Shoreline Deposits Research Articles

Geochemical characteristics of shoreline sediments from the Bay of Bengal, Bangladesh: Implications for provenance and source‐rock weathering

The detrital mode and geochemical composition of sediments from a coastal section of the Bay of Bengal, Bangladesh, were examined to identify sediment distribution, maturity, provenance and source‐area weathering. The sediments are quartz‐rich with little feldspar and few lithic fragments (Q78F10L12), indicating derivation from a quartzose recycled orogen. The sediments exhibit high SiO2 (88–94 wt%) and low Al2O3 (4–5 wt%) contents. SiO2 shows a marked linear trend and strong negative correlation with Al2O3 (r = −0.95), consistent with the high quartz content. The upper continental crust (UCC) normalization patterns for the sediments show marked depletion in Na2O, CaO, MgO, Sr, Sc and Fe–V, but slightly increased Th and SiO2, indicating a felsic UCC source. The sediments have low to moderate compositional maturity and are classified as sublitharenite. The Al2O3/TiO2 ratio (15–38) suggests that the sediments were derived from intermediate to felsic igneous rocks. Rare‐earth element profiles, discrimination diagrams and various elemental ratios are all consistent with the derivation of the sediment from a felsic igneous source area. The values of the chemical index of alteration (~65–69), chemical index of weathering (~75–84) and plagioclase index of alteration (~70–81) indicate that the source rocks underwent moderate chemical weathering. Comparison with potential Himalayan sediment sources and rocks support derivation of the investigated shoreline sediments from felsic quartzose recycled detritus of that area.

Sedimentology and seismic geomorphology of Paleocene coastal peatlands from the offshore Gippsland Basin, SE Australia

The Eocene–Miocene succession of the onshore Gippsland Basin is host to some of the world's thickest coal seams. Here, we document well-preserved Paleocene coals from the offshore Gippsland Basin. The Paleocene sediments in the basin consist of three stacked coastal units, known informally here as T8, T7 and T6, in order of decreasing age. Each unit consists of, from seaward to landward, a sediment starved marine facies, a sand-rich, wave-dominated shoreface facies, lower coastal plain tidal and peatland facies, and upper coastal plain sandy, fluvial facies. Seismic amplitude extractions reveal unprecedented details of the peatland palaeogeography. The early Paleocene T8 palaeogeography reveals a wave-dominated, sandy strandplain seaward of a >1000 km2 lower coastal plain peatland. The peats extend inland to ~35 km from the paleocoastline and are dissected by a series of meandering and anastomosing channel systems. This geometry is remarkably similar to the modern tropical peatlands of the Rajang Delta in Sarawak, where forested domed peats have formed over tidal and shoreline sediments. The Paleocene coals of the Gippsland Basin have likely formed in a very similar stratigraphic setting and provide a large-scale ancient example of lower coastal plain coal deposition.

Effects of magnetite on phosphorus storage and carbon cycling in Lake Michigan shoreline sediments

Lake Michigan, one of the Laurentian Great Lakes, hosts the world's largest freshwater sand dune system and is ecologically and economically important. Phosphorus (P) plays a key role in the lake biota, while industrial P runoff, pollution controls, and invasive species add to the complexity of P dynamics in the shoreline ecosystem. Rich in iron oxide minerals, the Lake Michigan shoreline has been little studied with respect to P bioavailability and cycling. In this study, we analyzed magnetite concentrations in samples collected from 19 beach and sand dune sites located along the eastern shore of Lake Michigan, and we examined the mineral effects on P bioavailability through adsorption experiments, sediment fractionation and extraction, and microcosm incubations. We find that magnetite is widely distributed in the sand dune ecosystem and its content can reach very high levels (>30% dry weight) in natural beach sediments. P has the strongest adsorption affinity to magnetite when compared to prominent sediment minerals calcite and quartz, and the native magnetite holds up to 10 and 28 times more moderately and strongly bound P, respectively, than the bulk sediments. Microcosm incubations with native sediments showed that the addition of P significantly increased microbial decomposition of labile organic carbon, whereas the added synthetic magnetite did not significantly reduce the P bioavailability or decrease the carbon degradation. This research highlights the multiple effects of magnetite on P storage, bioavailability, and labile organic carbon degradation in the shoreline sand dunes, which may provide new insights into understanding nutrient and carbon cycling in the Great Lakes ecosystem.

