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

Abstract

Large, shallow‐water lakes located on floodplains play an important role in creating highly productive ecosystems and are prone to high concentrations of suspended solids due to sediment resuspension. In this study, the aim was to determine the dominant processes governing the total suspended solid (TSS) concentration at the water surface in Tonle Sap Lake, Cambodia, which is a large, shallow‐water lake. Satellite remotely sensed daily reflectance data from 2003 to 2017 were used. Seasonal changes in TSS concentration indicated that bottom sediment resuspension during dry seasons was mostly caused by wind and the TSS concentration was closely correlated with the water depth of the lake. The TSS concentration during flood periods was controlled by both wind and inflow currents from the Tonle Sap River. Additionally, we confirmed that surface/subsurface flow with a low TSS concentration from forests on the floodplain lowered the TSS concentration year round, except during August and September. This fact implied that the floodplain forest area decrease may increase the lake TSS concentration. An analysis of the long‐term changes in TSS indicated that a decrease in the water level during flood periods resulted in the high TSS concentrations observed during the subsequent dry periods. Therefore, climate change and water resource development, which are likely to cause water level reductions in the Mekong River during flood periods, may increase the TSS concentration in Tonle Sap Lake, particularly during the dry season.

Spatial and Long-Term Temporal Changes in Water Quality Dynamics of the Tonle Sap Ecosystem

“…Sediment contributions are an important factor for explaining potential changes in the decline of fish catch in the Lower Mekong Basin. In some locations of the lake, increasing floodplain vegetation density also reduces soil erosion and TSS concentrations [25]. The decline in forest cover and water level [5,25] leads to spatial variability in the sediment pulse and increased TSS.…”

“…In some locations of the lake, increasing floodplain vegetation density also reduces soil erosion and TSS concentrations [25]. The decline in forest cover and water level [5,25] leads to spatial variability in the sediment pulse and increased TSS. Quantifying new sediments deposition from sub-watersheds surrounding the lake versus internally cycled sediment from lake mixing is an important next step for understanding TSS dynamics in the TSE.…”

“…DO trends were variable depending on sediment flux, air temperature, forest cover, and flooded forest [25,27,43]. Chea et al [2] found a decline in DO in the northern part of the lake due to human activities.…”

“…Sediment is also delivered to the lake through tributary inputs. At the same time, sediment at the bottom of the lake is resuspended due to wind movement and increased chemical concentration i.e., TSS, TP, NH 4 + , and NO 3 − [5, 25,65]. However, at PK in the TSR, sediment during the wet season was about 20% higher than the dry season [66].…”

“…Dams built on the Mekong River mainstem and its tributaries have reduce streamflow and sediments flowing to TSL [11,[22][23][24]. Also, flooded forest loss in the TSE watershed, increasing agriculture runoff and climate change are causing physical and chemical changes and water quality problems in TSL [16,25]. The flooded forest in the TSE has a constant annual loss rate of 1.2% for the last 25 years (from 1993 to 2017) [26].…”