Remote Mountain Research Articles

Regeneration of an endangered plant species endemic to the remote mountain areas: Anthropogenic disturbance matters

The regeneration of plants endemic to remote mountain areas is thought to be relatively unimpacted by human disturbances but rather dominated by abiotic factors, such as geography, climate, and soil. However, because human disturbances are accelerating the extinction of montane plants and the loss of montane forest, this balance may be shifting. Yet, the relative effects of abiotic factors and human disturbances to montane plant regeneration are still largely unclear. Here, we investigated the geographic pattern of regeneration (ratio of seedling and ratio of sprout) and assessed the impacts of abiotic and anthropogenic factors for an endangered montane tree species (Davidia involucrata) across its distribution range in China. We found that the ratio of seedling increased from south to north, whereas the ratio of sprout exhibited an opposite pattern, indicating that under climate warming this species may adopt sprout regeneration as a potential strategy to buffer population contraction at the southern edge. Moreover, while climatic factors were the main drivers of regeneration, anthropogenic factors were also important. Of note, the proportion of pasture land area had a significant positive effect on sprouting, with more sprout regeneration at grazed sites and a higher ratio of sprout at sites with a greater intensity of human disturbance. Our findings suggested that, in addition to climate change, human disturbance is also an important driving factor of the regeneration of plants native to remote mountain areas, and we emphasized that researchers and policymakers should take it into account when protecting endangered plants and managing forest biodiversity.

Sources Affecting Microplastic Contamination in Mountain Lakes in Tatra National Park

The global atmospheric transport of microplastics (MPs) plays a crucial role in the contamination of remote, especially higher-elevation, environments. Precipitation is considered the main source of MP pollution. Meanwhile, plastic waste generated from, for example, tourism activities can be a local source of MP pollution. In this study, we specify which of the mentioned sources of MP, global or local, have a higher impact on the pollution level in the high-elevation oligotrophic lakes of Tatra National Park in Poland. Due to its unique natural value, it is listed by UNESCO as an international biosphere reserve and meets the criteria for Natura 2000 areas. We comprehensively analyzed the morphometric and anthropogenic features of 11 lakes in terms of the contamination level, color, shape, and polymer type of the MPs found in the surface waters. MP fibers were found to be present in all studied lakes, with contamination ranging from 25 to 179 items/m3. Polypropylene, polyethylene terephthalate, and natural or semi-natural cellulose fibers—black or red in color with a length of 0.2–1.0 mm—predominated, which corresponds with other studies conducted on remote mountain ecosystems. We did not find any correlation of the number of MPs with local anthropogenic pressure characteristics. In turn, the significant correlation with lake area, coastline length, lake volume, and catchment area indicated airborne sources, including global transport of MPs to the lakes with reduced water outflow.

Brickwork in Norway: tradition encounters a new age of industrial construction, 1905–1912

During the first decades of the twentieth century, construction technology experienced rapid developments, which also affected industrial buildings. This paper demonstrates this evolution between 1905 and 1912 through the case of the Rjukan and Notodden UNESCO World Heritage site in central southern Norway. The site was established for the purpose of producing synthetic nitrogen fertiliser by the company Hydro. There, building systems changed from timber frames with brick infill to pure brick bearing walls and finally to more sophisticated wall-braced cage buildings where steel was incorporated. Increasing the structural capacity was the answer to the growing demand for higher and larger industrial buildings. This case study presents the characteristics and establishes an initial account of the types of construction systems. Embedded steel that is concealed within brickwork can be subject to corrosion and compromise structural integrity. Studying these systems and materials in greater detail and identifying conservation issues will support future repair work. The studied buildings reveal also that used systems were not unique to this remote mountain area, but the technology used was in line with developments in leading industrial nations around the world. This places the site also in an international context of architecture and engineering history.

Depopulation in the Central Apennines in the Twentieth Century: An Empirical Investigation

AbstractWe propose an empirical investigation of the population dynamics between 1931 and 2011 in a mountain area in Italy. The main novelty of our work is the usage of sub-municipal data, which makes it possible to disentangle several drivers of the overall depopulation trend. All these factors had been considered previously by separate strands of literature, but never jointly, as we do. One of our most interesting results is that different factors operate in different historical periods. Therefore, we use a flexible strategy by which we divide the sample in four different 20-year spans and adopt a different statistical model for each. Another notable result is that an appropriate quantitative description of the phenomenon must take into account the disappearance of inhabited centres separately from their size in terms on inhabitants. Consequently, the concept of local community is crucial for a systematic understanding of population change and “place-sensitive” policies in remote mountain areas.

