High mountain palaeoecology and palaeolimnology fo Central Pyrenees, based on pollen and diatom analyses

[eng] High-mountain ranges are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes. Sedimentary records obtained from those regions contain information that allows to understand past environmental changes that would help to predict the influence of the ongoing climate warming. This thesis is focused in the palaeoecology and palaeolimnology of Central Pyrenees. In order to understand the ecosystem responses to past environmental changes and climate, we analysed several proxies from sedimentary sequences extracted from Bassa Nera pond. We combined biological indicators (pollen, diatoms, chrysophytes, non-pollen palynomorphs, microscopic charcoal particles, macroremains, tree-rings and DNA metabarcoding) and inorganic proxies (Loss-on-ignition and chemical elements) to assess the diverse questions proposed in this work. To infer vegetation shifts and aquatic changes during the past millennium, we analysed pollen and diatom at multidecadal resolution. A montane pollen ratio was introduced as a new palaeoecological indicator of altitudinal shifts in vegetation. Results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the development of the peat bog in the coring site around AD 1565. Overall, the studied proxies suggest that Bassa Nera had a low-intensity human pressure and that people changed from farming in the Medieval Climate Anomaly to livestock in the Little Ice Age. To reconstruct the vegetation and lacustrine dynamics during the last 10,000 years we analyzed pollen, plant macroremains, charcoal, chemical elements and loss-on-ignition. The montane ratio was also applied to track altitudinal shifts and it was compared to the ice-rafted debris index. Results revealed upward shifts of deciduous forest and its presence in Bassa Nera from the onset of the Holocene until 4200 cal yr BP. The montane ratio showed a link between vegetation and North Atlantic influence, while changes in macroremains and aquatic taxa allowed the description of the transition from the initial pond to the present peatland. First anthropic pressures were grazing activities by 7300 cal yr BP, while cereal agriculture appeared around 5190 cal yr BP. The late Bronze Age, Roman Period and Middle Ages periods presented the highest human pressure. To assess the dynamics of subalpine forests of Central Pyrenees for the last 700 years, we compared the sedimentary pollen and montane ratio from Bassa Nera with nearby Pinus uncinata tree-rings. To study the climate-growth associations, we related the chronologies with instrumental meteorological records of the 1901-2010 period and with temperature reconstructions for the Pyrenees and Northern Hemisphere for the last 700 years. Few robust associations were found between any specific arboreal pollen taxa and tree-rings. However, a significant correlation was found between the montane ratio and the pine growth of nearby subalpine forests. Results suggest that tree-growth variability at high elevations is more constrained by low than by high temperatures, although a relaxation of this constrain in recent decades was also noted. To explore the eukaryotic communities of Bassa Nera, we performed a metabarcoding study of four different micro-habitats and five sedimentary depths using 18S and COI genetic markers. The sedimentary DNA from palaeoecological communities were compared to the modern communities and also to the environmental reconstruction from pollen and macroremains from the same record. Results show that even though 18S could amplify a broader group of organisms, the taxonomic resolution was lower than that obtained from COI and that the taxonomic assignment of the COI sequences yielded mostly metazoans. This first molecular approach has allowed to prove that the diversity of modern and past eukaryotic peat bog communities can be assessed using universal metabarcoding markers.[spa] Los registros sedimentarios obtenidos en ecosistemas de alta montaña contienen información que permite entender los cambios ambientales ocurridos en el pasado que ayudarían a predecir la influencia del calentamiento climático actual. Esta tesis se centra en el estudio de la paleoecología y paleolimnología de los Pirineos Centrales a lo largo del Holoceno basado en el análisis de diversos proxis de dos secuencias sedimentarias de Bassa Nera. También se introdujo un índice de polen montano como un nuevo indicador paleoecológico para resaltar cambios altitudinales en la vegetación caducifolia. Nuestros resultados mostraron cambios en el ascenso de los bosques caducifolios y su presencia en Bassa Nera desde el inicio del Holoceno hasta el año 4200 años BP, así como su ascenso durante la Anomalía Climática Medieval. El índice montano mostró una relación entre la vegetación y la influencia del Atlántico Norte, así como una correlación significativa entre el índice de polen montano y el crecimiento del pino de bosques subalpinos cercanos. Mientras que los cambios en los macrofósiles de Sphagnum y los taxones acuáticos permitieron la descripción de los cambios ontogénicos locales desde el estanque inicial hasta la turbera actual. Los cambios en los taxones acuáticos también permitieron datar cuando la turbera circundante se desarrolló y colmató el lugar donde se extrajo el sondeo, siendo esta en 1565 AD. En general, los resultados sugieren que Bassa Nera tuvo una presión humana de baja intensidad. Las primeras inferencias de presión antrópica en Bassa Nera datan de 7300 años BP y fueron actividades de pastoreo, mientras que los cereales aparecieron alrededor de 5190 años BP. Por otro lado, nuestros resultados sugieren que la sensibilidad del crecimiento del pino al clima ha variado en los últimos 700 años y que la variabilidad del crecimiento arbóreo en localidades altas está más limitada por las temperaturas bajas que por altas, aunque también observamos una relajación de esta restricción en las últimas décadas. Los resultados del estudio metabarcoding utilizando los marcadores genéticos universales 18S y COI sugieren que la diversidad de comunidades de turberas eucariotas modernas y pasadas pueden ser evaluadas usando marcadores genéticos universales

