Coarse Sediment Research Articles

The Rupturing Phenomena in the Deltaic Deposits of Cape Rytyi on the Northwestern Shore of Lake Baikal

Abstract —We present materials of aerial photography of Cape Rytyi, a unique and most mysterious place on the northwestern shore of Lake Baikal. Photogrammetric survey was carried out using a DJI Phantom 4 Pro V2.0 UAV and provided an orthophoto and a digital terrain model of an 11.074 km2 area. When deciphering the images obtained in the Rita River deltaic sediments composing the cape, surface ruptures trending north and northeast at 30–150 m from the shore of Lake Baikal were discovered. The ruptures are a clearly localized zone 2.9 km in total length. The performed analysis showed that the structural features of the zone obey the general laws of the development of faults resulted from prevailing extension. It has been established that the formation of the ruptures was predetermined by tectonics and is a secondary effect of resonant oscillations from the M = 5.2 earthquake of 08.13.1962, the epicenter of which was located ~35 km southeast of Cape Rytyi, in the Morskoi fault zone. The seismic event initiated the formation of surface ruptures, which led to a gravitational subsidence of coarse deposits of the fan in the shore zone. It is concluded that the development of modern geomorphologic forms in the peripheral part of the Rita River fan on land is similar to the formation of an underwater topography in the region of the Selenga River delta. It occurs under the influence of seismogenic rupturing and following gravitational movements, which intensify in a water-saturated environment and are subsequently complicated by erosion processes.

Restoring morphodynamics downstream from Alpine dams: Development of a geomorphological version of the serial discontinuity concept

There is well-established evidence that dams disconnect upstream to downstream sediment flux in rivers and that this may have negative impact on downstream ecosystems. For this reason, the development of environmental flows now includes sediment supply and transport whether through reconnecting upstream supplied sediment to a river downstream of a dam, eco-morphogenic flows to rework the stream bed, or artificial sediment supply. However, especially in Alpine systems, there may be unregulated tributaries that are able to deliver gravel and coarser sediment naturally to compensate for the effects of dam-related sediment disconnection. To represent these effects we propose a geomorphic form of the serial discontinuity concept and apply it to two hydropower dam-impacted Alpine streams in the Swiss Pennine Alps. Conceptually, the relative position of a dam influences the degree of coarse sediment disconnection as well as the rate of coarse sediment recovery, especially as many Alpine valleys have strong down-valley gradients in tributary sediment delivery. In both case-studies, there was rapid recovery in likely coarse sediment delivery downstream of the dams. By following geomorphic response of the rivers to eco-morphogenic flow trials, proposed as a solution to perceived dam-driven coarse-sediment disconnection, we confirmed that both rivers are likely to have more than sufficient natural coarse sediment supply and unregulated floods. Natural coarse sediment supply is rarely considered in the management of Alpine streams impacted by hydropower but it needs to be evaluated through a geomorphological assessment, considering both the geomorphic context of the river reaches downstream of the dam and the geomorphic attributes of the basin in which the dam is found.

Modulating the lateral migration of a gravel bed channel using the coarse tail of the bed material distribution

SummaryMost stream channels around the world have been, to some extent, laterally constrained by non‐erodible banks constructed of concrete or large angular boulders (called riprap). These lateral constraints generally have a negative impact on aquatic ecosystems by reducing stream channel complexity, and limiting the natural disturbance processes that are critical for renewing the physical habitat. In this paper, we test a novel approach to limiting stream channel instability by exploiting the stabilizing effects of the coarsest grains in the bed material distribution, which we call geomorphic river engineering. This approach modulates the rate of bank erosion rather than halting it altogether. It also exploits the geomorphic feedback between bank erosion, channel width, and mean boundary shear stress during a flood event to limit the potential for vertical incision into the stream bed. The basic premise of the geomorphic river engineering approach is to place the coarse sediment on the floodplain adjacent to the channel margins, and rely on bank erosion by the river to recruit the sediment, allowing the river to remain the architect of its own configuration. Our results suggest that the recruitment of a modest volume of coarse sediment to a coarse, gravel bed stream during a flood could potentially dramatically reduce the amount of lateral migration that would otherwise occur, and that the degree of stabilization could be modified by changing the volume of coarse sediment per unit area placed on the floodplain. More generally, our results confirm the fundamental role that the coarse tail of the bed material distribution plays in dictating the channel dynamics of gravel bed streams with cohesionless banks, and indicate the potential for future river stabilization projects to focus on the engineering that can be done by rivers, rather than to them.

