Sediment Grain Size Research Articles

Environmentally sensitive grain-size component records and its response to climatic and anthropogenic influences in Bosten Lake region, China

Using 137Cs and 210Pb dating and multi-proxy evidence from a 41-cm sediment core from Bosten Lake in China, the responses of sediment grain size to environmental changes were reconstructed over the past 150 years. After the end of the Little Ice Age, the climate of the Bosten Lake region became warmer and drier, and the lake water level decreased. The results indicated that the lowest water storage periods occurred at approximately 1920–1930 AD. Decreases in the Siberian High intensity and water vapour transport from the Indian Ocean during this period led to a reduction in the water vapour supply, which resulted in reduced lake levels in the period 1920–1930 AD. Then, the lake was at a high level until the 1960s. The water storage then declined in the 1960s. Since the 1960s, the contents of total organic carbon and total nitrogen have significantly decreased, which is closely related to the significant decline in water level and increased water salinity caused by enhanced water demands. Increased irrigation water demand as a result of expanding cultivated areas and climate change, coupled with a reduced input of water vapour, resulted in the worst water environment in approximately 1980–1990 AD. Since the late 1980s, the water level of the lake has risen, and the lake primary productivity of Bosten Lake has improved. Through the application of statistical methods to grain size data from Bosten Lake combined with the abovementioned data on climate change and human activities, two major potential factors influencing the grain size of terrigenous clastic material were revealed. The first factor, consistent with a grain size of 3.31 μm, is related to the recent increase in agricultural acreage in the Bosten Lake watershed and may reflect increases in atmospheric dust. The second factor, correlated with grain sizes of 11.48 μm and 69.18 μm, can be used to reflect changes in the lake hydrological state. It is suggested that the grain sizes of these lake sediments sensitively reflect changes in the hydrological characteristics of the basin and can be used to reconstruct the history of climate change and human activities.

Potential source contributions and risk assessment of PAHs in sediments from the tail-reaches of the Yellow River Estuary, China: PCA model, PMF model, and mean ERM quotient analysis.

Principal component analysis (PCA), positive matrix factorization (PMF), and the mean effects range-median quotient (MERM-Q) models were employed to determine occurrence levels, sources, and potential toxicological significance of polycyclic aromatic hydrocarbons (PAHs) in surface sediments of the Yellow River Estuary, China. Due to the grain size of sediments, cumulative effects, and distribution of oil fields, the total concentration of the 16 U.S. Environmental Protection Agency (US EPA) priority PAHs (T-PAHs) measured in sediments along transects in the offshore area was 119.51 ± 39.58ngg-1 dry weight (dw), which is notably higher than that measured in rivers (75.00 ± 12.56ngg-1 dw) and estuaries (67.94 ± 10.20ngg-1 dw). PAH levels decreased seaward along all the studied transects in coastal Bohai Bay. Multivariate statistical analyses supported that PAHs in sediments were principally derived from coal and biomass combustion, oil pollution, and vehicular emissions. Based on the MERM-Q (0.0050 ± 0.0017), PAHs were at low potential of ecotoxicological contamination level. These results provide helpful information for protecting water resources and serving sustainable development in Construction of Ecological Civilization in the Yellow River Delta.

Spatial Characteristics, Risk Assessment, and Source Analysis of Elements in Surface Sediments from the Baiyangdian Lake