The Sant Maurici Lake sedimentary record (Central Pyrenees)

The St. Maurici Lake (1.004818 E, 42.580801 N, 1924 m a.s.l.) is located in the eastern area of "Parc Nacional d’Aigüestortes i Estany de Sant Maurici", Central Pyrenees, Catalonia. The lake occupies an overexcavated basin behind a terminal moraine. This paper aims to reconstruct the evolution of depositional environments and their relation to climate evolution since deglaciation to the present, based on a 8.7-m long sequence retrieved in the deepest part of the lake and a preliminary chronological model with three 14C AMS dates. After the glacial retreat carbonatic very fine sands and silts without organic matter were deposited in a proglacial environment. Early Holocene sediments are massive fine sands to laminated sandy silts with increasing organic content and some sand layers. A sedimentary hiatus occurred during the mid Holocene and the sedimentation re-started after ca. 4 ka with deposition of organic facies. Changes in clastic content reflect centennial scale run-off variability during the last millenniaEl Lago de St. Maurici (1.004818 E, 42.580801 N, 1924 m s.n.m) se localiza en la zona oriental del "Parc Nacional d’Aigüestortes i Estany de Sant Maurici", Pirineos Centrales, Catalunya. El lago ocupa una cuenca de sobreexcavación detrás de una morrena terminal. El objetivo de este trabajo es reconstruir la evolución de los ambientes de depósito y su relación con la variabilidad climática desde la deglaciación hasta la actualidad, basándose en un sondeo de 8,7 m de longitud de la zona profunda del lago y un modelo de edad preliminar con tres dataciones AMS 14C. Tras la retirada del glaciar, se sedimentó una secuencia de arenas carbonatadas muy finas y limos arcillosos sin materia orgánica, propios de un lago pro-glacial. El Holoceno temprano se caracteriza por facies de arenas finas masivas que pasan a facies de limos arenosos laminados con un aumento progresivo del contenido en materia orgánica y con algunas capas de arenas. La secuencia presenta un hiato sedimentario durante el Holoceno medio. Desde el re-inicio de la sedimentación en el Holoceno tardío (ca. 4 ka) se han depositado facies organógena

El registro sedimentario del lago Sant Maurici (Pirineos Centrales)

[spa] El Lago de St. Maurici (1.004818 E, 42.580801 N, 1924 m s.n.m) se localiza en la zona oriental del 'Parc Nacional d'Aigüestortes i Estany de Sant Maurici', Pirineos Centrales, Catalunya. El lago ocupa una cuenca de sobre- excavación detrás de una morrena terminal. El objetivo de este trabajo es reconstruir la evolución de los ambientes de depósito y su relación con la variabilidad climática desde la deglaciación hasta la actualidad, basándose en un sondeo de 8,7 m de longitud de la zona profunda del lago y un modelo de edad preliminar con tres dataciones AMS 14C. Tras la retirada del glaciar, se sedimentó una secuencia de arenas carbonatadas muy finas y limos arcillosos sin materia orgánica, propios de un lago proglacial. El Holoceno temprano se caracteriza por facies de arenas finas masivas que pasan a facies de limos arenosos laminados con un aumento progresivo del contenido en materia orgánica y con algunas capas de arenas. La secuencia presenta un hiato sedimentario durante el Holoceno medio. Desde el re-inicio de la sedimentación en el Holoceno tardío (ca. 4 ka) se han depositado facies organógenas.[eng] The St. Maurici Lake (1.004818 E, 42.580801 N, 1924 m a.s.l.) is located in the eastern area of 'Parc Nacional d'Aigüestortes i Estany de Sant Maurici', Central Pyrenees, Catalonia. The lake occupies an overexcavated basin behind a terminal moraine. This paper aims to reconstruct the evolution of depositional environments and their relation to climate evolution since deglaciation to the present, based on a 8.7-m long sequence retrieved in the deepest part of the lake and a preliminary chronological model with three 14C AMS dates. After the glacial retreat carbonatic very fine sands and silts without organic matter were deposited in a proglacial environment. Early Holocene sediments are massive fine sands to laminated sandy silts with increasing organic content and some sand layers. A sedimentary hiatus occurred during the mid Holocene and the sedimentation re-started after ca. 4 ka with deposition of organic facies. Changes in clastic content reflect centennial scale run-off variability during the last millennia