Learning lightweight tea detector with reconstructed feature and dual distillation

Currently, image recognition based on deep neural networks has become the mainstream direction of research; therefore, significant progress has been made in its application in the field of tea detection. Many deep models exhibit high recognition rates in tea leaves detection. However, deploying these models directly on tea-picking equipment in natural environments is impractical; the extremely high parameters and computational complexity of these models make it challenging to perform real-time tea leaves detection. Meanwhile, lightweight models struggle to achieve competitive detection accuracy; therefore, this paper addresses the issue of computational resource constraints in remote mountain areas and proposes Reconstructed Feature and Dual Distillation (RFDD) to enhance the detection capability of lightweight models for tea leaves. In our method, the Reconstructed Feature selectively masks the feature of the student model based on the spatial attention map of the teacher model; it utilizes a generation block to force the student model to generate the teacher’s full feature. The Dual Distillation comprises Decoupled Distillation and Global Distillation. Decoupled Distillation divides the reconstructed feature into foreground and background features based on the Ground-Truth. This compels the student model to allocate different attention to foreground and background, focusing on their critical pixels and channels. However, Decoupled Distillation leads to the loss of relation knowledge between foreground and background pixels. Therefore, we further perform Global Distillation to extract this lost knowledge. Since RFDD only requires loss calculation on feature map, it can be easily applied to various detectors. We conducted experiments on detectors with different frameworks, using a tea dataset collected at the Huangshan Houkui Tea Plantation. The experimental results indicate that, under the guidance of RFDD, the student detectors have achieved performance improvements to varying degrees. For instance, a one-stage detector like RetinaNet (ResNet-50) experienced a 3.14% increase in Average Precision (AP) after RFDD guidance. Similarly, a two-stage model like Faster RCNN (ResNet-50) obtained a 3.53% improvement in AP. This offers promising prospects for lightweight models to efficiently perform real-time tea leaves detection tasks.

Effectiveness of NGOs in mountainous solid waste management: A case study from Healing Himalayas in Rakchham, Himachal Pradesh, India.

Non-governmental organizations (NGOs) play a critical role in addressing solid waste management (SWM) challenges in remote mountain communities, including the ecologically fragile Himalayan region. This study evaluates the impact of Healing Himalayas, an NGO, in Rakchham village, Himachal Pradesh, India. The objectives were to evaluate the effectiveness of Healing Himalayas' decentralized SWM model in promoting stakeholder engagement and resource recovery, assess the role of collaborations between local authorities and the NGO in financing waste management practices, investigate the influence of tourism and seasonal variations on solid waste generation patterns and waste management practices in Rakchham, and material recovery facilities, followed by glass (36.7%), paper/cardboard (18.4%) and metal (4.1%). A fee-based system involving the local village council funded waste operations. Waste generation exhibited significant seasonal fluctuations, with tourism influxes driving increased volumes. Healing Himalayas' initiatives promoted community participation, with over 15 awareness workshops conducted. Key challenges included limited financial resources, inadequate infrastructure, lack of advanced treatment facilities and need for context-specific solutions like efficient wet waste management in cold climates. The study highlights Healing Himalayas' decentralized model's success in fostering stakeholder engagement, behavioural change and resource recovery. The findings inform effective strategies for NGO-led waste management initiatives tailored to remote Himalayan communities.

Species limits and hybridization in Andean leaf-eared mice (Phyllotis).