In this paper, nutrient elements (N and P), heavy metals (Pb, Cu, Zn, Cd, Cr, Co, Ni, and Sn), and grain size in surface sediments of Baiyangdian Lake, northern China, are studied. We also analyze the spatial variation in elemental characteristics and undertaken a pollution risk assessment. By combining data with information on the river sediment characteristics, we use multivariate statistical methods to reveal the sources and variation of elements in sediments. The results showed that the average contents of heavy metals in surface sediments from the lake and associated rivers were higher than background values. Within the area of the lake, nutrient elements are relatively high in the northwest region but low in the southeast region, and heavy metals are relatively high in the middle of the lake but low in the southern and northern areas. The sequence of comprehensive pollution index (I) in sediments was Cd > Pb > Cr > Cu=Zn > Ni > Sn > Co, with Cd being assessed as severe pollution and other elements as moderate pollution, although severe pollution of Cr was found in the Zaolinzhuang area. The order of potential ecological risk coefficients (Eri) was determined as Cd > Pb > Cu > Cr > Ni > Zn, whereby Cd was associated with a strong potential ecological risk (except in the Caiputai area) and other elements were associated with a slight potential ecological risk. Differences in the lake sediment texture were found to be slight. Non-point source pollution after rivers flow into the lake was determined as the main reason for the spatial variation of elements in the surface sediments of Baiyangdian Lake, although point source pollution in the villages surrounding the lake should not be ignored, especially with respect to N, P, Pb, and Cr.

The effect of diatoms on the grain size of lake sediments: a case study of the sediments of Lake Kanas

The grain size of lake sediments has been widely used to reconstruct environmental processes. However, the various components of lake sediments are influenced by different factors, and therefore the environmental significance of grain-size variations may be complex. For example, in situ authigenic biological siliceous components cannot be used to indicate variations in hydrodynamic conditions. Here we present a case study of the effects of diatoms on the grain size of the sediments of Lake Kanas in NW China. The analyses consist of measurements of bulk sediment grain size and biogenic silica, together with microscope observations. Based on both light and scanning electronic microscope observations, two large diatom species, Campylodiscus hibernicus Ehrenberg and Ellerbeckia arenaria (Moore) Crawford, were found to be abundant in sediment samples with a large bulk-sediment grain size, and they contributed substantially to the biogenic silica content and the measured bulk sediment grain size of the core. A quantitative assessment of the effects on grain size was made, and the study has a broad significance for evaluating the effects of diatoms on sediment grain-size distributions in other lakes. Because diatoms may deposit in situ or could be transported differently from other clastic material, the explanation of hydrodynamics could be misled if the influence of diatom has not been excluded. Therefore, we suggest BSi content should be tested to assess the diatom effect prior to grain-size analysis of lake sediments, together with microscope check of diatoms if BSi content is higher than 10%.

The dust storm events recorded in DaQaidam region of Qaidam Basin since Late Glacial period: evidence from the grain size of lake sediment

The paper focused on the study of detrital yellow layer from sediment profile D3 of DaQaidam Salt Lake, based on AMS 14C chronologic and mineralogical methods, aimed to discuss the dust storm events recorded by detrital yellow layer of DaQaidam region since Late Glacial period. The results showed that the grain-size distribution curve displayed double kurtosis, the main peak (10 µm in average) reflected the fine-grained fractions into lake by fluviation, and the secondary peak (> 32 µm) reflected the coarse silt fractions into lake by wind effect and fluviation. Finally, the coarse-grained fractions (> 64 µm) from sediment profile D3 probably recorded the dust storm events since Late Glacial period.

Grain Size and Pollen of Sediments in Wanghu Lake (Central China) Linked to Hydro-Environmental Changes

Grain size of lake sediments is often measured in paleolimnological studies, especially investigations of past paleoclimatic and paleohydrologic changes. The implications of such measures, however, remain unclear, since watershed hydrology and the related transfer of materials to the lake are affected by local climate variables, hydrological shifts, and vegetation cover variables. Sediment from Wanghu Lake in the middle reaches of the Yangtze River have apparently been affected by land cover changes and lake-river system transitions caused by a sluice gate built at Fuchi in 1967. These changes influenced the watershed hydrology, thereby confounding paleoclimatic and paleohydrologic interpretations by proxy records in sediment cores. We collected sediment cores from the center of Wanghu Lake and analyzed trends in pollen and physical properties through sedimentary records to investigate land cover changes and hydrological transitions during the past 90 years. The grain size of the sediment core increased with precipitation and the significant relationships between pollen and grain size after 1967 indicated that sediment transfer to the lake was controlled by rainfall and land cover changes due to human-induced deforestation and farming in the lake catchment. Interestingly before 1967, there was no significant relationship between the pollen and grain size or between the precipitation and grain size, indicating that the sediment of WanghuLake was not simply from the lake catchment. The different relationships patterns before and after 1967 indicated that the sediments in the lake were not only transported following precipitation and discharge from the lake catchment but also came from the Yangtze River draining back into the lake during the flood seasons before 1967. These results highlight matters needing attention and the potential application of grain size of sediments for reconstructions of past hydro-environmental changes.