Spatial distribution and response of dunes to anthropogenic factors in the lower Yangtze River

Spatial distribution and morphological scales of dunes in the lower Yangtze River (YR) have not been investigated in detail because of the lack of large-scale high-resolution bathymetric data. However, they are critical for understanding bedload transport and flow resistance, thereby predicting river channel evolution. In this study, to determine the characteristics and spatial distribution of dunes, high-resolution bathymetry surveys were conducted in 2015–2016 in a 235-km channel of the lower YR using a multibeam echo sounder. Overall, dunes were found to be commonly developed, with bottom-bed velocity and bed shear stress ranging between 0.47 and 0.84 m·s−1, and 2.11–4.86, respectively. Laterally, the bathymetric data from 22 cross-sections showed that dunes pervasively covered over 63.6% (even reaching 100% in some cross-sections) of the investigated areas. Longitudinally, bathymetric data along the deep-water channel showed that dunes developed over nearly 84% of the area. Moreover, a power function relationship between dune length and height was established: H=0.0979L0.737 (R2 = 0.84, n = 1,157). The maximum dune length and height were found to reach up to 441 and 10 m in the lower YR, respectively. The operation of dams in the upper and middle YR significantly decreased the sediment supply to the lower YR, leading to bed sediment coarsening, which promotes the development of dunes. In addition, deep-water channel regulation, sandbank regulation, and the enclosure of mudflats in the lower YR narrowed the channel width, resulting in an increase in flow strength, which could further enhance the development of larger dunes. Therefore, a re-evaluation of the impact of dunes on river channel evolution, as well as regulation projects for the lower YR are urgently needed.

Environmental and land use changes in a Mediterranean landscape: Palynology and geoarchaeology at ancient Metapontum (Pantanello, Southern Italy)

The paper presents the results of palynological and geoarchaeological investigation carried out on the Greek-Roman site of Pantanello – ancient Metapontum – in the Metaponto Plain (southern Italy). This area, archaeologically investigated since the ‘70s, is an example of the long-term interaction between human communities and the environment. A total of 29 pollen samples and 43 bulk samples for sedimentological and mineralogical analyses were collected from three 2-m-deep trenches excavated in the vicinity of the archaeological complex of Pantanello and the alluvial plain of the Basento River. Our multidisciplinary investigation permitted to elucidate the main natural and human-controlled sedimentary processes that took place in the last two millennia. Large part of sedimentation occurred in fluvial environments and led to the accumulation of fine and organic matter-rich deposits. This happened in alluvial to swampy environments at the margin of the Basento River plain. Since the Greek occupation of the area, human communities contributed to the sedimentation with different degree of intensity. In fact, human agency (herding and cultivation) tuned the intensity of soil erosion and slope processes, thus activating the colluvial mobilization of coarse sediments into the sedimentary sequence. Pollen analyses allowed exhaustive landscape reconstructions of the site, giving specific details on the land use and its transformations during the Greek and Roman phases. The increased human exploitation of the area altered the intensity of surface processes (erosion and sedimentation) and the evolution of plant cover promoted by natural dynamics.

