Can Unleveed Agricultural Fields in Deltas Keep Pace With Sea‐Level Rise?

Abstract

Many tropical and subtropical deltas are densely populated centers of agriculture that are threatened by sea-level rise (SLR). Local SLR can be amplified by anthropogenic activities that enhance land-surface subsidence, such as damming, fluid extraction, coastal deforestation, and levee or polder construction (Syvitski et al., 2009). Often, these alterations to the landscape are driven by the need to expand agriculture and aquaculture, and local stakeholders must balance economic stability against future declines in coastal resilience . Economically viable policies to promote delta stability require a fundamental understanding of the individual impacts of anthropogenic activities on sediment dynamics, yet it is often challenging to isolate the impact of a specific intervention in heavily altered regions.Extensive mangrove removal has occurred globally in the past century with the expansion of agriculture and aquaculture (Duke et al., 2007;Giri et al., 2011). This agricultural expansion is frequently accompanied by the construction of levees or polders, making it difficult to isolate the impact of the change in land cover. Levees allow a second or third round of crops to be grown in monsoonal deltas during the dry season when river or distributary water is saline . Unfortunately, levees also isolate the floodplain, significantly decreasing the potential for sediment deposition. For example, embanked regions in the Ganges-Brahmaputra and Mekong Deltas are experiencing rapid subsidence (

InSAR-Derived Coastal Subsidence Reveals New Inundation Scenarios Over the Yellow River Delta

“…However, there is a weak surface uplift signal in the new land area of the estuary, which is mainly due to the continuous siltation of large amounts of sediment brought by the upper Yellow River [74]. A recent study has also shown that in the Ayeyarwady Delta, Myanmar, unleveed agricultural fields in deltas are less vulnerable to subsidence than leveed or poldered fields [75]. As a result, the rich wetland vegetation in the Yellow River estuary, such as Suaeda sala, Tamarix chinensis, Spartina alterniflora, Phragmites australis, can help capture sediment in a similar way to mangroves or crops, making levee land less likely to sink than levee land.…”

What is coastal subsidence?

“…A related, widespread source of confusion is associated with the interplay between deposition and subsidence. For example, studies of river delta vulnerability have implied that a reduction of sediment supply increases subsidence (e.g., Becker et al, 2020;Glover et al, 2023). However, the opposite is true: vertical accretion and subsidence from compaction in the upper portion of the sediment column are closely coupled (Saintilan et al, 2022) due to the effective stress exerted by newly accumulated sediment (Zoccarato and Da Lio, 2021).…”

What is coastal subsidence?

“…A related, widespread misconception is associated with the interplay between deposition and subsidence. For example, studies of river delta vulnerability have implied that a reduction of sediment supply increases subsidence (e.g., Becker et al 2020;Glover et al 2023). However, the opposite is true: vertical accretion and subsidence from compaction in the upper portion of the sediment column are closely coupled (Saintilan et al 2022) due to the effective stress exerted by newly accumulated sediment (Zoccarato and Da Lio 2021).…”