Glacial lakes appear remarkably gorgeous, with their clear, blue water. Glacial lakes, formed from the meltwater of retreating glaciers, are critical features of high-altitude mountain landscapes. These lakes are rapidly expanding due to climate change, increasing the risk of glacial lake outburst flood events that threaten downstream communities and ecosystems. Beyond their immediate hydrological significance, glacial lakes act as natural archives, preserving evidence of past environmental variability. The sediments within these lakes hold valuable records of glacial dynamics, offering crucial insights into Earth’s climatic history while also serving as vital freshwater reservoirs in fragile mountain regions.

The aquatic ecosystems of Ladakh are characterized by cold-arid climatic conditions and persistent nutrient limitation, resulting in low primary productivity and constrained ecosystem functioning. This study aims to evaluate ecosystem productivity and nutrient availability within this fragile high-altitude landscape. To achieve this, sediments from the sediment–water interface of Tsoltak glacial lake and its associated microhabitats was analyzed for biological proxies (diatoms, desmids, and pollen/spores), electrical conductivity (EC), and stable carbon (δ13C) and nitrogen (δ15N) isotopes. These aquatic systems are primarily fed by glacial meltwater and winter snow cover regulates ice-free duration, nutrient availability, and algal biomass, maintaining predominantly oligotrophic conditions. However, recent observations suggest a shift towards meso-oligotrophic conditions under prolonged summer seasons, reflected by moderate primary productivity dominated by diatom taxa such as Didymosphenia, Cymbella, Diatoma, and Pinnularia, and desmids including Cosmarium, Staurastrum dilatatum, and S. punctulatum. The pollen assemblage is dominated by Artemisia-Tanecetum-Apiaceae-Ephedra assemblage indicating desert steppe vegetation influenced by moist summers. The δ13C values of the sediment samples indicate a dominance of C3 and CAM vegetation, along with lower δ15N, indicating atmospheric nitrogen fixation in sediments. Overall, the integration of biological assemblages with EC and stable isotope proxies provides insights into primary productivity patterns and nutrient cycling processes within this Trans-Himalayan glacial lake ecosystem.

This article introduces the exciting world of environmental DNA (eDNA) metabarcoding, a cutting-edge tool for studying biodiversity without even seeing the organisms. It explains how tiny traces of DNA left behind by animals, plants, or microbes in water, soil, or air can be collected and used to identify what species are or were present in that environment. The process is broken down step-by-step: from collecting and properly preserving the samples to amplifying the DNA and sequencing it. The article highlights why sample quality is crucial and explains how common mistakes, such as missing PCR controls or failing to account for inhibitors, can compromise results. It also discusses how long eDNA persists in the environment and the factors that cause it to break down. Despite some challenges, such as incomplete reference databases, eDNA is already being used to estimate which species are present, how abundant they are, and even to reconstruct past ecosystems. By combining eDNA methods with high-tech sequencing and powerful computer tools, scientists are now able to monitor biodiversity more effectively and often more easily than with traditional methods. It is a fast-growing field that is opening up new possibilities in ecology, conservation, and even in archaeology.

Among Gomphonema species, those with broad axial areas are found predominately in tropical and subtropical habitats. However, taxonomic clarity within this group has historically been elusive, leading to misinterpretations and wrong proposals of synonymies. Recent research has introduced many new species with broad axial areas, shedding light on their distribution patterns, and biogeographical analyses have further elucidated geographic ranges, revealing both regional endemism and cosmopolitan distributions of some of the species of Gomphonema in this group, especially across Asia and Africa. In this study, a new freshwater Gomphonema species with a broad axial area, Gomphonema sangamii sp. nov., is described from an epilithic sample at the Muvattupuzha River, situated in the Southern Western Ghats of Kerala, India. The present study describes the new species based on light and scanning electron microscopy. Features that distinguish this new species from others in the genus include valve shape, striae, areolae, and raphe structures. Description of the new species from this region will increase the biodiversity value of Western Ghats. We also discuss the distribution of Gomphonema species with broad axial areas.

