Search

Mercury (Hg) is among the most toxic metals possessing a major threat to human health and aquatic ecosystems over the globe. However, measurement of Hg concentrations and seasonal variability remain poorly understood over the Indo-Gangetic Plain (IGP) in northern India. In this study, we present one-year data of particulate-bound mercury (HgP) in aerosol samples (PM10) collected from Kanpur to understand seasonal variability and factors influencing concentration, as well as dry deposition flux. The HgP concentration exhibit a large temporal variability and ranged between 100 (on 14 June 2007) to 4340 pg m–3 (on 4 March 2007) with an annual average concentration of HgP is 776 ± 846 pg m–3. The HgP concentrations and HgP/PM10 ratios showed a marked seasonality with the highest in winter (Dec-Feb) followed by post-monsoon (Oct–Nov) and summer (April–June) seasons. HgP and HgP/PM10 were positively correlated (r2 = 0.77, p < 0.05, N = 58) during the sampling period and the estimated dry deposition flux of HgP was 104.7 µg m–2 y–1. Although this study provides a comprehensive data set on HgP in an urban atmosphere of the IGP revealing high levels of HgP, measurement of gaseous Hg is needed for estimation of the total Hg budget. Therefore, future studies should focus on identification of different sources as well as emission characteristics of all forms of Hg (organic and inorganic forms) for better mitigation strategy to prevent health risks associated with toxic Hg in the region.

Precipitation represents an important phenomenon for carbon and nitrogen deposition. Here, the concentrations and fluxes of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) with their potential sources were analyzed in wet precipitation during summer monsoon from the Northern Indo-Gangetic Plain (IGP), important but neglected area. The volume-weighted mean (VWM) concentration of DOC and TDN were 687.04 and 1210.23 µg/L, respectively. Similarly, the VWM concentration of major ions were in a sequence of NH4+ > Ca2+ > SO42- > Na+ > K+ > NO3− > Cl− > Mg2+ > F− > NO2−, suggesting NH4+ and Ca2+ from agricultural activities and crustal dust played a vital role in precipitation chemistry. Moreover, the wet deposition flux of DOC and TDN were 9.95 and 17.06 kg/(ha⋅year), respectively. The wet deposition flux of inorganic nitrogen species such as NH4+-N and NO3−-N were 14.31 and 0.47 kg/(ha⋅year), respectively, demonstrating the strong influence of emission sources and precipitation volume. Source attribution from different analysis suggested the influence of biomass burning on DOC and anthropogenic activities (agriculture, animal husbandry) on nitrogenous species. The air-mass back trajectory analysis indicated the influence of air masses originating from the Bay of Bengal, which possibly carried marine and anthropogenic pollutants along with the biomass burning emissions to the sampling site. This study bridges the data gap in the less studied part of the northern IGP region and provides new information for policy makers to deal with pollution control.

The fragile Himalayan region could be regarded as the sink for various pollutants transported from urbanized and polluted areas of South Asia. Therefore, in order to understand the concentrations, spatial distribution, pollution, and risk assessments of toxic heavy metal, mercury (Hg), surface soil samples were taken from the central Himalayas in the Langtang region. The average THg concentration in the Langtang Himalayas was 35.75 ± 24.41(ngg⁻¹), which is comparable to the Tibetan top soil values and slightly lower than world average soil values. In addition, an inverse relationship of THg with elevation were observed (i.e. decrease in concentration with increase in elevation) in the Langtang Himalayan soils. Meanwhile, THg concentrations and TOC% were significantly positively correlated at both the depths (0–10 and 10–20 cm), inferring the sorption capacity of organic carbon for Hg. The results of the geo-accumulation index (Igₑₒ), enrichment factor (EF), and pollution index (PI) indicated limited or no pollution by Hg in the Himalayan soils. Further, surface soils had a low potential ecological risk in the region. Therefore, the Hg value from this study could be used for the further evaluation and calculation of Igₑₒ, EF, and PI for water, soil, and aerosol in the Himalayan region as background reference value. However, Hg pollution from long-range transport and atmospheric deposition (wet/dry) in future could not be ignored in the Himalayan region.

