Assessment of Environmental Water Security of an Asian Deltaic Megacity and Its Peri-Urban Wetland Areas

Subham Mukherjee,Brigitta Schütt,Pradip Kumar Sikdar,Sukdeb Pal

doi:10.3390/su13052772

Abstract

Achieving urban water security requires sustaining the trade-offs between the exploitation of water/environmental resources and ecosystem services. This achievement not only reduces the pollution and contamination in the environment, level of water stress, but also secures good ambient water quality and future for people’s well-being and livelihoods. Changes in land use and land cover and growth of impervious structures can immediately generate severe ecological and social issues and increase the level of natural or manmade risks, affecting the condition of ecosystem services within and in the vicinity of an urban region. As a result of these transformations and further exploitation, due to the growing anthropogenic pressure, surface water and groundwater quality can be deteriorated compared to ambient water quality standards (for both chemical and biological pollutants). Based on land use and land cover (LULC) data retrieved from remote sensing interpretation, we computed the changes of the ecosystem service values (ESV) associated with the LULC dynamics, water quality and, finally, urban water security during the pre- and post-monsoon periods of 2009, 2014 and 2019 in Kolkata, an Asian deltaic megacity, and its peri-urban wetlands named East Kolkata Wetlands (EKW). The area under wetlands reduced comprehensively in 2009–2019 due to the conversion of wetlands into various other classes such as urban settlement, etc. The quality of surface water bodies (such as rivers, lakes, canals and inland wetlands) deteriorated. The groundwater quality is still under control, but the presence of arsenic, manganese and other metals are a clear indication of urban expansion and related activities in the area. As a result, there was a change in the ESV during this timeframe. In the pre-monsoon period, there was an increase in total ESV from US$53.14 million in 2009 to US$53.36 million and US$59.01 million in 2014 and 2019, respectively. In the post-monsoon period, the ESV decreased from US$67.42 million in 2009 to US$64.13 and US$61.89 million in 2014 and 2019, respectively. These changes can be attributed to the peri-urban wetlands and the benefits or services arising out of them that contribute more than 50% of the total ESV. This study found that the area under wetlands has reduced comprehensively in the past 10 years due to the conversion of wetlands for various other uses such as urban expansion of the Kolkata City, but still, this peri-urban wetland supports the urban water security by providing sufficient ecosystem services. In conclusion, the transformation in extent of the water-related ecosystem is a crucial indicator of urban water security, which also measures the quantity of water contained in various water-related ecosystems. Quantitative analysis of the LULC change, hence, is important for studying the corresponding impact on the ecosystem service value (ESV) and water quality that helps in decision-making in securing urban water future and ecosystem conservation.

Highlights

Water security is widely regarded as the key natural resource challenge facing humanity
Urban settlement dominates the urban area of the Kolkata Municipal Corporation, while in the East Kolkata Wetlands, agricultural land is the dominant
The areas covered by inland wetlands varied seasonally in distribution, i.e., during post-monsoon periods, the area covered by inland wetlands was generally higher than during the pre-monsoon periods

Summary

Introduction

Water security is widely regarded as the key natural resource challenge facing humanity. The availability of water in the appropriate quantity (including avoiding scarcity and overabundance) with the appropriate quality and at the appropriate time for both human consumption and ecosystems is a basic requirement for sustainable development [1]. Ecosystems provide cultural, regulating and supporting services that contribute directly and indirectly to human well-being through recreation, scenic values and maintenance of fisheries [3]. Fresh water is a provisioning ecosystem service as it provides water for human use including domestic use, irrigation, power generation and transportation. Fresh water and the hydrological cycle sustain inland water ecosystems, including rivers, lakes and wetlands. Provisioning of fresh water plays a role in sustaining freshwater-dependent ecosystems such as mangroves, inter-tidal zones and estuaries, which provide another set of services to local communities and tourists alike [3]

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