6. Conclusions
The Ming Yong glacier catchment in the upper Mekong basin is characterized by distinct wet and dry seasons, with discharge and suspended sediment concentrations (SSC) increasing from February to July and decreasing from August to January. The yearly variations in sediment load for Ming Yong glacier are large (44 kt in 2013 to 91 kt in 2015, and 73 kt in 2016), despite small variations in water discharge. More than 65% of the annual sediment load is contributed between June and August. These observed seasonal variations in the sediment load indicate the complex competing influences of the supply and storage of suspended sediment load. Specifically, the clockwise hysteresis relationship suggest that sediment is stored during the low flow season and transported when flow increased from February to July, with the exhaustion of sediment supply after July. Even though discharge and SSC are generally positively correlated, seasonal variations result in different sediment rating relationships due to the influence of glacial meltwater. Based on the in-situ observations over three hydrological years, the sediment yields are estimated to be 1104 t/km2/year in 2013, 2283 t/km2/year in 2015, and 1833 t/km2/year in 2016.
This study provides baseline measurements for potential future monitoring of the glacial catchment in response to climate change. Concurrently, the data fills the knowledge gap in sediment data for the headwaters of the Mekong River. As this study was conducted in-situ, data was collected manually. For instance, the collection of water samples for filtration or the measurements of water depth could introduce random errors. Thus, the use of specific hydrology equipment in subsequent studies such as data loggers or turbidity meters can increase the sampling frequency and accuracies of future sediment load estimates. Furthermore, installation of a nearby weather monitoring station can give more insight into the diurnal and seasonal ablation patterns of the Ming Yong Glacier, allowing better attribution of the variation in its discharge or transport capacity to climatic or other environmental factors.