Sarwar Nizam

Coastal mangrove habitats are among the most efficient natural carbon sinks on the planet: their upper soil typically contains about 3–5 times more soil organic carbon than the global average and can sequester carbon at rates 2–4 times greater than tropical terrestrial forests. Nevertheless, degradation and hydrological disruption driven by climate change and anthropogenic perturbations jeopardize these carbon reservoirs, potentially transforming mangroves from net carbon sinks into carbon sources. We hypothesized that restoring hydrological connectivity and vegetation would enhance soil organic carbon accumulation and reactivate blue carbon cycling. To test this, we examined the Sundarbans—the largest contiguous mangrove forest in the world, extending across India and Bangladesh. Three sites under distinct ecosystem conditions in the Indian part of the Sundarbans were selected: a degraded mangrove site—where vegetation loss and hydrological disruption have promoted oxidation and loss of soil organic carbon; a restored mangrove forest maintained by a local NGO; and a mature old-growth mangrove. Soil core samples collected up to 35 cm depth at 3–5 cm intervals were analyzed for total organic carbon (TOC) and nitrogen (N), stable carbon isotopes (δ¹³C), n-alkane biomarkers, and radiocarbon abundance. Soils from the degraded mangrove site contained low TOC, high δ¹³C values, a high ratio of aquatic-to-terrestrial n-alkanes (Paq), and a consistent decrease in terrestrial plant wax n-alkanes (Pwax) with depth, along with variably lower C/N ratios, signifying heterogeneous carbon inputs dominated by aquatic sources. In contrast, soils from the restored mangrove site showed TOC and δ¹³C values comparable to mature systems, higher Pwax, longer n-alkane average chain lengths (ACL), and consistently elevated C/N ratios, indicating stable, plant-dominated carbon inputs under restored vegetation and hydrological connectivity. The relationship between C/N ratios and δ¹³C values further confirmed a shift from aquatic-derived carbon in the degraded site to terrestrial C3 plant carbon in the restored site, with the old-growth mangrove site exhibiting mixed-source signatures. Radiocarbon profiles revealed a gradual decrease with depth, reflecting the aging and stabilization of organic matter. Our results highlight the dual role of mangrove restoration in rapidly rebuilding carbon stocks while enhancing carbon turnover, underscoring its importance for climate mitigation strategies and blue carbon credit frameworks.[Keywords: mangrove restoration, blue carbon, carbon sequestration, n-alkane biomarker, carbon isotopes]

Climate change threatens the Himalayas and the billions of people dependent on its resources and water. Warming temperatures lead to melting glaciers, extended growing seasons, and the degradation of permafrost and peatlands, releasing significant amounts of carbon stored for millennia. This process alters ecosystems and triggers cascading effects on soil and vegetation. How permafrost thaw alters carbon cycling within different landscapes is an open question in many ecosystems. Here, we investigate soil organic carbon dynamics in a permafrost and two wetland sites located at different elevation in the western Himalayas also characterized by cold arid climate, glacial and riverine resources, and geothermal activity in one wetalnd. Gas chambers were deployed to quantify CO2 and CH4 fluxes and revealed that the permafrost (Tsoltak) and wetland sites (Ganglass and Puga) are substantial sources of CH4 during the post monsoon season in 2023. While Ganglass and Puga (water–logged sites at lower elevations) act as CO2 sinks, Tsoltak, a more arid site at higher elevation, predominantly exhibits CO2 emissions indicating different microbial decomposition. High methane fluxes observed at wetter locations exhibited by relatively lower stable carbon isotope ratio (δ¹³C) indicating predominance of hydrogenotrophic methanogenesis. In contrast, relatively lower CH4 fluxes with enriched δ¹³C–CH4 signature at Tsoltak point towards acetoclastic methanogenesis coupled with limited CH4 oxidation. Upscaling the median permafrost carbon flux measurements from our study sites to the estimated permafrost area in the entire western Himalaya suggests a potential annual CO2–equivalent carbon emission of up to 1.2 Tg (1 Tg = 1012 g). The bulk soil organic matter analyzed near each chamber revealed 8.5–9.5 kg C m-2 in permafrost soil, nearly three times the amount observed in marshy grassland. Organic matter source proxies, including bulk soil δ¹³C and biomarker (n–alkanes) characteristics such as average chain length, carbon preference index, odd–over–even preference index, and n–alkane ratio, exhibited consistent signatures across the sites. This indicates similar organic matter sources, primarily C3–type grasses, macrophytes, aquatic plants and possibly microbes. The subsurface soil-respired δ¹³C–CO₂ values were higher compared to bulk organic matter but significantly lower than the local ambient air. The ¹⁴C–CO₂ ages indicated a mixture of modern and ancient carbon sources, suggesting the release of legacy carbon from the permafrost. Our findings offer initial insights into the organic carbon cycling in degrading Himalayan permafrost and peatlands under increasing stress of global warming. This will enhance understanding and predictions of soil carbon dynamics in the warmer and wetter Himalayas projected for the late 21st century.

