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Coastal bedrock islands sea areas have a unique natural environment, frequent human activities, and complex sedimentary dynamic processes. In this paper, we select the Chudao Island sea area off the coast of Shandong Peninsula, China, as a typical research area to investigate the sediment transport trends and influencing factors by means of high-precision bathymetric survey, high-density sediment sampling, grain-size trend analysis and hydrodynamic numerical modeling. Results and analysis indicate that the grain size parameters including mean grain-size, sorting coefficient and skewness are zonal distributed, roughly parallel to the isobaths. While the overall sediment transport trend is from island shore to sea, with several convergence centers near the loop centers of bottom flow and at the edge of the agriculture area. The near-bottom flow velocity is primary factor that controlling the significance of sediment transport trend, while the flow decides the general patterns of sediment transport trend and sediment distribution. Submarine topography can either directly transport sediments down its slope, or indirectly affect the direction of sediment transport by constraining the near-bottom flow from shallow to deep waters. Besides the natural factors of bottom flow and submarine topography, human activities represented by aquaculture also affect the sediment transport trend in coastal bedrock island sea areas. First, the increased sedimentation rate caused by organic matters and the diffusion of scallop fragments may cause sediment coarsening. Second, the artificial aquaculture facilities can reduce flow velocity and therefore hinder the initiation, suspension and transport of sediment near the aquaculture areas. Our methods and findings provide high-resolution details to insight into the sediment transport trends to improve the understanding of the modern sediment dynamics in small-scale coastal bedrock island sea areas and provide reference for corresponding engineering and agriculture activities.

Pollution by microplastics is of increasing concern due to their ubiquitous presence in most biological and environmental media, their potential toxicity and their ability to carry other contaminants. Knowledge on microplastics in freshwaters is still in its infancy. Here we reviewed 150 investigations to identify the common methods and tools for sampling microplastics, waters and sediments in freshwater ecosystems. Manta trawls are the main sampling tool for microplastic separation from surface water, whereas shovel, trowel, spade, scoop and spatula are the most frequently used devices in microplastic studies of sediments. Van Veen grab is common for deep sediment sampling. There is a need to develop optimal methods for reducing identification time and effort and to detect smaller-sized plastic particles.

This research investigates the present status and decadal variability of element distributions in the marine sediments off Doha, on the east coast of Qatar. Twenty elements were considered from 11 sediment sampling stations and 3 dust sampling stations by grouping them into major elements, toxic elements, and other trace elements. The results show elevated concentrations of certain toxic and trace elements, including Ba, Be, Co, Cr, Cu, Fe, Mg, V, Zn, Mg, and Ti, in the nearshore region, primarily influenced by the settling of dissolved elements under weak hydrodynamic circulations in the Doha Bay. The relatively higher currents in offshore enable quick advection and dispersion of the elements. On the other hand, the dust deposits have caused significant contributions to the Al, As, Mg, Ca, Sr, Fe, Zn, and Cd concentrations. Decadal variability is evident in element concentrations, which are linked to the urbanisation of the capital city in the State of Qatar. The Cu, Ni, V, Zn, and Cd concentrations indicate a notable increase in recent years compared to the last two decades, with values of about 20.7, 17.9, 25.0, 25.9, 0.66 ppm in 2022. In contrast, a few other elements fluctuate between the decades/years. The results pointed out the increased elemental concentrations in the bay due to the vast expansion of infrastructure facilities in the vicinity of Doha Bay in recent years. The Geoaccumulation Index resulted in a slight pollution of Cd, while other elements are unpolluted. The Degree of Contamination reveals low degree of contamination of sediments, and the Pollution Load Index illustrates no significant pollution in the sediments off Doha.

Quantitative estimates of particulate organic carbon (POC) flux and burial in coastal systems are critical for constraining coastal carbon budgets and understanding their role in regional and global carbon cycling. In this study, POC export fluxes were quantified in the Bedford Basin, a coastal inlet in the Northwest Atlantic, based on measurements of 234Th/238U disequilibria and the POC : 234Th ratio on small (1–51 µm) and large (>51 µm) particles. These water column export fluxes were compared to sediment accumulation fluxes of 234Th and POC to refine the carbon budget in the Bedford Basin. The coupled water column-surficial sediment sampling approach, which is relatively new, was applied quasi-seasonally throughout 2021–2024, including for the first time in boreal winter. Total 234Th activities reveal persistent deficits with respect to 238U throughout the water column, likely due to extensive particle scavenging, which is also indicated by high 234Th activities on particles. Here, we find that the removal of 234Th in the water column is typically balanced, within uncertainties, by the inventory of excess 234Th in underlying marine sediments. This finding reveals that on the timescale of ∼100 d, the 234Th budget in the Bedford Basin is in balance, and no major particle loss is occurring. Using the POC : 234Th ratio on sinking particles and integrated 234Th water column fluxes, we report a mean (± s.d.) depositional flux of 20±14 mmol C m−2 d−1 (range 3.6 to 44.5 mmol C m−2 d−1) to the seafloor. This mean flux translates to an annual molar flux of 7.3±5.1 mol C m−2 yr−1, within a factor of 2 of model estimates and previous sediment trap results at this site. Our findings contribute to ongoing research efforts in the Bedford Basin, and aid in the evaluation of coastal regions in local carbon budgets.