Hydrodynamics and sediment transport on the North Canterbury Shelf, New Zealand

ABSTRACT This study uses a combination of regional ocean modelling systems (ROMS), a sediment transport model (sedtrans05) and detailed grainsize data with the aim of determining the hydrodynamics and primary sediment transport pathways on the North Canterbury Shelf (NCS), South Island of New Zealand. Combining the results from the hydrodynamic model, sediment grainsize data and sediment transport model in an unsupervised classification scheme, highlights 5 classes of sediment on the shelf. These classes include a high energy inner shelf with coarse sands and gravels (Class 1), a low to medium energy mid shelf allowing for the deposition of fine sediments in a large depocenter (Class 2 and 3), and an area on the mid to outer shelf of relict coarse sediments (Class 4). With the exception of Class 4, the sediment distribution is in equilibrium with the modern hydrodynamics and validates the ROMS and SedTrans05 models. This understanding of the NCS hydrodynamic and sedimentary system will help with the management of the marine environment, with the caveat that this is a highly dynamic environment which is influenced of earthquakes and large storms influencing erosion, transport and distribution of sediment in this region.

Deep pockmarks as natural sediment traps: a case study from southern Santos Basin (SW Atlantic upper slope)

This study examines the role of deep pockmarks in acting as natural sediment traps. Multibeam bathymetry, single-channel seismic and sediment samples data were used for describing the morphology of pockmarks as well as the nature of sediments inside and outside these depressed features, in an area of Santos Basin (SW Atlantic upper slope), dominated by the strong flow of Brazil Current. Results show that the grain size and chemical composition of sediments inside pockmarks are distinct from the outside. Also, radiocarbon dating shows that Holocene ages are found only in samples located inside the pockmarks. Combination of sedimentological, geochemical and geochronological data allowed to recognise that deep pockmarks might present distinct sediment deposition processes when compared with those of shallow pockmarks, in which turbulence impedes sediment deposition, as reported in the literature.

Spatial and seasonal variability in grain size, magnetic susceptibility, and organic elemental geochemistry of channel-bed sediments from the Mekong Delta, Vietnam: Implications for hydro-sedimentary dynamic processes