The water quality of the river basins in the Third Pole has a direct impact on the well-being of millions of people. Rivers are critical bonds for nutrients, such as organic carbon and nitrogen cycles, in the aquatic, terrestrial, and atmospheric environments. In this chapter, riverine organic carbon and nitrogen exports in nine large rivers on the Tibetan Plateau (TP)—the “water tower of Asia”—are introduced. Compared with the world average, the concentrations of dissolved organic carbon (DOC, 1.16 mg L−1) are at the low end, which is likely because of the low temperature and unproductive land vegetation environments. However, the average concentrations of dissolved organic nitrogen (DON 0.35 mg L−1) in this region are close to the world average. It is noticeable that, despite its dominant pristine environment, discharge from agricultural activities and urban areas has raised riverine N export. In addition, the DOC/DON ratio (C/N, ~6.5) was much lower than the global average, indicating that DOC in the rivers of the TP might be more bioavailable. Only a few studies on persistent organic pollutants (POPs) have been carried out in rivers of the Third Pole region. Nevertheless, there are few datasets to understand the levels and spatial distribution of these pollutants over the region. The concentration of POPs in the Koshi River basin was much higher than that in the remote areas and it was comparable to rivers in remote parts of India, however, much lower levels were observed than in the rivers in polluted areas of India. Furthermore, total suspended/insoluble particles in rivers are an emerging area of interest in river system monitoring as carriers of water pollutants. However, there is scant information on this matter in the Third Pole region. Insufficient measuring systems and lack of attention to total suspended solids and water turbidity has rendered inadequate information about pollution loads and water quality, and hence this has caused a severe impact on health, environment, and ecosystem.

The “Third Pole,” centered on the Tibetan Plateau, is also known as the “Water Tower of Asia.” The Third Pole region feeds more than 10 large rivers (e.g., the Yellow River, the Yangtze River, the Yarlung Tsangpo, the Indus, the Amu Darya, etc.) in Asia and there are more than one billion people dependent on the water resources provided by these river basins. In this chapter, an overview of the water chemistry and the geochemical mechanisms that govern the characteristics of major ions and trace elements in rivers of the Third Pole are presented. In general, most rivers of the Third Pole have an alkaline water environment with an average pH of 8.7. As a result of intensive rock weathering within the catchments, the averaged total dissolved solids (~380 mg L−1) in the rivers of the Third Pole are much higher than the global median level. It was found that the dissolved contents in rivers of the Third Pole are dominated by Ca2+, Mg2+, HCO3−, Cl−, and SO42− with a spatial heterogeneity due to the different climates, hydrography, and geology conditions over the region. The main mechanisms that control the water chemistry in the rivers of the Third Pole are natural processes, such as rock weathering, ground discharge, and evaporation-crystallization, and most of the rivers remain pristine. However, it should be noted that due to human factors, such as urbanization and mining operations, toxic elements such as As, Cd, Hg, Mn, and Pb concentrations in some of the rivers in the Third Pole are higher than the permissible limits for drinking water as established by the WHO. With increasing anthropogenic activities and changes within the river basins of the Third Pole, further monitoring of the hydrochemical compositions in rivers over this eco-fragile region is warranted.

Atmospheric nitrogen is ubiquitous in the environment and hence plays an essential role in the nutrient balance over the whole ecosystem. However, its abundance and characteristics, particularly in the Himalayas, are not well understood. Therefore, to understand the abundance, sources, and seasonality of soluble nitrogenous species in the middle hills of the central Himalayas, aerosol samples were collected at Dhulikhel in Nepal from January to December 2018. The results of this study revealed that water-soluble inorganic nitrogen (WSIN) contributed the most to water-soluble total nitrogen with an abundance of ammonium nitrogen (NH4+–N). Moreover, water-soluble organic nitrogen (WSON) contributed approximately 18% to aerosol total water-soluble nitrogen. The aerosol mass and WSIN species exhibited strong seasonality with considerably higher concentrations during dry periods and lower concentrations during the wet period. Furthermore, for dry periods, the HYSPLIT model revealed that nitrogen aerosols mainly originated from the Indo-Gangetic Plain region and were transported and deposited in the Himalayas through long-range atmospheric transport. The strong correlations of WSON with nss K+ (biomass burning) and nss Ca2+ (crustal sources) and lack of a significant correlation with SO42− indicated that primary sources are responsible for generating WSON rather than secondary processes in the Himalayas. The estimated dry deposition fluxes for NO3−–N, NH4+–N, and WSON were 1.56, 8.35, and 4.06 kg ha−1 y−1, respectively. This study also shows that increasing air contaminants and emissions over South Asia can enter the Himalayas and affect the human health and ecology of this fragile area.