Habitat complexity is widely recognised as a fundamental driver of biodiversity patterns in aquatic ecosystems; yet, its role in structuring diatom assemblages across different substrate types remains poorly understood in tropical systems. We tested whether differences in substrate complexity between epilithic (rock) and epiphytic (macrophyte) habitats structure benthic diatom communities in Western Ghats montane streams. Paired samples from 40 sites revealed that both substrates supported comparable diversity levels with high species overlap and similar rank abundance patterns. In line with the initial hypothesis, a statistically significant but ecologically negligible substrate effect was detected, with only two habitat-specific indicator taxa identified at p < 0.05 within the total assemblage. Environmental gradients, rather than substrate-associated habitat complexity, primarily structured community composition. These results indicate comparable assemblage patterns between epilithic and epiphytic substrates under the sampled conditions, with environmental gradients accounting for proportionally more community variance than substrate identity (13.2

Natural and anthropogenic changes can alter the surface water quality, and diatoms can be used to assess or track these alterations with effective biomonitoring. This requires consistent and reliable identification. The diatom flora in the present study is intended to serve as an image voucher of epilithic diatom taxa from the Mula-Mutha River Basin, a tropical river system located in the Western Ghats of India. These samples were collected seasonally from 19 stations during 2022 and 2023. 170 diatom taxa were documented and identified in this study. The morphological range of each taxon was imaged. Nitzschia (24), Navicula (20), and Gomphonema (17) commonly occurred across sites in the river basin. Approximately 4.11% (7 taxa) of the documented diatoms are potentially novel and have been provisionally numbered. There is a distinct and significant seasonal trend with seven taxa indicative of pre-monsoon conditions, eight taxa associated with monsoon flows, and a single post-monsoon indicator. To our knowledge, there are no previous studies that have comprehensively documented diatom diversity across the entire river basin. This study will serve as a reliable diatom identification resource and contribute towards improving taxonomic consistency and enabling comparisons for future monitoring efforts.

A detailed reconstruction of Late-Holocene environmental and climatic dynamics has been achieved through systematic investigations conducted at Bandhavgarh National Park and Tiger Reserve in the Umaria district of Madhya Pradesh, Central India. Proxies such as mineral magnetism, textural analysis, carbon/nitrogen ratios, diatoms and pollen have been utilized in this research to elucidate the profound influence of climate on the region's history and cultural evolution over the past 2600 years (525 BCE to present). The diverse landscapes of the area have experienced significant climatic shifts, shaping its architectural and societal developments. The archeological record reveals a progression from prehistoric activity to the construction and habitation of 90 artificial caves, followed by the creation of early medieval temples and large-scale sculptures, culminating in further architectural consolidation during the medieval period which has a distinct record in the sediment characteristic and ecology of the wetland. This evolution reflects the region's dynamic interaction with its environment, shaped by alternating wet periods and environmental stress episodes. These changes are vividly captured in the five climatic zones identified in the sediment core from Bandhavgarh, underscoring the intricate relationship between human societies and climatic patterns over millennia.

Indoplatessa, a new monoraphid diatom genus, is described based on a detailed morphological investigation using light and scanning electron microscopy analysis. The type species for this genus was previously described as Platessa arborea Radhakrishnan, Sherly & Karthick from tree bark moss habitat from Eastern Himalayas, India. This species differs from all other monoraphid genera by predominantly uniseriate striae on both valves, central raphe endings that are located in a rounded depression externally and distinctly hooked internally, slit-like areolae and internally thickened interstriae. The morphological resemblance was assessed in relation to all other Platessa species and compared with other monoraphid genera.

We present a new version of a barcoding reference library dedicated to diatoms, Diat.barcode v12, with newly published sequences, annotated with ecological, and biological traits (size class, life forms, ecological guilds, etc) and curated by a college of experts. Diat.barcode incorporates rbcL data on all diatoms, though freshwater taxa are better represented. We used this library in two different areas, one where the taxonomic coverage of the library was good (mainland France) and another where it was poor (French Guyana) with about 320 diatom samples collected for river monitoring across both regions. We show that a direct bioinformatic assignment of environmental sequences to traits (ecological guilds, habitats, morphology) has great potential in French Guyana where species knowledge is poor and therefore the proportion of assigned environmental sequences is much lower (12.8%) than trait assignation (30%). We used co-correspondence analyses to show that, unlike mainland France where all species and trait assignation datasets were significantly correlated, in French Guyana only 7 out of 13 trait categories showed a significant correlation. This indicates a significant loss of ecological information through species assignment in French Guyana. Consequently, directly assigning environmental sequences to traits can be useful and provide more ecological information in regions with poor taxonomic knowledge because of the many rbcL sequences without taxonomic assignations.

