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Water use and competition in the Mekong Delta, Vietnam

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Abstract Safeguarding limited resources of water is a major challenge for sustainable food production. This study analyses water use and competition, identifies possible options to contribute to more efficient and equitable arrangements and gives recommendations to support policy-making for sustainable water resource management in agro-ecological zones within the Mekong delta. Rice farming and aquaculture development are recognised as major driving factors of water competition among water users in and between three major agro-ecological zones: (1) upper delta irrigated zone; (2) acid sulphate soil (ASS) zone; (3) downstream coastal zone. In the upper delta, intensive rice development abstracts a large quantity of freshwater and then results in salinity intrusion in the downstream delta during low flow periods of the Mekong River. Aquaculture expansion contributes to further water pollution in the downstream areas through flushing pond/cage effluents during water exchange. The reclamation of ASS for food production pollutes water in canals and shallow ground water by acidic substances, aluminium, iron and other heavy metals. In coastal zones, water has multiple values. Rice and shrimp development causes conflicts over water among crop and shrimp production, fishing and mangrove forests. Water access and sharing are determined by a wide range of local bio-physical and socio-economic settings and institutional aspects at household and community scale. Efficient and equitable arrangements of water use need both structural (technical) and non-structural (planning and institutional) solutions implemented at different spatial scales - from crop and field to community and regional levels. Water provides a range of goods and services, which greatly differ between users and locations. Possible options therefore need to consider the needs of all resource users at multiple scales rather than focusing on only one particular sector or scale. Strong evidence of water competition, however, is still inadequate in the Mekong delta. Further investigations are suggested to provide a clear picture of water conflicts, cause-effect relationships and guidelines to policy-makers and managers.
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143
Water Use and Competition in the Mekong Delta, Vietnam
Dang Kieu Nhan1, Nguyen Van Be2 and Nguyen Hieu Trung3
1Mekong Delta Development Research Institute, Can Tho University, Vietnam. Email: dknhan@ctu.edu.vn
2Department of Environment and Natural Resources Management, College of Agriculture and Applied Biology,
Can Tho University. Email: nvbe@ctu.edu.vn
3Department of Environmental Engineering and Water Resources, College of Technology, Can Tho University.
Email: nhtrung@ctu.edu.vn
Chapter 4:
Water Use and Competition in the Mekong Delta, Vietnam
c WWF-Canon/Elizabeth KEMF
144 Water Use and Competition in the Mekong Delta, Vietnam
4
Chapter 4 :
Water Use and Competition in the Mekong Delta, Vietnam
1. Introduction 146
2. Relevant issues to water-based competition 148
3. Current state of knowledge 152
3.1. Upstream-downstream water competition 152
3.1.1 Rising water use in rice farming 152
3.1.2 Salinity intrusion 154
3.1.3 Water use and effluent discharge in fish farming 156
3.1.4 Possible solutions and constraints 158
3.2 Impacts of the reclamation of acid sulphate soils 161
3.2.1 Current uses of acid sulphate soils 161
3.2.2 Water acidification and metal pollution 162
3.2.3 Possible solutions 166
3.3 Water conflicts in coastal zones 168
3.3.1 Multiple values of water and its associated livelihoods 168
3.3.2 Local and regional water conflicts 169
3.3.3 Possible solutions 170
3.4 Constraints to water access and sharing 172
4. Conclusions on the major issues to be addressed 173
4.1. Upstream-downstream water competition 173
4.2. Impacts of acid sulphate soil reclamation 174
4.3. Water conflicts in coastal zones 175
4.4. Constraints to water access and sharing 176
5. Contested issues 176
6. Research priorities 177
6.1. Crop and field levels 177
6.2. Zone and regional levels 177
7. Conclusion: Policy linkages 178
References 181
145
Water Use and Competition in the Mekong Delta, Vietnam
Abstract
Safeguarding limited resources of water is a major challenge for sustainable
food production. This study analyses water use and competition, identifies
possible options to contribute to more efficient and equitable arrangements
and gives recommendations to support policy-making for sustainable water
resource management in agro-ecological zones within the Mekong delta.
Rice farming and aquaculture development are recognised as major driving
factors of water competition among water users in and between three major
agro-ecological zones: (1) upper delta irrigated zone; (2) acid sulphate soil
(ASS) zone; (3) downstream coastal zone. In the upper delta, intensive rice
development abstracts a large quantity of freshwater and then results in
salinity intrusion in the downstream delta during low flow periods of
the Mekong River. Aquaculture expansion contributes to further water
pollution in the downstream areas through flushing pond/cage effluents
during water exchange. The reclamation of ASS for food production
pollutes water in canals and shallow ground water by acidic substances,
aluminium, iron and other heavy metals. In coastal zones, water has
multiple values. Rice and shrimp development causes conflicts over water
among crop and shrimp production, fishing and mangrove forests. Water
access and sharing are determined by a wide range of local bio-physical
and socio-economic settings and institutional aspects at household and
community scale. Efficient and equitable arrangements of water use need
both structural (technical) and non-structural (planning and institutional)
solutions implemented at different spatial scales - from crop and field to
community and regional levels. Water provides a range of goods and
services, which greatly differ between users and locations. Possible options
therefore need to consider the needs of all resource users at multiple scales
rather than focusing on only one particular sector or scale. Strong evidence
of water competition, however, is still inadequate in the Mekong delta.
Further investigations are suggested to provide a clear picture of water
conflicts, cause-effect relationships and guidelines to policy-makers and
managers.
146 Water Use and Competition in the Mekong Delta, Vietnam
1. Introduction
In the 21st century, Asian agriculture faces two major challenges: improving total food
productivity for food security and farmers’ welfare while safeguarding the
natural resource base, including water (Edwards, 1993; Cantrell, 2004; Bouman, 2007).
As rice is the staple food in Asia, the great challenge is how to increase the current
annual rice production from 545 million tons to more than 700 million tons to feed an
additional 1.3 billion rice consumers by 2025. This increase will mainly rely on
irrigated rice systems (Guerra et al, 1998; Cantrell, 2004). There are warnings that
food production is likely to be seriously constrained by freshwater shortages in the
next century. It is noted that the need for irrigation water is likely to be greater than
currently anticipated, and the available supply of it less than anticipated (Smith and
Gross, 1999). The available amount of water for irrigation, however, is becoming
increasingly scarce due to decreasing resources, declining water quality and
increasing competition among multiple water users and environmental factors in some
Asian countries, including Vietnam (FAO/NACA, 1995; Pimentel et al, 2004;
Rijsberman, 2006).
In the Vietnamese Mekong delta, soil and hydrology are the major physical factors
determining agricultural land use. Combined local rainfall and seasonal discharges of
the Mekong River cause seasonal and spatial variations in water availability within
the delta. The upper region is subjected to prolonged and deep flooding in the wet
season coinciding with the high flow period, while the coastal region downstream
faces freshwater scarcity and salinity intrusion in the dry season during the low
flow period (February-April). In 2004, about 74% of the delta surface was devoted
to agriculture, and rice farming constituted about 70% of agricultural land
(CSO, 2005). Over time, agriculture and aquaculture have shifted from subsistence-to
market-orientated production and progressively intensified. Intensive rice culture
expanded during the 1990s and is still the principal farming activity (Figure 1). Most
rice growing areas are irrigated with about 80% of the total surface water volume
diverted for agriculture uses, mostly rice, while only 5% is devoted to domestic
consumption (White, 2002). Recognising the potential of aquaculture (as discussed
by Loc et al and Can et al in this volume), since 1999 the Vietnamese government has
promoted diversification in agriculture, aiming to increase the contribution of
aquaculture to economic growth (Nhan et al, 2007a). Between 1999 and 2004, the
growth rate of aquaculture production was rapid, annual growth rates of 31% for
production and only 19% for farming areas (GSO, 2003; GSO, 2005) suggesting a
gradual intensification of aquaculture. Coastal shrimp farming and intensive fish
culture upstream have been the main drivers of this expansion of aquaculture
production, but there are indications that this growth is not sustainable globally (Naylor
147
Water Use and Competition in the Mekong Delta, Vietnam
et al, 2000) nor regionally (see Loc et al., this volume). Intensive rice farming and
aquaculture practices are both water-intensive (Boyd and Gross, 2000; Cantrell, 2004;
Tuong et al, 2005). Sustainable rice culture and aquaculture should be water-efficient.
These farming sectors have to meet increasing demands for food supplies and income
generation.
As demands and competition over water and related resources has increased, the
spectre of conflict has emerged. In this context conflict is understood as interest
incompatibility or livelihood loss among various water users as a result of access to
water of inadequate quantity and quality (Ohlsson, 1995; Smith and Gross, 1999).
Two levels of conflict are international and within the country. In the Vietnamese
Mekong delta conflict is identified mainly on the latter scale, community or region.
Rivers and canals serve as both water supply and drainage, with the former function
more important in the dry season while the latter is dominant in the wet season.
Numerous studies have reported water conflicts in rice farming and aquaculture
practices in irrigated, acid sulphate soil or coastal zones. The water conflicts relate to
intensive water abstraction for rice farming in the upper delta (Tin and Ghassemi,1999;
Hashimoto, 2001), effluent discharges from aquaculture farming (Nhan and Be, 2005;
Nhan et al, 2006), acidity and metals released from land reclamation in acid sulphate
Figure 1: Changes in land use between 1990 and 2004 in the Mekong delta. Total agricultural
land was expressed as the surface area, while areas devoted to rice, upland crops, fruit
and aquaculture were based on growing areas. For HYR rice growing, 2 or 3 crops of rice are
practiced per year Key: DS (dry season), WS (wet season), HYR (high yielding rice), TR
(traditional rice).
(Source: Adapted from Nhan et al, 2007a).
148 Water Use and Competition in the Mekong Delta, Vietnam
soil zones (Minh et al, 1997), and water conflicts among crop culture, shrimp
farming, mangrove forests and fishing in coastal zones (Tuong et al, 2003; Binh et al,
2005; Trung, 2006). Policies and infrastructure investments of the State and local
government have encouraged intensification of agriculture and aquaculture, but the
tensions between different water users and environmental impacts have not received
sufficient attention. In the Mekong delta, rice farming and aquaculture will remain
important for food production and economic development. Combined increases in
urbanisation and industrialisation, as well as further agricultural intensification is likely
to contribute to greater socio-economic differentiation and water conflicts unless careful
attention is given to sustainable water resources management. Moreover, the
Vietnamese Mekong delta is characterised as being at high risk to water-related
natural disasters, due to the pressure from population growth and accumulative
impacts of upstream interventions for irrigation and hydropower schemes in the Mekong
Basin (Kristensen, 2001; White, 2002; Miller, 2003; Molle, 2005). Negative impacts
of the development interventions schemes might contribute to changes in the
flood regime, a reduction in dry season flows, an increase in water pollution, and
changes in sedimentation. Appropriate solutions therefore need to be realised to
improve productivity of production systems while safeguarding the environment and
ensuring more equitable arrangements for water access among water users in order
to reduce the vulnerability of the delta’s inhabitants.
This study is based on a complete review of existing knowledge and information. This
paper analyses water conflicts among water users and identifies possible options to
contribute to more efficient and equitable arrangements in agro-ecological zones in
the delta. Special attention is paid to impacts of the water use of the current rice
farming and aquaculture practices. Further investigations and recommendations are
suggested to support policy-making for sustainable water resources management in
the delta.
