Effects of nutrient availability and temperature on phytoplankton development: a case study from large lakes south of the Alps

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 eutrophicsensitive 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.

Strict coupling between the development ofPlanktothrix rubescensand microcystin content in two nearby lakes south of the Alps (lakes Garda and Ledro)

“…rubescens is a very well-known cyanobacterium which develops in many deep lakes north and south of the Alps. Besides Lake Garda and the deep lakes south of the Alps (Buzzi, 2002;Morabito et al, 2002;Salmaso, 2002Salmaso, , 2011Salmaso et al, 2012a), the environmental factors controlling the development of this cyanobacterium were extensively studied in other large subalpine lakes Jacquet et al, 2005;Gallina et al, 2011Gallina et al, , 2013Dokulil and Teubner, 2012), as well as in smaller, deep lakes (Nu¨rnberg et al, 2003;Carraro et al, 2012) and reservoirs (Naselli-Flores and Barone, 2000; Almodo´var et al, 2004;Paulino et al, 2009). The increase of P. rubescens during the summer months is partly due to its ability to form strong thickening in the metalimnetic layers provided that the light intensity is not below the Lim.…”

“…Lake Ledro is connected by a penstock to a pumped-storage plant on the shores of Lake Garda (Ponale), from which water may be again pumped to Lake Ledro. The two lakes host populations of P. rubescens, which represents the dominant cyanobacterium in both basins (Salmaso et al, 2012a). In Lake Ledro, this species was the cause of many recent red water blooms (2009)(2010).…”

“…Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis and Koma´rek is the most typical and abundant cyanobacterium in many deep Italian lakes (Messineo et al, 2006;D'Alelio et al, 2011;Salmaso et al, 2012aSalmaso et al, , 2012b and in many Italian reservoirs (Naselli-Flores et al, 2007). In this paper, we report the results of a study carried out in two populations of P. rubescens in two nearby subalpine lakes in Northeastern Italy, namely lakes Garda (a natural large and deep lake) and Ledro (a natural lake with artificial water regulation for hydroelectric purpose).…”

Modelling the plankton groups of the deep, peri-alpine Lake Bourget

“…Starting from 1996, the toxic cyanobacterium, Planktothrix rubescens became a dominant species in the lake (Vinçon-Leite et al, 2002;Jacquet et al, 2005, see also Fig.1). P. rubescens is a wide-spread cyanobacterial species especially prevalent in peri-alpine lakes (e.g., Ernst et al, 2009;Salmaso et al, 2012;Dokulil and Teubner, 2012;Posch et al, 2012), but also observed elsewhere (e.g., Konopka, 1982;Halstvedt et al, 2007;Naselli-Flores et al, 2007;Padisák et al, 2010). Being a potentially microcystin producing species , its occurrence in lakes and reservoirs has been of major concern for livestock and human health (Naselli-Flores et al, 2007;Ernst et al, 2009).…”

Long-term trends of chemical and modelled photochemical parameters in four Alpine lakes

“…The lake underwent a relatively rapid eutrophication in the seventies, the main reason being the large nutrient loading from the inflows. Since 1992, many studies have been conducted in Lake Iseo; water samples taken continuously over the last decades at the deepest point of the basin form the basis for a description of its trophic evolution (see Salmaso et al, 2012, and references therein; Salmaso et al, 2014, and references therein).…”