| 1. |
- Milan, Manuela, et al.
(författare)
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Combining sediment Cladocera remains and geochemistry to reveal the role of a large catchment in driving changes in a small subalpine lake (Lake Ledro, N-Italy)
- 2016
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Ingår i: Advances in Oceanography and Limnology. - : PAGEPress Publications. - 1947-5721 .- 1947-573X. ; 7:2, s. 220-234
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Tidskriftsartikel (refereegranskat)abstract
- Sediment Cladocera remains and geochemistry were analyzed at Lake Ledro, a small subalpine lake with a large catchment area located in northern Italy. The aim of the study was to investigate human, climate and hydrological impacts on the Cladocera community and on the geochemical components during the last few centuries. A sediment core was collected from the deepest point of Lake Ledro and radiometrically dated. Cladocera remains were analyzed to track the trophic lake evolution. The core bottom section revealed the dominance of Bosminidae in concomitance with nutrient pulses entering into the lake during major flood events. The abundance of species preferring cold water temperatures confirmed the deposition of this core section during the Little Ice Age. The flood event occurred in the first half of the 19th century produced a drastic increase in littoral species, due to the development of new habitats. The decrease in Cladocera densities during the following lake stage was followed by a rapid increase in planktonic species during the nutrient enrichment after the 1960s. Statistical analyses revealed a clear response of Cladocera community to climate variability during oligotrophic periods, while no relation to temperature changes was recorded during high nutrient levels. A preliminary study on Bosminidae and Daphnidae body size and appendages length was carried out to reconstruct major changes in the lake food web. Only Bosmina spp. revealed clear body size changes: minor shifts were recorded before the 1930s in relation to the low nutrient concentrations, while the major changes occurred during the 1980s were interpreted as related to the appearance of Cladocera invertebrate predators. Geochemical components were studied using X-ray fluorescence spectroscopy (XRF) analysis in order to recognize the impact of the large catchment area and from the lake-level regulations on the lake hydrology. Moreover the Si:Al ratios profile confirmed the increase in lake productivity after the 1960s. Although both Cladocera and geochemical analysis indicate major changes since the 1960s, they also revealed diverse responses to common external and local forcing, thus confirming the value of a multi-proxy approach for disentangling the lake responses to different environmental stressors. Moreover, it outlined the importance of larger catchment areas on small lakes as they are to a larger extent influenced by the modifications occurring in the drainage basin.
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| 2. |
- Ruiz-González, Clara, et al.
(författare)
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Contrasting dynamics and environmental controls of dispersed bacteria along a hydrologic gradient
- 2017
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Ingår i: Advances in Oceanography and Limnology. - : PAGEPress Publications. - 1947-573X .- 1947-5721. ; 8:2, s. 222-234
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater bacterioplankton communities are influenced by the transport of bacteria from the surrounding terrestrial environments. It has been shown that, although most of these dispersed bacteria gradually disappear along the hydrologic continuum, some can thrive in aquatic systems and become dominant, leading to a gradual succession of communities. Here we aimed at exploring the environmental factors driving the structure of such contrasting bacterial populations as well as their functional properties. Using Illumina sequencing of the 16S rRNA gene, we characterized the taxonomic composition of bacterioplankton communities from 10 streams and rivers in Québec spanning the whole hydrologic continuum (river Strahler order 0 to 7), which were sampled in two occasions. With the aim to understand the fate and controls of the transported bacteria, among the taxa present at the origin of the hydrologic gradient (i.e., in the smallest headwater streams) we identified two types of dynamics: i) ‘Tourist’ taxa, which were those that decreased in abundance from the headwaters towards the largest rivers, and ii) ‘Seed’ taxa, those that increased their abundances along the hydrologic continuum. Communities changed gradually from the fast-flowing headwater streams dominated by ‘Tourist’ taxa (ca. 95% of the sequences) towards the largest rivers (Strahler order 4-7) where ‘Seed’ taxa comprised up to 80% of community sequences. Variation in taxonomic composition of the communities dominated by ‘Tourist’ taxa in streams seemed related to different degree of terrestrial inputs, whereas compositional changes in ‘Seed’ communities in the large rivers were linked to differences in autochthonous processes. Finally, the two types of communities differed significantly in their metabolic potential assessed through Biolog Ecoplates. All this suggests that hydrologic transport modulates the gradual replacement of two contrasting population types subjected to different environmental controls and with different metabolic potentials. Moreover, we show that the separate exploration of the two pools of taxa allows unveiling environmental drivers and processes operating on them that remain hidden if explored at the whole community level.
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| 3. |
- Salmaso, Nico, et al.
(författare)
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Historical colonisation patterns of dolichospermum lemmermannii (Cyanobacteria) in a deep lake south of the alps
- 2015
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Ingår i: Advances in Oceanography and Limnology. - : PAGEPress Publications. - 1947-5721 .- 1947-573X. ; 6:1-2, s. 33-45
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Tidskriftsartikel (refereegranskat)abstract
- Since the beginning of the 1990s, Lake Garda showed the appearance of extended surface water blooms of Dolichospermum lemmermannii (Nostocales, Cyanobacteria). Between the 1990s and the 2000s, the blooms appeared also in the other large lakes south of the Alps (Iseo, Como and Maggiore). Despite the sudden appearance of the blooms, the correct identification of the establishment time of the populations of Dolichospermum in the southern subalpine lake district remained unclear. In this work, the establishment of the populations of D. lemmermannii in Lake Garda has been evaluated by the direct counting of sub-fossil akinetes extracted from sediment cores, and by estimating the abundance of filaments germinated from sub-fossil viable akinetes. The two techniques provided comparable results, allowing locating the beginning of the establishment of Dolichospermum around the middle of the 1960s. Four strains of Dolichospermum germinated from akinetes isolated from the core sediments between around the 1989 and 2012 did not show any mutation or recombination signal in the rpoB gene sequences, suggesting a strong founder effect. The establishment of Dolichospermum coincided with the beginning of the rapid increase of total phosphorus as inferred from the distribution of sub-fossil diatoms in the sediment core. These results supported the hypothesis of a strong link between the shift of Lake Garda from ultraoligotrophy/oligotrophy to oligo-mesotrophy and the development of Dolichospermum. This colonisation pattern was possibly reinforced by the increase in the water temperatures in the subalpine lake district during the last 3 decades. In warmer lakes, gas-vacuolated Nostocales are favoured by high replication rates and, in particular, by their ability to control vertical movements in stratified water columns. This allows these species to exploit the gradients of light and nutrients, giving them a competitive advantage compared to other species. From a management point of view, the control and decrease of Dolichospermum should be obtained through the reduction and control of nutrient loads to the lake.
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| 4. |
- Tolotti, Monica, et al.
(författare)
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Subfossil cladocera as a powerful tool for paleoecological reconstruction
- 2016
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Ingår i: Advances in Oceanography and Limnology. - : PAGEPress Publications. - 1947-5721 .- 1947-573X. ; 7:2, s. 125-130
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Tidskriftsartikel (refereegranskat)abstract
- Subfossil Cladocera (Crustacea, Branchiopoda) represent one of the most valuable biological proxies preserved in lake sediments that can be studied for reconstruction purposes. They are widespread in both the pelagic and littoral zones of lakes of different geographical distribution, altitude and typology, where they often represent the dominant component of zooplankton in terms of biomass. The chitinous parts of their body are well preserved in lake sediments, and the taphonomic taxonomy is well established, thanks to the numerous studies that followed the first pioneer works by Frey (1960).
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