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Results for “Coastal Sediments”

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At least 127 records · Page 7Linked to original sources
USGS1997

Effect of hydrologic management on marsh surface sediment deposition in coastal Louisiana

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.

Louisiana↗
USGS2011

Soil characteristics of sediment-amended baldcypress ( Taxodium distichum ) swamps of coastal Louisiana

Amendments of sediment from dredging activities have played an important role in raising the elevation of sinking coastal wetlands. This study compared the soil characteristics of sediment- amended coastal swamps in the Barataria Preserve unit of Jean Lafitte National Historical Park and Preserve with natural swamps along Bayou des Familles. The sandy sediment amendments used in the coastal forests had different soil texture and characteristics than the more organic soils of the natural swamps. Three years after the application of these sediments on the sediment-amended swamps, dewatering and compaction of the sediment had occurred but the sediment still had high salinity and bulk density, and low organic matter content. The two sediment-amended swamps differed from each other in that Site 1 had a higher elevation (mean = 25 cm higher) and drier soil than Site 2. The effects of sediment in coastal forested wetlands require separate consideration from studies of salt marshes, e.g., the weight of the sediment might damage tree roots, or the amendments might influence soil stability during storms in a different way. Generally, this study suggests that shallower depths of sediment are more likely to yield environments beneficial to these sinking baldcypress swamps in coastal Louisiana.

Louisiana↗
USGS2020

Controls on sediment distribution in the coastal zone of the central California transform continental margin, USA

We use >10,000 km of high-resolution seismic-reflection data together with multibeam bathymetry to document complex and highly variable post-Last Glacial Maximum (LGM) sediment distribution and thickness in the coastal zone (~10 m isobath to 5.6 km offshore) along a ~800 km section of central California's transform continental margin. Sediment thickness ranges from 0 (seafloor bedrock) to 64 m with a mean of 8.7 m. We delineate 25 coastal zone “sediment domains,” and group them based on common geomorphology and sediment occurrence. Thickest sediment occurs in “mountain front” and “large river” domains, which comprise 14.5% and 7.9% of the coastal zone and contain 30.1% and 18.2% of coastal zone sediment, respectively. In contrast, “small river” domains and “sediment-poor shelf” domains comprise 50.7% and 15.7% of the coastal zone and contain 18.4% and 12.7% of its sediment. The distribution and thickness of post-LGM sediment in the coastal zone is controlled by a combination of tectonics, sediment supply, and eustasy. Sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts, more slowly uplifting marine terraces, and fault-bounded headlands and alluvial-estuarine troughs. Sediment supply is maximized along steep, landslide-prone, mountain fronts and at the mouths of large watersheds, and minimized along lower-relief, terraced coastal landscape drained by smaller rivers and creeks. In the offshore coastal zone, tectonics generates local uplifts and basins, and influences shelf width and gradient as well as the locations of some shelf-incised submarine canyons. Sea-level rise raises base level, drowns estuaries, creates accommodation space on the shelf (amount based on gradient), and isolates the heads of many submarine canyons at or near the shelfbreak. Comparison of shelf sediment volumes with estimates of “unaltered” watershed sediment supply reveals that a relatively small proportion of post-LGM sediment supply is preserved on the shelf offshore of some of the largest rivers. Sediments deposited in shoreline and shelf environments have limited preservation potential, and the most complete long-term geologic record of the post-LGM transgression and highstand is likely represented in slope and submarine fan deposits.

California↗
USGS1995

The influence of Hurricane Andrew on sediment distribution in Louisiana coastal marshes

