 AD. Los perfiles de C/N y sílice biogénica (SiB) sugieren una alta productividad durante un periodo equivalente a la Pequeña Edad del Hielo (1650-1850 AD), con una máxima intensidad durante ~1800 AD. Desde 1850 AD hasta la actualidad, los perfiles de LOI 550ºC y SiB evidencian una reciente eutrofización y aumento del nivel del lago (asociado con aumento de temperaturas y humedad). Además, los perfiles de SiB presentan una correlación inversa con las temperaturas reconstruidas por anillos de árboles en la Patagonia. El contenido de diatomeas es dominado por especies planctónicas (Aulacoseira sp. y Cyclotella sp.), mientras que taxa bentónicos no muestran una buena diversificación en comparación a otros lagos de la Patagonia. La abundancia de diatomeas muestra respuestas específicas a los depósitos volcánicos con una disminución de Aulacoseira sp.. La relación planctónica/bentónica permite identificar dos periodos de alto y bajo nivel del lago coincidiendo con fases húmedas y secas de la Pequeña Edad de Hielo (1200-1650 y 1650-1850 AD). La realización de análisis sedimentológicos, geoquímicos y de microfósiles permitiría una mejor caracterización de los modelos de depositación del sedimento (impregnación del núcleo sedimentario) y de la interacción entre depósitos volcánicos y diatomeas. Agradecimientos a Fondecyt Nº1070508, FNRS 1360 2007-2010 y ULg CFRA 1060 2009-2010. [less ▲]

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See detailLast millenium environmental changes in Lake Bertrand sediments, Chilean Patagonia
Sacré, Vincent ULg; Fagel, Nathalie ULg; Schmidt, Sabine et al

Poster (2012, April 23)

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See detailLate Holocene environmental changes inferred from diatom, chironomid, and pollen assemblages in an Andean lake in Central Chile, Lake Laja (36°S)
Urrutia, Roberto; Araneda, Alberto; Torres, Laura et al

in Hydrobiologia (2010), 648

A sediment core encompassing the last 2000 years was extracted from Lake Laja, Chile, (36°54′S, 71°05′W) using an Uwitec drilling platform. The sediment was subsampled for loss on ignition, nutrients ... [more ▼]

A sediment core encompassing the last 2000 years was extracted from Lake Laja, Chile, (36°54′S, 71°05′W) using an Uwitec drilling platform. The sediment was subsampled for loss on ignition, nutrients, biogenic silica, and biological proxies (diatoms, chironomids, pollen). The sedimentary profile was characterized by several coarse volcanic layers. Loss on ignition, nutrients, and biogenic silica showed an increasing trend that suggests a recent shift to a higher trophic status. Diatom assemblages also suggested higher nutrient content with increased abundances of Aulacoseira granulata, A. distans, and Asterionella formosa. At the same time, a marked change in the benthic and facultative planktonic taxa may be associated with cooling. This period of change coincides with the European Little Ice Age (LIA). The chironomid profile showed four key zones distinguished largely by changes in the abundance of Tanytarsini, Parachironomus, and Macropelopia. Like diatoms, chironomids also seemed to reflect a shift to higher trophic conditions in the upper part reflected by increasing abundance of taxa such as Tribelos/Phaenopsectra, Cricotopus/Orthocladius, and Ablabesmyia. The most striking feature in the chironomid assemblage is the abundance of Podonominae, Parapsectrocladius, and Limnophyes/Compterosmittia, which could be associated with a cold-dry period between 1500 and 1900 AD in Lake Laja (the period of the European LIA). Pollen assemblages indicated fluctuations in humidity through changes in Nothofagus dombeyi-type, Poaceae, and Ephedra, and we inferred a strong human impact over the last 100 years from the appearance of Plantago and increased levels of Poaceae and Asteraceae subf. Cichorioidae. Finally, the three proxies showed the occurrence of a cold-dry event in Lake Laja (~1550–1900 AD), which roughly coincides with the European LIA. However the data from this research, does not prove neither rejects the existence of the occurrence of the MWP in the central Andes. [less ▲]

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See detailGeochemical evidence (C, N and Pb isotopes) of recent anthropogenic impact in south-central Chile from two environmentally distinct lake sediment records
Fagel, Nathalie ULg; Bertrand, Sebastien; Mattielli, Nadine et al

in Journal of Quaternary Science (2010), 25(7), 1100-1112

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south-central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is ... [more ▼]

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south-central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is situated in the urbanised area of the Biobio Region (36°S). The second lake, Lago Puyehue (40° S), is located 400 km to the southeast of LCSP and within an Andean national park. Our aim is to identify environmental impacts associated with increasing industrial activities and land degradation during the last 150 a. In LCSP, shifts in C/N atomic ratios, 13C and 15N from 1915-1937 to the late 1980s are attributed to successive land degradation episodes in the lake watershed. Based on a Pb isotopic mixing model, we estimate that up to 20% of lead in LCSP sediments is supplied from urban atmospheric pollution. By contrast, human impact in the watershed of Lago Puyehue is very limited. We observe no change in organic geochemistry during the last 150 a and lead contamination remains lower than 5%, even during the last decades. Although contamination levels are much higher in LCSP than in Lago Puyehue, a peak in anthropogenic Pb is recorded during the same period (1974-1976) at both sites. This maximum contamination level is consistent with increased industrial activity in the vicinity of Concepción. [less ▲]

