Sedimentation strategies provide effective but limited mitigation of relative sea-level rise in the Mekong delta

AbstractThe Mekong delta is experiencing rapid environmental change due to anthropogenic activities causing accelerated subsidence, sea-level rise and sediment starvation. Consequentially, the delta is rapidly losing elevation relative to sea level. Designating specific areas for sedimentation is a suggested strategy to encourage elevation-building with nature in deltas. We combined projections of extraction-induced subsidence, natural compaction and global sea-level rise with new projections of fluvial sediment delivery to evaluate the potential effectiveness of sedimentation strategies in the Mekong delta to 2050. Our results reveal that with current rates of subsidence and sediment starvation, fluvial sediments alone can only preserve elevation locally, even under optimistic assumptions, and organic sedimentation could potentially assume a larger role. While sedimentation strategies alone have limited effectiveness in the present context, combined with enhanced organic matter retention and interventions reducing anthropogenic-accelerated subsidence, they can considerably delay future relative sea-level rise, buying the delta crucial time to adapt.

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Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

10.5194/egusphere-egu21-5140 ◽

2021 ◽

Author(s):

Frances E. Dunn ◽

Philip S. J. Minderhoud

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Mekong Delta ◽

Sediment Deposition ◽

Sediment Supply ◽

Sediment Flux ◽

Relative Sea Level ◽

Fluvial Sediment ◽

Relative Sea Level Rise

As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.

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Sedimentation and Survival of the Mekong Delta: A Case Study of Decreased Sediment Supply and Accelerating Rates of Relative Sea Level Rise

Oceanography ◽

10.5670/oceanog.2017.318 ◽

2017 ◽

Vol 30 (3) ◽

pp. 98-109 ◽

Cited By ~ 18

Author(s):

Mead Allison ◽

◽

Charles Nittrouer ◽

Andrea Ogston ◽

Julia Mullarney ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Mekong Delta ◽

Sediment Supply ◽

Relative Sea Level ◽

Relative Sea Level Rise

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A global analysis of subsidence, relative sea-level change and coastal flood exposure

10.5194/egusphere-egu21-14985 ◽

2021 ◽

Author(s):

Daniel Lincke ◽

Robert J. Nicholls ◽

Jochen Hinkel ◽

Sally Brown ◽

Athanasios T. Vafeidis ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Global Analysis ◽

Relative Sea Level ◽

Sea Levels ◽

Coastal Flood ◽

Global Issue ◽

Flood Exposure ◽

Relative Sea Level Rise ◽

Global Sea Level

Climate-induced sea-level rise and vertical land movements, including natural and human-induced subsidence in sedimentary coastal lowlands, combine to change relative sea levels around the world's coast. Global-average coastal relative sea-level rise was 2.5 mm/yr over the last two decades. However, as coastal inhabitants are preferentially located in subsiding locations, they experience an average relative sea-level rise up to four times faster at 7.8 to 9.9 mm/yr. This first global quantification of relative sea-level rise shows that the resulting impacts, and adaptation needs are much higher than reported global sea-level rise measurements would suggest. Hence, coastal subsidence is an important global issue that needs more assessment and action. In particular, human-induced subsidence in and surrounding coastal cities can be rapidly reduced with appropriate policy measures for groundwater utilization and drainage. This offers substantial and rapid benefits in terms of reducing growth of coastal flood exposure due to relative sea-level rise.

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Assessment of Sea Level Rise at West Coast of Portugal Mainland and Its Projection for the 21st Century

Journal of Marine Science and Engineering ◽

10.3390/jmse7030061 ◽

2019 ◽

Vol 7 (3) ◽

pp. 61 ◽

Cited By ~ 5

Author(s):

Carlos Antunes

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

21St Century ◽

West Coast ◽

Satellite Altimetry ◽

Tide Gauge ◽

Relative Sea Level ◽

Mean Sea Level ◽

Relative Sea Level Rise ◽

Global Sea Level

Based on the updated relative sea level rise rates, 21st-century projections are made for the west coast of Portugal Mainland. The mean sea level from Cascais tide gauge and North Atlantic satellite altimetry data have been analyzed. Through bootstrapping linear regression and polynomial adjustments, mean sea level time series were used to calculate different empirical projections for sea level rise, by estimating the initial velocity and its corresponding acceleration. The results are consistent with an accelerated sea level rise, showing evidence of a faster rise than previous century estimates. Based on different numerical methods of second order polynomial fitting, it is possible to build a set of projection models of relative sea level rise. Applying the same methods to regional sea level anomaly from satellite altimetry, additional projections are also built with good consistency. Both data sets, tide gauge and satellite altimetry data, enabled the development of an ensemble of projection models. The relative sea level rise projections are crucial for national coastal planning and management since extreme sea level scenarios can potentially cause erosion and flooding. Based on absolute vertical velocities obtained by integrating global sea level models, neo-tectonic studies, and permanent Global Positioning System (GPS) station time series, it is possible to transform relative into absolute sea level rise scenarios, and vice-versa, allowing the generation of absolute sea level rise projection curves and its comparison with already established global projections. The sea level rise observed at the Cascais tide gauge has always shown a significant correlation with global sea level rise observations, evidencing relatively low rates of vertical land velocity and residual synoptic regional dynamic effects. An ensemble of sea level projection models for the 21st century is proposed with its corresponding probability density function, both for relative and absolute sea level rise for the west coast of Portugal Mainland. A mean sea level rise of 1.14 m was obtained for the epoch of 2100, with a likely range of 95% of probability between 0.39 m and 1.89 m.