Leaf-eared mice (genus Phyllotis) are among the most widespread and abundant small mammals in the Andean Altiplano, but species boundaries and distributional limits are often poorly delineated due to sparse survey data from remote mountains and high-elevation deserts. Here we report a combined analysis of mitochondrial DNA variation and whole-genome sequence (WGS) variation in Phyllotis mice to delimit species boundaries, to assess the timescale of diversification of the group, and to examine evidence for interspecific hybridization. Estimates of divergence dates suggest that most diversification of Phyllotis occurred during the past 3 million years. Consistent with the Pleistocene Aridification hypothesis, our results suggest that diversification of Phyllotis largely coincided with climatically induced environmental changes in the mid- to late Pleistocene. Contrary to the Montane Uplift hypothesis, most diversification in the group occurred well after the major phase of uplift of the Central Andean Plateau. Species delimitation analyses revealed surprising patterns of cryptic diversity within several nominal forms, suggesting the presence of much undescribed alpha diversity in the genus. Results of genomic analyses revealed evidence of ongoing hybridization between the sister species Phyllotis limatus and P. vaccarum and suggest that the contemporary zone of range overlap between the two species represents an active hybrid zone.

Women in mountain tourism: exploring the links between women tourism entrepreneurship and women empowerment in Hunza Valley

ABSTRACT Tourism entrepreneurship is crucial to boosting household income and fostering gender equality in Pakistan. However, the involvement of women in mountain tourism entrepreneurship remains rather limited. This study examines the experiences of women entrepreneurs in the Hunza Valley of Pakistan, highlighting their transformative journey into the tourism market despite facing various obstacles. Through qualitative research involving 24 women-led tourism enterprises, the study illuminates the positive outcomes these women have achieved, including greater control over finances, enhanced decision-making power, boosted self-confidence, expanded networks, and overall societal empowerment. The study also identifies internal and external constraints faced by these entrepreneurs, emphasising the need for immediate policy interventions to support women's entrepreneurship in the region. Recognising the catalytic role these women play in promoting gender equality and social innovation, the study advocates for greater recognition and appreciation of their contributions to inspire other women in the region. Based on the study's findings, a framework for women's tourism entrepreneurship is proposed, emphasising the potential of such initiatives to empower women, drive social change, and foster gender equality in remote mountain regions.

Microplastic assessment in remote and high mountain lakes of Gilgit Baltistan, Pakistan

Microplastic (MP) pollution is a critical environmental challenge worldwide, however limited research is reported in remote lakes of Pakistan. This study assessed MPs (>5 mm) prevalence, distribution and risk perspective in water and sediment of eight remote and high-altitude lakes (>1500 m above sea level) of Gilgit Baltistan, Pakistan. The lakes exhibited an average abundance of 152.6 ± 104.6 to 12.1 ± 7 MP/kg of dry sediments and 2 ± 0.9 to 17.1 ± 17.2 MP/L of surface water. MPs <200 μm dominated in both matrices. Surface water predominantly contained polyester and polypropylene, while polypropylene and polyethylene dominated in sediments. The gradient of elevation did not show any pronounced impact on the fiber loading or MP count in both matrices. Backward air mass trajectory revealed that air masses vastly travelled from western-Asia, Arabian sea and Bay of Bengal with an average transmission distance of 2500–3500 km (500 m a.s.l) that can be a potential deposition MP source in the area. Pollution Load Index of the lakes were >1 exhibiting pollution. All other lakes except Batura and Borith manifested a moderate hazard index. Naltar lake along with aforementioned two lakes also manifested high polymer toxicity. Further research should emphasize understanding the mechanisms and biotic interactions in high-mountain ecosystems.

Discovery in leaf litter: uncovering the systematics of Porcelloderes (Heteroptera: Reduviidae: Phimophorinae)

Abstract The subfamily Phimophorinae includes ~113 species of cryptic assassin bugs found in the Neotropics and Paleotropics. Presumably due to its small size, cryptic coloration, and occurrence in the remote Eastern Arc Mountains (EAM), Porcelloderes impenetrabilis Rédei, 2012 (Heteroptera: Reduviidae: Phimophorinae), was only recently described as the first representative of this subfamily from mainland Africa. Previous morphology-based phylogenetic research on Phimophorinae (then known as Physoderinae or Epiroderinae) recovered Porcelloderes as sister taxon to the remaining epiroderine-lineage of Phimophorinae. Recent fieldwork in Tanzania has resulted in 241 additional specimens of Porcelloderes from 3 EAM) ranges. We used molecular and morphological analyses for these 241 specimens to (i) determine their species identity, (ii) test the phylogenetic position of Porcelloderes within Phimophorinae, and (iii) determine if divergence within Porcelloderes coincides with periods of climate-driven forest fragmentation in the EAM. Specimens from the Kimboza and Nguru Mountains likely represent P. impenetrabilis, but we here describe Porcelloderes harles, n. sp., from the Udzungwa Mountains. Our molecular phylogeny shows Porcelloderes nested within the epiroderine-lineage of Phimophorinae and as sister taxon to a Madagascar clade. We estimate that the epiroderine-lineage diverged from other Phimophorinae ~44 MYA. The divergence estimates for the 2 Porcelloderes species is ~15 MYA, consistent with proposed dates for other EAM assassin bugs and a period of forest fragmentation.

