Environmental dimension

The environment dimension of the Indicator Framework reflects the MRC’s intent to protect the environment, natural resources, aquatic life and conditions, and ecological balance of the Mekong River Basin from pollution and other harmful effects. Impacts may result from development activities and the use of water and related resources. Four strategic indicators supported by twelve assessment indicators have been selected to measure whether objectives have been achieved.

↓ Scroll down to view the four strategic indicators supported by twelve assessment indicators

Note: The selected findings presented here should be interpreted considering the assumptions, methodologies and data sources of the SOBR 2018. For complete assessments, consult the SOBR 2018 report.

Water flow conditions

Assessment indicators:

  • Dry season flows - compliance with PMFM
  • Flood season peak flows - compliance with PMFM
  • Tonle Sap reversal flows - compliance with PMFM
  • Timing of onset of wet season flows

Both dry season and wet season flows over the last five years were found to be generally in conformity with PMFM thresholds, with occasional but non-systemic exceptions. Reverse flow in Tonle Sap, which is a function of floods in the mainstream pushing water up to the Tonle Sap Lake (which then flow back out during the flood recession period), is also broadly in line with the Guidelines. The maximum (severe) flow threshold was breached on average 10 days per year and the more modest low flows threshold somewhat more frequently. Continued monitoring is recommended, particularly with respect to Tonle Sap reverse flows. It is noted also that the timing of the onset of wet season flows has been quite variable in recent years along with the duration of the wet season. It is also observed that below average flows are seen during the flood recession period, particularly in the downstream reaches of the mainstream.

Observed flows and trends for the Mekong mainstream stations over the period 2000-2017

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Whilst the findings above demonstrate that the requirements of the PMFM are generally being met, the flow monitoring data for Chiang Saen (the northern most station in the Lower Mekong Basin (LMB) mainstream) shows that, although total annual flow volume remains broadly the same, flood season flows have reduced somewhat and the dry season flow is markedly increased following the development of the large reservoirs in China. The data for Kratie shows a similar but less marked increase in dry season flows. However, the data for Tan Chau show no discernible trend, notwithstanding the increases predicted in both the modelling undertaken in MRC’s Scenario Assessments reported in 2010 and the recent MRC Council Study in 2017.

Water quality and sediment conditions

Assessment indicators:

  • Water quality and ecological health - compliance with PWQ
  • Sediment transport
  • Salinity intrusion in the delta

Water quality conditions

Water quality conditions within the LMB are regularly monitored in line with the MRC’s Procedure for Water Quality Monitoring (PWQ) and Technical Guidelines (TGWQ), taking into consideration the requirements for human health, aquatic life, and agricultural use.

The data show no apparent trend over time and therefore there should be no immediate concern over water quality conditions within the LMB in the near future. Nevertheless, with increasing industrialisation, growth in urban centres and rising fertiliser and pesticide use, continued monitoring of water quality is recommended.

Water quality conditions for the protection of human health

Between 2010 and 2017, water quality for the protection of human health was almost good or very good along the mainstream, with only a few stations during 2010-14 occasionally having a lower but still acceptable rating.

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Water quality conditions for the protection of aquatic life

For aquatic life, records for 2010-17 show that the average rating across all stations has been good, with only one station in Viet Nam, My Tho, having a consistently low rating due to failure to meet targets for total phosphorous and nitrate-nitrite. For agricultural use, over the same period only one monitoring station, My Tho again, was rated less than very good. This was due to a failure to meet the target for electrical conductivity in 2016.

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Suspended sediment concentrations at Chiang Saen

Suspended sediment concentrations have been monitored since 1994, demonstrating that the concentration and the variability of suspended sediment have decreased considerably since 2001. At Chiang Saen, sediment flows have decreased from about 85 Mt/yr to 10.8 Mt/yr, meaning that the sediment contribution from China to the Mekong mainstream sediments has decreased to about 16% of all sediments in the LMB as compared to about 55% historically. A similar trend is seen downstream at Pakse, where average loads have decreased from 147 Mt/yr to 66 Mt/yr between 1994 and 2013.

