Resuspension Of Surface Sediments Research Articles

Spatial distribution and influencing mechanism of CO2, N2O and CH4 in the Pearl River Estuary in summer

Estuaries, considered as the important carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) sources to the atmosphere, are increasingly affected by near-bottom hypoxia. However, the impact of estuarine hypoxic zone development on GHGs production and discharge remains poorly understood due to the seasonal and spatially distributed heterogeneity of estuarine hypoxia occurrence and the lack of simultaneous monitoring of the distribution of bottom hypoxic waters and the vertical distribution of GHGs. Here, we conducted high spatial resolution vertical stratification sampling and analysis of water column GHGs in the Pearl River Estuary (PRE), a large estuary with frequent hypoxia in recent years. Our results showed that Pearl River runoff is the main source of GHGs in the PRE. Strong nitrification is an important N2O production mechanism in the PRE. In situ generation of water and resuspension of surface sediments were the main sources of CH4 in bottom water, while massive organic matter (OM) mineralization is the main driver of CO2 in bottom water. The development of a hypoxic zone in the PRE significantly increased the concentration of N2O and CH4 in the bottom water and thus increased air-water fluxes. The air-water fluxes of N2O, CH4 and CO2 of PRE in summer were 31.9 ± 7.5 μmol m−2 d−1, 192.5 ± 229.4 μmol m−2 d−1 and 51.9 ± 14.1 mmol m−2 d−1, respectively. This study reveals that GHGs fluxes from estuarine waters to the atmosphere will increase significantly with increasing eutrophication caused by human activities and the expansion of hypoxic zones in estuarine waters.

Isoprenoid tetraether lipids in suspended particulate matter from the East China Sea and implication for sedimentary records

A total of 90 samples of suspended particulate matter (SPM) collected in surface waters of the East China Sea (ECS) in summer and winter were studied for archaeal isoprenoid glycerol dialkyl glycerol tetraether lipids (iGDGTs) and the derived sea surface temperature (SST) proxy, i.e. TEX86H. Our data showed that in summer SPM TEX86H correlated well with in-situ measured SST, but in winter the relationship became much poorer. We found that the bottom water depth (BWD) of 70 m was a critical depth when studying the TEX86H-SST relationship in winter SPM. In locations with BWD < 70 m, concentrations of iGDGTs in SPM were > 5x higher in winter than in summer, but TEX86H showed a much weaker correlation with in-situ measured SST. This was speculated to be caused by lateral transport of SPM and resuspension of surface sediments in winter due to strong winds. Whereas in locations with BWD > 70 m, TEX86H correlated well with in-situ measured SST, suggesting a minor influence of SPM lateral transport and sediment resuspension. Moreover, although only core iGDGTs were analyzed, we found that both summer and winter TEX86H values correlated better with in-situ measured SST than with seasonal and annual mean SST, suggesting that SPM iGDGTs were dominantly produced around the sampling time rather than encompassing longer time input. The linear relationships of SPM TEX86H with in-situ measured SST were different between winter (BWD > 70 m) and summer, likely due to seasonal archaeal community change. Published sedimentary TEX86H data in the ECS were reexamined here, and a BWD of 70 m was also found to be a critical depth. At sites with BWD > 70 m, TEX86H in sediments correlated well with annual mean SST, whereas the correlation became poor at BWD < 70 m, suggesting that sedimentary GDGTs were also greatly influenced by resuspension and lateral transport, and hence complicating the application of the proxy to shallow locations in the ECS.

Sediment size fractionation and focusing in the equatorial Pacific: Effect on 230Th normalization and paleoflux measurements

