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To evaluate the seasonal water circulation of Tonle Sap Lake and its tributary rivers in Cambodia, the spatial distribution patterns of major and trace elements in surface water were investigated. Based on the similarity of the dissolved elemental concentrations, the water samples were mainly divided into the three groups: samples with relatively high percentages of Ca, Mo, and Sb (Subcluster B1); samples with high Si, Al, and Fe (B2); and samples with high Na, K, and Mg (B3). During the rainy season, the elemental composition of lake water (B1) appeared to be greatly influenced by the intrusion of water from the Mekong River (B1) through the Tonle Sap River (B1). During the dry season, the type of lake water shifted to B3, suggesting that the lake water stored during the rainy season was replaced by inflow from other tributaries and groundwater in its vicinity. Thus, the seasonal changes in the elemental composition of the lake water were largely controlled by surface water and groundwater circulation. The dissolved As concentration was higher in the lake water and during the dry season than that in the river water and during the rainy season, indicating the discharge of As from the lake's bottom sediment during the dry season. Although the redox cycling of Fe and Mn appeared to be less important due to the shallow water depth in the lake, there are potential risks of As poisoning induced by the formation of an anoxic water mass and increment in the concentration of phosphorus if eutrophication continues to progress.

The potential of catch per unit effort (CPUE) analysis based on statistics of local fisheries in Tonle Sap Lake in Cambodia was evaluated. The fishery statistics system was improved through a cooperative project conducted by the Department of Fisheries and the Mekong River Commission between 1994 and 2000, especially in the seven provinces adjacent to Tonle Sap Lake. However, the fisheries statistics were not effectively utilized for sustainable stock management. After the cooperative project, fish catch data sorted by species or species group were collected at the province level in the seven provinces. Another recent project also revealed the numbers of fishing gears that operated in the seven provinces. The CPUEs of ten species in Kampong Thom Province—including Channa micropeltes and Cirrhinus spp.—could be calculated from 1994 to 2007, because these are caught solely using bamboo fence systems or barrages. CPUE analysis clarified that stocks of high-price fishes such as Ch. micropeltes, Hampala spp., and Pangasius spp. have deteriorated while those of relatively low-price fishes such as Cirrhinus spp., Cirrhinus microlepis, Cyclocheilichthys enoplos, and Channa striata have increased in recent decades.