MODELING THE EFFECT OF ORGANIC SEDIMENT DYNAMICS ON COASTAL PLAIN DEPOSITIONAL SYSTEMS UNDER SEA-LEVEL CYCLES

Coastal salt marshes, which provide valuable ecosystem services such as flood mitigation and carbon sequestration, are threatened by rising sea level. In response, these ecosystems migrate landward, converting available upland into salt marsh. In the coastal-plain surrounding Chesapeake Bay, United States, conversion of coastal forest to salt marsh is well-documented and may offset salt marsh loss due to sea level rise, sediment deficits, and wave erosion. Land slope at the marsh-forest boundary is an important factor determining migration likelihood, however, the standard method of using field measurements to assess slope across the marsh-forest boundary is impractical on the scale of an estuary. Therefore, we developed a general slope quantification method that uses high resolution elevation data and a repurposed shoreline analysis tool to determine slope along the marsh-forest boundary for the entire Chesapeake Bay coastal-plain and find that less than 3% of transects have a slope value less than 1%; these low slope environments offer more favorable conditions for forest to marsh conversion. Then, we combine the bay-wide slope and elevation data with inundation modeling from Hurricane Isabel to determine likelihood of coastal forest conversion to salt marsh. This method can be applied to local and estuary-scale research to support management decisions regarding which upland forested areas are more critical to preserve as available space for marsh migration.

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Establishing a sediment budget in the newly created “Kleine Noordwaard” wetland area in the Rhine–Meuse delta

Earth Surface Dynamics ◽

10.5194/esurf-6-187-2018 ◽

2018 ◽

Vol 6 (1) ◽

pp. 187-201 ◽

Cited By ~ 4

Author(s):

Eveline Christien van der Deijl ◽

Marcel van der Perk ◽

Hans Middelkoop

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Sediment Budget ◽

Sediment Dynamics ◽

Sediment Deposition ◽

Created Wetlands ◽

Intertidal Area ◽

Soil Subsidence ◽

Elevation Data ◽

Marsh Erosion

Abstract. Many deltas are threatened by accelerated soil subsidence, sea-level rise, increasing river discharge, and sediment starvation. Effective delta restoration and effective river management require a thorough understanding of the mechanisms of sediment deposition, erosion, and their controls. Sediment dynamics has been studied at floodplains and marshes, but little is known about the sediment dynamics and budget of newly created wetlands. Here we take advantage of a recently opened tidal freshwater system to study both the mechanisms and controls of sediment deposition and erosion in newly created wetlands. We quantified both the magnitude and spatial patterns of sedimentation and erosion in a former polder area in which water and sediment have been reintroduced since 2008. Based on terrestrial and bathymetric elevation data, supplemented with field observations of the location and height of cut banks and the thickness of the newly deposited layer of sediment, we determined the sediment budget of the study area for the period 2008–2015. Deposition primarily took place in channels in the central part of the former polder area, whereas channels near the inlet and outlet of the area experienced considerable erosion. In the intertidal area, sand deposition especially takes place at low-lying locations close to the channels. Mud deposition typically occurs further away from the channels, but sediment is in general uniformly distributed over the intertidal area, due to the presence of topographic irregularities and micro-topographic flow paths. Marsh erosion does not significantly contribute to the total sediment budget, because wind wave formation is limited by the length of the fetch. Consecutive measurements of channel bathymetry show a decrease in erosion and deposition rates over time, but the overall results of this study indicate that the area functions as a sediment trap. The total contemporary sediment budget of the study area amounts to 35.7×103 m3 year−1, which corresponds to a net area-averaged deposition rate of 6.1 mm year−1. This is enough to compensate for the actual rates of sea-level rise and soil subsidence in the Netherlands.

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Sediment starvation destroys New York City marshes’ resistance to sea level rise

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1715392115 ◽

2018 ◽

Vol 115 (41) ◽

pp. 10281-10286 ◽

Cited By ~ 17

Author(s):

Dorothy M. Peteet ◽

Jonathan Nichols ◽

Timothy Kenna ◽

Clara Chang ◽

James Browne ◽

...

