Climatic effects on vertical mixing and deep-water oxygen content in the subalpine lakes in Italy

Rogora, Michela; Buzzi, Fabio; Dresti, Claudia; Leoni, Barbara; Lepori, Fabio; Mosello, Rosario; Patelli, M; Salmaso, Nico

doi:10.1007/s10750-018-3623-y

Cited by 95 publications

(119 citation statements)

References 55 publications

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“…One of the most important consequences of this temperature increase is stronger thermal stratification, which is caused by the temperature-dependent density difference between the epilimnion and hypolimnion [78], as well as the decrease in the intensity of deep mixing, which has been observed in Lake Iseo since the mid-1980s [25]. The most recent episodes of full circulation occurred at the end of winter in 2005 and 2006, and were due to extremely cold winters and sufficient kinetic energy [35,36,79]. From 2007 until 2014, the mixing depths likely did not exceed 100 m, and the most recent years (2014-2016) have been characterized by a mixing depth accounting for no more than 20% of the water column [35,36,80].…”

Section: Discussionmentioning

confidence: 99%

“…The most recent episodes of full circulation occurred at the end of winter in 2005 and 2006, and were due to extremely cold winters and sufficient kinetic energy [35,36,79]. From 2007 until 2014, the mixing depths likely did not exceed 100 m, and the most recent years (2014-2016) have been characterized by a mixing depth accounting for no more than 20% of the water column [35,36,80]. By analyzing the available discrete data for 2016, we detected a maximum deep water mixing of 50 m.…”

Section: Discussionmentioning

confidence: 99%

“…Over the last twenty years, complete winter mixing occurred only in 2005 and 2006, so the lake can now be regarded as holo-oligomictic [21,22,36,39,40]. Except for these two years, the spring mixing depth from 1998 to 2016 in Lake Iseo ranged between 30 and 150 m, and in 2016 it reached about 50 m [35,36]. The extent of the mixing depth was determined by analyzing the homogeneity of the depth profiles of physical and chemical data recorded along the water column [35].…”

Section: Sampling Field Measurements and Laboratory Analysesmentioning

confidence: 99%

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Interspecific Relationship and Ecological Requirements of Two Potentially Harmful Cyanobacteria in a Deep South-Alpine Lake (L. Iseo, I)

Nava

Patelli

Soler

et al. 2017

Water

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Abstract:In Lake Iseo (Lombardia, Italy), the predominant species in the cyanobacterial taxa was Planktothrix rubescens. However, since 2014, the presence of an allochthonous Cyanobacteria, Tychonema bourrellyi, able to produce consistent biomasses and harmful toxins, was detected. The causes of this expansion are poorly understood. Many studies have linked the development of allochthonous Cyanobacteria populations with climate change. This study shows the spatio-temporal dynamics, the ecological requirements, and the interspecific relationship of P. rubescens and T. bourrellyi. Samples were collected monthly in 2016 at six different depths in the water column; 20 chemico-physical characteristics were measured; and Cyanobacteria density, morphology, and biovolume were evaluated. The results allowed a comparison of the spatial pattern of the two species, which showed a greater distribution at a depth of 10-20 m, and their seasonal dynamics. Both Cyanobacteria were present throughout the year, with the greatest abundance during the period from March to May. A temporal shift was observed in their development, linked to different capacities for overcoming winter and mixing periods. Principal Component Analysis, performed on 20 observations (4 months × 5 depths), highlighted the important role of the stability of the water column in determining T. bourrellyi settlement in Lake Iseo and the role of solar radiation in spring population development.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Sampling Field Measurements and Laboratory Analysesmentioning

confidence: 99%

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Interspecific Relationship and Ecological Requirements of Two Potentially Harmful Cyanobacteria in a Deep South-Alpine Lake (L. Iseo, I)

Nava

Patelli

Soler

et al. 2017

Water

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“…always nearly always stratified, with occasional and irregular complete mixing events occurring only after exceptionally cold and windy winters. In both lakes, the last two complete mixing events occurred in 2005 and 2006 (Rogora et al, ).…”

