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Dynamic transport of the sediment and nutrient in the Mekong River Basin and the role of the Tonle Sap Lake : Assessment coupling data and modelling approaches

Sok, Ty. Dynamic transport of the sediment and nutrient in the Mekong River Basin and the role of the Tonle Sap Lake : Assessment coupling data and modelling approaches. PhD, Ecologie Fonctionnelle, Institut National Polytechnique de Toulouse, 2021, 271 p.

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Abstract

The Asian river basins are great contributors to sediments and nutrient to the seas. These rivers are subject to the influence of climate variability and human activities, which alter the nutrient transport and fate of water quality. The Mekong River is a transboundary river in Southeast Asia and plays an important role in economy, agriculture and also by contributing fluxes into the Mekong delta and into the sea. Within the Mekong basin, the Tonle Sap area is a complex system with a unique reverse flow between Tonle Sap Lake and the Mekong River. Sediment and nutrient in the Mekong River are important to sustain the geomorphology of the floodplains and particularly the Tonle Sap Lake. At the same time, Tonle Sap Lake are contributing the sediment and nutrient for the Mekong delta. Therefore, the sediment and nutrient assessment in the Mekong River and its linkage between the Mekong mainstream and the Tonle Sap Lake would be necessary to evaluate. The study was to assess the dynamic transport of sediment and nutrient in the Mekong River Basin and evaluate the role of the Tonle Sap to the Mekong River through the coupling data and modelling approaches. The physical-based SWAT model was used upstream of the Mekong delta to simulate the water regime and suspended sediment and nutrient flux of the Mekong River. The SWAT model was calibrated based on observed discharge at eight gauge stations, suspended sediment load at six stations and nutrient data at five stations from 1995 to 2016 at a monthly time step. To understand the role of Tonle Sap Lake in sediment and nutrient to Mekong River, the study considered the balanced of the Tonle Sap reverse system at seasonal and annual scales. Before entering the confluence of Mekong and Tonle Sap Lake and delta, the sediment load is found 72±26 Mt/year with a decreasing annual trend from 1995 to 2018. The annual sediment yield of the upper 80% Mekong River basin (310 t/km2/year) is comparable with sediment yields reported for other world major rivers. The Mekong annual average riverine nitrate yield was 202 kg/km2/year with 361.8±83.5 kt/year from 1985-2016 of annual nitrate flux before entering the Mekong delta. The sediment loads variability of the Mekong River and Tonle Sap system presented in this study helps clarify the exchange annual discharge and sediment load toward the Mekong delta. The study also highlighted that the fact that Tonle Sap is the sediment sink (1.35±0.7 Mt annually) in the Mekong basin lead to a reduction in sediment supply, which compounds the threat to the delta from accelerated subsidence and sea-level rise. The study has emphasized the interaction role of Tonle Sap Lake and Mekong in nutrient supply for the Mekong delta. On the annual scale, it is worth discussing these interesting results revealed Tonle Sap Lake contributed 34 kt/year of nitrate and 6.6 kt/year of total phosphorus to the Mekong system or Mekong Delta. In contrast, the Mekong River shared nitrate flux 35.8 kt/year and 8.7 kt/year of total phosphorus to Tonle Sap Lake and its floodplain during the high flow season. Future studies of hydrology together with sediment and nutrients can be carried on based on this model with scenarios of global changes, such as climate changes and land-use changes and include the sediment and nutrient input to Tonle Sap Lake system from the lake tributaries and interconnect with the Mekong River basin model.

Item Type:PhD Thesis
Uncontrolled Keywords:
Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Laboratory name:
Research Director:
Sanchez-Pérez, José Miguel and Oeurng, Chantha
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Deposited On:23 Feb 2022 15:31

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