ABSTRACT Understanding the subaerial dispersal of desert sediments along a downwind aridity gradient is challenging but crucial for promising sustainability in habitable semiarid boundary regions. The Thar Desert of Rajasthan (India) emits copious fine dust towards the Himalayas before the onset of the Indian Summer Monsoon every year. However, the climatic influence (especially of eolian processes and aridity conditions) on the provenance characteristics, downwind dispersal, and postdepositional alteration of sandy sediments across the desert is poorly understood. This knowledge is essential for reliable provenance tracing in arid and semiarid environments. For this purpose, 52 surface sediment samples, spanning the hyperarid southwestern area to the semiarid eastern and northeastern fringes of Rajasthan, have been characterized for geochemical, isotope, mineralogical, and grain-size data. The measured properties reveal a consistent upwind provenance of sandy sediments across the desert, as well as the variable impacts of wind forcing, elevation, and aridity conditions. The Thar sediment signatures from upwind Jaisalmer and Barmer districts can be reliably traced at downwind locations in the Jhunjhunu, Churu, and Jaipur districts. The dune-profile sediments from Jhunjhunu and Rajgarh (Churu), located in the northeastern semiarid fringes, are more weathered chemically and show higher Zr abundances and lower εNd than the other samples. Notably, higher 87Sr/86Sr and quartz enrichment are found in fine sand, especially from the Aravalli highlands. The plausible reason for the grain-size variability of Sr isotopes seems to be K-feldspar or mica preferentially retained in fine sand delivered to highlands under stormy conditions. This study highlights the widespread eolian transport of sandy Thar sediments to downwind locations at distances of ∼ 400–500 km. The widespread Thar sediment dispersal is also accompanied by spatially variable grain size, mineral sorting, and postdepositional chemical weathering under favorable conditions. The modification in geochemical and isotope compositions of widespread desert sediments owing to spatially varying sedimentary processes needs to be accounted for in future provenance studies of downwind eolian sediments.

Groundwater is the main source of drinking water globally; however, its quality has been deteriorated due to various geogenic and anthropogenic activities. The groundwater quality of Naini Industrial Area, Prayagraj was studied seasonally to evaluate the fluoride and nitrate contamination pertaining to human health risk assessment. The samples were collected from 60 locations in the pre-monsoon, monsoon, and post-monsoon season. The fluoride and nitrate were assessed with the help of Ion chromatography. The NO3- concentration exceeded the Indian drinking water quality standards in 27% of the groundwater samples. The NO3- contamination is predominantly associated with agricultural practices, while F- can be linked to natural geological sources. The noncarcinogenic human health risk assessment was quantified by calculating the Hazard Quotient (HQ) and Hazard Index (HI) were calculated as per USEPA methodology for male, female and child population. The findings indicate that the child population is particularly susceptible to health risks associated with the ingestion of Fand NO3- through the drinking water pathway. Across all the sampled sites, the Hazard Index (HI) values varied from 0.10 to 12.3 for males, 0.09 to 10.6 for females, and 0.16 to 19.7 for children suggesting substantial risk to the local populace at more than half of the locations which is largely related to nitrate contamination. Thus, the study suggests that groundwater at many locations is unsuitable for drinking without treatment pertaining to the probable health risk they pose to consumers advocating upgraded water management plan for the residents.