AbstractWe use flux, dissolution, and excess 230Th data from the Joint Global Ocean Flux Study and Manganese Nodule Project equatorial Pacific study Site C to assess the extent of sediment focusing in the equatorial Pacific. Measured mass accumulation rates (MAR) from sediment cores were compared to reconstructed MAR by multiplying the particulate rain caught in sediment traps by the 230Th focusing factor and subtracting measured dissolution. CaCO3 MAR is severely overestimated when the 230Th focusing factor correction is large but is estimated correctly when the focusing factor is small. In contrast, Al fluxes in the sediment fine fraction are well matched when the focusing correction is used. Since CaCO3 is primarily a coarse sediment component, we propose that there is significant sorting of fine and coarse sediments during lateral sediment transport by weak currents. Because CaCO3 does not move with 230Th, normalization typically overcorrects the CaCO3 MAR; and because CaCO3 is 80% of the total sediment, 230Th normalization overestimates lateral sediment flux. Fluxes of 230Th in particulate rain caught in sediment traps agree with the water column production‐sorption model, except within 500 m of the bottom. Near the bottom, 230Th flux measurements are as much as 3 times higher than model predictions. There is also evidence for lateral near‐bottom 230Th transport in the bottom nepheloid layer since 230Th fluxes caught by near‐bottom sediment traps are higher than predicted by resuspension of surface sediments alone. Resuspension and nepheloid layer transport under weak currents need to be better understood in order to use 230Th within a quantitative model of lateral sediment transport.

Characteristics of Suspended Sediment and Resuspension Process in Wendeng Coastal Area, Shandong Peninsula

Based on the field observations and laboratory analysis data of the suspended sediment of Wendeng coastal area, this paper studied the change process of suspended sediment concentration and characteristics of surface sediment resuspension in the study area. In results: (1) In vertical, the suspended sediment concentration of each station increased gradually from surface to bottom, and the maximum value could reach 0.11 kg/m3; (2) Suspended sediment concentration is well correlated with velocity variation in a tidal cycle, and the peak of suspended sediment concentration occurs four times in a tidal cycle, indicating that there are four resuspension processes during a tidal cycle in the study area; (3) According to the suspended sediment concentration at different times and the content of the previous time, the maximum settlement is between 0.063~0.092kg/m3, and the maximum resuspension is between 0.057~0.125kg/m3 in the study area.

Effect of a physical disturbance event on deep-sea nematode community structure and ecosystem function

Numerous studies have been conducted on the effect of physical disturbance on shallow water benthic communities, but there is a paucity of data from deep-sea environments. We conducted a laboratory experiment using undisturbed sediment cores from Chatham Rise (water depth=345m), Southwest Pacific, to investigate the effects of a physical disturbance event (resuspension of surface sediments) on sediment characteristics (sediment grain size, pigment content), nematode community attributes (abundance, diversity, community structure) and ecosystem function (sediment community oxygen consumption (SCOC)) over a period of 9days. Disturbance did not have any noticeable impact on sediment characteristics, SCOC, or nematode species richness, but led to changes in vertical distribution patterns and shifts in nematode community structure. The magnitude of disturbance-related effects was, however, much smaller than the effect of sediment depth (0–1, 1–3, and 3–5cm), and the main impact of disturbance on nematode vertical distribution patterns and community structure appeared to be related to a vertical re-shuffling of nematodes in the sediments rather than mortality. We did not observe substantial increases in the abundance of nematode genera generally regarded as disturbance-tolerant, such as Sabatieria. The worst-affected species belongs to the Stilbonematinae, a group of typically long and slender nematodes that may be easily damaged by physical disturbance. The limited impact of physical disturbance on benthic community structure and function suggests that the Chatham Rise nematode community is relatively resilient to sediment resuspension. This resilience may have arisen from frequent exposure to disturbance in the field (e.g., from strong currents), or may be a more widespread feature of nematode communities.

Experimental study on sediment resuspension in taihu lake under different hydrodynamic disturbances

Contaminants resuspension in sediments induced by wind-wave could influence the water quality in shallow lakes. Resuspension of surface sediments from the Zhushan Bay, Taihu Lake was simulated under different wind forcing by using a pneumatic annular flume in this study. Acoustic Doppler Velocimeter (ADV) was used to measure flow velocity at each wind speed, and the characteristics of sediment resuspension were studied with the layered sampling technology. The experimental results show that the flow velocity increases with wind speed obviously and 6m/s is a critical wind speed which affected hydrodynamic conditions significantly. The distribution of flow velocity and water depth is different from that in ordinary open channel. With the enhanced hydrodynamic factors, the Suspended Solids Concentration (SSC) in water increases accordingly, and the incipient velocity of sediment resuspension is about 0.21 m/s. Based on the analysis of wind speed and average SSC in water column, the quantitative relationship is obtained. The SSC of the bottom layer is higher than the content of surface layer under different hydrodynamic conditions, and there are similar distributions between SSC and flow velocity in different water layers.