Dams and climate change accelerate channel avulsion and coastal erosion and threaten Ramsar-listed wetlands in the largest Great Barrier Reef watershed

• Dam-induced sand settling in the Burdekin River delta is raising the flood levels and threatening channel avulsion. • This trapping of sand in the Delta is starving the coast of sand and generating rapid coastal erosion. • Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. • This is threatening Ramsar-listed wetlands of international significance. • The connectivity of water and sediment between the various parts of river basin demonstrates the need to manage the river at the basin scale using ecohydrology principles. This study documents the impact of climate change and human activities on the Burdekin River delta and coast. The Burdekin River is located in the dry tropics with a seasonally and interannually highly variable discharge, controlled by occasional cyclones and the ENSO-dependent monsoon. Even though the peak discharge from cyclonic rainfall is decreased by a dam, large floods still occur during long-duration monsoon. While the dam traps much of the coarse sediment runoff, large amounts still reach the Delta originating from catchments downstream of the dam. The riverbed in the Delta has measurably risen in recent decades. In turn, this increases the flood levels and the threat of channel avulsion. Sand trapping by the dam and in the Delta is also starving the coast of sand, and this generates rapid coastal erosion along the 11 km long Cape Bowling Green peninsula. Climate change is enhancing this coastal erosion as in the last few decades the mean sea level and the frequency of strong winds have increased significantly. The peninsula may breach soon. As the peninsula protects Ramsar-listed wetlands of international significance, its breaching is predicted to impact the fisheries that depend on the Cape (the black marlin billfish) and on the wetlands (mud crabs, barramundi and mangrove jacks), as well as shorebirds and waterbirds. These findings demonstrate the connectivity of water and sediment throughout the river basin and the coast, and the need for management at the basin scale using ecohydrology principles.

Coarsening of sediments from the Huanghe (Yellow River) delta-coast and its environmental implications

We studied temporal-spatial variations in the grain size of sediments from the Huanghe (Yellow River) delta-coast. Four sediment push-cores and more than 200 surface sediment samples were collected. Key factors that control the sediment variability were revealed, as well as their environmental significance. Analytical results indicated that sediments of the Huanghe delta-coast have coarsened over the past decades, and that this coarsening has intensified in recent years. The average mean grain size (Mz) of two cores in the offshore area from the abandoned delta lobe increased by approximately 18%–32% in the 2010s compared to the 1990s. Surface sediments in the nearshore area were coarsened by about 25% on average from 28.6 μm in 1992 to 35.7 μm in 2000. The sediment coarsening of the abandoned delta lobe began in the 1990s due to the extensive erosion caused by the absence of riverine-sediment supply. Coarse-grained sediments that were resuspended and transported offshore also made the sediment of the abandoned delta lobe coarser. In contrast, sediments of two cores in the offshore area of the active delta lobe were coarsened by more than 30% in the 2010s compared to the 1990s. The average Mz of surface sediments in the nearshore area increased by more than 22% from 23.5 μm in 1992 to 28.7 μm in 2000. The sediment coarsening of the active delta lobe began in the 1990s and became more significant in the 2000s. This trend was due to the rapid decrease of the sediment load from the Huanghe, as well as the coarsening of river-delivered sediments (from 17.7 μm to 22.9 μm) caused by the Water-Sediment Regulation Scheme that has been in place since 2002. Increasing coastal hydrodynamics and the loss of riverine sediment also account for the coarsening of sediments of the delta lobe. Our data clearly indicate that the critical bed-shear stress of the Huanghe delta-coast increased significantly. As a result, it was more difficult to initiate motion of the seabed sediments, leading to the decline of resuspension and erosion. Moreover, since the content of sedimentary organic carbon is negatively correlated with sediment grain size, the coarsening sediment of the study area will have inevitably degraded the carbon-related biogeochemical processes of the Huanghe delta-coast. Our findings have significant implications for the evolution of large river deltas, which are now threatened by sediment starvation and erosion.

