The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Ital... more The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Italy, is described for the last ca 2000 years. Sediment samples from a sediment core collected in autumn 1995 were analysed for a range of palaeolimnological indi-cators, which included the principal algal and sulphur photosynthetic bacterial pigments, as well as magnetic susceptibility, organic matter, carbonates, organic carbon, total nitrogen, total sulphur and various forms of phosphorus. An accurate sediment chronology was determined using 210Pb, 137Cs and 14C. The results show that throughout a first, long phase of the history of this period (from ca AD 100 to 1830; zone 1) the sediments have an organic carbon content of ca 10 % d.w. and low concentrations of algal pigments, suggesting a moderately productive environment. Sedimentary carotenoids unique to anaerobic photosynthetic bacteria indicate a seasonally hypolimnetic anoxia during the whole ca 2000 year period. Clear effects of ...
The aim of this study is to test a series of methods relying on hyperspectral measurements to cha... more The aim of this study is to test a series of methods relying on hyperspectral measurements to characterize phytoplankton in clear lake waters. The phytoplankton temporal evolutions were analyzed exploiting remote sensed indices and metrics linked to the amount of light reaching the target (EPAR), the chlorophyll-a concentration ([Chl-a]OC4) and the fluorescence emission proxy. The latter one evaluated by an adapted version of the Fluorescence Line Height algorithm (FFLH). A peculiar trend was observed around the solar noon during the clear sky days. It is characterized by a drop of the FFLH metric and the [Chl-a]OC4 index. In addition to remote sensed parameters, water samples were also collected and analyzed to characterize the water body and to evaluate the in-situ fluorescence (FF) and absorbed light (FA). The relations between the remote sensed quantities and the in-situ values were employed to develop and test several phytoplankton primary production (PP) models. Promising resu...
Global spread of hypoxia and less frequent mixing in lakes is a major growing environmental conce... more Global spread of hypoxia and less frequent mixing in lakes is a major growing environmental concern. Climate change and human impact are expected to increasingly deteriorate aquatic ecosystems. The study of processes and drivers of such changes in the past provides a great asset for prevention and remediation in the future. We used a multiproxy approach combining high-resolution bulk pigment data measured by hyperspectral imaging (HSI) with lowerresolution specific chlorophyll types and carotenoids measured by HPLC to examine Holocene trophic state changes and anoxia evolution in the meromictic Lake Jaczno, NE Poland. A redundancy analysis (RDA) including polleninferred vegetation cover, temperature and human impacts provides insight into specific conditions and drivers of changing trophic and redox states in the lake. Anoxic and sulfidic conditions were established in Lake Jaczno after initial basin infilling 9500 years ago. Until 6700 cal BP, lake trophy was relatively low, water turbidity was high and green sulfur bacteria (GSB) were abundant within the phototrophic community, suggesting a deep oxic-anoxic boundary and weak stratification. The period between 6700-500 cal BP is characterized by constantly increasing lake production and a gradual shift from GSB to purple sulfur bacteria (PSB), suggesting a shallower oxic-anoxic boundary and pronounced stratification. Yet, the presence of spheroidene and speroidenone in the sediments indicates intermittent anoxia. After 500 cal BP, increasing human impact, deforestation and intensive agriculture promoted lake eutrophication, with a shift to PSB dominance and establishment of permanent anoxia and meromixis. Our study unambiguously documents the legacy of human impact on processes determining eutrophication and anoxia.
Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments' concent... more Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments' concentrations in lake sediments and carbon stable isotopic composition of chironomid (Diptera, Chironomidae) remains (d 13 C HC). We aimed to reconstruct temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; 5,067 m a.s.l.) located in the Nepalese Himalayas. Both pigments and d 13 C HC trends followed a similar fluctuating pattern over time, and we found significant positive relationships between these proxies, suggesting the strong reliance of benthic consumers on the aquatic primary production. Temporal trends matched well with main known climatic phases in the Eastern part of the Himalayan Mountains. Past glacier dynamics and associated in-lake solute concentrations appeared to be the main driver of autochthonous primary productivity, suggesting then the indirect impact of climate change on carbon processing in the benthic food web. During warm periods, the glacier retreat induced a rise in in-lake solute concentrations leading to an increasing primary productivity. Complementary investigations are still needed to strengthen our understanding about the response of past aquatic carbon cycling in CO 2-limiting environments.
High mountain lakes are biodiversity treasures. They host endemic taxa, adapted to live in extrem... more High mountain lakes are biodiversity treasures. They host endemic taxa, adapted to live in extreme environments. Among adaptations, production of diapausing eggs allows for overcoming the cold season. These diapausing eggs can rest in the sediments, providing a biotic reservoir known as an egg bank. Here, we estimated changes in abundance of the egg bank in two lakes in the Khumbu Region of the Himalayas, during the last ca. 1100 and 500 years, respectively, by analyzing two sediment cores. We tested viability of the diapausing eggs extracted from different layers of the sediment cores under laboratory conditions. We found that only diapausing eggs of the Monogont rotifer Hexarthra bulgarica nepalensis were able to hatch, thus suggesting that a permanent egg bank is lacking for the other taxa of the lakes, not least for the two Daphnia species described from these sites. Our results confirm previous studies suggesting that in high mountain lakes, the production of diapausing is main...
Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Clad... more Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Cladocera occupy a central role in food webs and are an excellent paleoecological indicator of food web structure and trophic status. We conducted a paleolimnological study in Lake Blanca Chica (Argentina) to detect changes on the planktivory and herbivory regimes over the last 250 years. Generalized additive models were fitted to the time series of fish predation indicators (ephippial abundance and size, mucrone size, fish scales, and the planktivory index) and pheophorbide a concentration. The cladoceran assemblage changed from littoral-benthic to pelagic species dominance and zooplankton switched from large-bodied (Daphnia) to small-bodied grazers (Bosmina) ca. 1900 due to increased predation. The shift in planktivory regime (ca. 1920–1930), indicated by fish scales and the planktivory index, as well as herbivory (ca. 1920–1950), was triggered by eutrophication. Changes in planktivory aff...