Understanding the relationship between depositional processes and their products in the fluvial–marine transition zone in tide-dominated depositional systems is fundamental to improving environmental and stratigraphic interpretations of long-term sedimentary records. The distributary channels of the Mekong Delta represent a typical example of a complex sedimentary environment characterized by strong fluvial and tidal interactions, and seasonal variability in hydro-sedimentary dynamic processes, particularly the migration of a salt wedge front linked to seasonal fluctuations in freshwater discharge. For this study, we analyzed grain size, magnetic susceptibility, and organic elemental geochemistry of channel-bed surficial sediments collected in 2015 from all distributary channels during the dry season and from the Mekong–Co Chien River during the flood season. This paper reports spatial and seasonal differences in the characteristics of channel-bed surficial sediments, which are closely linked to sediment sources and depositional processes during the dry and flood seasons.Distributary channels are characterized by coarse-grained sediments in the upper reaches and fine-grained sediments in the lower reaches, in both dry and flood seasons, reflecting the difference between the upstream fluvial-dominated environment and the downstream tide-dominated environment. Flood season samples from the Co Chien River show higher magnetic mineral contents and a terrestrial source of organic carbon compared with dry season samples, indicating sourcing from the drainage basin and trapping of suspended materials in the distributary channel due to the barrier effect of the saltwater wedge at the river mouth. Compared with the flood season, during the dry season the mud content was lower in the downstream reach close to the river mouth and higher in the upstream reach of the Co Chien River, and the content of magnetic minerals was lower in both reaches, indicating dissolution of magnetic minerals during early diagenesis. Furthermore, the lower C/N ratios (<10) and slightly enriched δ13C values of the dry season samples from the Co Chien River imply an additional contribution of organic carbon from a marine source. These various features imply a landward import of mud into the Co Chien River induced by stronger salinity intrusion during the dry season. Along the downstream tract of the Bassac River, two mud-dominated reaches were identified during the dry season. The magnetic mineral contents, C/N ratios and δ13C values indicate that the mud-dominated reach near the Bassac River mouth is also supplied from resuspended sediments by estuarine circulation and tidal pumping, whereas the mud in the reach that is transitional from fluvial to tide dominance has a riverine supply. The results suggest that the Mekong distributary channels are important sinks for suspended sediments during both the flood and dry seasons, controlled by a sediment trapping mechanism provided by either estuarine processes or the morphological configuration of the channels, both of which are controlled by fluvial–tidal dynamics. These depositional processes may be compensating for the incision of channels induced by sand mining in recent decades.

Distribution and degradation of terrestrial organic matter in the sediments of peat-draining rivers, Sarawak, Malaysian Borneo

Abstract. Tropical peatlands are one of the largest pools of terrestrial organic carbon (OCterr); however, our understanding of the dynamics of OCterr in peat-draining rivers remains limited, especially in Southeast Asia. This study used bulk parameters and lignin phenol concentrations to investigate the characteristics of OCterr in a tropical peat-draining river system (the main channel of the Rajang and three smaller rivers: the Maludam, Simunjan, and Sebuyau) in the western part of Sarawak, Malaysian Borneo. The depleted δ13C levels and lignin composition of the organic matter indicates that the most important plant source of the organic matter in these rivers is woody angiosperm C3 plants, especially in the three small rivers sampled. The diagenetic indicator ratio, i.e., the ratio of acid to aldehyde of vanillyl phenols ((Ad∕Al)V), increased with decreasing mean grain size of sediment from the small rivers. The selective sorption of acid relative to aldehyde phenols might explain the variations in the (Ad∕Al)V ratio. Elevated (Ad∕Al)V values observed from the Maludam's sediments may also be attributed to source plant variations. The (Ad∕Al)V ratio appears to be related to the C∕N ratio (the ratio of total organic carbon to total nitrogen) in the Rajang and small rivers. In small rivers, a quick decline of C∕N ratios is a response to the slower modification of (Ad∕Al)V ratios due to better preservation of lignin phenols. An accumulation of lignin phenols with higher total nitrogen percentages (TN%) in the studied systems was observed. Most of the OCterr discharged from the Rajang and small river systems was material derived from woody angiosperm plants with limited diagenetic alteration before deposition and thus could potentially provide significant carbon to the atmosphere after degradation.

Impacts of cascade reservoirs on the longitudinal variability of fine sediment characteristics: A case study of the Lancang and Nu Rivers

The Lancang River and Nu River are parallel rivers located in southwestern China; while the Lancang River has several dams, the Nu River has none. To explore the impacts of cascade reservoirs on the grain size and mineral composition of fine sediments, 9 fine sediment samples from the Nu River and 29 samples from the Lancang River were collected and tested. The results indicate that in the free-flowing reaches (FFRs) of the Lancang River, the sediment grain sizes fined systematically and the mineral compositions varied slightly, and these results were similar to those of the Nu River without dams along the whole mainstream. In the regulated reaches (RRs) of the Lancang River, the sediment grain sizes and mineral compositions indicated discontinuous fluctuations due to the dams trapping. In the reservoir head areas, the sediments were composed of fine silt or medium silt with 50% clay minerals, but the sediments immediately downstream of the dams were fine sand or medium sand with 71% quartz and feldspar. The relative abundance of each mineral was altered differently by passing through the RRs: quartz, chlorite, and illite increased by 13%, 33% and 20%, respectively, while feldspar and calcite decreased by 26% and 80%, respectively, and dolomite and pyrite were completely trapped in the cascade reservoirs. All these common minerals may be replenished except pyrite, which originates from mining areas in the Lancang subbasin.

