Limnología inicial de Laguna Pozo Verde, Costa Rica: Batimetría, agua, sedimentos y diatomeas

Introducción : Costa Rica tiene cientos de lagos, muchos de los cuales nunca han sido estudiados científicamente.  Objetivo: Conocer limnológia  de la Laguna Pozo Verde en el Parque Nacional Juan Castro Blanco, Costa Rica (~1935 m de elevación), para proporcionar datos de referencia para estudiar cambios futuros. Métodos: Medimos la profundidad y temperatura del agua y la profundidad de Secchi; sedimentos superficiales analizados; y examinó mapas e imágenes de satélite. Resultados: Aunque algunos la describen como formada por procesos volcánicos, la Laguna Pozo Verde probablemente se formó en un deslizamiento de tierra, que ocurre con frecuencia en esta zona lluviosa en la empinada ladera sur del inactivo volcán Porvenir. Nuestros sondeos mostraron una profundidad máxima de 9,25 m cerca del centro del lago. El agua era moderadamente transparente (profundidad de Secchi 2,6 m), con pH circunneutro y temperaturas de 15,9 a 18,1 °C, con estratificación débil a 0,5 m. Los sedimentos superficiales contenían 27% de materia orgánica y tenían relaciones C/N y valores de isótopos de carbono estables consistentes con algas lacustres y plantas C 3 ; Surirella angusta compuso más del 90% de las diatomeas. Conclusión: La laguna es significativamente más omera de lo informado y los sedimentos superficiales albergar una combinación de diatomeas única entre los 88 lagos examinados en Costa Rica.Introducción: Costa Rica tiene cientos de lagos, muchos nunca estudiados científicamente. Objetivo: Conocer la limnología de Laguna Pozo Verde en el Parque Nacional Juan Castro Blanco, Costa Rica (~1935m de elevación), como referencia para estudiar futuros cambios. Métodos: Medimos la profundidad y temperatura del agua y la profundidad de Secchi; analizamos sedimentos superficiales; y examinamos mapas e imágenes satelitales. Resultados: Aunque algunos la describen como formada por procesos volcánicos, es probable que Laguna Pozo Verde se haya formado en un deslizamiento de tierra, algo común en esta zona lluviosa de la empinada ladera sur del Volcán Porvenir (inactivo). Hallamos una profundidad máxima de 9,25m cerca del centro. El agua era moderadamente transparente (profundidad de Secchi 2,6m), con un pH cercano a neutro y temperaturas de 15,9-18,1°C, y una débil estratificación a 0,5m. Los sedimentos superficiales contenían un 27% de materia orgánica y tenían cocientes C/N y valores de isótopos de carbono estables, coherentes con algas lacustres y plantas C 3 ; más del 90% de las diatomeas eran Surirella angusta . Conclusión: La laguna es significativamente más somera de lo informado y los sedimentos superficiales albergan una combinación de diatomeas única entre los 88 lagos examinados en Costa Rica

Aquatic community response to volcanic eruptions on the Ecuadorian Andean flank: evidence from the palaeoecological record

Aquatic ecosystems in the tropical Andes are under increasing pressure from human modification of the landscape (deforestation and dams) and climatic change (increase of extreme events and 1.5 °C on average temperatures are projected for AD 2100). However, the resilience of these ecosystems to perturbations is poorly understood. Here we use a multi-proxy palaeoecological approach to assess the response of aquatic ecosystems to a major mechanism for natural disturbance, volcanic ash deposition. Specifically, we present data from two Neotropical lakes located on the eastern Andean flank of Ecuador. Laguna Pindo (1°27.132′S–78°04.847′W) is a tectonically formed closed basin surrounded by a dense mid-elevation forest, whereas Laguna Baños (0°19.328′S–78°09.175′W) is a glacially formed lake with an inflow and outflow in high Andean Páramo grasslands. In each lake we examined the dynamics of chironomids and other aquatic and semi-aquatic organisms to explore the effect of thick (> 5 cm) volcanic deposits on the aquatic communities in these two systems with different catchment features. In both lakes past volcanic ash deposition was evident from four large tephras dated to c.850 cal year BP (Pindo), and 4600, 3600 and 1500 cal year BP (Baños). Examination of the chironomid and aquatic assemblages before and after the ash depositions revealed no shift in composition at Pindo, but a major change at Baños occurred after the last event around 1500 cal year BP. Chironomids at Baños changed from an assemblage dominated by Pseudochironomus and Polypedilum nubifer-type to Cricotopus/Paratrichocladius type-II, and such a dominance lasted for approximately 380 years. We suggest that, despite potential changes in the water chemistry, the major effect on the chironomid community resulted from the thickness of the tephra being deposited, which acted to shallow the water body beyond a depth threshold. Changes in the aquatic flora and fauna at the base of the trophic chain can promote cascade effects that may deteriorate the ecosystem, especially when already influenced by human activities, such as deforestation and dams, which is frequent in the high Andes

Exploring the impact of cumulative testing on academic performance of undergraduate students in Spain