DNA metabarcoding reveals modern and past eukaryotic communities in a high-mountain peat bog system

Peat bogs located in high mountains are suitable places to study local environmental responses to climate variability. These ecosystems host a large number of eukaryotes with diverse taxonomic and functional diversity. We carried out a metabarcoding study using universal 18S and COI markers to explore the composition of past and present eukaryotic communities of a Pyrenean peat bog ecosystem. We assessed the molecular biodiversity of four different moss micro-habitats along a flood gradient in the lentic Bassa Nera system (Central Pyrenees). Five samples collected from different sediment depths at the same study site were also analysed, to test the suitability of these universal markers for studying paleoecological communities recovered from ancient DNA and to compare the detected DNA sequences to those obtained from the modern community. We also compared the information provided by the sedimentary DNA to the reconstruction from environmental proxies such as pollen and macro-remains from the same record. We successfully amplified ancient DNA with both universal markers from all sediment samples, including the deepest one (~ 10,000 years old). Most of the metabarcoding reads obtained from sediment samples, however, were assigned to living edaphic organisms and only a small fraction of those reads was considered to be derived from paleoecological communities. Inferences from ancient sedimentary DNA were complementary to the reconstruction based on pollen and macro-remains, and the combined records reveal more detailed information. This molecular study yielded promising findings regarding the diversity of modern eukaryotic peat bog communities. Nevertheless, even though information about past communities could be retrieved from sediment samples, preferential amplification of DNA from living communities is a caveat for the use of universal metabarcoding markers in paleoecology

Modern Analogue Approach Applied to High-Resolution Varved Sediments-A Synthesis for Lake Montcortès (Central Pyrenees)

In Quaternary paleosciences, the rationale behind analogical inference presupposes that former processes can be explained by causes operating now, although their intensity and rates can vary through time. In this paper we synthesised the results of di erent modern analogue studies performed in a varved lake. We discuss their potential value to obtain best results from high resolution past records. Di erent biogeochemical contemporary processes revealed seasonality and year-to-year variability, e.g., calcite precipitation, lake oxygenation, production and deposition of pollen and phytoplankton growth. Fingerprints of the first two of these processes were clearly evidenced in the varve-sublayers and allow understanding related to past events. Pollen studies suggested the possibility of identifying and characterizing seasonal layers even in the absence of varves. Marker pigments in the water column were tightly associated with phytoplankton groups living today; most of them were identified in the sediment record as well. We observed that 50% of these marker pigments were destroyed between deposition and permanent burying. In another study, seasonality in the production/distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) and derived temperature estimates were investigated in catchment soils and particles settling in the lake. The signatures of brGDGTs in depositional environments mainly were representative of stable conditions of soils in the catchment that last over decades; no brGDGTs seemed to be produced within the lake. The main contribution of this review is to show the advantages and limitations of a multiproxy modern-analogue approach in Lake Montcortès as a case study and proposing new working hypotheses for future research

High resolution ancient sedimentary DNA shows that alpine plant diversity is associated with human land use and climate change.