Sediment archives in different climatic zones respond variedly to changing climatic conditions. Hyper-arid climatic zones, known for their extreme temperatures and precipitation, have complex interactions due to changing climatic conditions. The study investigated a shallow core of 5 m from a lacustrine environment in the marginal part of the Little Rann of Kachchh, Kachchh, Western India. The hyper-arid climate and active tectonism make the site crucial for reconstructing changes in the Holocene epoch, which is known to have experienced rapid climatic shifts affecting ancient human settlers. The core has been subjected to a multiproxy (grain size analysis, elemental geochemistry, environmental magnetism, organic carbon, palynology, and chronology) assessment for the three periods of varying environmental conditions during Greenlandian (similar to 11-8.2 ka), Northgrippian (similar to 8.2-4.2 ka), and Meghalayan (similar to 4.2-2 ka) stages of the Holocene epoch. The Early Holocene sediments suggest arid conditions with high-energy depositional environments and weak monsoons, transitioning to fluctuating monsoonal activity by the Middle Holocene. The Mid-Holocene Climatic Optimum (similar to 6-5 ka) marks a peak in monsoonal intensity, with heightened chemical weathering and organic productivity. In contrast, the Late Holocene is characterized by reduced hydrological variability and episodic climatic perturbations, including the 4.2 ka arid event. The climatic conditions during the prominent short-lived arid episode (8.2 ka) exhibit contrasting anomalies, revealing intriguing environmental patterns in the region due to the lack of response by the hyper-arid landscape. These findings provide valuable insights into the unique behavior of hyper-arid regions and their relevance to broader regional climatic reconstructions, with caution.

This study investigates the trace element concentrations in the surface waters of four north-joining Himalayan tributaries of the Ganga river (Ramganga, Ghaghara, Gandak, and Kosi), highlighting the combined effects of geogenic processes and anthropogenic activities on trace element chemistry and water quality. A knowledge gap exists in understanding the sources of trace elements in these tributaries and the contribution of trace elements from these tributaries to the Gangariver. The novelty of the study lies in its assessment of sources, human health risks, and ecological impacts. The investigation was conducted by assessing trace element concentrations and comparing them with national and international standards. Various human health and ecological risk indicators, including the Heavy Metal Pollution Index (HPI), Hazard Quotient (HQ), Health Index (HI), Chronic Daily Intake (CDI), and the Potential Ecological Risk Index (PERI), were applied. The results reveal high concentrations of copper (Cu), zinc (Zn) and lead (Pb) in the Ramganga, indicating contamination from industrial activities in the catchment. Although most trace element concentrations are within safe limits, Pb concentration in the Ramganga exceeds the limit prescribed by WHO. The Ramganga shows the highest health risks, with a HItotal of 1.876 for adults and 1.616 for children. In contrast, the Ghaghara, Gandak, and Kosi exhibit lower but moderate contamination levels. HPI values for these rivers- 93.74 for the Ghaghara, 83.95 for the Kosi, 83.13 for the Gandak, and 80.43 for the Ramganga-indicate that although contamination is below critical thresholds, targeted mitigation strategies are needed. The findings provide valuable insights into trace metal sources and their implications for human health and ecological risks, and emphasize the need for frequent monitoring and pollution control measures for maintaining sustainable water quality in these tributaries.

Formation of ferromanganese nodules (FMNs) is an important pedogenic process which is commonly observed in the Ganga alluvium. We have studied geochemistry of the host alluvium and FMNs from the eastern Uttar Pradesh, India. The FMNs were categorized in three sizes (>5.6mm, 5.6 to 2mm, and 2 to 0.5mm). The major and trace elements present in the sediments and FMNs of three size ranges were analysed using XRF and ICP-OES. The geochemical composition of the sediments and FMNs were compared with the geochemical values of the Upper Continental Crust (UCC). The enrichment factor (EF) of the analysed elements were calculated for both the host sediments and the FMNs. Additionally, the Chemical index of weathering (CIA) was calculated to quantify the extent of chemical weathering of the sediments and FMNs in the alluvium. The sediments and FMNs both showed moderate chemical weathering. We propose that the weathering of aluminosilicate stages may have given Fe, Mn, and related trace elements for the nodule formation. Prolonged dry spells and monsoonal wet seasons in the Ganga plain region may be key contributors to the weathering, mobilization, precipitation, and redistribution of the Fe and Mn phases in nodules. Certain elements, such as Pb and Cr, which are considered to be harmful to the environment got sequestered in FMNs. This helped immobilization of these contaminants. Whereas, elements like P, Co, Zn, and Cu were also got sequestered during the formation of FMNs. Therefore, it has also impacted soil nutrient availability.