2. Relevant issues to water-based competition
Impacts of the current intensive rice and aquaculture farming systems and
institutional constraints on water access and sharing among different water users were
identified in the three major agro-ecological zones of the Mekong delta: (1) upper
delta irrigated zone, (2) acid sulphate soil (ASS) zone and (3) downstream coastal
zone. Possible solutions and constraints were analysed in specific contexts for policy
recommendations. In the study zones, rice and aquaculture farming systems are
important activities and people’s livelihoods are highly vulnerable to natural
water-related problems, whether due to changes in quality or quantity. Surface water
149
Water Use and Competition in the Mekong Delta, Vietnam
is the focus of this paper because of its importance to Mekong delta people’s
lives, and increasing competition for its use within the delta. In addition, surface
water is a transboundary resource and has a strong link with hydrology and
development project interventions in upstream parts of the Mekong River. Therefore,
understanding surface water uses in the study zones are of great importance for policy
considerations to sustainable water resources not only within the Vietnamese Mekong
delta but also the Mekong River Basin.
The overall question guiding this study is: based on a comprehensive review of
the state-of knowledge on water, how are recommendations made to support
policy-making to contribute to more efficient and equitable arrangements of water
sharing in the study zones as well as the delta as a whole, in terms of economic,
environmental and social welfare aspects? The study considers water conflicts
between upstream and downstream areas, impacts of ASS reclamation for agriculture
and recent aquaculture, competition among multi-values of water within the coastal
zone, and common constraints to water access existing in the study zones. These
issues were identified by the authors as priority concerns affecting sustainable water
resources management in the delta. To answer the questions, six major issues are
raised as follows:
First, what evidence exists for a rise in competition between upstream and
downstream water uses in the delta? State and local policies and infrastructure
investments for intensification of agriculture, including aquaculture, in the upper delta
have resulted in positive impacts on food production and economic development, but
contributed to an increase in tensions of water conflicts within and between users and
zones. Intensification of high-yielding rice varieties with double and triple cropping
ensures national and household food security and improvements in rice farmer
income. Intensive rice culture, however, requires heavy application of agro-chemicals
and a large amount of fresh water for irrigation (Berg, 2002; Cantrell, 2004). Rice
farming that is practised during the dry season consumes a lot of water. Intensive
abstraction of water for the rice farming in the upper delta might also exacerbate
salinity intrusion downstream of the delta during low flow periods of the Mekong
River, which in turn has negative consequences on agriculture and aquaculture,
domestic water supplies and the environment (Sam, 1997; Hashimoto, 2001). For
aquaculture, semi-intensive and intensive farming systems consume a large volume
of water through water exchange in order to dilute metabolites within ponds or cages
(Nhan et al, 2007a,b). Consequently, the farming practices discharge a large quantity
of effluents, which might eutrophy surface water bodies in surrounding and
downstream areas, in turn constraining fish culture, domestic water supplies and
environment protection.
150 Water Use and Competition in the Mekong Delta, Vietnam
Second, what are the impacts of acid sulphate soil reclamation and to what extent do
impacts still continue? The reclamation of acid sulphate soils, particularly in the Plain
of Reeds, the Long Xuyen Quadrangle and the Ca Mau peninsula since 1975,
has significantly contributed to increased food production and improved farmers’
livelihoods at the expense of surface water pollution of acidity and heavy metals (mainly
aluminium and iron), due to the oxidation of the sulphidic layer as the water table falls
(Minh et al, 1997; Husson, et al, 2000). Water pollution poses adverse effects on
aquatic organisms, aquaculture practices, potential risks to human health and
estuarine ecosystems when the early rains wash out toxic substances from fields into
drainage canals (Minh et al, 1997; Nhe, 2006). Some studies indicate that the level of
acidity does decline with water flushing of fields after an initial peak, but the impacts
can remain for decades (Husson, et al, 2000). Trade-offs exist between improved soil
fertility and enhanced crop productivity on the one hand and the environmental and
social impacts on the other. So, benefits may be accrued privately yet the costs are
dispersed to all, harming common natural resources.
Third, what are the land and water conflicts identified in the coastal zone and how
have the conflicts been addressed at a local and regional level? Have these conflicts
been successfully resolved, and if so how? The coastal zone is a highly vulnerable
agro-ecosystem, and water has multiple values for crop and shrimp production,
fishing and mangrove forests. On the one hand, crop farming - a freshwater farming
activity, shrimp culture - a brackish water farming, and the wetland ecosystem
require different land and water resources, making water resource management more
complex (Gowing et al, 2006). Water competition depends highly on the water use in
the upper delta, within the zone and the process of salinity intrusion. Salinity-control
infrastructure was developed intentionally for rice farming, but presently attempts to
adapt it for use by both rice and shrimp farming concurrently have occurred. A proper
operation of this infrastructure for both purposes, agriculture and aquaculture, is not
an easy task. More saline water taken in for shrimp farming results in losses of crop
production in immediate communities or in upper parts of the river basin. In contrast,
shrimp farming might suffer from fresh water diverted and field water discharges
from crop production areas. On the other hand, the development of shrimp farming
has resulted in significant losses of coastal mangrove forests, resulting in declined
aquatic resources, on which livelihoods of the poor depend (Binh et al, 2005). Local
authorities are confronting the challenge in order to achieve a compromise between
agriculture and aquaculture. Nonetheless, development of aquaculture or agriculture
is likely to impact adversely on the ecosystems. In the coastal zone, development
plans for water resources were formulated at zonal level whereas water conflicts have
to now be resolved at local community scale. Information on those conflicts and
scenarios for further improvements at community and regional scales are still limited.
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Water Use and Competition in the Mekong Delta, Vietnam
Fourth, what are factors that affect the equity and efficiency of water access? A wide
range of local bio-physical and socio-economic settings and institutional aspects
affecting water access have been recognized at household and community scale
(Miller, 2003). Socio-economic and individual cooperation play an important role
in water access at household level while coordination and participation of all local
stakeholders, including authorities, are crucial at the community level. Participatory
approaches, and good planning, coordination and regulation of local authorities are
necessary, and contribute to greater equities in water access not only at the individual
household level but also at the community level.
Fifth, what are principles on which potential solutions are suggested in order to
reduce water competition among water users while improving rice and aquaculture
productivity to meet food security, economic growth and environmental
conservation? The major challenge for rice farming and aquaculture is how to
increase productivity with less water use and rational discharge rates. Possible
solutions include technical, planning and institutional principles at different scales;
from crop, field to community and regional levels. For technical principles, the
potential solutions can be identified by improving technology components and
farming diversification to reduce water competition. In general, there are four major
principles: (1) reducing non-beneficial depletion of water, (2) reducing water discharges,
(3) maximising non-irrigation water inflow, and (4) using water from the storage
effectively (Tuong et al, 2005; Bouman, 2007). Technological measures include crop
variety selection (crop level), cropping technology, crop diversification and resource
management practices (field and community level). For planning principles, at the
community and regional level, water provides a wide range of goods and services.
Different communities or regions have different options for using water to achieve
different social, economic and environmental goals. Possible solutions therefore need
to consider the needs of all resource users at multiple scales rather than focusing on
only one particular scale. For institutional measures, participatory and bottom-up
approaches, dialogue among various local stakeholders and their participation in
decision-making, are required to support well-informed planning, management and
policy options to ensure equities in water access and sharing. Participatory structures
and the extent to which water use equity is based on these are important because of the
need to represent and respond to local interests and needs.
Finally, what are the research and development gaps? Constraints for the potential
solutions are identified. Further investigations are suggested to provide a clear picture
of water conflicts, cause-effect relationships and guidelines to policy-makers and
managers.
152 Water Use and Competition in the Mekong Delta, Vietnam
3. Current state of knowledge
In this section we outline the state of knowledge on the three key axes of competition
over water: between upstream and downstream areas; impacts of reclamation of acid
sulphate soil areas; and, in the coastal zone. In each section, after the issue is
described, potential ways forward to address the problem are introduced.
3.1. Upstream-downstream water competition
3.1.1 Rising water use in rice farming
Intensive-rice growing areas are mainly located in upstream and mid-stream
provinces. During 2000 and 2004, the upper provinces Long An, Tien Giang, Dong
Thap, An Giang, Kien Giang, Can Tho, Vinh Long and Hau Giang shared an average
of 85% in the dry season crop and 73% in the wet season crop of the total rice farming
area and productivity in the delta (CSO, 2005). Rice is mainly grown with two or three
crops a year (CSO, 2005; Figure 2). The double rice farming pattern is practiced
with high-yielding rice in the dry season crop plus the wet season crop in the
irrigated or flood-prone areas, while the wet season crop plus traditional rice
crop occurs in rain-fed areas. The triple rice farming is mainly practiced in areas
with well-developed irrigation systems or well-controlled flood systems.
Intensification of rice production systems is highly reliant on water availability, as
well as access to other key inputs (fertilizers, pesticides, seed, labour, etc.). Intensive
rice farming consumes a large volume of water during the dry season. The specific
water requirements of different cropping regimes in the delta are shown in Table 1,
and discussed further in section 3.1.4.
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Water Use and Competition in the Mekong Delta, Vietnam
There is limited information on actual water demands per crop and the following is
based on total water requirement and analysis of rainfall. Water productivity
is estimated at about 0.8 and 1.2 kg rice m-3 water input from irrigation for the
winter-spring and the summer-autumn crops, respectively. These figures are in the
range of the water productivity of continuous flooding rice farming but are much lower
than that obtained from water-saving irrigation techniques (1.6-1.9 kg rice m-3 water
input) in other tropical countries in Asia (Bouman and Tuong, 2001; Tuong et al,
2005). The water productivity of rice farming greatly varies with rice variety, growth
duration, soil and hydrological conditions and farming practices (Bouman and Tuong,
2001). There is still room for further water efficiency improvements of rice irrigation
in the Mekong delta.
Figure 2: Monthly rainfall and cropping calendar of double- or triple-rice
farming patterns in the Mekong delta. (Source: Reproduced from CSO, 2005)
Table 1: Estimated water productivity (kg rice m-3 water input) of rice production in the Mekong delta.
Based on average rainfall and cropping seasons given in Figure 2 and calculated as kg rice per m3 water
input from irrigation
154 Water Use and Competition in the Mekong Delta, Vietnam
Water requirement for rice greatly varies with cropping calendars, cropping patterns
and areas. The earlier the wet season rice crop is established, the more water is
required to irrigate the rice during early periods of the crop (see Figure 2). In the
early stages of the wet season rice crop, rainfall is low and field water losses through
evapo-transpiration and percolation are significant, due to high air temperature, deep
levels of the water table and soil cracks during field drying after the dry season crop.
Therefore, rice cultivation consumes more water in the triple cropping than in the
double cropping patterns. Sam (1997) estimated that the water requirement to irrigate
the rice averages about 1470 mm in the upstream area (i.e. An Giang) and about 1060
mm in the central part (i.e. Can Tho). The water requirement is higher in the upstream
area, due to the early establishment of the wet season crop and deep levels of the
groundwater table. In the upstream provinces, rice irrigation is practiced by pumping
mostly and irrigation costs share an average of 8% and 10% of the total input costs of
the 1st wet season and the dry season crops, respectively (Nhan, unpublished data in
2000 and 2006). On the contrary, in the mid-stream provinces (i.e. Vinh Long), the
irrigation is practiced mainly with gravity through the tidal effect from the estuary,
making irrigation costs much lower.
