Summary of the natural environmental key issues in the Mekong River Delta basing on the upadated documents summary of the natural environmental key issues in the Mekong River Delta basing on the upadated documents

Preamble
The Resolution 120/NQ-CP dated 17/11/2017 of the Vietnam Government on the Sustainable Development of the Mekong River Delta in response to climate change clearly states the special importance of the Mekong Delta for the whole country and identifies: “The Mekong Delta has many development opportunities but is also facing many challenges because it is a land sensitive to natural changes, climate change and exploitation of water resources in the upstream areas causing negative impacts on the development of the region. The downside from economic development activities in the region has been increasingly fierce, causing many consequences such as environmental pollution, serious ecological imbalance, land subsidence, groundwater level decline, land and coastal erosion. That reality requires a new vision, strategic orientation, comprehensive solutions, radical, synchronous, maximum mobilization of resources and the participation of all economic sectors for sustainable development of the Mekong Delta ”.
Implementing the Law on Planning No. 21/2017/QH14 and Resolution No. 120/NQ-CP dated November 17, 2017 of the Government the Ministry of Planning and Investment (MPI) was assigned by the Government to organize the planning of the Mekong Delta Region, period 2021-2030, vision to 2050 (hereafter: "Mekong Delta Planning" or "Regional Planning").
The JV Royal HaskoningDHV and GIZ (German International Cooperation) were assigned to research and formulate the Regional Planning and GIZ in the JV was responsible for the research and preparation of the strategic environmental assessment report (SEA). The SEA consultant team consists of 4 Vietnamese environmental and social experts and  2 international experts chaired by Assoc. Prof. Dr. Le Trinh (VESDEC). The duration of the SEA, included many consultations and revisions, was 12 months.
The outstanding feature of this SEA research process is that it is conducted almost concurrently with the regional planning study, so the environmental and social issues of the SEA are fully integrated. into the planning process. The main advantage of SEA is to use the latest sources of data on natural, economic and social components (up to 2020), including maps and directions, planning projects provided by the Planning Team, combining with application of advanced international SEA methods. Therefore, it may predicts, assesses at a quantitative or semi-quantitative level of changes in the key environmental issues, including changes in environmental quality and pollution, waste generation, greenhouse gas emissions, changes in ecological and social resources. The SEA must comply with the Vietnam Laws and the World Bank Safeguard Policies.
Below we would like to provide summary of some specific natural environmental issues of the Mekong Delta basing on the latest data and information for people studying or teaching in environmental science.

Part One: Summary of special issues of topography, land subsidence and soils part one: summary of special issues of topography, land subsidence and soils
1.1. Geographical Location
The Mekong Delta is bordered by the Kingdom of Cambodia and Tay Ninh province to the north. Ho Chi Minh City to the Northeast; The West Sea (Gulf of Thailand) to the West and the East Sea to the South and Southeast.
The Mekong Delta has an area of 4,067,138 ha of land (93.9%) and about 245,000 ha of rivers and canals (accounting for 6.1% of the total Region area), accounting for about 5.1% of the total Mekong basin. The Mekong Delta has a vast sea area, closed to the main maritime routes connecting with the world.
1.2. Topography, Geomorphology
The Mekong Delta is a relatively young delta, with an average elevation of 0.5 to 1.2 meters above mean sea level, and many areas with altitudes below 0.5 meters.
 

 

                                  Figure 1. Topographic map of the Mekong Delta Region of Vietnam

  Source: Royal HaskoningDHV - GIZ, Atlas, Feb./2021.

The coastal area has high sand dunes, alternating with low tide flooded areas, most commonly in the provinces of Bentre, Travinh, Soctrang. Dongthap Muoi is a low-lying area, so it is often flooded during the flood season. The lower catchments of Cailon - Caibe rivers and Uminh Thuong and Uminh Ha are the lowest land areas with elevations from 0.1 to 0.7 m, always flooded during high tide, heavy rain and upstream flood water. Some areas in An Giang and Kien Giang provinces near the border with Cambodia have many mountains, rocky mountains and high terrain.
With the dominance of the wetland at the end of the large river basin the Mekong Delta has nearly 20 geomorphologic units: coastal area, mangrove area, alluvial area, floodplain area, tidal zone, floodplains, swamp areas….
1.3. Coastal Sedimentation Process and Erosion Problem
The Mekong is one of the 10 rivers in the world in terms of flow, with the largest amount of alluvium and sediment, which can reach 160 million tons. Much of this sediment is transferred into the East Sea. The river's huge amount of sediment has created great effects on the geochemical - biochemical changes of the region, water quality as well as coastal erosion. In fact, the transport and deposition of sediments over the course of 6,000 years formed the deltas. Some studies confirm that most of the sediment flows southward to the southernmost tip of the Camau peninsula, causing sedimentation to continue to expand the peninsula to the south and west (about 26 m/year). Meanwhile, erosion is happening along the coast of the East Sea (about 16 m/year) (Figure 2).
 