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See detailChanges in diatom, pollen, and chironomid assemblages in response to a recent volcanic event in Lake Galletue (Chilean Andes)
Urrutia, Roberto; Araneda, Alberto; Cruces, Fabiola et al

in Limnologica (2007), 37(1), 49-62

Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past environmental changes. In this study, we report ... [more ▼]

Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past environmental changes. In this study, we report changes in diatoms, pollen, and chironomids assemblages after a tephra deposition in Lake Galletue (Chilean Andes). A sediment core obtained from Lake Galletue (40 m water depth) was sliced in I cm intervals and subsamples were taken to analyze each proxy. Pb-210 and 137 Cs activities were measured to obtain the geochronology and mineralogical analyses were performed to determine the mineral composition of the tephra. Diatom species composition and productivity were modified when the lake received the tephra; Aulacoseira granulata decreased and was later replaced by Cyclotella af. glomerata. After the tephra input, Aulacoseira granulata abundance increased to pre-disturbance levels and Cyclotella af. glomerata decreased. These changes seem to suggest a momentary increase in lake nutrient levels after the tephra deposition. Chironomid assemblages also decreased in head capsules just after the tephra deposition, but the most important change was the replacement of Ablabesmyia by Parakiefferiella, probably due to the sedimentological changes produced by the input of coarse tephra grains. Furthermore, unlike other studies, chironomid assemblages in Lake Galletue did not show a decrease drastically in diversity within the tephra layer. The pollen analysis indicated that, prior to the volcanic event, the vegetal community was dominated by Nothofagus sp., Araucaria araucana, and Blechnum sp.-type. After the tephra deposition, the same taxa are dominant, indicating that the volcanic event seems not produce changes in the vegetation. Nevertheless, within the tephra layer it is possible to see an increase in Poaceae, which represent - due to the percolation process - the effect of eruption on the vegetation. According to our results, diatoms were the most sensitive proxy for describing the changes produced by tephra deposition into the aquatic ecosystem and, despite the noticeable changes in its sedimentological properties; the lake seems to have a high resilience capacity, allowing it to return to pre-tephra input conditions. (c) 2006 Elsevier GmbH. All rights reserved. [less ▲]

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See detailChanges of sub-fossil chironomid assemblages associated with volcanic sediment deposition in an Andean lake (38 degrees S), Chile
Araneda, Alberto; Cruces, Fabiola; Torres, Laura et al

in Revista Chilena de Historia Natural (2007), 80(2), 141-156

Chironomid assemblages and sedimentological parameters (grain size, organic content, mineralogy) of a short sediment core from Lake Galletue (38 degrees 41' S, 71 degrees 17' W) were analysed. The ... [more ▼]

Chironomid assemblages and sedimentological parameters (grain size, organic content, mineralogy) of a short sediment core from Lake Galletue (38 degrees 41' S, 71 degrees 17' W) were analysed. The sedimentary record includes one volcanic ash (tephra) layer, which has a completely different composition than the host sediment in terms of organic content, grain size, and mineralogy. According to the geochronology (Pb-210 and Cs-137), this ash layer corresponds to the eruption of Llaima Volcano in 1956-1957. The tephra deposition had an impact on chironomid assemblages producing, among other changes, an increase in Parakiefferiella and a decrease in Ablabesmyia, although no noticeable change was detected in the diversity index. When compared with other studies, our results also show an impact in terms of the presence of chironomid head capsules within the tephra. The presence of these head capsules could result from the effects of percolation, since the coarse grain size of the tephra particles provides large interstitial spaces. The recovery in the abundances of some taxa after the tephra input, suggests the lake is probably restoring the conditions prevailing before the tephra fall. [less ▲]

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See detailChanges in diatom assemblages in an Andean lake in response to a recent volcanic event
Cruces, Fabiola; Urrutia, Roberto; Parra, Oscar et al

in Archiv für Hydrobiologie (2006), 165(1), 23-35

Galletue Lake (38 degrees 41'S; 71 degrees 17'W, IX Region-Chile) is located in an area that is highly influenced by eruptive activity of the Lonquimay and Llaima volcanoes. As a consequence, during the ... [more ▼]

Galletue Lake (38 degrees 41'S; 71 degrees 17'W, IX Region-Chile) is located in an area that is highly influenced by eruptive activity of the Lonquimay and Llaima volcanoes. As a consequence, during the last century tephra was deposited into the lake. Sedimentary diatom assemblages were reconstructed in order to establish the tephra effect on their composition and productivity. This was done by taking a sediment core from Galletue Lake at 40 m depth and sectioning it in 1 cm intervals. The core age was obtained with Pb-210 and Cs-137 activities and the mineral composition of the tephra was determined with mineralogical analyses. Furthermore, sedimentological analyses were performed and total organic matter was determined in the profile. The diatom assemblages were analysed using light and electronic microscopy. The results showed that the diatom stratigraphy can be separated in three zones recognizing the periods before and after tephra input. Aulacoseira granulata decreased during the tephra influx and was replaced by Cyclotella aff. glomerata. When the tephra disappeared from the sedimentary record, A. granulata returned to pre-volcanic event levels. At the same time, Cyclotella aff. glomerata decreased within the assemblages. Asterionella formosa and Urosolenia eriensis increased after the tephra input, with values surpassing earlier ones. These results indicate that, after the tephra input, the lake recovered its previous nutrient levels, which agrees with the organic matter content in the sedimentary matrix. Finally, the results reveal that the volcanic disturbance changed the structure and productivity of diatom assemblages in Galletue Lake. [less ▲]

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