Microplastic (MP) pollution is a growing public health concern, yet its presence in groundwater, a critical potable water source, remains underexplored. This study investigates MPs in groundwater from open and closed well systems, as well as in sediment samples, in the semi-arid region of Didwana-Kuchaman, Rajasthan, Northwest India. The MPs, identified using a fluorescence microscope, were ubiquitous at all sampling sites, with groundwater concentrations ranging from 3 to 122 particles/L (average = 35.46 particles/L) and sediment abundance ranging from 170 to 1140 particles/kg (average = 505.52 particles/kg). Morphologically, beads/pellets within the 20-200 mu m size range dominated the MP samples, while polyethylene and polystyrene were identified as the dominant polymer types. A significant positive correlation (r = 0.65) between MP concentration in the sediment and open-well samples was noted, with the highest values observed near landfills and agricultural areas. Heavy metals (HMs) concentrations (ppb) in groundwater samples were ranked in the following order: As (396.11) > Mn (280.18) > Zn (184.67) > Co (71.8) > Ni (60.56) > Pb (24.24) > Cr (1.26). The hazard quotient derived for both children and adults indicates As > Mn > Pb > Co, significantly above the acceptable threshold (HQ > 1), suggesting a considerable contamination risk. Although no significant correlation was observed between MPs and HMs in the water samples, SEM-EDX analysis revealed the adherence of HMs, including Ni, As, Co, Cr, Zn, Mn, and Pb, to MP surfaces, suggesting potential interactions and co-transport mechanisms. The results underscore the concerning co-occurrence of MPs and HMs in groundwater, raising alarming concerns about potential synergistic health effects. This study highlights the urgent need for comprehensive risk assessments and mitigation strategies addressing MP and HM contamination in critical groundwater resources.

Diatoms are ubiquitous unicellular microalgae that play a crucial role in ecosystems and serve as bioindicators for monitoring environmental conditions in aquatic and terrestrial habitats. While extensive research has been conducted on marine and freshwater diatoms, studies on soil diatoms remain limited. Numerous studies have concentrated on the indicator properties of diatoms in soil without adequately understanding their ecological roles. Understanding soil diatom assemblages and their diversity across different geographical regions is essential for improving their application in environmental studies. This review examines the current state of soil diatom research globally, analyzing 122 studies from Google Scholar. It explores key aspects, including the historical development of soil diatom research, taxonomic advancements, ecological interactions, and their application in environmental monitoring. Despite their ecological significance, soil diatoms are influenced by natural and anthropogenic factors, impacting soil quality. Human activities in forests and agricultural lands have contributed to pollution, underscoring the need for soil diatom-based indices to assess soil health. However, existing assessments primarily rely on aquatic indices, such as the Specific Pollution Sensitivity Index, highlighting the necessity for soil-specific pollution indices. By synthesizing current knowledge, this review emphasizes the importance of soil diatoms in ecological studies and environmental assessments. Future research should focus on their ecological functions and develop targeted soil diatom-based monitoring tools to enhance soil management, environmental monitoring, and pollution assessment strategies.

Microplastic (MP) contamination in freshwater systems is a prevalent and persistent environmental issue, yet their occurrence and distribution remain poorly constrained. The present study examines the MPs abundance in sediment and water samples and factors controlling their distribution in the Manasbal Lake, north-western (NW) Himalaya. Additionally, the study investigates the relationship between heavy metals and the distribution of MPs in sediment, as well as their potential interactions. The MPs counts in lake surface sediment and water samples varied from 840 nkg−1 to 4020 nkg−1 and 13 nL−1 to 89 nL−1, respectively. The MPs distribution in Manasbal Lake exhibited spatial heterogeneity, with the greatest abundance observed in the eastern and northeastern areas near lake inlets. Grain size and land use appear to collectively modulate the variability of MPs in Manasbal Lake sediments. Five main MPs types were identified: beads/pellets, fragments, fibres, foams, and films, with beads being the predominant type. Polypropylene, polyethylene, and polystyrene are the dominant constituents of the observed MPs, with domestic sewage suggested as the predominant source for their abundance in the lake. Furthermore, the contamination factor for heavy metals indicated a high level of lead contamination in surface sediments, while copper and cobalt showed moderate contamination near the lake inlet. The SEM-EDS analysis illustrated the presence of toxic elements such as Hg, Zn, Pb, Cr, Cd, Ni, and Cu to the surface of MPs. This study expands the baseline characterization of MPs in freshwater systems and enhances our understanding of the potential sources and factors influencing MP distribution.