The areal extent and temporal patterns of sediment deposition in delta marshes and shallow water bodies of Louisiana associated with the passage of Hurricane Andrew were determined from sediment traps, marker horizons, and benchmarks deployed for other studies. Data were collected over different time scales from 11 sites representing salt, brackish, and intermediate marshes, shallow water substrates, and regularly-flooded and partially impounded marshes located in Terrebonne, Barataria, and Pontchartrain basins. Storm tide data were collected at 6 hydrograph stations located in the vicinity of the sediment sampling sites. Significant sediment deposition and surface elevation changes were associated with the occurrence of storm tides both near and far (up to 130 km away) from the track of the storm. Short-term sediment deposition indicated an increase of up to 1–3 orders of magnitude compared to pre-storm rates. This increased rate remained high for up to 12 weeks, suggesting that material brought in by the storm was available for resuspension and deposition. But short-term sediment deposition decreased precipitously after passage of the first major cold front across Louisiana, suggesting that the sediment made available by the storm was removed or consolidated. The storm-associated sediments were characteristically coarser with lower organic matter content than the pre-storm marsh soils. Marsh vertical accretion and surface elevation change were enhanced on both semi-annual and annual time scales for all sites we studied. This single storm generated 2–6 cm more vertical accretion than occurred in either the year before or after the storm. Sediment was both introduced from outside the coastal marsh system and redistributed as the marsh substrate eroded. At shallow water sites, elevation increases were greater and were maintained near wave barriers constructed to baffle water movement while unprotected areas had smaller increases and quickly lost whatever gains had occurred. These findings indicate the potential importance of hurricanes in providing a pulse of sediment on a broad geographic scale to balance the effects of subsidence in this rapidly subsiding delta. These results further suggest that hurricanes play a large role in coastal marsh survival, particularly for marshes remote or isolated (i.e., impounded) from a riverine source of sediment.

Louisiana↗
USGS2000

Suspended-sediment and fresh-water discharges in the Ob and Yenisey rivers, 1960-1988

Of the world's great rivers, the Ob and Yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean. Sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains. Sediment in the lower reaches of these great rivers is deposited and stored (permanently, on a millennial time scale) in flood plains. Sediment discharges, already small under natural conditions, are diminished further by large manmade reservoirs that trap significant proportions of the moving solids. The long winter freeze and sudden spring breakup impose a peakedness in seasonal water runoff and sediment discharge that contrasts markedly with that in rivers of the tropics and more temperate climates. Very little sediment from the Ob and Yenisey rivers is being transported to the open waters of the Arctic Ocean under present conditions.

Arctic Ocean, Gulf of Ob, Irtysh River, Ob River, ↗
USGS2024

Twentieth century extreme precipitation detected in a high-resolution, coastal lake-sediment record from California

California faces increasing economic and societal risks from extreme precipitation and flooding associated with atmospheric rivers (ARs) under projected twenty-first century climate warming. Lake sediments can retain signals of past extreme precipitation events, allowing reconstructions beyond the period of instrumental records. Here, we calibrate AR-related extreme precipitation from the last century to proxy data from lake sediments collected in the latitudinal zone of the highest frequency landfall for modern ARs in California. Excursions in erosional proxy data (Ti/Al) are positively and significantly correlated (r median = 0.45, p median = 0.04) with modern records of integrated vapor transport (IVT, kg m −1 s −1 ), a key metric of AR intensity, using correlations that incorporate age-model uncertainty. Despite the land-use change near the study site, the data suggest intense and long-lasting AR storms are identifiable in this sedimentary record. These results allow conservative inferences concerning past extreme hydrology at this site.

California↗
USGS2019

High-Resolution mapping of biomass and distribution of marsh and forested wetlands in southeastern coastal Louisiana

This study estimates herbaceous and forested wetland coverage and aboveground biomass (AGB) within the Atchafalaya and Terrebonne coastal basins representing sediment rich and sediment poor coastal regions of southern Louisiana. Louisiana coastal wetlands account for approximately one third (37%) of the estuarine wetland area in the conterminous United States, yet the spatial distribution of their extent and aboveground biomass estimates are not well defined. Despite the importance of Louisiana’s coastal wetlands, existing maps on their extent are often outdated yet repeatedly used in national greenhouse gas (GHG) inventories and within regional aboveground biomass and carbon content estimates. Sentinel-2 optical satellite data was used within an object-oriented machine learning approach to classify wetland extent, mapping the spatial distribution of the coastal wetlands at high-resolution. A total wetland extent of 2950 km2 was mapped during a period of peak biomass in September 2017, comprised of forested and herbaceous wetlands (accuracy >90%) and demonstrated considerable differences (793.7 km2) from currently available estimates of wetland area. The distribution of aboveground biomass (AGB) was mapped using class averaged values derived from field data collected during May and September 2015. Total herbaceous biomass at the study site increased by 108.9% from May (668,684.5 Mg) to September (1,396,969.2 Mg) whilst the total woody vegetation biomass (27,667,232.1 Mg) was sampled in May only. This method provides a tractable means of mapping wetland extent and biomass, in a region threatened with wetland loss under projections of increasing sea-level rise and local subsidence.

