Mangroves and shoreline erosion in the Mekong River delta, Viet Nam

Abstract

The question of the rampant erosion of the shorelines rimming the Mekong River delta has assumed increasing importance over the last few years. Among issues pertinent to this question is how it is related to mangroves. Using high-resolution satellite images, we compared the width of the mangrove belt fringing the shoreline in 2012 to shoreline change (advance, retreat) between 2003 and 2012 for 3687 crossshore transects, spaced 100 m apart, and thus covering nearly 370 km of delta shoreline bearing mangroves. The results show no significant relationships. We infer from this that, once erosion sets in following sustained deficient mud supply to the coast, the rate of shoreline change is independent of the width of the mangrove belt. Numerous studies have shown that: (1) mangroves promote coastal accretion where fine-grained sediment supply is adequate, (2) a large and healthy belt of fringing mangroves can efficiently protect a shoreline by inducing more efficient dissipation of wave energy than a narrower fringe, and (3) mangrove removal contributes to the aggravation of ongoing shoreline erosion. We fully concur, but draw attention to the fact that mangroves cannot accomplish their land-building and coastal protection roles under conditions of a failing sediment supply and prevailing erosion. Ignoring these overarching conditions implies that high expectations from mangroves in protecting and/or stabilizing the Mekong delta shoreline, and eroding shorelines elsewhere, will meet with disappointment. Among these false expectations are: (1) a large and healthy mangrove fringe is sufficient to stabilize the (eroding) shoreline, (2) a reduction in the width of a large mangrove fringe to the benefit of other activities, such as shrimpfarming, is not deleterious to the shoreline position, and (3) the effects of human-induced reductions in sediment supply to the coast can be offset by a large belt of fringing mangroves. Highlights ► We compared Mekong delta shoreline change between 2003 and 2012 and width of fringing mangroves. ► We found no significant relationships between the rate of shoreline change and mangrove width. ► Large tracts of the delta shoreline are eroding due to inadequate mud supply. ► When mud supply replenishment is low, even a wide mangrove belt will retreat. ► Mangrove protection initiatives need to consider sustained sediment supply as a key parameter.

Characterising spatiotemporal vegetation variations using LANDSAT time‐series and Hurst exponent index in the Mekong River Delta

“…Mekong River Delta is one of 10 deltas that are severely vulnerable from the impacts of global warming and sea-level rise (IPCC, 2007). The natural vegetation strips along coastal zone (e.g., mangrove forest) play a vital role in the climate adaptation and mitigation strategies for this delta (Besset et al, 2019). They can serve as natural buffers against extreme climate and weather events such as changing rainfall patterns, droughts, storms, and other disasters (Nardin et al, 2016).…”

Long-term sediment decline causes ongoing shrinkage of the Mekong megadelta, Vietnam

“…Recent dam constructions, fluvial sand mining, and a local decline in mangroves 36 cannot account for the current erosion of the eastern coast of the Camau Peninsula and for the correlative erosional features identified in the nearby subaqueous delta 30 . Our data reveal that the significant decrease in the sediment supply and ensuing erosion likely started between 1885 and 1940.…”

Variable Impacts of Climate Change on Blue Carbon

“…128 For example, shoreline retreat in the Mekong Delta, Vietnam, is occurring at rates of up to 100 m per year due to reduced sediment supply, subsidence of the land, and mangrove removal. 129 Although in some locations, human activities have led to increases in sediment delivery to the oceans and accretion of mangrove and saltmarsh habitats. 130,131 For example, in New Zealand, increased sediment availability due to deforestation in the catchments has led to expansion of mangroves $1 km in a seaward direction since the 1950s.…”