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The existential crisis of the Mekong delta: Impact of accelerating land subsidence

10.5194/egusphere-egu2020-9841 ◽

2020 ◽

Author(s):

Philip S.J. Minderhoud ◽

Gilles Erkens ◽

Hans Middelkoop ◽

Esther Stouthamer

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Land Subsidence ◽

Mekong Delta ◽

Relative Sea Level ◽

Natural Processes ◽

Existential Crisis ◽

The World ◽

Relative Sea Level Rise ◽

Imminent Threat

Land subsidence is one of the slowest, natural processes faced by deltas throughout the world, yet it acts as an important catalyst which exacerbates all other threats associated with relative sea-level rise, such as increased flood vulnerability and salinization. This presentation summarizes the results of five years of research on land subsidence in the Mekong delta and highlights the major advances in approaches and insights gained in subsidence processes and rates of an entire mega-delta system.The Mekong delta is heading towards an existential crisis as land subsidence rates are rapidly accelerating over the past decades up to ~5 cm/yr. As sediment starvation in the Mekong river greatly reduces the adaptive capacity to counterbalance subsidence, this results in wide-spread loss of delta elevation. With the Mekong delta having an average elevation of less than 1 meter above local mean sea level, these elevated rates of relative sea-level rise pose an imminent threat of land loss and permanent submersion in the coming decades.Like in many densely populated and rapidly developing coastal-deltaic areas around the world, the main anthropogenic driver that causes accelerated subsidence is the overexploitation of groundwater. A range of future delta elevation projections, considering sea-level rise and simulated groundwater extraction-induced subsidence following extraction pathways, show the dire situation of the delta in spatial-temporal explicit maps of future elevation relative to local sea level.Adequate (ground)water management aimed at strongly reducing current extractions is key in mitigating accelerating sinking rates and crucial to ensure the survival of the Mekong delta. The window of opportunity to act is swiftly closing as the delta is rapidly running out of elevation, and therefore time.

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Submergence, nutrient enrichment, and tropical storm impacts on Spartina alterniflora in the microtidal northern Gulf of Mexico

Marine Ecology Progress Series ◽

10.3354/meps13342 ◽

2020 ◽

Vol 644 ◽

pp. 33-45

Author(s):

JM Hill ◽

PS Petraitis ◽

KL Heck

Keyword(s):

Gulf Of Mexico ◽

Sea Level Rise ◽

Sea Level ◽

Spartina Alterniflora ◽

Anthropogenic Impacts ◽

Interactive Effects ◽

Relative Sea Level ◽

Hurricane Disturbance ◽

Submergence Stress ◽

Relative Sea Level Rise

Salt marshes face chronic anthropogenic impacts such as relative sea level rise and eutrophication, as well as acute disturbances from tropical storms that can affect the productivity of these important communities. However, it is not well understood how marshes already subjected to eutrophication and sea level rise will respond to added effects of episodic storms such as hurricanes. We examined the interactive effects of nutrient addition, sea level rise, and a hurricane on the growth, biomass accumulation, and resilience of the saltmarsh cordgrass Spartina alterniflora in the Gulf of Mexico. In a microtidal marsh, we manipulated nutrient levels and submergence using marsh organs in which cordgrasses were planted at differing intertidal elevations and measured the impacts of Hurricane Isaac, which occurred during the experiment. Prior to the hurricane, grasses at intermediate and high elevations increased in abundance. After the hurricane, all treatments lost approximately 50% of their shoots, demonstrating that added nutrients and elevation did not provide resistance to hurricane disturbance. At the end of the experiment, only the highest elevations had been resilient to the hurricane, with increased above- and belowground growth. Added nutrients provided a modest increase in above- and belowground growth, but only at the highest elevations, suggesting that only elevation will enhance resilience to hurricane disturbance. These results empirically demonstrate that S. alterniflora in microtidal locations already subjected to submergence stress is less able to recover from storm disturbance and suggests we may be underestimating the loss of northern Gulf Coast marshes due to relative sea level rise.

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