A new study finds warning signs of ecosystem collapse at Lake Kutubu in Papua New Guinea, a wetland of international significance.
The warning signs come in the form of major shifts in algal composition and dung-inhabiting fungi in the lake sediment in the 1980s and 1990s, indicating a drop in water quality and coinciding with oil and gas extraction in the area.
The lake used to have extensive beds of microalgae known as charophytes, which provided a breeding ground for endemic fish and crayfish, but these beds have since all but disappeared.
The researchers have called for action such as monitoring of the lake’s algae and fish populations to save the lake from ecological collapse.
JAKARTA — Years of deforestation and mining have devastated a wetland of international importance in Papua New Guinea, which, if left unchecked, could lead to the collapse of the ecosystem, researchers have warned.
In a newly published study in the Proceedings of the National Academy of Sciences, researchers from Australian National University (ANU) identified signs of ecosystem collapse at Lake Kutubu, PNG’s second-largest lake and one of the most pristine freshwater systems in the Asia-Pacific region.
The lake has approximately 5,000 hectares (12,300 acres) of open water and 2,000 hectares (4,900 acres) of wetland swamp forest. It’s home to diverse rainforest flora and fauna, with at least 12 endemic fish species.
These fish are facing increased pressure, with mass die-offs reported in 2007 and 2013 after toxic chemicals from oil and gas companies allegedly entered the lake and polluted the water.
To understand the full extent of ecological change in Lake Kutubu, the researchers tried to chronicle its chemical composition going back to the 1930s by studying the sediment layers on the lake bed.
“Previous studies have focused on the fish kills and changes during extreme rare events and we are going to the very base of the food chain, systematically examining the sediments that have built up over time and tracking changes relative to earlier periods,” researchers Kelsie Long, Larissa Schneider, Simon Haberle, Simon Connor and Chris Ballard told Mongabay in an email.
The study, done in collaboration with the University of Papua New Guinea and local landowners, found that the lake’s ecosystem started showing signs of degradation as early as the 1980s, long before the fish die-offs began to be reported.
The researchers identified major shifts in algal composition and dung-inhabiting fungi in sediment dated to the 1980s, which could be attributed to a drop in water quality.
According to the study, the most significant shift in the algal composition occurred around 1990, when the abundance of algae such as Gomophenema angustum and Staurosira construens declined and were replaced by others such as Cyclotella stelligera.
“This shift is likely reflective of a loss of aquatic plant communities that were reported as abundant in the past but are now clearly absent or disappearing rapidly around the lake,” the researchers wrote in the study.
Other algae that have largely disappeared from the lake are charophytes (Characeae), a group of freshwater green algae whose beds serve as the main habitat for the endemic freshwater crayfish Cherax papuanus, categorized as vulnerable on the IUCN Red List.
The beds are also major feeding, spawning and nursery grounds for endemic fish.
These algae were observed in abundance during field work in the late 1980s and described in detail in a baseline hydrological study.
“[But now] the algae beds have since all but disappeared and this will have knock on effects for the ecosystem,” the researchers said.
This loss of biodiversity coincides with the period during which human settlements and livestock grazing in the area around Lake Kutubu began to increase as oil prospectors arrived in the 1980s. The latter brought with them test drilling equipment, which they began using in 1983 just to the south of the lake, according to the researchers.
“We can see these changes clearly in the chemical composition of sediments laid down at the bottom of the lake, before and after the start of resource extraction activities and increasing population growth in the region in the 1980s and ’90s,” said study co-author Long, an archaeologist at ANU.
The increase in population living around Lake Kutubu and the general intensification of associated infrastructure is expected to have contributed to the increase in metal deposition in the lake, she added. She called the changes in the chemical composition of sediments early indicators of ecosystem collapse.
There was even more degradation after the discovery of oil near the lake in 1990s. The exploration and extraction activities that followed resulted in large-scale land clearing, construction, and immigration into the area.
Major drilling and pipe-laying work for the oil and gas project allegedly resulted in toxic chemicals entering the lake and polluting the water. In 2007 and 2013, mass fish die-offs were reported in the lake, with the oil and gas companies blamed for the incidents.
The researchers said toxic chemicals can have devastating effects on the lake, as its catchment acts like a sponge due to the limestone formation.
“In lake environments, everything is connected,” they said. “If chemicals enter the lake, it may not only kill fish directly, but may affect the algae at the base of the food chain too, which means the whole ecosystem starts to shift and change in unpredictable ways. Add climate change, deforestation and resource extraction to the mix and we can end up with environmental instability that makes life tough for local communities.”
Local community members reported large numbers of sick and dead fish floating and rotting around the banks of the lake during the 2013 die-off. The fish were described as having red sores, swollen bodies, rotting or missing flesh, ulcers, and chemical-like burns.
Children who swam in the lake complained of their eyes being bloodshot, sore and feeling “scratchy,” and their skin as being dusty and dry “like sawdust.”
“The health of Lake Kutubu is changing,” Long said. “Villagers have been reporting the release of plumes of chemicals into the lake, fish kill events and subsequent health issues of people who rely on the lake for food and water.”
Decades of ecosystem degradation have pushed some of the fish species in the lake to the brink of extinction. While C. papuanus is listed as vulnerable, three species — Melanotaenia lacustris, Oloplotosus torobo and Craterocephalus lacustris — are endangered, and three others — Hephaestus adamsoni, Mogurnda variegata and Mogurnda furva — are critically endangered.
Chance of recovery
Lake Kutubu still has a chance to recover, but not if anthropogenic pressures from activities like mining keep increasing, the researchers said.
These continued activities will make life for the people and organisms that depend on the lake more difficult, they added.
“If the benefits of mining in the short term are outweighed by the long-term effects on human and environmental health, who is actually benefitting?” the researchers said.
They called on stakeholders to better track and assess the effects that resource extraction are having on the groundwater.
“The lake’s algae and fish populations should be monitored and we think that local people could play a key role in that important work,” they said.
Connor, a paleoecologist at ANU who did the statistical analysis for the study, said the findings can serve as a call for action to save Lake Kutubu from ecological collapse. The lake was declared a Ramsar site, a wetland of international importance, in 1998.
“We have to remember that Ramsar wetlands are not museum exhibits — they are the result of all the changes that went on in the past and are responding every moment to the changes happening now,” Connor said. “Scientific studies like ours don’t tell local communities anything they don’t already know, but they can force governments and corporations to take action to prevent further damage.”
Long, K. E., Schneider, L., Connor, S. E., Shulmeister, N., Finn, J., Roberts, G. L., … Haberle, S. G. (2021). Human impacts and Anthropocene environmental change at Lake Kutubu, a Ramsar wetland in Papua New Guinea. Proceedings of the National Academy of Sciences, 118(40), e2022216118. doi:10.1073/pnas.2022216118
Banner image: Lake Kutubu, Southern Highlands, Papua New Guinea. Image courtesy of Iain Taylor1/Wikimedia Commons.
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