Dramatic typhoon-induced variability in the grain size characteristics of sediments at a meso-macrotidal beach

Knowledge of sediment grain size characteristics is important for a better understanding of the morphodynamic behavior of beaches worldwide. In this paper, dramatic changes in the grain size of sediments at Yintan Beach, South China in response to Typhoon Rammasun (tropical storm no. 1409) were analyzed on the basis of the collected sediments, beach elevation, and hydrological data from June 1 to July 31. Variations in beach geomorphology were interpreted using the digital elevation taken by LiDAR technology, while changes in sediment grain size were detected by sediment parameters and associated sediment components. The results show that the sediments of Yintan Beach were nearly pure sand before Rammasun and became coarser and slightly better sorted with a higher negative skew after Rammasun. The sediment grain size pattern shifted from a high content (39%) of very fine sand in the lower intertidal zone pre-Rammasun to a high content (76%) of fine sand in the swash zone post-Rammasun. During Rammasun, wave action was responsible for the main transition of grain size pattern in the lower intertidal and mid-tidal zones, and tidal level and beach morphology could affect the grain size distribution of the sandbar and trough in the swash zone. In addition, the increase in the coarse-grained fraction in the upper beach and berm was primarily due to wind action.

A comparative study of the 2013 typhoon Haiyan overwash sediments from a coastal cave and beach system at Salcedo, Eastern Samar, central Philippines

Typhoon Haiyan crossed the central Philippines on 8 November 2013 and generated storm surge up to 7 m with runup reaching 12 m which deposited overwash sediments inland in many different locations and environments. Collectively, these overwash sediments serve as key modern analogs to compare with geological records of storm events in the region. To date, comparatively few studies have been conducted on sandy storm deposits in carbonate coasts with none to date on storm sediments in coastal caves. Here, we report the grain size and microfossil assemblages of the Typhoon Haiyan overwash sediments from a coastal cave and carbonate beach system in Eastern Samar, central Philippines and infer the source of the Haiyan overwash sediments. We show that overwash sediments inside and immediately outside the cave (beach system) are similar but they can be discriminated from the underlying pre-Haiyan soil through field evidence, grain size, organic matter, and microfossil content. To investigate the source of both the cave and non-cave overwash sediments and in the absence of pre-storm beach sediment samples, we collected post-Haiyan beach sediments in February 2018 when the beach has indicated recovery to its pre-storm condition. We assume that these post-Haiyan beach sediments are representative of pre-storm sediments. The underlying pre-Haiyan soil comprises poorly-sorted, coarse to very coarse sands with higher organic matter content, and a lower microfossil concentration. Also, the pre-Haiyan soil contains foraminifera species similar to those identified in the Haiyan overwash sediments, but rarely containing subtidal foraminifera species. In comparison, the Haiyan overwash sediments share similar attributes with the post-Haiyan coastal sediments, consisting of moderately-sorted gravelly sands predominantly carbonate grains with low organic matter content. The Typhoon Haiyan overwash sediments contain foraminifera species dominated by Amphistegina radiata, Baculogypsina sphaerulata, Calcarina gaudichaudii, Calcarina splengeri suggesting an intertidal environment. Although, lower abundances of benthic species Peneroplis planatus and Quinqueloculina parkeri imply contributions from the subtidal environment. Notably, the Haiyan overwash sediments dominantly contain intertidal foraminifera species with abraded tests similar to foraminifera found in the post-Haiyan beach sediments. The similarity of foraminiferal assemblage and taphonomic condition strongly indicates that the overwash sediments found on the coastal cave were most likely sourced from the beach and reef flat. Our results show overwash sediments in coastal caves are indistinct from those in the nearby beach system indicating the potential of coastal caves to harbor well preserved archives of paleo storm deposits.