Lakes are exposed to anthropogenic pollution including the release of allochthonous bacteria into... more Lakes are exposed to anthropogenic pollution including the release of allochthonous bacteria into their waters. Antibiotic resistance genes (ARGs) stabilize in bacterial communities of temperate lakes, and these environments act as long-term reservoirs of ARGs. Still, it is not clear if the stabilization of the ARGs is caused by a periodical introduction, or by other factors regulated by dynamics within the water column. Here we observed the dynamics of the tetracycline resistance gene (tetA) and of the class 1 integron integrase gene intI1 a proxy of anthropogenic pollution in the water column and in the sediments of subalpine Lake Maggiore, together with several chemical, physical and microbiological variables. Both genes resulted more abundant within the bacterial community of the sediment compared to the water column and the water-sediment interface. Only at the inset of thermal stratification they reached quantifiable abundances in all the water layers, too. Moreover, the bacte...
DDx, PCBs, PBDEs, Hg, and As contamination in sediments and aquatic organisms of different trophi... more DDx, PCBs, PBDEs, Hg, and As contamination in sediments and aquatic organisms of different trophic levels (zooplankton, mussel, fish) were analyzed in Lake Maggiore and Lake Lugano, two large deep perialpine lakes. In the period 2001–2015, we analyzed the spatial and temporal trends of the considered pollutants to detect potential contamination sources and to compare concentrations with Sediment Quality Guidelines (SQGs) or existing Quality Standards (QSs). DDx and Hg contamination deriving from past industrial activities in the Pallanza Basin still exceeded SQGs in sediments and QSs in fish, with potential risks for the ecosystem. Banned in Europe in 1985, PCBs showed low residual values, while recent PBDE peaks resulted in the exceedance of the QSs for biota in both lakes, probably due to current industrial activities. Arsenic mainly derives from geochemical origin. The analysis of the biomagnification of toxicants in a pelagic food chain in Lake Maggiore (zooplankton–fish) according to a stable isotope approach is also presented, according to both the Trophic Magnification Factor and the Trophic Level-adjusted BioMagnification Factor: the importance of seasonality and a Hg > DDx ≈ PBDEs biomagnification capacity were observed. Low PCB bioaccumulation was detected in biota, probably because equilibrium was not reached yet in young fish.
The aim of this study is to test a series of methods relying on hyperspectral measurements to cha... more The aim of this study is to test a series of methods relying on hyperspectral measurements to characterize phytoplankton in clear lake waters. The phytoplankton temporal evolutions were analyzed exploiting remote sensed indices and metrics linked to the amount of light reaching the target (EPAR), the chlorophyll-a concentration ([Chl-a]OC4) and the fluorescence emission proxy. The latter one evaluated by an adapted version of the Fluorescence Line Height algorithm (FFLH). A peculiar trend was observed around the solar noon during the clear sky days. It is characterized by a drop of the FFLH metric and the [Chl-a]OC4 index. In addition to remote sensed parameters, water samples were also collected and analyzed to characterize the water body and to evaluate the in-situ fluorescence (FF) and absorbed light (FA). The relations between the remote sensed quantities and the in-situ values were employed to develop and test several phytoplankton primary production (PP) models. Promising resu...
Information on the biodiversity of high altitude lakes in the Stelvio National Park was scarce an... more Information on the biodiversity of high altitude lakes in the Stelvio National Park was scarce and fragmentary, in most cases limited to a few studies on a single biological issue. To fill this gap, a multidisciplinary research program was established in 2011 to investigate macroinvertebrates, diatoms, and water chemistry in 8 high altitude lakes within the boundaries of the Park (Rhaetian Alps, Eastern Alps). The results of this study were compared with data on biological assemblages and chemical parameters of Alpine lakes in the Pennine-Lepontine Alps (Western Alps), to evaluate the role of local drivers with respect to regional ones. This comparison was possible thanks to the adoption of standardized sampling methodologies developed since the ’90s by the National Research Council-Water Research Institute (Verbania), in collaboration with several European Research centers. Despite located in a restricted geographical area, the lakes of the Stelvio National Park showed a high varia...
1. Hysteresis linked to alternative stable states may explain delays in water quality recovery de... more 1. Hysteresis linked to alternative stable states may explain delays in water quality recovery despite reduced nutrient loadings in shallow lakes. Because deep lakes are assumed to be less prone to critical transitions, similar delays are attributed to the confounding effects of additional environmental disturbances, such as climate warming. Herein, we hypothesised that the lack of evidence of nutrient-driven alternative stable states in a deep lake arises from the fact that the nutrient threshold that causes the critical transition is lower than the nutrient threshold in shallow lakes. Thereby, it might have been crossed much earlier in the lake history. 2. To test this hypothesis, we focused on the palaeo-ecological trajectory of Lake Varese, which is a deep, hypereutrophicated peri-alpine lake undergoing restoration. Proxies for drivers of ecological state (i.e. total phosphorus-TP-through diatoms and pigments) and ecological responses (Cladocera), as well as a repeatable analysis, were used to identify transitions and to distinguish hysteretic delays from those of the ecosystems responding to additional constraints over the past century. 3. Our results suggest spatial heterogeneity in the ecological response. The littoral habitats changed abruptly and prematurely for a low TP threshold, causing a shift that met many criteria of a flickering-type critical transition. Soon after the littoral shift, a striking increase in the lake phosphorous concentration was recorded and drove the pelagic assemblage towards a new state. This transition was abrupt, and the pelagic communities exhibited limited evidence of recovery; however, we found no evidence of hysteresis. Therefore, the modern ecological trajectory of the pelagic communities is currently driven by climate warming. 4. This detailed analysis allowed us to go beyond the general pattern that links ecological responses to drivers and suggest that a nonlinear transition following eutrophication can take place in a deep lake synchronously with linear transitions. Instead of triggering a new regime shift, climate warming, to which pelagic habitats are more sensitive than littoral ones, has driven the lake further from its safe operating space.
