Field work at Tonle Sap Lake during the dry season. Part II (2020).
All photos here are my own, taken during the dry season, January 2020. The purpose of this fieldtrip was to take the first samples of water and sediments from Tonle Sap River and Tonle Sap Lake for my PhD project. This was the start of ca. 5 trips planned for 2020, to sample throughout the wet and dry season. Ultimately, I made only one other (minor) trip to Cambodia in March 2020 — to collect drone images to be created into “plastic maps”, prior to the COVID-19 pandemic sweeping the world.
During the January 2020 trip, I was joined with another PhD student from the National University of Singapore and several helpful, enthusiastic and generally, exceptional undergraduate students from Paññāsāstra University of Cambodia. Over 2 weeks, we stayed in Phnom Penh, and in a small community to the south of Tonle Sap Lake, before finishing the sampling in the north, whilst staying in Siem Reap.
For background: Tonle Sap is the largest freshwater lake in southeast Asia and of great significance to Cambodian history, culture, food-security and economy. The lake is relatively shallow throughout the year, though a maximum depth of around 10 meters is observed during the wet season in September/October, with this decreasing to around 2 meters during the dry season in April/May. Similarly, the areal extent of the lake fluctuates from a maximum extent of approximately 250 km long and 100 km wide, to 120 km long and 35 km wide.
I hope you enjoy these pictures.
Flying into Phnom Penh from Singapore, my field assistant from Singapore and I stayed in a hotel in the city, to plan, obtain final permissions, and gather supplies for the upcoming trip. We enjoyed the luxuries of showers and cold beer, as we knew these were unlikely once we stayed in the communities close to Tonle Sap Lake. Although most households by the lake do have electricity, it is slightly intermittent and reliant on solar panels and batteries.
Once the logistics had been sorted; we had the important task of sampling Tonle Sap River also. Here, we used the brand-new Manta Trawl (Aquatic BioTechnology) obtained for the project, for the first time. This is used to collect floating material on the surface of water — often the place where microplastics will be found, as they are typically less-dense than water. Although smaller than the Mekong, the Tonle Sap River is still a behemoth and was at least 1 km across where we were sampling. This was a comparatively relatively narrow part of the river!
The next day, we arrived at the south of Tonle Sap Lake in the afternoon/evening. The water levels were very low, similar, but more extreme to what I had experienced almost exactly one year before. The area was visibly dry, with lots of plastic waste such as bottles, bags and other sheet plastic, littering across the landscape and the lake shoreline.
The next day, we took the equipment out and tested it on the lake. Here, we tried the brand-new Box Corer (Wildco), alongside the Manta Trawl. The Box Corer did not have to travel far in the water as the lake level was very shallow (i.e., less than 2 meters). The driving force of the corer is the weight of it (14 kg) which we had enhanced by extra lead weights (4 kg each), to ensure good penetration into the lake sediment, which it turned out, was very muddy and clayey.
Interestingly, we found it difficult in many areas to the south of the lake to collect any material at all. Often, we would collect a tiny scoop of compact clay. We determined that this was because these were areas which would dry-out completely during the peak of the dry season, forming hard-compacted surfaces dried out by the sun. Furthermore, we found large beds of freshwater mussels and also the occasional plastic bag in the mud, which made it challenging to do any “successful” tests.
In the south we also found it hard to collect good data with the Manta Trawl. We could only use the Manta Trawl for several minutes before it became fully-clogged with fine-organic material from the extremely high-productivity on the surface of the water. It took at least 1 day of practise with the equipment, before spending 1.5 days collecting data from the lake, learning from the first day and what we had experienced at Tonle Sap River.
After our half-day sampling (on the second day), we travelled to Siem Reap, one of the biggest cities in Cambodia, and conveniently for us, is close to the north of the lake. At Kampong Chhnang, which was about 1 hour away from where we were staying, we took a ferry across the Tonle Sap River, to save 2–3 hours of our journey and enjoyed a scenic river view for about 30 minutes. Still, it took around 5 hours to drive from the south to the north.
The next day, we enjoyed some much-needed rest and recreation, exploring the ruins of Angkor Wat and the great stone remnants of the mighty Khmer Empire, which existed some 1000 years before. It was incredible to see the forest reclaiming the stone ruins in many places and to imagine what life must have been like back then — free from plastic! Presumably, large, strong leaves from plants such as banana were used frequently instead! (no doubt causing their own unique environmental problems at the time)
Based on the experience of working on small boats for the fieldwork—I had estimated that we had two days of sampling for the north of the lake. We arrived at the jetty out of the main town, which was bustling with boatmen trying to get tourists to use their boats. We were pleased to get a relatively large boat for the day, which made a nice change from the south. As a reader it could be taken for granted: for the first time we had plenty of room, we were well-shaded, and could actually sit down comfortably and move around! It soon became apparent that the larger boat was much faster, and the planned sampling could be achieved in one day instead of two.
The boat went past some relative pristine areas of flooded forest, although there was still much plastic and other litter polluting the area. When the lake levels are higher during the wet season, by as much as 6 to 8 meters, only the tops of the trees would be visible here.
We were able to complete the sampling in record time — and we even spent 45 minutes stuck in the mud, as the boat grounded itself on a shallow mud bank close to the edge of the lake! Despite our best efforts to push the boat off the mud, we required another boat to tow us away. Interestingly — or quite horribly even, we could feel plastic wrappers, fishing nets and rope beneath our feet as we tried to pushed the boat. There was obviously a lot of plastic there which could not be seen with the chocolate-coloured water preventing us from seeing it.
With our record time, we had a relatively relaxed lunch between sampling locations, enjoying some fried rice we had brought with us, purchased from a vendor in the morning at the jetty.
We finished sampling in the late afternoon as the day was turning into night. We spent the journey back to the jetty cleaning equipment and organising our samples, before quickly stopping off at one of the few floating restaurants at the boatman’s request.
We were treated once again to a breathtakingly beautiful sunset. Without realising it at the time, this was the first the last sampling trip to Tonle Sap Lake and Tonle Sap River. In the few months that followed January 2020, the global landscape changed significantly and naturally, so did my PhD as I was unable to travel to do the fieldwork as I had planned.
As mentioned, I did one more trip to Cambodia in early March 2020, visiting Siem Reap to collect data using the drone. At this time, the atmosphere was very different to just a couple of months previous. There were no tourists and most people seemed quite uneasy, almost waiting for something big to happen. The rapidly-changing landscape at that time meant that I came back to Singapore approximately 2 weeks before the implementation of a nationwide lockdown which eventually lasted until June.