Generally, fluvial systems are used for different objectives including energy production, water supply, recreation, and navigation. Thus, many impacts must be considered with their use. An understanding of sediment dynamics in fluvial systems is often of value for a variety of objectives, given that erosion and depositional processes can change the fluvial system morphology and can substantially alter the fluvial environment. In this sense, sediment monitoring is important because it helps to explain and quantify sediment dynamics in the environment. Hence, this study presents an innovative sediment monitoring technique: the use of the acoustic Doppler current profiler, commonly used to obtain discharge measurements, to obtain suspended sediment concentration (SSC). This paper aims to describe the application of additional corrections to the ADP-M9 signal to obtain SSC from measurement campaigns that used the ADP only for discharge measurements. The analyses were based on traditional sediment sampling methods and discharge measurements, with the ADP-M9, from 7 field campaigns at the Taquari River, a major tributary from the Alto Paraguay Basin, in the Pantanal Biome, known as the largest freshwater wetland system in the world. The correlation was assessed considering the following: (a) the equipment frequency operation mode (Smart Pulse or Fixed Frequency) and (b) by checking the influence of the sediment attenuation coefficient. Furthermore, extrapolation was conducted in filtered and unmeasured areas of the ADP to map the suspended sediment concentration over the entire cross section. Results indicate that ADP correlations can be an effective tool for estimating SSC in the Taquari River when samples cannot be collected. Correlations could be applied to past and future ADP measurements made at the location where the correlation was created, as long as similar environmental conditions are present as when the correlation was developed. The described technique can expand the amount of sediment data available at a monitoring site even with reduced traditional sampling and by leveraging instruments used for other monitoring purposes.

PurposeAssessing the physicochemical characteristics of the stream suspended sediment phase (SSP) is a common component of watershed monitoring, whereas the biological attributes of the SSP are more rarely described. The microbial component is valuable to sediment apportionment studies and can inform on pathogen transport and in-stream biogeochemistry.MethodsAn established passive, flow-through sampling technique (Phillips Tube (PT) Sampler) was used for time-integrated evaluation of suspended phase microbial communities within an agricultural stream segment (≈ 0.7 km) in southern Ontario, Canada. Monthly DNA-metabarcoding of the SSP was conducted and contrasted with bed sediment phases (BSPs).ResultsPT samplers showed good spatial precision. Monthly sampled bed sediment microbial communities showed more similarity to each other than to suspended sediment communities. Suspended sediments were characterized by aerobic/facultative aerobic taxa with bed sediments defined by nitrate, iron, and sulfate metabolizing groups. Greater community diversity was observed in BSP samples, with biomarker analysis identifying more unique genera in SSP samples. In situ dissolved oxygen (DO) logging revealed a substantial decrease in PT sampler DO (12 to 3 mg L−1) after 3 weeks of deployment. Precipitation events caused in-stream DO concentrations to flatline temporarily, but increased concentrations within samplers.ConclusionsPT samplers collected adequate sediment volumes for microbial DNA metabarcoding and showed good replicability. Use of samplers during higher flow periods may collect a more representative microbial community that is less affected by within-sampler decreases in DO. Future use of PT samplers should consider microbial/redox effects that can alter in situ chemistries.

In this study, we used a comprehensive array of sampling techniques to examine the pollution caused by organic micropollutants in İzmit Bay for the first time. Our methodology contains spot seawater sampling, semi-permeable membrane devices (SPMDs) passive samplers for time-weighted average (TWA), and sediment sampling for long-term pollution detection in İzmit Bay, together. Additionally, the analysis results obtained with these three sampling methods were compared in this study. Over the course of two seasons in 2020 and 2021, we deployed SPMDs for 21 days in the first season and for 30 days in the second season. This innovative approach allowed us to gather sea water samples and analyze them for the presence of polycyclic aromatic hydrocarbons (Σ15 PAHs), polychlorinated biphenyls (Σ7 PCBs), and organochlorine pesticides (Σ11 OCPs). Using SPMD-based passive sampling, we measured micropollutant concentrations: PAHs ranged from 1963 to 10342 pg/L in 2020 and 1338 to 6373 pg/L in 2021; PCBs from 17.46 to 61.90 pg/L in 2020 and 8.37 to 78.10 pg/L in 2021; and OCPs from 269.2 to 8868 pg/L in 2020 and 141.7 to 1662 pg/L in 2021. Our findings revealed parallels between the concentrations of PAHs, PCBs, and OCPs in both SPMDs and sediment samples, providing insights into the distribution patterns of these pollutants in the marine ecosystem. However, it is worth noting that due to limited data acquisition, the suitability of spot sampling in comparison to instantaneous sampling remains inconclusive, highlighting the need for further investigation and data collection.