Environmental impacts of coastal fish farming: carbon and nitrogen budgets for trout farming in Kaldbaksfjør7%%FONT_ERR%%ur (Faroe Islands)

Flow of organic carbon (OC) and nitrogen through a sea cage trout farm was calculated on the basis of detailed studies of the farming operation, water circulation, OC and nutrient transport and recycling processes in sediment. A third of the OC and nitrogen provided by fish food was incorporated into fish biomass, which is more than has been found in previous studies. Most OC input was respired by the fish (52 to 70%), and ~63% of the associated nitrogen was lost as dissolved inorganic nitrogen (DIN), potentially stimulating pelagic primary production. Approx. 6% of carbon and 5% of nitrogen derived from fish food settled on the seabed, where it was either mineralized or accumulated in the sediment. Based on transect measurements of diagenetic activity, the farm footprint was found to cover an area ~10 times the farm area. OC mineralization in the sediment increased linearly with increasing food input; the divergence between carbon efflux and oxygen uptake in sediment likewise increased with increasing food input, reflecting an increasing level of sediment reduction. Directly below the farm, the dissolved organic carbon (DOC) efflux was high (on average 53% of dissolved inorganic carbon efflux), indicating that DOC efflux is an important pathway for benthic carbon release below aquaculture farms. Overall, microbial processes removed 56 and 38% of OC and nitrogen, respectively, that settled to the seabed. During a 39 d break in farming activity, due to the combined effect of mineralization and resuspension of surface sediment, sediment conditions improved considerably.

Deposition and fate of reactive Fe, Mn, P, and C in suspended particulate matter in the Bay of Biscay

Hydrographic structure of the water column, dissolved nutrient concentrations and the distribution of suspended particulate matter were recorded from CDT measurements and Niskin bottles sampling on the continental slope of the Bay of Biscay and on the axis of Capbreton canyon. Ascorbate extraction was applied here for the first time on marine suspended particles to determine the content of reactive Fe- and Mn-oxides, and P associated with Fe-oxides. Hydrographic structure of the south-eastern part of the Bay of Biscay did not change during the last three decades. Particulate organic carbon (POC) contents dropped strongly with depth, showing that organic matter mineralization was efficient in the water column. Organic matter mineralized in the water column had a Redfield N:P ratio. POC percent of particles collected at depth were higher during a bloom period, suggesting that some new organic matter reached the bottom. Contents of Fe and Mn extracted with the ascorbate leaching solution showed that suspended particles originated from the Gironde estuary, one of the major sources of particles in the Bay of Biscay. Intermediate and deeper nepheloid layers occurred in the Capbreton canyon. Particles of nepheloid layers were enriched in Mn- and Fe-oxides because they originated from resuspension of surface sediment.

Optimised recovery of lignin-derived phenols in a Scottish fjord by the CuO oxidation method

Lignin is found only in vascular plant tissues, hence monitoring of lignin in aquatic environments is important in the determination of the sources and fate of terrestrial organic matter (OM). Concentrations of lignin-derived phenols provide an estimate of the amount of terrestrial OM in a system. Other lignin parameters such as the ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) phenols provide information on vegetation sources; and the ratios of vanillic acid to vanillin, (Ad/Al)v, and syringic acid to syringaldehyde, (Ad/Al)s, indicate the degradation stage of lignin materials. Concentrations of lignin-derived phenols were determined for the surface and subsurface sediments of a Scottish sea loch, Loch Creran, using a CuO oxidation method. In order to achieve the highest methodological efficiency, a series of validation experiments for each procedural step were carried out. As a result, several procedural steps were optimized. It was found that a lower oxidation temperature resulted in higher product yield and the duration and temperature of the silylation step have no effect on the outcome of the process. Studies of seasonal variations of lignin parameters showed that the occasional increase in lignin content in sediment trap samples was attributable to materials discharged from River Creran and the incoming water from the direction of Creagan bridge. The flow regime caused resuspension of surface sediments and entrainment of lignin materials into the water column. Lignin parameters exhibited more significant trends across an axial transect of the loch (from the head to mouth). Total lignin content decreased and the C/V ratios increased from upper to lower Loch Creran as these lignin materials were transported further down the loch and were subjected to hydrodynamic sorting processes.