Louisiana↗
USGS2010

Aminostratigraphy of surface and subsurface Quaternary sediments, North Carolina coastal plain, USA

The Quaternary stratigraphy and geochronology of the Albemarle Embayment of the North Carolina (NC) Coastal Plain is examined using amino acid racemization (AAR) in marine mollusks, in combination with geophysical, lithologic, and biostratigraphic analysis of 28 rotasonic cores drilled between 2002 and 2006. The Albemarle Embayment is bounded by structural highs to the north and south, and Quaternary strata thin westward toward the Suffolk paleoshoreline, frequently referred to as the Suffolk Scarp. The Quaternary section is up to ∼90 m thick, consists of a variety of estuarine, shelf, back-barrier, and lagoonal deposits, and has been influenced by multiple sea-level cycles. The temporal resolution of the amino acid racemization method is tested statistically and with the stratigraphic control provided by this geologic framework, and it is then applied to the correlation and age estimation of subsurface units throughout the region. Over 500 specimens (primarily Mercenaria and Mulinia ) from the subsurface section have been analyzed using either gas chromatographic (GC) or reverse-phase liquid chromatographic (RPLC) techniques. The subsurface stratigraphic data are compared with AAR results from numerous natural or excavated exposures from the surrounding region, as well as results from NC beach collections, to develop a comprehensive aminostratigraphic database for the entire Quaternary record within the NC coastal system. Age mixing, recognized in the beach collections, is also seen in subsurface sections, usually where major seismic reflections or core lithology indicate the presence of stratigraphic discontinuities. Kinetic models for racemization are tested within the regional stratigraphic framework, using either radiocarbon or U-series calibrations or comparison with regional biostratigraphy. Three major Pleistocene aminozones [AZ2, AZ3, and AZ4] are found throughout the region, all being found in superposition in several cores. Each can be subdivided, yielding a total of at least eight stratigraphically and statistically distinct aminozones. Kinetic modeling, supplemented with local calibration, indicates that these aminozones represent depositional events ranging from ∼80 ka to nearly 2 Ma. Three prominent seismic reflections are interpreted to represent the base of the early, middle, and late Pleistocene, respectively, roughly 2 Ma, 800 ka, and 130 ka. The large number of samples and the available stratigraphic control provide new insights into the capabilities and limitations of aminostratigraphic methods in assessing relative and numerical ages of Atlantic Coastal Plain Quaternary deposits.

North Carolina↗
USGS1997

Shorebird-prey interactions in South Carolina coastal soft-sediments

We investigated the simultaneous influence of benthic prey (primarily insect larvae, oligochaetes, and polychaetes) on spring-migrating shorebirds (Charadriiformes) and shorebirds on prey in brackish managed wetlands of South Carolina. We proposed that positive correlations between shorebird and prey densities and between prey reduction and shorebird density might result in a negative feedback loop. The loop would be characterized by shorebird redistribution over time and equalization of shorebird and prey densities (and biomass) across the site. In support of the feedback loop ( i ) there were positive correlations between shorebird and prey densities (and biomass) early in migration; ( ii ) shorebird predation was responsible for declines of 49% in prey density and 50% in prey biomass in a shorebird exclosure experiment, with shorebird density positively correlated with prey decline in open plots; ( iii ) there was equalization of prey biomass across the site, and relative prey species abundance appeared to become more equal. Contrary to predictions, shorebirds did not redistribute after prey reduction, and patchiness of shorebird and prey densities persisted across the site. This failure was attributed to high prey density, even at the season's end, and high water depths. There were no confounding indirect trophic-level effects.

South Carolina↗
USGS2006

Coastal circulation and sediment dynamics in Hanalei Bay, Kaua'i, Hawaii: Part II: Tracking recent fluvial sedimentation: Isotope stratigraphy obtained in Summer 2005