Basalt is the most weatherable rock with its importance in sequestering atmospheric CO2. The Deccan basalts cover almost 15% of the geographical area of India. This study investigates the processes of chemical weathering operating in the modern basalt weathering profile and intertrappean beds in and around the district of Indore, Madhya Pradesh, India. There have been reports that the bole beds may have originated by aeolian deposition. The geochemical data was used to calculate the chemical index of alteration (CIA) and geochemical mass balance values (Ʈ). Weathered profiles have been studied for REE behaviour. The bole beds show a very high chemical index of weathering. The elemental mobility does not show any regular pattern. However, the REE patterns show slight depletion or enrichment, with stronger Ce mobility in some horizons. The geochemical study suggests that the highly weathered bole beds have originated from the chemical weathering of the surrounding basaltic rocks, not from the other external materials.

The Deccan basalts have been undergoing intense weathering in the tropical conditions since the passage of India through the equator. This study is on the basalts' weathering from central India's present-day semiarid climate. Two weathering profiles from the districts of Indore and Dhar, Madhya Pradesh, have been studied using mineralogy and geochemistry. The profiles show incipient weathering with low to medium Chemical Index of Alteration (CIA) and Mafic Index of Alteration-oxidising (MIA(O)) values. The presence of smectite in weathered zones, mineralogically attests to incipient weathering. The pyroxene and plagioclase-rich zones have produced smectite clays in the basalts. The rare earth elements (REE) and, to a greater extent, the heavy (H) REE show mobility during incipient weathering, which appears to be due to differential retention of REE in the clay minerals. The smectites seem to retain light (L) REE more significantly than HREE. The ancient terrain showing currently incipient weathering indicates recent exposure of the profiles by the erosion under neotectonic activity. In this fashion, the frequent exposures of new weathering surfaces on the basalts may have played a significant role in the uninterrupted consumption of CO2 by silicate weathering since around 50 Ma.

A sediment core from a palaeochannel distributary of the Saraswati River basin in western India was investigated through a multi-proxy study using palynology, phytoliths, sedimentology, geochemistry, magnetic mineralogy and chronology. The site is located at the eastern margin of the Little Rann of Kachchh in the northwestern part of the Gujarat Alluvial Plains. The goal was to reconstruct the paleoclimatic and sea level flucutations spanning from the last deglaciation to the late Holocene in the area. The core records suggest at least four episodes of marginal marine environment between the last deglaciation and the late Holocene. The first phase of sediment deposition under marine influence was observed post LGM. The signatures of coeval dry climatic conditions of Older Dryas and Younger Dryas periods besides warm and humid conditions of B & oslash;lling-& Aring;ller & oslash;d period are reflected in the core records. The second phase of rise in sea level occurred between -11,210 and -9795 cal yr BP, which falls within the period of high gradient of sea-level rise of western India. The third phase of global sea level rise in the area is at around -5747 cal yr BP which coincides with a high sea level phase along the west coast of India. The final recurrence of sediments with predominant marine signatures post -2650 +/- 180 cal yr BP until -1530 +/- 350 cal yr BP suggests marine to marginal marine conditions in the area.

Water resources are important to economic development, as water is essential to the production of agricultural goods and services. To enhance crop yield per unit of scarce water requires both good cultivars and agronomy. The challenge is to manage the crop or improve its genetic makeup to capture more of the water supply for use in transpiration; exchange transpired water for CO2 more effectively in producing biomass; and convert more of the biomass into grain or other harvestable product. Irrigation with poor quality waters may transport unwanted elements to the soil in high quantities affecting its fertility. The computed values of Na%, Sodium Absorption Ratio (SAR), Residual Sodium Carbonate (RSC), Permeability Index (PI), Magnesium Hazard (MH) and Kelly’s Index (KI) have shown that except at very few locations, most of water samples are suitable for irrigation purposes.