Characteristics and distribution of microplastics in shoreline sediments of the Yangtze River, main tributaries and lakes in China-From upper reaches to the estuary.

Microplastics (MPs) pervade the environment and increasingly threaten both natural ecosystems and human health. In this study, we investigated MP particle concentrations in sediment samples collected from 54 sites along the banks of the YangtzeRiver and its major tributaries and on lakeshores. The main polymer types found in the samples were polypropylene (PP), polystyrene (PS) and polyethylene (PE). MP particle abundance in the various types of locations was 35-51,968 particles/kg dry weight (d.w.) on the banks of the main river, 52-1463 particles/kg (d.w.) on the banks of tributaries and 2574-23,685 particles/kg (d.w.) on lakeshores. Correlation between MP abundance and mean annual runoff of each upstream tributary was significant, which suggests that increased runoff brings more microplastic waste to streambank sediments. The most common shape of MP particles in all upstream samples was flake, and in downstream samples it was foam. Small microplastic particles (< 0.50mm) were predominant at all sites in this study, and the minimum particle size in samples from the Yangtze river banks was 0.065mm. Average abundance of MP particles on the shores of the source lake was 9069 particles/kg around the inlet but only 866 particles/kg around the outlet; the difference was due to interception associated with sedimentation and precipitation in the lake. Our study represents the large-scale study of MPs contamination in sediment along the Yangtze River and provides important data regarding the accumulation and distribution of MPs in shoreline sediments of the upper, middle and lower reaches of the Yangtze River, main tributaries and lakes in China.

Shoreline evolution from the Late Cretaceous to the Miocene: A record of eustasy, tectonics and palaeoceanography in the Gippsland Basin

AbstractWell‐developed clastic shoreline systems have been deposited in the Gippsland Basin over a 70 Ma period, from the latest Cretaceous to the present day. Twenty‐three stacked coastal units have been mapped and described in the Traralgon and Balook formations of the Latrobe and Seaspray groups. These units are made up of prograding and backstepping shoreface deposits, which, in plan view, display well‐developed strandline geometries at the terrestrial–marine interface. Shoreface deposits are interpreted to include prograding beach, barrier island and transgressive beach deposits. The lower coastal plain is characterised by persistent deposition of coals despite changes in shoreface type and significant palaeoclimate fluctuations. These coastal deposits display approximately 123 km of transgression from the Late Cretaceous shoreline at the base of the study interval to the mid Miocene Yallourn Formation near the top. The Late Cretaceous and Palaeocene shoreline deposits individually prograde and are separated by flooding surfaces reflecting eustatic changes. Overall they display long‐term backstepping behaviour (retrogradation) as a result of basin subsidence. Though shorelines of the Eocene–Miocene are distinctly transgressional, probably reflecting basin subsidence, in the mid‐Miocene they become individually and collectively progradational. A series of unconformities in the Oligocene, coupled with Miocene progradation, likely reflects a combination of a compressional tectonic regime and glacioeustatic fluctuations. Despite major changes in the tectonics and palaeoclimate, basin subsidence appears to be the dominant driver for changes in shoreline location.

