It has been two years, starting from the end of 2019 to early 2021, since we noticed the unusual aquamarine hue of the Mekong River, the freshwater algae bloom[1] and their adverse impacts on the Mekong ecosystems and fishing livelihoods of the Isan people in northeastern Thailand. Yet, we have not seen any formal statements by responsible official government departments to explain their analyses on what caused such an unusual phenomenon: the Office of National Water Resources (ONWR) as the Thai National Mekong Committee Secretariat and the Department of Fishery as the key authority for fishery resources. Even though the Thai National Mekong Committee held a meeting on 23 March 2020 and specifically stated it had “analyzed the phenomenon where the Mekong river color turned from turbid brown to very-low-sediment aquamarine (or indigo blue). The Mekong River water quality analysis at Muang Nakhon Phanom, Thailand and Thakhek, Lao PDR reveals the quality is normal and not dangerous to aquatic animals or ecosystems. An exception is the level of suspended solids load which has declined significantly. It is predicted that the suspended solids load would return to normal by the upcoming flood season.” 

Prior to this, the office of the Mekong River Commission’s news release on 9 December 2019 noted the aforementioned phenomenon. The MRC’s analysis on low sediments and algae blooms pointed to the very low flow of the Mekong River. However, this news release only mentioned data from the Nakhon Phanom hydrological station. It did not conduct a comparable analysis to see whether data upstream at the Chiang Saen hydrological station in Chiang Rai was similar. Later, the MRC’s news release on 8 December 2020 continued to relate the algae bloom at the Mekong River to the same cause, a very unusual low flow. 

How can suspended sediments in the whole Mekong River disappeared?

The suspended sediments load at Chiang Saen, where the Mekong River flows to meet Thailand’s territory, is high enough to make the river turbid. However, once the river flows into Lao PDR at Keng Pha Dai in Wiang Kaen, Chiang Rai and reappears at the Thailand-Laos border again at Chiang Khan, Loei, the Mekong River became aquamarine and nearly zero-sediment. The most directly responsible Thai authority and regional organizations that deal with the Mekong River issues seem to not concern with this phenomenon. Even though this has adversely affected local ecosystems and communities, they only refer to the “very good” water quality appeared on the WQI study.

The Xayaburi Dam officially began its operation on 29 October 2019. The dam sits on the Mekong River in Xayaburi (Saiyabuli) province where the Mekong River flows into the Laos’ territory and only 200 kilometers upstream of Thailand’s border at Chiang Khan. The beginning of the operation coincided with the beginning of winter and also the time that an unprecedented phenomenon occurred. The sediment starved aquamarine Mekong River and algae blooms began in November 2019 along the Thailand-Laos border–not too long after the operation of the dam. Previously, algae blooms and low sediment river might occur between February and April of every year as it was when the water volume declined to its lowest in a year. A similar phenomenon occurred around the same time in 2020 and lasted until the beginning of 2021. Is there a correlation between the Xayaburi Dam and the sediment starved aquamarine Mekong? This is the question the community and the society must seek answers.

Mekong River Turbidity by Citizen Science

The meeting of the Mekong People Council at Chiang Khong, Chiang Rai on 2-3 December 2020 finally consolidated the idea of sediment load monitoring by using citizen science approach among the network of community participatory research group, consisting of the Network of Communities in Seven Northeast Provinces of the Mekong River Basin, Rak Chiang Khong Group and the Mekong Butterfly. The monitoring process used turbidity tubes (2-inch diameters and 120 centimeter long) and Secchi disks to measure turbidity in the following 6 sites

The monitoring site at Hong Hian Nam Kong in Chiang Khong is the only monitoring site upstream of the Xayaburi dam. Other monitoring sites are all located in northeastern Thailand and downstream of the Xayaburi dam. Nonetheless, there are several major tributaries of the Mekong that flow into the Mekong mainstream. These major tributaries do not affect the sediment loads or turbidity much during the dry season. However, they have great influences on the Mekong mainstream in the rainy season.

turbidity tubes

The less turbid the water, the more visible the water. 

Data between February and May 2021 clearly show the turbidity of the Mekong River decreases significantly as the river flows more than 700 km downstream from the Hong Hian Nam Khong to the temple at Moo 10 in Ban Pak Chom. The unit of measurement is in centimeters to reveal more differences between low and high turbidity. The more turbid the water, the less visible the water and the more difficult it is to read the marks. The less turbid the water, the more visible the water. 

