In the last years, blooms of Planktothrix rubescens were observed in several lakes undergoing re-oligotrophication. Lake Ledro (zmax=48 m) is a mesotrophic, hardwater lake (650 m a.s.l.) located in SW Trentino (Eastern Italian Alps). It is an impacted lake exploited for hydropower production. In the 70s and the 80s the lake suffered from eutrophication, but in the past two decades water quality improved most likely as consequence of the introduction of a waste water treatment plant. Despite this, the cyanobacteria contribution increased and a very intense bloom of Planktothrixrubescens was observed during the 2009 fall and subsequent winter and spring. In an attempt to solve this problem, the Autonomous Province of Trento funded a multidisciplinary research project to study the environmental and biotic factors promoting the development of Planktothrix populations. The annual nutrient load from the catchment area was calculated from water balance and surface and groundwater nutrient inputs, with the identification of the possible sources of nutrients. Environmental variables were acquired on discrete samples and in situ by multiparameter probes and instrumentations fixed on the principal inlet, in piezometers and on a platform, equipped with meteorological 59 instrumentation, moored to the lake bottom. A hydrodynamic and water quality model was adopted to simulate water quality conditions in the lake during scenarios of decreased phosphorus loading and a combined modification of parameters like hydroelectric withdrawal and depth of the intake. Paleolimnological investigations have been conducted aimed at the definition of reference conditions and, through cyanobacterial pigments, at the evaluation of secular fluctuations of Planktothrix in relation to climatic variability, human impact and lake basin management. During stratification, Planktothrix mainly developed in 2-4 m thick water layers located just below the euphotic depth (10-18 m in summer), with biovolumes ranging between 4 and 12 mm3 l-1
Boscaini, A.; Bellin, A.; Brescancin, F.; Castagna, M.; Cerasino, L.; Defrancesco, C.; Fedrigotti, C.; Marcazzan, G.; Menapace, E.; Pellegrini, G.; Piccolroaz, S.; Rauzi, F.; Salmaso, N.; Toffolon, M.; Tolotti, M. (2013). An interdisciplinary research project aimed at understanding and controlling blooms of cyanobacteria in Lake Ledro (eastern ItalianAlps). In: XXI Congresso Associazione Italiana di Oceanologia e Limnologia (AIOL) “Limnologia e Oceanografia nel Terzo Millennio: nuove frontiere o assenza di frontiere?” Lignano Sabbiadoro (Ud), 23-26 SETTEMBRE 2013: 58-59. handle: http://hdl.handle.net/10449/23081
An interdisciplinary research project aimed at understanding and controlling blooms of cyanobacteria in Lake Ledro (eastern Italian Alps)
Boscaini, Adriano;Brescancin, Flavia;Cerasino, Leonardo;Fedrigotti, Chiara;Salmaso, Nico;Tolotti, Monica
2013-01-01
Abstract
In the last years, blooms of Planktothrix rubescens were observed in several lakes undergoing re-oligotrophication. Lake Ledro (zmax=48 m) is a mesotrophic, hardwater lake (650 m a.s.l.) located in SW Trentino (Eastern Italian Alps). It is an impacted lake exploited for hydropower production. In the 70s and the 80s the lake suffered from eutrophication, but in the past two decades water quality improved most likely as consequence of the introduction of a waste water treatment plant. Despite this, the cyanobacteria contribution increased and a very intense bloom of Planktothrixrubescens was observed during the 2009 fall and subsequent winter and spring. In an attempt to solve this problem, the Autonomous Province of Trento funded a multidisciplinary research project to study the environmental and biotic factors promoting the development of Planktothrix populations. The annual nutrient load from the catchment area was calculated from water balance and surface and groundwater nutrient inputs, with the identification of the possible sources of nutrients. Environmental variables were acquired on discrete samples and in situ by multiparameter probes and instrumentations fixed on the principal inlet, in piezometers and on a platform, equipped with meteorological 59 instrumentation, moored to the lake bottom. A hydrodynamic and water quality model was adopted to simulate water quality conditions in the lake during scenarios of decreased phosphorus loading and a combined modification of parameters like hydroelectric withdrawal and depth of the intake. Paleolimnological investigations have been conducted aimed at the definition of reference conditions and, through cyanobacterial pigments, at the evaluation of secular fluctuations of Planktothrix in relation to climatic variability, human impact and lake basin management. During stratification, Planktothrix mainly developed in 2-4 m thick water layers located just below the euphotic depth (10-18 m in summer), with biovolumes ranging between 4 and 12 mm3 l-1
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