Lipid biomarkers in the Enol Lake (Asturias, Northern Spain): coupled natural and human induced environmental history

The lipid content of three cores from Lake Enol (Picos de Europa National Park, Asturias, Northern Spain) was studied. The n-alkane profiles indicated a major input from terrigenous plants [predominance of high molecular weight (HMW) alkanes] since ca. 1695 AD to the water body, although the uppermost cm revealed a predominance of organic matter (OM) derived from algae, as the most abundant alkane was C17. Three units revealing different environmental conditions were defined. Unit A (ca. 1695–1860 AD) in the lowermost parts of ENO13-10 (< 12 cm) and ENO13-15 (< 28 cm) was identified and was characterized by higher OM input and evidence of minimal degradation (high CPI values, predominance of HMW n-alkanoic acids and good correspondence between the predominant n-alkane and n-alkanoic acid chains). These findings could be linked to the Little Ice Age, when cold and humid conditions may have favored an increase in total organic carbon (TOC) and n-alkane and n-alkanoic acid content (greater terrigenous OM in-wash), and may have also reduced bacterial activity. In Unit B (ca. 1860–1980 AD) the lack of correspondence between the n-alkane and n-alkanoic acid profiles of ENO13-10 (12–4 cm) and ENO13-15 (28–8 cm) suggested a certain preferential microbial synthesis of long chain saturated fatty acids from primary OM and/or bacterial activity, coinciding with a decrease in OM input, which could be linked to the global warming that started in the second half of the 19th century. In ENO13-7 the low OM input (low TOC) was accompanied by some bacterial degradation (predominance ofHMWn-alkanoic acids but with a bimodal distribution) in the lowermost 16–5 cm. Evidence of considerable phytoplankton productivity and microbial activity was especially significant in Unit C (ca. 1980–2013 AD) identified in the uppermost part of all three cores (5 cm in ENO13-7, 4 cm in ENO13-10 and 8 cm in ENO13-15), coinciding with higher concentrations of n-alkanes and n-alkanoic acids, which were considered to be linked to warmer and drier conditions, as well as to greater anthropogenic influence in modern times. Plant sterols, such as b-sitosterol, campesterol and stigmasterol, were significantly present in the cores. In addition, fecal stanols, such as 24-ethylcoprostanol from herbivores, were present, thereby indicating a continuous and significant pollution input derived from these animals since the 17th century, being more important in the last 20 years.

Test on Tile Vaults in France in the 19th Century

Durante el s. XIX las bóvedas tabicadas se desarrollan enormemente, ampliando sus usos a nuevos tipos y extendiendose por zonas dónde no se habían utilizado tradicionalmente. Además, comienza a utilizarse el cemento como aglomerante en lugar del yeso. En este contexto se realizan muchos ensayos sobre ellas, con el objeto de validar un sistema que resultaba nuevo por estas razones. Se estudian a continuación una serie de ensayos de resistencia realizados en Francia entre 1837 y 1865, todos ellos sobre bóvedas de tamaño y geometría similar: entre 4 y 5 m de luz, y con flecha 1/10 de la luz, un tipo muy empleado en ese momento para la construcción de fábricas. El primero de ellos busca medir experimentalmente el empuje de una de estas bóvedas, para cerrar un debate sobre la existencia o no de empujes en las bóvedas tabicadas. Los siguientes quieren obtener la carga de rotura de las bóvedas, con el objeto de construir después unas similares.