Upslope migrating sand waves on sediment-starved shelves: An example from the southeastern continental margin of the Korean Peninsula

An uncharted field of sand waves was discovered in a low-relief submarine canyon incised in the outer shelf on the southeastern continental margin of the Korean Peninsula in water depths of 180–190 m. We characterize the nature and origin of the waves and the sand forming them using sub-bottom chirp profiles, eXpendable bathythermograph (XBT) profile, multibeam echosounder (MBES) data, and sediment samples from four piston cores. Two types of sand waves characterized by distinct height versus wavelength relationships were found in the study area. The sand waves in the upper, narrower part of the shelf-incised canyon are sinuous-crested, with amplitudes of 0.3–2.1 m (mean: ~1 m) and wavelengths of 10–45 m (mean: ~24 m). Their asymmetry indicates migration upslope in a southwesterly direction, opposite to the surface currents. In contrast, the lower part of the canyon that is wider and closer to the margin of the continental shelf hosts nine long (ca. 1 km) curvilinear-crested sand waves with symmetrical crests; these waves likely reflect transient bedforms forming under fluctuating current conditions.The sediment of the sand waves consists of a variable mixture of siliciclastic and carbonate materials. The carbonate fraction (~22–55%; mean: ~34%) is derived mainly from the remains of bryozoans, bivalves, echinoderms, foraminifers, gastropods, and serpulids. Six bioclasts were dated by the radiocarbon method between ca. 41.3 and 11.8 ka BP. These relatively old ages and palaeontological data supports reworking from a shallow-marine environment during the last glacial transgression and limited sedimentation/sediment supply in the study area. The siliciclastic fraction (~44–79%; mean: ~37%) is composed of rounded to subrounded quartz and feldspar of moderate to good sorting and a mean grain size of ~1.3 phi (medium sand). The uppermost ~30 cm of all the sand wave cores reveals a decrease in the grain size of the siliciclastic fraction coupled with an increase in the carbonate/siliciclastic ratio, suggesting episodic sediment reworking and migration of the sand waves in response to fluctuating bottom currents. The coarser sediment that forms the core of the sand waves records bedload transport during periods of stronger currents. Finer carbonate-rich pelagic sediment (i.e., plankton) accumulated at the top of the sand waves during periods of weaker bottom currents. Significantly, our results show that the grain size and mineralogy of the sediment composing the sand waves are controlled by changes in hydrodynamic conditions. Our study provides novel geomorphological evidence for the influence of SW-flowing cold-water incursions (Korean Strait Bottom Cold Water) on the seafloor sediments.

Relative effects of static and dynamic abiotic conditions on foraging behaviour in breeding Sandwich terns

Where and when animals forage depends on the spatio-temporal distribution and catchability of their prey. In dynamic environments, animals can repeatedly target areas that provide predictable availability of prey or may search for ephemeral conditions of high prey availability. However, how foraging behaviour is initiated in response to static versus dynamic environmental conditions is difficult to study, since both environmental data sources are often lacking. In this study, central-place foraging Sandwich terns were tracked using GPS loggers during foraging. Hidden Markov models showed that the probability of switching between transit and foraging was most strongly affected by the static variable sediment type. Wave period (a dynamic variable related to weather), salinity (a dynamic variable) and water depth (another static variable) affected the transition probability to a lesser extent. Cloud cover, wind speed and current speed were only included in lower ranked models. Air and water temperature were not included in any model. Consistent with the greater importance of static versus dynamic abiotic conditions, consistency between foraging trips of the same individual varied irrespective of tidal, diurnal or seasonal cycles, although trips made close in time within a season were slightly more similar than trips with a larger time gap. We suggest that Sandwich terns target broad areas with coarser sediments, where sandeels (Ammodytidae) are more common, and that weather variables may be related to prey visibility. Our study suggests that even in highly dynamic environments, static environmental variables may more strongly affect foraging behaviour of coastal seabirds than dynamic variables.

Origin and evolution of the Paleo‐Kuril arc inferred from detrital zircon U–Pb chronology in eastern Hokkaido, NE Asia

