Water Quality in the Third Pole: The Roles of Climate Change and Human Activities

Water Quality in the Third Pole: The Roles of Climate Change and Human Activities offers in-depth coverage of water quality issues (natural and human-related), the monitoring of contaminants, and the remediation of water contamination. The book's chapters assess years of research on water quality and climate change in this fascinating and scientifically important region. Topics addressed include climate change impacts on water qualities of freshwater bodies, such as glaciers, lakes, rivers and precipitation. In addition, the book explains the growing concerns over water quality, such as mercury, trace elements, major ions, persistent organic pollutants and their circulation.

As such, it is an essential reference for academics and policymakers interested in the water quality of natural bodies.

• Identifies key issues and problems, focusing on water quality in the Third Pole region under the changing scenarios of global climate change
• Provides updated information on water quality in a compiled form, mainly from climatically and lithologically distinct Himalayan regions
• Highlights the local and long-range transported inputs of pollutants in water bodies

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 12, 2019
• ISBN: 9780128175248

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Section I

Atmosphere

Outline

Chapter One Chemical components and distributions in precipitation in the Third Pole

Chapter Two Chemical components and distributions of aerosols in the Third Pole

Chapter One

Chemical components and distributions in precipitation in the Third Pole

Lekhendra Tripathee¹, Shichang Kang¹,², Chaoliu Li²,³, Shiwei Sun¹ and Chhatra Mani Sharma¹,⁴,    ¹State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences (CAS), Lanzhou, P.R. China,    ²CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing, P.R. China,    ³Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, P.R. China,    ⁴Central Department of Environmental Science, Institute of Science and Technology, Tribhuvan University, Kathmandu, Nepal

Abstract

This chapter highlights important findings on precipitation chemistry including spatial distribution, seasonality and possible sources of major ions, trace elements, toxic heavy metal (e.g., mercury), and carbonaceous species in wet deposition over the Third Pole (TP) region. In general, similar seasonal variations were observed for all the components in precipitation with higher concentrations in nonmonsoon and lower concentrations during monsoon seasons. The influence of a recent increase in anthropogenic activities can be clearly observed in the enhanced concentrations of certain ions (e.g., SO4²−, NO3−, and NH4+), trace metals, mercury, and dissolved organic carbon (DOC) in atmospheric wet precipitation. Moreover, the light absorption characteristic of precipitation DOC and its role on climate forcing are presented. The transport pathways of inorganic and carbonaceous species in wet precipitation indicate that DOC in precipitation over the TP was mainly influenced by combustion emissions in South Asia and local Tibetan residents. This chapter could act as the base for precipitation chemistry over the TP and direct for future needs of studies into this fragile region.

Keywords

Precipitation chemistry; major ions; trace elements; mercury; dissolved organic carbon; wet deposition; Third Pole

1.1 Background

Atmospheric pollutants impose a severe impact on human and ecosystem health, and water quality in the Third Pole (TP) region could be influenced via transport and deposition (wet/dry) from urbanized areas of South Asia. Precipitation chemistry has been the subject of active research over the last few decades due to increased awareness of environmental problems and acid rain (Kulshrestha et al., 2003). Precipitation chemistry is a result of a complex interaction between cloud dynamics and microphysical processes with a series of in-cloud and below-cloud atmospheric chemical reactions. The chemical substances are eventually removed from the atmosphere by wet/dry deposition and investigation of the chemical composition of precipitation gives information on the regional and long-range transportation of anthropogenic aerosol and its impact on ecosystems (Tripathee et al., 2014a). Additionally, changes in precipitation chemistry are useful indicators of trends in atmospheric chemistry. Because of the importance of precipitation chemistry, systematic studies have been carried out by the World Meteorological Organization, Global Atmosphere Watch, and Scientific Advisory Group for Precipitation Chemistry in many stations around the world (Vet et al., 2014).

Wet deposition is enriched with anthropogenic trace elements and serves as a potential source of environmental pollutants to aquatic and terrestrial ecosystems (Nriagu and Pacyna, 1988). However, because of the differences in sources, transport pathways, and residence time of potentially toxic trace metals in the atmosphere, the composition and concentration of elements (Kaspari et al., 2009) may vary significantly from region to region. Especially, wet depositions of trace elements are essential as their long-term excessive inputs may impose adverse impact on ecosystems and human health through various biogeochemical cycles (Tripathee et al., 2014b).

