Coastal Sediment Accumulation Research Articles

Unveiling the impact and mechanisms of Cd-driven ecological assembly and coexistence of bacterial communities in coastal sediments of Yellow Sea

The microbial community assembly processes and underlying mechanisms in response to heavy metal accumulation in coastal sediments remain underexplored. In this study, the heavy metal concentration in samples were found below the marine sediment quality standards. Through partial Mantel tests and linear regression analysis, Cd was identified as the major influencing factor, displaying strongest correlation with the bacterial community in the sediments. The class Desulfuromonadia was identified as a biomarker which showed enrichment in the sediments with high Cd content. Additionally, the results of null model and the neutral community model demonstrated the prominent role of stochastic processes in the assembly of bacterial community. However, with the increase in Cd concentration, the influence of selection processes intensified, resulting in a decline in species migration rate and subsequent reduction in ecological niche width. Furthermore, the intensified competition and an increase in keystone species among bacterial populations further enhanced the stability of the microbial co-occurrence network in response to high Cd concentration. This study offers an insight into the effects of heavy metal on microbial assembly and coexistence, which are conducive to marine ecosystem management and conservation.

Surface Deformation Mechanism Analysis in Shanghai Areas Based on TS-InSAR Technology

To address the problem that surface deformation causes in urban areas by affecting urban security and threatening human life and property, this study first measured the surface deformation in Shanghai from 2016 to 2020 using the time series InSAR method. Then, the spatial–temporal distribution and evolution characteristics of deformation were investigated in detail. The deformation mechanism is explained by factors including groundwater and rainfall. By introducing the seasonal changes of tides and sediment accumulation, the reason for the uplift in the Shanghai area is further explained. Finally, the surface deformation of the reclamation area is detected further. Meanwhile, the spatial–temporal variation characteristics of the surface in the reclamation area are explored. Through time series InSAR technology, the results of surface deformation in Shanghai demonstrate the following: (1) The deformation in the study area is uneven in time, and the subsidence is especially apparent during the 2016–2017 period. The maximum cumulative subsidence amounts to −131.1 mm, and the PS points with subsidence rates greater than −5 mm/y occupy 41.36% of all the subsidence points. In addition, PS points with uplift rates greater than 5 mm/y account for 39.55% of all the uplift points. The overall spatial distribution in the Shanghai area is characterized by the uplift in the north and subsidence in the south, whereas the cumulative subsidence in the time series presents a slowing trend; (2) Surface subsidence and groundwater, rainfall, and urban development in the Shanghai area are correlated. Seasonal changes in tides contribute to surface uplift in coastal areas. Coastal sediment accumulation and soil changes also make direct contributions to the occurrence of surface uplift; (3) The deformation of the reclamation area and the completion time are correlated, and the subsidence points of the reclamation area are mainly concentrated on the surrounding dikes from 2016 to 2020. The cumulative subsidence of the two years from 2016 to 2017 is up to −102.2 mm. The results of this study systematically explore the spatial–-temporal evolution and causes of surface deformation in Shanghai, providing scientific data which can support the development of Shanghai.

Physical and chemical evolution of a Pleistocene marginal marine gold paleoplacer deposit, southern New Zealand

Pleistocene placer gold accumulation in coastal sediments during fluctuating Pleistocene sea levels and active tectonic uplift in southern New Zealand provides a well-constrained model for processes that have affected paleoplacers formed in similar settings in older rocks, going back to the Archean. Initial gold concentration occurred > 200 ky ago on exposed sandy beaches, where sand-blasting processes deformed fluvially-transported (~200 km) flakes into toroids, dumbells and spheroids. This gold was recycled into younger gravel-bearing sediments < 30 m thick during subsequent uplift (>50 m) with negligible morphological changes during < 10 km of fluvial transport. Most of the gold accumulated in basal fluvial gravels hosted in channels incised into gabbroic basement. Groundwater in the sedimentary sequence was derived from rain with marine aerosols and had the composition of dilute sea water. This low-temperature groundwater interaction has altered mafic clasts and immediately underlying basement to clays dominated by smectites and kaolinite, with some clay cementation. Groundwater alteration occurred under a wide range of redox and pH conditions that were lithologically controlled, principally by permeability contrasts at the centimetre to metre scale. Hence, oxidised waters produced clays impregnated with ferric iron oxyhydroxide, and reduced waters generated authigenic pyrite. Some of this pyrite was subsequently oxidised with localised acidification. Micron scale dissolution of gold via chloride, thiosulphate and bisulphide ligands led to authigenic gold impregnation of clays. Basal gravels contain clasts that have been pervasively clay-altered, partially clay-altered, and only incipiently clay-altered, attesting to repeated fluvial reworking to basement of the channelised sediments, and progressive gold concentration.

