Effects of Multi-Dike Protection Systems on Surface Water Quality in the Vietnamese Mekong Delta

Huynh Vuong Thu Minh,Tran Van Ty,Dat Quoc Tran,Md Mostafizur Rahman,Masaaki Kurasaki,Mitsuru Osaki,Kieu Ngoc Le,Ram Avtar

doi:10.3390/w11051010

Abstract

The Vietnamese Mekong Delta (VMD) is one of the largest rice-growing areas in Vietnam, and exports a huge amount of rice products to destinations around the world. Multi-dike protection systems have been built to prevent flooding, and have supported agricultural intensification since the early 1990s. Semi-dike and full-dike systems have been used to grow double and triple rice, respectively. Only a small number of studies have been conducted to evaluate the water quality in the VMD. This study aimed to analyze the spatiotemporal variation of water quality inside the dike-protected area. Surface water samples were collected in the dry and wet seasons at 35 locations. We used multivariate statistical analyses to examine various water quality parameters. The mean concentrations of COD, NH4+, NO3−, PO43−, EC, and turbidity were significantly higher in water samples inside the full-dike system than in water samples from outside the full-dike systems and inside the semi-dike systems in both seasons. High concentrations of PO43− were detected in most of the primary canals along which residential, tourist areas and local markets were settled. However, NO3− was mainly found to be higher in secondary canals, where chemical fertilizers were used for rice intensification inside the dike system. Water control infrastructures are useful for preventing flood hazards. However, this has an adverse effect on maintaining water quality in the study area.

Highlights

Water quality has become a major concern in the environmental debate [1,2,3,4], and about 80% of the world’s population currently faces the threat of water scarcity [2]
In the Vietnamese Mekong Delta (VMD), agricultural intensification has been applied for nearly 40 years to adapt to economic development and population growth
The results indicated that water quality in the dry season was significantly different from its quality in the wet season

Summary

Introduction

Water quality has become a major concern in the environmental debate [1,2,3,4], and about 80% of the world’s population currently faces the threat of water scarcity [2]. The intensification of agriculture has been implemented to meet the rising food demand in conjunction with the limitation of land due to excessive urban development [11,14]. In Southeast Asia, the irrigated rice system area accounts for more than 50% of the total agricultural area in Indonesia, the Philippines, and Vietnam, and rice intensification often results in more than one crop per year and accounts for 79.4% of the total area under rice cultivation [15]. In the VMD, agricultural intensification has been applied for nearly 40 years to adapt to economic development and population growth. The Renovation policies (a set of economic reforms aimed at moving the Vietnamese economy towards a market-based economy) issued by the Vietnamese government in 1986 have had a role in leading Vietnam to become one of the largest rice exporting countries in the world since the 2010s [17,18,19,20,21]

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Conclusion