Anthropogenic eutrophication can initiate vast and persistent ecosystem state changes in lakes. S... more Anthropogenic eutrophication can initiate vast and persistent ecosystem state changes in lakes. Such changes may be characterized by increased phytoplankton taxa variability, which can affect the effectiveness and time of lake recovery mechanisms. Lake Morat in Switzerland has undergone intense eutrophication in the 20 th century (phosphorous concentrations up to 150 μg L-1) caused by excessive nutrient loadings from agricultural intensification and urbanization. Phosphorous reduction measures since 1986, such as the ban of phosphates in detergents and decreased use of fertilizers in agriculture, have resulted in total phosphorous concentrations up to 20 μg L-1 today. Despite this drastic reduction of total phosphorous, total biomass production stays high. We investigate historical changes in the phytoplankton community during the eutrophication and re-oligotrophication periods by comparing historical limnological data with sediment pigment concentrations measured by HPLC and other geochemical proxies in a radiodated sediment core. For the last 90 years, we identified four major trophic state changes in Lake Morat. The first period (AD 1924-1937) is characterized by low pigment concentrations and nutrient inputs, with good oxygen conditions. This section represents trophic conditions before the intensive eutrophication phase. The second period (AD 1937-1970) revealed an abrupt increase in pigment concentrations with higher primary production, cyanobacteria dominance and reduced oxygen levels. Oscillaxanthin indicated a Planktothrix rubescens dominance (AD 1954-1970) with concentrations up to 800 nmol g-1 OM. Their decline after AD 1970 suggests the initiation of an intense eutrophication phase (AD 1970-1983) associated with the dominance of other cyanobacteria species, higher total phosphorous inputs, and intense anoxia. In the restoration period (AD 1983-2014), there was a shift in the phototrophic community from cyanobacteria to green algae dominance, yet some cyanobacteria species remain present. Rapid phytoplankton community changes were identified in the studied period, yet overall primary production response was low. Limnological data revealed a delay of phosphorous reduction due to phosphorous recycling from the sediments. The observation of complex lake ecosystem reactions to prolonged eutrophication and subsequent reoligotrophication, as shown by the paleolimnological and limnological data in this study, emphasize the importance of careful lake management to revert eutrophication back to historical reference biomass values.
The cyanobacterium Synechocystis sp. PCC 6803 is a model species commonly employed for biotechnol... more The cyanobacterium Synechocystis sp. PCC 6803 is a model species commonly employed for biotechnological applications. It is naturally able to accumulate zeaxanthin (Zea) and echinenone (Ech), but not astaxanthin (Asx), which is the highest value carotenoid produced by microalgae, with a wide range of applications in pharmaceutical, cosmetics, food and feed industries. With the aim of finding an alternative and sustainable biological source for the production of Asx and other valuable hydroxylated and ketolated intermediates, the carotenoid biosynthetic pathway of Synechocystis sp. PCC 6803 has been engineered by introducing the 4,4' β-carotene oxygenase (CrtW) and 3,3' β-carotene hydroxylase (CrtZ) genes from Brevundimonas sp. SD-212 under the control of a temperature-inducible promoter. The expression of exogenous CrtZ led to an increased accumulation of Zea at the expense of Ech, while the expression of exogenous CrtW promoted the production of non-endogenous canthaxanthin and an increase in the Ech content with a concomitant strong reduction of β-carotene (β-car). When both Brevundimonas sp. SD-212 genes were coexpressed, significant amounts of non-endogenous Asx were obtained accompanied by a strong decrease in β-car content. Asx accumulation was higher (approximately 50% of total carotenoids) when CrtZ was cloned upstream of CrtW, but still significant (approximately 30%) when the position of genes was inverted. Therefore, the engineered strains constitute a useful tool for investigating the ketocarotenoid biosynthetic pathway in cyanobacteria and an excellent starting point for further optimisation and industrial exploitation of these organisms for the production of added-value compounds.
1. A palaeolimnological study, covering the last c. 12,000 years, was conducted in a small subalp... more 1. A palaeolimnological study, covering the last c. 12,000 years, was conducted in a small subalpine lake located in the Alps to study climate change impacts on carbon flows through food webs in small lakes. We used analysis of sedimentary pigments and carbon stable isotopic composition of chironomid remains (d 13 C HC) to reconstruct past dynamics of phytoplankton community and carbon sources sustaining benthic consumers. 2. Chironomid biomass was sustained by a combination of allochthonous, autochthonous and CH 4-derived organic matters, and their relative contributions were correlated to changes in temperature. Relatively high terrestrial contributions to chironomid biomass were observed during period of the Holocene when in-lake production was low. Relatively high incorporation of CH 4-derived carbon to chironomid biomass was found during anoxic events co-occurring with the Holocene thermal maximum. 3. Results were then compared with those collected in a small boreal lake in Estonia. We tested the hypothesis that responses in carbon flows through benthic food web to past climate change would be similar between these lakes. We found a negative correlation between d 13 C HC values of both lakes and inferred air temperature, suggesting that temperature was the major driver to different food sources being incorporated into chironomid biomass. 4. Our study demonstrated that air temperature was the principal driver of the energy flows through benthic food web in the studied small lakes. We conjectured that carbon cycling in food webs of small lakes might be strongly sensitive to climate change. K E Y W O R D S carbon stable isotope, climate change, holocene, palaeolimnology, subfossil chironomid 1 | INTRODUCTION Global warming (IPCC 2014) and increase in mean temperature are pointed out as one of the major threats to inland aquatic ecosystems (Goldman, Kumagai, & Robarts, 2012). While it is well-known that temperature is the driver of many processes in lakes (Wilhelm & Adrian, 2008), our understanding of ecosystem responses to climate change is still limited (Keller, 2007; Mooij et al., 2005). Indeed, effects of climate change have mainly been studied at individual level and community level (Walther, 2010). A more integrative and holistic approach is needed to better understand ecosystem responses to climate change, and to predict future trends during warmer climate.
Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs b... more Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the H → τ µ CMS hint and at the same time respect (as they do) the severe limits on H → µe inherited from the non-observation of µ → eγ. We compute the predictions of the Simplest Little Higgs Model for the H → ℓℓ ′ decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) would, under reasonable assumptions, disfavor this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.