Groundwater contamination throughout India is a global concern as it feeds more than a billion people. Of all the contaminants, fluoride (F) is one of the most widespread and well documented since its toxic nature pose serious threats to human health. In India, groundwater F concentrations have been extensively studied over the past decades. These studies have generally concluded that the groundwater F concentrations are typically higher than the drinking water standard for human health. Here, we present the occurrence, distribution, and sources of groundwater F in the Kanpur Nagar and Kanpur Dehat districts covering ~ 6000 km² of the area in the central part of the Ganga Basin. The result revealed significant spatial variability in dissolved F concentration ranging between 0.2 and 5.2 mg/L (average 0.9 ± 0.7 mg/L, n = 172, 1 SD), which is beyond the drinking water guideline (0.5–1.5 mg/L) of the Indian Standards. We find that 31% of groundwater sampled have F content below the optimal requirement of 0.5–1.0 mg/L causing dental caries problems. The F levels only exceeded the safe drinking water limit of 1.5 mg/L in 8% of the groundwater sampled mostly in the urban regions. Fluoride distribution shows a closer resemblance with the spatial distribution pattern of electrical conductivity, and total dissolved solids demonstrate that F in the shallow alluvial aquifers is largely derived from geogenic sources. This is further confirmed by a strong positive correlation (r = 0.91, p < 0.05) observed between chloride-normalized concentration of F and the sum of geogenic elements (∑Li, Rb, Sr, Ba). We additionally performed health risk assessments, which revealed that children are most vulnerable to dental caries (commonly known as tooth decay) and dental fluorosis problems. As F concentrations show large spatial variability in the studied aquifer, we suggest that uniform application of a single de-fluoridation and fluoridation technology on an aquifer or sub-aquifer scale without a detailed well-designed groundwater F survey will have an adverse health impact on local residents as optimal level of F in drinking water may not be compromised.

Himalayan glaciers are invariably covered by supra‐glacial debris. Of these glaciers, the Chhota Shigri Glacier (CSG) in the western Himalaya has minimal debris cover (3.4%), yet has a comparable melt rate to other Himalayan glaciers. Utilizing osmium isotopic composition, and major and trace element geochemistry of cryoconite, a dark colored aggregate of mineral and organic materials on the surface of the ablation zone of the CSG, we show that the surface of CSG is essentially free of anthropogenically emitted particles, contrary to many previous findings. Given this and the overall lack of debris, we conclude that the high melt rate of CSG is primarily related to the increase of the Earth's near‐surface temperature linked directly to global warming. Therefore, the future meltwater supply for glacial‐fed rivers originating from Lahaul and Spiti region would be most vulnerable for >50 million population living downstream and requires immediate attention.

The Indo-Gangetic Plain (IGP) is one of the most highly polluted regions of the world, yet the temporal pattern of transport of anthropogenic aerosols from this region to the Himalayas is poorly constrained. On the basis of the seasonal variation of planetary boundary layer heights, air mass back trajectory analysis, and year-long time-series data for ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, and ¹⁴³Nd/¹⁴⁴Nd from aerosols collected over a high-altitude station, we demonstrate that anthropogenic Pb transport to the glacierized catchment has a seasonal pattern. The Pb isotope data reveal that during winter, the thinned boundary layer traps up to 10 ± 7% more coal-derived Pb in the IGP. In contrast, in nonwinter months, a thicker boundary layer and enhanced subtropical westerly winds result in efficient Pb transport to the Himalayas. As Pb isotope ratios are robust conservative chemical tracers and Pb is predominantly derived from anthropogenic sources, these observations suggest that enhanced transport of anthropogenic aerosols to the glacierized catchment of the Himalayas coincides with higher near-surface temperatures in the summer, creating positive feedback that enhances melting. Our results further suggest that >50% of Pb in the Himalayan aerosols originates from the resuspension of historic Pb derived from phased out leaded gasoline, highlighting the importance of legacy Pb stored in the Indo-Gangetic Plains.

Himalaya glaciers are invariably covered by supra-glacial debris. Of the glaciers, the Chhota Shigri Glacier (CSG) in the western Himalaya is basically debris-free yet has the highest melt rate compared to other central and eastern Himalayan glaciers. Here, utilizing osmium isotopic composition and major and trace element geochemistry of cryoconite — a dark-colored aggregate of mineral and organic materials —and glacial surface materials on the ablation zone of the CSG, we show that the surface of CSG is essentially free of anthropogenically emitted particles, contrary to many previous findings. Given this and the lack of debris, we conclude that the high melting rate in CSG is primarily related to the increase of the Earth’s near-surface temperature in direct response to global warming. Thus, monitoring the ice mass loss is further critical given the water source to millions of people.

Himalaya glaciers are invariably covered by supra-glacial debris. Of the glaciers, the Chhota Shigri Glacier (CSG) in the western Himalaya is basically debris-free yet has the highest melt rate compared to other central and eastern Himalayan glaciers. Here, utilizing osmium isotopic composition and major and trace element geochemistry of cryoconite — a dark-colored aggregate of mineral and organic materials —and glacial surface materials on the ablation zone of the CSG, we show that the surface of CSG is essentially free of anthropogenically emitted particles, contrary to many previous findings. Given this and the lack of debris, we conclude that the high melting rate in CSG is primarily related to the increase of the Earth’s near-surface temperature in direct response to global warming. Thus, monitoring the ice mass loss is further critical given the water source to millions of people.