Delivery and dispersal of fluvial sediment in Hanalei Bay, Kaua’i, Hawaii, have important implications for the health of local coral reefs. The reef community in Hanalei Bay represents a relatively healthy ecosystem. However, the reefs are periodically stressed by storm waves, and increases in sediment and dissolved substances from the Hanalei River have the potential to cause additional stress. Increased turbidity and sedimentation on corals during Hanalei River floods that occur in seasons of low wave energy, when sediment would not be readily remobilized and advected out of the bay, could affect the health and sustainability of coral reefs and the many associated species. Measurements of short-lived isotopes 7 Be and 137 Cs in sediment cores have been used to trace the thickness and distribution of terrestrial sediment in Hanalei Bay, in order to assess spatial and temporal patterns of sediment deposition and remobilization relative to coral-reef locations. A third isotope, 210 Pb, derived primarily from seawater, provides additional information about recent sedimentary history. Isotope profiles and observations of sedimentary facies from cores collected at multiple locations in June 2005, and again in August 2005, indicate the presence of recent fluvial sediment and organic debris in the east part of the bay near the mouth of the Hanalei River. Away from the immediate vicinity of the river mouth, sediment in the uppermost 1 m below the sea floor had not retained a significant quantity of fluvial sediment within the eight months prior to either sampling effort. During the study interval in summer 2005 the Hanalei River had no major floods and there was relatively little sediment input to the bay. Sediment away from the river mouth was dominated by carbonate sand, although some terrestrial sediment was present in sub-sea-floor horizons. Sedimentary facies and isotope inventories throughout the bay showed substantial spatial heterogeneity. Sediment cores will be collected again at the same sites discussed here during early and late summer 2006. If possible, additional sites will be sampled in the Black Hole depocenter near the river mouth. Major floods in winter and spring 2006 are expected to leave a significant new sediment signal in the bay that should be detected in summer 2006.

Hawaii↗
USGS2010

Geohydrology of the Aucilla-Suwannee-Ochlockonee River Basin, south-central Georgia and adjacent parts of Florida

Major streams and tributaries located in the Aucilla-Suwannee-Ochlockonee (ASO) River Basin of south-central Georgia and adjacent parts of Florida drain about 8,000 square miles of a layered sequence of clastic and carbonate sediments and carbonate Coastal Plain sediments consisting of the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower confining unit. Streams either flow directly on late-middle Eocene to Oligocene karst limestone or carve a dendritic drainage pattern into overlying Miocene to Holocene sand, silt, and clay, facilitating water exchange and hydraulic connection with geohydrologic units. Geologic structures operating in the ASO River Basin through time control sedimentation and influence geohydrology and water exchange between geohydrologic units and surface water. More than 300 feet (ft) of clastic sediments overlie the Upper Floridan aquifer in the Gulf Trough-Apalachicola Embayment, a broad area extending from the southwest to the northeast through the center of the basin. These clastic sediments limit hydraulic connection and water exchange between the Upper Floridan aquifer, the surficial aquifer system, and surface water. Accumulation of more than 350 ft of low-permeability sediments in the Southeast Georgia Embayment and Suwannee Strait hydraulically isolates the Upper Floridan aquifer from land-surface hydrologic processes in the Okefenokee Basin physiographic district. Burial of limestone beneath thick clastic overburden in these areas virtually eliminates karst processes, resulting in low aquifer hydraulic conductivity and storage coefficient despite an aquifer thickness of more than 900 ft. Conversely, uplift and faulting associated with regional tectonics and the northern extension of the Peninsular Arch caused thinning and erosion of clastic sediments overlying the Upper Floridan aquifer southeast of the Gulf Trough-Apalachicola Embayment near the Florida-Georgia State line. Limestone dissolution in Brooks and Lowndes Counties, Ga., create karst features that enhance water-transmitting and storage properties of the Upper Floridan aquifer, promoting groundwater recharge and water exchange between the aquifer, land surface, and surface water. Structural control of groundwater flow and hydraulic properties combine with climatic effects and increased hydrologic stress from agricultural pumpage to yield unprecedented groundwater-level decline in the northwestern and central parts of the ASO River Basin. Hydrographs from continuous-record observation wells in these regions document declining groundwater levels, indicating diminished water-resource potential of the Upper Floridan aquifer through time. More than 24 ft of groundwater-level decline occurred along the basin's northwestern boundary with the lower Apalachicola-Chattahoochee-Flint River Basin, lowering hydraulic gradients that provide the potential for groundwater flow into the ASO River Basin and southeastward across the Gulf Trough-Apalachicola Embayment region. Slow-moving groundwater across the trough-embayment region coupled with downward-vertical flow from upper to lower limestone units composing the Upper Floridan aquifer resulted in 40-50 ft of groundwater-level decline since 1969 in southeastern Colquitt County. Multi-year episodes of dry climatic conditions during the 1980s through the early 2000s contributed to seasonal and long-term groundwater-level decline by reducing recharge to the Upper Floridan aquifer and increasing hydrologic stress by agricultural pumpage. Unprecedented and continued groundwater-level decline since 1969 caused 40-50 ft of aquifer dewatering in southeastern Colquitt County that reduced aquifer transmissivity and the ability to supply groundwater to wells, resulting in depletion of the groundwater resource.

Florida, Georgia↗