Mississippi River subaqueous delta is entering a stage of retrogradation

Maloney, J. M.; Bentley, Samuel J.; Xu, Kehui; Obelcz, J.; Georgiou, Ioannis Y.; Miner, Michael D.

doi:10.1016/j.margeo.2018.03.001

Cited by 71 publications

(42 citation statements)

References 33 publications

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“…Over the past century, many rivers beyond the Changjiang have experienced human‐induced catchment changes that have reduced their sediment loads (e.g., damming, irrigation, and improved land‐use practices) (Milliman, ; Syvitski et al, ). These effects have triggered sediment starvation and subsequent erosion in estuarine shoals and subaqueous deltas of the Ebro, Nile, Mississippi, Mekong, Colorado, and Huanghe Rivers (Stanley, ; Syvitski et al, , 2009; Chu et al, ; Blum & Roberts, ; Anthony et al, ; Maloney et al, ). The conversion of deltas from accretion to erosion will inevitably change their sedimentary environment, affecting regional geomorphologic stability and ecological environments.…”

Section: Resultsmentioning

confidence: 99%

“…Over the past century, many rivers beyond the Changjiang have experienced human-induced catchment changes that have reduced their sediment loads (e.g., damming, irrigation, and improved land-use practices) (Milliman, 1997;Syvitski et al, 2009 Anthony et al, 2015;Maloney et al, 2018). The conversion of deltas from accretion to erosion will inevitably change their sedimentary environment, affecting regional geomorphologic stability and ecological environments.…”

Section: Discussionmentioning

confidence: 99%

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Shifts in the Distribution and Fate of Sedimentary Polycyclic Aromatic Hydrocarbons Within the Estuarine‐Inner Shelf Areas of the East China Sea: Response to Human‐Induced Catchment Change

et al. 2020

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Human-induced changes in river catchments, such as damming, can affect estuarine depositional settings and further affect the transport of sediments and associated pollutants. Polycyclic aromatic hydrocarbons (PAHs) in surface sediments from the East China Sea (ECS) at two time nodes (2006 and 2018) were compared to understand the response of PAHs to human-induced catchment changes. PAH concentrations in the ECS ranged from 8-414 ng g −1 (dry weight), with a mean value of 112 ± 77 ng g −1 , relatively low than that in 2006 (38-308 ng g −1 , with a mean of 122 ± 60 ng g −1 ). Sharp decreases in sediment loads have triggered erosion in subaqueous delta and changed the distribution of sediment components, which may eventually influence the distribution pattern of PAHs. The obvious spatial differentiation of PAHs between 2006 and 2018 suggested that the depositional center of PAHs shifted from the estuary to the inner shelf area. PAH deposition patterns in the ECS were primarily influenced by riverine input before 2006 but are now dominated by winnowing processes related to long-distance transport due to sharply decreased sediment loads. Dam construction in the river catchment intercepted large amounts of sediments and PAHs, shifting the Changjiang-derived PAH depositional center from the ocean to reservoirs. Overall, depositional patterns of PAHs in the ECS were largely altered by human-induced catchment changes, which may cause significant impacts on the region's biogeochemical cycles and ecosystem health. Plain Language SummaryCoastal oceans are usually considered important sinks of terrestrial materials, especially river-dominated coastal margins. However, river-derived terrestrial materials have decreased drastically in the last several decades worldwide, due to intensified human activities that have changed the local sedimentary environment. In this study, changes in the surface sediment grain size within the East China Sea from 2006 to 2018 indicated that the sedimentary environment in this region was clearly altered. Similarly, the distributions and compositions of PAHs in surface sediments changed from 2006 and 2018. Based on combined analysis of grain size and PAHs, we found that PAH dynamics in this region were primarily influenced by riverine inputs before dam construction in the Changjiang (Yangtze) River basin but are now dominated by winnowing processes related to long-distance transport due to sharply decreased sediment loads. Therefore, intensified human-induced catchment changes have significant influenced the fate of PAHs in the East China Sea.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Shifts in the Distribution and Fate of Sedimentary Polycyclic Aromatic Hydrocarbons Within the Estuarine‐Inner Shelf Areas of the East China Sea: Response to Human‐Induced Catchment Change

et al. 2020

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“…Continental shelf sediment dynamics will influence the indirect TE as well. The discovery of sediment starvation on the proximal continental shelf (Maloney et al, 2018) and frequent resuspension events (Obelcz et al, 2018) are both consistent with the export of continental shelf muds into indirectly nourished basins. If there was no mineral sediment deposited in the indirectly nourished wetlands, the sediment deficit would be 76%.…”

