Long-term rates of sediment accumulation in the Tonle Sap, Cambodia: a threat to ecosystem health?

Abstract

The Tonle Sap is an invaluable resource for the people of Cambodia, and is a globally significant ecological site. Much of the literature published on the environmental health and management of the lake suggests that its sustainability is threatened by accelerated rates of infilling related to unfettered land-use in the catchment. However, the evidence for supposedly increased sedimentation rates is confused and contradictory, and there have been very few studies that have attempted to actually measure the rate at which sediment is accumulating on the bed of the lake. This research measures long-term sedimentation rates in the Tonle Sap in an attempt to provide an empirically derived ‘baseline’ against which more recent and allegedly accelerated sedimentation rates can be compared. Radiometric dating techniques (14C, 210Pb, 137Cs) reveal that sediment has been accumulating in the lake at an average long-term rate of less than 1 mm per year. There is a clear and consistent decline in the rate of sediment accumulation in the lake basin over time, with the highest rates recorded in the middle to early Holocene epoch. It is recommended that research be directed toward measuring changes in the morphology of the lake margin over time, rather than focus on changes in the bathymetry of the lake basins themselves, which are here shown to be effectively stable in terms of sediment accumulation.