Karst landscapes are important for the climate because of their carbon dioxide binding capacity. Through their complex underwater systems they provide drinking water to people all over the world. With more than eight million sq. km of karst, Asia has the largest share worldwide. But karst areas like the Kendeng mountains in Indonesia are under threat to be destroyed by the cement industry. This article highlights the long-term value of intact karst systems.
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The Blautopf Cave is the best known of the more than 2,000 caves in the Swabian Alb in southern Germany. It was not too long ago that its entrance was discovered at a depth of more than 20 meters in Lake Blautopf. It is now known that water from many underground streams of the karst mountains flow together in the Blautopf. They come from a cave system that extends deep into the Swabian Alb. The accessible caves and the prehistoric drawings discovered in them were declared a UNESCO World Heritage Site in 2017. Tens of thousands of tourists visit the region every year.
Karst caves offered people not only protection from storms and predators as early as the Stone Age, but also water through their underground springs. These caves are witnesses of history. Time and again, speleologists and archaeologists find bones, man-made objects or drawings that are tens of thousands of years old. One of these karst caves, the Chauvet Cave in France, so captivated the famous filmmaker Werner Herzog that he memorialized it in his film "Cave of forgotten dreams" . The Chauvet Cave has also been a UNESCO World Heritage Site since 2014. The same applies to the Castillo cave complex in Spain, where the oldest cave wall paintings in Europe have been discovered.
There are even older finds in Southeast Asia: recently, researchers discovered the earliest known representational artwork in the world, a depiction of the Sulawesi warthog, in an Indonesian karst cave. Cave paintings like these provided important insights about human migration of the time, experts say. Leang Tedongnge Cave, where the painting was discovered, is surrounded by limestone cliffs. It is part of the Maros-Pangkep-karst, one of the largest karst regions in the world.
The term karst comes from Slowenian kras, Croatian krš and Serbian крш, meaning "stony ground". In geological terms karst is a terrain formed of water-soluble rocks (e.g. limestone, gypsum, salts) leached by surface and ground water. Surface formations of this type are called surface karst, underground ones are called karst caves. Dissolution processes result in the characteristic karst phenomena, such as sinkholes, caves as well as underground river courses and karst lakes. About 15 percent of the (ice-free) earth's surface consists of karst rock. With 8.35 million sq. km of karst areas, Asia has the largest share worldwide. (Goldscheider, N., Chen, Z., Auler, A.S. et al., 2020).
Because of their underground and aboveground bizarre rock formations, karst mountains have been fixed points for mystical stories and places of spiritual ceremonies of the local inhabitants for thousands of years. At the same time, they are a magnet for tourists, such as the karst landscape along the Li Jiang River in China, the karst rocks of Halong Bay in Vietnam, Phang Nga Bay in Thailand, or the so-called "Chocolate Hills of Bohol" in the Philippines.
Karst as climate archive and climate protector
Karst landscapes are not only a mirror of the cultural history of mankind. "Karsts are climate archives," says German speleologist Oliver Heil. "Karst caves conceal a great variety of stalactites. Their individual layers contain information about temperature and vegetation changes during their formation." For example, researchers used analyses of dripstones in the Yok Balum cave in Belize, Central America, to find out the amount of precipitation in the years 300 to 1100 A.D. and were able to explain that the Maya advanced civilization perished about 1,000 years ago because of severe droughts.
Karsts are not only climate archives, researchers believe they are also climate protectors. Karst landscapes are important carbon sinks, because they store carbon binding rocks and karstification itself is a carbon dioxide sequestration process. According to Chinese researchers Zaihua Liu and J. Zhao, “karst regions absorb some 0.41 billion tons of carbon dioxide annually from the atmosphere and discharge 0.3 billion tons by way of the karsting process. That means, they store some 0.11 billion tons annually”.
As far as the dimension of karst landscapes as natural CO2 reservoirs is concerned, researchers come to different conclusions depending on which karst areas they study. Karstification processes vary depending on the climatic zone in which they take place and on the amount of water circulating above ground through precipitation or underground through springs. And, of course, karst landscapes are also exposed to the effects of climate change. Thus, the international team of authors (Zeng et al) of the study "Comparisons on the effects of temperature, runoff, and land-cover on carbonate weathering in different karst catchments: insights into the future global carbon cycle that under future global warming" concluded that "karst regions in cold climates with vegetation cover will have increasing CO2 consumption potential, whereas karst regions in warm climates will have decreasing CO2 consumption potential."
Controversial processes for CO2 storage
Some scientists also see karst landscapes as a potential source of man-made CO2 storage, a process known as carbon capture and storage, or CCS. George Veni, a U.S. hydrogeologist and current president of the International Union of Speleology (IUS), has done research on this: „Many of the world’s greatest deposits of oil come from paleokarst. This is where ancient karst landscapes were pushed underground and buried long ago. Then over millions of years, if the chemical conditions were right, oil formed and collected in the cavernous spaces of the paleokarst. Veni is of the opinion that “there should be more space in paleokarst to drill wells and sequester carbon than in other types of rocks. If this can be proven, then potentially carbon could be removed from the atmosphere with more of it stored in paleokarst, to make the storage more cost effective.”
Critics of such procedures, on the other hand, argue that research for underground CO2 storage projects would be driven and funded by energy corporations in order to continue their interests, namely mining and burning fossil fuels on a large scale. This was the case in Germany, for example, where the power company RWE had funded positions at the Federal Institute for Geosciences and Natural Resources. The staff was to develop proposals for regulations and permits for CO2 storage facilities.