Section: Journal Of Geophysical Research: Earth Surfacementioning

confidence: 53%

Field‐Based Estimate of the Sediment Deficit in Coastal Louisiana

2020

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Coastal and deltaic sediment balances are crucial for a region's sustainability. However, such balances remain difficult to quantify accurately, particularly for large regions. We calculate organic and mineral sediment mass and volume balances using field measurements from 273 Coastwide Reference Monitoring System sites across the Louisiana Coast between 2006 and 2015. The rapid relative sea level rise rate (average 13.4 mm/year) is offset by the small dry bulk densities observed (average 0.3 g/cm3) to produce a 16.2 ± 41.1% mass deficit and 24.1 ± 14.0% volume deficit, significantly smaller than recent predictions for 2000–2100 (73–79% mass deficit). Geostatisical estimates show that this deficit is primarily located in areas not directly nourished by major rivers, yet these regions still accumulate ~24 MT/year of mineral sediment. A fluvial sediment discharge of 113.8 MT/year suggests a coast‐wide trapping efficiency of 31.5 ± 15.8% of the riverine sediment, excluding subaqueous deposition. Organic accumulation accounts for 25% of all mass accumulation during our study period, and total organic mass accumulation per unit area is relatively constant in both directly and indirectly nourished regions. Sediment characteristics in the modern coastal wetlands differ from the Holocene deposit, suggesting secular changes within the system that will likely continue to influence coastal dynamics over the coming decades. Our results suggest that the gap between accommodation and accumulation (mass or volume) during this decade was not as large as the previously predicted century average.

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“…Coastal zones that experience high sedimentation are more susceptible to develop slope stability issues, as the weight of the newly added sediment increases shear stress which can lead to slope failure and trigger powerful downslope flows in already unstable area even with a very low gradient slope (Coleman and Garrison 1977;Clare et al 2016;Maloney et al 2018Maloney et al , 2020. Additionally, newly deposited sediment lacks the consolidated cohesive strength of older sediment, compounding the problem of an already unstable seafloor (Obelcz et al 2017).…”

Section: Discussionmentioning

confidence: 99%

Oceanic sediment accumulation rates predicted via machine learning algorithm: towards sediment characterization on a global scale

2020

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Observed vertical sediment accumulation rates (n = 1031) were gathered from ~ 55 years of peer reviewed literature. Original methods of rate calculation include long-term isotope geochronology (14C, 210Pb, and 137Cs), pollen analysis, horizon markers, and box coring. These observations are used to create a database of global, contemporary vertical sediment accumulation rates. Rates were converted to cm year−1, paired with the observation’s longitude and latitude, and placed into a machine learning–based Global Predictive Seabed Model (GPSM). GPSM finds correlations between the data and established global “predictors” (quantities known or estimable everywhere, e.g., distance from coastline and river mouths). The result, using a k-nearest neighbor (k-NN) algorithm, is a 5-arc-minute global map of predicted benthic vertical sediment accumulation rates. The map generated provides a global reference for vertical sedimentation from coastal to abyssal depths. Areas of highest sedimentation, ~ 3–8 cm year−1, are generally river mouth proximal coastal zones draining relatively large areas with high maximum elevations and with wide, shallow continental shelves (e.g., the Gulf of Mexico and the Amazon Delta), with rates falling exponentially towards the deepest parts of the oceans. The exception is Oceania, which displays significant vertical sedimentation over a large area without draining the large drainage basins seen in other regions. Coastal zones with relatively small drainage basins and steep shelves display vertical sedimentation of ~ 1 cm year−1, which is limited to the near shore when compared with shallow, wide margins (e.g., the western coasts of North and South America). Abyssal depth rates are functionally zero at the time scale examined (~ 10−4 cm year−1) and increase one order of magnitude near the Mid-Atlantic Ridge and at the Galapagos Triple Junction.

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Mississippi River subaqueous delta is entering a stage of retrogradation

Cited by 71 publications

References 33 publications

Shifts in the Distribution and Fate of Sedimentary Polycyclic Aromatic Hydrocarbons Within the Estuarine‐Inner Shelf Areas of the East China Sea: Response to Human‐Induced Catchment Change

Shifts in the Distribution and Fate of Sedimentary Polycyclic Aromatic Hydrocarbons Within the Estuarine‐Inner Shelf Areas of the East China Sea: Response to Human‐Induced Catchment Change

Field‐Based Estimate of the Sediment Deficit in Coastal Louisiana

Oceanic sediment accumulation rates predicted via machine learning algorithm: towards sediment characterization on a global scale

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