In response to anthropogenic eutrophication and global warming, deep-water oxygen depletion is ex... more In response to anthropogenic eutrophication and global warming, deep-water oxygen depletion is expected to have large effects on freshwater lake biogeochemistry and resident communities. In particular, it has been observed that deep-water hypoxia may potentially lead to regime shifts of lake benthic communities. We explored such community shifts by reconstructing a high-resolution subfossil chironomid record from a sediment core collected in the sub-alpine lake Remoray in France. We identified an abrupt shift in chironomid composition triggered by the collapse of the dominant Sergentia coracina-type chironomids around 1980. We found that the collapse of Sergentia coracina type was coupled to a gradual increase in organic matter content in lake sediments caused by eutrophication. We concluded that the most probable cause for the collapse of Sergentia coracina type was a change in oxygen concentrations below the minimal threshold for larval growth. We also analyzed trends in variance and autocorrelation of chironomid dynamics to test whether they can be used as early warnings of the Sergentia collapse. We found that variance rose prior to the collapse, but it was marginally significant (Kendal rank correlation 0.71, p = 0.05), whereas autocorrelation increased but insignificantly and less strongly (Kendal rank correlation 0.23, p = 0.25). By combining reconstructions of ecosystem dynamics and environmental drivers, our approach demonstrates how lake sediments may provide insights into the long-term dynamics of oxygen in lakes and its impact on aquatic fauna.
Over the past two decades, we observed a substantial rise in ionic content that was mainly determ... more Over the past two decades, we observed a substantial rise in ionic content that was mainly determined by the sulfate concentration at 20 remote high elevation lakes located in central southern Himalaya. At LCN9, which was monitored on an annual basis for the last twenty years, the sulfate concentrations increased over 4-fold. Among the main causes, we exclude a change in the composition of wet atmospheric deposition, as well as a possible influence of decrease in seasonal snow cover duration, which could have exposed larger basin surfaces to alteration processes. Glacier retreat likely was the main factor responsible for the observed increase of sulfate concentrations. We attribute this chemical changes mainly to the sulfide oxidation processes that occur in subglacial environments. Moreover, we observe that the weakened monsoon of the past two decades has only partially contributed to the lakes enrichment through runoff waters that are more concentrated in solutes or lowering the water-table, resulting in more rock exposed to air and enhanced mineral oxidation. INTRODUCTION High mountain ecosystems are especially vulnerable to climate change, and lakes in particular may act as sentinels. 1,2 An evaluable opportunity for a fine-scale investigation is particularly evident on the south slope of Mt. Everest (Nepal), which is one of the most heavily glacierized parts of Himalaya 3. At the same time, this region is the most densely populated by glacial lakes in the overall Hindu-Kush-Himalaya range 4. In this region, Lami et al. 5 observed a significant relationship between the increase in the annual temperature recorded in the area and the enhanced conductivity detected in two glacial lakes located above 5000 m a.s.l. in the last decades, but without inferring any undergoing physical process or source of ionic release. At the same time, an increase in conductivity and sulfate concentrations has been observed in a few lakes of the European Alps, but in this case, the changes have been specifically ascribed to the solute release from an active rock glacier as a response to climate warming 6. An increase in sulfate from melting ice during drought years is also reported by Williams et al. 7 in the outflow of a rock glacier in the Colorado Front Range and by Mast et al. 8 in southwestern Colorado. Even in this last case the authors consider temperature as the main climatic driver of change and sulfate as largely derived from pyrite (watershed weathering sources), although the undergoing physical processes are only supposed. In this study, after exploiting the recently reconstructed 9 daily temperature and precipitation time series and the available accurate tracing of the glacier shrinkage in the region 10 , we discuss changes in the water chemistry of 20 remote lakes located on the south slopes of central Himalaya that were sampled approximately after twenty years, starting in the early 1990s. Furthermore, during this period, two selected lakes (named Lake Cadastre Number (LCN) 11 9 and 10) were monitored yearly. We consider several drivers of changes of the in-lake chemistry, including temperature, precipitation, atmospheric deposition, rocks and soil weathering processes (periglacial environment), seasonal snow cover duration, and, in particular, the role of glaciers (subglacial and surrounding periglacial components). With regard to permafrost, little is known about its distribution in Himalaya. 12 Therefore the subsurface ice and its possible degradation is not included in this analysis, although its influence on in-lake chemistry evolution cannot be excluded as reported by other authors 13,14 in the Colorado Front Range. MATERIAL AND METHODS Study area. The monitored glacial lakes are located in Sagarmatha (Mt. Everest) National Park (SNP), Nepal, which lies in the central southern Himalayas (Fig. 1a, 1c). The SNP (1148 km 2), crossed by the Khumbu valley, is the world's highest protected area, extending from an elevation of 2845 to 8848 m a.s.l.. 15,16 According to Searle et al. 17 , the Khumbu valley substratum is dominantly made up of crystalline rocks (e.g,, sillimanite gneisses calc-silicates, amphibolites and K-feldspar augen gneisses) and leucogranites that intrude the metasediments as dykes, sills and bodies. The overlying Everest series (weakly metamorphosed shales and pelites with limestone bands), the Yellow band unit (limestones, marbles and calc-silicates) and the Ordovician limestones are only present in the eastern part of the basin. Extensive moraine debris of different ages, alluvial deposits and glacio-fluvial deposits host sub-surface aquifers in close connection with the hydrographic network. The land cover classification shows that almost one-third of the territory is characterized by temperate debriscovered glaciers, with 75% of glacier surface area lying between 5000 m and 6500 m a.s.l. 10 and with less than 10% of the park area being forested 15,16. The soils in the high valleys are primarily Entisols. 18
The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Ital... more The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Italy, is described for the last ca 2000 years. Sediment samples from a sediment core collected in autumn 1995 were analysed for a range of palaeolimnological indi-cators, which included the principal algal and sulphur photosynthetic bacterial pigments, as well as magnetic susceptibility, organic matter, carbonates, organic carbon, total nitrogen, total sulphur and various forms of phosphorus. An accurate sediment chronology was determined using 210Pb, 137Cs and 14C. The results show that throughout a first, long phase of the history of this period (from ca AD 100 to 1830; zone 1) the sediments have an organic carbon content of ca 10 % d.w. and low concentrations of algal pigments, suggesting a moderately productive environment. Sedimentary carotenoids unique to anaerobic photosynthetic bacteria indicate a seasonally hypolimnetic anoxia during the whole ca 2000 year period. Clear effects of ...