Exceptional preservation of a barred shoreline under forced‐regressive conditions (Lower Cretaceous, Neuquén Basin, Argentina)

AbstractForced‐regressive conditions have been widely described by sequence‐stratigraphic conceptual models, and the resulting deposits have been widely documented in sequences and parasequences. However, how forced‐regressive conditions might impact on the short‐term to mid‐term evolution and the high‐resolution stratigraphic record (102 to 105 kyr) of barred shoreline environments represents an unexplored issue. This contribution presents a bedset characterization of Lower Cretaceous, barred shoreline deposits accumulated after a relative sea‐level fall. Parasequence PS400 of the Pilmatué Member in the Neuquén Basin (Argentina) comprises several bedsets, most of them bounded by transgressive surfaces. However, one of them, the bedset BS400.5, is bounded below by a high‐relief surface of truncation, here interpreted as an erosional regressive surface. This surface indicates incision of the underlying deposits and the onset of forced‐regressive conditions at intra–parasequence scale. The internal architecture of the studied bedset exhibits seaward‐dipping clinoforms that bound clinothems within the upper‐shoreface deposits. These clinoforms were interpreted as the result of seaward‐shifting events during the shoreline progradation. A sequence‐stratigraphic conceptual model is proposed for the high‐frequency evolution of a barred shoreline under forced‐regressive conditions. The model explains how the intra–bedset evolution under low and stillstand sea‐level conditions and cross‐shore imbalances in the sediment budget controlled the exceptional preservation of bar and rip‐channel deposits.

Criteria for the recognition of clastic halite: The modern Dead Sea shoreline

AbstractSedimentological studies of modern halites have focused on shallow water to subaerially‐exposed saline pans, where in‐place crystal growth, dissolution and cementation textures dominate. Clastic halite transported and deposited by waves and unidirectional currents as bedload is poorly known. This paper: (i) describes and interprets the diagnostic sedimentary features of clastic halite from a modern outcrop exposed along the north‐western coastline of the Dead Sea; and (ii) provides criteria for recognition of clastic halite in the rock record. The 2 m thick halite unit at Nahal Og was deposited within the last four decades at water depths &lt;30 m as Dead Sea levels fell ca 30 m. Clastic halites consist of frameworks of sorted crystals with point contacts and no preferred growth fabrics. Halite cumulates, deposited as suspended load, precipitated in the water column and sank to the brine bottom. The excellent sorting and purity of halite crystal layers are unique to cumulates. Small‐scale ripple cross‐stratified thin beds and intraclast conglomerates were deposited from bedload. Halite bedload deposits (composed of halite flat pebbles, ooids, rafts, single clear crystals, cumulate crystals, mud intraclasts and rounded mudballs, foraminifera, gypsum) reflect wave transport and deposition via oscillatory flow above wave base, or by unidirectional flow in the breaker and surf zones. In addition, waves on the Dead Sea coast generate longshore currents. Thin beds produced by wave‐influenced oscillatory transport of halite are symmetrical in cross‐section. Less common cross‐stratified units with asymmetrical cross‐sections indicate unidirectional currents. Clastic halite, especially as a bedload deposit, has rarely been identified in ancient evaporites. Shoreline deposits from ancient halites, however, must contain wave‐reworked and current‐reworked layers and should be common in saline giants, given their enormous size and potential for generating waves and currents. Documentation of modern clastic halite may lead to a better understanding of ancient hypersaline environments on Earth.

Trace elements in the shoreline and seabed sediments of the southern Caspian Sea: investigation of contamination level, distribution, ecological and human health risks, and elemental partition coefficient.