Isotopic evidence revealing spatial heterogeneity for source and composition of sedimentary organic matters in Taihu Lake, China

Abstract Tracing the formation processes of sedimentary organic matter (SOM) pools is crucial for understanding the carbon cycling of lake ecosystems, yet the source and composition of SOM, especially their spatial heterogeneity, in large and shallow lakes are still far from clear. In this study, SOM and its potential organic matter (OM) sources, including terrestrial particulate organic matter (POM), algae and aquatic macrophytes, were systematically investigated in Taihu Lake. We highlight the application of the end-member mixing model (EMM) based on Monte Carlo simulations of δ13C and δ15N ratios to more precisely depict the spatial heterogeneity for source and composition of SOM in such a large and shallow lake. The isotopically distinct signatures of SOM well displayed its sources obviously corresponded to the observed ecotypes of algae-type lakeshores, macrophyte-type lakeshore and groove in reed-belt. The results of EMM presented the higher proportion of terrestrial POM (46.8%–55.0%) than algae source (13.8%–23.4%) and macrophytes sources (20.0%–30.0%) in sediments from estuary and open water regions. The relative contribution proportions from three potential OM sources statistically correlated with relative contents of clay, silt and sand in sediments. The hydrodynamic force affected the grain size of sediments and drove the gradient distribution of SOM source contributions. These isotopic evidences revealed that aquatic macrophytes, algae bloom, inflow/outflow rivers and hydrodynamic changes could cause the spatial heterogeneity of SOM source and composition in large and shallow eutrophic lakes.

Age and sedimentary characteristics of beach sediments from Yongle Atoll, South China Sea: Implications for sediments supply in a coral reef system

Low-lying reef islands constructed from unconsolidated sediments are of growing interest due to concerns over the future stability of island landforms in response to climatic change and sea-level rise. Sediment characteristics, combined with the constituents and physical processes, are fundamental to understand the links between sediment production and their supply to an island’s beach reservoir. The grain size, constituents, and 230Th age of beach sediments from five islands at Yongle Atoll in the South China Sea were analyzed. Data reveal that coral grains are the dominant constituents of the beach sediments, followed by mollusks, coralline algae, foraminifera, Halimeda, and bryozoans. The mean grain sizes of the beach sediment were within a range of 226–4215 μm, and the coarsest sands were located near the passages in the atoll rim. Transportation by tropical cyclone–generated waves and winnowing by tides are potentially the main factors that influenced the grain-size characteristics. Calibrated 230Th age dates for bulk sand samples date the beach sediment between 424 yr BP and 5953 yr BP. Dating of coral sand samples from the beach sediment provides ages of 686–5780 yr BP; the coral sands from a vertical section (1.2 m depth) located on the beach at Jinqing Island were dated at 1154–3824 yr BP. The age reversal on the vertical section, with similar ages of beach sediment on any single island and different age ranges on different islands in an atoll, indicates that the coral sediment supply processes occurred within a relatively close time period and that different islands had different sediment supply rates. The temporal link between the coral-dominated sediment production and the beach reservoir provides an important insight into understanding the sediments supply mechanism of atoll islands in the northwestern Pacific Ocean.