The Mesoarchean Kalva Rangan Durga Formation of the Shimoga greenstone belt in the western Dharwar Craton consists of orthoquartzite, ferruginous phyllite, banded ferruginous chert, and conglomerates. Thick beds of orthoquartzites of this formation are well exposed in Kalva Rangan Durga ridge, trending northeast to southwest for about 9 km, in the southwest part of the Honnali Dome. Quartzites are fine‐grained in nature and mostly composed of quartz grains and fuchsite mica. In the present study, we have collected quartzite samples and carried out geochemical, Sr, and Nd isotope analyses to decipher their paleo‐weathering conditions, provenance characteristics, and possible tectonic setting of deposition. Geochemical data indicate they are arkose to subarkose in nature. Moderate to intense chemical weathering of the source rocks of these quartzites during the Mesoarchean is suggested based on various weathering indices and ternary plots. Enriched LREE and flat to variably fractionated HREE patterns with negative Eu anomalies of quartzites indicate that they were mainly derived by weathering of tonalities, trondhjemite, and granodiorites (TTG) gneisses and granites. The relatively high concentration of Cr with variable Th/Sc and high Cr/Th ratios indicate both felsic and mafic sources for quartzites. Initial εNd values (t = 3.0 Ga) of quartzites range from −3.04 to +1.24 which further support their derivation from both older evolved continental crustal and juvenile sources. The presence of symmetrical ripple marks on the surface of quartzite indicates a shallow marine environment.

Atmospheric dust originating from the Thar Desert (India) acts as the local source of mineral dust in South Asia, spreading over an area of 0.32 × 106 km2. Regional studies conducted during peak boreal summer are required to characterize this mineral dust that blows in form of episodic dust storms towards Indo-Gangetic Plains (IGP), using a multi-tracer approach. To achieve this goal, atmospheric PM10 particles were collected along with surface dry soils between 3 and 11 June, 2013, from in and around the Jodhpur city (26.2389°N, 73.0243°E) to glean elemental composition, stable isotopic and palynological (pollen types) database. Typical crustal elemental ratios, e.g. Si/Al, Ca/Al, Fe/Al, K/Al, Mg/Al, Ti/Al, varied in narrow ranges 8.1 ± 1.21, 1.02 ± 1.53, 0.50 ± 0.14, 0.34 ± 0.06, 0.19 ± 0.06 and 0.06 ± 0.02, respectively. Average Sr/Al, Rb/Al and Zr/Al ratios were found to be 39.70 ± 12.24, 18.00 ± 2.0 and 70.83 ± 13.11 (μg gm−1/wt%), respectively. Average δ13C, δ15N, δ34S values of surface soils were − 10.5‰ ± 4.0, 11.4‰ ± 1.6 and 3.6‰ ± 2.1, while δ13C and δ15N of atmospheric PM10 particles varied in ranges − 25.6‰ ± 0.67 and 9.9‰ ± 1.7, respectively. Observed palynoassemblage indicated the open nature of vegetation that usually grows under warm-humid conditions with traces of few allergens and pathogens. Generated chemical-isotopic-pollen database could be utilized for deciphering origin of dust storms in IGP. Detailed multi-proxy characterization of mineral dust from the Thar Desert can further help to determine its role in influencing air quality and human health.

Weathering is controlled by factors such as lithology, geological structures, topography climate, tectonics and biota. The present study aims to highlight the manifestations of weathering in two contrasting settings- the Himalaya and Bundelkhand. The study area in the Himalayan region is characterised by active tectonics, steep topography, rugged landscape, cold and semi-arid climate, and sparse vegetation cover. The Bundelkhand region, however, is characterised by stable, undulatory topography, warm and sub-humid climate, and tropical dry deciduous forest. This study mainly presents field observations made during field campaigns to Gemur and Jispa (Lahul Valley) and Rohtang in the Himalaya; Jhansi, Orchha and Lidhora in the Bundelkhand region. Contrasting features about weathering, erosion and sediment generation in the Himalaya and the Bundelkhand were observed. Weathering through physical heterogeneities are common in the Himalaya as water is lost through surface run off due to steep slopes. Presence of large fragmented materials weathered in the Himalaya is relatable to the erosion dominated regime corresponding to the tectonically active steep topography. On the other hand, gently sloping areas in the Bundelkhand, experience lower surface runoff and higher infiltration. Therefore, weathering in the Bundelkhand proceeds to a greater depth contributing to deep weathering profiles characterized by weathering layers such as sap rock, saprolite and soil. Series of events like the exposure of parent granite, development of physical openings along joints and fractures, erosional activities, transport of eroded materials, and chemical weathering due to longer residence time and longer interaction with water would have supported the development of deep weathering profiles in the Bundelkhand region.