AbstractThe Nemuro and Saroma Groups and Yusenkyo Formation occur in eastern Hokkaido and are considered to be forearc or intra‐arc basin sediments of the Paleo‐Kuril arc (PKA) deposited during the Late Cretaceous to middle Eocene. To further clarify the origin of the PKA, we examined the U–Pb ages of detrital zircons within these sandstones and acidic tuff beds; based on our results, we drew the following conclusions. (1) The PKA originated from an oceanic island arc on the oceanic Izanagi Plate around 85 Ma, to which the Nikoro Group greenstone complex was accreted between 81–80 Ma; the Lowest Unit of the Saroma Group covered the surface of the Nikoro accretional greenstone complex. (2) The PKA then first collided with NE Asia around the beginning of the deposition of the Hamanaka Formation (~70 Ma) and transitioned to a continental arc adjacent to NE Asia. This collision generated giant slump beds during deposition of the Akkeshi Formation. During deposition of the Kiritappu Formation, the entire Nemuro Peninsula was uplifted, supplying large volumes of clastic sediments. (3) Although we do not have data directly bearing on why the North American Plate was established in the edge of NE Asia, we speculate that it separated from the Eurasian continent around ~70 Ma when NE Asia first collided with the PKA. Subsequently, the PKA has behaved as part of the North American Plate. The Paleo‐Japan arc (or East Sikhote–Alin arc) and the PKA became joined via the Hidaka Belt. Around 40 Ma, during the deposition of coarse conglomerate beds of the Urahoro Group, the PKA was uplifted and bent clockwise due to a second collision with NE Asia. (4) The modern Kuril arc was established around 36 Ma (late Eocene–early Oligocene), and the Kuril backarc basin opened into the present tectonic setting in the late Oligocene–early Miocene.

Sources of Coarse Sediment Grain-Size Variability Along the Upper Sandy River, Oregon Revealed by Uav Remote Sensing

Sources of Coarse Sediment Grain-Size Variability Along the Upper Sandy River, Oregon Revealed by Uav Remote Sensing

Complex genesis of N-channel eskers illustrated with the example of an esker near Tosie (east-central Poland)

The study presents the problem of complex genesis of eskers formed in N-channels on the example of an esker located near Tosie in east-central Poland. The lithofacies analysis revealed a high diversity of structural and textural characteristics of sediments in this form. The esker consists of three sedimentation units. Coarse sediments of the esker core were deposited in the subenvironment of a subglacial tunnel, as an effect of bedforms migration under hydrostatic pressure. Opening of the tunnel resulted in the forming of an open crevasse, in which the cover of the esker core sediments was accumulated. These deposits recorded a significant variability of flow energy and sedimentation mechanisms, which indicates a strong influence of the ice-sheet ablation dynamics. During the final deglaciation stage, a part of the esker was covered with diamicton. Numerous soft-sediment deformation structures were identified within the esker. The sediments were dislocated vertically to the elevation of more than 8 metres. They constitute the record of buried dead-ice masses melting in the esker core sediments. Melting of the masses resulted in vertical displacement of sediments and formation of "the dead-ice structure". The complexity of esker genesis is characteristic of postglacial areas in Poland, where most eskers were formed in subglacial N-channels. Numerous research results confirm a considerably more frequent occurrence of the facies sequence of subglacial tunnel and open crevasse in eskers formed in N-channels than R-channels. This is indicated by a much greater dissimilarity of processes during different stages of esker formation on soft bed and solid substratum.

Sediment Recruitment and Redistribution in Mountain Channel Networks by Post‐Wildfire Debris Flows

AbstractWe used lidar differencing and field observations to map volumes, and interpret the origins of, sediment mobilized from mountain canyons by large post‐wildfire debris flows near Montecito, CA, USA in 2018. The debris flows progressively entrained and partially redeposited 550,000 m3 of previously stored channel sediments throughout the canyon networks. The observations that scour depths and volumes were highest where the largest volumes of bouldery colluvium and debris‐flow deposits had accumulated, and that scour persisted beyond the mountain front, indicates that debris‐flow volumes in this extreme event were ultimately controlled by the coarse sediment reservoir available for scour. Because the volumes of available stored sediment result from the stochastic interaction of colluvial mass wasting, the magnitude and frequency of previous debris flows, and the accommodation space provided by valley morphology, the study reinforces the importance of estimating stored sediment volumes when developing debris‐flow hazard assessments.

