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Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, 50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

International audience; This brief contains the data needed to calculate and assess the robustness of a water level – flood link (WAFL) in the Cambodian Mekong Delta, which was used to analyze changes in the long-term behavior of Monsoon inundations in the region. The data comprises the WAFL raster (.tif) files for two zones in the delta. Zone A is located on the right bank of the Bassac River, a distributary of the Mekong. Zone B is bracketed between the Mekong River and the Bassac River. The WAFL was calculated by linking water levels measured by the Mekong River Commission (MRC) at the hydrological station in Koh Khel, with inundation maps derived from Sentinel-1 and -2 images taken between 2017 and 2021. The final WAFL raster files provides a basis for estimating inundation extents using in-situ water levels. Furthermore, this brief includes data used for the assessment of WAFL, including in-situ water level data and the extents of natural vegetation in the case study area in 1990, 2000, 2010 and 2020. The former was collected using a differential pressure logger. The latter was calculated from historical Landsat image composites. Finally, raster files representing the incidence and duration of inundations in the case study area before and after the year 2008 are provided. These were calculated based on the WAFL and the MRC water levels. For each area, before- and after-images are available, as well as a raster representing the change between the two. To simplify visualization and geographical location, shapefiles (.shp) of the study area and the location of the in-situ logger are also provided.

The management of the ecological integrity of the aquatic ecosystem requires monitoring, analysis, and assessment of the water quality. Thus, this chapter presents the spatiotemporal distribution of basic physicochemical water quality in Tonle Sap Lake based on our recent extensive field survey. The water temperature ranged from 25.6 to 36.9 °C and a region of low water temperature (approx. 29 °C) from 30 to 40 km along the Longitudinal transect. The ranges of pH, electrical conductivity (EC), and total dissolved solids (TDS) were 5.1–9.5, 11–610 μS/cm, and 7–366 mg/L, respectively. Elevated EC and TDS indicated pollution at both ends of the lake. Dissolved oxygen (DO) in Tonle Sap LakeTSL was highly dynamic, varying from anoxic (0.1 mg/L) to highly saturated conditions (16.1 mg/L). Localized anoxia and hypoxia existed, especially in the floating villages and the densely populated northern upstream. Dissolved organic carbon (DOC), particulate organic matter (POM), and oxidation–reduction potential (ORP) varied within the range of 1.6–16.8 mg/L, 0.2–145.7 mg/L, and −212–472 mV, respectively. Turbidity exhibited high seasonal variability, fluctuating by three orders of magnitude with a typical high value during the low-water season.

Sediment resuspension in Tonle Sap Lake (TSL) occurs predominantly during the period from March to June when the lake is shallow. According to our survey in 2016–2017, the average resuspension rate ± standard error in the whole lake was 115 ± 66 g/m2/day in September, 93 ± 128 g/m2/day in December, 260 ± 246 g/m2/day in March, and 348 ± 227 g/m2/day in June. Resuspension rates in the low-water period (i.e., March and June) had a positive correlation with the concentration of total suspended solids (r = 0.45, p < 0.01). These results indicate that sediment in TSL and its floodplain is a major source of suspended solids during the low-water period. The resuspension rate is reduced by floodplain vegetation to approximately one-third of that in the open water of TSL. Besides water level and vegetation, several factors such as the dynamic ratio, wind, human activity, and aquatic fauna affect resuspension, and their relative importance varies with the water level. Overall, the flood pulse substantially influences sediment dynamics in TSL, especially resuspension, as a distinct seasonal process.

Water level variation substantially affects the trophic levels in a lake. The primary objective of this research is to investigate the impact of water level fluctuation on sediment and phosphorous (P) dynamics in Tonle Sap Lake (TSL), Cambodia. Water samples were collected from eight cross sections in a lake at 3-month intervals for 3 years, during the low-water period (March and June) and high-water period (September and December) from December 2016 to June 2019. Water quality parameters—temperature, conductivity, salinity, dissolved oxygen, pH, oxidation reduction potential, chlorophyll-a (Chl-a), and blue green algae—were measured using an EXO(R) sensor. The sedimentation and resuspension rates of the sediment were measured using a sediment trap. Sediments were collected during the low-water period of March 2017. The sediment resuspension condition was simulated via centrifugation (150 rpm, end-to-end mechanical shaker, room temperature 25 °C for 24 h) to assess phosphorous dynamics. The P content in the bed sediment was fractionated to obtain loosely bound, metal oxide bound, apatite bound, and organic bound P. Sediment resuspension was greater during the low-water period (< 1 m) than that during the high-water period (> 4.8 m). The sites exhibited significant variation (p < 0.05) in terms of dissolved oxygen, pH, oxidation–reduction potential, Chl-a, and depth during low- and high-water periods. In general, the Chl-a concentration throughout the sampling campaigns ranged between 1.7 and 9.0 μg/L, suggesting the existence of a mesotrophic state in the TSL. The zero equilibrium P concentration of sediment in TSL was greater when the sediment was under the resuspension condition (18.9 ± 3.0 μg/L) than under the static condition (7.7 ± 1.1 μg/L). In TSL, during resuspension (low-water) conditions, sediments act as a source and release P (apatite bound, loosely bound, metal oxide bound, and soluble reactive P). However, in static (high-water) conditions, sediments act as a sink by adsorbing P from the overlying water.