This study assesses the occurrence of trace elements (TEs) in sediments of the southern Caspian Sea. A total of 16 shoreline sediment samples and 15 seabed sediment samples along five coastal transects were studied. The mean concentration of TEs follows the order of Zn > V > Cr > Ni > Cu > Pb > Co > As > Sb > Mo > Cd. The TEs had an uneven, heterogeneous distribution within the shoreline and seabed sampling sites. This is due to that the study area comprises a large number of different pollution sources, also different sediment physicochemical characteristics. Levels of individual TEs within the seabed sediment transects were higher where their shoreline sites had higher concentrations, reflecting that the coastal sites play an important role in diffusing the contaminants towards the sea. The main anthropogenic source of TEs in this highly populated region, especially in the western part, is likely a large number of discharge points of greywater entering the sea. In addition, dominant fishing industry, tourism, intense agriculture, and textile and paper industry, as well as several other commercial activities, contribute significantly to the overall loading of TEs. Based on the statistical analyses, the organic matter and mud fraction had a strong explanatory value for the spatial variation of Cu, while oxyhydroxides of Fe and Mn had good explanatory factors to govern the spatial variation of other TEs. Pb and Zn had a relatively high partition coefficient (Kd), reflecting the affinity of these elements to be sorbed to the sediment phase. Cd and Sb had lower Kd, tending to remain in the aqueous phase. Geochemical indices indicated high enrichment of Cd, Sb, Zn, and Pb at a number of sampling sites, reflecting potential local sources of contamination. The Sisangan recreational area was identified as the most contaminated site. From a public health perspective, the non-carcinogenic risk of TEs was significant only at this site. The carcinogenic risks of Pb(II) and As(III) in adults, and Pb(II), Cd(II), and As(III) in children, were tolerable.

Microplastic pollution of Calicut beach - Contributing factors and possible impacts

Annual monitoring was carried out in the shoreline sediments of the Calicut beach, from 2016 to 2019 to understand the distribution and abundance of microplastics and its environmental implications. Further, the impact of the severe fluvial floods of Kerala during the August months of 2018 and 2019, on the microplastic pollution of the Calicut beach was also determined. Microplastic concentrations ranged between 80.56 items/kg of dry sand to 467.13 items/kg of dry sand during the sampling period. Polyethylene type was consistently higher in all the samples. There was a surge in microplastics concentration during both the floods with a higher proportion of low-retention-period microplastics. Among the different oceanographic parameters, it was found that significant wave height and surface wind speed are positively correlated to the number of the microplastics in Calicut beach.

Molluscan aminostratigraphy of the US Mid-Atlantic Quaternary coastal system: Implications for onshore-offshore correlation, paleochannel and barrier island evolution, and local late Quaternary sea-level history

The Quaternary record of the US Mid-Atlantic coastal system includes onshore emergent late Pleistocene shoreline deposits, offshore inner shelf and barrier island units, and paleovalleys formed during multiple glacial stage sea-level lowstands. The geochronology of this coastal system is based on uranium series, radiocarbon, amino acid racemization (AAR), and optically stimulated luminescence (OSL) methods. We report over 600 mollusk AAR results from 93 sites between northeastern North Carolina and the central New Jersey shelf, representing samples from both onshore cores or outcrops, sub-barrier and offshore cores, and transported shells from barrier island beaches. AAR age estimates are constrained by paired 14C analyses on specific shells and associated U-series coral ages from onshore sites. AAR data from offshore cores are interpreted in the context of detailed seismic stratigraphy. The distribution of Pleistocene-age shells on the island beaches is linked to the distribution of inner shelf or sub-barrier source units. Age mixing over a range of time-scales (~1 ka to ~100 ka) is identified by AAR results from onshore, beach, and shelf collections, often contributing insights into the processes forming individual barrier islands. The regional aminostratigraphic framework identifies a widespread late Pleistocene (Marine Isotope Stage 5) aminozone, with isolated records of middle and early Pleistocene deposition. AAR results provide age estimates for the timing of formation of the three major paleochannels that underlie the Delmarva Peninsula: Persimmon Point paleochannel ≥800 ka; Exmore paleochannel ~400–500 ka (MIS 12); and Eastville paleochannel > 125 ka (MIS 6). The results demonstrate the value of synthesizing abundant AAR chronologic data across various coastal environments, integrating multiple distinct geologic studies. The ages and elevations of the Quaternary units are important for current hypotheses about relative sea-level history and crustal dynamics in the region, which was likely influenced by the Laurentide ice sheet, the margin just ~400 km to the north.

A Shoreline Response Program (SRP) Decision Support Tool based on the Geographic Variability in Attenuation and Weathering of Stranded Oil.