 

Figure 2. Erosion and sedimentation of the East Sea coast from Soctrang to Camau, 1973 - 2014

Note: Red: Eroding area, loss of coastal land; Green: Sea accretion area.

Source: Royal HaskoningDHV - GIZ, Baseline Report, Mekong Delta Region Plan for the period 2021 - 2030, vision to 2050.

Sedimentation is an important factor for delta formation and agricultural potential. However, over the past 20 years, with the construction of more and more ring dikes and the development of upstream hydropower reservoirs, the sediment load of the river has decreased significantly in the downstream area. According to the Mekong River Commission (MRC, 2015), the amount of sediment to the Mekong Delta can be reduced by 56 to 64% compared to the natural average (previously, the annual sediment flow into the Mekong Delta was estimated to be about 150 million tons). A severe decline has been observed in recent years, with a major impact on soil fertility, river morphology and wetlands, the morphology of shallow seas and the productivity of the seas. and shoreline stability. In addition, the drastic change in runoff flow and sediment depletion in the downstream area are among the causes of riverbank erosion.
Coastal and riverbank erosion is a growing phenomenon in the Mekong Delta, not only causing loss of land, obstructing the flow, but also seriously harming housing and the safety of the people. This is one of the environmental issues that need special attention in the planning and development of the Mekong Delta. According to the report of the General Department of Natural Disaster Prevention and Control (Ministry of Agriculture and Rural Development, June 18, 2018) at the time of statistics: In the Mekong Delta, there are 562 sites of landslides over a length of nearly 800km, of which 55 are particularly dangerous. and 140 at critical level (Figure 3).
 

 

Figure 3. Location od the sites with a particularly dangerous landslide hazard

Source: General Department of Disaster Prevention and Control, Ministry of Agriculture and Rural Development, 18, June 2018 (Tổng cục Phòng chống thiên tai - Bộ NN&PTNT, Trang tin, 18/06/2018).

With the above information, it can be seen: coastal erosion is and will have great environmental and social consequences. Therefore, this is one of the main environmental issues that need to be overcome in the Mekong Delta.
1.4. Land Subsidence
In the Mekong Delta, an important environmental risk phenomenon is land subsidence that is becoming more and more rapid and serious. Report of the Department of Water Resources Management - Ministry of Natural Resources and Environment (June 18, 2019) shows: in the period of 2014, 2015 and 2017 with 339 monitored sites in the Mekong Delta and Ho Chi Minh City, compared with the elevation value in 2005 there are 306 site of subsidence, only 33 sites that were not changed. In 306 site of subsidence the settlement rate changes from 0.01 to 6.8 cm/year, and an average of 1.07 cm/year.
Based on the level of subsidence measured at 339 above-mentioned sites, preliminary zoning according to the level of subsidence was implemented. The results show that the areas with subsidence level less than 5cm is about 12,160km² (including Vinhlong, Dongthap, Tiengiang, Longan ); the 5 - 10cm subsidence area is about 8,430km² (Cantho, Soctrang, Baclieu, Haugiang); Large subsidence area over 10cm is about 3,390km² (Ho Chi Minh City, Vinhlong, Cantho, Haugiang, Soctrang, Dongthap, Angiang, Baclieu, Camau). The subsidence area below 5cm has 97 sites, mainly distributed in the provinces of Tiengiang with 23 sites, Longan with 28 sites, and Kiengiang with 16 sites. The subsidence area of 5 - 10cm has 72 sites, mainly distributed in Soc Trang province with 17 site, Kiengiang with 11 sites, Cantho with 9 sites; Vinhlong province currently has no site with subsidence level of 5 - 10cm.
The hydrogeological model was used by Minderhoud et al. (2017) to quantify the degree of subsidence due to groundwater extraction (Figure 4 below). The results showed t the areas in the Mekong Delta had a level of land subsidence of about 30-35cm over 25 years and that the annual subsidence rate in 2015 was 2.5cm in some areas, significantly higher than the region of Ho Chi Minh City.
 

 

(a) Cumulative land subsidence resulting from groundwater extraction (1991-2016); (b) The rate of subsidence in 2015.

          Figure 4. Subsidence rate in the Mekong Delta due to groundwater extraction

Source: Royal HaskoningDHV - GIZ, Baseline Report, Mekong Delta Integrated Region Plan for the period 2021 - 2030, vision to 2050.

