Long-term challenge to mangrove in the National park Xuanthuy – data released from shallow subsidence monitoring

Abstract

A small mangrove colony growing for several decades on a mud flat on the left side of Balat River mouth has become today a large and healthy forest, containing a high ecosystem service value in the core of the Red River biosphere reserve. As a pioneer ecosystem located at land– water interface in the tropic, there exist always risks to mangroves, especially due to climate change and sea level rise. Sea level rise is a worldwide process, but subsidence is a local problem that can exacerbate these geo-hazards. A monitoring of shallow subsidence has been carried out by using SET-MH technique (developed by the United States Geological Survey) to track the both accretion and land sinking in the core zone of the National Park. The measurement shows the average sedimentation rate of 2.9 cm / yr and the sinking rate of 3.4 cm / yr, since Dec. 30th 2012. This is the first ground-based observation of shallow subsidence under mangroves in the Tonkin Gulf. As a simple and low cost method, so further expansion of this monitoring could provide more useful information to help identify the generally sinking trend of coastal areas in the Red River Delta and also to protect its own biosphere reserve.