The role and distribution of total suspended solids in the macrotidal coastal waters of Korea

Spatial and temporal distribution patterns of total suspended solids (TSS) in the shallow and macrotidal regions of the Korean peninsula indicated there were significant changes in TSS concentrations. These were seasonally influenced by the wind, river input and tidal cycle. There were high TSS values at estuarine and river mouth stations and during low tide due to the re-suspension of bottom sediment by strong wind action during winter months, in addition the land input through rivers and strong tidal current during ebbing. Monthly mean values of TSS significantly correlated with wind speed and nitrate concentration (p < 0.01). This indicated that the resuspension of surface sediment was a more important source of TSS than the river input, and that nitrate was introduced into the water column during the resuspension process. TSS were seven times higher at low tide than in high tide. Light penetration was significantly inhibited by TSS; as >98% of incident light was absorbed within 2 m and zero photosynthetically active radiation (PAR) under 2 m in the estuarine stations during winter. Removal of heavy metals and nutrients by TSS in the water column was evident. Over 80% of the initial concentration of nutrients was removed within 10 min under various concentrations of TSS and also TSS contained significantly higher concentration of heavy metals than surface sediment. The concentration levels of nutrients and chemical oxygen demand in the west coast were comparable with the East and South Sea, even the major rivers in the Korean peninsula flow into the West Sea with major pollutant loadings into the coastal areas. High concentration of TSS is likely to contribute to the removal process of these pollutants, resulting in relatively lower levels of nutrients and organic materials in these coastal waters.

Silicic acid enrichment in the deep water of the Faeroe–Shetland Channel

To evaluate the relative contribution of continental slope sediments, resuspended particles and settling material to the refuelling of dissolved silica in a high-energy environment, a study was conducted in the Faeroe–Shetland Channel (FSC), one of the main pathways of the newly formed Atlantic Deep Water. Fluxes of silicic acid (DSi) to the water column determined by multiplying the DSi concentration gradient by the vertical eddy diffusion coefficient showed a maximum at mid-slope (600–800 m) with values reaching up to 1700 μmol m−2 d−1 near the seabed. The mere dissolution of settling biogenic silica, estimated at 30–120 μmol m−2 d−1, cannot account for this refuelling of the deep-waters of the FSC with DSi. Benthic DSi effluxes on the slope, obtained both from incubations and from modeling pore water DSi profiles, indicated higher fluxes at mid-depth which corresponds to a zone of enhanced deposition and higher biogenic silica content. Contribution of DSi from benthic fluxes range from 370 to 740 μmol m−2 d−1 and can, to a large extent, sustain the enhanced calculated flux in the water column. Furthermore, the recurrent resuspension of bottom material, as observed at mid-slope being associated with turbulent flow, contributes to the increase in DSi concentrations in the deep water of the FSC with fluxes ranging from 60 to 800 μmol m−2 d−1. Our data illustrate the importance of the geomorphological setting of the basin which, with its shallow depth, funnel shape and turbulent conditions, favors the erosion and resuspension of surface sediment and the deposition of relatively fresh sediments at mid-slope, hence focusing the refuelling of passing waters with DSi.

Silicic acid enrichment in the deep water of the Faeroe–Shetland Channel

To evaluate the relative contribution of continental slope sediments, resuspended particles and settling material to the refuelling of dissolved silica in a high-energy environment, a study was conducted in the Faeroe–Shetland Channel (FSC), one of the main pathways of the newly formed Atlantic Deep Water. Fluxes of silicic acid (DSi) to the water column determined by multiplying the DSi concentration gradient by the vertical eddy diffusion coefficient showed a maximum at mid-slope (600–800m) with values reaching up to 1700μmolm−2d−1 near the seabed. The mere dissolution of settling biogenic silica, estimated at 30–120μmolm−2d−1, cannot account for this refuelling of the deep-waters of the FSC with DSi. Benthic DSi effluxes on the slope, obtained both from incubations and from modeling pore water DSi profiles, indicated higher fluxes at mid-depth which corresponds to a zone of enhanced deposition and higher biogenic silica content. Contribution of DSi from benthic fluxes range from 370 to 740μmolm−2d−1 and can, to a large extent, sustain the enhanced calculated flux in the water column. Furthermore, the recurrent resuspension of bottom material, as observed at mid-slope being associated with turbulent flow, contributes to the increase in DSi concentrations in the deep water of the FSC with fluxes ranging from 60 to 800μmolm−2d−1. Our data illustrate the importance of the geomorphological setting of the basin which, with its shallow depth, funnel shape and turbulent conditions, favors the erosion and resuspension of surface sediment and the deposition of relatively fresh sediments at mid-slope, hence focusing the refuelling of passing waters with DSi.