Moreover, mercury (Hg) is a highly toxic trace metal, and is well known as a globally hazardous pollutant due to its particular characteristics, such as its potential for long-range transport via the atmosphere, persistence, biomagnification through food chains, and its role as a neurotoxin (Schroeder and Munthe, 1998; Selin, 2009). Wet and dry deposition of atmospheric Hg represents an essential source of Hg to terrestrial environments, particularly in remote areas where there are minimal anthropogenic Hg emissions. Dry deposition of Hg is challenging to scale because of the lack of direct and accurate measurements (Castro et al., 2012; Graydon et al., 2008; Sexauer Gustin et al., 2012; Zhang et al., 2009). In contrast to dry deposition, wet deposition of atmospheric Hg to aquatic and terrestrial ecosystems can be directly and accurately estimated by monitoring Hg in precipitation (Keeler et al., 2006; Prestbo and Gay, 2009; Selin and Jacob, 2008). Monitoring wet deposition flux and concentration of Hg have been extensively carried out in remote and urban sites in many regions, such as in eastern Asia (e.g., China, Korea, and Japan) (Ahn et al., 2011; Chen et al., 2018; Fu et al., 2010; Sakata and Marumoto, 2005; Seo et al., 2012; Wan et al., 2009), the United States, and Europe (Keeler et al., 2006; Lynam et al., 2014; Michael et al., 2016; Siudek et al., 2016). Also, monitoring wet mercury deposition and the concentration of Hg in precipitation have been conducted in both remote and polluted sites in the Tibetan Plateau and its surrounding mountainous regions, that is, the TP (Fu et al., 2010; Huang et al., 2013, 2015; Yuan et al., 2015; Tripathee et al., 2019).

Wet deposition also plays a primary role in the global removal of dissolved organic carbon (DOC) from the atmosphere (Cerqueira et al., 2010). However, the wet deposition of DOC is still poorly constrained worldwide, mainly due to the limited availability of in situ data (Custodio et al., 2014). In addition to the role that precipitation DOC plays in the carbon cycle, the presence of precipitation DOC may be an essential component in atmospheric radiative forcing studies due to its role in the scattering of sunlight that reaches the Earth’s surface (Kieber et al., 2006). In this chapter, DOC characteristics in the precipitation of three representative remote stations in the Himalayas and Tibetan Plateau (HTP), namely the Nam Co, Lulang, and Everest stations, are investigated.

Therefore it is essential to understand the precipitation chemistry and rainwater quality in the TP region. The details on the status of inorganic species (mercury, major ions, and trace elements) and carbonaceous matters (DOC) in wet precipitation over the TP are presented in this chapter. This chapter can provide essential insights in understanding of the biogeochemical cycling of Hg on a regional/global scale, evaluating disturbance of anthropogenic Hg emission on the atmospheric environment, and assessing the potential environmental Hg risk to the fragile ecosystem of the TP.

1.1.1 Third Pole region

In this chapter, particular focus is given to the TP region, especially the southern and northern sides of the Himalayas as shown in Fig. 1.1. The TP region has an average elevation of above 4000 m above sea level with an area of about 2.5×10⁶ km², which exerts a considerable impact on the global and regional climate by thermal and mechanical forcing mechanisms (Kang et al., 2010).

Figure 1.1 Map showing the Third Pole region. The bar at the top of the figure shows the elevation in meters.

The TP region is a crucial and susceptible area regarding the dynamics of atmospheric circulation with its role in meteorology and climate at a regional to global scale (Kang et al., 2010; Liu and Chen, 2000; Thompson et al., 1997). Knowing the importance of the region, some environmental observations and monitoring programs have been implemented in this critical region. Furthermore, the TP region consists of the most extensive mountainous areas in the world. The high Himalayan region is an ideal place to monitor atmospheric chemistry due to its remoteness, pristine environment, and lower human impact (Kang et al., 2004, 2007; Shrestha et al., 2002), and to monitor the chemistry of the remote troposphere and study the evolution of atmospheric composition (Shrestha et al., 1997). Furthermore, the composition and concentration of pollutants may vary significantly from region to region in precipitation and the atmosphere. Further, long-range transport of pollutants plays a significant role in the deposition of pollutants to the TP region.

Moreover, the glaciers in the TP are regarded as vast reservoirs of fresh water in the frozen state, maintaining perennial flow to the major rivers of the region (Tripathee et al., 2016). Numerous studies have revealed that glaciers in the region have retreated considerably (Kang et al., 2010; Yao et al., 2012). In particular, anthropogenic aerosols may play a significant role in climatic change by accelerating the rate of glacier retreat. The study of chemical characteristics in precipitation has increased in the last few decades in the TP region due to their adverse effects on glaciers and the riverine environment. Studies in the region have suggested that Asian countries are more prone to atmospheric pollution due to its rapid development (e.g., industrialization, urbanization, energy demands, transportation). However, the rural and background sites have minimal concentrations with less anthropogenic input in the environment. Moreover, atmospheric brown cloud (ABC) emitted from fossil fuel combustion, and biomass burning have been observed over South Asian regions which have adverse impacts on the hydrological cycle in the region (Ramanathan et al.,