title: Tracking climate change in oligotrophic mountain lakes: Recent hydrology and productivity synergies in Lago de Sanabria (NW Iberian Peninsula).
abstract: Mountain lakes are particularly sensitive to global change as their oligotrophic conditions may be rapidly altered after reaching an ecological threshold, due to increasing human impact and climate change. Sanabria Lake, the largest mountain lake in the Iberian Peninsula and with a recent history of increased human impact in its watershed, provides an opportunity to investigate recent trends in an oligotrophic, hydrologically-open mountain lake, and their relationship with climate, hydrological variability and human pressure. We conducted the first systematic and detailed survey of stable isotope compositions of Sanabria Lake and Tera River together with limnological analyses during 2009-2011. δ18Olakewaterand δDlakewaterseasonal fluctuations are strongly linked to river discharges, and follow the monthly mean isotopic composition of precipitation, which is controlled by NAO dynamics. δ13CPOMand δ13CDICrevealed higher contribution of allochthonous organic matter in winter and spring due to higher river inflow and lower primary productivity. Increased phytoplankton biomass in late summer correlated significantly with higher pH and Chl-a, and higher nutrient input and lower river inflow. However, the small δ13CPOMseasonal amplitude underlines the stability of the oligotrophic conditions and the isotopic variation in POM and DIC reflect small seasonal fluctuations mostly as a consequence of strong throughflow. The stability of hydrology and productivity patterns is consistent with Holocene and last millennium reconstructions of past limnological changes in Sanabria Lake. The results of this study indicate that trophic state in this hydrologically-open mountain lake is strongly controlled by climate variability, but recent changes in human-land uses have increased sediment delivery and nutrients supply to the lake and have to be considered for management policies. Monitoring surveys including isotope techniques provide snapshots of modern isotope variability, and serve as a benchmark for assessing the environmental impacts of future developments and long-term climate changes in mountain lakes.
authors.affiliation: Facultad de Ciencias, Universidad de Salamanca, Plaza de los Caidos, s/n, 37008 Salamanca, Spain. Electronic address: margajambrina@usal.es.
authors.forename: Margarita
authors.initials: M
authors.lastname: Jambrina-Enríquez
authors.affiliation: Facultad de Ciencias, Universidad de Salamanca, Plaza de los Caidos, s/n, 37008 Salamanca, Spain. Electronic address: crecio@usal.es.
authors.forename: Clemente
authors.initials: C
authors.lastname: Recio
authors.affiliation: Laboratorio de Limnologia del Parque Natural del Lago de Sanabria, Eras 1, 49300 Puebla de Sanabria, Zamora, Spain.. Electronic address: josecvega@telefonica.net.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Vega
authors.affiliation: Instituto Pirenaico de Ecologia (IPE-CSIC), Av. Montañana 1005, 50059 Zaragoza, Spain; Laboratorio Internacional de Cambio Global (LINCGlobal), Avda Montañana 1005, 50059, Zaragoza, Spain. Electronic address: blas@ipe.csic.es.
authors.forename: Blas
authors.initials: B
authors.lastname: Valero-Garcés
keywords: Carbon cycle; Global change; Hydrology; Isotopes; Mountain lakes; Oligotrophic lakes