Geostatistical Integration of Field Measurements and Multi-Sensor Remote Sensing Images for Spatial Prediction of Grain Size of Intertidal Surface Sediments

Park, N.-W., 2019. Geostatistical integration of field measurements and multi-sensor remote sensing images for spatial prediction of grain size of intertidal surface sediments. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 190-196. Coconut Creek (Florida), ISSN 0749-0208.The objective of this paper is to demonstrate the potential benefit of using high-resolution optical and SAR images for the geostatistical mapping of grain size of intertidal surface sediments. The grain size values from field measurements are integrated with reflectance and backscattering coefficients from multi-sensor images via regression kriging. The trends of grain size variations are estimated using support vector regression (SVR) modeling to account for a nonlinear relationship, and rank transformation is applied to original input variables to highlight the relative differences in input values from multi-sensor images. Unlike the conventional regression-based mapping approach, the residual component that cannot be explained by the multi-sensor remote sensing images is considered and predicted via kriging. The final grain size values are then obtained by adding these two components. From a case study on the Baramarae tidal flats in Korea with KOMPSAT-2 and COSMO-SkyMed images, the integration of multi-sensor images with field measurements via SVR and rank transformation could explain 58 % of grain size variance, leading to a significant improvement in predictive performance (approximately 29 %) over ordinary kriging based on field measurements only. Furthermore, using reflectance and scattering information from multi-sensor images generated the grain size distribution with more detailed variations in the study area. Therefore, the synergistic use of multi-sensor images within an advanced geostatistical integration framework is expected to be very effective for the reliable mapping of the grain size of intertidal surface sediments when only a limited number of field measurements are available.

Sandification vs. muddification of tidal flats by benthic organisms: A flume study

Bioturbating benthic organisms have typically been characterised by how they modify the vertical sediment erosion thresholds. By means of several annular flume experiments, we aimed to understand how benthic organisms may affect grain-size sediment properties over time, and how this depends on the sediment type and the sediment loading of the water column. We compared the effect of two bioturbating macroinvertebrate species: a local dominant species, the cockle Cerastoderma edule and a spreading non-indigeneous species, the clam Ruditapes philippinarum. Our results indicate that the effect of benthic organisms on sediment dynamics is strongly dependent on both the prevailing environmental conditions and the benthic species present. If sediment is sandy, the benthos can gradually enhance the silt content of the sediment by mixing in part of the daily tidal sediment deposition. In contrast, if sediment is muddy, benthos can gradually decrease the silt content of the sediment by specifically suspending the fine fraction. Moreover, we observed that the native cockles had a stronger impact than invasive clams. Therefore, bioturbating benthos can have an important effect in determining the local sediment properties, with the outcome depending both on the species in question and the environmental conditions the bioturbator lives in. Our findings show that sediment bioturbation may have strong implications for tidal flat stability undergoing major changes from natural or anthropogenic sources.

Assessment of liquefaction susceptibility in Quaternary deposits: A case study from Jhapa Bazar area, eastern Nepal

Liquefaction is generally experienced in unconsolidated fine- grained sediments during the large earthquakes. In Nepal, the southern part of the country comprises Quaternary deposits called as Indo-Gangetic deposit. Sand and silts are dominant in this zone, where groundwater level is also relatively high. In eastern Nepal, several places have experienced ground fissures, sand boiling, and liquefaction during the large earthquakes in the past history. There are several factors including soil properties, groundwater level, grain size of sediments and ground acceleration that contribute to ground liquefaction. The eastern Nepal faced a devastating earthquake in 1934 (magnitude of 8.4), Udaypur earthquake in 1988 (magnitude of 6.6) and Sikkim-Nepal earthquake in 2011 (magnitude of 6.8) and there is still possibility of similar large earthquakes in future. Liquefaction was reported in many places during Nepal-Bihar earthquake that indicates possibility of liquefaction during similar earthquakes. Liquefaction potential values are calculated from sediment grain size, subsurface geology, groundwater level and standard penetration test (SPT)-N values. The epicenter, magnitude, and other parameters of Nepal-Bihar earthquake have been used to calculate the liquefaction potential. A liquefaction susceptibility map has been prepared in the study area that comprises low, medium, and high liquefaction potential zones. About 20% of the study area including Jhapa Bazar and its surrounding area seems highly susceptible to liquefaction.