Based on rice growing areas, irrigation requirements of the dry season and 1st wet
season crops and rainfall records in 2004 (i.e. Figure 2 and Table 1), it is estimated
that rice cultivation in the upper provinces can abstract a water volume between 900
and 1,200 m3 s-1 from December to May. This water consumption by rice farming
equals about one-half of flow rates of the Mekong during the dry season within
Vietnam (Tin and Ghassemi, 1999). Water abstraction is greater if triple rice
cropping is expanded and the wet season crop is established as soon as possible to
avoid possible crop damages from flooding. Sam (1997) calculated irrigation water
requirement for the whole Mekong delta to be about 400-900 m3 s-1 in 1990-1991
period, and predicted an increase demand of 900-1,100 m3 s-1 by 2010. The intensive
water demands in the upper and mid delta have implications for dry season water
availability and related salinity intrusion in the coastal zone - a clear trade-off occurs
between expansion of dry season rice production upstream and downstream impacts
of salinity. This suggests that monitoring impacts of water extraction for rice farming
in the dry season and appropriate solutions to improve water use efficiency in rice
culture need to be considered.
3.1.2 Salinity intrusion
The intensive agriculture and coastal aquaculture development strategy pursued in the
delta, reliant upon the provision of reliable and sufficient dry season flows, has made
the delta increasingly vulnerable to a decline in dry season water flows and salinity
intrusion. The salinity intrusion in the downstream part is a function of the discharge
from the upstream of the Mekong River, tidal effects in the South China Sea and the
Gulf of Thailand, surface water storages in the Tonle Sap, on river/canal systems and
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Water Use and Competition in the Mekong Delta, Vietnam
backswamps within the delta, irrigation canal systems, coastal water-management
infrastructure (i.e. canals, salinity-control dikes and sluice gates), morphology and
coastal land uses. Over 85 % of the total annual discharge occurs during the flood
season (Tin and Ghassemi, 1999), while in April the discharge of the Mekong river
branches is less than 10% of the discharge in October (Wassmann et al, 2004). During
the dry season, the low river flow period, the tidal influence extends throughout most
of the delta. Seawater enters distributaries and intrudes into a range of 40-60 km
upstream (Figure 3) (Wolanski et al, 1998). About 2.1 million ha was affected by
saline water of 1 g l-1 and about 1.7 million ha of 4 g l-1 (Sam, 2006).
Economical and ecological consequences of extended salinity intrusion are:
insufficient freshwater for agricultural production and domestic water supplies,
damaging the aquatic ecosystem and threatening bio-diversity. When such ecological
changes occur, livelihoods of downstream communities are adversely affected,
sometimes leading to conflicts. In estuaries on the east and west coasts and in Vam Co
rivers during 1992-2004, the salinity was observed to be high in 1998, 2004, 1992,
1993 and 1995, and low in 2000, 2002 and 2003 (Sam, 2006). In 1998, the extent of
salinity intrusion was high, 10-15 km further inland than the average for previous years,
because of a serious drought in the region (Miller, 2003). Dry season rice
expansions in the Plain of Reeds probably resulted in an increase in salinity intrusion in
the Mekong and Vam Co rivers for the period 1977-1982 compared with the
1936-1940 period (Hoanh, 1987). In the 1990s, there was a trend of increasing salinity
intrusion up the West Vam Co system and canals connecting the Bassac river with the
western delta part (Truong, 1999). This spatial pattern of salinity intrusion is more
Figure 3: Average maximum distance (km) of salinity intrusion (4 ppm) up Mekong and
Bassac branches in April (Source: Reproduced from Miller, 2003).
156 Water Use and Competition in the Mekong Delta, Vietnam
severe up smaller canals than in the main branches of the Mekong and Bassac rivers
and is likely to accompany water resources development and a reduction in low flow
(cited in Miller, 2003).
Rice intensification in the upper delta could increase the extent and the severity of the
salinity intrusion in the downstream part, due to significant decrease in the river flows
(Miller, 2003). In the past, flood water maintained in backswamp areas supplemented
freshwater flow in main canals during the early dry season. For the last three decades,
the development of canal systems and the expansion and intensification of the rice
culture have reduced the flood-plain water storage, particularly in the Plain of Reeds
and the Long Xuyen Quadrangle, while increasing the abstraction of the discharge in
the upstream areas. Consequently, the discharge of main rivers and canals decreased,
and hence saline water intruded further into many parts of the delta downstream
(Hashimoto, 2001). This could increase the duration and extent of saline intrusion.
Since the 1980s, salinity intrusion in canals or rivers of the Bassac and Mekong has
generally increased in duration (Tin and Ghassemi, 1999). The salinity intrusion into
the upstream is likely severe as the construction of new water-control structures,
population growth, urbanisation and industrialisation will continue in the future
(Hashimoto, 2001). Non-structural options are of great importance to ensure river
flows are not further lowered and to make use of saline water efficiently through
agricultural diversification and strengthened awareness of risks.
Salinity intrusion is not only influenced by processes within Vietnam, but also wider
global climate changes and Basin water resources developments. Sea water rise and
interventions in upstream countries are likely determinants. A rise of sea water level has
already been observed along many shore lines in Southeast Asia, including
Vietnam (Perez et al, 1996; Tuong, 2001). Combining intensive water withdrawal for
agricultural irrigation in upstreams, a rise of the sea level might have an impact on
salinity intrusion in the Mekong delta during the lowest flow periods. A further and
growing threat is posed by ambitious schemes of dam and reservoir construction in the
catchment upstream of the delta (Lang, 2005). The Tonle Sap in Cambodia plays an
important role in the natural regulation of the river flow. An example of this threat is
that an estimated average of monthly dry season flows (February- April) into the delta,
in the absence of mainstream storage dams, would decrease by 37 per cent if dry
season irrigation is expanded in upstream countries (cited in Miller, 2003).
3.1.3 Water use and effluent discharge in fish farming
As discussed in other papers in this monograph the government has more recently
promoted diversification to improve farmer incomes in the delta. Part of this strategy
has been the promotion of fish farming. However, as with intensive rice production,
fish farming has impacts on water, but these impacts are on water quality rather than
quantity.
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Water Use and Competition in the Mekong Delta, Vietnam
Access to high quality water and minimising effluent discharges is a key principle
(and challenge) for sustainable aquaculture development in the Mekong delta. In
freshwater areas, four major aquaculture systems are practised: (1) intensive cage/pen
culture, (2) intensive pond culture, (3) semi-intensive pond culture, and (4) extensive
or semi-intensive aquaculture integrated with rice culture systems (Nhan et al, 2004).
Aquaculture is commonly practised in upper provinces and unlike rice farming,
aquaculture systems do not “consume” water but pollute surface water bodies. Except
for aquaculture integrated with rice farming (with low nutrient inputs and low water
exchange rates) other systems have an impact on the aquatic environment from
intensive water use and high rates of effluent discharge (Nhan and Be, 2005; Son et al,
2005; Hao, 2006; Nhan et al, 2006; Nhan et al, 2007a,b). This constrains the use of
water for intensive aquaculture systems themselves and limits domestic consumption
locally and downstream.
In general, farmers use water lavishly in aquaculture. Cage and pen culture systems can
be considered as flow-through systems (Son et al, 2005). Semi-intensive and
intensive pond farming systems are practised with high water exchange rates. The
water exchange rate practised increases with increasing intensification levels of the
pond to avoid water quality deterioration within the pond through high discharge rates
of nutrient-rich effluents (Figure 4) (Nhan et al, 2007b). In the pond aquaculture
systems, the intentionally regulated inflow or outflow usually accounts for about 80%
(in extensive and semi-intensive systems) and 98% (in intensive systems) of the total
inflow or outflow water of the pond. Nhan et al (2006) observed that in semi-intensive
systems, about 1.5 times more nitrogen and organic carbon, and 3.1 times more
phosphorus were discharged than the amounts received through inflowing water. Only
about 11% food nitrogen input is recovered in fish and about 30% is discharged through
the pond into surrounding canals (Nhan et al, 2007a). Unnecessary loss of pond
nutrients as a result of high water exchange rates could reduce economic benefits to
farmers while causing eutrophication in downstream ecosystems. This problem might
result in “water scarcity” for aquaculture, industrialisation and domestic water
supplies. For example, in An Giang province in 2006, the number of catfish
(Pangasianodon hypophthalmus) cages reduced by about 40% compared with that in
2005, while catfish pond culture, where water intake for ponds was easier controlled,
was expanded. One of major reasons is the increased pollution of the Mekong and
Bassac river water. In the Mekong delta in 2005, about 5,000 ha were devoted to
catfish pond culture, annually producing about 370,000 tons of fish, which was 4 times
higher than that in 1997 (unpublished data). To 2010, this type of aquaculture is planned
to expand to 10,200 ha, annually producing about 850,000 tons of fish. It is estimated
that an average of 20 per cent of food nitrogen input is recovered in fish and about 45
per cent is flushed out to surrounding canals (Nhan, unpublished data). Based on this
estimation, in 2005 about 13,300 tons of nitrogen and in 2010 about 30,600 tons of
nitrogen would be flushed into surrounding rivers through pond water
exchange. Therefore, proper management of effluent discharges from the aquaculture
158 Water Use and Competition in the Mekong Delta, Vietnam
farming practices could not only optimise nutrient use efficiency and economic
benefits, but also improve farming sustainability and reduce water competition
among users.
3.1.4 Possible solutions and constraints
On a global scale, the Challenge Program on Water and Food, coordinated by the
Consultative Group on International Agricultural Research (CGIAR), recognises that
increasing competition from different water users is creating an urgent need to
improve water productivity of agricultural production (Cantrell, 2004). In the delta,
increasing water productivity while retaining high incomes is identified as an
important challenge that needs to be given special attention in order to alleviate water
upstream-downstream competition. Water productivity is expressed as the ratio of
food output derived from water use to water input. Water productivity can be increased
Figure 4: Pond water inflows and outflows of freshwater
aquaculture systems in the Mekong delta
(Source: Nhan, unpublished data)
159
Water Use and Competition in the Mekong Delta, Vietnam
by producing more output per unit of water used or by reducing water losses (or
discharges), or by a combination of both.
For rice farming, in general, there are four major principles contributing to improving
water productivity (see section 2). There are several strategies and technologies or a
combination of them for increasing water productivity. For irrigated rice farming,
several water saving techniques have been reported and the potential for water savings
is substantial (Bouman and Tuong, 2001; Belder et al, 2004; Tuong et al, 2005; Bouman,
2007). Possible solutions are:
Appropriate variety selection and good crop husbandry that allow reduce
water consumption. Rice varieties with high harvest-indexes, short-growth duration
and good seedling vigour should be grown (Bouman, 2007).
Land preparation period should be short to reduce water loss through
evaporation and percolation (Bouman, 2007).
Alternative wetting and drying irrigation methods, which reduce the
duration that the field is flooded, would be advisable (refer to Belder et al 2004 for
description of this practice in China, and Tabbal et al, 2002 for Philippines example).
Soil mulching has also been shown to reduce water inputs and increase water
productivity in rice, especially in combination with the alternative wetting and drying
technique (cited in Tuong et al, 2005).
Choosing the appropriate cropping season in order to maximise use of
available soil water storage and rain water (Tuong et al, 2005). In the Mekong delta,
for example, if the summer-autumn crop is established at an appropriate time, the rice
crop can use rainfall more effectively than the commonly-practised method, which
could abstract less fresh water diverted during low flow periods.
Integrating rice-based farming systems with upland crops, as total water
requirements for many upland crops are lower than rice (Sam, 1997). During low
water flow periods, appropriate upland crops instead of rice could be practised.
Water pricing could be an option (Fujimoto and Tomosho, 2003). Although
water pricing has not been commonly applied for agriculture in the delta, it could be
a possible solution to encourage farmers to adopt water conservation techniques.