The Geomechanics of the Dangkhar Landslide, Himachal Pradesh, India

The Dangkhar Landslide is an extremely large landslide located in the Spiti Valley of Himachal Pradesh, India. The landslide is situated in a remote high mountain desert within the Tethys Himalaya at elevations between 3400 m and 5600 m. It is amongst the five largest continental landslides on earth, covering an area of approximately 54 km2 and having an estimated volume of 15–20 km3. Geomechanical evaluations based on the block theory indicate that the Dangkhar Landslide formed as a result of unfavorable combinations of structural geological features and complex surface morphology. A massive kinematically removable block is created by a regional synclinal flexure that is crosscut and kinematically liberated by bounding side valleys. Three-dimensional block kinematics are necessary to permit the release of the giant block and its sliding along the synclinal flexure. Pseudostatic slope stability sensitivity analyses incorporating estimates of site seismicity and shear strength parameters suggest that earthquake shaking could have triggered instability if the static factor of safety was less than or in the range of about 1.5–1.9. Considering the glacial history of the region, ice debuttressing represents an additional potential triggering mechanism.

Ancient and remote quartzite caves as a novel source of culturable microbes with biotechnological potential

Quartzite caves located on table-top mountains (tepuis) in the Guyana Shield, are ancient, remote, and pristine subterranean environments where microbes have evolved peculiar metabolic strategies to thrive in silica-rich, slightly acidic and oligotrophic conditions. In this study, we explored the culturable fraction of the microbiota inhabiting the (ortho)quartzite cave systems in Venezuelan tepui (remote table-top mountains) and we investigated their metabolic and enzymatic activities in relation with silica solubilization and extracellular hydrolytic activities as well as the capacity to produce antimicrobial compounds. Eighty microbial strains were isolated with a range of different enzymatic capabilities. More than half of the isolated strains performed at least three enzymatic activities and four bacterial strains displayed antimicrobial activities. The antimicrobial producers Paraburkholderia bryophila CMB_CA002 and Sphingomonas sp. MEM_CA187, were further analyzed by conducting chemotaxonomy, phylogenomics, and phenomics. While the isolate MEM_CA187 represents a novel species of the genus Sphingomonas, for which the name Sphingomonas imawarii sp. nov. is proposed, P. bryophila CMB_CA002 is affiliated with a few strains of the same species that are antimicrobial producers. Chemical analyses demonstrated that CMB_CA002 produces ditropolonyl sulfide that has a broad range of activity and a possibly novel siderophore. Although the antimicrobial compounds produced by MEM_CA187 could not be identified through HPLC-MS analysis due to the absence of reference compounds, it represents the first soil-associated Sphingomonas strain with the capacity to produce antimicrobials. This work provides first insights into the metabolic potential present in quartzite cave systems pointing out that these environments are a novel and still understudied source of microbial strains with biotechnological potential.

Exploring Reasons and Perspectives Behind Decisions to Forego Hospital Births Among Remote Rural Populations in Bokeo Province, Lao PDR