Sedimentological and Grain Size Characteristics of Two Lake Cores from Himachal Pradesh, India

Two lake cores from Khajjiar (length 746 cm) and Rewalsar lakes (length 647 cm) in Himachal Pradesh (India) were retrieved to understand the sedimentological characteristics and variation in grain size distribution. Both the lake cores are Upper Holocene in age. The Rewalsar lake sediments are composed predominantly of silt with small amounts of clay, whereas the Khajjiar sediments contain sand, silt and clay and both cores have high carbonaceous matter. The standard deviation ranges from 0.88 ϕ to 2.56 ϕ for Khajjiar lake and from 0.957 ϕ to 2.264 ϕ for Rewalsar lake, indicating poorly to very poorly sorted core sediments. The values of the Kurtosis vary between 0.678 ϕ and 1.205 ϕ for Khajjiar lake and from 0.8 ϕ to 1.2.4 ϕ for Rewalsar lake, viewing platykurtic to leptokurtic nature. Further, the skewness value ranges from -0.097 ϕ to 0.240 ϕ for Khajjiar lake and 0.079 ϕ to 0.25 ϕ for Rewalsar lake revealing fine to symmetrical skewness model. The bivariate plots by using the grain-size parameters were also interpreted. The Total Organic Carbon (TOC) is higher in the Khajjiar lake sediments (0.9 to 31.2%; av. 10.6%), compared to that in the Rewalsar lake sediments (1.0 to 9.0; av. 2.6%). The sedimentological characteristics indicate that the energy conditions were linked to the climatic conditions prevailing in the area. In general, the Khajjiar lake core is composed of relatively coarser sediments and more affected by arid conditions while the fine fraction of the Rewalsar shows the consequence of lower energy conditions. The Khajjiar lake shows the transition from fluctuating conditions (zone 1) to humid (zone 2) to arid (zone 3), while the Rewalsar shows the change from fluctuating (zone 1) to humid conditions (zones 2 and 3). The similarity between zone 1 and 2 of both the lake profiles shows that both lakes have experienced similar climatic conditions during the deposition, revealing domination of fluctuating and arid conditions.

Review article: Extreme marine events revealed by lagoonal sedimentary records in Ghar El Melh during the last 2500 years in the northeast of Tunisia

Abstract. The Tunisian coast has been affected in the past by many events of extreme marine submersion (storms and tsunamis). A high-resolution study along two sediment cores taken from the lagoon of Ghar El Meleh was performed to identify the different paleoextreme events and to reconstruct the paleoenvironmental changes in the northeastern part of Tunisia during the Late Holocene. A very high-resolution sedimentological analysis (granulometric and geochemical) was applied to these cores. These cores were also dated with isotopic techniques (137Cs, 210Pbex, 14C), and the outcomes reveal five phases of paleoenvironmental changes in this lagoonal complex and identify two sediment layers that are in connection with two major historical marine submersion events. The first layer is mentioned as E1 and seems to fit with the great tsunami of 365 cal CE. This event was marked by an increase in the coarse sediment, and it is correlated for the first time with the immersed city of Neapolis in the northern Gulf of Hammamet discovered in 2017 by the same tsunamis of 365 cal CE. The other sandy layer, referred to as E2, was dated from 1690 to 1760 cal CE and is marked by one specific sedimentological layer attributed to a marine submersion event. This layer could be associated with the 1693 tsunami event in southern Italy or an increase in extreme storm events.

Long‐Term Changes in Runoff Generation Mechanisms for Two Proglacial Areas in the Swiss Alps II: Subsurface Flow