Section: Methodsmentioning

confidence: 99%

Causes of Daphnia midsummer decline in two deep meromictic subalpine lakes

2019

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Daphnia are key organisms in pelagic food webs, acting as a food resource for fish and predatory zooplankton and regulating phytoplankton through grazing. Its population dynamic follows regular seasonal patterns, with spring peaks followed by summer population declines (midsummer declines, MSDs). Midsummer declines show high inter‐annual variation, which has been attributed to different causes. However, the mechanisms controlling the MSD remain poorly understood, especially in deep stratified lakes. We tried to disentangle the factors causing Daphnia MSDs in Lake Lugano and Lake Iseo (in Switzerland and Italy), two deep peri‐alpine lakes with similar trophic status and vertical mixing dynamics, characterised by phosphorus accumulation in the hypolimnion and variable mixing during late‐winter turnovers. Specifically, we assessed the effects of three different hypothetical pathways according to which: (1) winter air temperature controls MSDs by influencing mixing depth during turnovers and epilimnetic phosphorus replenishment; (2) vernal air temperature influences MSD by accelerating the timing of spring population peak; and (3) summer temperature influences MSDs by increasing fish predation. We assessed the relative strength of these pathways using structural equation modelling on long‐term datasets for the two lakes (29 years for Lake Lugano and 19 years for Lake Iseo). Between the hypothesised pathways, the one driven by winter air temperature (through P replenishment) influenced Daphnia abundance in spring in both lakes, but the effects propagated to summer Daphnia abundance only in Lake Lugano. Additionally, summer Daphnia abundance was influenced by the summer air temperature through a positive (although weak) effect. By comparison, vernal air temperature had no detectable effects on summer Daphnia abundance. The results revealed marked differences between the meromictic study lakes and the shallow hypertrophic water bodies that were the focus of previous research on Daphnia MSD, and also between the two study lakes. The influence of epilimnetic P replenishment on the summer Daphnia abundance in Lake Lugano, which was recovering from past eutrophication, may have reflected the greater susceptibility of deep, stratified lakes to P depletion after spring compared to shallow hypertrophic lakes or reservoirs. This effect might not have been detected in Lake Iseo because P was more consistently depleted during the study period (i.e. variance in the predictor was too low to detect an effect). This study highlighted the complexity of the effects of climate variability on Daphnia MSD in deep lakes, showing that the responses can differ even between two neighbouring lakes with similar vertical mixing dynamics and trophic status. At the same time, the results suggest that future increases in winter air temperature, caused by global warming, may cause critically low densities of Daphnia during spring and summer and compromise the ability of zooplankton to control phytoplankton biomass.

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“…High mountain habitats are vulnerable because of human impacts, such as global change (e.g., rising temperatures, changes in precipitation patterns, and nitrogen deposition) and land abandonment, which influence biodiversity and ecosystem functioning [1][2][3][4]. Consistent changes in biodiversity have been observed in numerous central European mountains using short-term [5][6][7] and long-term vegetation analyses [8][9][10][11][12][13][14][15][16], and upward migration of alpine species toward mountain summits, shrub displacement, changes in community composition, and local extinctions have also been documented [17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Long-Term Changes in the Composition, Ecology, and Structure of Pinus mugo Scrubs in the Apennines (Italy)

et al. 2018

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Mountain ecosystems are vulnerable because of land-use and climate change. In this study, we performed a re-visitation study using historical and newly collected vegetation plots to explore the primary trends in the floristic, ecological, and structural features of Mediterranean Pinus mugo krummholz over past decades. The plant community composition over time (1992 vs. 2016-17) was analyzed by a detrended correspondence analysis followed by a statistical comparison of time steps and an analysis of the contribution of each species to temporal differences. Ecological and structural changes were analyzed by a permutational multivariate analysis of variance followed by a post hoc comparison. We observed relevant changes in the floristic composition, structure, and ecological characteristics of Pinus mugo scrub. Some subalpine and treeline species that characterize the early stages of Pinus mugo succession declined as several warm-adapted species increased. Furthermore, these changes were most likely due to the natural evolution of high-mountain krummholz combined with a thermophilization process occurring in alpine habitats. In contrast, a small group of cold-adapted species also increased, probably because the patchy spatial pattern of Pinus mugo scrubs gives rise to "mesic patches" in a matrix of arid grasslands. The re-visitation approach adopted for long-term analysis in this study can potentially be applied to other mountainous regions to better understand long-term ecological changes in high alpine vegetation.

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Climatic effects on vertical mixing and deep-water oxygen content in the subalpine lakes in Italy

Cited by 95 publications

References 55 publications

Interspecific Relationship and Ecological Requirements of Two Potentially Harmful Cyanobacteria in a Deep South-Alpine Lake (L. Iseo, I)

Interspecific Relationship and Ecological Requirements of Two Potentially Harmful Cyanobacteria in a Deep South-Alpine Lake (L. Iseo, I)

Causes of Daphnia midsummer decline in two deep meromictic subalpine lakes

Long-Term Changes in the Composition, Ecology, and Structure of Pinus mugo Scrubs in the Apennines (Italy)

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