ABSTRACT #1141234 The coastal waters of Canada embrace a wide range of physical environments and ecosystems from the warm, sediment-rich waters of the Bay of Fundy to the nutrient-limited cold waters of the high Arctic. This range of biophysical characteristics impacts natural attenuation and weathering processes for oil stranded on shorelines. This study was conducted to: 1) identify and quantify the primary regional parameters that control shoreline oil translocation (removal) processes and pathways and 2) define the effectiveness and environmental consequences of current and potential oiled shoreline treatment strategies and tactics. A specific knowledge gap, here and elsewhere in the world, has been in understanding how the distribution and character of fine-grained sediments affect stranded oil attenuation. Fine-grained sediments (&amp;lt;1mm) can play a critical role in natural or induced (that is, shoreline treatment) oil dispersal. Shoreline sediment samples were collected and analyzed from representative locations on Arctic, Atlantic, and Pacific Ocean beaches to provide a broad geographic characterization of mineral fines at the regional level. This knowledge is the basis for an “Oiled Shoreline Response Program (SRP) Decision Support Tool” to aid spill scientists, students, environmental resource managers, spill responders and the public in understanding the response methods and the ramifications and consequences of their shoreline treatment options without the need to digest technical papers, large reports, or data bases. This MPRI SRP Decision Support Tool is intended to be a dynamic, interactive, multi-layered, geographically and seasonally-based model for shoreline oil spill response decision analyses. A goal of this interactive model is to move away from the traditional static format of learning from explanations in text reports and publications to an interactive tool that encourages its users to explore and fully understand the significance of the different environmental factors outlined in publications and data bases. Recent advances in web technology make this possible. The development of user interface platforms such as React, libraries such as D3, and notebook forms like Observable has created a palette of technologies that together make web application patterns such as Documodels a much more streamlined development process. The power of this medium is to convey a complex subject and to enable a user to grasp keen insights and so understand the consequences of intervention decisions.

Evolution of a complex early Permian coarse-grained shoreline along a rift basin margin

ABSTRACT Tectonic activity in extensional basins has a profound control on accommodation and sediment supply through the interplay between footwall uplift and hanging-wall subsidence, and thus largely influences the three-dimensional architecture of syn-rift sequences. This is emphasized in areas close to major rift-border faults, where steep coastal reliefs and fluvial gradients produce compound facies zonation and stratigraphic styles with strong lateral variability. The lower Permian High Cliff Sandstone was deposited in an array of shallow marine environments along the margin of the northern Perth Basin during a protracted late Paleozoic rifting episode in Western Australian basins. The formation is composed of fluvio-deltaic and nearshore strata sharply overlying a thick succession of offshore mudstone that was deposited during a phase of tectonic quiescence. This basal contact likely reflects submarine erosion and is, therefore, interpreted as a regressive surface of marine erosion generated in response to forced regression. The facies arrangement consisting of interbedded sandstone, conglomerate, and heterolithic facies chiefly records the evolution of a low- to high-gradient paleoshoreline punctuated by coastal streams, steep sea cliffs, and back-barrier lagoons. Extraformational outsized clasts were probably emplaced by the erosion of exhumed basement and older sedimentary rocks through fluvial incision, wave sapping, or landsliding. The along-strike variability between low- and high-gradient shoreline deposits indicates a dynamic depositional setting with a complex tectonic influence. The basal regressive surface of marine erosion is attributed to footwall uplift during the early reactivation stage of basin-bounding normal faults and, therefore, records the initiation of a new syn-rift phase in the northern Perth Basin.

Prevalence and persistence of microcystin in shoreline lake sediments and porewater, and associated potential for human health risk

