Suspended solids concentration (SSC) in a river is closely relevant to river water turbidity. Investigation of their relationship in this study is accompanied by observed turbidity and SSC values, which were obtained from the testing results of water samples and monitored conditions in streamflow. The water samples were collected from two observation stations with a broad range of sediment concentrations in the Lai Chi Wo catchment in Hong Kong, China. We classified the target rainfall events into single-peak event type and dual-peak event type for a distinguished discussion of the relationship between SSC and turbidity in this study. At a finer classification, each event is separated into defined processes for the analysis, where two main processes refer to the periods that SSC rises from a normal state to a peak state first and the followed periods that SSC recesses to ordinary status gradually. It is advised by the analysis results that the estimation of SSC through turbidity values should be based on the same rainfall types for the upstream station. However, the results show that the classification of rainfall types does not need to take downstream areas into consideration. Furthermore, current research implies that the individual established connections between SSC and turbidity value at different stages (particularly referring to the rising period and recessing period) could be applied to estimate SSC at the same station via continuous turbidity values for both this and other ungauged stations with similar topographical features in the future. Meanwhile, this research approach provides new insight exploring various behaviors of sediments at different stages during an integral rainfall event. A comparison of distinguished performances of sediment during corresponding stages in a rainfall event makes contributions to diverse relationship between SSC and turbidity in the mountainous river.

Riverbed sediments have been identified as temporary and long-term accumulation sites for microplastic particles (MPs), but the relocation and retention mechanisms in riverbeds still need to be better understood. In this study, we investigated the depth-specific occurrence and distribution (abundance, type, and size) of MPs in river sediments down to a depth of 100 cm, which had not been previously investigated in riverbeds. In four sediment freeze cores taken for the Main River (Germany), MPs (≥ 100 µm) were detected using two complementary analytical approaches (spectroscopy and thermoanalytical) over the entire depth with an average of 21.7 ± 21.4 MP/kg or 31.5 ± 28.0 mg/kg. Three vertical trends for MP abundance could be derived, fairly constant in top layers (0-‍30 cm), a decrease in middle layers (30-60 cm), and a strong increase in deep layers (60-100 cm). The dominant polymer types were polyethylene (PE), polypropylene (PP), and polystyrene (PS). Polyethylene terephthalate (PET) and PP were also found in deep layers, albeit with the youngest age of earliest possible occurrence (EPO age of 1973 and 1954). The fraction of smaller-sized MPs (100-500 µm) increased with depth in shallow layers, but the largest MPs (> 1 mm) were detected in deep layers. Based on these findings, we elucidate the relationship between the depth-specific MP distribution and the prevailing processes of MP retention and sediment dynamics in the riverbed. We propose some implications and offer an initial conceptual approach, suggesting the use of microplastics as a potential environmental process tracer for driving riverbed sediment dynamics.

Ecosystem engineers alter their environment often benefiting their own survival and growth yielding self-reinforcing feedbacks. Moreover, these habitat modifications have been found to facilitate recruitment of conspecifics for some species, while for others engineering inhibits recruitment. Whether dune grasses facilitate or inhibit recruitment of conspecifics is yet unknown. Here, we investigated how habitat modification by European marram grass (Ammophila arenaria) through embryonic dune development affects recruitment from seeds and marine dispersed rhizome fragments. Specifically, we tested at three locations with different dune morphologies how habitat modification affected natural seed and rhizome presence and shoot emergence from plots in which seeds or rhizome fragments were added. In addition, we investigated how sediment burial (i.e., the main effect of habitat modification by dune grasses) affected germination and emergence in a controlled experiment. Results show that regardless of habitat modification or beach width, seeds and rhizomes were absent in natural conditions. Habitat modification negatively affected shoot emergence from seeds (8 × less) and rhizomes (4 × less) and was negatively related to sediment dynamics. Furthermore, fewer seedlings were found with higher elevations. In controlled laboratory conditions, the highest seedling emergence was found with slight burial (0.5-3 cm); both germination and seedling emergence decreased as seeds were buried deeper or shallower. Overall, habitat modification by marram grass negatively affects recruitment of conspecifics through increased sediment dynamics and elevation. Consequently, storm events or eradication programs that include removal of adult vegetation-which leads to an unmodified system-might benefit new recruitment from seeds or clonal fragments.

