Organic matter sources and distribution along land-use gradient in a Himalayan foothills River: Insights from molecular markers.

The analysis of hydrocarbon biomarkers in surface sediments along the Markanda River in the foothills of the Indian Himalayas was conducted to gain insights into the distribution and composition of organic matter (OM) within the sediments. This investigation is essential for comprehending how anthropogenic changes are influencing the OM dynamics in river systems. The study involved identification and quantification of various compound groups such as n-alkanes, hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), linear alkyl benzenes (LABs) and phthalate esters along with their respective parametric ratios. The variation in distribution of n-alkanes and associated indices (odd-even carbon number predominance (OEP), average chain length (ACL), terrigenous to aquatic ratio (TAR), carbon preference index (CPI), and natural n-alkanes ratio (NAR)) were used to distinguish the natural source of organic content from those influenced by anthropogenic contamination. The detection of petroleum contamination was indicated by the presence of prominent unresolved complex mixtures (UCM) as well as specific petroleum biomarkers such as hopanes, diasteranes, and steranes. The study revealed varying concentrations of the analyzed organic pollutants, with the average of PAHs at 24.6 ng/g dw, LABs at 18.1 ng/g dw, and phthalates at 8.3 µg/g dw. The variability in concentration of the investigated compound groups across different locations indicated spatial heterogeneity, and the land use patterns appears to modulate the sources of OM in surface sediments. The source contribution of PAHs and phthalates determined by positive matrix factorization (PMF) shows the predominant sources of the anthropogenic hydrocarbons were linked primarily to petroleum/petroleum-derived products emissions, industrial discharges, cultural practices and common household waste/sewage disposal. This analysis provides insights for developing mitigation strategies and informing relevant policy changes globally, thereby contributing to the broader understanding of anthropogenic impacts on water ecosystems.

Occurrence, distribution and sources of phthalates and petroleum hydrocarbons in tropical estuarine sediments (Mandovi and Ashtamudi) of western Peninsular India.

The present study provides baseline information on the concentration levels, distribution characteristics and pollution sources of environmental contaminants, such as phthalic acid esters (PAEs or phthalates) and petroleum hydrocarbons in surface sediments of the tropical estuaries (Mandovi and Ashtamudi) from western Peninsular India. Total PAEs (∑5PAEs), hopanes, steranes and diasteranes concentrations from Ashtamudi estuary ranged from 7.77 to 1478.2 ng/g, n.d.-363.2 ng/g, n.d.-121.5 ng/g and n.d.-116.6 ng/g, respectively. Likewise, PAEs (∑6PAEs), steranes and diasteranes concentrations from Mandovi estuary ranged from 60.1 to 271.9 ng/g, 2.33-40.1 ng/g and 2.28-23.0 ng/g, respectively. The PAEs comprising di-isobutyl phthalate (DIBP), dibutyl phthalate (DBP), an isomer peak for DBP, di(2-ethylhexyl) phthalate (DEHP), di-isononyl phthalate were dominant in Ashtamudi estuary sediments, while PAEs including diethyl phthalate, DIBP, DBP and its isomer, DEHP, di(2-ethylhexyl) terephthalate were detected in the Mandovi sediment samples. The results of this study show an insignificant correlation of TOC with PAEs, and indicates that the varying spatial distributions of the PAEs in both the estuaries can be the result of discharge sources. The higher concentration of PAE congeners was noticed in Ashtamudi, a Ramsar wetland site, that can be attributed to land-based plastic waste. The petroleum biomarkers were abundantly present in Mandovi estuary due to anthropogenic activities such as boating and spillage from oil tankers. The findings of the present study will serve as a reference point for future investigation of organic contaminants in Indian estuaries, and calls for attention towards implementing effective measures in controlling the pervasion of the PAEs and petroleum biomarkers.

Apportioning sedimentary organic matter sources and its degradation state: Inferences based on aliphatic hydrocarbons, amino acids and δ15N.