The final publication is available at Springer via http://dx.doi.org/10.1007/s11092-014-9208-zFrequent testing provides opportunities for students to receive regular feedback and to increase their motivation. It also provides the instructor with valuable information on how course progresses, thus making it possible to solve the problems encountered before it is too late. Frequent tests with noncumulative contents have been widely analysed in the literature with inconclusive results. However, cumulative testing methods have hardly been reported in higher education courses. This paper analyses the effect of applying an assessment method based on frequent and cumulative tests on student performance. Our results show that, when applied to a microeconomics course, students who were assessed by a frequent, cumulative testing approach largely outperformed those assessed with a single final exam.Doménech I De Soria, J.; Blázquez Soriano, MD.; De La Poza, E.; Muñoz Miquel, A. (2015). Exploring the impact of cumulative testing on academic performance of undergraduate students in Spain. Educational Assessment, Evaluation and Accountability. 27(2):153-169. https://doi.org/10.1007/s11092-014-9208-zS153169272Adelman, HS, & Taylor, L. (1990). Intrinsic motivation and school misbehaviour some intervention implications. Journal of Learning Disabilities, 23, 541–550.Biggs, J, & Tang, C. (2007). Teaching for quality learning at university 3rd edn. Open University Press.Boston, C. (2002). The concept of formative assessment. Practical Assessment Research & Evaluation 8.Brown, GA, Bull, J, Pendlebury, M. (1997). Assessing Student Learning in Higher Education, 1st edn. Routledge.Cano, MD. (2011). Students’ involvement in continuous assessment methodologies: a case study for a distributed information systems course. IEEE Transactions on Education, 54, 442–451.Casem, ML (2006). Active learning is not enough. Journal of College Science Teaching, 35.Chen, J, & Lin, TF. (2008). 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Dordrecht: Springer Netherlands.Eikner, AE, & Montondon, L. (2001). Evidence on factors associated with success in intermediate accounting I. Accounting Educators’ Journal 13.Emerson, TLN, & Mencken, KD. (2011). Homework to require or not? online graded homework and student achievement Perspectives on Economic Education Research 7.Fulkerson, F, & Martin, G. (1981). Effects of exam frequency on student performance, evaluations of instructor, and test anxiety. Teaching of Psychology, 8, 90–93.Furnham, A, & Chamorro-Premuzic, T. (2005). Individual differences and beliefs concerning preference for university assessment methods. Journal of Applied Social Psychology, 35, 1968–1994.Gibbs, G, & Simpson, C. (2005). Conditions under which assessment supports students’ learning Learning and Teaching in Higher Education 1 (August 5, 2011)3–31.Haberyan, KA. (2003). Do weekly quizzes improve student performance on general biology exams?. 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Volcanic Gases:Silent Killers

This is the accepted manuscript. The final version is available at http://link.springer.com/chapter/10.1007%2F11157_2015_14.Volcanic gases are insidious and often overlooked hazards. The effects of volcanic gases on life may be direct, such as asphyxiation, respiratory diseases and skin burns; or indirect, e.g. regional famine caused by the cooling that results from the presence of sulfate aerosols injected into the stratosphere during explosive eruptions. Although accounting for fewer fatalities overall than some other forms of volcanic hazards, history has shown that volcanic gases are implicated frequently in small-scale fatal events in diverse volcanic and geothermal regions. In order to mitigate risks due to volcanic gases, we must identify the challenges. The first relates to the difficulty of monitoring and hazard communication: gas concentrations may be elevated over large areas and may change rapidly with time. Developing alert and early warning systems that will be communicated in a timely fashion to the population is logistically difficult. The second challenge focuses on education and understanding risk. An effective response to warnings requires an educated population and a balanced weighing of conflicting cultural beliefs or economic interests with risk. In the case of gas hazards, this may also mean having the correct personal protection equipment, knowing where to go in case of evacuation and being aware of increased risk under certain sets of meteorological conditions. In this chapter we review several classes of gas hazard, the risks associated with them, potential risk mitigation strategies and ways of communicating risk. We discuss carbon dioxide flows and accumulations, including lake overturn events which have accounted for the greatest number of direct fatalities, the hazards arising from the injection of sulfate aerosol into the troposphere and into the stratosphere. A significant hazard facing the UK and northern Europe is a “Laki”-style eruption in Iceland, which will be associated with increased risk of respiratory illness and mortality due to poor air quality when gases and aerosols are dispersed over Europe. We discuss strategies for preparing for a future Laki style event and implications for society

Orbital forcing of glacial/interglacial variations in chemical weathering and silicon cycling within the upper White Nile basin, East Africa: Stable-isotope and biomarker evidence from Lakes Victoria and Edward