Midlatitude waterbodies are experiencing increased cyanobacteria blooms that necessitate health advisories to protect waterbody users. Although surface waters may contain cyanotoxins such as microcystin (MC), at concentrations that pose potential public health risks, little is known about MC contamination of shoreline sediments. Based on growing evidence that lake and reservoir sediments can accumulate MCs, we hypothesized that shoreline sediments (i.e., recreational beaches) may accumulate MCs and thereby pose a potential health risk to recreational users even if people stay out of contaminated water. We sampled nearshore surface water, shoreline sediment, and porewater from seven Washington State, USA, lakes/reservoirs recreational beaches to determine MC presence/absence during or immediately following cyanobacteria blooms. We found MCs in shoreline sediments at all waterbodies using ELISA and LC-MS/MS. MC concentrations in shoreline sediments and porewaters persisted for 20 days following dissipation of cyanobacteria blooms when MC concentrations were near analytical reporting limits in corresponding surface waters. A human health risk assessment based on potential MC exposure through incidental ingestion of porewaters and sediments found, even when very high MC concentrations occur in surface waters (i.e., >11,000 μg/L), estimated ingestion doses are below MC World Health Organization tolerable daily intake and U.S. Environmental Protection Agency’s risk reference dose. While our findings suggest MCs in Washington State recreational beaches in 2018 did not present a significant human health risk, future blooms with higher MC concentrations could pose human health risks via the shoreline sediment/porewater exposure pathway.

Sedimentology and stratigraphy of a modern halite sequence formed under Dead Sea level fall

AbstractHalite sequences in the geological record accumulated in deep hypersaline basins. However, such halite sequences are interpreted based on modern analogues of halite deposition in shallow hypersaline environments. Recently, halite deposition in the deep, hypersaline Dead Sea has been studied together with its coeval environmental and limnogeological forcing. This is the closest modern analogue for deep environments. Therefore, stratigraphy, sedimentology and petrography of a well‐dated, high‐resolution modern Dead Sea halite sequence are explored. The sequence was deposited during a ca 30 m lake‐level decline since the onset of modern halite deposition in 1980, and was compared with sub‐annual lake levels, precipitation and flood records. The sedimentology of the sequence documents the trend of shallowing water depth, including individual floods. The sequence base is composed of alternating bottom growth‐cumulate halite annual couplets, typical of deep hypolimnetic water deposition. Up‐sequence, the annual couplets disappear and towards its top are composed of cumulate layers with dissolution features, typical of shallow epilimnetic water deposition. Halite deposition rate is reduced by 60% at the shallow lakefloor compared with the deep lakefloor, mainly due to the summer undersaturation that leads to depocentre ‘halite focusing'. The top of the sequence contains shoreline deposits, halolites (halite ooids) and polygonal surface cracks, indicating subaerial exposure. This study shows petrographic indicators for summer thermal dissolution (partially dissolved crystals), which are distinct from dissolution features by winter floods that generate a regional truncation surface. Spatial variations in halite thickness and facies, indicating much thinner and spatially limited halite units compared to modelled halite units based on mass balance considerations were also observed. These observations provide criteria for: (i) recognizing water depths and shallowing lake‐level trends from halite sequences throughout the geological record; and (ii) interpreting palaeolimnology, water column structure and the relations between stratigraphic horizons and corresponding shorelines.

A novel method to evaluate chemical concentrations in muddy and sandy coastal regions before and after oil exposures.

Oil spills can result in changes in chemical concentrations along coastlines. In prior work, these concentration changes were used to evaluate the date sediment was impacted by oil (i.e., oil exposure date). The objective of the current study was to build upon prior work by using the oil exposure date to compute oil spill chemical (OSC) concentrations in shoreline sediments before and after exposure. The new method was applied to OSC concentration measures collected during the Deepwater Horizon oil spill with an emphasis on evaluating before and after concentrations in muddy versus sandy regions. The procedure defined a grid that overlaid coastal areas with chemical concentration measurement locations. These grids were then aggregated into clusters to allow the assignment of chemical concentration measurements to a uniform coastal type. Performance of the method was illustrated for ten chemicals individually by cluster, and collectively for all chemicals and all clusters. Results show statistically significant differences between chemical concentrations before and after the calculated oil exposure dates (p<0.04 for each of the 10 chemicals within the identified clusters). When aggregating all chemical measures collectively across all clusters, chemical concentrations were lower before oil exposure in comparison to after (p<0.0001). Sandy coastlines exhibited lower chemical concentrations relative to muddy coastlines (p<0.0001). Overall, the method developed is a useful first step for establishing baseline chemical concentrations and for assessing the impacts of disasters on sediment quality within different coastline types. Results may be also useful for assessing added ecological and human health risks associated with oil spills.