Maternal mortality remains high among marginalized rural populations in Laos. Remote mountain villages in Bokeo Province typify persistent health access divides facing minor subgroups amidst infrastructure gaps and scattered habitation. This study explores complex drivers behind shunning hospital births using focused rural ethnography. Between October and November 2023, this qualitative study interviewed 40 participants including pregnant women, postpartum women, and their relatives across 5 villages in Bokeo Province regarding barriers to hospital births. Open-ended discussions aimed to elucidate motivations and barriers embedded in their decision to avoid formal delivery care, despite mortality awareness. Transcriptions from Lao were translated to Thai, maintaining cultural nuances. Thematic analysis identified patterns in women’s attitudes and barriers to hospital childbirth. A collaborative coding process revealed constraints on access, affordability, and autonomy, explaining why vulnerable groups often forego hospital births despite risks. The result founded that prohibitive transportation deficiencies including impassable roads, exorbitant driver fees and unreliable conveyance options were primary obstacles. Prohibitive direct and indirect costs compounded struggles for impoverished families. Restrictive traditions persisted among certain ethnicities. Discrimination fears and hospital foreignness also provoked wariness among a minority. Multidimensional geographical, financial and sociocultural barriers intersect to obstruct rural groups from accessible emergency obstetric care in Laos. Infrastructural strengthening, financial protection and public education can relieve these pronounced constraints denying the marginalized realization of maternal health rights.

Ultrasonography screening of hepatic cystic echinococcosis in sheep flocks used for evaluating control progress in a remote mountain area of Hejing County, Xinjiang

BackgroundAlthough ultrasonography (US) has been widely used in the diagnosis of human diseases to monitor the progress of cystic echinococcosis (CE) control, the screening method for hepatic CE in sheep flocks requires adjustment. In this study, we used a US scanner to screen sheep flocks and evaluated the efficacy of dosing dogs once a year with praziquantel for 7 years from 2014 to 2021.MethodsAll sheep in the three flocks were screened using an ultrasound scanner in 2014 and compared with the prevalence of infection in 2021 in Bayinbuluke, Xinjiang, China. Sheep age was determined using incisor teeth. Cyst activity and calcification were determined using US images. The dogs were dewormed with praziquantel once a year to control echinococcosis in the community.ResultsThree flocks had 968 sheep in 2014, with 13.22%, 22.62%, 18.7%, 27.27%, 11.88%, and 6.3% of sheep aged 1, 2, 3, 4, 5, and ≥ 6 years old, respectively. US scanning revealed that the overall CE prevalence was 38.43% (372/968), with active cysts and calcified cysts present in 9.40% (91/968) and 29.02% (281/968) of the sheep, respectively. For the young sheep aged 1 and 2 years, the prevalence of active and calcified cysts was: 1.56% and 0.91%, and 10.94% and 18.72%, respectively. Approximately 15.15% and 16.52% of the 4- and 5-year-old sheep, respectively, harbored active cysts. There was no significant difference in the infection rates of sheep between 2014 and 2021 (P > 0.05).ConclusionsUS is a practical tool for the field screening of CE in sheep flocks. One-third of the sheep population in the flocks was 1–2 years old, and these sheep played a very limited role in CE transmission, as most of the cysts were calcified. Old sheep, especially culled aged sheep, play a key role in the transmission of CE. Dosing dogs once a year did not affect echinococcosis control.

Survey of a snow petrel nesting site in a remote high mountain region to inform designation of an Antarctic Specially Protected Area

Despite the sensitivity of ecosystems in extreme conditions, only 0.029% of the Antarctic continent is currently granted special protection as Antarctic Specially Protected Area (ASPA). Additionally, protected areas are unevenly distributed and unrepresentative of the biodiversity of Antarctica. The Antarctic Treaty Consultative Parties are thus striving to establish a more coherent network of protected areas. In this context, the Otto-von-Gruber-Gebirge was identified as an area highly worthy of protection due to its unique ecosystem including one of the largest snow petrel breeding sites, and relative pristine nature. However, in the process of designation, an update of knowledge, particularly of the population status of snow petrel in the area, was recognized to be needed. This study was aimed at estimating a population census of snow petrel breeding pairs in the Lake Untersee catchment, an important subarea of the potentially protected area. Investigations were severely limited by the remoteness and harsh conditions of the area, enabling only a short fieldwork period with limited resources. Thus, a combination of remote sensing and traditional methods was applied. We conducted a ground survey of a smaller reference area, including locating nest sites and assessing nest site characteristics. Snow petrels usually nest in the cavities of large boulders and we thus classified habitat suitability based on boulder presence. To do so, the study area was remotely surveyed by unpiloted aerial vehicles to gain orthophotomosaics in sufficient resolution to distinguish on-ground conditions for breeding. We then calculated nest site densities for the reference area. We also studied nest site data such as nest cavity depth, orientation, and attendance to gain basic knowledge of the characteristics of the breeding site. Finally, we measured a sample of four live snow petrels to determine which morph was present at the site. We were able to obtain nest site data and to extrapolate it, which produced population numbers of 11,765 breeding pairs for the whole study area. This underpins the size of the breeding site and thereby its importance for the species.