An analysis of the factors responsible for the shoreline retreat of the Chao Phraya Delta (Thailand)

Deltas are inherently low-lying structures and thus subject to large threats due to sea level rise, erosion and other coastal processes. The shorelines in many deltas around the world are now retreating and most cases appear to result from a decreasing sediment supply as a consequence of upstream dam construction. We present here results of an investigation of riverine sediment fluxes, coastal retreat, and coastal sediment accumulation in the Chao Phraya River and Delta (Thailand). This deltaic shoreline has one of the highest rates of shoreline retreat in the world. Surprisingly, our results show that in spite of the construction of two large storage dams, one on the Ping River (Bhumibol Dam, 1964) and the other on the Nan River (Sirikit Dam, 1972) that merge to form the Chao Phraya, sediment accumulation in the delta was actually higher over the last several decades than prior to dam construction. The recent higher rates of sediment accumulation, based on 210Pb dating, appear to be the result of increased sediment supply in the lower reaches of the river relating to expansion of aquaculture and other activities in the delta beginning in the 1970s. We also show that mangrove removal, in order to further develop shrimp farming, charcoal production, and other pursuits, was not responsible for most of the shoreline erosion. Rather, subsidence, mainly induced by groundwater withdrawal, together with worldwide sea level rise appears to be the main factor affecting the very rapid shoreline retreat of the Chao Phraya Delta.

Response of the barrier island coastal region of southwestern Nigeria to climate and non-climate forcing

Despite threats emanating from the influence of climate and non-climate forcing on the barrier island coastal region of southwestern Nigeria, the extent of the coastal erosion is poorly understood. We report evidence of coastal erosion and sediment accumulation in the region over a 34-year period (1973–2017), using Landsat imagery at intervals of approximately six years. Landsat image corrections and various water-extraction algorithms were used to systematically delineate coastal erosion and accumulation in the area. The region was subdivided into western and eastern subregions separated by Lagos Harbour. In the west, erosion took place during the periods 1973–1979, 1979–1984, 1990–1999 and 2005–2011, whereas in the east, erosion occurred during 1973–1979, 1990–1999 and 1999–2005. Coastal sediment accumulation occurred in the east during 1979–1984, 1984–1990, 2005–2011 and 2011–2017, whereas gains in the west occurred during 1984–1990, 1999–2005 and 2011–2017. The study revealed substantial net erosion of 1 228.1 ha in the region as a whole, over the full period. Sediment accumulation accompanying the coastal erosion appears to be linked to longshore drift. Erosion between 1973 and 2011 was probably attributable to climate change (storms and tidal conditions), longshore drift, the inflow and outflow of water at Lagos Harbour, coastal morphology and, possibly, human impacts. However, the coastal changes between 2011 and 2017 were more obviously associated with human activities, such as development of the Eko Atlantic construction project. Coastal surveillance, together with the use of environmentally sensitive protective measures, could possibly help to reduce coastal erosion in the region. Careful coastal management practices, including artificial nourishing and the installation of resilient structures (e.g. seawalls), should be undertaken to protect human settlements that are already at risk from sea-level rise.

Phthalate acid esters (PAEs) accumulation in coastal sediments from regions with different land use configuration along the Persian Gulf