Characteristics of microplastics in shoreline sediments from a tropical and urbanized beach (Da Nang, Vietnam)

Microplastics in shoreline sediments were investigated from Da Nang beach for the first time. Sediment samples at the two depth strata (0–5 cm and 5–10 cm) at eight sites along the entire coast were collected for identifying the characteristics of microplastics, including their concentration, size, shape, color, and nature. The synthetic fiber was the predominant type of microplastics, accounting for 99.2% of the total items. Blue (59.9%) and white (22.9%) were the most common colors of the fibers. Synthetic fibers showed a homogenous distribution at all sampling sites with a mean concentration of 9238 ± 2097 items kg−1 d.w. Meanwhile, the fibers tended to concentrate much more at the surface stratum than the deeper stratum. A large number of synthetic fibers (81.9%) were in the size range of 300–2600 μm, which might pose a threat to marine biota and human health.

When the River Began—The Formation of River Motala Ström and Human Presence in the Early Holocene, Sweden

In conjunction with the extensive archaeological projects conducted at the current outlet of Sweden’s second largest lake, Lake Vättern, macrofossil, pollen and diatom records have been studied from 14C-dated lake and river sediments from River Motala Ström in Motala and Lake Boren. These investigations have revealed sedimentary evidence of the Yoldia Sea regression, the Ancient Lake Vättern transgression, and the following stepwise river formation process. Around 9000 cal BC, two small kettlehole basins at Strandvägen and Kanaljorden became isolated from the Baltic basin. As the ice sheet retreated further north, the isostatic uplift isolated the Vättern basin from the Baltic basin. Due to the uneven isostatic uplift, the basin tilted toward the south, and the Ancient Lake Vättern transgression started in Motala. The threshold in Motala at 92.5 m a.s.l. was reached around 7200 cal BC, and River Motala Ström was formed. 14C-dated diatom records from Lake Boren, and shoreline deposits in Motala, confirm this event. The water level in Lake Vättern initially fell around 1.5 m, and around 5800 cal BC, a second erosional event cut down the threshold to modern day level. At this time, the Late Mesolithic settlements in Motala were established and expanded.

Microplastic particles in sediments and waters, south of Caspian Sea: Frequency, distribution, characteristics, and chemical composition

This study assesses the occurrence of microplastics (MPs) in coastal and sea surface sediments, as well as water samples, collected from the coastal region of the southern Caspian Sea, Mazandaran province, Iran. A total of 32 sediment and 10 water samples were studied. The mean concentration of MPs was 15 units kg−1 in the sediments and 710 units m−3 in the coastal water. Fibers constituted by far the dominant MPs in both media, accounting for 97% of the MPs in both sediment and water samples. The MPs were mainly black in color. The dominant size of MP particles in sediment samples was between 250 and 500 μm, while the fraction >1000 μm dominated in the water samples. Polyethylene terephthalate (PET), polystyrene (PS), and nylon (NYL) were the main polymers and/or copolymers composing MPs in both sediment and water samples. The MP particles had a relatively smooth surface morphology, although signs of weathering were observed. The number of MP particles in sediment and water samples showed a general decrease from west to east in the study area. This may be reflecting the spreading of MP loading from the outlets of Sefidrud, Tonekabon, Chalus, the major rivers entering the Caspian Sea just west of the study area, and the overall decrease in the spatial distribution of touristic and fishery activity. The main sources of MP particles could be local emissions from a large number of domestic wastewater effluents and urban surface runoff due to high population density, and industrial and fishing activities in this region. This study indicated that MP particles, based on their characteristics and chemical composition, are circulated between coastal waters, and shore and sea surface sediments of the Caspian Sea, leading to their uneven distribution in the different depths. To the best of our knowledge, this is the first work studying the distribution of MP particles in sea surface sediments and also the most comprehensive on MPs in shoreline sediments and coastal waters in the southern Caspian Sea.

