In March 2016 Living Seas launched a new style of trip which we are calling Extreme Week. These trips offer more challenging, objective driven projects for our base of competent divers to get involved with. Our first Extreme Week trip saw us return to Lake Batur, with a team of divers capable of exploring a larger area of the lake. This project also saw Living Seas collaborate with a group of scientists from NTU. Our divers provided RNA samples from the lake so scientist could identify the microorganisms (bacteria, fungi and algae) living in the lake.

Depth charts of the lake show an underwater ridge connects the east and west coasts of the lake. This ridge is located midway along the lake (see graphic below) and lies at a depth of 45m or so. Emerging from the lake is Mount Batur, a stratovolcano, with multiple vents throughout the caldera. First recorded eruption was in 1804 and the volcano has remained active ever since. The latest eruption was in 2000. We wondered whether there was an active vent beneath the lake which had caused the ridge to form. If nothing else, it would make for an interesting feature to explore.

This year, we Teresa Chang flew in from Singapore to join the Living Seas Bali crew (Leon, Jevry and Agus) for the expedition. Our long lost DM Joakim from Norway, was in Bali for a few months decompressing from school also joined the expedition. Teresa and Leon formed the deep team and Joakim and Agus were the shallow team. Jevry, recovering from an injury, was surface support for both teams.

The team set out early on the 3^rd of March for the mountain, after loading up the tanks and water collection gear that we had prepared the night before. It was great to be back in Batur, with the cool winds and fresh air, but the sun was really beating down, and quite a few of us got a few shades darker after everything was done.

Jevry, being the social animal that he is, managed to get some anecdotal stories from the locals about the condition of the lake. Apparently, the water had been rising rapidly for the last 3 years. Back in the 1960s, the shore area was all used for agriculture, and the waterline was at least 50m from the current shoreline, all of which were used for growing crops like corn and onion. The water quality was reported to be much better back in the 1950s; with one old guy saying that he remembers the water being very clear. Historically the water level would rise during the rainy season, and drop in the dry season. However, in recent years the average water level has been rising steadily over the years, despite the seasonal fluctuations.

We also heard from the villagers that occasionally a natural phenomenon causes the death of thousands of fresh water fish (tilapia). Reports say that the water of the lake suddenly changed colour to a white/blue shade, smelt really bad and then the fish died. In 2011 several fish farmers lost their fish in the shallows of the lake as the colour spread. The villagers blamed an underwater explosion for releasing sulfur into the water, which they believe ultimately their fish. Others believe an explosion could have altered the water temperature, pH or released unknown toxins into the water. After the latest mass fish death in 2011, the chief of the Disaster Alleviation Office for Bali said the natural phenomenon was not due to volcanic activity, but potentially strong winds had blown sulfuric soil into Lake Batur. There is much speculation as to the cause of these changes in conditions in the lake, which happens annually during the transition from the wet to the dry season (but rarely on the scale seen in 2011, which cause the death of thousands of fish). The latest theory put forward by scientists is that the event was not volcanically triggered nor due to eruptive activity. Scientists noted the comparatively high diurnal-temperature (highest and lowest temperatures of the day) difference during the onset of the dry season. As a result of these temperature differences, the lake water developed currents, which carried mud from the lake bottom to the surface. This was thought to correspond to the observed odours (‘muddy smells’) and colour changes on the lake surface. In a broad sense, the currents and mud were thought to upset the lake’s ecological balance in a manner toxic to the fish. (http://volcano.si.edu/volcano.cfm?vn=264010, n.d.) Would we find an active vent on the ridge, or was the ridge responsible for directing these muddy waters to the surface. Whatever we would find, this would be an interesting area of the lake to explore.

Our Balinese diver, Agus, related that he had heard a story about the lake being cursed. In ancient times, when the water level was much lower than today, there was an army that tried to cross the lake to Trunyan. For some unknown reason, the entire army ran into some trouble and their boats sank, killing the entire army. Ever since then, folklore has it that people shouldn’t cross the lake at night for fear of getting pulled down by the drowned soldiers…

Thankfully, we had no plans to do any night diving, but either way, I don’t think we wanted to find out if the story was true.

Day 1 – Getting our hands dirty

During this expedition we planned to collect water from the surface, 30m and from the bottom of the lake. We would isolate the RNA from the water samples, so that the scientists would be able to see if there was any variation in the microorganisms found at different depths in the late. At each of these depths, we would need to fill two 6 litre containers and get them back onto the boat. This water would then be pushed through an RNA filter, trapping the proteins and RNA of the microbial organisms found in the water. At the end of the trip, we planned to send these filters (6 of them) to NTU for analysis.

Our first objective was to collect water from 30m, once the containers were filled we used a lift bag to send the water containers to the surface. Jevry retrieved the containers and started to push the 6L of water through the RNA filters. As you can see in the picture below, the water had a lot of sediments in it, so pushing the water through the filter became quite a task for Jevry.

After sending the containers to the surface, the two dive teams ventured south, continuing to explore the volcanic lake. During the dive, we found another sunken ghostly tree, petrified by its’ time under the water. Similar to the tree we found last year, these trees are ghostly beautiful. As on our previous trip, we saw trash both deep and shallow, it’s astounding how much trash is under there. Bottles, plastic bags, food wrappers, the list goes on. We are pretty sure that there are bigger and heavier items there too, just hidden from view as they have sunk deep into the silt.

