Sediment dynamics in a large shallow lake characterized by seasonal flood pulse in Southeast Asia

Abstract

Most of studies on sediment dynamics in stable shallow lakes focused on the resuspension process as it is the dominant process. However, understanding of sediment dynamics in a shallow lake influenced by flood pulse is unclear. We tested a hypothesis that floodplain vegetation plays as a significant role in lessening the intensity of resuspension process in a shallow lake characterized by the flood pulse system. Therefore, this study aimed to investigate sediment dynamics in this type of shallow lake. The target was Tonle Sap Lake (TSL), which is a large shallow lake influenced by a flood pulse system of Mekong River located in Southeast Asia. An extensive and seasonal sampling survey was conducted to measure total suspended solid (TSS) concentrations, sedimentation and resuspension rates in TSL and its 4 floodplain areas. The study revealed that sedimentation process was dominant (TSS ranged: 3-126mgL) in the high water period (September-December) while resuspension process was dominant (TSS ranged: 4-652mgL) only in the low water period (March-June). In addition, floodplain vegetation reduced the resuspension of sediment (up to 26.3%) in water. The implication of the study showed that resuspension is a seasonally dominant process in shallow lake influenced by the flood pulse system at least for the case of TSL.

Characterization of total suspended solid dynamics in a large shallow lake using long‐term daily satellite images

“…During the period in which water from the Mekong River flows into the lake, the volume of the lake increases from approximately 1.8 km 3 in the driest month to the peak volume of 31.1 to 73.9 km 3 , depending on the flood intensity. The lake area also expands from approximately 2,500 km 2 during the dry season to up to 15,000 km 2 during the flood period (Fujii et al, ; Siev et al, ). The annual inflow from the Mekong River, rivers around the lake, and direct rainfall to the lake accounted for 52.5%, 34.0%, and 12.5% of the total inflow, respectively, from 1997 to 2004.…”

“…Siev et al() collected water samples from the surface/subsurface layers and bottom sediment samples every 3 months from September 2016 to July 2017 at 39 points along Tonle Sap Lake. The researchers estimated the spatial distribution of TSS concentrations in the surface/subsurface layers by interpolating the TSS concentrations measured from the water samples, and the sedimentation/resuspension rate was obtained through analysis of the bottom sediment samples.…”

“…Lakes located on floodplains tend to be shallow and are prone to sediment resuspension (Siev et al, ). Total suspended solids (TSSs) or suspended particulate matter, including suspended sediment, are closely related to the lake environment.…”

“…The survey revealed a detailed seasonal pattern in TSS concentrations and their differences in the lake and floodplain areas. Siev et al () collected water and bottom sediment samples at 39 points along Tonle Sap Lake every 3 months from September 2016 to July 2017 and estimated the spatial distribution of TSS concentrations, sedimentation/resuspension rates, and their seasonal changes.…”

Modelling inundation patterns and sediment dynamics in the extensive floodplain along the Tonle Sap River

“…Being a natural conduit for the bidirectional flow, the TSR serves as an important segment for hydrological connectivity between TSL and the MR and its floodplain. Although there are many studies on sediment transport in the MR basin (Kummu, Lu, Wang, & Varis, ; Kummu & Sarkkula, ; Kummu & Varis, ; Lu, Kummu, & Oeurng, ) and on sedimentation in TSL (Kummu, Penny, Sarkkula, & Koponen, ; Penny, Cook, & Sok, ; Siev et al, ; Tsukawaki, ), a substantial study on sediment dynamics that refers to the spatial distribution of sediment erosion, transport, and deposition influenced by hydrodynamic processes and vice versa in the TSR has not been conducted. Furthermore, climate change and water‐related infrastructure developments in mountainous areas of the MR basin (e.g., constructed and planned hydropower dams) have had a significant hydrological impact on the TSR and TSL and its downstream as a result of the natural flow alteration (Arias et al, ; Arias et al, ; Cochrane, Arias, & Piman, ; Västilä, Kummu, Sangmanee, & Chinvanno, ).…”