These changes in sediment concentrations, brought about by the construction of storage reservoirs principally in China, signal a substantial and seemingly permanent change in the river’s morphology. Impacts of these changes can be expected all along the river as it seeks to readjust to its new regime. Furthermore, few nutrients will reach the remaining wetlands and the delta and coastal building processes will be modified. Understanding how these changes will impact on the river, the environment and the socio-economic development of the LMB needs to be strengthened, so that coping strategies can be determined.

Salinity intrusion

Salinity intrusion within the Viet Nam delta is a function of the flow volumes that reach Viet Nam. Typically, each year, a total of 1.85 million ha are affected annually be elevated salt concentrations. There are no time- series data available to demonstrate whether there are any trends in the extent of area affected, although the fact that dry season flow volumes at Tan Chau have changed little in recent years suggests that the area affected is unlikely to vary much.

Status of environmental assets

Assessment indicators:

  • Wetland area
  • Condition of riverine habitats
  • Condition and status of fisheries and other aquatic resources
  • Condition and status of ecological significant areas

The LMB wetlands are important biodiversity hotspots that play an important role in the economy, society, and culture of the region. Nevertheless, LMB wetlands are being gradually either lost or degraded, mostly as a result of agricultural and other developments. With a little over 100,000km2 of wetlands left in the LMB in 2010, MRC has estimated that less than two per cent of the original wetland area in the Mekong Delta remains. Data for the extent of wetlands in 2015 are being compiled at present and are expected to show a continued reduction in area. If this trend continues, the remaining wetlands may all but disappear, resulting in a significant impact on bio-diversity in the basin. Steps are urgently needed to go beyond assessing individual projects and to develop a strategy by which all, or at least a large number, of the remaining wetlands can be both protected and nurtured on behalf of future generations.

Exposed sandy and rocky riverine habitats are important habitats for vegetation, herpetofauna, and birds in the dry season. Deep pools in the LMB are recognised as important geomorphic features, providing refuge and spawning habitats for a variety of fish species. Whilst no up-to-date information is available to state whether there has been a significant change overall in their condition, it is expected that rising dry season water levels from increased flow regulation, together with backwaters from planned reservoirs and the resulting changes in sediment concentrations, pose a threat to these environmental assets. Well-prepared and sensitive design guidance remains important to minimise these potentially damaging impacts.

The Mekong River system hosts one of the most diverse and prolific freshwater capture fisheries in the world. Recent estimates of the biota of the greater Mekong region include up to 1,148 species of fish, as well as 20,000 plant species, 430 mammals, 1,200 birds and 800 reptiles and amphibians. However, accelerating economic development, population growth, and increased consumption patterns are placing pressure on the environment. Currently, 14 species are listed as critically endangered (including the Irrawaddy dolphin and Mekong giant catfish), 21 species are listed as endangered, and a further 29 species are considered vulnerable.

Total capture fisheries production in the Lower Mekong Basin from the early 1990s to 2015 (mt)

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Over the last decade and a half, the amount of reported wild fish catch has risen from 0.4 MT in 1991-92 to 2.3MT in 2015. However, fishing effort has increased and smaller fish now make up an increasing proportion of the total catch. Separately, with increased urbanisation, changing consumption patterns and growing export markets, the aquaculture sector is growing rapidly and is increasingly important to the basin’s economy and food security.

Aquaculture production has grown significantly from 0.7 MT in 2002 to 2.1 MT in 2012, 86% of which was in Viet Nam. With growing pressures on capture fisheries from new developments and increased consumption, a proactive approach is needed to manage the sector in a sustainable manner.

Aquaculture production in the LMB from 2002 to 2014 (tons)

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Ecologically significant areas encompass a range of different ecosystem types, including rivers, wetlands, forests, and grasslands. A substantial number are under some form of protection as Ramsar sites, biosphere reserves, national parks, and other forms of conservation measure. After decades of declining forest cover there are recent signs of an increase in forested area, especially in Lao PDR. Increasing protection for important natural habitats should over time help support the LMB’s threatened plants and animals. Connecting habitats through biodiversity corridors and taking a cooperative landscape approach to management and enforcement of regulations with the engagement of local communities will be important.