Loading Criteria and Deposit Layer Characteristics as Causes of Sediment Settlement in an Estuary

Sediment compaction due to the extraction of groundwater and self-weight consolidation, and monitoring land settlement of the river delta using geodetic measurement has been executed in several studies, while sediment settlement in the estuary is hypothesized due to dynamic loads. The present study aimed to observe clues for the occurrence of sediment settlement due to loading variation and deposit layer characteristics in the estuary. This research was based on four loading data for examination, i.e., hydraulic head pressure, sediment transport rate, sediment deposition, and water density. Two years of previous research simulations, including the rainy and dry seasons, were recalculated to gain the load pressure and were considered to assess the maximum load prediction. This review found evidence that dynamic loads predominated in maximum pressure changes in boreholes (BH2) and (BH3), and were due to river discharge and tidal occurrence, respectively. The dynamic load of sediment in BH2 contributed more than in BH3, where it was almost nonexistent. Observing the sediment layer characteristics, both settled for almost a month and two weeks, respectively, showed sediment settlement of more or less than 2 and 8 mm. Despite insignificant loading changes, these findings can further our understanding of loading criteria and settlement in different geometric locations.

Sedimentary response of a structural estuary to Holocene coseismic subsidence

Stratigraphic evidence for coseismic subsidence has been documented in active-margin estuaries throughout the world. Most of these studies have been conducted in subduction zone or strike-slip settings; however, the stratigraphic response to coseismic subsidence in other tectonic settings would benefit from further study. Here we show evidence of late Holocene coseismic subsidence in a structural estuary in southern California. Below the modern marsh surface, an organic-rich mud containing marsh gastropods, foraminifera, and geochemical signatures indicative of terrestrial influence (mud facies) is sharply overlain by a blue-gray sand containing intertidal and subtidal bivalves and geochemical signatures of marine influence (gray sand facies). We use well-established criteria to interpret this contact as representing an abrupt 1.3 ± 1.1 m rise in relative sea level (RSL) generated by coseismic subsidence with some contribution from sediment compaction and/or erosion. The contact dates to 1.0 ± 0.3 ka and is the only event indicative of rapid RSL rise in the 7 k.y. sedimentary record studied. Consistent with observations made in previous coseismic subsidence studies, an acceleration in tidal-flat sedimentation followed this abrupt increase in accommodation; however, the recovery of the estuary to its pre-subsidence elevations was spatially variable and required 500−900 years, which is longer than the recovery time estimated for estuaries with larger tidal ranges and wetter climates.

Land subsidence and aquifer compaction in Montgomery County, Texas, U.S.: 2000–2020

Groundwater-withdrawal-induced land subsidence has been a big concern in Montgomery County, Texas, U.S. since the 2000s. As of 2020, approximately half of the entire county is experiencing subsidence over 5 mm/year. This study aims to investigate ongoing land subsidence in Montgomery County using groundwater-level, extensometer, and GPS datasets. According to this study, land subsidence in Montgomery County since the mid-2000s is primarily contributed by sediment compaction in the Evangeline and Jasper aquifers; the compaction of Jasper aquifer contributes approximately one-third of the land subsidence since the mid-2000s; the pre-consolidation heads of the Chicot, Evangeline, and Jasper aquifers in Montgomery County are close to each other, approximately 15–25 m below mean sea level; the virgin-compaction/head-decline ratio is approximately 1:250 in the Evangeline aquifer and 1:800 in the Jasper aquifer in central and southern Montgomery County. As of 2020, the Jasper groundwater-level altitude is approximately 20–40 m below the pre-consolidation head in the central and southern Montgomery County; the Evangeline groundwater-level altitude is about 40–60 m below the pre-consolidation head. Land subsidence will continue to occur as long as the groundwater-level altitude in either the Evangeline or the Jasper aquifer remains below the pre-consolidation head.