Formation of In‐Cloud Aqueous‐Phase Secondary Organic Matter and Related Characteristic Molecules

AbstractThe formation process of in‐cloud aqueous‐phase secondary organic matter (aqSOM) and its characteristics are unclear. Herein, water‐soluble inorganic ions, oxalate, and water‐soluble organic carbon (WSOC) were determined in cloud water and aerosol (PM2.5) samples simultaneously collected at a remote mountain site in southern China during spring 2018 and winter 2020. The molecular compositions of water‐soluble organic matter (WSOM) in cloud water and aerosols were analyzed by a Fourier transform ion cyclotron resonance mass spectrometer in negative electrospray ionization (ESI‐) mode. The results showed that the mean concentration of WSOC was 6.27–8.54 mg C L−1 in cloud water and 0.60–1.37 μg C m−3 in aerosols. The strong correlation observed between WSOM and aqueous secondary matter (e.g., NO3− and oxalate), the positive matrix factorization results, and the elevated WSOM/K+ ratios observed in cloud water suggested enhanced aqSOM formation in cloud water. According to random forest analysis, the factors related to in‐cloud WSOM variation mainly included secondary ions, K+, cloud water pH, and atmospheric NOx. Additionally, 37 characteristic in‐cloud aqSOM molecules, classified as ‐Ox, ‐NOx, ‐N2Ox, and ‐N1‐2OxS, mainly consisting of dicarboxylic acids, nitrophenols, and dinitrophenols, were identified using linear discriminant analysis effect size (LefSe). The characteristic N‐ and S‐containing molecules in in‐cloud aqSOM with carbon numbers &gt;10 had low or extremely low volatility; therefore, they might contribute to secondary organic aerosol formation after droplet evaporation. The results revealed the modifying effects of in‐cloud processes on aerosol organic composition at the molecular level and could improve our understanding of aerosol–cloud interactions.

Improving Mountain Snowpack Estimation Using Machine Learning With Sentinel‐1, the Airborne Snow Observatory, and University of Arizona Snowpack Data

AbstractAccurate mapping of snow amount in the mountains is critical as mountain snowpacks are water supply for millions of people. Satellite remote sensing has been largely unable to reliably detect the amount of snowpack in these areas. Recently, C‐band Synthetic Aperture Radar (SAR) data from the Sentinel‐1 (S1) satellites have shown potential for measuring snow depth in the mountains. However, their spatiotemporal coverage is incomplete, and their evaluation with robust, aerial snow depth data is limited. Here, we evaluate two S1 snowpack datasets with some of the best available gridded snowpack data over the Colorado Rockies and Sierra Nevada mountains in the western US: the Airborne Snow Observatory (ASO) and the University of Arizona (UA) snowpack datasets. Compared to ASO and UA data, the S1 data are biased high when snow is shallow, and biased low when snow is deep (particularly later in spring when there is wet snow), though these biases are reduced for deep snow areas when wet snow pixels are removed. We then apply corrections based on machine learning that account for physiographic characteristics to improve the accuracy of the S1 data. Furthermore, we fill gaps in the S1 data by using snow persistence, but also account for potential snow accumulation and ablation, to generate temporally complete snow depth maps over mountainous areas. Corrected and gap‐filled S1 snow depth mapping could be especially important for snow monitoring in remote mountain areas where other techniques for snow mapping do not work or are logistically infeasible or cost‐prohibitive.

