A Severe Decline in the Mekong Plume's Extent and Seasonality After 2000

www.hapri.org

Dung Duc Tran — Senior Research Associate

A study co-authored by Yikang Feng, Edward Park, Jingyu Wang, Lian Feng and Dung Duc Tran (HAPRI Senior Research Associate) finds a severe decline in the extent and seasonality of the Mekong plume after 2000. The plume matters because it sustains the geomorphology and rich biodiversity along the coastal zone of the Vietnamese Mekong Delta.

Context

The Mekong plume, the sediment-laden river water reaching the sea off the Vietnamese Mekong Delta, has been under intensifying threats from dams, riverbed mining and sea level rise. The authors note that understanding of how much these intensifying stressors have altered the long-term spatiotemporal dynamics of the plume remains limited.

What the authors link the decline to

Methods

The study examines the Mekong plume over 1988–2022 using remote sensing, in-situ hydrological data and continuous wavelet transform. It analyzes the long-term average seasonal plume extent, the interannual trends of seasonal suspended sediment discharge and alongshore drift, and changes in the long-term exposure of coastal mangroves to suspended sediment. Field suspended sediment concentration data from five major gauging stations across the upstream, midstream and downstream sections of the delta between 2010–2021 were used to calibrate 101 Landsat surface reflectance observations to estimate suspended sediment concentration.

Key findings

• Comparing 1988–1999 with 2000–2022, the study reports a 63 % decline in plume extent in the dry season (December to May) and an 83 % decline in the wet season (June to November).

• Along the coastline of the Mekong Delta, the annual exposure to suspended sediments declined by 37–54 % between 1988–1999 and 2000–2022, corresponding to a maximum annual mangrove loss of 15 % by coastal erosion.

• Despite the decline in the plume, surface suspended sediment concentration at the alongshore drift began to rise in 2008, marking a reversal in the trend after two decades of descent.

• The authors primarily attribute the decrease in plume and coastal exposure to reduced terrestrial sediment flux, largely influenced by the construction and operation of transnational dams.

How the study was done

Keywords:

• Vietnamese Mekong Delta

• River Plume

• Suspended Sediment

• Remote Sensing

• Coastal Mangroves

• Transnational Dams

Link:

https://doi.org/10.1016/j.jhydrol.2024.132026

Citation:

Feng, Y., Park, E., Wang, J., Feng, L., & Tran, D. D. (2024). Severe decline in extent and seasonality of the Mekong plume after 2000. Journal of Hydrology, 643, 132026.