Distribution of microplastic and small macroplastic particles across four fish species and sediment in an African lake

Pollution with microplastics has become an environmental concern worldwide. Yet, little information is available on the distribution of microplastics in lakes. Lake Ziway is one of the largest lakes in Ethiopia and is known for its fishing and drinking water supply. This study aims to examine the distribution of plastic particles, of all sizes (micro- and small macro-plastics) in four of the major fish species of the lake and in its shoreline sediment. The gastrointestinal tracts analysis showed that 35% of the sampled fishes ingested plastic particles. The median number of particles per fish was 4 (range 1–26). Benthic (Clarias gariepinus) and benthopelagic (Cyprinus carpio and Carassius carassius) fish species were found to contain a significantly higher number of plastic particles in comparison to the planktivorous fish species (Oreochromis niloticus). More fishes ingested plastic particles in the wet compared to the dry season. The maximum plastic size (40 mm fibre) was found in C. carpio. Estimated median mass of plastic particles in fish was 0.07 (0.0002–385.2) mg/kg_ww. Fish and sediment samples close to known potential sources of plastic particles had a higher plastic ingestion frequency (52% of the fish) and higher plastic concentration compared to the other parts of the lake. The median count and mass of plastic particles measured in sediment of the lake were 30,000 (400–124,000) particles/m3 and 764 (0.05–36,233) mg/kg_dw, respectively, the upper limits of which exceed known effect thresholds. Attenuated total reflection (ATR) - Fourier-transform infrared (FTIR) spectroscopy showed that polypropylene, polyethylene and alkyd-varnish were the dominant polymers in fishes and in sediment. The plastic particles size distributions were Log-linear and were identical for plastic particles found in fish and in sediment, suggesting strong benthic-pelagic coupling of plastic particles transfer.

A 50,000-year record of lake-level variations and overflow from Owens Lake, eastern California, USA

A continuous lake-level curve was constructed for Owens Lake, eastern California by integrating lake-core data and shoreline geomorphology with new wind-wave and sediment entrainment modeling of lake-core sedimentology. This effort enabled refinement of the overflow history and development of a better understanding of the effects of regional and global climate variability on lake levels of the paleo-Owens River system during the last 50,000 years. The elevations of stratigraphic sites, plus lake bottom and spillway positions were corrected for vertical tectonic deformation using a differential fault-block model to estimate the absolute hydrologic change of the watershed-lake system. New results include 14C dating of mollusk shells in shoreline deposits, plus post-IR-IRSL dating of a suite of five beach ridges and OSL dating of spillway alluvial and deltaic deposits in deep boreholes. Geotechnical data show the overflow area is an entrenched channel that had erodible sills composed of unconsolidated fluvial-deltaic and alluvial sediment at elevations of ∼1113–1165 m above mean sea level. Owens Lake spilled most of the time at or near minimum sill levels, controlled by a bedrock sill at ∼1113 m. Nine major transgressions at ∼40.0, 38.7, 23.3, 19.3, 15.6, 13.8, 12.8, 11.6, and 10.6 ka reached levels ∼10–45 m above the bedrock sill. Several major regressions at or below the bedrock sill from 36.9 to 28.5 ka, and at ∼17.8, 12.9, and 10.4–8.8 ka indicate little to no overflow during these times. The latest period of overflow occurred ∼10–20 m above the bedrock sill from ∼8.4 to 6.4 ka that was followed by closed basin conditions after ∼6.4 ka. Previous lake core age-depth models were revised by accounting for sediment compaction and using no reservoir correction for open basin conditions, thereby reducing discrepancies between Owens Lake shoreline and lake-core proxy records. The integrated analysis provides a continuous 50 ka lake-level record of hydroclimate variability along the south-central Sierra Nevada that is consistent with other shoreline and speleothem records in the southwestern U.S.