Diatoms are commonly employed in aquatic environments to evaluate habitat quality based on their sensitivity to local and regional factors. Limited knowledge exists regarding the significance of these factors in shaping the distribution of pseudoaerial diatoms. The present study analyses the impact of local and regional factors on the composition of pseudoaerial diatom communities in the Eastern Himalayas. The primary objective of this study is to examine the relationship between pseudoaerial diatom communities and water chemistry. We chose 53 samples out of 191 and identified 341 species from 59 genera. The dominant species across the sampling sites were Achnanthidium minutissimum, Adlafia sinensis, Achnanthidium subhudsonis and Humidophila delognei. The water chemistry in the northern part of the Brahmaputra River exhibits environmental characteristics similar to those of the southern region, though with a slightly broader range of variation. The northern region is mainly affected by altitude, whereas the south region is influenced by electrical conductivity and phosphate levels. Electrical conductivity correlates strongly with species diversity compared to other environmental characteristics. Regarding the ecological association with diatoms, the CCA analysis demonstrated that human activities influence the presence of pollution-tolerant species. The dissimilarity among communities was predominantly noticed with environmental and altitudinal distances except geographical distance. This research offers preliminary information on the composition of pseudoaerial diatom communities in the Northeast region. This enables us to identify this region’s indicator species and endemic species. Ultimately, it will facilitate the development of metrics using these species to estimate the ecological condition of this region.

The newly identified diatom species, Climaconeis heteropolaris sp. nov., stands out due to its distinctive heteropolar valve shape. The valve structure is lanceolate-clavate with rounded capitate apices. The middle of the valve is slightly wider but gradually tapers towards the ends. Its size ranges from 76.5 to 120.5 mu m in length and 9.5-14.5 mu m in width. The striae radiate outward near the centre, align parallelly in the middle section and converge near the tips, with 17-22 per 10 mu m. A rectangular stauros intersects the valve, flanked by short striae. The areolae vary in shape, ranging from round to more elongated forms. A narrow, linear axial area runs through the valve, bordered by longitudinal ribs that meet linear helictoglossae near the ends. The raphe is straight and forms a 'tuning fork' shape at the centre. Scanning electron microscopy reveals a generally flat valve with a slightly curved mantle. The striae near the raphe have a parallel orientation but radiate outward as they extend from the centre. The shapes of the areolae also vary depending on their position on the valve. Internally, the raphe is flanked by longitudinal ribs, while a raised stauros occupies the central area. At the raphe's tips, a 'porte-crayon'-like feature marks the distal terminations. When compared to other members of the Climaconeis genus, C. heteropolaris is distinguished by its unique valve shape and stria patterns. This feature differentiates it from relatives like C. colemaniae, C. undulata, C. stromatolitis, C. mabikii, C. scalaris and C. scopulorioides. Differences in valve shape and stria arrangement confirm its placement within Climaconeis while also hinting at possible affinities with Stauroneis and Frustulia.

Diatom taxonomy has undergone significant revisions, particularly within the order Cymbellales, where species boundaries remain challenging due to transitional morphological characters and emerging new insights from molecular data. In this study, Encyonema meghamalaiense sp. nov. is described from the Meghamalai Hills, Western Ghats, Tamil Nadu, India. This species is characterised by its asymmetric, lanceolate valves with subcapitate apices. The striation is irregular, becoming uniseriate to biseriate near the apices. While it shares similarities with Encyonema keshrii in the areolae pattern, it differs in valve outline and raphe structure, highlighting its taxonomic distinction. Given the taxonomic complexity of the Encyonema- Encyonopsis-Kurtkrammeria complex, detailed comparative morphological assessments were conducted to clarify its classification using a light and scanning electron microscope. These findings contribute to the growing understanding of species diversity within Encyonemataceae and underscore the need for further integrative taxonomic studies to resolve complex species boundaries in this group, especially from the tropics.

