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Effects of nutrient availability and temperature on phytoplankton development: a case study from large lakes south of the Alps |
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| Authors: | Nico Salmaso Fabio Buzzi Letizia Garibaldi Giuseppe Morabito Marco Simona |
| Institution: | 1. Sustainable Agro-ecosystems and Bioresources Department, IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all??Adige, Fondazione E. Mach, Via E. Mach 1, S. Michele all??Adige, 38010, Trento, Italy 2. Dipartimento di Lecco, ARPA Lombardia, Via I Maggio, 21/b, 23848, Oggiono, Lecco, Italy 3. Dipartimento Scienze Ambiente e Territorio, Universit?? di Milano, Piazza della Scienza 1, 20126, Milano, Italy 4. C.N.R. Istituto per lo Studio degli Ecosistemi, L.go Tonolli, 50, 28922, Verbania Pallanza, Italy 5. Istituto Scienze della Terra, Scuola Universitaria Professionale della Svizzera Italiana (SUPSI), Blocco C - Ufficio 109, Via Trevano/Casella Postale 72, 6952, Canobbio, Switzerland |
| Abstract: | This work investigated the combined effects of nutrient availability and temperature on phytoplankton in large and deep lakes south of the Alps (lakes Garda, Iseo, Como, Lugano and Maggiore). The more eutrophic basins (Lugano and Iseo) showed a higher presence of cyanobacteria, green algae (Chlorophyta and Charophyta) and dinoflagellates (Dinophyta). Besides these two water bodies, high biomasses of cyanobacteria were recorded also in the oligo-mesotrophic Lake Garda. The development of these algal groups during the growing season showed a strong dependence on the surface spring availability of SRP, which, in turn, was related to winter climatic oscillations, deep mixing dynamics, and trophic status. A specific analysis carried out by applying additive mixed modelling, generalized least squares and mixed modelling, allowed investigation of the direct, seasonal effects of water temperature variations and trophic status on different algal groups. The dominant cyanobacteria (Oscillatoriales) showed only a partial relationship with temperature, while Nostocales and Chroococcales, which did not appear to have a close relationship with the trophic status of the lakes, were characterised by abrupt increases during the warmer months. High positive relationships with temperature were found for a few other algal groups (e.g., Chlorophyta, Charophyta and Dinophyta). Overall, the results indicated a positive relationship between the seasonal development of the more abundant and eutrophic-sensitive algal groups and the concurrent effect of trophic status and water temperature. Nevertheless, it was stressed that specific differences could be interpreted taking into account the different autoecological characteristics and susceptibilities of different species and functional groups to other stressing factors favouring losses, including, e.g., vertical sinking and grazing. |
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