This investigation analyzed shoreline evolution along India\'s Digha Coast from 1992 to 2022, using multispectral Landsat satellite images and the Digital Shoreline Analysis System (DSAS). Methods included identifying zones and transects, shoreline extraction, and applying spatial statistical techniques. The study area, divided into five zones with 587 transects, enabled both short- and long-term analysis. Key findings indicate that the mean long-term rate of shoreline change is -0.54 m per year, with 70.70 % of transects experiencing erosion and 29.30 % accretion. Notably, Zone V had the highest accretion rate (8.55 m/year), while Zone III faced the most erosion (-7.47 m/year). Short-term analysis from 1997 to 2017 indicated significant erosion, contrasting with accretion during 1992-1997 and 2017-2022. Particularly, Zones II, III, and IV underwent major erosion, especially from 1997 to 2002. The study underscores the need for continuous shoreline management strategies and demonstrates geospatial technology\'s effectiveness in capturing coastal landscape changes.

One of the primary drivers of Phosphorus (P) limitation in aquatic systems is P adsorption to sediments. Sediments adsorb more P in freshwater compared to other natural solutions, but the mechanism driving this difference is poorly understood. To provide insights into the mechanism, we conducted batch experiments of P adsorption to calcite in freshwater and seawater, and used computer software to develop complexation models. Our simulations revealed three main reasons that, combining together, may explain the greater P adsorption to calcite in freshwater vs. seawater. First, aqueous speciation of P makes a difference. The ion pair CaPO4- is much more abundant in freshwater; although seawater has more Ca2+ ions, MgHPO40 and NaHPO40 are more thermodynamically favored. Second, the adsorbing species of P make a difference. The ion pair CaPO4- (the preferred adsorbate in freshwater) is able to access adsorption sites that are not available to HPO42- (the preferred adsorbate in seawater), thereby raising the maximum concentration of P that can adsorb to the calcite surface in freshwater. Third, water chemistry affects the competition among ions for surface sites. Other ions (including P) compete more effectively against CO32- when immersed in freshwater vs. seawater, even when the concentration of HCO3-/CO32- is higher in freshwater vs. seawater. In addition, we found that under oligotrophic conditions, P adsorption is driven by the higher energy adsorption sites, and by the lower energy sites in eutrophic conditions. This study is the first to model P adsorption mechanisms to calcite in freshwater and seawater.

Globally, rivers systems are under considerable and increasing threat from multiple anthropogenic stresses, including different types of direct (e.g. channel engineering) and indirect human impacts (e.g. land cover and land use changes) that alter water and sediment dynamics. (Dis)connectivity relationships determine the source, timing and rates of water and sediment flux in catchments and thus their geomorphic sensitivity to disturbance. However, most river and catchment management plans overlook the role of sediment (dis)connectivity. Here we use examples from different environmental settings with different sediment-related problems to show how understandings of sediment (dis)connectivity can inform catchment-based management plans. We focus on concerns for river conservation and recovery, using examples from Austria, New Zealand and Australia. Finally, we present questions for practitioners to consider to appropriately contextualise management applications when using (dis)connectivity concepts in practice. Our findings revealed that differences in sediment (dis)connectivity relationships exert profound catchment-specific variability in (eco)-geomorphic response to disturbance. Understanding (dis)connectivity and system history is therefore essential to forecast the effects of on-ground management actions.

Coastal systems worldwide deliver vital ecosystem services, such as biodiversity, carbon sequestration, and coastal protection. Effectivity of these ecosystem services increases when vegetation is present. Understanding the mechanisms behind vegetation establishment in bio-geomorphic systems is necessary to understand their ability to recover after erosive events and potential adaptations to climate change. In this study, we examined how seed availability affects vegetation establishment in the salt marsh-intertidal flat transition zone: the area with capacity for lateral marsh expansion. This requires vegetation establishment; therefore, seed availability is essential. In a 6-month field experiment, we simulated a before and after winter seed dispersal at two locations, the salt-marsh vegetation edge and the intertidal flat, and studied seed retention, the seed bank, and the seed viability of three pioneer marsh species: Salicornia procumbens, Aster tripolium, and Spartina anglica. During winter storm conditions, all supplied seeds eroded away with the sediment surface layer. After winter, supplied seeds from all three species were retained, mostly at the surface while 9% was bioturbated downwards. In the natural seed bank, A. tripolium and S. anglica were practically absent while S. procumbens occurred more frequently. The viability of S. procumbens seeds was highest at the surface, between 80% and 90%. The viability quickly decreased with depth, although viable S. procumbens seeds occurred up to 15 cm depth. Only when seeds were supplied after winter, many S. procumbens and some S. anglica individuals did establish successfully in the transition zone. Viable seed availability formed a vegetation establishment threshold, even with a local seed source. Our results suggest that, although boundary conditions such as elevation, inundation, and weather conditions were appropriate for vegetation establishment in spring, the soil surface in winter can be so dynamic that it limits lateral marsh expansion. These insights can be used for designing effective nature-based coastal protection.