Sedimentation of planktonic foraminifera in the East China Sea: evidence from a sediment trap experiment

The particle flux from sediment traps moored in the East China Sea from the continental shelf to the Okinawa Trough between 25 February 1993 and 22 February 1994 was analyzed for particle transport processes based on planktonic foraminifera. Conventional sediment traps were moored at points from the continental shelf to the shelf edge. These experiments revealed that benthic foraminifera occurred along with planktonic foraminifera, with contained mud, particularly in sediment traps moored at 10–40 m above the bottom. This finding implies that surface sediment resuspension from the sea bottom is active in this region. In addition, time-series sediment traps were deployed in the Okinawa Trough at three depths (606, 813 and 1017 m) under the main stream of the Kuroshio Current. The total planktonic foraminiferal flux increased with increasing depth and was associated with very few benthic foraminiferal specimens in the two deeper traps. However, planktonic foraminiferal tests filled with mud as seen in traps on the continental shelf were not found in the three traps. This observation suggests that the planktonic foraminifera did not originate in the sediments of the continental shelf and were likely carried laterally during settling. Furthermore, based on comparing the species composition of the foraminiferal flux for the Okinawa Trough station with that for the shelf edge in late October, planktonic foraminifera were considered to arrive at the deeper traps in the Okinawa Trough from the Kuroshio front area which was characterized by high productivity.

The effect of resuspension on chemical exchanges at the sediment-water interface in the deep sea — A modelling and natural radiotracer approach

Abstract We review the processes responsible for the formation of vertical gradients in the chemical composition of suspended particles across the benthic nepheloid layer. Such gradients have usually explained by resuspension of surface sediments, but it is shown here that these gradients can only be understood as part of a dynamic exchange between the water column and the sediments. A coupled model, developed in a companion paper, is expanded to include chemical reactions above and below the sediment-water interface. Three cases are discussed: A tracer with first-order decay (Model 1), the dissolution of a major constituent (Model 2), and a particle-reactive tracer with first-order decay and production in the water column (Model 3). Using typical parameter values for a well-developed benthic nepheloid layer, the three models reproduce typical distributions of C org (organic carbon), opal, and 234 Th, respectively, on particles above and below the sediment-water interface. Sensitivity analyses illustrate how bioturbation can cause the large discrepancy observed between suspended and surface sediment C org values (Model 1). The model also reconciles this observed discrepancy with observations that the major part of the decomposition takes place within the sediment. For opal (Model 2), the influence of resuspension on the burial rate of opal is shown to be negligible, as long as dissolution follows first-order kinetics and is not enhanced by turbulence in the suspended phase. The modelling of 234 Th (Model 3) successfully links the depletion of 234 Th in bottom waters with the distribution of excess 234 Th in surface sediments and on resuspended particles. 234 Th is a powerful example of the tools supplied by the radioactive daughters of the natural U and Th decay series in studying fluxes and exchange rates of solutes and particles across the sediment-water interface. A short review is given of these tools, and it is shown how they can be used to obtain rate information required to apply and calibrate specific resuspension models.

Polychlorinated biphenyl pollution caused by resuspension of surface sediments in the lagoon of Venice

A mechanical device was used to reproduce in the laboratory the sediment resuspension caused by tidal currents and wind waves in the lagoon of Venice. Shear stresses comparable to those observed in the field were applied to the sediment surface. Series of experiments were run at 6.6 and 9.0 dyn/cm 2. The concentrations of polychlorinated biphenyls (PCBs) were determined in the sediments and resuspended particulate matter by means of gas chromatographic techniques. At the two different stresses, particulate matter with different grain size and different concentrations of PCBs was resuspended. However, no significant differences were observed in the amounts of PCBs mobilized per litre of water. In fact, by increasing the applied stress, coarser particulate matter was resuspended with a lower concentration of PCBs per unit of dry weight.