By the time we surfaced, Jevry had been working hard to filter all the water samples, but was getting pretty sore arms. Everyone jumped in and helped out while sailing back to shore. It was certainly a long day, but a new experience for Joakim, Agus and Teresa. They were all excited to be going back the next day.

Day 2 – The deep dive

On the second day, the deep team comprising Teresa and Leon planned to get the water samples from the bottom of the lake. This meant that we had to do a decompression dive on trimix.

Picking a corner of the lake that had the steepest sides, we descended down the slope, hitting the bottom roughly 8 mins into the dive.

The boat tracks from Day 2

Once there, we could smell the sulfur in our masks, but thankfully it wasn’t bad enough to induce vomiting. Similar to my previous dive here, the visibility cleared up significantly once passing 30m. It was still pitch black, but our canister lights were able to penetrate the darkness much better, indicating lesser particles in the water. However, there was still this constant rain of particles from the surface, slowly drifting down to rest on the silty bottom.

Not wanting to stay down any longer than we needed to, we collected the water and sent it up on the lift bag for the surface team to pick it up and begin the filtration. Jevry and Joakim picked up the water samples successfully and proceeded to take the boat over to the ridge to see if they could use a little sonar device they had to find out where the ridge was located. They managed to find a depth of 40m just off shore from the hot springs, verifying the bathymetry map that we had.

After marking the ridge and collecting the deep team part one of our objectives had been achieved. As a reward the whole team headed off to the hot springs for a late lunch and a dip in the springs.

While at lunch, (unaware of the potential upwelling being responsible for the fish death) we hypothesised that the ridge was actually still somewhat active, considering the stories about the sulfur and that the hot springs were located just west of the ridge. The next day would be interesting, as we would test our hypothesis about the hot springs.

Day 3 – The ridge

Day 3 started well, but quickly got worse as a storm cloud moved in right as we were about to descend. This caused the boat to drift, and made our entry complicated with all the heavy gear. With no way to anchor the boat above the ridge we moved to a permanent mooring line to secure the boat during the storm. The depth sounder read 24m, so we decided to do a line descent to reach the bottom and then venture out to explore the ridge.

Funnily enough, the mooring was located near to the east coast of the lake, along a path that the ancient army would have taken. Could this be the reason why it was suddenly storming? Undeterred but definitely spooked, we decided to carry on, partly because we had already come so far, and partly for the lure of ancient artefacts lying below!

The boat tracks from Day 3

The rain created some delays, and so the shallow team descended first, while the deep team came later. The shallow team was to hit 30m and turn south, crossing the supposed ridge. The deep team was to hit 45m and travel west along the ridge for as long as they could.

The bottom composition here was slightly different from what we had dived before, it was greener and there wasn’t much trash to be found (did the yearly upwelling move the trash to deeper parts of the lake?). That kind of made sense, considering that we were close to the middle of the lake, and we were also closer to the agricultural plots of Trunyan village. Any plastic floating trash would have been blown to the side of the lake, rather than stay in the middle.

The deep team only made it to 38m, but according to our GPS tracks, we did manage to go in the correct direction, verifying the existence of the ridge. However, we didn’t make it far enough, considering our starting point was too close to the east coast of the lake, and we didn’t get to see the western edge, where the hot springs are located.

Conclusions

During my initial visit to Batur, my original hypothesis of why the water quality is dropping was the mining activity located on the slopes of the caldera west of the lake. However, having explored deep and shallow and in more areas on the lake, the rain of silt is found to be constant throughout and at all depths. The turbidity of the water is also really bad until a depth of 15-20m, corresponding to the loss of ambient light from the sun at this point.

My new hypothesis is that the rain of silt is comprised of organic matter (an algal bloom) from the surface caused by the fertiliser run off from the agricultural activity on shore. This organic matter then dies at a certain depth due to the lack of light. The dead material then drifts down to the bottom, resulting in the observed rain of silt.

The silty bottom is also very spongy and light, which is different from a mineral based silt which would probably be heavier and more clay like. The green layer observed during the ridge dives made me suspect that this might be the case, as the depth was shallower, so some of the organic material may still be alive at that point.

We can test this hypothesis by sampling or coring the bottom substrate and analysing for mineral or organic content. If the organic content is extremely high, then the fertiliser theory may be proven, especially if this can be compared with an analysis of silt rain or surface algal content. We would also need to verify if fertilizers were in fact being used on the farms by the shore.

This is pretty exciting, because if the fertilizer theory can be proven, then we do have a means of slowly cleaning up the lake! All we’d need to do is show the locals that the fertilizer use is causing the degradation of their water quality, and perhaps this may create some lasting change!

New objectives for our next Batur trip

1. Coring the bottom with clear acrylic pipe and sealing it to be able to see strata delineation and bring up for analysis
2. Follow ridge to western edge to see if there is any recent volcanic activity
3. Measure visibility, turbidity and colouration of different depths
4. Measure depth of sediment with an extremely long pole
5. Analysis of silt rain and algal content at surface