Assessing the Impacts of Dike Systems on Water Quality in Natural Reserves of the Vietnamese Mekong Delta

Bui Thi Bich Lien,Pankaj Kumar,Tran Van Ty,Nguyen Thi Thanh Ngan,Tran Thi Kim Hong,Huynh Vuong Thu Minh,Ram Avtar,Trinh Trung Tri Dang

doi:10.3390/urbansci6010021

Abstract

Protected places such as nature reserves (NRs) are used to maintain ecological balance, biodiversity, and support surrounding ecosystems. However, the development and operation of infrastructure such as dikes and sluice gates in NRs, as seen in the Vietnamese Mekong Delta (VMD), often adversely affects the hydrological regime and water quality at both local and regional scales. This study analyzes the consequences of a constructed dike system on the hydrological regime and water quality in the NRs through an integrated approach including hydrochemical analysis (using descriptive statistics and weighted arithmetic water quality index (WAWQI) analysis), traditional interviews (face to face), using semi-structured questionnaires, field surveys, and secondary data. Results show that constructed infrastructure has helped maintain water supplies for both livelihoods and forest fire prevention. However, considerable impacts on the hydrological regime and water quality have occurred. From water quality assessments in three NRs, 29% of sampling sites in the My Phuoc melaleuca forest (MPMF) had WAWQI values over 100, while all sites in Lung Ngoc Hoang NR (LNHNR) and Mua Xuan Agriculture Center (MXAC) had WAWQI values over 100. This was to a large extent due to elevated concentration of chemical oxygen demand (COD), biological oxygen demand (BOD5), and phosphate (PO43−). Meanwhile, during the wet season, pollution was marginally reduced by dilution, with 42.86% of sites at Lung Ngoc Hoang NR, 28.57% of sites at MXAC, and 78.57% of sites at MPMF having WAWQI values of less than 100. These results show the issue of water pollution at spatio-temporal scales, and call for better holistic management options for improving the hydrological regime and water quality.

Highlights

The water resources of the Vietnamese Mekong Delta (VMD) are vulnerable to both anthropogenic and natural changes, affecting both the quantity and quality of the hydrological regime [1–3]
The water quantity was circulated throughout the wet season, but flow directions were problematic due to the geography, which included several intersecting canals
The construction of infrastructure has had a significant impact on the hydrological regime and degradation of the water quality due to water retention for firefighting and livelihood provision for the inhabitants

Summary

Introduction

The water resources of the Vietnamese Mekong Delta (VMD) are vulnerable to both anthropogenic and natural changes, affecting both the quantity and quality of the hydrological regime [1–3]. Recent socioeconomic development and transformation of the delta has resulted in increased agricultural and aquaculture production; increased pollution; urban sprawl; and a scarcity of human, financial, and technical resources, which in turn have led to poor governance and challenges to nature protection and biodiversity conservation efforts. The most recent climate change scenarios for Vietnam forecast a sea level rise of between 0.75 to 1 m by year 2100. This would inundate about 20–38% of the VMD, seriously affecting 27% of Vietnam’s listed critical natural habitats, 33% of protected areas, 23% of nationally and internationally important biodiversity sites, and 23 other important conservation sites. The LNHNR was formed with the objectives of safeguarding a habitat for different species, maintaining the ecological balance, maintaining and increasing forest cover, and safeguarding the sustainable development of the VMD [5]

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Conclusion