The European Alps are highly rich in species, but their future may be threatened by ongoing changes in human land use and climate. Here, we reconstructed vegetation, temperature, human impact and livestock over the past ~12,000 years from Lake Sulsseewli, based on sedimentary ancient plant and mammal DNA, pollen, spores, chironomids, and microcharcoal. We assembled a highly-complete local DNA reference library (PhyloAlps, 3923 plant taxa), and used this to obtain an exceptionally rich sedaDNA record of 366 plant taxa. Vegetation mainly responded to climate during the early Holocene, while human activity had an additional influence on vegetation from 6 ka onwards. Land-use shifted from episodic grazing during the Neolithic and Bronze Age to agropastoralism in the Middle Ages. Associated human deforestation allowed the coexistence of plant species typically found at different elevational belts, leading to levels of plant richness that characterise the current high diversity of this region. Our findings indicate a positive association between low intensity agropastoral activities and precipitation with the maintenance of the unique subalpine and alpine plant diversity of the European Alps

High resolution ancient sedimentary DNA shows that alpine plant diversity is associated with human land use and climate change

The European Alps are highly rich in species, but their future may be threatened by ongoing changes in human land use and climate. Here, we reconstructed vegetation, temperature, human impact and livestock over the past ~12,000 years from Lake Sulsseewli, based on sedimentary ancient plant and mammal DNA, pollen, spores, chironomids, and microcharcoal. We assembled a highly-complete local DNA reference library (PhyloAlps, 3923 plant taxa), and used this to obtain an exceptionally rich sedaDNA record of 366 plant taxa. Vegetation mainly responded to climate during the early Holocene, while human activity had an additional influence on vegetation from 6 ka onwards. Land-use shifted from episodic grazing during the Neolithic and Bronze Age to agropastoralism in the Middle Ages. Associated human deforestation allowed the coexistence of plant species typically found at different elevational belts, leading to levels of plant richness that characterise the current high diversity of this region. Our findings indicate a positive association between low intensity agropastoral activities and precipitation with the maintenance of the unique subalpine and alpine plant diversity of the European Alps. Here, the authors use sedimentary DNA, pollen, fungal spores, chironomids, and microcharcoal from an alpine lake core to reconstruct vegetation across 12,000 years. They find that vegetation responded to climate in the early Holocene, followed by a shift to human activity from 6000 years onward corresponding with an increase in deforestation and agropastoralism

Machine Learning-Based Analysis in the Management of Iatrogenic Bile Duct Injury During Cholecystectomy: a Nationwide Multicenter Study

Background Iatrogenic bile duct injury (IBDI) is a challenging surgical complication. IBDI management can be guided by artificial intelligence models. Our study identified the factors associated with successful initial repair of IBDI and predicted the success of definitive repair based on patient risk levels. Methods This is a retrospective multi-institution cohort of patients with IBDI after cholecystectomy conducted between 1990 and 2020. We implemented a decision tree analysis to determine the factors that contribute to successful initial repair and developed a risk-scoring model based on the Comprehensive Complication Index. Results We analyzed 748 patients across 22 hospitals. Our decision tree model was 82.8% accurate in predicting the success of the initial repair. Non-type E (p < 0.01), treatment in specialized centers (p < 0.01), and surgical repair (p < 0.001) were associated with better prognosis. The risk-scoring model was 82.3% (79.0-85.3%, 95% confidence interval [CI]) and 71.7% (63.8-78.7%, 95% CI) accurate in predicting success in the development and validation cohorts, respectively. Surgical repair, successful initial repair, and repair between 2 and 6 weeks were associated with better outcomes. Discussion Machine learning algorithms for IBDI are a novel tool may help to improve the decision-making process and guide management of these patients

High mountain palaeoecology and palaeolimnology fo Central Pyrenees, based on pollen and diatom analyses

High-mountain ranges are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes. Sedimentary records obtained from those regions contain information that allows to understand past environmental changes that would help to predict the influence of the ongoing climate warming. This thesis is focused in the palaeoecology and palaeolimnology of Central Pyrenees. In order to understand the ecosystem responses to past environmental changes and climate, we analysed several proxies from sedimentary sequences extracted from Bassa Nera pond. We combined biological indicators (pollen, diatoms, chrysophytes, non-pollen palynomorphs, microscopic charcoal particles, macroremains, tree-rings and DNA metabarcoding) and inorganic proxies (Loss-on-ignition and chemical elements) to assess the diverse questions proposed in this work. To infer vegetation shifts and aquatic changes during the past millennium, we analysed pollen and diatom at multidecadal resolution. A montane pollen ratio was introduced as a new palaeoecological indicator of altitudinal shifts in vegetation. Results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the development of the peat bog in the coring site around AD 1565. Overall, the studied proxies suggest that Bassa Nera had a low-intensity human pressure and that people changed from farming in the Medieval Climate Anomaly to livestock in the Little Ice Age. To reconstruct the vegetation and lacustrine dynamics during the last 10,000 years we analyzed pollen, plant macroremains, charcoal, chemical elements and loss-on-ignition. The montane ratio was also applied to track altitudinal shifts and it was compared to the ice-rafted debris index. Results revealed upward shifts of deciduous forest and its presence in Bassa Nera from the onset of the Holocene until 4200 cal yr BP. The montane ratio showed a link between vegetation and North Atlantic influence, while changes in macroremains and aquatic taxa allowed the description of the transition from the initial pond to the present peatland. First anthropic pressures were grazing activities by 7300 cal yr BP, while cereal agriculture appeared around 5190 cal yr BP. The late Bronze Age, Roman Period and Middle Ages periods presented the highest human pressure. To assess the dynamics of subalpine forests of Central Pyrenees for the last 700 years, we compared the sedimentary pollen and montane ratio from Bassa Nera with nearby Pinus uncinata tree-rings. To study the climate-growth associations, we related the chronologies with instrumental meteorological records of the 1901-2010 period and with temperature reconstructions for the Pyrenees and Northern Hemisphere for the last 700 years. Few robust associations were found between any specific arboreal pollen taxa and tree-rings. However, a significant correlation was found between the montane ratio and the pine growth of nearby subalpine forests. Results suggest that tree-growth variability at high elevations is more constrained by low than by high temperatures, although a relaxation of this constrain in recent decades was also noted. To explore the eukaryotic communities of Bassa Nera, we performed a metabarcoding study of four different micro-habitats and five sedimentary depths using 18S and COI genetic markers. The sedimentary DNA from palaeoecological communities were compared to the modern communities and also to the environmental reconstruction from pollen and macroremains from the same record. Results show that even though 18S could amplify a broader group of organisms, the taxonomic resolution was lower than that obtained from COI and that the taxonomic assignment of the COI sequences yielded mostly metazoans. This first molecular approach has allowed to prove that the diversity of modern and past eukaryotic peat bog communities can be assessed using universal metabarcoding markers.Los registros sedimentarios obtenidos en ecosistemas de alta montaña contienen información que permite entender los cambios ambientales ocurridos en el pasado que ayudarían a predecir la influencia del calentamiento climático actual. Esta tesis se centra en el estudio de la paleoecología y paleolimnología de los Pirineos Centrales a lo largo del Holoceno basado en el análisis de diversos proxis de dos secuencias sedimentarias de Bassa Nera. También se introdujo un índice de polen montano como un nuevo indicador paleoecológico para resaltar cambios altitudinales en la vegetación caducifolia. Nuestros resultados mostraron cambios en el ascenso de los bosques caducifolios y su presencia en Bassa Nera desde el inicio del Holoceno hasta el año 4200 años BP, así como su ascenso durante la Anomalía Climática Medieval. El índice montano mostró una relación entre la vegetación y la influencia del Atlántico Norte, así como una correlación significativa entre el índice de polen montano y el crecimiento del pino de bosques subalpinos cercanos. Mientras que los cambios en los macrofósiles de Sphagnum y los taxones acuáticos permitieron la descripción de los cambios ontogénicos locales desde el estanque inicial hasta la turbera actual. Los cambios en los taxones acuáticos también permitieron datar cuando la turbera circundante se desarrolló y colmató el lugar donde se extrajo el sondeo, siendo esta en 1565 AD. En general, los resultados sugieren que Bassa Nera tuvo una presión humana de baja intensidad. Las primeras inferencias de presión antrópica en Bassa Nera datan de 7300 años BP y fueron actividades de pastoreo, mientras que los cereales aparecieron alrededor de 5190 años BP. Por otro lado, nuestros resultados sugieren que la sensibilidad del crecimiento del pino al clima ha variado en los últimos 700 años y que la variabilidad del crecimiento arbóreo en localidades altas está más limitada por las temperaturas bajas que por altas, aunque también observamos una relajación de esta restricción en las últimas décadas. Los resultados del estudio metabarcoding utilizando los marcadores genéticos universales 18S y COI sugieren que la diversidad de comunidades de turberas eucariotas modernas y pasadas pueden ser evaluadas usando marcadores genéticos universales

Palaeoecological proxies from peat core HM15, Holcroft Moss, NW England

Palaeoecological proxies from peat core HM15, Holcroft Moss, NW England, including radiocarbon data, age-depth model, physical, chemical and biological proxies (pollen and non-pollen palynomorphs)