Keyword(s):

New York ◽

New York City ◽

Sea Level Rise ◽

Sea Level ◽

York City ◽

Organic Sediment ◽

Jamaica Bay ◽

Structural Weakness ◽

Global Sea Level ◽

Matter Flux

New York City (NYC) is representative of many vulnerable coastal urban populations, infrastructures, and economies threatened by global sea level rise. The steady loss of marshes in NYC’s Jamaica Bay is typical of many urban estuaries worldwide. Essential to the restoration and preservation of these key wetlands is an understanding of their sedimentation. Here we present a reconstruction of the history of mineral and organic sediment fluxes in Jamaica Bay marshes over three centuries, using a combination of density measurements and a detailed accretion model. Accretion rate is calculated using historical land use and pollution markers, through a wide variety of sediment core analyses including geochemical, isotopic, and paleobotanical analyses. We find that, since 1800 CE, urban development dramatically reduced the input of marsh-stabilizing mineral sediment. However, as mineral flux decreased, organic matter flux increased. While this organic accumulation increase allowed vertical accumulation to outpace sea level, reduced mineral content causes structural weakness and edge failure. Marsh integrity now requires mineral sediment addition to both marshes and subsurface channels and borrow pits, a solution applicable to drowning estuaries worldwide. Integration of marsh mineral/organic accretion history with modeling provides parameters for marsh preservation at specific locales with sea level rise.

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Exploring the relationship between organic deposition resulting from marshes and autogenic scales in deltaic stratigraphy

10.5194/egusphere-egu21-12844 ◽

2021 ◽

Author(s):

Jose Silvestre ◽

Kelly Sanks ◽

Sam Zapp ◽

Dutt Ripul ◽

John Shaw ◽

...

Keyword(s):

Sea Level ◽

Sediment Accumulation ◽

Organic Production ◽

Transport Systems ◽

Constant Input ◽

Kaolinite Clay ◽

Clastic Sediment ◽

Organic Sediment ◽

Stratigraphic Architecture

<p>Many deltas contain extensive marshes, typically defined as laterally extensive, low energy settings tied to a narrow elevation window around sea level. Biological activity in marshes results in in-situ organic sediment accumulation that has the potential to be stored in the sedimentary record. However, it is unclear how marshes interact with channels that transport the clastic sediment and typically control autogenic stratigraphic architecture. We present results from a physical experiment designed to explore the coupled evolution of marshes and deltas over geologic timescales. In the experiment, deltaic channels self-organized due to constant input rates of water and clastic sediment that experience constant long-term accommodation production through sea-level rise. A low bulk density kaolinite clay was deposited on the delta-top following rules developed by the ecology community for in-situ organic production. The kaolinite clay serves as a proxy for the in-situ organic sediments in overbank regions. As such, the autogenic processes of the clastic transport system, which influence elevation relative to sea-level, also exert a control on the scales of preserved organic-rich strata. We quantify the fraction of the organic sediment proxy in the fluvio-deltaic deposit to define a transfer function between the accumulation of organic sediment and its preservation beneath the morphodynamically active layer. We also use synthetic stratigraphy and images of the preserved strata to characterize the spatial arrangements of organic strata, and the influence of marshes on the resulting arrangement of channel bodies. Initial findings suggest that the thickest seams are located near the mean shoreline but extend significant distances from this location due to autogenic shoreline transgressions and regressions. Quantifying these trends will inform our understanding of how in-situ organic sediment accumulation influences clastic transport systems and the structure of deltaic stratigraphy.</p>

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Introduction

Early Human Life on the Southeastern Coastal Plain ◽

10.5744/florida/9781683400349.003.0001 ◽

2018 ◽

pp. 1-7

Author(s):

Albert C. Goodyear ◽

Christopher R. Moore

Keyword(s):

Sea Level ◽

Late Pleistocene ◽

Coastal Plain ◽

Younger Dryas ◽

Archaeological Sites ◽

Impact Hypothesis

This chapter reviews the significant features of early prehistoric occupations of the Southeastern U.S. Coastal Plain. Along with the Pleistocene age archaeological sites, salient aspects of the geology, including sea level positions, are presented. Possible Pre-Clovis sites dating from pre-LGM to late Pleistocene times are considered. Clovis is seen to have a Coastal Plain settlement focus that includes the now-drowned shelf. The dramatic onset of the Younger Dryas and its potential effects on people, including the “Younger Dryas Impact Hypothesis,” are reviewed.

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