Freshwater lenses in coral atolls

Coral atolls have only two sources of freshwater: rainfall, which — though easily accessible — can become scarce during drought episodes, and freshwater lenses, which are subterranean aquifers found beneath certain islets. The presence, volume and condition of these freshwater lenses depend on various factors, including the width of the motu, land use, and surface vegetation.

Despite the importance of this resource, it remains very poorly studied, even though it could become vital to the survival of inhabitants in the event of a crisis (climatic, sanitary, etc.). The stakes associated with freshwater lenses are therefore significant, both for maintaining human presence and for agriculture on atolls, as well as for the preservation of ecosystems. Indeed, anthropogenic pressure is the principal — if not the sole — cause of quality degradation in atoll lenses. Overly frequent and excessive abstraction (for example for tourism or industry) raises the salinity level in wells, ultimately rendering them unusable.

Vai Natura has developed expertise in atoll freshwater lenses that has been consolidating for nearly 10 years. We have established a stable and reproducible monitoring protocol that enables us to formulate simple yet effective recommendations for ensuring sound resource management (water intake depth, pumping duration, etc.).