The above proposed measures for increasing water productivity in rice farming,
however, face challenges. The methods for reducing non-beneficial depletion and
outflows of water are labour- or cost-intensive (Tuong et al, 2005). The alternative
wetting and drying or keeping soil saturation techniques is likely to result in a
reduction of rice yields (Bouman and Tuong, 2001; Tuong et al, 2005). Changes from
flooded to partially aerobic soil conditions could result in the occurrence of weeds or
grass in the field (Singh et al, 2003), in losses of phosphorus and nitrogen (Muirhead et
al, 1989), in increased nitrous oxide, a greenhouse gas, and in nitrate leaching into
groundwater (Dittert et al, 2002).
160 Water Use and Competition in the Mekong Delta, Vietnam
In the Mekong delta rice farming is small-scale, crop performance and water
requirement differ from field to field, water saving techniques are likely not feasible
at large-scales, unless the production is well-organised within a community or a zone.
The most widely used irrigation cost system is commonly based on growing area per
crop, sharing only about 9% of the total production costs (Nhan, unpublished data),
which seems not to encourage farmers to apply water saving techniques. A system
that is based on “water volume supplied” instead needs to be considered. Moreover,
the harvest of the summer-autumn crop is highly vulnerable to floods. A delay of the
crop establishment could increase the use of available rainwater and reduce
freshwater consumption during the low flow periods at the expense of harvest
losses by flooding. Therefore, the choice obviously depends on the economic
effectiveness of the strategies. Soil type, labour cost and availabilit, existing
irrigation infrastructure and markets for crop inputs and outputs are important factors.
Possible solutions at a broader scale rather than at the field level therefore are likely to
be more feasible and needs to be discussed with the appropriate stakeholders.
Unlike in rice farming, in aquaculture further improving fish yields or aquaculture
incomes while minimizing effluent discharges is of great importance. Practically,
flushing of ponds/cages with “clean” water from the river results in pollution of
surrounding surface waters and a loss of nutrients, which otherwise could have been
used for other products. “Ecological or sustainable aquaculture”, a new paradigm for
aquaculture development, is therefore necessary in the near future as the following
indicate (Costa-Pierce, 2002; Frankic and Hershner, 2003):
Proper fish species combinations and stocking rates to allow for high yields
and stimulate a healthy pond ecosystem (Delince, 1992).
Pond (cage) nutrient-rich effluents can be re-used to produce an extra crop of
fish, terrestrial or aquatic plants before discharge (Beveridge et al, 1997; McMurtry
et al, 1997; Naylor et al, 2000; Yi et al, 2003). Fish or plants can extract nutrients from
wastewaters while producing more food for human, fish or livestock. Although this
proposed system looks promising, it has not been commonly practised by farmers in
the delta. In contrast, the production of aquatic vegetables using wastewater is
well established on the urban fringes of Ho Chi Minh City and other urban centers
of Southeast Asia (Rigg and Salamanca, 2004). One possible reason is that a
wastewater-fed wetland system consumes land at the expense of other more profitable
or less risky farming activities. If applied, such approach could create more jobs, food
and income for the poor and reduce environmental impacts.
The maximum allowable amount of pond/cage effluent discharged needs to
be determined. This depends on many factors, including the density of ponds/cages,
distribution patterns and the absorptive capacity of the surrounding environment.
161
Water Use and Competition in the Mekong Delta, Vietnam
Water pricing or polluter pay policies are possible options, but they are
difficult to impose, especially with small-scale and resource-poor farmers.
Like in rice farming, the proposed measures for reducing effluent discharges of
aquaculture still face difficulties. Current aquaculture farming is mostly practised on a
small-scale and in diverse forms. The proposed measures should be considered not
only at a farm level but at larger scales.
3.2 Impacts of the reclamation of acid sulphate soils
3.2.1 Current uses of acid sulphate soils
Acid sulphate soils are a particular problem in newly formed riverine landscapes
at the interface with the sea. Overall, in the Mekong delta acid suphate soils have
implications for water competition because acidity and metals released from the soil
results in negative impacts on natural aquatic resources, agriculture and aquaculture
and domestic water supplies downstream. Much has been written on acid sulphate
soils, however, few authors have discussed this problem from the perspective of water
competition or conflict.
Since the late 1970s, most of acid sulphate soil areas have been converted into
agricultural areas, especially rice cropping, increasing the portion of actual acidic soils
significantly. The acid sulphate soil zone, including the Long Xuyen Quadrangle, the
Plain of Reeds and the Ca Mau Peninsula, are mostly located in low-lying backswamp
areas far from main distributaries. The conversion of acidic soil low-lying backswamps
into agricultural and aquaculture areas was encouraged by extensive development of
canal systems and human settlement in combination with improved cropping
practices. Consequently, larger areas of actual acidic soils are formed. In 2005, about
60% total surface area in the Long Xuyen Quadrangle and 80% in the Plain of Reeds
and the Ca Mau Peninsula were devoted to agricultural and forestry activities (Figure
5a). Most of the agricultural land was used for rice farming, accounting for 74-81%,
and a small portion for forestry, sharing 12-20% (Figure 5b). Upland crop and fruit
production are not important activities in acid sulphate soil zones. Recently, in coastal
regions of the Long Xuyen Quadrangle and the Ca Mau Peninsula, a large portion of
rice growing areas has been converted into coastal shrimp farming. Between 2000 and
2005, the rice growing area decreased by 35% in Bac Lieu and 56% in Ca Mau
province, while the coastal shrimp culture area increased by 184% and 62% in the
respective provinces. During the same period in Kien Giang province, rice growing
area increased by 10%, while the shrimp culture area increased five-fold (CSO, 2006).
162 Water Use and Competition in the Mekong Delta, Vietnam
3.2.2 Water acidification and metal pollution
An important impact of actual acidic soils is the acidification of soils and water bodies
(Tin and Wilander, 1995). The potential acidic soils becomes actual acidic soils when it
is exposed to oxygen through a fall in water table during the dry season, deeper
drainage of land, increased evaporation soil surfaces or canal excavation (Hashimoto,
2001). The acidification of soil and water results in the increased mobility of potential
metals (i.e. iron, manganese, aluminium, arsenic, cadmium, etc.). When the flood
recedes, the acidic substances and the metals are drained from fields into drainage canal
systems. As a result, pH values in secondary canals suddenly drop (from 6 to less than
3.5) and metal concentrations increase (Husson et al, 2000b). During the dry season,
the soils dry out and cracks form, resulting in oxygen penetrating to deeper layers and
the oxidation of pyrite occurring. The evaporation results in acidic substances and
metals moving upward through capillary action and concentrating at the surface (Minh
et al, 1998). At the beginning of the rainy season (April-May), first rains can reduce the
soil acidity or metals accumulating during the dry season to some extents, by leaching
acidic products into field ditches. In May-June, the following heavy rains continue to
flush a large quantity of acidic water with high concentrations of metals to irrigation/
drainage canals (Tin and Wilander, 1995). As the rainy season progresses, the quantity
of acidity flushed decreases gradually. In addition, farming practices also flush acidity
Figure 5: Relative percentages of (a) agricultural land and (b) of crops,
aquaculture and forestry (b) in some of the districts located in the major
areas of acid sulphate soils. Moc Hoa, Vinh Hung and Tan Hung districts
of Long An (the Plain of Reeds), Tri Ton of An Giang and Kien Luong of
Kien Giang (the Long Xuyen Quadrangle), An Minh and Vinh Thuan of
Kien Giang (the Ca Mau Peninsula). Key: UC (upland crops).
(Source: Reproduced from provincial and district statistics, 2005)
163
Water Use and Competition in the Mekong Delta, Vietnam
and metals from the field to canal water in order to prevent crop losses (Husson et al
2000a). These processes result in acidification and pollution of surface water bodies,
detrimental to domestic water supplies, crop and aquaculture farming practices,
and aquatic ecosystems in surrounding and downstream parts. Such
degradation of water quality and aquatic ecosystems has serious consequences for
resource-poor households, who depend more on open-access aquatic resources than
better-off households with land for economic production. The impacts can last for
many years (Husson et al 2000b).
Recent studies have provided evidence of impacts of acidic soil reclamation on
surface water acidification. Husson et al (2000a) observed that pH values of the
surface water are usually lower than 5 during the rainy season in the Plain of Reeds.
Studying on quality of canal and shallow ground water in the Long Xuyen
Quadrangle during May and July, Hoa et al (2006) and Nhe (2006) found that water
pH values were below 4 in actual acid soils compared with above 6 in potential acidic
and alluvial soils (Figure 6). pH values in canal water decrease in this order: primary
canal > secondary > tertiary > ground table water; they are above 5 in primary canals
while this is below 5 in secondary and tertiary canals, and below 4 in shallow ground
water (Figure 7a). This has important implications for water access. Farmers tend to
gain water directly from tertiary canals. In general, pH of water in secondary and
tertiary canal systems and in ground water in acidic soils exceed the maximum
allowable limits applied for domestic supplies and agriculture or aquaculture uses (TCVN
5942-1995) (Trinh, 1997). In the Long Xuyen Quadrangle, the impact of acid sulphate
soils on soil and water acidification is still going on although the land have been
reclaimed for agricultural production since the late 1980s.
Figure 6: pH values in canal water sampled during May-Jul in different acid
sulphate soils in the Long Xuyen Quadrangle and the alluvial soil. Mean with
standard error. Key: ASS (acid sulphate soils)
(Source: Reproduced from Nhe, 2006).
164 Water Use and Competition in the Mekong Delta, Vietnam
uu
Figure 7: Values of pH (a) and concentrations of As (b), Cd (c) and Zn (d)
in canal and table water sampled during May-Jul in the Long Xuyen Quadrangle.
Mean with standard error (Source: Reproduced from Nhe, 2006).
165
Water Use and Competition in the Mekong Delta, Vietnam
Acid sulphate soil reclamation brings about potential risks to human health and aquatic
ecosystems. Aluminium is considered the most important toxic element in acid
sulphate soil zones. At the start of the rainy season, aluminium concentrations in the
leachate or canal water can exceed the normal tolerance of local fish or plant roots, and
causes the mass mortality of fish (NEDECO, 1993; Tin and Wilander, 1995; Minh et al,
1997). The rainfall and discharge from the Mekong River is not adequate to dilute the
toxic substances to an acceptable level, and an extremely large amount of water is
needed to dilute the leachate in order to prevent negative impacts to the
environment (Minh et al, 1997).
Consequently, surface water in a large acid sulphate soil zone is heavily polluted with
acidity and metals. The pollution from the soil leaching is most severe in mid-June due
to a combination of the highest total amount of aluminium released to the canals and
low river discharges (Nien, 1995; Minh et al, 1997). Recently, studying on water
quality in acid sulphate soils in the Long Xuyen Quadrangle during May-July, Hoa
et al (2006) and Nhe (2006) found high concentrations of arsenic, cadmium, copper,
manganese, nickel and zinc in shallow ground water (Figure 7b, c & d). The
concentrations of these metals in canal water in acid sulphate soils are from 4 to 54
times higher than in other soils. Although the metal concentrations in the water sources
are still lower than the maximum limits for domestic water supplies, aquaculture and
the environment (TCVN 5942-1995) (Trinh, 1997), one should be aware of the
potential risk of human health and the environment by water heavily polluted with
heavy metals.