On Quaternary time scales, the global biogeochemical cycle of silicon is interlocked with the carbon cycle through biotic enhancement of silicate weathering and uptake of dissolved silica by vascular plants and aquatic microalgae (notably diatoms, for which Si is an essential nutrient). Large tropical river systems dominate the export of Si from the continents to the oceans. Here, we investigate variations in Si cycling in the upper White Nile basin over the last 15 ka, using sediment cores from Lakes Victoria and Edward. Coupled measurements of stable O and Si isotopes on diatom separates were used to reconstruct past changes in lake hydrology and Si cycling, while the abundances of lipid biomarkers characteristic of terrestrial/emergent higher plants, submerged/floating aquatic macrophytes and freshwater algae document past ecosystem changes. During the late-glacial to mid-Holocene, 15–5.5 ka BP, orbital forcing greatly enhanced monsoon rainfall, forest cover and chemical weathering. Riverine inputs of dissolved silica from the lake catchments exceeded aquatic demand and may also have had lower Si-isotope values. Since 5.5 ka BP, increasingly dry climates and more open vegetation, reinforced by the spread of agricultural cropland over the last 3–4 ka, have reduced dissolved silica inputs into the lakes. Centennial-to millennial-scale dry episodes are also evident in the isotopic records and merit further investigation

Basic limnology of fifty-one lakes in Costa Rica

We visited 51 lakes in Costa Rica as part of a broad-based survey to document their physical and chemical characteristics and how these relate to the mode of formation and geographical distribution of the lakes. The four oxbow lakes were low in elevation and tended to be turbid, high in conductivity and CO2 , but low in dissolved O2 ; one of these, L. Gandoca, had a hypolimnion essentially composed of sea water. These were similar to the four wetland lakes, but the latter instead had low conductivities and pH, and turbidity was often due to tannins rather than suspended sediments. The thirteen artificial lakes formed a very heterogenous group, whose features varied depending on local factors. The thirteen lakes dammed by landslides, lava flows, or lahars occurred in areas with steep slopes, and were more likely to be stratified than most other types of lakes. The eight lakes that occupy volcanic craters tended to be deep, stratified, clear, and cool; two of these, L. Hule and L. Río Cuarto, appeared to be oligomictic (tending toward meromictic). The nine glacial lakes, all located above 3440 m elevation near Cerro Chirripó, were clear, cold, dilute, and are probably polymictic. Cluster analysis resulted in three significant groups of lakes. Cluster 1 included four calcium-rich lakes (average 48 mg l-1), Cluster 2 included fourteen lakes with more Si than Ca+2 and higher Cl- than the other clusters, and Cluster 3 included the remaining thirty-three lakes that were generally less concentrated. Each cluster included lakes of various origins located in different geographical regions; these data indicate that, apart from the high-altitude glacial lakes and lakes in the Miravalles area, similarity in lake chemistry is independent of lake distribution.Se visitaron 51 lagos en Costa Rica como parte de un sondeo de lagos más amplio, con el fin de documentar sus carácteristicas físicas y químicas y las relaciones entre estas carácteristicas y el modo de formación y distribución geográfico de los lagos. Los cuatro lagos en U tienden a ser de baja altitud y turbios, así como a tener alta conductividad y CO2 , pero baja concentración de O2 ; uno de estos, L. Gandoca, tuvo un hipolimnion compuesto esencialmente por agua de mar. Estos lagos fueron similares a los cuatro lagos de humedales, pero estos últimos presentaron en cambio baja conductividad y pH, y la turbidez se debió a menudo a taninos en vez de sedimentos en suspensión. Los trece lagos artificiales forman un grupo heterogéneo, cuyos rasgos variaron dependiendo de factores locales. Los siete lagos formados por represamiento debido a derrumbes, flujos de lava o lahares ocurren generalmente en áreas de pendientes pronunciadas, y son más probables de estar estratificados que la mayoría de los otros tipos de lagos. Los ocho agos que ocupan cráteres volcánicos tienden a ser profundos, estratificados, de aguas claras y de baja temperatura; dos de estos, L. Hule y L. Río Cuarto, parecen ser oligomícticos (con tendencia a la meromixis). Los nueve lagos glaciales, todos localizados arriba de los 3 440 m de altitud cerca del Cerro Chirripó, fueron de aguas claras, fríos, diluidos y son probablemente polimícticos. Un análisis de conglomerados dio como resultado tres grupos distintos. El Grupo 1 incluyó cuatro lagos ricos en calcio (promedio de 48 mg l-1 ), el Grupo 2 incluyó catorce lagos con más Si que Ca +2 y una concentración de Cl - más alta que los otros grupos, y el Grupo 3 incluyó los restantes treinta y tres lagos que fueron en general menos concentrados. Los lagos en cada grupo tienen varios orígenes y están distribuidos en diferentes regiones geográficos; estos datos indican que, aparte de los lagos glaciales de gran altitud, la similitud en la química de los lagos es independiente de su distribución

Limnología de Las Lagunas Glaciales en el Páramo del Chirripó, Costa Rica. (Limnology of Glacial Lakes in the Chirripó Páramo of Costa Rica.)

More than 30 lakes of glacial origin exist within the Chirripó páramo in the Cordillera de Talamanca of Costa Rica. This chapter describes the geomorphic setting and physical and chemical limnology of 19 lakes located between 3450-3570 m elevation in the upper basins of five glaciated valleys. All lakes are clear, dilute, and apparently polymictic. Water chemistry data from 1998, 2000, and 2001 are similar from lake to lake and year to year, and are consistent with sparse prior measurements between 1966 and 1991. However, the lake water temperatures we have measured are much higher than those reported by earlier researchers, possibly indicating a change in climate in the páramo