How does climate change impact remote mountain communities? An empirical investigation in Gilgit-Baltistan

How does climate change impact remote mountain communities? An empirical investigation in Gilgit-Baltistan

Higher absorption enhancement of black carbon in summer shown by 2-year measurements at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Abstract. Black-carbon-containing particles strongly absorb light, causing substantial radiative heating of the atmosphere. The climate-relevant properties of black carbon (BC) are poorly constrained in high-altitude mountain regions, where many complex interactions between BC, radiation, clouds and snow have important climate implications. This study presents 2-year measurements of BC microphysical and optical properties at the Pic du Midi (PDM) research station, a high-altitude observatory located at 2877 m above sea level in the French Pyrenees. Among the long-term monitoring sites in the world, PDM is subject to limited influence from the planetary boundary layer (PBL), making it a suitable site for characterizing the BC in the free troposphere (FT). The classification of the dominant aerosol type using aerosol spectral optical properties indicates that BC is the predominant aerosol absorption component at PDM and controls the variation in single-scattering albedo (SSA) throughout the 2 years. Single-particle soot photometer (SP2) measurements of refractory BC (rBC) show a mean mass concentration (MrBC) of 35 ng m−3 and a relatively constant rBC core mass-equivalent diameter of about 180 nm, which are typical values for remote mountain sites. Combining the MrBC with in situ absorption measurements, a rBC mass absorption cross-section (MACrBC) of 9.2 ± 3.7 m2 g−1 at λ=880 nm has been obtained, which corresponds to an absorption enhancement (Eabs) of ∼2.2 compared to that of bare rBC particles with equal rBC core size distribution. A significant reduction in the ΔMrBC/ΔCO ratio when precipitation occurred along the air mass transport suggests wet removal of rBC. However we found that the wet removal process did not affect the rBC size, resulting in unchanged Eabs. We observed a large seasonal contrast in rBC properties with higher MrBC and Eabs in summer than in winter. In winter a high diurnal variability in MrBC (Eabs) with higher (lower) values in the middle of the day was linked to the injection of rBC originating from the PBL. On the contrary, in summer, MrBC showed no diurnal variation despite more frequent PBL conditions, implying that MrBC fluctuations are rather dominated by regional and long-range transport in the FT. Combining the ΔMrBC/ΔCO ratio with air mass transport analysis, we observed additional sources from biomass burning in summer leading to an increase in MrBC and Eabs. The diurnal pattern of Eabs in summer was opposite to that observed in winter with maximum values of ∼2.9 observed at midday. We suggest that this daily variation may result from a photochemical process driving the rBC mixing state rather than a change in BC emission sources. Such direct 2-year observations of BC properties provide quantitative constraints for both regional and global climate models and have the potential to close the gap between model-predicted and observed effects of BC on the regional radiation budget and climate. The results demonstrate the complex influence of BC emission sources, transport pathways, atmospheric dynamics and chemical reactivity in driving the light absorption of BC.

Watershed, lake, and food web factors influence diazotrophic cyanobacteria in mountain lakes

AbstractCyanobacterial blooms can occur in freshwater ecosystems largely isolated from development and not experiencing extensive cultural eutrophication. For example, remote mountain lakes can experience intense blooms of diazotrophic (nitrogen‐fixing) cyanobacteria caused by factors acting at different spatial and temporal scales. In this study, we examined how cross‐scale interactions among watershed, lake, and food web characteristics influence diazotrophic cyanobacteria biovolume in mountain lakes. We quantified diazotrophic cyanobacteria biovolume, zooplankton abundance, and physico‐chemical variables for 29 lakes in the Cascade Mountains of Oregon, USA, in summer 2019. Watershed characteristics were compiled from historical datasets available for the region. Diazotrophic cyanobacteria biovolume ranged across the lakes from 0 to 1,930,000 μm3 mL−1; Dolichospermum was the most common genus. Random forest models showed that 11 watershed, lake, and food web characteristics explained 76% of the variance in diazotrophic cyanobacteria biovolume among the sampled lakes. Structural equation models suggested that the drainage ratio (i.e., the relative area of the lake to the watershed) was positively related to phosphorus concentrations and, in turn, to diazotroph biovolume. Among lakes, hypolimnetic dissolved oxygen was negatively correlated with diazotroph biovolume, possibly due to the release of nutrients, like phosphate and iron, bound to sediments. In addition, zooplankton grazers were negatively related to diazotrophic cyanobacteria biovolume, potentially reflecting the influence of stocked fish. Thus, lake management must account for bottom‐up factors, such as nutrient loading, which is influenced by lake morphometry and watershed size, as well as top‐down factors, such as fish stocking, to effectively mitigate diazotrophic cyanobacterial blooms.