Phthalate acid esters (PAEs) are widely used as plasticizers in various plastic products and have aroused considerable concern over their ubiquitous presence and potentially hazardous effects on the environment. This research provides the first data on PAEs distribution in the sediments of northern part of the Persian Gulf. To determine the concentration of 16 PAEs, 26 samples of sediments were collected from industrial stations (IS), urban stations (US), agricultural stations (AGS), and natural field stations (NS) from Asalouyeh Harbor coasts from Nov 2016 to Jan 2017. The mean values of Ʃ16PAEs in the samples taken from IS, AGS, US, and NS were 78.08, 11.69, 46.56, and 5.180 µg/g, respectively. The results indicated that the mean concentrations of Ʃ16PAEs in the samples taken from IS and AGS areas were significantly higher (p < 0.05) than the ones taken from US and NS areas. The order of PAEs concentrations in sediment samples were as di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DnBP), butylbenzyl phthalate (BBP), and di-n-octyl phthalate (DnOP), respectively. DEHP was detected in all collected samples and the mean ± SD of its concentration in the IS, US, AGS, and NS regions were as 28.15 ± 4.9, 4.040 ± 0.53, 11.58 ± 1.2, and 1.780 ± 0.78 µg/g, respectively. The major sources of PAEs in the sediments collected from the study region were associated with the industrial and agricultural activities. The findings of this study indicated that the sediments of the Asalouyeh coasts are heavily contaminated with PAEs. They have shown potential ecotoxicological effects on the aquatic organisms and benthic. Therefore, more attention should be paid to prediction of the marine ecosystem in this region by the authorities.

Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity Zostera marina and Warm Affinity Halophila nipponica in Temperate Coastal Waters

To evaluate the impact of invading seagrass on biogeochemical processes associated with sulfur cycles, we investigated the geochemical properties and sulfate reduction rates (SRRs) in sediments inhabited by invasive warm affinity Halophila nipponica and indigenous cold affinity Zostera marina. A more positive relationship between SRR and below-ground biomass (BGB) was observed at the H. nipponica bed (SRR = 0.6809 × BGB − 4.3162, r2 = 0.9878, p = 0.0006) than at the Z. marina bed (SRR = 0.3470 × BGB − 4.0341, r2 = 0.7082, p = 0.0357). These results suggested that SR was more stimulated by the dissolved organic carbon (DOC) exuded from the roots of H. nipponica than by the DOC released from the roots of Z. marina. Despite the enhanced SR in spring-summer, the relatively lower proportion (average, 20%) of acid-volatile sulfur (AVS) in total reduced sulfur and the strong correlation between total oxalate-extractable Fe (Fe(oxal)) and chromium-reducible sulfur (CRS = 0.2321 × total Fe(oxal) + 1.8180, r2 = 0.3344, p = 0.0076) in the sediments suggested the rapid re-oxidation of sulfide and precipitation of sulfide with Fe. The turnover rate of the AVS at the H. nipponica bed (0.13 day−1) was 2.5 times lower than that at the Z. marina bed (0.33 day−1). Together with lower AVS turnover, the stronger correlation of SRR to BGB in the H. nipponica bed suggests that the extension of H. nipponica resulting from the warming of seawater might provoke more sulfide accumulation in coastal sediments.

Geographic variability in organic carbon stock and accumulation rate in sediments of East and Southeast Asian seagrass meadows

AbstractOrganic carbon (OC) stored in the sediments of seagrass meadows has been considered a globally significant OC reservoir. However, the sparsity and regional bias of studies on long‐term OC accumulation in coastal sediments have limited reliable estimation of the capacity of seagrass meadows as a global OC sink. We evaluated the amount and accumulation rate of OC in sediment of seagrass meadows and adjacent areas in East and Southeast Asia. In temperate sites, the average OC concentration in the top 30 cm of sediment was higher in seagrass meadows (780–1080 μmol g−1) than in sediments without seagrass cover (52–430 μmol g−1). The average OC in the top 30 cm of subtropical and tropical seagrass meadow sediments ranged from 140 to 440 μmol g−1. Carbon isotope mass balancing suggested that the contribution of seagrass‐derived carbon to OC stored in sediments was often relatively minor (temperate: 10–40%; subtropical: 35–82%; tropical: 4–34%) and correlated to the habitat type, being particularly low in estuarine habitats. Stock of OC in the top meter of sediment of all the studied meadows ranged from 38 to 120 Mg ha−1. The sediment accumulation rates were estimated by radiocarbon dating of six selected cores (0.32–1.34 mm yr−1). The long‐term OC accumulation rates calculated from the sediment accumulation rate and the top 30 cm average OC concentration for the seagrass meadows (24–101 kg ha−1 yr−1) were considerably lower than the OC accumulation rates previously reported for Mediterranean Posidonia oceanica meadows (580 kg ha−1 yr−1 on average). Current estimates for the global carbon sink capacity of seagrass meadows, which rely largely on Mediterranean studies, may be considerable overestimations.