Acid sulphate soil reclamation causes economic loss for agriculture and aquaculture
downstream. Rice yields are low, particularly in the wet season crop, mainly due to low
pH, high metal-toxicity and phosphorus-deficiency (Minh, 1996). During
2000-2005, average rice yields in the wet season crop were lower in low-lying
severely acidic soil areas in Long An, An Giang and Kien Giang provinces than in
neighbouring provinces (provincial statistics in 2006). Coastal shrimp farming in Bac
Lieu province (Dong Hai, Gia Rai, Phuoc Long and Hong Dan districts) suffers from
water discharges from agricultural acid sulphate soil areas in their upstream parts.
The extent and severity of water acidification and pollution depend on land use and
the arrangement of irrigation or drainage canal systems. On the one hand, the farming
practice of raised beds for upland crop production commonly applied in acid sulphate
soil areas, discharges significantly larger amounts of acidic substances and metals
than do rice fields (Minh et al, 1997). Under rice cropping, fields are submerged and
pH increases, resulting in aluminium precipitation. In the raised beds, in contrast,
soils are mostly in an oxidized condition, allowing more dissolved aluminium to
166 Water Use and Competition in the Mekong Delta, Vietnam
raised-beds release higher quantities of acidity and metals than the low raised-bed
practice (Minh et al, 1997). In addition, the release of aluminium tends to decrease
with land usage (Minh et al, 2002). On the other hand, if canal systems are long and
complex, such as in the Plain of Reeds, the discharge and the dilution of acidic water is
far from the acid source area to the sea. In contrast, canal systems which are short and
simple, such as the Long Xuyen Quadrangle, the acid discharge and dilution is rapid.
The acid discharge seems to have a small impact on the main rivers of the Mekong
and the Bassac, as the discharge is rapidly diluted by a large volume of
freshwater (Hashimoto, 2001).
3.2.3 Possible solutions
Particularly, acid sulphate soils reclamation for agricultural development aims at food
security, at both household and national levels, as the first priority at the expense of
water conflicts among water users, including resource-poor households depending on
open-access aquatic resources. The challenge is how to improve soil quality and
further enhance crop productivity while minimising the flushing of toxic substances
from the field to surrounding and downstream areas. Water acidification and metal
pollution is expected to decrease gradually once the Plain of Reeds, the Long Xuyen
Quadrangle and the Camau Peninsula are mostly reclaimed for agriculture. In the past,
acid sulphate soil reclamation was subsistence-oriented, thus farmers and authorities
were willing to endure the problems. From now onwards, however, the use of the soils
is commercially-oriented, improving economic growth and farmerÌs welfare. Human
health and environmental protection therefore need to be given special attention.
In acid sulphate soils, deep oxidation and its associated acidification and solubilisation
of metals can be minimized through appropriate management of water in fields and in
drainage canals and improved farming practices. Based on the literature, the following
possible solutions are identified. For rice farming:
Pyrite and the sulphuric horizons should be submerged in order to prevent
further formation of acidity, which was generated by oxidation of the sulphuric
horizons when the water table is further lowered;
Strong reduction of the topsoil in fields, however, should be avoided in order
to further improve rice yields. This can be achieved by improving the drainage or
removing surface water from the field for a number of days at mid-season or at the
reproductive stage of the rice plant while maintaining the water table at the desired
depths (Hanhart et al, 1997). Practically, this water management is quite difficult at a
large scale, because of the high spatial variability of sulphidic horizons of acid
sulphate soils and natural water table levels of surrounding canals, which complicate
be removed by leaching. In raised-bed farming practice, the traditional and high
management of the system (Tuong et al, 1998; Husson et al, 2000a);
167
Water Use and Competition in the Mekong Delta, Vietnam
In addition, improved farming practices are also important solutions (Hanhart
and Ni, 1993). Farmers have to establish their winter-spring crop as early as possible
to avoid strong oxidation at the end of the crop season; thereby the need for irrigation
could be reduced; and
Rice varieties with a short-growth duration and tolerance to aluminium need to
be selected and utilised.
For upland crop farming:
Land preparation, such as ploughing and harrowing, which leads to rapid
development of a plough-pan, and careful maintenance of field dikes and drainage
ditches would be advisable;
Water table control and the minimization of the upward movement of toxic
substances in the soil are recommended. Some aluminium might move upward to the
topsoil by capillary forces which could take place during the dry season or dry days
between the rains. However, it is essential to control the water table levels such that it
will not reach the topsoil layers at the beginning of the rainy season (Hanhart and Ni,
1993; Minh et al, 1998);
Mulching and surface tillage help reduce evaporation and therefore are
effective means of reducing aluminium accumulation (Minh et al, 1998); and,
Enhancing bypass flow is an effective way of improving soil quality of acid
sulphate soils by improved leaching efficiency of rain water, but this intervention has
a negative environmental impact (Minh et al, 2002).
For extensive or semi-intensive coastal shrimp farming practices, farmers usually dig
surrounding trenches to make shelters for shrimps, and dry out the field between the
rice and shrimp crops in the beginning of the dry season. Therefore, the trenches should
not be dug deeper than pyrite layers in acid sulphate soils. In addition, an appropriate
water table level needs to be maintained during drying out of the field so that sulphidic
horizons can not be oxidized. However, appropriate interventions have not been fully
devised to minimise possible negative effects of the use of acid sulphate soils for coastal
shrimp farming practices.
Proper management of embankments and drainage canals and promotion of recycling
of field effluents in acid sulphate soils are also crucial. Embankments of newly dug
canals and road construction are important sources of pollution (Tuong et al, 1998).
Soil compaction may help reduce the bypass flow in these structures and minimise
environmental hazards (Minh et al, 2002). Appropriately high water levels in drainage
canals need be maintained in the dry season to maintain field water table and to save
168 Water Use and Competition in the Mekong Delta, Vietnam
precious irrigation water. Field effluent water can be re-used or purified with plants
tolerant to acidity and aluminium such as Melalueca spp. or Eleocharis spp., instead of
directly discharged to surrounding canals. This option looks promising, but in reality
a vast area of Melalueca forests in the Mekong delta is being converted into rice or
brackish water shrimp farming for economic reasons, resulting in a more intense
water competition. For long-run sustainability, integrated solutions, including
incentive policies, monitoring, assessment and prediction of temporal variations of soils
and water quality are of great importance (Minh et al, 1997). Sustainable
management of land and water in the acid sulphate soils zone also means benefitting
ecosystems and other water users in coastal areas.
3.3 Water conflicts in coastal zones
3.3.1 Multiple values of water and its associated livelihoods
In coastal zones of the Mekong Delta, water conflicts are more complex compared to
those in the upper delta and acid sulphate soil zones. Freshwater is a scarce resource in
the coastal zone of the delta, yet there are multiple values and associated livelihoods
dependent on this resource, as well as brackish and saline water. The coastal zones
seem to favour aquaculture over agriculture development, due to salinity intrusion.
The zone is under-developed in socio-economic terms, compared to the other areas in
the delta because of its poor physical and social services, and infrastructure (Hossain et
al, 2006; Sam, 2003; Truong and Anh, 2002). People’s livelihoods rely mainly on
agriculture, aquaculture, wild fisheries and forestry. Poor households, small-land
holders or landless families, live on natural resource exploitation or waged labour
(Hossain et al, 2006; Sam, 2003).
Rice farming is the main agricultural activity. Farmers can earn an additional income by
exploiting natural aquatic resources. Rice farmers in the coastal zone earn a lower
income than those on alluvial soil and irrigated areas of the delta, due to water and land
constraints. In salinity areas, traditional rice is practised with one crop per year and rice
yields are low (Gowing et al, 2006; Sam, 2003; Trung, 2006). Upland crop production
is an economically promising activity but its marketing is constrained (Sam, 2003; Trung
et al, 2006). In salinity-controlled areas, on the contrary, high-yielding rice is grown
with double or triple crops a year. This rice intensification has been commonly
observed in national water resources development project areas such as the Camau
Peninsula (Quan Lo Phung Hiep), Tra Vinh (South Mang Thit), Soc Trang (Tiep Nhat)
and Tien Giang (Go Cong) provinces (Miller, 2003).
Shrimp production continues to expand though it is considered economically risky.
Rice farming area in the coastal zone decreased from 970,000 ha in 2000 to 800,000 ha
in 2002, whereas shrimp area increased from 230,000 ha to 390,000 ha in the same
period (cited in Gowing et al, 2006). However, shrimp culture needs high inputs and is
169
Water Use and Competition in the Mekong Delta, Vietnam
economically risky (Koopmanschap et al, 2002; Sam, 2003; Kempen, 2004). Shrimp
farming income is not stable and varies greatly among farmers and locations, due to
the poor quality of shrimp seed, the limited technological knowledge of farmers, and
the poor quality of intake water (Be et al, 2003; Minh et al, 2003; Trung, 2006). About
half of shrimp farming households become poorer and/or indebted, due to failures in
shrimp farming (Sam, 2003).
For resource-poor households, income largely depends on wild fishery capture, and
thus fishing equipment and access to resources are important. Poor households
without adequate fishing equipment usually exploit inland natural resources and earn
low incomes, due to the decline of natural aquatic resources. Consequently, the
livelihoods of most of the poor fishing households are mainly reliant on waged labour
(Hossain et al, 2006; Sam, 2003).
In the coastal region, mangrove forests are usually managed as state-run farms. The
mangrove forest includes two zones: the core and the buffer zones. The core zone is
fully protected yet in the buffer zone, the state-run farms make contracts with local
farmers to manage and harvest the forest. The local people are allowed to use 30% of
the forestland under the contract for shrimp culture (Koopmanschap et al, 2002; Sam,
2003). In addition, there is a small proportion of people living on illegal exploitation
of the forest and natural aquatic products (Hossain et al, 2006). According to Sam
(2003), approximately 28,740 households in the Mekong Delta coastal areas live on
forest exploitation.
3.3.2 Local and regional water conflicts
Before 2000, the state and local governments put a lot of effort into rice development
and related programmes. Salinity-control infrastructure was constructed and
consequently, salinity in canal water was reduced and high-yielding rice farming was
expanded in the salinity-free areas (Hossain, 2006). This intervention benefits rice
farming households but impedes those who rely on aquaculture and inland fisheries
(Tuong et al, 2003). In addition, this intervention has negative impacts on the
livelihoods of the poor, who depend mainly on inland natural aquatic resource
exploitation. In marginal land areas, farmers lack technological knowledge and capital
to adopt the new technologies of high-yielding rice farming (Hoanh et al, 2003; Hossain
et al, 2006). In the western part of Quan Lo Phung Hiep, socio-economic problems
have arisen due to the creation of a weakly brackish zone at the front of the expanding
irrigation area; here, the salinity levels are too low for shrimp aquaculture, yet too high
for rice, undermining the livelihoods of many former shrimp farmers (Hashimoto, 2001).
Since 2000, a large number of rice farmers shifted to shrimp culture. This shift brings
about conflicts between shrimp and rice farming within the community or between
those upstream (rice area) and those downstream (shrimp area) (Gowing et al, 2006).
170 Water Use and Competition in the Mekong Delta, Vietnam
This is because rice and shrimp farming practices use the same irrigation or drainage
systems. As a result, if more saline water is intentionally taken in for shrimp in the dry
season, neighbouring or upstream rice fields are affected by saline water. For example,
combined with shrimp farming expansion, the high tide from the western coast results
in further salinity intrusion into the Ca Mau Peninsula, damaging about 6,550 ha of the
dry season rice crops in Bac Lieu province (Hong Dan district, unpublished data). On
the contrary, if more freshwater is supplied to the rice farming areas, the salinity in the
shrimp farming areas is diluted. In addition, farmers heavily apply agro-chemicals in
their intensive rice culture. Thus, effluent discharges from rice fields result in negative
impacts on shrimp culture (Trung et al, 2006).