AbstractLateral subsurface stormflow (SSF) is the most important runoff generation mechanism for most hillslopes in temperate climates. It is influenced by pedological, biological, and topographic factors that change during landscape evolution, but so far little is known about how SSF changes over long‐time scales. Therefore, we conducted sprinkling experiments on a silicate and carbonate moraine chronosequence in the Swiss Alps. Each chronosequence consisted of four moraines ranging between a couple of decades and ∼13,500 years in age. On each moraine, we installed three plots and measured shallow SSF in a trench. We added tracers (δ2H and NaCl) to the sprinkling water to identify mixing and flow pathways in the subsurface. The coarse and drainable sediments on the young moraines provoked more frequent and larger SSF responses than for the old moraines. There was no SSF during the sprinkling experiments on the older moraines at the calcareous study area, but SSF occurred during larger natural rainfall events. The pre‐event water fractions in SSF were higher for the old moraines than the young moraines due to the increase in silt, clay, and soil organic matter content, and subsequent increase in the amount of water stored in the soil. The results of this study suggest that soil and vegetation development affect SSF characteristics and help—together with the results for overland flow (companion paper; Maier & van Meerveld, 2021, https://doi.org/10.1029/2021WR030221)—to improve hydrological models and our understanding of the changes in near‐surface runoff generation processes during the first millennia of landscape evolution in Alpine areas.

Oncholaimus tripapillatus sp. nov., a New Free-Living Marine Nematode of the Genus Oncholaimus Dujardin, 1845 (Nematoda: Enoplida: Oncholaimidae) from the Subtidal Sediment of Dokdo Island, East Sea, Korea, with a New Record of O. qingdaoensis Zhang & Platt, 1983

During a survey of the free-living marine nematodes of Korea, two species belonging to the genus Oncholaimus Dujardin, 1845 were discovered. A new species, Oncholaimus tripapillatus sp. nov. and a newly recorded species, Oncholaimus qingdaoensis Zhang & Platt, 1983, are reported. Oncholaimus tripapillatus sp. nov. was collected from the washing of subtidal coarse sediments around Dokdo Island of the East Sea, Korea. Oncholaimus tripapillatus sp. nov. is characterized by a relatively long (4071–4435 µm in males and 4514–4661 µm in females) and slender body, a slightly constricted head region, relatively long cephalic setae (10–12 µm), males having a precloacal sexual protuberance bearing two small cone-shaped supplementary spines, five pairs of long cloacal setae (three pairs of precloacal and two pairs of postcloacal setae in subventral position), and three remarkable papillae near the end of the tail, with two pairs of subventral setae. The Korean specimens of Oncholaimus qingdaoensis Zhang & Platt, 1983 are almost identical to the Chinese specimens of the original description from the intertidal sand of Qingdao, China. However, the Korean specimens differ from the Chinese specimens in the longer body length in males (3379–3715 µm vs. 2380–2640 µm), the larger spicule length (47–52 µm vs. 34–36 µm), and the presence of ventral tail papillae situated around 14–16 µm from the tail tip. Detailed morphological features and illustrations of two Oncholaimus species from Korea were obtained by differential interference contrast microscopy and scanning electron microscopy. A pictorial key to the species group with distinct tail papillae among the genus Oncholaimus is also provided.

Development of the Nile Littoral Cell during the past 8.2 kyr

The depositional history of the Nile Littoral Cell (NLC) in the past 8.2 kyr was reconstructed from two radiocarbon-dated cores retrieved down-flow the Nile Delta at the southeastern Mediterranean-Levantine continental shelf. The two cores are located ∼80 km apart at the inner shelf off-shore Israel: core V115 at a southern proximal site and core V101 at a northern distal site. Grain-size distribution, chemical composition, and εNd and 87Sr/86Sr isotope ratios and marine derived variables such as carbonate content, total organic carbon and its δ13C composition record the temporal and spatial variations in transport processes and sediment provenance.From ∼8.2 to ∼5.5 ka BP the record is dominated by coarse quartz sands from the Nile Delta front that were recycled along the NLC due to shelf transgression along with the post glacial sea level rise. Oligotrophic conditions prevailed in the inner shelf, and the relatively high carbonate content reflects the decrease in Nilotic fine particles due to increased vegetation and decrease in surface erosion related to the African Humid Period (AHP) wetter conditions. The chemical and isotope signature of the fine fractions indicates mostly remobilization of dust-driven surface cover soils from the surrounding lands that originated from the granitoid terrains of the Sahara-Arabia deserts.Sea level stabilization, termination of the AHP at ∼5.5 ka BP and the partial drying of the Ethiopian Highlands resulted in the increase of fine sediments with a basaltic signature. After ∼5.5 ka BP, fine sediments were supplied seasonally by the Nile, creating a distinct mud belt along the Israeli coast and Nile Delta at water depth exceeding ∼35 m. Occasional sediment coarsening in the distal NLC likely reflects periodical decrease in Nile floods discharge or contribution from shallower water depth due to increased storminess. With the continuation of the regional aridification and decreasing intensity of the Nile River flow during the last 2 kyr, higher contribution of surface cover particles from the nearby lands was recorded in the distal northern site, while the southern site continued to be affected mostly by the Nilotic contribution.A distinct increase in grain size and carbonate content, and decrease in TOC content and δ13Corg values at the topmost part of the sedimentary record represent the Nile River damming during the modern period, which resulted in halting of the Nile fine suspension and lead to ultra-oligotrophic conditions in the Levantine basin.