The Kalahari Epeirogeny and climate change: differentiating cause and effect from core to space

Southern Africa’s high Kalahari plateau and its flanking mountain ranges formed over an extended period of ∼200 million years through vertical tectonic processes different from those at convergent plate boundaries. We refer to this as the Kalahari epeirogeny. Episodic uplift and erosion during the Kalahari epeirogeny is inferred from thermo-chronology and from stratigraphy of sediment accumulated around its continental margin. A total thickness of 2 to 7 km of rock (of which basalt was a major component) was eroded from the subcontinent’s surface during two punctuated episodes of exhumation, in the early-Cretaceous and in the mid-Cretaceous. Major exhumation was over by the end of the Cretaceous, and the rate of erosion decreased by more than an order of magnitude to remove less than 1 km thickness of rock during the Cenozoic. Cosmogenic dating shows that erosion rates today are almost an order of magnitude less still. The cause for the Kalahari epeirogeny remains elusive, but three striking observations stand out: (i) major exhumation occurred during the late Mesozoic break-up of Gondwana; (ii) large scale basaltic magmatism closely match two accelerated episodes of exhumation: first along the west coast (∼132 Ma, Etendeka large igneous province [LIP], associated with vast amounts of underplating along this entire passive margin), and the second flanking the sheared south coast margin (∼90 Ma, Agulhas oceanic LIP). Yet exhumation that might have accompanied the vast Karoo LIP (∼180 Ma) is not readily detected; (iii) the two main regional episodes of accelerated exhumation and coastal sediment accumulation are near synchronous with two regional ‘spikes’ of kimberlite intrusions: >450 kimberlites at ∼90 Ma, and >200 kimberlites at ∼120 Ma. Southern Africa is underlain by an anomalous warm region in the lowermost ∼1500 km of the mantle that is linked to core to mantle heat loss. This warm region was inherited from a large Cretaceous thermo-chemical anomaly in the mantle created during long-lived subduction beneath Gondwana. Associated Mesozoic kimberlite genesis and basaltic magmatism may have been sufficient to cause volatile/heat-induced density changes in the lithospheric mantle of southern Africa to sustain the Kalahari plateau. In addition, such changes may have been induced by tectonic uplift and decompressional melting resulting from far-field collision processes between Africa and Europe, and/or final continental lithosphere decoupling between the Falkland plateau and southern Africa. CO 2 released into the ocean-atmosphere system during the Kalahari epeirogeny contributed to the global mid-Cretaceous hot-house conditions. However, because the CO 2 -consumption rate associated with basalt weathering is about eight times that of granite, atmospheric CO 2 was also efficiently sequestrated during the rapid erosion of Karoo basalt. Thus, the Kalahari epeirogeny also may have catalysed the onset of long-term global Cenozoic cooling.

Coupling of the Perturbed C–N–P Cycles in Industrial Time

Coupling of the C–N–P biogeochemical cycles is effected by the dependence of the land and aquatic primary producers on the availability of N and P. In general, the Redfield ratios C:P and N:P in the reservoirs supplying nutrients for primary production on land, in the oceanic coastal zone, and in the surface ocean differ from these ratios in the land phytomass and aquatic plankton. When N:P in the source is higher than in primary producers, this results in a potential accumulation of some excess nitrogen in soil water and coastal water, and increased denitrification flux to the atmosphere. The oceanic coastal zone plays an important role in the coupled C–N–P cycles and their dynamics because of its intermediate position between the land and oceanic reservoirs. These coupled cycles were analyzed for the last 300 years of exposure to four human-generated forcings (fossil fuel emissions, land use change, chemical fertilization of land, and sewage discharge to the coastal zone) and global temperature rise. In the period from 1700 to 2000, there has been a net loss of C, N, and P primarily from the land phytomass and soil humus, despite the rise in atmospheric CO2, increased recycling of nutrients from humus, chemical fertilization, and re-growth of forests on previously disturbed land. The main mechanisms responsible for the net loss were increased riverine transport to the coastal zone of dissolved and particulate materials and, for N, increased denitrification on land. The oceanic coastal zone gained N and P, resulting in their accumulation in the organic pool of living biomass and dissolved and reactive particulates, as well as in their accumulation in coastal sediments from land-derived and in situ produced organic matter. Pronounced shifts in the rates and directions of change in some of the major land reservoirs occurred near the mid-1900s. Denitrification removes N from the pool available for primary production. It is the strongest on land, accounting for 73–83% of N removal from land by the combined mechanisms of denitrification and riverine export.