Sediment Bulk Density Effects on Benthic Macrofauna Burrowing and Bioturbation Behavior

Benthic macrofauna are a key component of intertidal ecosystems. Their mobility and behavior determine processes like nutrient cycling and the biogeomorphic development of intertidal flats. Many physical drivers of benthic macrofauna behavior, such as sediment grain size, have been well-studied. However, little is known about how sediment bulk density (a measure of sediment compaction and water content) affects this behavior. We investigated the effect of bulk density on the burrowing rate, burrowing depth, bioturbation activity, and oxygen consumption of bivalves (Limecola balthica, Scrobicularia plana, and Cerastoderma edule) and polychaetes (Hediste diversicolor and Arenicola marina) during a 29-day mesocosm experiment. We compared four sediment treatments consisting of two sediments of differing grain size classes (sandy and muddy) with two bulk densities (compact and soft). Overall, bulk density had a strong effect on benthic macrofauna behavior. Benthic macrofauna burrowed faster and bioturbation more intensely in soft sediments with low bulk density, regardless of grain size. In addition, L. balthica burrowed deeper in low bulk density sediment. Finally, we found that larger bivalves (both C. edule and S. plana) burrowed slower in compact sediment than smaller ones. This study shows that benthic macrofauna change their behavior in subtle but important ways under different sediment bulk densities which could affect animal-sediment interactions and tidal flat biogeomorphology. We conclude that lower bulk density conditions lead to more active macrofaunal movement and sediment reworking.

Three-dimensional electrical conductivity of the world ocean and seabed sediments: effect on EM induction responses

<p>This work presents global 3-D electrical conductivity atlas of the world ocean and seabed sediments. Ocean salinity and temperature data were converted to electrical conductivity by solving a thermodynamic equation of state of seawater. A sediment compaction model was used to estimate the depth-dependent electrical conductivity of the seabed sediments. Electromagnetic responses in a wide period band, including typical ranges used in CSEM, MT and Global studies, are significantly affected by varying ocean and sediments conductivity. Incorporating this information in a model prior to inversion helps avoid artifacts and improve data fit. The atlas is openly available along with a concise and easy to use Python toolbox.</p>

Particularities of Vertical Displacements Along the Delta Fault During the 1862 Tsagan Earthquake on Lake Baikal

Based on the ground penetrating radar, geological and morphostructural data, the particularities of single-event vertical displacements in Holocene sediments of various competencies along the land and underwater segments of the Delta fault activated on January 12, 1862 during the M ~ 7.5 Tsagan earthquake (southeastern side of the Baikal rift.). It is shown that the slip determined from the scarp morphology and the position of the main rupture in the section reflects the total displacement value, which is the sum of the brittle and plastic deformational components. The presence of water-saturated poorly consolidated sediments in the geological section increases the contribution of the plastic component. In this case, the width of the rupture zone increases. Despite the fact that the northeastern segment of the Delta Fault was submerged in the water of Proval Bay, the largest seismotectonic displacements occurred between the villages of Kudara and Sherashevo and on the outskirts of the village Dubinino in the land southwestern part of the structure, where the total displacement was 9,59 and 9,28 m, respectively. No such depths were recorded in Proval Bay after the earthquake. Along the Delta Fault under water, seismotectonic displacements were relatively small with a rather significant contribution of the plastic component from 26 to 53 %. This slip was a trigger for the seismic- gravity subsidence of the bay and sediment compaction, which continues to this day, judging by its almost unchanged depth since 1862 and the proximity of numerous seismic events, including the last Мs = 5.4 09.12.2020 earthquake happened on December 9, 2020 and strongly felt in Irkutsk.

Sediment Selection: Range Expanding Fiddler Crabs are Better Burrowers Than Their Historic Range Counterparts

ABSTRACTSpecies ranges are shifting in response to climate change. In New England saltmarshes, the mud fiddler crab, Minuca pugnax, is expanding north of Cape Cod, MA into the Gulf of Maine (GoM) due to warming waters. The burrowing lifestyle of M. pugnax means sediment compaction in saltmarshes may influence the ability for crabs to dig, with more compact soils being resilient to burrowing. Previous studies indicate that saltmarshes along the GoM have higher soil strength (i.e., compaction) relative to marshes south of Cape Cod. Together, physical characteristics and temperature of this habitat may be influencing the burrowing performance of M. pugnax, and therefore the continuation of their northward range expansion into the GoM. To determine if compaction affects burrowing activity of M. pugnax in historical and range expanded populations, we conducted a controlled laboratory experiment. We manipulated soil compaction in standardized lab assays and measured crab burrowing performance with individuals collected from Nantucket (i.e., historical range) and the Plum Island Estuary (PIE, i.e., expanded range). We determined compaction negatively affected burrowing ability in crabs from both sites; however, crabs from PIE burrowed in higher soil compactions than Nantucket crabs. In addition, PIE crabs were more likely to burrow overall. We conclude that site level differences in compaction are likely altering burrowing behavior in the crab’s expanded range territory by way of phenotypic plasticity or rapid evolution. Our study demonstrates that non-temperature physical habitat traits can be as important as temperature in influencing climate driven range expansions.