| Abstract | Influence of climatic fluctuations on the large lakes south of the AIps: implications in the context of global warming Synoptic analyses carried out in the largest lakes south of the Alps demonstrated a tight coupling between deep mixing dynamics and winter climatic fluctuations strictly controlled by atmospheric modes of variability relevant for the Mediterranean region, namely the Atlantic pattern and the Eastern Mediterranean Pattern. In winter, the EA and EMP modes are associated with an intense north easterly airflow bringing cold air from continental Europe over the Mediterranean basin. In turn, harsh winters had a strong impact on the lake water temperatures, deep lake circulation episodes, higher replenishment of epilimnetic phosphorus and hypolimnetic oxygen at spring overturn. Fertilisation was greatly enhanced in the meromictic and more eutrophic lakes. The effects of such a linked chain of events on phytoplankton were studied in Lake Garda where harsh winters and higher P-replenishment had a positive impact on the development of diatoms in spring and cyanobacteria in summer and autumn. Timing of Daphnia population density peak in lakes Garda, Maggiore and Iseo was directly correlated with water temperatures, while the level of peak density was mediated by the extent of spring mixing and food availability. It was hypothesized that an increase in the winter temperatures could cause a decrease in the occurrence of complete overturn episodes. In the short period, this should improve water quality, decreasing the replenishment of phosphorus and - as demonstrated in Lake Garda- the development of cyanobacteria. On the long-term, the lake warming could increase the risk of triggering meromictic conditions. |
| Text | 329125 2014 Laghi sudalpini Eutrofizzazione Cambiamenti climatici East Atlantic pattern Eastern Mediterranean Pattern Influenza delle fluttuazioni climatiche sui grandi laghi a sud delle Alpi implicazioni nel contesto del riscaldamento globale Nico Salmaso; Fabio Buzzi; Leonardo Cerasino; Letizia Garibaldi; Barbara Leoni; Marina Manca; Giuseppe Morabito; Michela Rogora; Marco Simona Nico Salmaso 1, Fabio Buzzi 2, Leonardo Cerasino 1, Letizia Garibaldi 3, Barbara Leoni 3, Marina Manca 4, Giuseppe Morabito 4, Michela Rogora 4, Marco Simona 5 1 IASMA Research and Innovation Centre, Ist. Agr. S. Michele all Adige Fondaz. E. Mach; 2 ARPA Lombardia, Dipartimento di Lecco; 3 Dip. Scienze dell Ambiente e del Territorio e Scienze della Terra, Univ. Milano Bicocca; 4 CNR Istituto per lo Studio degli Ecosistemi; 5 Istituto Scienze della Terra, Scuola Universitaria Professionale della Svizzera Italiana SUPSI eport /Casella Postale 72, 6952 Canobbio, Switzerland. Influence of climatic fluctuations on the large lakes south of the AIps implications in the context of global warming Synoptic analyses carried out in the largest lakes south of the Alps demonstrated a tight coupling between deep mixing dynamics and winter climatic fluctuations strictly controlled by atmospheric modes of variability relevant for the Mediterranean region, namely the Atlantic pattern and the Eastern Mediterranean Pattern. In winter, the EA and EMP modes are associated with an intense north easterly airflow bringing cold air from continental Europe over the Mediterranean basin. In turn, harsh winters had a strong impact on the lake water temperatures, deep lake circulation episodes, higher replenishment of epilimnetic phosphorus and hypolimnetic oxygen at spring overturn. Fertilisation was greatly enhanced in the meromictic and more eutrophic lakes. The effects of such a linked chain of events on phytoplankton were studied in Lake Garda where harsh winters and higher P replenishment had a positive impact on the development of diatoms in spring and cyanobacteria in summer and autumn. Timing of Daphnia population density peak in lakes Garda, Maggiore and Iseo was directly correlated with water temperatures, while the level of peak density was mediated by the extent of spring mixing and food availability. It was hypothesized that an increase in the winter temperatures could cause a decrease in the occurrence of complete overturn episodes. In the short period, this should improve water quality, decreasing the replenishment of phosphorus and as demonstrated in Lake Garda the development of cyanobacteria. On the long term, the lake warming could increase the risk of triggering meromictic conditions. Le ricerche condotte nei grandi laghi a sud delle Alpi hanno dimostrato una stretta dipendenza dei processi di mescolamento da modi di circolazione atmosferica rilevanti per l area mediterranea East Atlantic pattern, EA e Eastern Mediterranean Pattern, EMP . In inverno, EA e EMP sono associati a una situazione di alta pressione nell Oceano Atlantico settentrionale, e a un forte afflusso di aria fredda dall Europa settentrionale e centrale verso il Mediterraneo. Il raffreddamento dell aria, causando una diminuzione delle temperature lacustri, favorisce una maggiore estensione della circolazione primaverile, e un maggiore rifornimento di nutrienti verso la superficie e di ossigeno verso l ipolinmio. L impatto sulle comunita biologiche e stato studiato nel Garda e, in parte, nel lago Maggiore e nel lago d iseo. Nel Garda, a seguito di inverni piu freddi e all aumentare della disponibilita primaverile di nutrienti, sono stati osservati significativi aumenti nella crescita delle diatomee in primavera e dei cianobatteri in estate e autunno. Nel Garda e nel lago Maggiore, mentre la temperatura ambientale e risultata influenzare la tempistica del picco primaverile in densita di Daphnia, l entita dello stesso e apparsa mediata dal mescolamento e dalle disponibilita alimentari. Risultati simili sono stati verificati nel lago d Iseo. Un aumento delle temperature invernali potrebbe determinare una diminuzione nella frequenza degli episodi di mescolamento completo. Nel breve periodo cio porterebbe ad un miglioramento della qualita delle acque superficiali, diminuendo la fertilizzazione primaverile e, come finora dimostrato nel Garda, lo sviluppo di cianobatteri. Nel lungo periodo aumenterebbe invece il rischio di innesco di condizioni meromittiche. 28 Published version Articolo 2014_Biologia_Ambientale_28_2_17_32.pdf Articolo in rivista C.I.S.B.A. 1129 504X Biologia ambientale Biologia ambientale Biol. ambient. giuseppe.morabito MORABITO GIUSEPPE michela.rogora ROGORA MICHELA marinamarcella.manca MANCA MARINA MARCELLA TA.P02.014.002 Impatto dei cambiamenti globali sugli ecosistemi acquatici |