Major and trace element accumulation in coastal sediments along southeastern Baja California studied by instrumental neutron activation analysis and 210Pb age-dating

The vertical distribution of K, Rb, Cs, Ca, Sr, Ba, Fe, Cr, Co, Ni, Zn, Sc, Zr, Sb, Se and As was studied by means of instrumental neutron activation analysis in four sediment cores collected from the eastern shelf of tectonically active Baja California peninsula accompanied by 210Pb age-dating. 210Pb analysis was performed by extraction chromatography with measuring the ingrowing daughter 210Bi radioactivity by liquid-scintillation spectrometry. It was found that concentration variations of Se, As, Sb, Zr and Zn are probably controlled by the intensity and composition of the material supplied from the drainage basin constituted by volcanic and sedimentary rocks.

Shoreline Trajectories and Sequences: Description of Variable Depositional-Dip Scenarios

ABSTRACT Shoreline migration patterns can be described in terms of the shoreline trajectory, which is the shoreline path viewed along a cross-sectional depositional-dip section. Discrete classes of shoreline trajectories can be defined: accretionary and forced regression; normal regression; and accretionary and transgression. implies that sediment supplied to the shoreline participates in determining the shoreline trajectory, whereas non-accretionary implies that existing topography dictates the trajectory. In the latter case, translation of the shoreline takes place without significant deposition. The directions of the shoreline trajectories and the above classes provide a basis for describing variable shoreline behavior for individual shorel ne excursions, for stacked shoreline migration patterns, for systems tracts, and for depositional cycles. A forced regression takes place when little or no sediment is deposited at the shoreline as sea level falls. Accretionary forced regressions occur when sea-level fall is accompanied by coastal sediment accumulation. The architecture of accretionary forced regressions is controlled by the slopes of the alluvial and marine environments, and the shoreline trajectory. A regressive surface of marine erosion is most likely to be formed when the path of the shoreline converges with the fronting depositional foundation. During normal regression, the shoreline trajectory and the depositional foundation usually diverge, with accompanying deepening of water in front of the prograding shoreline. A transgression is defined as a transgression with a shoreline trajectory coinciding with the alluvial depositional surface at the onset of transgression. Accommodation may or may not be present at the landward side of the shoreline at the onset of transgression, but will not be generated there during transgression. An accretionary transgression takes place when the shoreline trajectory diverges relative to the alluvial depositional surface at the onset of transgression. This implies that accommodation is continuously generated and filled behind the retreating shoreline. If a ravinement surface is formed during transgression, its chronostratigraphic significance is maintained only if sediments accumulating during transgression are solely preserved seaward (and not lan ward) of the transgressing shoreline. As the shoreline migrates in various directions, composite stacking patterns, systems tracts, and depositional cycles, as well as surfaces or thin intervals of slow deposition, nondeposition, or erosion are formed. These levels can be used to envelop the depositional cycles. The cycles can be subdivided into two or four systems tracts. The maximum transgressive surface is the most applicable for delineation of cycles. A ravinement surface that merges with or erodes into the subaerial unconformity, in combination with the maximum regressive surface, can also be useful for bracketing cycles.

Forms of phosphorus and its accumulation in coastal sediments of Kieler Bucht

Abstract To study the fate of natural and anthropogenic phosphorus input to a coastal system, the removal of P by accumulation in fine-grained sediments of Kieler Bucht (Western Baltic) was investigated. A phosphorus fractionation scheme was applied to 12 cores from mud, sandy mud and muddy sand sediments. Most phosphorus is contained in the moderately reducible and organic fractions. Almost all excess P in the top enrichment zone is chemisorbed or bound to iron. Evaluation of dated cores from the different sediment types yielded a natural background accumulation of 702 × 106 g P · yr−1 for the whole Kieler Bucht from erosion of till and fluvial input. There is an additional accumulation of up to 538 × 106 g P · yr−1 in recent years which is partly due to diagenetic mobilization and redistribution. In any case, the accumulation of P in fine-grained sediments of Kieler Bucht is far less than published input rates from streams and sewage plants. Thus, in addition to sediment accumulation, a substantial part...