Many culturally significant sites such as Rongtse Ney, Meritsemo Ney, Goen Tshephu, and others are part of limestone landscapes technically referred to as karst systems. The unique shapes of hills and structures inside the caves have been carved by erosion of the carbonate rocks over millennia. Hydrogeologists in 2019 estimated that such Karst aquifers supply drinking water to approximately 10 percent of the world’s population. However, how well we understand the hydrogeology of such culturally significant sites in Bhutan determines our ability to sustainably manage and ensure the availability of ‘holy water’ in these karst systems.
Unlike general groundwater dynamics and surface water hydrogeology, understanding the hydrogeology of karst aquifer systems has always been challenging given its high specificity in karst aquifer anisotropy and heterogeneity, mechanisms of recharge and their intensity, the role of epikarst and soil cover, the prevalence of turbulent regime rather than laminar flow in large channels and cavities, complex variations of karst dissolution rates depending on geochemical zoning, deep water recharge, and circulation. The conduits are characteristic of karst water systems, responsible for most of the flow, conveying large volumes of fast-flowing water under a turbulent regime and resulting in limited water storativity. Thus, a karst hydrogeologic system is often known for the world’s most powerful springs – a high discharge within a short period of time. However, even such high-discharge springs may dry up during the long recession and dry periods.
For Bhutanese communities losing such a unique system is beyond imagination given strong spiritual significance. In this article, we explored the threats to these systems in Bhutan and suggested management options based on hydrogeological science explained using plain language.
Limiting introduction of foreign substances – Spilling milk and applying paints on land formations inside the limestone caves would erode the unique shapes of land formations. High organic matter content in milk and the acidity of paints could erode the highly alkaline carbonate rock materials. The impacts, however, will be determined by the quantity of foreign substances and the dilution factor by water seepages. The use of cement and metal structures for improving accessibility to the limestone caves also needs to be carefully considered to minimize introducing substances that could reduce the pH of the system. The smoke offerings inside the caves could also trigger the production of acidic conditions which can dissolve carbonate rocks structure such as stalagmites and stalactites – the unique structure is the main attraction of the limestone caves.
Unlike surface water or dynamic groundwater systems, Karst water is known for its extremely low capacity for self-purification and pollution dispersion, increasing the risk of pollution of water. The low capacity of the self-purification level could be attributed to: the high velocity of karst water flow; the high level of channeling of groundwater flows; the low adsorption capacity of the host rocks; the low eliminating capacity for different classes of pollutants. Because of this, karst water is especially sensitive to different types and kinds of pollutants (Zhang et al, 2020). Any construction in karst, especially the creation of dams and reservoirs, is also a very delicate undertaking since prediction of the location and size of karst voids remains challenging, resulting in leakages, and even failures, sometimes with catastrophic consequences.
Limiting excess to narrow gorges – The limestone caves and underground land formations are fragile, unlike other rock types. For the safety of visitors and to reduce physical and chemical degradation, visitor access to narrow passages and gorges should be restricted. In many spiritual places around Bhutan, visitors often try to push through the gorges for spiritual reasons. The sharp and pointed soft rocks are always a risk of self-injury, while breakage of the fragile rocks can significantly alter the overall hydrogeological integrity and may also lose culturally significant land formations. Using basic principles of risk assessment and management frameworks, cautionary signages could be installed for improving safety while at the same time enriching the visitors with scientific and cultural information.
Consider catchment level protection – For maintaining the long-term significance of the karst systems, a catchment level management needs to be considered. Such large-scale geographical approach would ensure these sites receive the required level of protection. For example, reducing disturbance to water balances through deforestation or aforestation would ensure the continuous flow of ‘drupchu or duetse’. For example, Rangtse Ney protection zone should at least ensure the protection of whole catchment as shown in the map. Any kind of big industrial development needs to be avoided within the catchment too, so that acidic pollution is reduced, which can dissolve limestone land formations.
Encourage maintenance of local biodiversity – Limiting the introduction of new plant and animal species within the system would ensure that the ecological equilibrium is not disturbed. Planting a new variety of trees or ornamental plants should be discouraged unless proven otherwise. The maintenance of above ground vegetation could potentially be useful in storing water in soil, because quick infiltration of rainwater in karst commonly results in a shortage of surface water and lack of perennial streams in the mountainous areas. Further, any individual should also refrain from pouring water from different locations (e.g. River Ganga) and pouring in ponds inside the caves for ‘enhancing’ water production inside the caves. This is often a common local practice observed around Bhutan.
Upscaling indigenous knowledge and enhancing the scientific database – We suggest gathering local indigenous oral history to record the historical changes supported by the improvement of scientific-based investigations. The merging of these knowledge bases would fill in the lack of historical records about water balance through record of drying ‘drupchus’ and the disappearance of ‘tshebums’ at the sites. The karst springs are recharged by the catchment streams at different elevations. Currently, few culturally significant places in Bhutan have their hydrogeology, biodiversity, and socio-ecology studied.
Start mapping Bhutan’s karst hydrogeology – Globally the karst aquifer systems are protected under the umbrella of UNESCO’s categories of protection: Biosphere Reserves, Global Geoparks, Ramsar sites and World Heritage Properties. Thus, protection and management of karst systems in Bhutan could fall within the realm of water source protection and protection of culturally significant sites. The changes in the trend of precipitation, temperature, glacier melt, and air pollution are expected to impact the quantity and quality of spring water and significantly affect water security in the Himalayan region. However, as of today, our understanding on karst aquifer sensitivity for implementing water supply protection schemes within the Himalayan region including Bhutan is very limited. This knowledge gap provides a perfect opportunity for the scientific community and cultural organizations to work together. The scientist could firstly, apply GIS and remote sensing tools for mapping karst-spring discharge for Bhutan using a global soil-moisture monitoring program and a global dataset of karst-spring discharge. The results may enable improvements in karst groundwater governance by identifying karst areas under water scarcity at a global scale. Later research could explore the threats to karst systems from carbon dioxide sequestration, climate change and generate vulnerability mapping, through the concentration-overburden-precipitation (COP) methodology (Jones et al. 2019), to protect the water quality in Bhutan’s karst systems.
The article is published based on personal experiences and observations by a group of water researchers from Bhutan. The group can be contacted at firstname.lastname@example.org