The aim of this study is to test a series of methods relying on hyperspectral measurements to cha... more The aim of this study is to test a series of methods relying on hyperspectral measurements to characterize phytoplankton in clear lake waters. The phytoplankton temporal evolutions were analyzed exploiting remote sensed indices and metrics linked to the amount of light reaching the target (EPAR), the chlorophyll-a concentration ([Chl-a]OC4) and the fluorescence emission proxy. The latter one evaluated by an adapted version of the Fluorescence Line Height algorithm (FFLH). A peculiar trend was observed around the solar noon during the clear sky days. It is characterized by a drop of the FFLH metric and the [Chl-a]OC4 index. In addition to remote sensed parameters, water samples were also collected and analyzed to characterize the water body and to evaluate the in-situ fluorescence (FF) and absorbed light (FA). The relations between the remote sensed quantities and the in-situ values were employed to develop and test several phytoplankton primary production (PP) models. Promising resu...
Global spread of hypoxia and less frequent mixing in lakes is a major growing environmental conce... more Global spread of hypoxia and less frequent mixing in lakes is a major growing environmental concern. Climate change and human impact are expected to increasingly deteriorate aquatic ecosystems. The study of processes and drivers of such changes in the past provides a great asset for prevention and remediation in the future. We used a multiproxy approach combining high-resolution bulk pigment data measured by hyperspectral imaging (HSI) with lowerresolution specific chlorophyll types and carotenoids measured by HPLC to examine Holocene trophic state changes and anoxia evolution in the meromictic Lake Jaczno, NE Poland. A redundancy analysis (RDA) including polleninferred vegetation cover, temperature and human impacts provides insight into specific conditions and drivers of changing trophic and redox states in the lake. Anoxic and sulfidic conditions were established in Lake Jaczno after initial basin infilling 9500 years ago. Until 6700 cal BP, lake trophy was relatively low, water turbidity was high and green sulfur bacteria (GSB) were abundant within the phototrophic community, suggesting a deep oxic-anoxic boundary and weak stratification. The period between 6700-500 cal BP is characterized by constantly increasing lake production and a gradual shift from GSB to purple sulfur bacteria (PSB), suggesting a shallower oxic-anoxic boundary and pronounced stratification. Yet, the presence of spheroidene and speroidenone in the sediments indicates intermittent anoxia. After 500 cal BP, increasing human impact, deforestation and intensive agriculture promoted lake eutrophication, with a shift to PSB dominance and establishment of permanent anoxia and meromixis. Our study unambiguously documents the legacy of human impact on processes determining eutrophication and anoxia.
Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments' concent... more Using a sediment core covering the last 3,500 years, we analysed photosynthetic pigments' concentrations in lake sediments and carbon stable isotopic composition of chironomid (Diptera, Chironomidae) remains (d 13 C HC). We aimed to reconstruct temporal changes in aquatic primary productivity and carbon resources sustaining chironomid larvae in a high mountain lake (Lake Pyramid Inferior; 5,067 m a.s.l.) located in the Nepalese Himalayas. Both pigments and d 13 C HC trends followed a similar fluctuating pattern over time, and we found significant positive relationships between these proxies, suggesting the strong reliance of benthic consumers on the aquatic primary production. Temporal trends matched well with main known climatic phases in the Eastern part of the Himalayan Mountains. Past glacier dynamics and associated in-lake solute concentrations appeared to be the main driver of autochthonous primary productivity, suggesting then the indirect impact of climate change on carbon processing in the benthic food web. During warm periods, the glacier retreat induced a rise in in-lake solute concentrations leading to an increasing primary productivity. Complementary investigations are still needed to strengthen our understanding about the response of past aquatic carbon cycling in CO 2-limiting environments.
High mountain lakes are biodiversity treasures. They host endemic taxa, adapted to live in extrem... more High mountain lakes are biodiversity treasures. They host endemic taxa, adapted to live in extreme environments. Among adaptations, production of diapausing eggs allows for overcoming the cold season. These diapausing eggs can rest in the sediments, providing a biotic reservoir known as an egg bank. Here, we estimated changes in abundance of the egg bank in two lakes in the Khumbu Region of the Himalayas, during the last ca. 1100 and 500 years, respectively, by analyzing two sediment cores. We tested viability of the diapausing eggs extracted from different layers of the sediment cores under laboratory conditions. We found that only diapausing eggs of the Monogont rotifer Hexarthra bulgarica nepalensis were able to hatch, thus suggesting that a permanent egg bank is lacking for the other taxa of the lakes, not least for the two Daphnia species described from these sites. Our results confirm previous studies suggesting that in high mountain lakes, the production of diapausing is main...
Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Clad... more Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Cladocera occupy a central role in food webs and are an excellent paleoecological indicator of food web structure and trophic status. We conducted a paleolimnological study in Lake Blanca Chica (Argentina) to detect changes on the planktivory and herbivory regimes over the last 250 years. Generalized additive models were fitted to the time series of fish predation indicators (ephippial abundance and size, mucrone size, fish scales, and the planktivory index) and pheophorbide a concentration. The cladoceran assemblage changed from littoral-benthic to pelagic species dominance and zooplankton switched from large-bodied (Daphnia) to small-bodied grazers (Bosmina) ca. 1900 due to increased predation. The shift in planktivory regime (ca. 1920–1930), indicated by fish scales and the planktivory index, as well as herbivory (ca. 1920–1950), was triggered by eutrophication. Changes in planktivory aff...