In the present investigation, lignite samples from working seams of Matasukh mines, Nagaur, Rajasthan have been subjected to optical microscopy and mineralogy to determine their mineralogical characteristics and paleodepositional condition. Petrographic analysis of composite samples indicates that these lignites are dominated by carbonate minerals followed by sulfides and clay minerals. Framboidal pyrites have also been recorded in the Nagaur lignite samples, which reveals marine incursion into the study area. The occurrence of clay mineral in cell cavities, fissure, and cracks indicates authigenic and syn-depositional origin of the Nagaur lignite. The study reveals Nagaur lignites deposited under terrestrial oxic to marine terrestrial oxic to sub-oxic condition and semi-arid to slightly arid paleoclimatic conditions.

The article by Perakis and Pett-Ridge in PNAS (1) stimulated an interesting discussion (2) on the role of nitrogen-fixing alder in enhancing rock weathering and supply of rock-derived nutrients. The authors ascribe the accelerated rate of weathering to the generation of acidic conditions in the soil due to excess nitrogen (1). Our work on Alnus nepalensis (Himalayan alder) may offer an alternative explanation to the role of alder on rock weathering. We focused on the changes in bacterial diversity and community structure in soil with the development of alder stands. These stands were designated as juvenile, young, and mature depending upon the stages of alder growth. We assessed the patterns, degree of chemical weathering, and the enrichment and … [↵][1]1To whom correspondence may be addressed. Email: mayankrishna{at}gmail.com or sgarkoti{at}yahoo.com. [1]: #xref-corresp-1-1

Synergistic coexistence of nitrogen fixing cyanobacteria such as Anabaena variabilis, Nostoc muscorum and Westiellopsis prolifica with green algae namely Scenedesmus obliquus, Chlorella vulgaris and Botryococcus braunii was studied under nitrogen deficient conditions. The effect of these interactions was investigated on growth, fixed nitrogen content, lipid content and their secretomes in individual cultures and cocultures. Based on the cocultivation studies, it was found that out of the nine interactions studied, B. braunii-N. muscorum synergism was best established. This interaction resulted in a maximum of 50% enhancement in nitrogen fixation in B. braunii-N. muscorum co-culture leading to 27% enhancement in lipid content (membrane and neutral lipid). In general, B. braunii co-cultures showed an enhancement in biomass content of up to 38%. Secretome analysis showed presence of new and modified secondary metabolites having roles in quorum sensing/quenching, interspecies signaling, N-fixation, carbon metabolism, lipid metabolism, antimicrobial activity. Compounds such as trichloroacetic acid and hexadecane were identified that are known to have roles in nitrogen assimilation and carbon metabolism, respectively, were present in some of the co-culture secretomes. The combination of B. braunii-N. muscorum led to the formation of new compounds such as triacontanol which have role in improvement of glucose-lipid metabolism and 9-octadecenamide that is known to be a phytohormone.

The Son River originates in the Amarkantak hills of Maikal range at an elevation of ~600 m in Madhya Pradesh and then flows through the north of Kaimur plateau of Vindhya ranges. This river is an important tributary of the Ganga River, and after flowing through the parts of Madhya Pradesh, Uttar Pradesh, Jharkhand and Bihar states, it joins the Ganga River on its southern bank near Patna. The major tributaries of the Son River emerge in the highlands and flow in a northward direction to join the main river. The major tributaries of the river are the Rihand, North Koel, Gopad, Banas and Kanhar rivers. The Son River drains through the Gondwana and Vindhyan Supergroups, Mahakoshal Group, Central Granitic Complex (CGC) and Quaternary alluvium. Five widespread alluvial formations have been proposed by others in the Son River valley, namely the Sihawal, Khunteli, Patpura, Baghor and Khetaunhi, in the oldest to youngest sequence. The Son River water has been found good to excellent in quality for irrigation and also suitable for drinking purposes. Many dams, reservoirs and hydropower generation plants occur on the Son River and its tributaries; these resources are serving for irrigation and electricity generation in the Son River valley. It has been reported that the hydropower generation has been decreasing in the last three decades for the Son River valley.

