Sediment Traps

The natural Park of Peñalara consists of a small mountainousarea near Madrid and includes a series of water bodies (fromsmall mountain lakes to temporary ponds and peat bogs), the mostknown of them being the so-called `Laguna Grande dePeñalara'. Due to growing numbers of visitors theenvironmental conditions of this lake started to decline in theearly 1970s because of: (1) the start

Molybdenum (Mo) isotope studies in black shales can provide information about the redox evolution of the Earth's oceans, provided the isotopic consequences of Mo burial into its major sinks are well understood. Previous applications of the Mo isotope paleo-ocean redox proxy assumed quantitative scavenging of Mo when buried into sulfidic sediments. This paper contains the first complete suite of Mo isotope fractionation observations in a sulfidic water column and sediment system, the meromictic Lake Cadagno, Switzerland, a small alpine lake with a pronounced oxygen-sulfide transition reaching up to H 2 S $ 200 lM in the bottom waters (or about 300 lM total sulfide: RS 2À = H 2 S + HS À + S 2À ). We find that Mo behaves conservatively in the oxic zone and non-conservatively in the sulfidic zone, where dissolved Mo concentrations decrease from 14 nM to 2-8 nM across this transition. Dissolved Mo in the upper oxic waters has a d 98 Mo oxic = 0.9 ± 0.1&, which matches that of the riverine input, d 98 Mo river = 0.9 ± 0.1&. In the deeper sulfidic waters, a subaquatic source delivers Mo at 1.55 ± 0.1&, but the dissolved Mo is even heavier at d 98 Mo sulfidic = 1.8&. Sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in Mo with depth, with d 98 Mo values significantly fractionated at À0.8& to À1.2& both near the chemocline and in the deepest trap. Suspended particulates in the sulfidic waters carry lighter Mo than the ambient dissolved Mo pool by $0.3-1.5&. Sedimentary Mo concentrations correlate with total organic carbon and yield Mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area. Solid-phase Mo in the sediment shows a slightly positive d 98 Mo trend with depth, from d 98 Mo = 1.2& to 1.4& while the pore waters show dramatic enrichments of Mo (>2000 nM) with a relatively light isotope signature of d 98 Mo = 0.9-1.0&.

This paper summarizes our results on the changes in pelagic calci"cation and the standing stock of calcium carbonate associated with the SW Monsoon and NE Monsoon (cruises TN049 and TN053 of the U.S. JGOFS study, respectively) in the northern portion of the Arabian Sea. Mean calci"cation was &3X greater during the SW Monsoon than during the NE Monsoon. Calci"cation per coccolithophore was 7}10X higher, and the ratio of calci"cation to photosynthesis (C/P) was 40}45% higher during the SW Monsoon. The turnover time of PIC was not statistically di!erent between the two cruises (&4.5 d averaged over the euphotic zone). Turnover time of POC increased signi"cantly between TN049 and TN053 (from &3 to 6 d over the euphotic zone). We discuss vertical sections of coccolithophore abundance, carbon standing stocks and carbon "xation. Coccolithophore calci"cation was usually about 1}5% of community photosynthesis. The ratio of calci"cation to photosynthesis spanned almost 2 orders of magnitude, and was not signi"cantly di!erent from the ratio of the PIC and POC standing stocks. We compare surface PIC and POC production rates to sediment trap #uxes from the same region.

We compared the community structure of benthic algae inside and outside pomacentrid damselfish (Stegastes nigricans) territories in a moat at Sesoko Island, Okinawa, Japan. S. nigricans maintained ''algae farms'' that were dominated by the filamentous rhodophyte, Womersleyella setacea. Species richness and biomass were higher inside damselfish territories than outside, while species diversity and evenness were higher outside. Detrended correspondence analysis (DCA) based on species composition showed that the dominance of W. setacea was maintained throughout the year in all samples collected from inside damselfish territories. The observed strong dominance of filamentous rhodophytes was consistent with the findings of most studies on damselfish territories worldwide. However, the dominance of a single species of alga and low species diversity inside the territories was in contrast to the findings of previous studies, in which the reduction of grazing pressure caused intermediate disturbance and enhanced algal species diversity. This discrepancy in algal species diversity inside the damselfish territories seems to have been caused by unique characteristics of the alga and the fish. W. setacea traps sediment, which reduces the availability of firm substrata for attachment and inhibits the recruitment of some algae. Moreover, S. nigricans ''weeds'' indigestible calcareous and thicker algae. The algal assemblage outside damselfish territories varied among samples, and included mat-forming cyanophytes (Calothrix aeruginosa and Calothrix codicola), a prostrate laminar phaeophyte (Padina sp.), thin and small-scaled algae (Cladophora sp. and Feldmannia indica), finely branched filamentous rhodophytes (Taenioma perpusillum and Herposiphonia obscura), and a coarsely branched rhodophyte (Gelidiopsis variabilis).