Lakes are exposed to anthropogenic pollution including the release of allochthonous bacteria into... more Lakes are exposed to anthropogenic pollution including the release of allochthonous bacteria into their waters. Antibiotic resistance genes (ARGs) stabilize in bacterial communities of temperate lakes, and these environments act as long-term reservoirs of ARGs. Still, it is not clear if the stabilization of the ARGs is caused by a periodical introduction, or by other factors regulated by dynamics within the water column. Here we observed the dynamics of the tetracycline resistance gene (tetA) and of the class 1 integron integrase gene intI1 a proxy of anthropogenic pollution in the water column and in the sediments of subalpine Lake Maggiore, together with several chemical, physical and microbiological variables. Both genes resulted more abundant within the bacterial community of the sediment compared to the water column and the water-sediment interface. Only at the inset of thermal stratification they reached quantifiable abundances in all the water layers, too. Moreover, the bacte...
DDx, PCBs, PBDEs, Hg, and As contamination in sediments and aquatic organisms of different trophi... more DDx, PCBs, PBDEs, Hg, and As contamination in sediments and aquatic organisms of different trophic levels (zooplankton, mussel, fish) were analyzed in Lake Maggiore and Lake Lugano, two large deep perialpine lakes. In the period 2001–2015, we analyzed the spatial and temporal trends of the considered pollutants to detect potential contamination sources and to compare concentrations with Sediment Quality Guidelines (SQGs) or existing Quality Standards (QSs). DDx and Hg contamination deriving from past industrial activities in the Pallanza Basin still exceeded SQGs in sediments and QSs in fish, with potential risks for the ecosystem. Banned in Europe in 1985, PCBs showed low residual values, while recent PBDE peaks resulted in the exceedance of the QSs for biota in both lakes, probably due to current industrial activities. Arsenic mainly derives from geochemical origin. The analysis of the biomagnification of toxicants in a pelagic food chain in Lake Maggiore (zooplankton–fish) according to a stable isotope approach is also presented, according to both the Trophic Magnification Factor and the Trophic Level-adjusted BioMagnification Factor: the importance of seasonality and a Hg > DDx ≈ PBDEs biomagnification capacity were observed. Low PCB bioaccumulation was detected in biota, probably because equilibrium was not reached yet in young fish.
The aim of this study is to test a series of methods relying on hyperspectral measurements to cha... more The aim of this study is to test a series of methods relying on hyperspectral measurements to characterize phytoplankton in clear lake waters. The phytoplankton temporal evolutions were analyzed exploiting remote sensed indices and metrics linked to the amount of light reaching the target (EPAR), the chlorophyll-a concentration ([Chl-a]OC4) and the fluorescence emission proxy. The latter one evaluated by an adapted version of the Fluorescence Line Height algorithm (FFLH). A peculiar trend was observed around the solar noon during the clear sky days. It is characterized by a drop of the FFLH metric and the [Chl-a]OC4 index. In addition to remote sensed parameters, water samples were also collected and analyzed to characterize the water body and to evaluate the in-situ fluorescence (FF) and absorbed light (FA). The relations between the remote sensed quantities and the in-situ values were employed to develop and test several phytoplankton primary production (PP) models. Promising resu...
Information on the biodiversity of high altitude lakes in the Stelvio National Park was scarce an... more Information on the biodiversity of high altitude lakes in the Stelvio National Park was scarce and fragmentary, in most cases limited to a few studies on a single biological issue. To fill this gap, a multidisciplinary research program was established in 2011 to investigate macroinvertebrates, diatoms, and water chemistry in 8 high altitude lakes within the boundaries of the Park (Rhaetian Alps, Eastern Alps). The results of this study were compared with data on biological assemblages and chemical parameters of Alpine lakes in the Pennine-Lepontine Alps (Western Alps), to evaluate the role of local drivers with respect to regional ones. This comparison was possible thanks to the adoption of standardized sampling methodologies developed since the ’90s by the National Research Council-Water Research Institute (Verbania), in collaboration with several European Research centers. Despite located in a restricted geographical area, the lakes of the Stelvio National Park showed a high varia...
1. Hysteresis linked to alternative stable states may explain delays in water quality recovery de... more 1. Hysteresis linked to alternative stable states may explain delays in water quality recovery despite reduced nutrient loadings in shallow lakes. Because deep lakes are assumed to be less prone to critical transitions, similar delays are attributed to the confounding effects of additional environmental disturbances, such as climate warming. Herein, we hypothesised that the lack of evidence of nutrient-driven alternative stable states in a deep lake arises from the fact that the nutrient threshold that causes the critical transition is lower than the nutrient threshold in shallow lakes. Thereby, it might have been crossed much earlier in the lake history. 2. To test this hypothesis, we focused on the palaeo-ecological trajectory of Lake Varese, which is a deep, hypereutrophicated peri-alpine lake undergoing restoration. Proxies for drivers of ecological state (i.e. total phosphorus-TP-through diatoms and pigments) and ecological responses (Cladocera), as well as a repeatable analysis, were used to identify transitions and to distinguish hysteretic delays from those of the ecosystems responding to additional constraints over the past century. 3. Our results suggest spatial heterogeneity in the ecological response. The littoral habitats changed abruptly and prematurely for a low TP threshold, causing a shift that met many criteria of a flickering-type critical transition. Soon after the littoral shift, a striking increase in the lake phosphorous concentration was recorded and drove the pelagic assemblage towards a new state. This transition was abrupt, and the pelagic communities exhibited limited evidence of recovery; however, we found no evidence of hysteresis. Therefore, the modern ecological trajectory of the pelagic communities is currently driven by climate warming. 4. This detailed analysis allowed us to go beyond the general pattern that links ecological responses to drivers and suggest that a nonlinear transition following eutrophication can take place in a deep lake synchronously with linear transitions. Instead of triggering a new regime shift, climate warming, to which pelagic habitats are more sensitive than littoral ones, has driven the lake further from its safe operating space.