Conflicts also occur within the shrimp farming area. The effluent discharge from a
shrimp farm might become the water intake of another. Therefore, the periodic
discharge from shrimp farms brings about the potential of adverse effects on the
receiving waters (Hoanh et al, 2001; Tuong et al, 2003). The shrimp farm effluents
contain a high concentration of suspended solids, nutrients and bio-active chemicals,
particularly in semi- and intensive shrimp farming systems.
Development of rice and recently of shrimp culture both result in losses of coastal
mangrove forests. In the eastern coastal zone, the mangrove area significantly
decreased, from 190,812 ha in 1953 to 29,534 ha in 1995, (Minh et al, 1999; Minh
et al, 2001). In the Ca Mau Peninsula, the largest area of mangroves in Vietnam, a vast
area of mangroves was deforested for rice and shrimp farming. Between 1983-1995,
about 66,253 ha of mangrove forest were converted into shrimp farms in Ca Mau and
Bac Lieu provinces (Cuong and Vuong, 1996). Using aerial photographs in Cai Nuoc
district of Ca Mau province between 1968 and 2003, Binh et al (2005) calculated that
about 40% of the loss of the mangrove could be attributed to shrimp farming, while
the remaining 60% was attributed to needs for agricultural land. Presently, shrimp
farming is the major source of mangrove loss in the district. They also estimated that
in 1968 saline water covered about 220 km2, in 1992, 1998 and 2003 about 92,135
and 835 km2, respectively. These figures could confirm the rice expansion in
the 1990s and the fast growth of shrimp culture since 2000. This reduction of coastal
mangrove forests leads to deterioration of water quality and fish populations.
Consequently the productivity of shrimp farms and the livelihoods of the poor who
strongly depend on the wild fish catch are threatened (Hirsch and Cheong, 1996).
3.3.3 Possible solutions
The current conflicts of water uses among agriculture, aquaculture, fisheries and
environment in the coastal zone have prompted a rethinking of the government policy
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Water Use and Competition in the Mekong Delta, Vietnam
with implications for water and land-use management in the coastal region, where
water values are recognized as multiple rather than for rice or shrimp production only.
Local authorities are challenged to turn around a conflicting situation of incompatible
land and water use to achieve a workable compromise that can accommodate the needs
of both the shrimp and rice farmers as well as minimize adverse effects on the poor
and the environment (Tuong et al, 2003). The following are possible solutions:
Multiple values of land and water uses need to be identified. An integrated
approach to land and water management is required, encompassing much broader
perspectives and including conflict resolution as an integral strategy (White, 2002).
Geographical Information Systems and hydraulic models could be appropriate tools
to support this integrated approach (Tuong et al, 2003).
Appropriate farming systems should be promoted to minimize water
conflicts among the water users and to further improve shrimp productivity. Integrated
farming systems such as rice-shrimp and mangrove-shrimp farming can help reduce
the economic risks of shrimp farming and stimulate environmental sustainability
(Preston and Clayton, 2003). Integrated mangrove-shrimp farming systems can bring
higher incomes than systems without mangroves (Gowing et al, 2006).
Technical solutions for shrimp culture are of importance. Possible options
include reducing water exchanges of shrimp farms and improving the quality of
hatchery-reared post-larvae. Reducing the release of acidity from acid sulphate soils
would be advisable (Gowing et al, 2006; see discussion in section 3.2.3).
Participatory approaches are of importance to solve the conflicts. The
participation of local farmers and other stakeholders (i.e. decision makers, extension
workers, researchers and service providers) in land use planning and management
allows not only decision makers and land use planners to understand the real needs,
but also stimulates farmers’ awareness of the possible conflicts and their consequences.
Hence, the potential conflict can be minimized (Trung, 2006).
Institutional improvements are an important option for the reduction of water
conflicts. The institutional improvement includes better coordination and
participation among stakeholders, from planning, implementing and monitoring to
evaluation. Within this option, the concept of integrated coastal management needs to
be considered. Conflict resolution should be shifted to the design and building of
institutions, where they are absent, or the strengthening of those that already exist
(Brugere, 2006).
172 Water Use and Competition in the Mekong Delta, Vietnam
3.4 Constraints to water access and sharing
The above sections have highlighted important areas of competition within the
delta that limit easy access to water in adequate quantity and quality. There are
also important social and micro level factors that influence access. Major factors
influencing the water access and sharing include a number of bio-physical and
socio-economic and institutional aspects, at household and community levels
(Table 2). During the dry season, tertiary canal networks are usually shallow and their
flow rates are low, due to poor maintenance and sedimentation. Consequently, within a
community, upstream households can access to water better than those downstream, in
terms of water availability, quality and timing. This constraint also limits possible
options for people to deal with risks. Fields with low elevation levels can access to
water better than those with a high elevation, or that are distant from canals. On the
other hand, better-off people or people with good social connections can access water
better than those who are worse-off. The combined constraints of bio-physical and
socio-economic factors might cause severe effects on poor people’s livelihoods. For
example, poorer households with poor access to water have little choice but to rely on
un-safe water sources. This makes them more susceptible to crop loss and illness,
hastening economic decline (Miller, 2003).
Cooperation amongst neighbours plays an important role in water access at household
level while coordination and participation of all local stakeholders, including
authorities, are crucial at the community level. Livelihoods of farmers and local
communities crucially depend on availability and quality of water resources. Thus, they
understand how to adapt to scarce water resources. In many areas, farmers
contribute about 40%-60% of their total budget for annual maintenance of tertiary
canals, dikes or sluice gates (Nhan, unpublished data). Appropriate cooperation
mechanisms can help alleviate inequities apparent in water access. Communication
between farmers and local authorities plays a role in individual decision-making on
production within the context of collective constraints, as it is difficult for gates to be
operated to balance the needs of people pursuing different local interests and needs. In
reality, a top-down approach or one lacking communication is still common in some
areas (Miller, 2003). Good planning, coordination and regulation of local authorities is
necessary, and helps contribute to greater equities in water access of a community
(Hedelin, 2007). An appropriate combination of structural and non-structural
measures is advisable when governmental budgets for water resource development
and management are still limited.
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Water Use and Competition in the Mekong Delta, Vietnam
4 Conclusions on the major issues to be addressed
4.1. Upstream-downstream water competition
Policies and infrastructure investments of the government have encouraged
intensification of rice and aquaculture in the upper and mid-delta, resulting in impacts
on water use downstream. Intensive rice farming with two or three crops a year, mainly
relying on water availability and other inputs, consumes much water during the dry
season. The rice farming in the upstream and mid-stream delta might abstract about
one-half of flow rates of the Mekong within Vietnam from December to May. This
implies more tension between further expansion or intensification of dry-season rice
farming upstream and freshwater availability and salinity intrusion downstream. Thus,
possible solutions to improvement to water use efficiency in rice culture needs to be
considered and impacts of water abstraction in rice farming in upstream delta needs to
be monitored.
The salinity intrusion in the downstream Mekong delta is complex, depending on
not only water abstraction and storage upstream but also environmental factors and
land uses downstream. The development of canal systems and the expansion and
intensification of the rice culture, which reduces the flood-plain water storage and river
flows, could increase the extent and the severity of the salinity intrusion in the
downstream part. Recently, the salinity intrusion has become more complicated due to
new construction of irrigation systems and salinity-control structures.
Table 2: Main factors affecting water assess and sharing at individual
and community levels.
174 Water Use and Competition in the Mekong Delta, Vietnam
Freshwater aquaculture competes for water through the discharge of a large quantity
of pond (cage) effluents to surface water bodies. This might have negative impacts on
aquaculture itself, domestic water supplies and the aquatic environment downstream.
The extent of the negative impacts increases with increasing intensification levels of
the farming because of higher water exchange rates. Pond effluent discharges not only
pollute surface water bodies but also reduce economical benefit to aquaculture
farmers. While the government promotes freshwater aquaculture farming as a way to
develop the rural economy, water pollution and its associated impacts needs special
attention.
Further improvements in water use efficiency in rice and aquaculture farming
practices in the upper delta are identified as an important task to alleviate
upstream-downstream water competition. For rice farming, several technical options
could help improve efficiency of irrigation water use at both crop and field level. The
proposed options, however, still have limitations such as labour-or cost-intensity,
yield reduction, nutrient losses and nitrate leaching into groundwater. In addition,
options at crop and field level are not very practical with a small-scale production.
Solutions at community level are still being sought after. For aquaculture, minimizing
effluent discharges while maintaining high farming income is of great importance.
“Ecological or sustainable aquaculture” development should be promoted. Recycling
nutrient-rich outflows from ponds/cages is promising to produce an extra crop of fish,
terrestrial or aquatic plants before discharge. Water pricing or polluter pay policies are
possible options but are likely not to be practical with small-scale and resource-poor
farmers.
4.2. Impacts of acid sulphate soil reclamation
Most acid sulphate soil areas have been converted into agricultural areas, particularly
rice culture and aquaculture. This was encouraged by extensive development of canal
systems and human settlement in combination with improved cropping practices. An
important impact of reclamation of acid sulphate soil is the acidification of soils and
canal water and hence increased mobility of potential metals. The extent and the
severity of the problems depend on seasons, arrangement of irrigation or drainage
canal systems, land use patterns, water management in the field and crop farming
practices. The acidity and metals released from acid sulphate soils have adverse
impacts on domestic water use, agriculture and aquaculture practices, and aquatic
ecosystems in surrounding and downstream parts, and the impacts can last for many
years. The impacts are more severe in the beginning of the rainy season, in tertiary
canals or shallow ground water and in upland farming areas. After two decades of the
reclamation, pH values of canal water in the Plain of Reeds and in the Long Xuyen
Quadrangle are still exceeding the maximum allowable limits applied for both
domestic supplies and agriculture or aquaculture uses. With common farming
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Water Use and Competition in the Mekong Delta, Vietnam
practices, normal rainfall and discharge from the Mekong River is not sufficient to
dilute the leachate to an environmentally acceptable level.
The challenge of acid sulphate soil reclamation is how to further improve crop
productivity while minimizing environmental impacts in surrounding and downstream
areas. This is not an easy task because of trade-off between these two objectives. There
are possible technical options to solve this problem. The key principle is to prevent the
oxidation of the pyrite layer and to minimize the concentration of toxic metals in the
top soil through appropriate management of water in fields and in drainage canals
and improved farming practices. Unfortunately, the options seem to be very
promising at field scale but not at larger scales, due to high spatial variability of
sulphidic horizons of acidic soils and natural water table levels of surrounding canals
and small-scale farming production. In addition, proper management of
embankments and promotion of recycling of field effluents by appropriate integrated
farming systems are also crucial. Further disturbance of the soil could make the
impacts more severe. Recognizing these impacts, further expansion of agriculture and
aquaculture land in acid sulphate soil areas needs careful consideration because of
the potential risk to human health and environment. Monitoring, assessment and
prediction of temporal variations of soils and water characteristics are of great
importance.
4.3. Water conflicts in coastal zones
Water conflicts in the coastal zone are brought about by not only interventions in
the reaches but also changes made within the zone. In the inland coastal zone, the
ecosystems have undergone rapid changes in recent decades; there has been a clear
shift of natural mangrove forests and salt fields to rice and recently to shrimp culture.