During the expedition 908 survey in 2007, 539 seafloor surface sediment samples and two cores were collected over a narrow sector of the northeastern Beibu Gulf, South China Sea. Currently, three dynamic sedimentological processes prevail in the study area: circulation-controlled sand deposition, mud deposition under weak sediment dynamics, and fluvial input. Core A233 from the circulation-controlled sand area, with a 60 cm mixed layer, provides evidence of dynamics disturbance since the mid-Holocene. To reconstruct the anthropogenic heavy metal pollution history, we selected core A146 from the stable mud sector influenced by fluvial input. The dating of core A146 was based on 210Pb activity analysis, showing an ~90-year historical record in the upper 40 cm. The heavy metal contamination results showed a generally low pollution level. Nonetheless, increased pollution has happened since the 1950s, especially after 1978 A.D., corresponding to the beginning of China\'s reform and opening up.

Sediment connectivity, defined as the degree of linkage between the sediment sources to downstream areas, is one of the most important properties that control landscape evolution in river basins. The degree of linkages amongst different parts of a catchment depends mainly on the hinterland characteristics (e.g. catchment morphology, slope, shape, relief, and elevation), channel characteristics (e.g. slope, stream network density, valley confinement), and the combined effects of vegetation (e.g. land use changes and land abandonment). This paper evaluates the sediment connectivity of the upper Kosi basin covering an area of ~52,731 km2 including Tibet and Nepal at different spatial scales. We have computed the index of connectivity (IC) using the equations originally proposed by Borselli et al. (2008) and modified by Cavalli et al. (2013) to evaluate the potential connection of sediment source areas to the primary channel network as well to the catchment outlet. Our results highlight significant spatial variability in sediment connectivity across the basin and provide important insights on structural sediment dynamics in a complex geological and geomorphological setting. We compare our results with the observed sediment load data at certain outlets and demonstrate that sediment flux in different sub-basins is controlled by variable slope distribution and land use and land cover that are strongly related to the structural connectivity. We argue that IC model can be extremely beneficial to understand sediment dynamics at catchment scale in a large river basin (~103-104 km2 scale), where systematic field investigations for mapping hillslope-channel linkages are not feasible.

Rivers and streams continuously shape and reform their channels through the transport of sediment. One of the most important parameter used to assess this transformation is the threshold for incipient grain motion. To date, limited studies have reported that several biotic and abiotic factors can affect this parameter. However, the effects of tufa precipitation on sediment entrainment and dynamics are still unexplored. The Estero Morales is an Andean stream in Central Chile affected by the phenomenon of tufa precipitation during the winter. Along the wetted channels, tufa precipitate creates a thin solid layer that covers the sediments. A series of field surveys and flume experiments were conducted to analyze the effect of tufa precipitation on the initiation of motion and sediment dynamics. Along the wetted areas of the river, a portable dynamometer was used to explore the force needed to dislocate the grains affected by tufa precipitation from the surrounding sediments. Flume experiments were conducted to compare the incipient motion of sediment covered by tufa precipitation with unaffected sediment. Geochemical analyses were conducted to study the precipitate chemistry, mineralogy and texture. The results demonstrate that greater force is needed to move sediment particles affected by tufa precipitation compared to unaffected ones. In addition, lower sediment transport rates were measured on sediment affected by tufa precipitation, especially for the largest sediment size. These results could have important implications for studies concerning sediment dynamics and contaminant fate in the environment. Moreover, the results allow us to make some assumptions regarding the long-term role that tufa precipitation can play in rivers. Such analysis can help us to better understand and predict the changes in sediment transport rates due to tufa precipitation.