Anthropogenic eutrophication can initiate vast and persistent ecosystem state changes in lakes. S... more Anthropogenic eutrophication can initiate vast and persistent ecosystem state changes in lakes. Such changes may be characterized by increased phytoplankton taxa variability, which can affect the effectiveness and time of lake recovery mechanisms. Lake Morat in Switzerland has undergone intense eutrophication in the 20 th century (phosphorous concentrations up to 150 μg L-1) caused by excessive nutrient loadings from agricultural intensification and urbanization. Phosphorous reduction measures since 1986, such as the ban of phosphates in detergents and decreased use of fertilizers in agriculture, have resulted in total phosphorous concentrations up to 20 μg L-1 today. Despite this drastic reduction of total phosphorous, total biomass production stays high. We investigate historical changes in the phytoplankton community during the eutrophication and re-oligotrophication periods by comparing historical limnological data with sediment pigment concentrations measured by HPLC and other geochemical proxies in a radiodated sediment core. For the last 90 years, we identified four major trophic state changes in Lake Morat. The first period (AD 1924-1937) is characterized by low pigment concentrations and nutrient inputs, with good oxygen conditions. This section represents trophic conditions before the intensive eutrophication phase. The second period (AD 1937-1970) revealed an abrupt increase in pigment concentrations with higher primary production, cyanobacteria dominance and reduced oxygen levels. Oscillaxanthin indicated a Planktothrix rubescens dominance (AD 1954-1970) with concentrations up to 800 nmol g-1 OM. Their decline after AD 1970 suggests the initiation of an intense eutrophication phase (AD 1970-1983) associated with the dominance of other cyanobacteria species, higher total phosphorous inputs, and intense anoxia. In the restoration period (AD 1983-2014), there was a shift in the phototrophic community from cyanobacteria to green algae dominance, yet some cyanobacteria species remain present. Rapid phytoplankton community changes were identified in the studied period, yet overall primary production response was low. Limnological data revealed a delay of phosphorous reduction due to phosphorous recycling from the sediments. The observation of complex lake ecosystem reactions to prolonged eutrophication and subsequent reoligotrophication, as shown by the paleolimnological and limnological data in this study, emphasize the importance of careful lake management to revert eutrophication back to historical reference biomass values.
The cyanobacterium Synechocystis sp. PCC 6803 is a model species commonly employed for biotechnol... more The cyanobacterium Synechocystis sp. PCC 6803 is a model species commonly employed for biotechnological applications. It is naturally able to accumulate zeaxanthin (Zea) and echinenone (Ech), but not astaxanthin (Asx), which is the highest value carotenoid produced by microalgae, with a wide range of applications in pharmaceutical, cosmetics, food and feed industries. With the aim of finding an alternative and sustainable biological source for the production of Asx and other valuable hydroxylated and ketolated intermediates, the carotenoid biosynthetic pathway of Synechocystis sp. PCC 6803 has been engineered by introducing the 4,4' β-carotene oxygenase (CrtW) and 3,3' β-carotene hydroxylase (CrtZ) genes from Brevundimonas sp. SD-212 under the control of a temperature-inducible promoter. The expression of exogenous CrtZ led to an increased accumulation of Zea at the expense of Ech, while the expression of exogenous CrtW promoted the production of non-endogenous canthaxanthin and an increase in the Ech content with a concomitant strong reduction of β-carotene (β-car). When both Brevundimonas sp. SD-212 genes were coexpressed, significant amounts of non-endogenous Asx were obtained accompanied by a strong decrease in β-car content. Asx accumulation was higher (approximately 50% of total carotenoids) when CrtZ was cloned upstream of CrtW, but still significant (approximately 30%) when the position of genes was inverted. Therefore, the engineered strains constitute a useful tool for investigating the ketocarotenoid biosynthetic pathway in cyanobacteria and an excellent starting point for further optimisation and industrial exploitation of these organisms for the production of added-value compounds.
1. A palaeolimnological study, covering the last c. 12,000 years, was conducted in a small subalp... more 1. A palaeolimnological study, covering the last c. 12,000 years, was conducted in a small subalpine lake located in the Alps to study climate change impacts on carbon flows through food webs in small lakes. We used analysis of sedimentary pigments and carbon stable isotopic composition of chironomid remains (d 13 C HC) to reconstruct past dynamics of phytoplankton community and carbon sources sustaining benthic consumers. 2. Chironomid biomass was sustained by a combination of allochthonous, autochthonous and CH 4-derived organic matters, and their relative contributions were correlated to changes in temperature. Relatively high terrestrial contributions to chironomid biomass were observed during period of the Holocene when in-lake production was low. Relatively high incorporation of CH 4-derived carbon to chironomid biomass was found during anoxic events co-occurring with the Holocene thermal maximum. 3. Results were then compared with those collected in a small boreal lake in Estonia. We tested the hypothesis that responses in carbon flows through benthic food web to past climate change would be similar between these lakes. We found a negative correlation between d 13 C HC values of both lakes and inferred air temperature, suggesting that temperature was the major driver to different food sources being incorporated into chironomid biomass. 4. Our study demonstrated that air temperature was the principal driver of the energy flows through benthic food web in the studied small lakes. We conjectured that carbon cycling in food webs of small lakes might be strongly sensitive to climate change. K E Y W O R D S carbon stable isotope, climate change, holocene, palaeolimnology, subfossil chironomid 1 | INTRODUCTION Global warming (IPCC 2014) and increase in mean temperature are pointed out as one of the major threats to inland aquatic ecosystems (Goldman, Kumagai, & Robarts, 2012). While it is well-known that temperature is the driver of many processes in lakes (Wilhelm & Adrian, 2008), our understanding of ecosystem responses to climate change is still limited (Keller, 2007; Mooij et al., 2005). Indeed, effects of climate change have mainly been studied at individual level and community level (Walther, 2010). A more integrative and holistic approach is needed to better understand ecosystem responses to climate change, and to predict future trends during warmer climate.
Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs b... more Little Higgs Models are promising constructs to solve the hierarchy problem affecting the Higgs boson mass for generic new physics. However, their preservation of lepton universality forbids them to account for the H → τ µ CMS hint and at the same time respect (as they do) the severe limits on H → µe inherited from the non-observation of µ → eγ. We compute the predictions of the Simplest Little Higgs Model for the H → ℓℓ ′ decays and conclude that the measurement of any of these decays at LHC (even with a much smaller rate than currently hinted) would, under reasonable assumptions, disfavor this model. This result is consistent with our earlier observation of very suppressed lepton flavor violating semileptonic tau decays within this model.
In response to anthropogenic eutrophication and global warming, deep-water oxygen depletion is ex... more In response to anthropogenic eutrophication and global warming, deep-water oxygen depletion is expected to have large effects on freshwater lake biogeochemistry and resident communities. In particular, it has been observed that deep-water hypoxia may potentially lead to regime shifts of lake benthic communities. We explored such community shifts by reconstructing a high-resolution subfossil chironomid record from a sediment core collected in the sub-alpine lake Remoray in France. We identified an abrupt shift in chironomid composition triggered by the collapse of the dominant Sergentia coracina-type chironomids around 1980. We found that the collapse of Sergentia coracina type was coupled to a gradual increase in organic matter content in lake sediments caused by eutrophication. We concluded that the most probable cause for the collapse of Sergentia coracina type was a change in oxygen concentrations below the minimal threshold for larval growth. We also analyzed trends in variance and autocorrelation of chironomid dynamics to test whether they can be used as early warnings of the Sergentia collapse. We found that variance rose prior to the collapse, but it was marginally significant (Kendal rank correlation 0.71, p = 0.05), whereas autocorrelation increased but insignificantly and less strongly (Kendal rank correlation 0.23, p = 0.25). By combining reconstructions of ecosystem dynamics and environmental drivers, our approach demonstrates how lake sediments may provide insights into the long-term dynamics of oxygen in lakes and its impact on aquatic fauna.
Over the past two decades, we observed a substantial rise in ionic content that was mainly determ... more Over the past two decades, we observed a substantial rise in ionic content that was mainly determined by the sulfate concentration at 20 remote high elevation lakes located in central southern Himalaya. At LCN9, which was monitored on an annual basis for the last twenty years, the sulfate concentrations increased over 4-fold. Among the main causes, we exclude a change in the composition of wet atmospheric deposition, as well as a possible influence of decrease in seasonal snow cover duration, which could have exposed larger basin surfaces to alteration processes. Glacier retreat likely was the main factor responsible for the observed increase of sulfate concentrations. We attribute this chemical changes mainly to the sulfide oxidation processes that occur in subglacial environments. Moreover, we observe that the weakened monsoon of the past two decades has only partially contributed to the lakes enrichment through runoff waters that are more concentrated in solutes or lowering the water-table, resulting in more rock exposed to air and enhanced mineral oxidation. INTRODUCTION High mountain ecosystems are especially vulnerable to climate change, and lakes in particular may act as sentinels. 1,2 An evaluable opportunity for a fine-scale investigation is particularly evident on the south slope of Mt. Everest (Nepal), which is one of the most heavily glacierized parts of Himalaya 3. At the same time, this region is the most densely populated by glacial lakes in the overall Hindu-Kush-Himalaya range 4. In this region, Lami et al. 5 observed a significant relationship between the increase in the annual temperature recorded in the area and the enhanced conductivity detected in two glacial lakes located above 5000 m a.s.l. in the last decades, but without inferring any undergoing physical process or source of ionic release. At the same time, an increase in conductivity and sulfate concentrations has been observed in a few lakes of the European Alps, but in this case, the changes have been specifically ascribed to the solute release from an active rock glacier as a response to climate warming 6. An increase in sulfate from melting ice during drought years is also reported by Williams et al. 7 in the outflow of a rock glacier in the Colorado Front Range and by Mast et al. 8 in southwestern Colorado. Even in this last case the authors consider temperature as the main climatic driver of change and sulfate as largely derived from pyrite (watershed weathering sources), although the undergoing physical processes are only supposed. In this study, after exploiting the recently reconstructed 9 daily temperature and precipitation time series and the available accurate tracing of the glacier shrinkage in the region 10 , we discuss changes in the water chemistry of 20 remote lakes located on the south slopes of central Himalaya that were sampled approximately after twenty years, starting in the early 1990s. Furthermore, during this period, two selected lakes (named Lake Cadastre Number (LCN) 11 9 and 10) were monitored yearly. We consider several drivers of changes of the in-lake chemistry, including temperature, precipitation, atmospheric deposition, rocks and soil weathering processes (periglacial environment), seasonal snow cover duration, and, in particular, the role of glaciers (subglacial and surrounding periglacial components). With regard to permafrost, little is known about its distribution in Himalaya. 12 Therefore the subsurface ice and its possible degradation is not included in this analysis, although its influence on in-lake chemistry evolution cannot be excluded as reported by other authors 13,14 in the Colorado Front Range. MATERIAL AND METHODS Study area. The monitored glacial lakes are located in Sagarmatha (Mt. Everest) National Park (SNP), Nepal, which lies in the central southern Himalayas (Fig. 1a, 1c). The SNP (1148 km 2), crossed by the Khumbu valley, is the world's highest protected area, extending from an elevation of 2845 to 8848 m a.s.l.. 15,16 According to Searle et al. 17 , the Khumbu valley substratum is dominantly made up of crystalline rocks (e.g,, sillimanite gneisses calc-silicates, amphibolites and K-feldspar augen gneisses) and leucogranites that intrude the metasediments as dykes, sills and bodies. The overlying Everest series (weakly metamorphosed shales and pelites with limestone bands), the Yellow band unit (limestones, marbles and calc-silicates) and the Ordovician limestones are only present in the eastern part of the basin. Extensive moraine debris of different ages, alluvial deposits and glacio-fluvial deposits host sub-surface aquifers in close connection with the hydrographic network. The land cover classification shows that almost one-third of the territory is characterized by temperate debriscovered glaciers, with 75% of glacier surface area lying between 5000 m and 6500 m a.s.l. 10 and with less than 10% of the park area being forested 15,16. The soils in the high valleys are primarily Entisols. 18
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Papers by Andrea Lami