South Asian pollutants can be transported and deposited via wet/dry deposition to the remote areas of the Himalayas and could pose a serious threat to the mountain ecosystems. Therefore, in order to understand the concentrations, fluxes, seasonal variation and origin of the mercury (Hg), major ions and trace elements, precipitation samples were collected during 2012–2013 from a data gap region, Jomsom, the high elevation semi-arid mountain valley in the central Himalayas. The volume-weighted mean (VWM) concentrations of ions followed the order of Ca2+ > Mg2+ > Na+ > NH4+ > SO42− > Cl− > NO3− > K+. The concentration of Cd was lowest (0.07 μg L−1) whereas that of Fe was the highest (1073.59 μg L−1) in the precipitation samples. Wet deposition level of all the measured inorganic species was comparable to urban Lhasa but higher than those in remote alpine sites of the Tibetan Plateau (TP). This study shows that Hg and other inorganic constituents were higher in the non-monsoon season compared to monsoon due to enhanced washout of aerosols. Enrichment factor (EF), sea salt fraction, crustal and anthropogenic fractions, principal component analysis (PCA) and correlation coefficient analysis suggested that crustal dust and anthropogenic activities as the major sources of measured chemical species whereas the influence of sea-salt was minimal. In addition, local anthropogenic emissions were low suggesting that the majority of the pollutants could have been transported from the South Asian region to the high elevation mountains. Meanwhile, low precipitation and dry environment could have enhanced the concentrations of inorganic species in the arid region than other sites over the central Himalayas. This work adds new dataset of inorganic pollutants in wet precipitation and provides baseline information for an arid region environmental protection. However, there is a need for further long-term monitoring to understand the precipitation chemistry of the arid regions.

The studies on global pollutant mercury (Hg), which is of public concern due to its high toxicity and capacity to long-range transport via atmospheric circulation, is poorly characterized in wet deposition over the Nepal-Himalayas region. Therefore, in order to understand the concentration levels, spatial distribution and seasonal variation of total Hg, 333 precipitation samples were collected from south to north: Kathmandu (1314 m a.s.l.), Dhunche (2065 m a.s.l.), Dimsa (3078 m a.s.l.) and Gosainkunda (4417 m a.s.l.) characterized as urban, rural, remote forest and remote alpine sites, respectively, for over one-year period. The highest Hg concentration was found in Kathmandu comparable to the urban sites worldwide, and significantly lower concentrations at other three sites demonstrated similar levels as in rural and remote alpine sites worldwide. Higher wet deposition fluxes of 34.91 and 15.89 μg m−2 year−1 were found in Kathmandu and Dhunche respectively, due to higher precipitation amount. Clear and distinct seasonal differences were observed with higher concentrations in non-monsoon and lower values in monsoon periods due to less scavenging and high pollutant concentration loadings during the dry period. The positive correlation of Hg flux and precipitation amount with Hg concentration suggested that both precipitation amount and Hg concentration plays a vital role in Hg deposition in the central Himalayan region. Enrichment factor (EFHg) indicated that the anthropogenic emission sources play a significant role for Hg enrichment and a high ratio of EFmonsoon to EFnon-monsoon (>2.18) suggested that the anthropogenic atmospheric mercury could likely be long-range transported from south Asian regions to the Himalayas during the monsoon season. In addition, our results showed that the major ionic compositions (e.g., SO42−, NO3−, NH4+, K+, Ca2+) could influence Hg concentration in wet precipitation. The anthropogenic sources of Hg such as biomass and fossil fuel combustion, crustal aerosols may contribute to the Hg concentration in wet precipitation over the central Himalayas.