India National Gas Hydrate Program Expedition 02 Summary of Scientific Results: Gas hydrate systems along the eastern continental margin of India

Abstract The primary objectives of the India National Gas Hydrate Program Expedition 02 (NGHP-02) were to obtain new data on the occurrence of gas hydrate systems and to advance the understanding of the controls on the formation of gas hydrate accumulations in the offshore of India. In accordance with the ultimate overall goal of the NGHP effort to assess the energy resource potential of marine gas hydrates in India, particular focus was placed on the exploration and evaluation of gas hydrate occurrences at high saturations in sand-rich systems. NGHP-02 operations were conducted from 3-March-2015 to 28-July-2015 off the eastern coast of India and included logging while drilling (LWD) operations at 25 locations, and coring and wireline logging operations at 10 locations, in the Krishna-Godavari and Mahanadi Basins. The formation of highly concentrated gas hydrate accumulations, which are more suitable for energy extraction, requires the presence of relatively coarse-grained sediments with porosity needed to support the migration and accumulation of gas, and the nucleation of gas hydrate. The results of downhole logging, coring and formation pressure testing operations during NGHP-02 have confirmed the presence of extensive sand-rich depositional systems throughout the deepwater portions of the Krishna-Godavari and Mahanadi Basins. Two areas of the Krishna-Godavari Basin, referred to as Areas B and C, contain substantial gas hydrate accumulations in sand-rich systems and therefore represent ideal candidate sites for future gas hydrate production testing. This summary and technical report includes a comprehensive synthesis of the geologic, geophysical, geochemical, and physical property data acquired during NGHP-02 as it relates to the controls on gas hydrate occurrence, particularly with regards to sand-hosted accumulations. In the Mahanadi Basin, despite the confirmation of extensive reservoir capacity, gas supply at the NGHP-02 sites was insufficient to charge the reservoirs with gas hydrates. In the Krishna-Godavari Basin, extensive reservoir systems were confirmed with sediment grain-sizes ranging from coarse-silts to gravels. These reservoirs range from fully- to partially-filled with gas hydrate. The gas is determined to be from only microbial sources, and in part migrated into the reservoirs from deeper systems. The controls on gas hydrate occurrence are complex and varied; and include substantial reservoir heterogeneity and sufficient permeability throughout the reservoirs and seals that allowed pervasive fluid flow into and through the hydrate-bearing systems. These discoveries are the most significant confirmation of the exploration approach that focuses on direct detection of hydrate reservoirs supported by comprehensive petroleum systems analyses.

Distribution of grain size and organic elemental composition of the surficial sediments in Lingding Bay in the Pearl River Delta, China: A record of recent human activity

The Pearl River Delta (PRD) in China is severely affected by intensive human activities. In this study, we used surficial sediments collected in its Lingding Bay (LDB) in December 2016 to analyse the grain size and organic carbon composition and to identify the recent human impact recorded in the sediments. We examined the temporal variations in the spatial distribution of the grain size and organic elemental geochemistry of the surficial sediments by comparison with previous studies. Our study shows that in 2016, there were several patches of coarse-grained sediments, which were not consistent with the hydrodynamic conditions in LDB. Compared with the organic carbon composition in 2005–2006, the δ13C values in 2016 were more negative and the contribution of terrigenous organic matter (TOM) to the surficial sediments was significantly greater. There were also several patches of high TOM values in the outer LDB. The overall coarser sediments and lighter δ13C of organic carbon were in contrast to the decline in the riverine sediment supply and the increased eutrophication in recent decades. Furthermore, the anomalous patches of coarse-grained sediments and terrestrially sourced organic carbon were mainly distributed in the navigation channels and on their adjacent shoals, reflecting channel dredging, dumping, and sand mining activities. Therefore, the origins and spatial distributions of the grain size and organic carbon composition of the surficial sediments in LDB in 2016 were not controlled by hydrodynamic conditions and land–sea interactions, but overwhelmingly by human activities. We suggest that LDB of PRD exemplifies an anthropogenically controlled bay.