These changes have caused conflicts among three major water resource users: rice
cultivation, shrimp culture and fishing. The government promoted intensive rice
production in the past and shrimp farming in recent years. For rice farming, in the past
many large water management projects have been carried out and saline water was
replaced by freshwater. This lead to larger areas of mangrove forest being turned into
rice areas. Now, for shrimp farming, mangrove forest is also cut down. This causes
significant loss of mangrove land, in turn resulting in a decline of natural aquatic
resources. Shrimp farming is more profitable than rice but this farming practice needs
higher input costs and is economically risky. The zone comprises a mosaic of rice,
shrimp and natural forest lands, which use the same irrigation or drainage systems.
It is difficult to meet all needs of water use because of the different water requirements
and some of them are not compatible. Rice farming impedes downstream people who
rely on shrimp culture and inland fisheries, due to salinity dilution and effluents
discharged from rice areas. In contrast, shrimp culture adversely affects rice farming
due to soil and water salinisation. Water conflicts occur within the shrimp farming
community from pollution of water courses.
176 Water Use and Competition in the Mekong Delta, Vietnam
The current conflicts have prompted a rethinking of the government policy and the
planning of land and water use in the coastal region. Further promoting integrated
farming systems, improving farming technology packages, enhancing participation
of local people and improving institutions in land and water use planning and
management are possible solutions. Furthermore, the concept of integrated coastal
management needs to be vigorously promoted.
4.4. Constraints to water access and sharing
Increasing scarcity for water is associated with both quantity and quality. Major
factors influencing the water access and sharing are associated with a wide range of
physical settings, and socio-economic setting or coordination and cooperation, at both
household and community levels. The combined constraints of driving factors might
cause severe effects of poor water access on people’s livelihoods, especially the poor.
Individual cooperation and participation of all local stakeholders are crucial, at both
farm and community level, representing and responding to local interests and needs.
On top of that, good planning, coordination and regulation of local authorities are
necessary.
5 Contested issues
This review paper describes the current stage of rice cultivation and aquaculture and its
associated impacts on water conflicts in the major agro-ecological zones in Mekong
delta. Possible options are also suggested to alleviate the conflicts while maintaining
high productivity and income from rice and aquaculture farming. In general, however,
available information on water conflicts in the delta is still patchy and current
information is inadequate. The following are contested issues:
Strong evidence of the impacts of rice farming and aquaculture practices in
upper delta is still limited.
Patterns of the salinity intrusion in the delta are not yet fully understood. To
what extent the water abstraction by rice crops in the dry season causes salinity
intrusion downstream, and how recent changes in salinity-control structure and canal
development influence salinity intrusion, are still not clear.
Water-saving techniques have not yet been tested in rice farming and
aquaculture practices in the delta. Thus, how these techniques can be applied
successfully is unclear.
That to what extent the impacts of acid sulphate soils reclamation still continue
is not yet known.
Water has multiple values and water saving needs to be considered at larger
scales. In the long-run to further sustainability, solutions balancing interests among
water uses or regions are not yet well-known.
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Water Use and Competition in the Mekong Delta, Vietnam
Together with technical options, non-structural solutions are considered
important to reduce water conflicts and to strengthen people’s awareness of risks.
The non-structural options are still rarely applied to real situations.
Water conflict and its causal effects are dynamic. Thus, proposed solutions need
to be long-term and adaptable to constant changes of physical and socio-economic
circumstances within the delta, as well as in the whole Mekong River Basin.
6 Research priorities
6.1. Crop and field levels
Further improvements in water productivity in agriculture, mainly rice cultivation, and
aquaculture at a field level and maximizing water value at larger scales is the key to
alleviating water tension between the upper delta and the downstream, the impacts of
acid sulphate soils and conflicts in the coastal zones. Water productivity here means
less water input but maintaining high incomes. There seem to be trade-offs existing
between economics and water use efficiency or the environment in rice farming (Bouman
and Tuong, 2001) and aquaculture (Nhan et al, 2007b). Moreover, adoption of water
saving practices is influenced by a range of technical, physical and
socio-economic aspects (see section 3.1.4). Unfortunately, this knowledge and insight
are still limited in Vietnam, particularly in the Mekong delta. The following are gaps of
knowledge that need urgent investigation:
What is the water productivity of rice production in different agro-ecological
zones of the delta?
How can water productivity in rice farming and aquaculture systems be
improved while remaining high income production systems and still safeguarding
the environment?
Under what conditions could high-water-productivity practices be applied?
How can flood water at maximum volume be stored to irrigate crops during the
dry season in acid sulphate soil areas?
How can leachate from fields in acid sulphate soils be re-used or purified before
being released to drainage canals?
6.2. Zone and regional levels
Increased water productivity at the field level does not always translate into those at
larger scales (Molden et al, 2003). The effectiveness of the water use is also of great
importance. For example, in rice production, most water-saving technologies increase
water productivity through irrigation and save water through a reduction in seepage
and percolation flows, which can be re-used downstream (Tuong et al, 2005). At
the larger scales, moreover, water has multiple uses: crop production, aquaculture,
178 Water Use and Competition in the Mekong Delta, Vietnam
livestock production, domestic use, industries, fisheries, environment, etc. (Barker
et al, 2003; Mushtaq et al, 2006). Barker et al (2003) laid down some of the concepts
and complexities in economic analysis related to increasing water productivity and
show that increases in water productivity in one sector might reduce the water
productivity elsewhere - that is, in economic terms, there are significant externalities.
Moreover, institutional matters dealing with the distribution of deriving benefits from
different water use options among different water users are the crucial challenge.
Information on this matter is still little known in the Mekong delta. The following
questions need to be answered at zone or regional level:
Will impacts of acid sulphate soils reclamation still continue in the future? If
so, how can they be anticipated and what are the determinants?
What are spatial and temporal patterns of salinity intrusion, what are the
determinants, and what will the patterns be with the possible development of water
resources in upstream countries in the future?
What are linkages between poverty and depletion of natural resources,
particularly water?
What are risk strategies to increasing scarcity of water, when special attention
to the poor is given?
What are the total gains in upper delta and the total losses downstream, and
who will gain and lose in each option?
How can the economic value of water be maximized with less environmental
impacts, increased livelihoods of the poor and ensuring national food security?
And how are proposed interventions adapted to possible changes of physical and
socio-economic circumstances?
What are incentives to apply water-saving practices in agriculture and
aquaculture by farmers?
What are appropriate mechanisms for better local cooperation, participation
and coordination, especially the role the local community plays, in better arrangement
of water access?
What are mechanisms for secure and equitable water sharing at local and
delta scales? What are the social contexts and ways in which conflict over water
can be anticipated, reduced and eventually resolved at the community, project,
agro-ecological zone and delta wide scale?
7 Conclusion: Policy linkages
The current stage of rice farming and aquaculture practices and their impacts
and conflicts give some implications for policies on sustainable agriculture and
aquaculture development for the Mekong delta. Policies on, and investments for, rice
and aquaculture development resulted in water conflicts between the upper delta and
downstream, adverse impacts in acid sulphate soil areas and conflicts in coastal zones.
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Water Use and Competition in the Mekong Delta, Vietnam
These interactions are complex and more evidence of causal relationships are still
needed to provide policy makers clear trade-offs between different water users
and necessary guidelines of optimal water resources management. In the delta,
subsistence-orientated production shifted to market-orientated production with
improved welfare of people. The state and local governments need to balance
immediate food production and economic growth with sustainable resource-based
management. To do this, laws or decrees related to environment and water resources
protection need to be taken into account when strategies of agricultural, aquacultural
and socio-economic development are designed. The Mekong delta is highly
susceptible to the negative impacts of upstream development interventions, which
contribute to changes in the flood regime, reduction in total and dry season flows, an
increase in water pollution, and changes in sediment and nutrition loads (Miller, 2003).
The current water conflicts can be solved through a combination of a range of
technical, bio-physical, socio-economic and institutional aspects at community and
regional levels.
First, rice and aquaculture development in upper delta have impacts on water uses in
downstream areas. Land and water use planning needs to be considered at the regional
scale (i.e. upstream vs. downstream) rather than locally. For any intervention projects,
gain and loss trade-offs between upstream and downstream should be assessed and
valued.
Second, acid sulphate soils reclamation for rice farming development contributes to
national food security at the expense of the environment and human health risks. These
negative impacts should be considered when the expansion of acid sulphate soils
reclamation for aquaculture development is still going on in the coastal zone.
Third, the coastal ecosystem is very sensitive and water conflicts among water users
are complicated. Land and water use policies and planning therefore should take a
more holistic approach, taking into account interests of all resource users not only
within the zone but also with the upper delta, especially the poor and their related
resource base, instead of focusing on a single sector. Multi-objective decision-making
and predictive tools need to be developed at different spatial scales to provide
adequate options for policy making and planning.
Fourth, the equity of water access and sharing is determined by a combination of
physical and socio-economic settings. Participatory approaches are required to
support well-informed planning, policy options, intervention developments,
implementation, evaluation and feedbacks of local needs to policies (Roetter et al,
2007). The concept of integrated resources basin management should be given
priority, due to increasing water competition leading to increased efforts in
180 Water Use and Competition in the Mekong Delta, Vietnam
management. This shifts to a greater concern for water management institutions and
mechanisms for cooperation and coordination (Miller, 2003).
Fifth, water-saving practices in agriculture and aquaculture need to be considered at
different spatial scales. The water-saving practices should be realized as one of the
basic policies for sustainable agriculture development in the region. Incentives that
encourage farmers to apply water-saving practices are necessary. This measure is
successfully applied in China (Li, 2001; Hoanh et al, 2003; Gowing et al, 2006).
Sixth, further research should focus on both micro- (i.e. crop and field) and
macro-scale (zone and region), and consider both technical and socio-economic
solutions. Continuous monitoring of the environmental and socio-economic
conditions following intervention is essential for a timely supply of adequate data for
resource planning and management that would enhance the positive outcomes and
minimize the negative impacts.
Seventh, collaboration among countries in the Mekong Basin is of great importance
for better management of the same water resources, for greater gains in the whole but
least impacts downstream. More equitable approaches to water rights are necessary,
encapsulating principles such as riparian rights and equitable utilization, benefiting both
upstream and downstream countries (Nickum, 1999).
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Water Use and Competition in the Mekong Delta, Vietnam
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Supplementary resource (1)

... Recent reports indicated that, following natural regulations, SI occurred frequently between 1977-1996 2 . It was first recognized in 1998 as a natural hazard (Dang et al., 2007). Evidence suggests that SI correlates with environmental change and human development processes occurring not only in the VMD but also in the broader geographical scales (e.g., hydropower dam construction and land-use change in the Mekong region) (Dang et al., 2007;Nguyen, 2016a). ...
... It was first recognized in 1998 as a natural hazard (Dang et al., 2007). Evidence suggests that SI correlates with environmental change and human development processes occurring not only in the VMD but also in the broader geographical scales (e.g., hydropower dam construction and land-use change in the Mekong region) (Dang et al., 2007;Nguyen, 2016a). ...
... Highly intensive shrimp cultivation indicates higher density of shrimp larvae in the pond (around 100-150 larvae/m 2 ). Dang et al., 2007). According to an agricultural officer in Hiep My Dong commune, Cau Ngang district, shrimp culture brings relatively better income (T. ...
