Spatial and temporal variability of turbidity, dissolved oxygen, conductivity, temperature, and fluorescence in the lower Mekong River–Tonle Sap system identified using continuous monitoring

Abstract

Continuous monitoring of turbidity, dissolved oxygen (DO), conductivity, temperature, and fluorescence was done at five locations on the Tonle Sap Lake and the Mekong–Bassac Rivers near Phnom Penh, Cambodia, between 2004 and 2010 using autonomous datasondes. Seasonal, daily, and spatial trends were clearly identified in the data and were related to the annual monsoon rainy season–dry season cycle, system metabolism, system hydraulics, and in some cases, localized phenomena such as waste discharges. The datasondes were particularly useful to track the oxygenation of anoxic black water areas in the flooded forest fringe of the Tonle Sap that occurred during the rainy season freshwater pulse. A strongly developed vertical variation of turbidity, DO, and conductivity in the flooded forest fringe may be related to a combination of factors, including dissolved material release from bed sediment and a floating organic-rich particulate layer near the bottom of the lake. Grab samples for total suspended solids (TSS) were collected at the Preak Leap (PL) site (Mekong River) in 2009 and 2010. An excellent relationship was established between daily mean turbidity and TSS concentration for the PL site, with r ² = 0.95. Autoregressive, integrated, moving average models adequately forecast water level and water quality data one month ahead.

Keywords:

• Tonle Sap
• Mekong–Bassac Rivers
• flood pulse system
• dissolved oxygen
• turbidity
• continuous monitoring
• ARIMA models

Acknowledgements

Funding for this project came from a NASA IDS Grant, Number NNX07AL78G, the WUP-FIN programme under the auspice of Finland Ministry of Foreign Affairs, and the SUNY Research Foundation. This manuscript does not necessarily represent the views of these agencies and the mention of instrumentation does not indicate endorsement by these agencies. Field and lab assistance and data management over the years were capably provided by a number of Resource Development International–Cambodia staff, including U. Mengieng, O. Kagna, L. Moniphea, S. Bunseang, E. Dany, K. Sosamrach, T. Makara, K. Dina, and Andrew Shantz. Thanks to Mary Perrelli, Buffalo State, in helping to prepare the graphics.

Additional information

Notes on contributors

M. Sampson

Deceased