Data between February and March 2021 reveals the Mekong turbidity decreases significantly. Turbidity level at the Hong Hian Nam Khong is 79 centimeters. The measurements of all the monitoring sites downstream of the Xayaburi dam, from Moo 10 in Ban Pak Chom to Ban Samrong, exceed 120 centimeters. Turbidity levels at the monitoring site in Samrong are 177, 233 and 150 centimeters, respectively. This shows that the Mekong River is very clear in northeastern Thailand as shown in Figure 1-2

figure 1
figure 2

The community is able to use scientific tools to set up a monitoring system to track and compare the Mekong river turbidity between areas upstream and downstream of the Xayaburi Dam. The monitoring process reveals turbidity has decreased significantly and become unmeasurable in February. This finding confirms our hypothesis that the Xayaburi Dam greatly influences the suspended sediments load flowing from Chiang Khong. As a result, sediments deposit by the dam, causing the Mekong River to be sediment starved when the dam releases water to downstream. 

Science of Suspended Sediments/Solids by Government Departments

This section looks at the scientific process and analytic tools appeared in the “Study on Impact and Monitoring of Transboundary Environmental Impact Assessment of Hydropower Projects on the Mekong Mainstream” (Fiscal year: 2014, 2015, 2016, 2017, 2020) reported by the Department of Water Resources and the ONWR’s 2020 report.

The report released in each fiscal year shows monitoring tend to occur in the following 2-3 season: rainy season, winter and dry season. The time when monitoring happens at the site tends to overlap with the Mekong water quality stations. The following table compiles each year’s suspended solids load index. The below table shows the suspended solids load downstream of the Xayaburi Dam, starting from Chiang Khan, is very low or too low to measure in December 2020 and January 2021. However, we cannot directly compare this year’s and the previous year’s the suspended solids load because the weather and the Mekong River each year are not the same. To overcome this difference, we calculate the changes in ratio and use the Chiang Saen hydrological station as a reference. In any year that data from the Chiang Saen hydrological station is not available, we use other hydrological stations located upstream of the Xayaburi Dam as reference. We show the changes in suspended solids load ratio by comparing measurements between Chiang Khan and Chiang Saen and between all monitoring sites and Chiang Saen. See Figure 3-4

Table: Suspended solids monitoring sites at different times
Table: Comparing suspended solids load between measurements at all monitoring sites and the hydrological station at Chiang Saen or Chiang Khong.  
figure 3
figure 4

The ratio of the suspended solids load at the monitoring sites and at the station at Chiang Khan, specifically during the water-receding season and the dry season, before and after the construction of the Xayaburi Dam shows the suspended solids load visibly decline after the construction of the Xayaburi Dam. The ratio declines -77% in December 2020 and -98% in February 2021. The suspended solids load ratio prior to the construction of the Xayaburi Dam in 2014, 2015, 2016 and 2017 declines and increases -10.76, -7.83, -32.14 and 30.26 respectively. The ratio of suspended solids load at all monitoring sites downstream of the dam and Chiang Saen station also appears in similar trend. (Figure 4).

This means that the Department of Water Resources and the ONWR’s “Study on Impact and Monitoring of Transboundary Environmental Impact Assessment of Hydropower Projects on the Mekong Mainstream” can be adapted and applied to calculate the increase or decline ratio of the suspended solids load. The study already shows the significance of the suspended solids load. There is no further need to try to refer to a minimum standard level for the analysis. 

Conclusion

Environmental information upstream and downstream of the Xayaburi Dam in the government departments’ “Study on Impact and Monitoring of Transboundary Environmental Impact Assessment of Hydropower Projects on the Mekong Mainstream” and the aforementioned community-led data collection are important evidences to trace the causes of the sediment starved aquamarine Mekong River that occurred in the past two years since the operation of the Xayaburi Dam. 

In fact, all of the Mekong hydrological stations have been collecting data on the suspended solids/sediments load. All responsible government departments already have data on the suspended solids load. The only problem is that this data is not yet open to the public, even though such data can clearly reveal transboundary impacts of the Xayaburi Dam. Revealing such data is a great way to show the government’s sincerity to protect the interests of the Thai people and the Mekong ecosystems. This data is an important source to confirm the impacts on the people and to voice out along with the people at the bilateral and multilateral meetings. Revealing this data is much more meaningful than a ceremony by the Mekong River to set up a labeling sign and to release fish. Because the sign only stands for a few days before it is removed and abandoned. 

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