Sediment core samples from the Santa Monica (SM) Basin generaily contain three times as much DDEs (0,~' and p,p') as DDTs. Total DDTs (C o&-DDE,-DDD and-DDT and p&-DDE,-DDD and-DDT) are relatively higher in some cores than in others in nearsurface horizons. Further, the ratios of o,p'-DDT [l,l,l-trichloro-2(o-chtorophenyl)-2(p-chlorophenyl) ethanel to p,p'-DDT [l,l,l-trichloro-2,2-bis(p-chlorophenyl) ethanel in some slope samples (0.43-0.87) and that of a tar cake (0.90) from Dumpsite II, San Pedro (SP) Basin are significantly higher than that observed in caustic waste from a DDT factory discharged into the southern California sewers or technical grade DDT (O-2-0.3). This observation and the fact that o,p'-DDT metabolizes more readily than the p.p'-isomer, suggest that at least part of the DDTs, in the sediments could not have originated from the above two sources. The unique DDT signature of the samples is probably characteristic of the acid wastes of the DDT factory discharged along with refinery wastes into the Dumpsites I and II. The discharged wastes could have entered SM and SP Basins from the dumpsites. Or, more likely, in the absence of precise records before 1961, industrial wastes could have been 'short-dumped' in nearshore regions. This could explain the unique DDT profiles from the slope sediments. In contrast, the central basin cores document the history of wastewater input. Thus o,p'/p,p' DDT ratio could potentially be diagnostic of their sources. Contaminants have apparently migrated in the sediment column by both upward and downward diffusion. The presence of the refractory metabolites in sediment trap particles suggests upward diffusion and resuspension.

Particle fluxes measured continuously for one year at three locations in the Arabian Sea using time-series sediment traps show that lithogenic sedimentation processes are strongly coupled to biological processes. The vertical flux of lithogenic matter is controlled by episodic production and fluxes of biogenic matter.

Sediment traps were deployed on the Northwest Shelf (NWS) of Australia in November 1996, to determine fluxes of organic matter and inorganic elements from the photic zone to deeper waters in a transect extending from Exmouth Shelf to Exmouth Plateau. Infiltrex II water samplers collected particulate and dissolved organics from the water column near the trap sites. Surface sediments and sediment cores were also collected over the study region. Lipid biomarkers were used to determine the sources of organic carbon and its cycling processes on the NWS.Dry weight fluxes from the traps ranged from 124 to 616 mg m−2 day−1and particulate organic carbon (POC) fluxes ranged from 22 to 42 mg m−2 day−1. The biogenic lipids consisted of biomarkers indicative of marine zooplankton, phytoplankton and bacteria, plus traces of land plant markers. A large contribution of unresolved complex material (UCM), which is indicative of petroleum, was detected at four times the biogenic hydrocarbon flux at shallow stations, and up to seven times the biogenic hydrocarbon flux at the most offshore station.There is essentially no river input, and only trace aeolian-derived material to contribute to primary production on the NWS of Australia. Most of the organic matter produced are rapidly recycled in the water column and the small fraction of lipids that settle to the sediments is already partially degraded and undergoes further rapid degradation in the surface sediments. Natural oil seeps also provide utilisable organic carbon to the system. The production and vertical flux rates of organics determined in this study are comparable to those reported in studies of shallow traps in oceanic areas from long-term studies in the Arabian Sea, and other coastal margins such as the Bay of Biscay (France) and California (USA).In offshore areas, most “living” lipid materials passed through the GFF filters thus invalidating POC estimates based on high volume sampling. To adequately assess living (particulate) carbon, gentle filtration of low volume seawater samples is more accurate, as shown by this solid phase absorption study of individual lipid biomarkers.