The sources and state of sedimentary organic matter (SOM) in fresh water aquatic systems are important to understand the carbon cycling in terrestrial environments. The composition of organic matter in the lake sediments demonstrates the physical and chemical condition of the lake ecosystems. However, the systematic and structured investigations focussed on to understand the source and fate of organic matters within eutrophic lakes is still far from clear. The present study is focusing on the implications of amino acids (AA), aliphatic hydrocarbons and bulk geochemical (C/N, δ15N) proxies to understand the distribution, sources and state of sedimentary organic matter in Ahansar Lake from Kashmir valley, India. The relatively low C/N ratios along with high AA contents indicate enhanced aquatic productivity in the lake system. Likewise, the dominance of the mid-chain monomethyl alkanes (MMAs), highly branched isoprenoids (HBIs), botryococcenes, steroids and triterpenoids suggest OM sourced from periphyton remains. Furthermore, the presence of C27, C28 and C29 diagenetically altered steroids also reflects a major algal contribution. The spatial variability of Paq demonstrates their applicability as a proxy for the contribution of aquatic vegetation. The ratio of individual amino acids (oxic/anoxic ratio) and low Pr/Ph (pristane/phytane) values indicate anoxic nature of the current depositional environment. This also leads to significant organic matter preservation as revealed by amino acid indices (e.g., degradation index - DI and reactivity index - RI). These data collectively demonstrate the systematic investigation and comprehensive understanding of source of sedimentary organic matters and respective depositional condition via multiple indicators. Overall, understanding the OM molecular composition and its spatial heterogeneity in a lake system is important to better constrain the fate of organic carbon, and assess the pollution risks as well as adopt relevant management strategies.

Microplastics and heavy metal contamination along a land-use gradient in a Himalayan foothill river: Prevalence and controlling factors.

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.

Atmospheric deposition of microplastics in an urban conglomerate near to the foothills of Indian Himalayas: investigating the quantity, chemical character, possible sources and transport mechanisms.

The global apprehension regarding the ubiquitous presence of microplastics (MPs)and their associated health risks underscore a significant challenge. However, our understanding on the occurrence and characteristics of this emerging class of pollutants in the different environmental compartments remains limited. For instance, despite housing approximately 20-25% of the global population, the evidence of the atmospheric MPs in Indian Subcontinent is exceedingly rare. Hence, we for the first-time present data on the depositional flux, chemical composition, morphological features of the atmospheric MPs collected from the foothills of Indian Himalayas. The total number of MPs for the collected samples ranged from 65 to 752 particles, with an average of 317±171 particles count. The average flux of atmospheric MPs was 2256±1221 particles/m2/day and varied significantly from 462 particles/m2/day to 5346 particles/m2/day. The highest deposition (5346 particles/m2/day) of atmospheric MPs was recorded during the 3rd week of sampling, coinciding with the Diwali festival. Based on the visual characteristics, we determined that the size of MPs ranged from 67-2320 µm, with a predominant presence of smaller particles (<1200 µm), primarily composed of fragments and films/sheets. Raman spectroscopy indicated that the analyzed MPs were mainly composed of 4 different polymer types, including PE (46.8±7.2 %), PP (20.9±7.4 %), PS (15.6±3.8 %) and PET (16.7±9.9 %). We further highlighted the extent to which climate variables control the deposition of atmospheric MPs in this urban conglomerate located in the foothills of Himalayas. Our Lagrangian parcel tracking approach showed that the greater frequencies are of local origin and clustered near to the studied region. We also speculate that atmospheric microplastics can be transported along the westerly winds. Though we did not observe any significant relation (p>0.05, n=16) between meteorological parameters and the quantity of atmospheric MPs.

Occurrence, distribution and sources of petroleum contamination in reef-associated sediments of the Gulf of Mannar, India.

The distribution of saturated hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) was assessed in superficial sediment samples collected from Mandapam island groups, Gulf of Mannar, India. The hydrocarbon distribution pattern and the n-alkane indices (e.g., carbon preference index (CPI) and natural n-alkanes ratio (NAR)) were deployed to differentiate between the biogenic and anthropogenic sources. Petroleum pollution was indicated by the pristane/phytane ratio close to 1. Presence of a prominent unresolved complex mixture (UCM) as well as hopane concentrations further supported this assertion. The evaluation of petrogenic sources of contamination were also comprehended by various diagnostic ratios of PAHs. The sites associated with shipping activities, tourism, and located near the mainland and accessible portions of the islands exhibited high petroleum contamination. Correlation analysis underlines the significance of combining petroleum-specific marker compounds and diagnostic ratios to improve the assessment of human influence on marine ecosystems.

Spatial distribution and characteristics of microplastics and associated contaminants from mid-altitude lake in NW Himalaya.

