Mid-late Holocene lake levels and trophic states of a shallow lake from the southern Pampa plain, Argentina

Changes in trophic status of the shallow Lake La Brava (southeastern Pampa plain of Argentina) are evaluated based on geochemical, biological and sedimentological data. Based on a conceptual framework, we propose that the lake level defines the water column mixing conditions, affecting internal lake processes and determining the transparency of lake water. The shift between alternative states is reconstructed for the last ~4800 years. Four main lake stages have been recognized, although short term shifts characterize all stages. A turbid phytoplankton-dominated state prevailed between ~4700-4500 cal yr before present (BP). Drier conditions and low lake levels pushed the lake to a clear state until 2000 cal yr BP. Afterwards the lake switched back to a turbid state, and these conditions persisted until ~200 cal yr BP. In the last 200 years, the lake switched back and forth between clear and turbid states. The latter represents the modern conditions of the lake since ~1950 AD. These shifts can be attributed mainly to climatic drivers.We thank to Dr Juan Manuel Lirio and Lic Mario Núñez (Instituto Antártico Argentino) for field support. Nora Irene Maidana (Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina) help with diatom identification. Financial support was provided by PIP-CONICET 1265/08, PIP-CONICET 2142001100 100014, UBACyT 20020110100153 and CICYT project EROMED (CGL2011-25486). We thank the editor and two anonymous reviewers for their constructive comments, which helped us to improve the manuscript. This is the IDEAN contribution number R-112.Peer Reviewe

Mid-Late Holocene Climate and Trophic States in a Shallow Lake from the Southern Pampa Plain, Argentina

Changes in trophic status of the shallow Lake La Brava (southeastern Pampa plain of Argentina) are evaluated based on geochemical, biological and sedimentological data. Based on a conceptual framework, we propose that the lake level defines the water column mixing conditions, affecting internal lake processes and determining the transparency of lake water. The shift between alternative states is reconstructed for the last ~4800 years. Four main lake stages has been recognized, although short term shifts characterize all stages. A turbid phytoplankton-dominated state prevailed between ~4700-4500 cal yr BP. Drier conditions and low lake levels pushed the lake to a clear state until 2000 cal yr BP. Afterwards the lake switched back to a turbid state, and these conditions persisted until ~200 cal yr BP. In the last 200 years, the lake switched back and forth between a clear and a turbid state anew, the latter represents the modern conditions of the lake since ~1950 AD. These shifts can be attributed mainly to climatic drivers.Fil: Laprida, Cecilia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. Instituto de Estudios Andinos Don Pablo Groeber; ArgentinaFil: Plastani, María Sofía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geologicas. Instituto de Estudios Andinos Don Pablo Groeber; ArgentinaFil: Irurzun, Maria Alicia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Gogorza, Claudia Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Navas, Ana. Instituto Experimental Aula Dei; EspañaFil: Valero Garces, B.. Instituto Pirenaico de Ecología; EspañaFil: Sinito, Ana Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentin