Michael N Styllas - Profile on Academia.edu (original) (raw)

Papers by Michael N Styllas

Diversity and biogeography of the bacterial microbiome in glacier-fed streams

Zenodo (CERN European Organization for Nuclear Research), Jun 8, 2023

Introduction Water is essential for the survival and well-being of humanity and plays a vital rol... more Introduction Water is essential for the survival and well-being of humanity and plays a vital role in sustainable development. By continuing our "business as usual" model in freshwater consumption, the global demand for freshwater might exceed our viable resources by 40% in 2030 (Tahir et al., 2019). But by embracing Circular Economy (CE) principles and by supporting technological innovation, the linear model that assumes that water resources are abundant, available, and cheap to dispose, can be abandoned and instead the focus is transferred on preserving the natural capital and securing water supply where resources are scarce. The closure of this loop leads to a tighter nexus adding inter-connections that improve the autonomy and resilience at every level of the entire water management system (Μakropoulos et al., 2018). As water scarcity becomes more prevalent in semi-arid regions, new circular water management systems and actions establishing CE strategies in the water sector are of significant relevance for a sustainable environmental and economic development of these regions. Especially for the Mediterranean Basin, where high temperatures and minimal rainfall characterize the summer climate (Ulbrich et al., 2012), recent studies point to future trends towards even drier conditions with increased frequency of extreme rainfall events (Giorgi & Lionello, 2008). The total precipitation is expected to decrease, as longer dry spells and reduced rainfall intensity have been observed (Cramer et al., 2022). Therefore, these regions suffer from the limitation and irregular distribution of their water reserves, while the increasing touristic activities during the summer season put additional stress on their water supplies, both in terms of quantity and quality. The Mediterranean islands face even greater challenges and experience more severe water scarcity issues due to their relatively smaller size and isolation. To address such issues, transformative adaptation water management solutions, within the concept of CE are urgently required to increase community resilience, to enable effective and far-reaching changes, to adapt to the projected climate change and to carry out a sustainable transition.

Table S5 from The dark side of the moon: first insights into the microbiome structure and function of one of the last glacier-fed streams in Africa

Figshare, 2023

Table S3 from The dark side of the moon: first insights into the microbiome structure and function of one of the last glacier-fed streams in Africa

Figshare, 2023

Earthquakes, Tsunamis and HarboursA Geoarchaeological GPR-Based Approach for Depicting the Spatial Characteristics of Human Structures and Natural Hazards in Ancient Falasarna Harbour

A simple approach to define Holocene sequence stratigraphy using borehole and cone penetration test data

Sedimentology, Dec 11, 2013

Cone penetration testing has been widely used since the 1950s for determining the subsurface geot... more Cone penetration testing has been widely used since the 1950s for determining the subsurface geotechnical conditions of unconsolidated sediments. This paper highlights the potential value of cone penetration testing as an aid to define the stratigraphic structure of Holocene sedimentary deposits. By calibrating cone penetration test logs with adjacent borehole logs and by utilizing all the available information produced during geotechnical surveying, stratigraphic models that accurately describe the vertical and lateral boundaries, as well as the stacking pattern, of Late Quaternary systems can be constructed. The widespread application and technical simplicity of cone penetration testing, combined with simple data interpretation via correlation with adjacent borehole logs, yield a useful and inexpensive tool for sedimentological investigations. This methodology is illustrated using data from 36 cone penetration tests and 11 boreholes on the Holocene deltaic plain of the Aliakmon River, Greece. Sedimentological and stratigraphic information from core log correlations, the spatial distribution of cone penetration test parameters, sediment grain size and per cent concentration of organic matter are utilized. The results suggest, that in sequence stratigraphic terms, the delta is divided into a lowstand systems tract composed by fluvial gravels and sands (U0) of Late Pleistocene age, as well as from red oxidized clays, and a transgressive systems tract represented by fluvial channel sands (U1), overlain by a thin transgressive sand sheet of coastal origin (U2), characterized by fining upward trends. The highstand systems tract is constituted by a variety of stratigraphic units (U3 to U7) and depositional environments, characterized by coarsening upward sequences, representing both aggradational and progradational facies, and dominated by the presence of three prograding wedges. Detailed definition of the thickness, vertical boundaries and stacking pattern of the resolved stratigraphic units, presented as a two‐dimensional stratigraphic model, demonstrates the applicability of the proposed method.

is the second largest estuary on the Oregon coast, and concerns have been raised whether human in... more is the second largest estuary on the Oregon coast, and concerns have been raised whether human induced impacts have been responsible for the perceived increase in sedimentation rates during the past century. Major land-use practices within the five watersheds of the Bay include logging, forest fires, the construction of forest roads, the placement of dikes along the channels of the main rivers and in the estuary, the removal of riparian vegetation, and the construction of jetties at the tidal inlet. Each of these practices has led to impacts on the entire ecosystem of the watersheds and the Bay, but this study focuses on the effects of human disturbances on the Bay's sediment accumulation. This study examines in detail the land-use practices that have occurred in the watersheds, on the beaches, and in the estuary, focusing on those that have had a direct impact on the sedimentation regime of the Bay. One goal of the study is to assess the relative roles of natural processes versus human impacts on the sedimentation. gratitude to my advisor Paul D. Komar. His supervision, guidance and transmission of knowledge throughout the time that I was here are much more than I initially had expected. I also want to thank my committee members Nick Pisias, James McManus and Peter Klingeman, for their extensive help and helpful comments on my thesis. Their contribution to my education either through classes or by office meetings was truly significant. Special thanks to Gregory Bostrom for the sampling of the sediment samples and most important for the sieving analyses, which were at the highest possible amount of detail, and made my life much easier by saving me lots of time. For moral support I am really grateful to my lovely parents that have always stood behind me, and have helped me to overcome any difficulties that I have faced so far. Finally, a great thanks to the Corvallis ultra-running gang and especially Clem LaCava who showed me the most beautiful trails in Oregon, and kept me motivated and challenged so that I could keep some balance between my physical and mental worlds.

Natural Processes Versus Human Impacts During the Last Century: A Case Study of the Aliakmon River Delta

The handbook of environmental chemistry, 2017

The Aliakmon River flows down from the northwestern mountains of Greece and is one of the largest... more The Aliakmon River flows down from the northwestern mountains of Greece and is one of the largest fluvial systems in the Greek territory. Basin climate and geology favour the high rates of sediment production and transport and, consequently, the formation of an extensive (9.2% of basin area) bird-foot Holocene delta. Three phases (A, B and C) of human impacts over the past 90 years have caused pronounced changes on the natural evolution of the delta. During Phases A and B, a 50% increase of deltaic sedimentation rates in relation to Holocene pre-anthropogenic rates and an enrichment of deltaic deposits with heavy minerals occurred. Phase C, characterised by damming, increasing agricultural and industrial activities and population growth, resulted in 90% decrease in sedimentation rates compared to Phase B, a regulated hydrological regime with high electrical conductivity and nutrient concentrations of surface water, enhanced erosion of river channel and deltaic deposits and degradation of habitats along the lower Aliakmon River delta. Future climate scenarios and increasing environmental pressures are not compatible with current water use strategy and, given the vulnerability of the system (reservoirs and delta) to projected climate trends, stress for a new strategic natural resource management plan.

Mediterranean geoscience reviews, Apr 1, 2020

The Holocene glaciations in the majority of Eastern Mediterranean mountains are generally obscure... more The Holocene glaciations in the majority of Eastern Mediterranean mountains are generally obscured, as warm climate and their relatively low elevations prohibited the formation of glacial ice and discernible glacial landforms. This work reviews the Holocene glacial phases on Mount Olympus, emphasizes the relative roles of external forcing and of the climatic drivers that triggered each episode of glaciation and traces the climatic signal of a Late Holocene glacial phase from source to sink. The Late Holocene glacial phase on Mount Olympus took place between 3.3 and 2.3 ka BP, during a period of solar minima, a negative phase of NAO, and overall wet conditions characterized by enhanced fluvial inputs in the North Aegean Sea, and also by increasing human-induced erosion in the lowlands. The climatic expression associated with the Late Holocene inception of glacial ice on Mount Olympus, detected in speleothem, paleoflood, marine sedimentary and planktonic foraminiferal records, may have occurred in other high cirques of the Balkan Peninsular and the Eastern Mediterranean.

Η εξέλιξη των δελταϊκών ιζηματογενών αποθέσεων του ποταμού Αλιάκμονα στο Θερμαϊκό κόλπο από φυσικούς και ανθρωπογενείς παράγοντες κατά το ολόκαινο

Nature geoscience, Mar 1, 2024

Bulletin of the Geological Society of Greece, Jul 23, 2018

Analyses of sea level records within the Caldera of Santorini Island revealed the significance of... more Analyses of sea level records within the Caldera of Santorini Island revealed the significance of both oceanographic and atmospheric forcing on the observed signals. Sea level (msl) and sea surface temperature (sst) data were obtained from the four stations of the REMOS monitoring network. Out of the four stations Gialos station is located on the caldera whereas the remaining three (Erinia, Taxiarhis and Agios Nikolaos) are located on the young volcanic islands of Palaia and Nea Kameni. The record of sea level data contained a number of gaps. When possible, (i.e. small gaps) missing values were estimated with linear interpolation. Harmonic analysis on continuous parts of the record revealed a mixed type of tide with similar Nf values for the four stations, a result of their locations being close to each other. No co-oscillation phenomena were found within the caldera. Sea level at Taxiarhis station is affected more by atmospheric forcing and shallow water effects in contrast with Gialos station where mean sea level displays significant correlation (r=0.62) with sea surface temperature at lags 2-6 days. The annual cycle of mean sea level (amplitude=5.74cm) responds to seasonal variations in the thermal structure of the waters, and together with the semiannual cycle explains 9.02% of the variance in the annual frequency band. Existing data are not sufficiently long to develop a model, which will reconstruct sea level variability resulting from oceanographic and meteorological forcing and will be used for the detection of ground movements from future volcanic eruptions.

Microdiversity, the organization of microorganisms into groups with closely related but ecologica... more Microdiversity, the organization of microorganisms into groups with closely related but ecologically different sub-types, is widespread and represents an important linchpin between microbial ecology and evolution. However, the drivers of microdiversification remain largely unknown. Here we show that selection promotes microdiversity in the microbiome associated with sediments in glacier-fed streams (GFS). Applying a novel phylogenetic framework, we identify several clades that are under homogeneous selection and that contain genera with higher levels of microdiversity than the rest of the genera. Overall these clades constituted ∼44% and ∼64% of community α-diversity and abundance, and both percentages increased further in GFS that were largely devoid of primary producers. Our findings show that strong homogeneous selection drives the microdiversification of specialized microbial groups putatively underlying their success in the extreme environment of GFS. This microdiversity could ...

Nature Communications, Apr 20, 2022

In glacier-fed streams, ecological windows of opportunity allow complex microbial biofilms to dev... more In glacier-fed streams, ecological windows of opportunity allow complex microbial biofilms to develop and transiently form the basis of the food web, thereby controlling key ecosystem processes. Using metagenome-assembled genomes, we unravel strategies that allow biofilms to seize this opportunity in an ecosystem otherwise characterized by harsh environmental conditions. We observe a diverse microbiome spanning the entire tree of life including a rich virome. Various co-existing energy acquisition pathways point to diverse niches and the exploitation of available resources, likely fostering the establishment of complex biofilms during windows of opportunity. The wide occurrence of rhodopsins, besides chlorophyll, highlights the role of solar energy capture in these biofilms while internal carbon and nutrient cycling between photoautotrophs and heterotrophs may help overcome constraints imposed by oligotrophy in these habitats. Mechanisms potentially protecting bacteria against low temperatures and high UV-radiation are also revealed and the selective pressure of this environment is further highlighted by a phylogenomic analysis differentiating important components of the glacier-fed stream microbiome from other ecosystems. Our findings reveal key genomic underpinnings of adaptive traits contributing to the success of complex biofilms to exploit environmental opportunities in glacier-fed streams, which are now rapidly changing owing to global warming.

A Tropical Cocktail of Organic Matter Sources: Variability in Supraglacial and Glacier Outflow Dissolved Organic Matter Composition and Age Across the Ecuadorian Andes

Journal Of Geophysical Research: Biogeosciences, May 1, 2023

The biogeochemistry of rapidly retreating Andean glaciers is poorly understood, and Ecuadorian gl... more The biogeochemistry of rapidly retreating Andean glaciers is poorly understood, and Ecuadorian glacier dissolved organic matter (DOM) composition is unknown. This study examined molecular composition and carbon isotopes of DOM from supraglacial and outflow streams (n = 5 and 14, respectively) across five ice capped volcanoes in Ecuador. Compositional metrics were paired with streamwater isotope analyses (δ18O) to assess if outflow DOM composition was associated with regional precipitation gradients and thus an atmospheric origin of glacier DOM. Ecuadorian glacier outflows exported ancient, biolabile dissolved organic carbon (DOC), and DOM contained a high relative abundance (RA) of aliphatic and peptide‐like compounds (≥27%RA). Outflows were consistently more depleted in Δ14C‐DOC (i.e., older) compared to supraglacial streams (mean −195.2 and −61.3‰ respectively), perhaps due to integration of spatially heterogenous and variably aged DOM pools across the supraglacial environment, or incorporation of aged subglacial OM as runoff was routed to the outflow. Across Ecuador, Δ14C‐DOC enrichment was associated with decreased aromaticity of DOM, due to increased contributions of organic matter (OM) from microbial processes or atmospheric deposition of recently fixed and subsequently degraded OM (e.g., biomass burning byproducts). There was a regional gradient between glacier outflow DOM composition and streamwater δ18O, suggesting covariation between regional precipitation gradients and the DOM exported from glacier outflows. Ultimately, this highlights that atmospheric deposition may exert a control on glacier outflow DOM composition, suggesting regional air circulation patterns and precipitation sources in part determine the origins and quality of OM exported from glacier environments.

Global biogeography of the glacier-fed stream microbiome

&#160;Glacier-fed streams (GFSs) serv... more &#160;Glacier-fed streams (GFSs) serve as headwaters to many of the world&#8217;s largest river networks. Although being characterized by extreme environmental conditions (i.e., low water temperatures, oligotrophy) GFSs host an underappreciated microbial biodiversity, especially within benthic biofilms which play pivotal roles in downstream biogeochemical cycles. Yet, we still lack a global overview of the GFS biofilm microbiome. In addition, little is known on how environmental conditions shape bacterial diversity, and how these relationships drive global distribution patterns. This is particularly important as mountain glaciers are currently vanishing at a rapid pace due to global warming. Here, we used 16S rRNA gene sequencing data from the Vanishing Glaciers project to conduct a first comprehensive analysis of the benthic microbiome from 148 GFSs across 11 mountain ranges. Our analyses revealed marked biogeographic patterns in the GFS microbiome, mainly driven by the replacement of phylogenetically closely related taxa. Strikingly, the GFS microbiome was characterized by pronounced level of endemism, with >58% of the Amplicon Sequence Variants (ASVs) being specific to one mountain range. Consistent with the marked dissimilarities across mountain ranges, we found a very small taxonomic core including only 200 ASVs, yet accounting for >25% of the total relative abundance of the ASVs. Finally, we found that spatial effects such as dispersal limitation, isolation and spatially autocorrelated environmental conditions overwhelmed the effect of the environment by itself on benthic biofilm beta diversity. Our findings shed light on the previously unresolved global diversity and biogeography of the GFS microbiome now at risk across the world&#8217;s major mountain ranges because of rapidly shrinking glaciers.

Glacier-Fed Stream Biofilms Harbor Diverse Resistomes and Biosynthetic Gene Clusters

Microbiology spectrum, Feb 14, 2023

Antimicrobial resistance is an omnipresent phenomenon in the anthropogenically influenced ecosyst... more Antimicrobial resistance is an omnipresent phenomenon in the anthropogenically influenced ecosystems. However, its role in shaping microbial community dynamics in pristine environments is relatively unknown.

Research Square (Research Square), Apr 3, 2023

Applied and Environmental Microbiology, Jun 28, 2022

Microbial life in glacier-fed streams (GFSs) is dominated by benthic biofilms which fulfill criti... more Microbial life in glacier-fed streams (GFSs) is dominated by benthic biofilms which fulfill critical ecosystem processes. However, it remains unclear how the bacterial communities of these biofilms assemble in stream ecosystems characterized by rapid turnover of benthic habitats and high suspended sediment loads. Using16S rRNA gene amplicon sequence data collected from 54 GFSs across the Himalayas, European Alps, and Scandinavian Mountains, we found that benthic biofilms harbor bacterial communities that are distinct from the bacterial assemblages suspended in the streamwater. Our data showed a decrease in species richness in the benthic biofilms compared to the bacterial cells putatively free-living in the water. The benthic biofilms also differed from the suspended water fractions in terms of community composition. Differential abundance analyses highlighted bacterial families that were specific to the benthic biofilms and the suspended assemblages. Notably, source-sink models suggested that the benthic biofilm communities are not simply a subset of the suspended assemblages. Rather, we found evidence that deterministic processes (e.g., species sorting) shape the benthic biofilm communities. This is unexpected given the high vertical mixing of water and contained bacterial cells in GFSs and further highlights the benthic biofilm mode of life as one that is determined through niche-related processes. Our findings therefore reveal a "native" benthic biofilm community in an ecosystem that is currently threatened by climate-induced glacier shrinkage. IMPORTANCE Benthic biofilms represent the dominant form of life in glacier-fed streams. However, it remains unclear how bacterial communities within these biofilms assemble. Our findings from glacier-fed streams from three major mountain ranges across the Himalayas, the European Alps and the Scandinavian Mountains reveal a bacterial community associated with benthic biofilms that is distinct from the assemblage in the overlying streamwater. Our analyses suggest that selection is the underlying process to this differentiation. This is unexpected given that bacterial cells that are freely living or attached to the abundant sediment particles suspended in the water continuously mix with the benthic biofilms. The latter colonize loose sediments that are subject to high turnover owing to the forces of the water flow. Our research unravels the existence of a microbiome specific to benthic biofilms in glacier-fed streams, now under major threats due to global warming.

Global Change Biology, Apr 1, 2022

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-... more This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Diversity and biogeography of the bacterial microbiome in glacier-fed streams

Zenodo (CERN European Organization for Nuclear Research), Jun 8, 2023

Table S5 from The dark side of the moon: first insights into the microbiome structure and function of one of the last glacier-fed streams in Africa

Figshare, 2023

Table S3 from The dark side of the moon: first insights into the microbiome structure and function of one of the last glacier-fed streams in Africa

Figshare, 2023

Earthquakes, Tsunamis and HarboursA Geoarchaeological GPR-Based Approach for Depicting the Spatial Characteristics of Human Structures and Natural Hazards in Ancient Falasarna Harbour

A simple approach to define Holocene sequence stratigraphy using borehole and cone penetration test data

Sedimentology, Dec 11, 2013

Natural Processes Versus Human Impacts During the Last Century: A Case Study of the Aliakmon River Delta

The handbook of environmental chemistry, 2017

Mediterranean geoscience reviews, Apr 1, 2020

Nature geoscience, Mar 1, 2024

Bulletin of the Geological Society of Greece, Jul 23, 2018

Nature Communications, Apr 20, 2022

A Tropical Cocktail of Organic Matter Sources: Variability in Supraglacial and Glacier Outflow Dissolved Organic Matter Composition and Age Across the Ecuadorian Andes

Journal Of Geophysical Research: Biogeosciences, May 1, 2023

Global biogeography of the glacier-fed stream microbiome

Glacier-Fed Stream Biofilms Harbor Diverse Resistomes and Biosynthetic Gene Clusters

Microbiology spectrum, Feb 14, 2023

Research Square (Research Square), Apr 3, 2023

Applied and Environmental Microbiology, Jun 28, 2022

Global Change Biology, Apr 1, 2022

THE LATEGLACIAL AND HOLOCENE GLACIAL HISTORY OF THE NORTHEAST MEDITERRANEAN MOUNTAINS INFERRED FROM IN-SITU PRODUCED COSMIC RAY EXPOSURE DATINGS OF PALEO-GLACIERS DEPOSITS. IMPLICATIONS FOR THE RELATIVE ROLES OF EXTERNAL AND INTERNAL CLIMATE FORCING., 2018

A new glacial chronology from Mount Olympus in Greece, based on 20 36Cl in situ produced cosmic r... more A new glacial chronology from Mount Olympus in Greece, based on 20 36Cl in situ produced
cosmic ray exposure (CRE) datings is used to complement existing CRE chronologies from the
northeast Mediterranean (NEM) region. The new 36Cl ages of the glacial landforms range from
15.6 ± 2.0 to 0.6 ± 0.08 ka, spanning the Lateglacial and the Holocene. Based on the
Probability Density Functions of all existing CRE ages, the Lateglacial is partitioned in three
distinct phases (LG1-3): an initial phase of glacial moraine stabilization at 15.06 ± 0.53 ka with
subsequent deglaciation starting at ~14 ka (LG1) evident in Mount Pelister, Sâra Range, Galicica
Mountains, Mount Olympus, Rila Mountains and Mount Uludag. LG1 was followed by a transition
to conditions marginal for glaciation at 13.3 ± 1.21 ka (LG2), recorded only on Mount Olympus
that was characterized by enhanced aeolian activity (westerlies) and large amounts of
windblown snow. Glacial conditions characterized by low temperatures and low precipitation,
returned to the NEM mountains at 11.9 ± 0.56 ka (LG3), but they were not widespread as they
are found on Sâra Range, Mount Uludag, Mount Chelmos and Mount Olympus. NEM glacial
phases LG1-3 occurred during a period of increasing obliquity and peak eccentricity and exhibit
an out-of-phase behaviour with the local solar insolation record from Duhlata Cave. Phases LG1
and LG3 occurred during solar insolation maxima and also coincided with a shutdown of the
Atlantic Meridional Overturning Circulation (AMOC), whereas LG2 occurred during insolation
minima with concurrent establishment of the AMOC. The Holocene glacial phases (HOL1-3) are
recorded only in Mount Olympus. An early Holocene glacier stillstand (HOL1) at 9.6 ± 1.1 ka,
occurred during peak obliquity, increasing solar insolation close to the record's peak values and
is locally associated with a lagged recovery of north Aegean Sea Surface Temperatures (SST's).
No glacier activity is observed during the mid-Holocene (~9.0 – 3.0 ka). The Late Holocene
glacier expansions, include a moraine stabilization phase (HOL2) at 2.5 ± 0.3 ka, a period that
coincides with solar insolation minima (Homeric Low), combined with a negative North Atlantic
Oscillation (NAO) phase, which resulted in locally wet conditions, as recorded in Skala Marion
Cave speleothem record. The last phase of glacial activity (HOL3) corresponds to the early part
of the Little Ice Age (0.6 ± 0.08 ka). A link between the Holocene glaciations with the north
Atlantic climatic regime is evident, as HOL1, 2 and 3 glacial phases, broadly correspond to Bond
6, 2 and 0 events. The new Lateglacial and Holocene glacial chronology emphasizes the relative
controls of internal and external forcing along the headwaters of the major Northeast
Mediterranean fluvial systems, is in pace with numerous regional and local terrestrial and marine
proxies and establishes the basis for a source-to-sink approach to paleoenvironmental
reconstrunctions.

In the broader context of rapid environmental and climatic changes in the Mediterranean region, a... more In the broader context of rapid environmental and climatic changes in the Mediterranean region, a new 36 Cl nuclide glacial chronology from two small (0.5km 2) cirques on Mount Olympus in Greece (Throne of Zeus and Megala Kazania) is presented, spanning the Lateglacial and the Holocene. The new chronology contemplates few existing Surface Exposure Datings (SED) from cirques in the southern Balkan Mountains. Cirque glacier behaviour and solar radiation are out-of-phase during the Lateglacial and in-phase during the Holocene. The most recent glaciation episode occurred during the Little Ice Age (LIA) and has been confined only in the sheltered northwest facing cirque of Megala Kazania (MK), which is characterized by steep 500m-high headwalls and by large amounts of windblown and avalanching snow. Perennial snowfields and permanent ice bodies survived within the MK cirque during the entire 20 th century, despite the fact that the local ELA has been situated above Mount Olympus summit (2918m). Since 2010, pronounced shrinking of the snowfields has led to the exposure and melting of the basal ice, bringing them on the brink of extinction, due to reduced snowfall and increasing summer temperatures. The last ice of Mount Olympus, is preserved within vertical caves, guarding the last climatic information of the Ancient Greek Gods.