| Abstract | Piburger See is a soft-water mountain lake located in the Central Eastern Alps (47°11'42''N, 10°53'18''E, Tyrol, Austria). The increase in recreational activities, tourism, and the application of fertilizer on nearby fields, resulted in enhanced primary production and rising hypolimnetic oxygen depletion in the lake during the 1950s and 1960s (Pechlaner, 1968). Lake restoration started in 1970 by exporting anoxic and nutrient-rich hypolimnetic waters with an Olszewski tube, and by reducing external nutrient loading by altering fertilizer application and by diverting sewage from a public bath. Lake oxygenation rapidly improved after 1970 (Pechlaner, 1979), while the response of total phosphorus (TP) and phytoplankton biomass to lake restoration was delayed by two decades (Fig. 1). Since the early 2000s, phytoplankton biovolume has increased again, suggesting a reversing trend in lake trophic status (Tolotti et al., 2012). Simultaneously, small changes in TP were recorded (Fig. 1). Although Piburger See was part of the OECD study on eutrophication and is currently included in the Austrian LTER network, the 45 year-long data-base includes several data gaps (e.g. for phytoplankton). To compensate for gaps in moniroring data, a paleolimnological study has been carried out on a radiometrically dated sediment core in order to reconstruct the lakes' trophic state since the late-19th century and to define the reference conditions for the lake (Thies et al., 2012). Limnological data recorded during the last four decades provided the validation of the inferred TP concentration (Fig. 2). Changes in phytoplankton biomass and species composition were analyzed in relation to nutrients and water temperature. Epilimnetic temperatures of Piburger See, reconstructed by long-term air temperature records, showed a pronounced increase during the mid-1940s and also since the late-20th century. Both periods also show increasing algal growth and changes in diatom species composition (i.e. increase in centric diatoms and recent blooms in Asterionella formosa). The combination of paleo- and neolimnology allowed the analysis of the role of climate and nutrients in driving phytoplankton changes in Piburger See. In particular, the study on sediments showed that long-term phytoplankton changes were mainly attributed to increasing lake temperature, while nutrients acted as modulating factor. On the other side, short-term changes in the phytoplankton of Piburger See since the 2000s were explained by varying nutrient concentrations and ratios (i.e. nitrogen and silica), while rising water temperature and enhanced thermal stability regulated the inter-annual lake variability. Our results underline that the combined impact of nutrients and climate on phytoplankton development can sustain short-time phytoplankton pulses, and thus mimic short-term increases in the trophic level of less productive lakes. |
| Text | 355765 2013 Laghi montani Paleoecologia Ecologia del fitoplancton Nutrienti algali Cambiamento climatico Combined effects of nutrient and climate change interaction of Piburger See Austria . Results from Paleo and Neolimnology Monica Tolotti; Piero Guilizzoni; Andrea Lami; Simona Musazzi; Ulrike Nickus; Roland Psenner; Neil Rose; Handong Yang; Hansjorg Thies Monica TOLOTTI1, Piero GUILIZZONI2, Andrea LAMI2, Simona MUSAZZI2, Ulrike NICKUS3, Roland PSENNER4, Neil ROSE5, Handong YANG5, Hansjorg THIES4 1Iasma Research and Innovation Centre, Edmund Mach Foundation, Via E. Mach 1, 38010 S. Michele all Adige, Italy. monica.tolotti@fmach.it 2CNR Institute of Ecosystem Study, Verbania Pallanza, Italy. p.guilizzoni@ise.cnr.it, a.lami@ise.cnr.it, s.musazzi@ise.cnr.it 3Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria ulrike.nickus@uibk.ac.at 4Institute of Ecology, University of Innsbruck, Innsbruck, Austria. roland.psenner@uibk.ac.at, hansjoerg.thies@uibk.ac.at 5Environemntal Change Research Centre, University College London, London, UK. n.rose@ucl.ac.uk handong.yang@ucl.ac.uk Piburger See is a soft water mountain lake located in the Central Eastern Alps 47°11 42 N, 10°53 18 E, Tyrol, Austria . The increase in recreational activities, tourism, and the application of fertilizer on nearby fields, resulted in enhanced primary production and rising hypolimnetic oxygen depletion in the lake during the 1950s and 1960s Pechlaner, 1968 . Lake restoration started in 1970 by exporting anoxic and nutrient rich hypolimnetic waters with an Olszewski tube, and by reducing external nutrient loading by altering fertilizer application and by diverting sewage from a public bath. Lake oxygenation rapidly improved after 1970 Pechlaner, 1979 , while the response of total phosphorus TP and phytoplankton biomass to lake restoration was delayed by two decades Fig. 1 . Since the early 2000s, phytoplankton biovolume has increased again, suggesting a reversing trend in lake trophic status Tolotti et al., 2012 . Simultaneously, small changes in TP were recorded Fig. 1 . Although Piburger See was part of the OECD study on eutrophication and is currently included in the Austrian LTER network, the 45 year long data base includes several data gaps e.g. for phytoplankton . To compensate for gaps in moniroring data, a paleolimnological study has been carried out on a radiometrically dated sediment core in order to reconstruct the lakes trophic state since the late 19th century and to define the reference conditions for the lake Thies et al., 2012 . Limnological data recorded during the last four decades provided the validation of the inferred TP concentration Fig. 2 . Changes in phytoplankton biomass and species composition were analyzed in relation to nutrients and water temperature. Epilimnetic temperatures of Piburger See, reconstructed by long term air temperature records, showed a pronounced increase during the mid 1940s and also since the late 20th century. Both periods also show increasing algal growth and changes in diatom species composition i.e. increase in centric diatoms and recent blooms in Asterionella formosa . The combination of paleo and neolimnology allowed the analysis of the role of climate and nutrients in driving phytoplankton changes in Piburger See. In particular, the study on sediments showed that long term phytoplankton changes were mainly attributed to increasing lake temperature, while nutrients acted as modulating factor. On the other side, short term changes in the phytoplankton of Piburger See since the 2000s were explained by varying nutrient concentrations and ratios i.e. nitrogen and silica , while rising water temperature and enhanced thermal stability regulated the inter annual lake variability. Our results underline that the combined impact of nutrients and climate on phytoplankton development can sustain short time phytoplankton pulses, and thus mimic short term increases in the trophic level of less productive lakes. Published version Paleoecological reconstructions lacustrine, peat and cave sediments Bialka Tatrzanska, Polonia 22 24 maggio 2013 Internazionale Contributo Abstract 2013_Abstract_Polonia.pdf Presentazione simona.musazzi MUSAZZI SIMONA piero.guilizzoni GUILIZZONI PIERO andrea.lami LAMI ANDREA TA.P02.033.001 Dinamica degli Ecosistemi Conservazione e Gestione della Biodiversita |