Many domestic and foreign studies believe that excessive groundwater extraction has been occurring for many years as the main cause of rapid subsidence in the coastal areas, the Camau peninsula, the central Mekong Delta and the city area. According to the report of the Department of Water Resources Management (Ministry of Natural Resources and Environment): The total exploitation flow of the above wells is about 1.97 million m³/day, with the extraction density in the subsidence areas varying from 3 m³/day/km² (Angiang) to 249 m³/day/km² (Ho Chi Minh City), the entire region averages about 47 m³/day/km², estimated exploitation flow is about 840 thousand m³/day. Overall, the whole Mekong Delta and Hồ Chí Minh City: in the areas that are not subsidence there is a small density of water extraction and vice versa. For regions with different levels of subsidence, the highest subsidence area (over 10cm) has the largest density of groundwater extraction (111 m³/ngày/km²) "(cited document).
The most recent land subsidence study conducted by INDRA-GISAT (2019) is based on inSAR satellite data. Figure 5 below shows, areas in the Mekong Delta have different rates of land subsidence: In the period 2014-2019 there were locations with the rate of land subsidence above 3 cm/year, some locations land subsidence level of 5 cm/year. This is higher than the rate previously measured and modeled for subsidence due to groundwater extraction and 10 times higher than the current annual average sea level rise.

 

Figure 5. Results of subsidence monitoring in the Mekong Delta region based on INSAT satellite image analysis.

Source: GIZ - INDRA-GISAT (2019) (extracted from: Royal HaskoningDHV-GIZ, Baseline Report: Climate change, Feb./2020).

However, the scale, the level of impact that increases the settlement process also depends on the characteristics of natural factors and human activities: Young sedimentary characteristics in the process of consolidation, neovoltaic activities. tectonics, the process of deposition, accretion of the surface of the terrain ... and excessive exploitation of underground water, urban construction, infrastructure works, the process of impact impact of traffic activities.
With the above information, we can see: Land subsidence is and will cause big environmental and social consequences. Therefore, this is one of the key environmental issues that should be prevented in the Mekong Delta.
1.5.  Soils
The soil map of the Mekong Delta region is shown in Figure 6 below.
The main land groups in the Mekong Delta include:- Acid sulfate soils (WRB - FAO: Ortho - Thionic Gleysols), 1,600,263ha, accounting for nearly 41.1% of the Mekong Delta area): Characterized by high acidity (low pH), potential aluminum and iron content (pyrite, FeS₂) is high and lacks phosphorus. This soil group also includes acid sulfate soils, with heavy and moderate salinity. Acid sulfate soils are most concentrated in Dong Thap Muoi and Long Xuyen quadrangle, while saline acid sulfate soils are concentrated in the center of Ca Mau peninsula. If the water layer and vegetation are removed: the pyrite in the acid sulfate soil will be exposed to the air, which can produce sulfuric acid by a bio-chemical process, causing soil and water acidification.Acidification of river and canal water sources leading to harm to aquatic life, plants and water supply is a problem that has been and will continue. This is one of the specific environmental problems in the Mekong Delta.

 

 

                          Figure 6. Distribution of major land groups in the Mekong Delta

                        Source: Royal HaskoningDHV - GIZ, MDIRP, atlas, 2/2021.

- Alluvial soils (Fluvisols), 1,189,396 ha (30.4%): Concentrated in the central region of the Mekong Delta. This soil type has a high fertility, suitable for most crops.
- Salic Gleysols (Salic Gleysols) 744,547ha (19.10%): Distributed in the coastal area. Brackish water shrimp farming is developing in many areas. The coastal saline area from Tien Giang to Ca Mau is suitable for mangrove development.
- Other soils (0.35 million ha): including peat soil (Histosols) in U Minh region, gray soil on ancient alluvium (Plintosols) in the northernmost part of the Mekong Delta and eroded soil and rocky inert (Leptosols) in the Northwest Mekong Delta.
 
Next parts:
-  Part Two: Characteristics of water resource and hydrology.
-  Part Three: Current status of water quality and pollution.
-  Part Four: Current status of air and soil quality and pollution.
-  Part Four: Biological resource characteristics and biodiversity of inland freshwater area.
-  Part Five: Biological resources characteristics and biodiversity in coastal and marine area.
-  Part Six: Mekong Delta economic-ecological zoning.

Source: Report on the SEA for the Mekong Delta Integrated Regional Planning for the period 2021-2030, with a vision to 2050, prepared by the JV Royal HaskoningDHV - GIZ for the Ministry of Planning and Investment, March 2021 version, edited by Le Trinh).

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