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The ecosystem response of Lake Redo (Central Pyrenees) to fluctuations in seasonal air temperature during the last two centuries was investigated by comparison of reconstructed air temperatures with the sediment record. Fine slicing allowed a resolution of 3-6 years according to the Pb-210 dating, although it was still difficult to easily investigate the response to air temperature forcing, since extreme fluctuations in temperature occur on interannual time-scales. However, the resolution was sufficient to show responses on decadal and century scales. An overall tendency to warming in mean annual temperature in the Central Pyrenees has been caused by summer and in particular by autumn increases. Many of the measured sediment variables apparently responded to these long term trends, but the significance of the relationships was highly conditioned by the structure of the data. The variables responding most on the finer time scales were the microfossils. For diatoms, chironomids and chrysophytes the main variability correlated to summer and to autumn temperatures. For two planktonic species, Fragilaria nanana and Cyclotella pseudostelligera, we found a link of their variability with temperature fluctuations in their growing months ( September and October, respectively). This relationship appeared at a certain point during a general warming trend, indicating a threshold in the response. On the other hand, no significant changes in the dominant species could be linked to temperature, nor in any significant subgroup of the 180 diatom species present in the core. In contrast, for most chironomids ( particularly Paratanytarsus austriacus, Heterotrissocladius marcidus and Micropsectra radialis) a negative relationship with summer temperature extended throughout the studied period. This response of the whole group gives chironomids a more robust role as indicators for recording temperature changes on long time-scales( e. g., through the Holocene) and for lake signal inter-comparison. Finally, our results indicated that, in all cases, there was a significant resilience to high frequency changes and hysteresis despite extreme fluctuations. Although we were dealing with organisms with one or many generations per year, their populations seemed to follow the decadal trends in air temperature.

In 1999, a set of coordinated projects and investments whose principal objective was to transform Barcelona into one of the main distribution points of southern Europe resulted in the relocation of the Llobregat River mouth. The mouth was relocated by draining the old river mouth and constructing a new one. The aim of this study was to characterise the physico-chemical properties and the aquatic macroinvertebrate communities of the new river mouth and to monitor the changes experienced by the estuarine environment during its creation. A sampling point was established in the river 1.8 km upstream from its connection with the new mouth, and two sampling points were established in the new mouth. Samples of water and macroinvertebrates were collected every two months from May 2004 to June 2005, covering the periods before (from May to September 2004) and after (from September 2004 to June 2005) the new mouth was connected to the river and the sea. During the period before its connection to the river and the sea, the new mouth was functionally similar to a lagoon, with clear waters, presence of Chara and a rich invertebrate community. After the connection was completed, seawater penetrated the river mouth and extended to the connection point with the river (approximately 3.9 km upstream). An increase in conductivity from 4-6 mS cm-1 to 24-30 mS cm-1 caused important changes in the macroinvertebrate community of the new mouth. An initial defaunation was followed by a colonisation of the new mouth by brackish-water and marine invertebrate species. Due to its design (which allows the penetration of the sea) and the decreased discharge from the lower part of the Llobregat River, the new mouth has become an arm of the sea. En 1999 la desembocadura del Río Llobregat fue desviada como consecuencia de una acción coordinada de proyectos cuyo principal objetivo era el de transformar Barcelona en uno de los principales puntos de distribución de mercancías del sur de Europa. En el presente estudio se caracterizan las propiedades físico-químicas y la comunidad de macroinvertebrados acuáticos de la nueva desembocadura, y se monitorizan los cambios experimentados por el ecosistema durante su creación. Un punto de muestreo se situó en el Río Llobregat, 1.8 km aguas arriba de su conexión con la nueva desembocadura, y dos puntos de muestreo se situaron en la nueva desembocadura. Se recogieron muestras de agua y de macroinvertebrados cada dos meses desde Mayo de 2004 hasta Junio de 2005, período que incluyó el antes (desde Mayo hasta Septiembre de 2004) y el después (desde Septiembre de 2004 hasta Junio de 2005) de que la nueva desembocadura fuera conectada al río y al mar. Durante el período anterior a su conexión con el río y el mar la nueva desembocadura funcionaba como una laguna, presentando aguas claras, presencia de Chara y una comunidad de macroinvertebrados rica en especies. Después de ser conectada al río y el mar, el agua de mar penetró en la desembocadura hasta el punto de conexión con el río (aproximadamente unos 3.9 km aguas arriba). La conductividad de la desembocadura aumentó de 4-6 mS cm-1 a 24-30 mS cm-1, causando importantes cambios en la comunidad de macroinvertebrados acuáticos. Se registró una pérdida de fauna inicial seguida de una colonización de fauna marina y de aguas salobres. Debido a su diseño (que permite la entrada de grandes cantidades de agua de mar) y al escaso caudal del tramo bajo del Llobregat, la nueva desembocadura se ha convertido en un brazo de mar.