In the EU, too, corresponding pilot projects were initially discontinued. The situation is different in Norway, which also has very high CO2 emissions due to its high oil production. There, a carbon tax has been levied for 30 years and the funds flow into carbon capture and storage facilities, including the world's largest carbon capture test center. Advocates of CCS technology are also pinning their hopes on storage under the ocean floor. Critics, on the other hand, warn of the threat of environmental damage if leaks occur. And they point out that the energy required for underground CO2 storage could increase consumption of the limited fossil resources available by up to 40 percent.
Cement companies, whose energy-intensive production accounts for around eight percent of CO2 emissions on a global scale, are among the major proponents of CCS technologies. They are investing large sums in the relevant research. For example, the German group HeidelbergCement is planning the world's first industrial-scale CCS project at its cement plant in Brevik, Norway
The biggest enemy of karst is the cement industry
What the companies like to sell as an "investment in the future" or a "contribution to climate neutrality" is, however, ultimately fed by money that these companies initially earned by destroying natural carbon reservoirs such as karst mountains. After all, calcareous rock is the raw material from which cement is produced. "The biggest enemy of karst is the cement industry because they mine karst mountains, destroying caves and disrupting waterways" says Oliver Heil. "The water takes a certain path through the sinkholes," explains the speleologist. If these were destroyed, the water courses would change. Erosion would occur, which could result in landslides and flooding. In addition, the unique fauna and flora of the karst landscapes would be destroyed, Heil says.
Exactly these consequences can be observed in Indonesia at the Kendeng Mountains. People in seven counties depend on the watercourses of this karst mountain range. The Kendeng karst has unique flora and fauna and is indispensable as a historical and cultural site for the local population, including the indigenous Samin group. Nevertheless, the cement industry in the form of large factories and small limestone mines has already caused enormous damage to this mountain range.
The residents, predominantly local small farmers who have joined together in the citizens' initiative JM-PPK, have been drawing attention to the consequences for years and warn against continuing this overexploitation of nature. "Every year we see parts of our counties being flooded," JM-PPK said in a press release in December 2020, when severe flooding occurred once again, destroying crops on some 5,000 hectares of land. The JM-PPK estimated that 40,000 tons of rice worth IDR 45 billion (2.6 million euros) were destroyed. These floods were not the result of heavy rains alone, but of soil erosion caused by the destruction of the Kendeng karst, the civic group said. "Floods are not fate," the JM-PPK concludes. "They are calamities that could be avoided because their cause is the greedy behaviour of people who don't seem to care about the environment and the survival of their children and grandchildren."
Many governments fail to recognize the importance of karst
To highlight the importance of karst landscapes and caves and their worthiness of protection, the International Union of Speleologists has declared 2021 the Year of Karsts and Caves. "Caves and karst are home to many of the planet's most diverse, important, and rare ecosystems, supporting ecological diversity above and below the ground." the UIS justifies its initiative "Karst aquifers are the most complex, least understood, most difficult to model, and most easy to contaminate water supplies. They are often able to rapidly transmit pathogens and chemicals tens of kilometers undetected to vital human and ecological water sources." More knowledge and understanding of these complex systems is needed, UIS said. "As often, hidden features and landscapes, such as caves and karst are generally poorly understood. Few scientists and natural resource managers are adequately trained to properly study or manage them. Many governments do not recognize caves and karst at all or fail to recognize their importance."
Karsts are complex and unique ecosystems. They are natural areas that provide us humans with clean water and a good livelihood. Science refers to these benefits and many goods essential for human life as "ecosystem services".
Ecosystem services are divided into three categories:
1) Provisioning services: products provided by ecosystems, such as food, grain, fruits, herbs for medicine, fuel, fibre, etc.
2) Regulating services: providing stable and safe living conditions, such as climate, air and water quality, flood-regulation and -mitigation, pollination, pest control.
3) Cultural services: quasi-immaterial services, for example inspiration, relaxation, spiritual enrichment and cultural heritage, cognitive development, social aspects
For example, in Europe, the project "Ecosystem Services of Karst Protected Areas - Engine of Local Sustainable Development" (ECO KARST) studied in seven protected karst areas in seven countries how ecosystem services can contribute to the economic viability and sustainability of different sectors such as forestry, agriculture or tourism.
A significant part of the world's population obtains its drinking water from karst systems
The conclusion of the scientists involved was as follows: "Karst areas are special. They are very important sources of water – a significant part of the world’s population gets their drinking water from such systems. [...]The value of clean water for humans cannot be overstated. If karst systems did not provide it, water would need to be transported from large distances and probably would need to be purified by means of costly technological solutions. If we add up the costs of water transportation and cleaning, it becomes immediately clear how valuable the karstic system is to the local communities in economic terms."
The ECO KARST researchers also state, that “the role of karstic forests in climate regulation (including carbon sequestration) are services where the benefit is not limited to the karst area itself.” In addition, "karst areas often boast a unique richness of wildlife and special habitats, due to which they play an outstanding role in nature conservation. The natural beauty of landscapes and wildlife, and specific features such as caves or rock formations attract a large number of visitors." Tourism, especially ecotourism, can generate income for local people, they said. An assessment of the ecosystem services of karst areas “can help the local stakeholders and decision-makers to make a better use of their resources and increase quality of life for the local population" they concluded.
Anett Keller is a freelance journalist and environmental activist.
The views expressed by the author are not necessarily those of Heinrich Böll Stiftung.