Temporal Variation of Sediment and Nutrients(Nitrate and Phosphorus) Dynamics in the Mekong/Tonle Sap
River in Cambodia
V. Kaing1, T. Sok1, C. Oeurng1*, I. Ich1, M. Marith1, K. Chum1, and C. Yoshimura2
1Faculty of Hydrology and Water Resources Engineering, Institute of Technology of Cambodia,Cambodia
2Department of Civil and Environmental Engineering, Tokyo Institute of Technology, Japan

Dr. Oeurng Chantha
Faculty of Hydrology and Water Resources Engineering, Institute of Technology ofCambodia, Cambodia

WATER
RESOURCES| MODELLING|CLIMATECHANGE
GIS-REMOTESENSING | WATER & SANITATIONWATERRECOURSESENGINEERING
AND |RURALINFRASTRUCTURESវ �ទ���នបេច� ក វ �ទ�កម���Outline of Presentation

1INTRODUCTION

2MATERIALS &METHODOLOGY

3RESULTS &DISCUSSION

4CONCLUSIONSWATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

2Introduction

Materials &Methods

Results &Discussion

Conclusions

BACKGROUND Ecological and productivity ofTonle Sap Lake controlled by
Mekong’s seasonal water
delivery, sediments andnutrients.
 Development pressures in theupstream lead to changing insediment and nutrient load ofTonle Sap Lake
WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

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Sources of nutrients

WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION4Introduction

Materials &Methods

Results &Discussion

Conclusions

OBJECTIVESThe specific objectives to the study are:i.

To investigate temporal variation of discharge, TSS, NO3, and TOTPof the Mekong River and the Tonle Sap Lakeii.

To estimate sediment and nutrients load exchange between Tonle Sapand Mekong RiverMarch 2015

WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

Mekong River

Scope of study5Introduction

Materials &Methods

Results &Discussion

Conclusions

Study Site
 Mekong River Cambodia:
Located in Lower Mekong Basin Tonle Sap Lake
• Area: 85,790 km2 (11% of Mekong basin)• Connected the Mekong at Chaktomuk
confluence Discharge, TSS, NO3, and TOTP (fromMOWRAM):• Chroy Changvar (1993-2017)• Prek Kdam (1995-2018)
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Introduction

Materials &Methods

Results &Discussion

Conclusions

Load Estimator LOADEST program of USGS were used to calculate sediment andnutrients load.
 LOADEST estimates constituent loads in streams and rivers by using therating curve method.
 Input data: daily discharge and TSS, NO3, and TOTP monthly bases
 Analysis is base on hydrological year

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Introduction

Materials &Methods

Results &Discussion

Conclusions

Sediment and Nutrient Load of Mekong River
Annual Sediment load of Mekong River Annual water discharge: 368,000 MCM/year Annual sediment load: 77.44 Mt/year
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Introduction

Materials &Methods

Results &Discussion

Conclusions

Annual Nitrate load of Mekong River Minimum load=91 Kt/year and maximum load=200 Kt/year Annual nitrate load: 140 Kt/year
WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

9Introduction

Materials &Methods

Results &Discussion

Conclusions

Annual phosphorus load of Mekong River Minimum load=11 Kt/year and maximum load=77 Kt/year Annual phosphorus load: 38 Kt/year
WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

10Introduction

Materials &Methods

Results &Discussion

Conclusions

Sediment and Nutrient Exchange Between The Mekong andTonle Sap Lake
Seasonal sediment load of Tonle Sap River Lake inflow: water discharge 36,340 MCM/year, sediment load 3.7 Mt/year Lake outflow: water discharge 67,600 MCM/year, sediment load 2.9 Mt/year
WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

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Materials &Methods

Results &Discussion

Conclusions

Annual sediment flux of Tonle Sap Lake

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Introduction

Materials &Methods

Results &Discussion

Conclusions

Seasonal nitrate load of Tonle Sap River Nitrate load into the lake: 9.4 Kt/year Nitrate load flow out of the lake 10.4 Kt/year
WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION13Introduction

Materials &Methods

Results &Discussion

Conclusions

Seasonal phosphorus load of Tonle Sap River Phosphorus load into the lake: 4.6 Kt/year Phosphorus load flow out of the lake 5 Kt/year
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Introduction

Materials &Methods

Results &Discussion

Conclusions

Annual nitrate flux dynamics of Tonle Sap River

WATER RESOURCES | MODELLING|CLIMATE CHANGE | GIS-REMOTE SENSING | WATER & SANITATION

15Introduction

Materials &Methods

Results &Discussion

Conclusions

Annual total phosphorus flux dynamics of Tonle Sap River

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Materials &Methods

Results &Discussion

Conclusions

CONCLUSIONS
 4.8% (3.7 Mt/year) of Mekong’s sediment were delivered to TSL, while
TSL contributed 3.7% (2.9 Mt/year) to Mekong mainstream or Delta.
 The suspended sediment concentration during the lake inflow periods
was much higher than outflow period result in higher sediment load
influx even its water discharge was nearly twice lower.
 The Mekong River carried 140 Kt/year of nitrate and 37.8 Kt/year ofphosphorus.
 The Mekong and TSL exchanged in nearly equal the amount of bothnitrate and phosphorus load (lake’s inflow load: 9.4 Kt of NO3 and 4.6
Kt of TOTP; lake’s outflow load: 10.4 Kt of NO3 and 5.0 Kt of TOTP).
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End of presentation

Acknowledgement

Thanks for your attention

Question & Answer
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