Ten surface and ten groundwater samples were collected from the middle part of Subarnarekha River basin, Jharkhand, India, during the pre-monsoon, monsoon and post-monsoon periods in the year 2008 (n = 60) in order to outline the hydrogeochemical signatures and to assess their overall quality. The study area was selected for their significance to diverse physiographic characteristics, mining and cultivation practices. Samples were analyzed for totally 21 parameters, including of physicochemical properties (pH, electrical conductivity and total dissolved solids), major and minor ions (Na+, K+, Ca2+, Mg2+, F−, Cl−, SO42− and NO3−) and trace elements (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn). Results suggest that quality status, in general, is acceptable with few exceptions; however, issues related to the mining and imposed cultivation were identified which in turn could potentially lead to environmental degradation. The geogenic factors and anthropogenic influences are affecting the hydrogeochemical characteristics of water resources in the study area. The results were confirmed by numerical index Poseidon index (PoS) which has classified the samples according to their quality status. The PoS provides a generic water quality assessment through a single score that is representative of the overall hydrogeochemical characteristics of water, regardless of the processes involved, specific goals and characterization. Overall, the geological setup, hydrogeological regime, unmanaged cultivation practices and overexploitation of groundwater have adverse impacts on water resources of the region. Environmental protection and production optimization may be achieved through the implementation of custom actions and appropriate management measures in the region.

The Ganga River plays a major role in the transfer of materials from the Indian sub-continent to the Bay of Bengal, both in dissolved and particulate forms. To understand the present elemental dynamics of the Ganga River system, it is important to assess the hydrogeochemical contribution of its tributaries. In this paper, we present an updated database on dissolved and particulate fluxes and denudation rates of the Himalayan tributaries of the Ganga River (Ramganga, Ghaghara, Gandak and Kosi). Dissolved trace element concentrations, their fluxes and suspended sediment-associated elemental fluxes of the Himalayan tributaries have been reported for the first time. Total dissolved flux of the Ramganga, Ghaghara, Gandak and Kosi was estimated as 4, 19.1, 10.3 and 8.8 million tons year−1 accounting for ~ 5.7, ~ 27.3, ~ 14.7 and ~ 12.6%, respectively, of the total annual dissolved load carried by the Ganga River. The total particulate flux of the Ramganga, Ghaghara, Gandak and Kosi was computed as 8.2, 81.6, 30.9 and 19.5 million tons year−1, respectively. Compared to earlier studies, we have found a significant increase in the total dissolved flux and chemical denudation rate of the studied tributaries. The estimated particulate fluxes were found to be low in comparison to the previous studies. We suggest that a significant increase in the dissolved fluxes and a decrease in the particulate fluxes are an indication of the increasing anthropogenic disturbances in the catchment of these tributaries.

Spatial and temporal variation in the major ion composition of the waters in the Brahmaputra River has been measured to understand chemical weathering and the factors controlling these processes. Samples were collected from the Brahmaputra mainstream at five stations Pasighat, Dibrugarh, Tezpur, Guwahati and Dhubri during monsoon and post monsoon seasons. The total dissolved solids in the waters of the Brahmaputra system ranges between 62.5 and 192.5 mgl-1. The (Total dissolved solids) TDS of the Brahmaputra measured in this study are less than the values reported by earlier workers. Gibbs plot was plotted to investigate the dominant process controlling the water chemistry of the Brahmaputra. The plots of TDS vs. (Na + K)/(Ca + Na + K) and TDS vs. indicate that rock weathering is the main process controlling the chemistry of water in the Brahmaputra River. Factor analysis was done to study the factors controlling the water chemistry of the Brahmaputra.