Freshwater ecosystems are globally declining at an astronomical rate (MEA, 2005; Dudgeon et al. 2006). This holistic degradation of wetlands is triggered by unprecedented changes instigated by global climate crisis. A bouquet of factors is responsible for this phenomenon which includes anthropogenic driven landscape changes, species loss, biodiversity deterioration etc. (Allan and Flecker, 1993; Lemly, et al., 2000; Kingsford, et al., 2006). Wetland loss finds prominence with degradation of Aral Sea (Micklin, 1988) and Marshlands of Mesopotamia (Partow, 2001). Global temperature rise has not only resulted in wetland shrinkage in the arid zones of the world but also impacted the water volumes of downstream wetlands and estuaries (Kingsford et al. 2006). Scarcity in rain-fed river water volume and species loss is a testimony to the fact. Pollution load and acidification has caused irreversible damage on wetland ecology; the flora and fauna in particular. Examples include small lakes in northern Ontario (McNiol, et al., 1987) aquatic resources across North America, eastern Canada and Scandinivia (Baker, 1991), coastal wetlands of eastern Australia (White, et al., 1997). Nitrogen deposition and eutrophication of freshwater systems of Asia is a matter of grave concern and may be more important than Sulphur deposition. Regional acidification of soil is notable in parts of Eastern Asia (Duan, et al., 2016). Incidences of Nitrogen and Sulphur accumulation is observed in parts of India, Bangladesh, Pakistan, Myanmar, Thailand, Laos, North Korea, and Japan (Vet et al., 2014). Early acid deposition effects are recorded in Asia by (Bhatti, 1992). Global climate changes have direct and indirect impacts on patterns of biogeochemical cycling as well leading to decreasing pH trends in precipitation in southern China (Zhao and Sun, 1986; Galloway et al., 1987), south-eastern coastline and north-eastern India (Varma, 1989), in Japan (Hara, 1997) and Korea (Chung et al., 1996). Spatio-temporal assessments and ecosystem level surveys points to ecosystem degradation with increasing acid deposition effects. For example, acidification has led to mass elimination of freshwater fishes as recorded by (Hendrey, 1981).
The eastern peripheries of Kolkata, one of the most prominent cities in the eastern part of Indian subcontinent are bordered by East Kolkata Wetlands (EKW). It is one of the largest single-stretch aquaculture belts of the world with identified resource recovery opportunities thus increasing the total economic value of the wetland systems manifold. This wetland is currently under the double pronged impact of anthropogenic stress factors and climate fluctuations in the lower gangetic belts. The wastewater draining off perennially from in and around the city having recognizable limits of trace and toxic heavy metals such as Zinc, Copper, Manganese, Iron, Cobalt, Nickel, Lead, Chromium, Mercury reaches to EKW leading to subsequent dissolution and precipitation in the ambient media (Lakshmanan and Nambisan, 1983; Mitra, 2013). pH is one of the primary determining factors on heavy metal specification among other environmental variables (Mitra et.al, 1992; Mitra et.al, 2010; Mitra, 2013; Mitra and Zaman, 2016; Dutta et al., 2016). Slight changes in pH might cause humongous effects on wetland flora and fauna leading to major ecosystem losses worldwide. The cascading effects of global climate changes and anthropogenic stress is an adage to the problem. Several authors have been documenting how the regulatory role of pH on patterns of heavy metal accumulation but not much light is thrown on the issue of holistic restoration of ecosystems ameliorating the crisis (Ramamoorthy, 1988; Lakshmanan and Nambisan, 1983; Mitra et.al, 2011; Mitra et.al, 2012; Chakraborty et. al, 2009). The current study attempts to investigate in that direction the influence of aquatic pH on dissolved Lead in EKW with reference to acidification in freshwater systems induced by global climate change; a burning issue of our times. The bioaccumulation pathway of toxic heavy levels in the different trophic levels of the ecosystem is discussed in (Fig. 1).