The co-occurrence of microplastics (MPs) and heavy metals in aquatic systems has raised significant concerns, yet their relationship in freshwater ecosystems remains poorly understood. This study aims to evaluate the prevalence of MPs and factors controlling their distribution in both water and sediment in the Markanda River, Northwest India. MPs were extracted from sediment and water samples using density separation and classified through fluorescence microscopy and Raman spectroscopy. Metal concentrations in river water samples were analyzed using ICP-MS, and their correlation with MP abundance was explored. The results indicated the widespread occurrence of MP pollution across the Markanda River basin, with particle concentrations ranging from 10 to 530 particles L-1 in surface water and 1330-4330 particles kg-1 dry weight (dw) in sediment samples. The variability in MP abundance at sampling sites along the Markanda River courses results from factors such as the proximity of industrial establishments and human habitation, while the influence of grain size on MP distribution appears to be limited. Pellets (88.5 %) and fragments (8.5 %) were the most abundant types of MPs, with polyethylene (45.45 %) and polystyrene (30.9 %) being the dominant forms in water samples. The ICP-MS analysis of heavy metals in water samples indicated elevated levels of As (1.67 to 32.31 ppb) in downstream areas of the river system, influenced by human activities. While metals exhibited correlation with each other, there was a weak association, except for As, with the levels of MPs in the Markanda River. The SEM-EDX analyses to characterize chemical elements absorbed onto the surface of MP showed distinct variations in upstream and downstream sites, with the presence of elements such as Mn, Ni, Cr, Zn, As, Se, and Cu found in downstream areas. We conclude that MPs contaminated with heavy metals potentially threaten the ecological security of freshwater aquatic systems and highlight the importance of management action to reduce plastic pollution worldwide.

Diatom analysis, despite its existence in archaeological science for over seven decades, remains an underutilized technique. While diatoms are often employed in site-based palaeoenvironmental reconstructions, their application in pottery sourcing and typology is relatively limited. This study focuses on diatom analysis of pottery sherds collected from six Iron Age sites in the lower tron Microscopy was utilized to examine the diatoms in 78 samples from 26 pottery sherds across these sites. The analysis revealed the presence of aquatic diatoms, predominantly from freshwater environments, along with desiccation-tolerant taxa belonging to the genera nella. Notably, the dominant genera were Nitzschia (70.73%), Hantzschia (21.95%) and Luticola (4.87%). These findings confirm the presence of a lacustrine environment with mesotrophic to eutrophic conditions and suggest that the clay used in pottery originated from a freshwater source. Moreover, this study highlights the potential of diatom analysis in reconstructing local environments and shedding light on the palaeoenvironmental conditions underlying archaeological sediment deposition in a tropical context.

The present communication indicates the timeline-based on accelerator mass spectrometry (AMS) dates - that has emerged from a sediment core originating in the Pradesh, India) and attempts to see if those dates broadly coincide with the changing historical signature as recorded in archaeological evidence in this tract. A comprehensive overview of vegetational and climatic changes in the forested tract of Bandhavgarh across time is under preparation, and the present study aims to report on the first scientific dates from the Bandhavgarh National Park and Tiger Reserve and the rich possibilities that open up when they are juxtaposed with its archaeology.

While conducting a seasonal assessment of the Mula-Mutha River basin in Maharashtra, India, an unknown taxon of the genus Geissleria was observed from an oligotrophic stream connected to the Mutha River. This taxon is described here as new to science based on detailed light and scanning electron microscopic observations. The characteristics of this new species used to assign it to the genus Geissleria include triundulate valve margins, a straight and filiform raphe structure, lineolate striae, and the presence of annuli a circular or semi-circular hyaline area positioned on the valve apices. In G. triundulata sp. nov., the annulus is barely visible in light microscopy. The present study discusses the morphology of this new species compared to other Geissleria species, undertaking a thorough analysis of various morphological features observed in members of the genus Geissleria. This new taxon resembles G. lubilensis and G. fogedii in having a slightly triundulate margin but differs in their broad and protracted valve apices, holding differences from the new species. This study also presents a brief discussion concerning the ecology of the newly discovered species and the worldwide distribution of all Geissleria species.

Diatoms (siliceous microscopic algae) are one of the main biotic elements used in assessing the ecological state of all aquatic environments and play a vital role in understanding the ecological conditions in freshwater and marine environments. Being siliceous diatoms are often well preserved in stratigraphic deposits, where they can offer great potential to trace past environmental conditions. The sensitivity of diatoms to a large variety of environmental variables makes them the most widely used paleoecological proxies, providing many research opportunities in paleo sciences ranging from reconstructing present to past environmental conditions. Considering our limited knowledge of the diatom taxonomy and ecology from the tropics, database, including the list of taxa reported till today, and their ecological preferences are very scarce. The present work reviews studies from tropical Asia focusing on diatom-based paleoecological reconstructions covering climatology, hydrology, and paleo-water quality assessment using the fossil diatom taxa and their ecological indications. Further, this work provides the first comprehensive checklist of the fossil diatoms from tropical fresh and marine water from Asia, comprising 266 species from 64 genera. This list also provides each taxon's spatial and temporal extent for its meaningful application in environmental reconstruction. This taxa list will be a valuable resource for researchers across the tropics for paleoenvironmental reconstruction.