Spatial and temporal controls on proglacial erosion rates: A comparison of four basins on Mount Rainier, 1960 to 2017

SummaryThe retreat of alpine glaciers since the mid‐19th century has triggered rapid landscape adjustments in many headwater basins. However, the degree to which decadal‐scale glacier retreat is associated with systematic or substantial changes in overall coarse sediment export, with the potential to impact downstream river dynamics, remains poorly understood. Here, we use repeat topographic surveys to assess geomorphic change in four partly glaciated basins on a stratovolcano (Mount Rainier) in Washington State at roughly decadal intervals from 1960 to 2017. The proglacial extents of the four basins show distinct geomorphic trajectories, ranging from substantial and sustained net erosion to relatively inactive with net deposition. These different trajectories correspond to differences in initial (1960) valley floor gradients, and can be effectively understood as valley floor grade adjustments. Significant erosion was most often accomplished by debris flows triggered by extreme rainfall or glacial outburst floods, though a single rockfall mobilized more material than all other events combined. Year‐to‐year runoff events had little measurable geomorphic impact. Exported material tended to accumulate in broad deposits within several kilometers of source areas and largely remained there through the end of the study period. Over 10‐ to 100‐year timescales, we find that the impact of glacier retreat on coarse sediment yield may then vary substantially according to the geometry and storage trends of the newly exposed valley floor; the timing of that response may also be dictated, and potentially obscured, by stochastic and/or extreme events.

Solute transport in permeable porous media containing a preferential flow feature: Investigation of non-Darcian flow effects

Fractures, faults, karstic features and/or interbedded layers of coarse sediment often manifest in the form of preferential flow features (PFFs). Previous investigations into the effects of PFFs on solute plume distributions within otherwise permeable host rocks have treated flow in PFFs as Darcian. However, flow through faults and fractures is known to exhibit non-Darcian flow behavior. The current study extends previous investigations of the effects of PFFs (e.g., a fault or fracture) on solute plumes in permeable aquifers that assume Darcian flow in the fault/fracture. The finite-element model COMSOL Multiphysics was applied to examine how non-Darcian flow in a single PFF influences flow fields and steady-state solute plume distributions in permeable aquifers, compared with the Darcian flow assumption. The Forchheimer equation was applied within numerical models to represent flow in the PFF for a variety of PFF-permeability contrasts, PFF apertures and matrix flow directions. The refraction of flow lines at matrix-PFF interfaces and the specific discharge in the PFF were found to be smaller in non-Darcian models, leading to larger peak solute concentrations (by up to 160%) and narrower plumes compared to Darcian models. In addition, the impact of non-Darcian flow on flow fields and solute plumes was greater with smaller matrix hydraulic conductivity, larger PFF aperture and larger incidence angle at the matrix-PFF interface. Upstream dispersion at the matrix-PFF interface, observed in previous matrix-PFF studies of solute transport as the result of steep solute concentration gradients opposing head gradients, was found to be reduced when non-Darcian flow was considered in PFFs. This study highlights that non-Darcian flow effects may be significant in the simulation of flow and solute transport within high-permeability PFFs embedded in otherwise porous aquifers.