Water quality improvements in shallow eutrophic lakes are commonly delayed due to loading from legacy phosphorus (P)‐enriched sediments, even with reduced external nutrient loads. It is critical to understand the drivers of internal P loading to suppress or remove this source of P and meet water quality goals. We contrast the drivers of internal P loading in two shallow eutrophic systems (Lake Carmi and Missisquoi Bay). Legacy P dynamics in the unmanipulated systems were compared to Lake Carmi during aeration. In‐situ high frequency water column monitoring along with water and sediment sampling was used to study P dynamics in response to changing lake conditions and aeration. Despite both systems exhibiting P mobility controlled by iron redox cycling, we observed distinct differences in the spatial extent and drivers of internal P loading. Legacy P loading was controlled by seasonal drivers in Lake Carmi, but by spatially variable and highly transient wind driven forcing of hydrodynamics in Missisquoi Bay. Aeration altered the mixing regime of Lake Carmi and shifted loading dynamics to frequent wind‐driven pulses of legacy P to surface waters akin to those of Missisquoi Bay. Mean hypolimnetic dissolved oxygen increased with aeration, but greater oxygen demand rates and periods of anoxia under transient stratification still resulted in internal P loading. Surface P concentrations were higher in summer months with aeration compared to previous years. This research illustrates the dynamic nature of legacy P behavior within and between shallow eutrophic lakes and the challenges in addressing this common water resources threat. Plain Language Summary Shallow lakes with high amounts of nutrients like phosphorus often experience worsening water quality and harmful algae blooms. Even if less phosphorus enters the lake from the watershed, phosphorus already in the lake can cycle between the water and sediment for decades. It is important to understand how phosphorus moves within lakes to make management decisions. We studied what causes the release of phosphorus from sediment in Lake Carmi and Missisquoi Bay, Lake Champlain. These observations were compared to Lake Carmi during 4 years of whole‐lake aeration designed to limit phosphorus release. We found that the release of phosphorus at both study sites was tied to chemical reactions of iron. The timing of this release was controlled by seasonal changes in Lake Carmi before aeration, and by frequent wind‐driven mixing in Missisquoi Bay. Aeration changed the timing of mixing in Lake Carmi but did not decrease the amount of phosphorus recycled from the sediment. Aeration also increased the rate of oxygen consumption in Lake Carmi which quickly led to phosphorus release during periods of calm wind. This research shows the highly dynamic nature of phosphorus behavior within shallow lakes which is important to understand when making management decisions. Key Points Legacy phosphorus mobility was driven by either episodic wind‐mediated mixing or seasonal turnover in two proximal shallow eutrophic systems Aeration altered hydrodynamics to change from seasonal to wind‐driven internal loading of legacy phosphorus, but it was not suppressed Heterogeneous spatiotemporal controls on internal legacy phosphorus loading present challenges to achieving water quality goals

Artificial reefs are now commonly used as a tool to restore degraded coral reefs and have a proven potential to enhance biodiversity. Despite this, there is currently a limited understanding of ecosystem functioning on artificial reefs, and how this compares to natural reefs. We used water sampling (bottom water sampling and pore water sampling), as well as surface sediment sampling and sediment traps, to examine the storage of total organic matter (as a measure of total organic carbon) and dynamics of dissolved inorganic nitrate, nitrite, phosphate and ammonium. These biogeochemical parameters were used as measures of ecosystem functioning, which were compared between an artificial reef and natural coral reef, as well as a degraded sand flat (as a control habitat), in Bali, Indonesia. We also linked the differences in these parameters to observable changes in the community structure of mobile, cryptobenthic and benthic organisms between habitat types. Our key findings showed: (1) there were no significant differences in inorganic nutrients between habitat types for bottom water samples, (2) pore water phosphate concentrations were significantly higher on the artificial reef than on both other habitats, (3) total organic matter content in sediments was significantly higher on the coral reef than both other habitat types, and (4) total organic matter in sediment traps in sampling periods May and September were higher on coral reefs than other habitats, but no differences were found in November. Overall, in terms of ecosystem functioning (specifically nutrient storage and dynamics), the artificial reef showed differences from the nearby degraded sand flat, and appeared to have some similarities with the coral reef. However, it was shown to not yet be fully functioning as the coral reef, which we hypothesise is due its relatively less complex benthic community and different fish community. We highlight the need for longer term studies on artificial reef functioning, to assess if these habitats can replace the ecological function of coral reefs at a local level.

This study introduces an integrated sand transport model that considers wave and current actions alongside variable grain properties to explore sediment dynamics in river deltas. The research delves into a case study of a river delta region, examining sediment transport over a substantial stretch of the river's lower course. The study incorporates topographic data, sediment sampling, and remote sensing to validate the model against observed suspended sediment concentrations at a key monitoring station. The results reveal substantial sediment deposition in both the estuary and lower reaches of the river, influenced by hydrodynamic conditions and geological settings. Deposition patterns in the estuary are primarily driven by coastal currents and wave action, while river channel deposition is linked to river constriction and flow velocity variations. The study demonstrates that the residual current in the region consistently flows towards a nearby bay, suggesting that sediment in the lower reaches of the river will be directed by this residual flow. The study underscores the pivotal roles of current and wave action in sediment transport within a multi-branched estuary characterized by low sediment concentrations, which can inform coastal management and environmental planning.