Despite the worldwide concern over the impact of microplastics (MPs) and associated organic contaminants, the information regarding the occurrence and characteristics of these emerging class of pollutants is limited in freshwater environment. We present data on the distribution and concentration levels of MPs and phthalate esters (PAEs) from Rewalsar Lake, a shallow eutrophic lake in Northwest Himalaya. The MPs were identified in all samples, with concentration of 13-238 particles L-1 and 750 to 3020 particles kg-1 dry weight (dw) in surface water and sediments respectively. Majority of MPs were dominated by polystyrene, polyethylene, polypropylene polymers that principally occurred in the form of pellets and fragments. The MPs distribution was different among sampling sites, being more abundant to sites in the proximity of domestic sewage effluents and high level of religious and tourist activities. The di-isobutyl phthalate, dibutyl phthalate (DBP) and its branched isomer, di(2-ethylhexyl) phthalate (DEHP) are the identified PAE congeners in sediments, and the measured total concentrations of Σ3PAE ranged from 1.69 µg/g to 4.03 µg/g dw. Notably, concentration values of DEHP were higher as compared to other detected phthalates, and exceeded recommended environmental risk limit. The findings of this study emphasize the requirement for proper waste management measures in the region to reduce entry of these pollutants into the ecosystem. Further, this work contributes to the understanding of MPs and PAEs potential contamination profiles and sources in freshwater environments, and provides valuable information for future management decisions.

Investigating the impact of climate change on the lake ecosystem during the late Holocene using a sedimentary record from the southern Arabian Desert, Yemen.

Lake systems respond physically, chemically, and biologically to hydro-climatic change and variability, and these responses are documented in the sediments. Individual proxies and lacustrine environments may respond to climate variations in a nonlinear way, making it difficult to determine the direction and extent of a climatic shift. Here we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution from paleolake 'Gayal el Bazal (Yemen)'. A previous study from this site has provided a continuous, and high-resolution dataset providing an understanding of precipitation during the last ca 1200 years, particularly during Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). However, the response of the lake ecosystem to these changing hydro-climate conditions, including water-level, salinity, and productivity, remains unknown. The n-alkanes dataset shows that during pluvial interval such as the MCA, the lake experienced an increase in nutrient input resulting in enhanced aquatic productivity. Concurrently, ostracods assemblage displays an increased abundance of swimmer species (like Bradleytriebella lineata and Fabaeomiscandona cf. breuili), suggesting an indirect response between ostracods and climate shifts. The chironomid community during the MCA interval is dominated by taxa belonging to the subfamilies of Chironomini, suggesting a warm, shallow, productive environment with macrophyte vegetation. The LIA interval is marked by increased abundance of higher-chain length n-alkanes, suggesting increased contribution from higher plants. Furthermore, ostracod distribution revealed increased abundance of non-swimmer species like Vestalenula cylindrica., which thrive under saline conditions in the lake. Changes in abundances of Tanytarsini during the LIA interval, which are associated with higher oxygen levels, suggest changes in lake productivity. As a result, the overall patterns in biological indicators reveal that their individual abundance and species/tribe distribution fluctuates in response to changes in the climate and hydrological conditions.

Distribution and characteristics of microplastics and phthalate esters from a freshwater lake system in Lesser Himalayas.

The occurrence, distribution, characterization and quantification of microplastics (MPs) and phthalic acid esters (PAEs) from the freshwater aquatic environment are not thoroughly explored in the Indian Himalayas despite concern over their adverse effects on human health and ecosystem. In this study, we have investigated the presence of MPs and PAEs in an aquatic system from Indian subcontinent. The MPs were detected in all water and sediment samples with abundances ranging from 02-64 particles/L and 15-632 particles/kg dw, respectively. The abundance of MPs, dominated by polyethylene and polystyrene, with the majority being fibres and fragments indicated that they were derived from plastic paints, boats or synthetic products. The concentrations of PAEs in the surface sediment samples varied from 06-357 ng/g dw. The most abundant PAEs in the sediments were dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP), since they were present in all the samples collected from the lake basin. The relatively higher abundances of MPs and higher concentrations of PAEs were generally found in the vicinity of areas impacted by anthropogenic activities. A clear correlation between the abundance of microplastics and PAEs concentration was observed suggesting that they are closely attributed to a single source. This study also provides an alternative approach to utilize the chemical additives in plastics as markers to trace the presence and distribution of MPs in the aquatic environment.