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Saline intrusion (SI) is increasing at an accelerating rate in the coastal zones of the Vietnamese Mekong Delta (VMD). This challenges various crop production practices in these areas. Using ecological and social approaches, this paper aims to explore farmers’ perceptions of SI occurring in Tra Vinh and Kien Giang provinces, and their adaptation measures to deal with the situation. A mixed-method approach was used, including in-depth interviews, focus group discussions, and household surveys. The results demonstrated that farmers have implemented various adaptation measures in tackling SI impacts. High market demand for shrimp also contributed to farmers’ decisions in shifting farming practices. The study underscores the important role of the integrated shrimp-rice system as a more comparatively sustainable model to the intensive shrimp culture in the face of SI. Qualitative analysis revealed water conflicts occurring in mixed rice and shrimp farming areas driven by the poor performance of combined irrigation and drainage systems together with the undefined water demarcation zones between rice and shrimp farmers. The paper provides better insights into how farmers’ adaptation strategies could facilitate decision-making processes with regard to water management and adaptation policies in the coastal areas. It calls for local governments’ attention to modifying water infrastructure to better address water-related issues.
... In addition, the more intensive model required greater water consumption. In fact, if water requirement in WS, SA and AW are 8080; 7520; and 6500 m 3 /ha/crop respectively (Nhan et al., 2007) then the 2C1Y model in total would consume about 15,600 m 3 /ha/year compared to 22,100 m 3 /ha/year for the 3C1Y; 19,933 m 3 /ha/year for the 3Y8C; and 18,850 m 3 /ha/year for the 2Y5C. Therefore, the 2C1Y practice facilitates more freshwater conservation which in turn is very beneficial for communities a long or closer to the coastal areas as they are affected by a lack of freshwater supply during the dry season, which is exacerbated by hydropower development in upstream countries. ...
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The floodplains play an important role in agricultural development and rural livelihoods in the Vietnamese Mekong Delta. As an intensive rice production area of Vietnam, the floodplain has experienced significant changes in water management regime during the recent decades. Depending on specific locations and irrigation infrastructure investments, four main water management practices have been innovated, particularly a planting season of two crops per year (2C1Y), three crops per year (3C1Y), three years eight crops (3Y8C) and two years five crops (2Y5C). The 4R framework (Reform, Result, Resilience, and Return) was developed based on grounded theory approach for resilience assessment of various innovative water management practices. In terms of resilience, we found that each crop pattern involves pros and cons, and the intensive crop practices are less resilient systems, especially in social, environmental, and ecological aspects. The findings provide good lessons learned not only for Vietnam but also for the other rice-producing deltas implementing ecosystem resilience to adapt to global challenges such as flood, drought, and salinity intrusion.
... The summary of this debate about the low adoption of rice-fish coculture including inadequate knowledge of farmers for both fish and rice production (Li 1988;Berg 2002), and widespread chemical application in intensive rice monoculture that cannot favor fish growth (Wilson and Tisdell 2001). Moreover, financial constraints as well as higher labor requirement for rice-fish coculture (Horstkotte-Wesseler 1999; Ahmed and Garnett 2011), low fish productivity (Gurung and Wagle 2005;, technical and institutional constraints (Nabi 2008), and competition for water use (Nhan et al. 2007) were identified. One of the key bottlenecks and limiting factors for rice-fish coculture is water management, including drought, water scarcity, inadequate water depth, lack of irrigation facilities, and insufficient water control (Horstkotte-Wesseler 1999;Frei and Becker 2005a;Nabi 2008;. ...
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Integrated rice-fish culture is a competitive alternative to rice monoculture for environmental sustainability and food productivity. Compared to rice monoculture, rearing fish in rice field ecosystems could increase food (rice and fish) production from this coculture. Moreover, the water productivity of rice-fish coculture is considerably higher than that of rice monoculture, because of double cropping. Despite these benefits, rice-fish coculture has not yet been broadly practiced. One of the potential challenges for the wider adoption of rice-fish coculture is water management. There are two forms of water involved in rice-fish cultivation: (1) blue water-surface and groundwater, and (2) green water-soil water from rainfall. The aim of this article is to focus on key factors determining the adoption of rice-fish cultivation through the effective utilization of blue-green water. We suggest that the efficient application of blue and green water in rice-fish coculture could help confronting water scarcity, reducing water footprint, and increasing water productivity.
... Implementation of this plan could be regarded as a success. Rice areas expanded in the upper and middle parts of the delta, as sulphide acid soils were reclaimed (Nhan et al., 2007). This spurred rice exports to ever higher levels (see Table 4). ...
... -Đối với lĩnh vực sản xuất nông nghiệp: so sánh đơn thuần tổng lượng phân, thuốc hoặc tổng lượng nước/hecta giữa các hộ/nhóm hộ, ... (Dang, Nguyen, & Nguyen, 2007;H. B. Nguyen & Yabe, 2017). ...
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... Deeper confined aquifers, however, with better quality and higher potential yields, have become principal targets for exploitation at the industrial scale and for municipal and agricultural purposes (Dang et al. 2007;IUCN 2011;Wagner et al. 2012;Bui et al. 2014;Erban et al. 2014;Vo and Huynh 2015;Dao et al. 2016). The results of a groundwater-monitoring program that commenced in the early 1990s demonstrated piezometric heads at, or above, the ground-surface elevation in most parts of the Mekong River Delta (Minderhoud et al. 2017). ...
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The coastal aquifers and inland waters of the Long Xuyen Quadrangle and Ca Mau Peninsula of southern Vietnam have been significantly impacted by seawater intrusion as a result of recent anthropogenic activities. This study identified the evolution and spatial distribution of hydrochemical conditions in coastal aquifers at this region using Hydrochemical Facies Evolution Diagram (HFE‐D) and Geographical Information System mapping. Hydraulic heads and water chemistry were measured at thirty‐one observation wells in four layered aquifers during dry and rainy seasons in early (2005), and more recent (2016), stages of agricultural development. Hydrochemical facies associated with intrusion or freshening stages were mapped in each aquifer after assigning mixing index values to each facies. The position of groundwater freshening and seawater intrusion phases differed in Holocene, Upper Pleistocene, Middle Pleistocene, and Lower Pleistocene aquifers. The geographic position of freshening and intrusion fronts differ in dry and rainy seasons, and shifted after eleven years of groundwater abstraction in all four aquifers. The spatial and temporal differences in hydrochemical facies distributions according to HFE‐D reflect the relative impact of seawater intrusion in the four aquifers. The study results provide a better understanding of the evolution of groundwater quality associated with sea water intrusion in a peninsular coastal aquifer system, and highlight the need for improving groundwater quality and management in similar coastal regions. This article is protected by copyright. All rights reserved.
... The third possible sites for pilot SWS implementation are coastal industrial sites in Ca Mau and Tra Vinh. One example is the production site of the Fertilizer and Gas plant in Ca Mau, at the southernmost tip of the Mekong Delta whose water supply is also disrupted due to saline water intrusion into the estuary rivers (Nhan et al., 2007). The water price which is usually 0.2-1 $/m³ during the water supply period increases to 3-10 $/m³ when it is interrupted as it has to be brought by tanker boats or trucks. ...
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Groundwater is a critical component of water resources and has become the primary water supply for agricultural and domestic uses in the Vietnamese Mekong Delta (VMD). Widespread groundwater level declines have occurred in the VMD over recent decades, reflecting that extraction rates exceed aquifer recharge in the region. However, the impacts of climate variability on groundwater system dynamics in the VMD remain poorly understood. Here, we explore recent changes in groundwater levels in shallow and deep aquifers from observed wells in the VMD and investigate their relations to the annual precipitation variability and El Niño–Southern Oscillation (ENSO). We show that groundwater level responds to changes in annual precipitation at time scales of approximately 1 year. Moreover, shallow (deep) groundwater in the VMD appears to correlate with the ENSO over intra-annual (inter-annual) time scales. Our findings reveal a critical linkage between groundwater level changes and climate variability, suggesting the need to develop an understanding of the impacts of climate variability across time scales on water resources in the VMD. HIGHLIGHTS The connections between groundwater level change and climate variability in the Vietnamese Mekong Delta (VMD) are examined using vector autoregression and wavelet analysis.; Groundwater level response to changes in annual precipitation in the VMD is largest within the first year.; Groundwater level in shallow (deep) aquifers in the VMD appears to correlate with ENSO over intra-annual (inter-annual) time scales.;
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Food, energy, and water (FEW) resources are critical concerns to achieve long-term sustainability. Climate change and socio-economic development both affect the FEW Nexus, but the combined impacts of these two factors on a Nexus system is not well understood. An integrated management model was applied to quantify the combined impacts on the FEW Nexus through rice yield, power generation, and water withdrawal. Five scenarios from the Coupled Model Intercomparison Project Phase 6 were chosen as the inputs of the integrated model in the Mekong River Delta (MRD). Results showed that rice yields will be vulnerable to extreme climate events. The minimum autumn rice yield, 4.7 ton/ha in 2023 under the SSP1–2.6 scenario, will be as low as the yield of the 2016 drought year (4.6 ton/ha). Power generation will increase sharply due to socio-economic development. The power generation of SSP5–8.5 in 2050 will be about 10 times higher than that in 2010. The average total water withdrawal in 2050 was estimated to increase by 40% compared to that in the 2016 drought year and will be more than 3 times higher than the average withdrawal of 1995–2010. Nexus analysis found water is a central resource that connects food and energy sectors in MRD. Regional sustainability analysis showed that climate change and socio-economic development both have a significant impact through affecting the FEW Nexus. Specifically, the energy and water sectors will be more vulnerable to the combined impacts than the food sector due to the coal-fired power plants planned in the MRD.
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The coastal zone of the Mekong river delta has experienced rapid economic and environmental changes during the last decade. Given the nature of the environment and the level of dependence on the natural resources base, policies for land and water were very influential in this process. The emphasis on rice created an imperative to control saline intrusion, which was realized through the construction of major engineering works over an extended period (1994-2000). The inertia built up by this process led to a divergence between policy and practice, and adversely affected the livelihoods of fishers and of those farmers who live on aquaculture. This prompted the government to rethink the rice-focus policy, in favor of a land and water policy for balanced rice and aquaculture production. This paper describes an analytical process, which was adopted to explore the feasibility of adopting the new policy for the balanced development of both rice and shrimp production and discusses the impact of the new policy on farmers' livelihoods.
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The Integrated Tropical Coastal Zone Management at AIT is an area of specialization under the Schools of Environment, Resources and Development and Civil Engineering. This interdisciplinary field aims to develop human resources for coastal zone management in the Asia and the Pacific regions where the coastal areas encompass a diverse array of resources and ecosystems with intense human activities. ITCZM MONOGRAPH SERIES The series contains an extract based on the M.Sc. theses to reach the public.
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Global production of farmed fish and shellfish has more than doubled in the past 15 years. Many people believe that such growth relieves pressure on ocean fisheries, but the opposite is true for some types of aquaculture. Farming carnivorous species requires large inputs of wild fish for feed. Some aquaculture systems also reduce wild fish supplies through habitat modification, wild seedstock collection and other ecological impacts. On balance, global aquaculture production still adds to world fish supplies; however, if the growing aquaculture industry is to sustain its contribution to world fish supplies, it must reduce wild fish inputs in feed and adopt more ecologically sound management practices.
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Field studies of fine sediment dynamics carried out in the Mekong River estuary, Vietnam, during the low flow season in April 1996 show semidiurnal macrotides and shallow water effects result in a tidal asymmetry with peak flood tidal currents 10% stronger than peak ebb tidal currents. The salinity intrusion extended 50 km up-river with vertical stratification in salinity occurring around slack tidal currents. The suspended sediment was mainly fine silt, with flocculation occurring in the saline region. The asymmetry of tidal currents, along with the baroclinic circulation, pump sediment upstream. The saline water region of the estuary was more turbid than the freshwater region and the location of the turbidity maximum varied spatially with the tides. Our study suggests that the proposed construction of about 100 hydroelectric dams and water diversion schemes on the Mekong River and tributaries will impact negatively on the Mekong delta.