To evaluate the role of the sediment in the high primary production of a tropical coastal lagoon, "Ciénaga Grande de Santa Marta" (Caribbean, Colombia), the flux of nitrogen and phosphorous (dissolved, inorganic, particulate) in the water-sediment boundary was measured. From 1996 to 1997 sediment cores were incubated in the laboratory and sediment traps were deployed in the field, in two

Recent studies have confirmed the relationship between iron supply and phytoplankton growth rates in all three high-nitrate low-chlorophyll (HNLC) oceanic provinces. However, there is little evidence, so far, of the role of iron in altering the efficiency of the biological pump via increased downward export of particulate organic carbon (POC). The NE subarctic Pacific is unique among HNLC regions in that long time series pelagic observations and deep-moored sediment trap records exist which may provide the best opportunity thus far to test aspects of the iron hypothesis. Episodic elevated levels of chlorophyll a ( > 2.0 [tg L -l) were observed 6 times between 1964 and 1976 at the former site of Ocean Station Papa (OSP). In addition, between 1984 and 1990 on at least three occasions, concurrent pulses of POC and biogenic silica were recorded in deep-moored traps at OSP. Possible explanations for these events, such as lateral advection of more productive waters, iron-mediated blooms, or grazing by salp swarms are discussed and tested using an existing downward POC flux model. Owing to the episodic nature of such events, no available data are sufficiently comprehensive to unequivocally rule out any of these explanations. Nevertheless, from the data available, the occurrence of pelagic or deep water pulses, approximately once every 3 years, are most consistent with iron-mediated diatom blooms, and of the sinking of POC and biogenic silica (from such a bloom) to depth, respectively. A comparison of the timing of these iron-mediated pulses with that of the transport probabilities of atmospheric dust supply from Asia and Alaska provides an opportunity to assess the likelihood of a coupling between the atmosphere and the ocean.

We compared the community structure of benthic algae inside and outside pomacentrid damselfish (Stegastes nigricans) territories in a moat at Sesoko Island, Okinawa, Japan. S. nigricans maintained ''algae farms'' that were dominated by the filamentous rhodophyte, Womersleyella setacea. Species richness and biomass were higher inside damselfish territories than outside, while species diversity and evenness were higher outside. Detrended correspondence analysis (DCA) based on species composition showed that the dominance of W. setacea was maintained throughout the year in all samples collected from inside damselfish territories. The observed strong dominance of filamentous rhodophytes was consistent with the findings of most studies on damselfish territories worldwide. However, the dominance of a single species of alga and low species diversity inside the territories was in contrast to the findings of previous studies, in which the reduction of grazing pressure caused intermediate disturbance and enhanced algal species diversity. This discrepancy in algal species diversity inside the damselfish territories seems to have been caused by unique characteristics of the alga and the fish. W. setacea traps sediment, which reduces the availability of firm substrata for attachment and inhibits the recruitment of some algae. Moreover, S. nigricans ''weeds'' indigestible calcareous and thicker algae. The algal assemblage outside damselfish territories varied among samples, and included mat-forming cyanophytes (Calothrix aeruginosa and Calothrix codicola), a prostrate laminar phaeophyte (Padina sp.), thin and small-scaled algae (Cladophora sp. and Feldmannia indica), finely branched filamentous rhodophytes (Taenioma perpusillum and Herposiphonia obscura), and a coarsely branched rhodophyte (Gelidiopsis variabilis).

Purpose At the land-ocean interface, large river deltas are major sinks of sediments and associated matter. Over the past decennia, many studies have been conducted on the palaeogeographic development of the Rhine delta and overbank deposition on the Rhine floodplains. This paper aims to synthesise these research results with special focus on the amounts and changes of overbank fines trapped in the Rhine delta and their controls at different time scales in the past, present and future. Materials and methods Sediment trapping in the Rhine delta throughout the Holocene was quantified using a detailed database of the Holocene delta architecture. Additional historic data allowed the reconstruction of the development of the river's floodplain during the period of direct human modification of the river. Using heavy metals as tracers, overbank deposition rates over the past century were determined. Measurements of overbank deposition and channel bed sediment transport in recent years, together with modelling studies of sediment transport and deposition have provided detailed insight in the present-day sediment deposition on the floodplains, as well as their controls. Results and discussion Estimated annual suspended sediment deposition rates were about 1.4×10 9 kg year -1 between 6,000 and 3,000 years BP and increased to about 2.1×10 9 kg year -1 between 3,000 and 1,000 years BP. After the rivers were embanked by artificial levees between 1100 and 1300 AD, the amount of sediment trapped in the floodplains reduced to about 1.16×10 9 kg year -1 . However, when accounting for reentrainment of previously deposited sediment, the actual sediment trapping of the embanked floodplains was about 1.86×10 9 kg year -1 . Downstream of the lower Waal branch an inland delta developed that trapped another 0.4× 10 9 kg year -1 of overbank fines. Since the width of channel was artificially reduced and the banks were fixed by a regular array of groynes around 1850, the average rates of deposition on the embanked floodplains have been 1.15×10 9 kg year -1 . Scenario studies show that the future sediment trapping in the lower Rhine floodplains might double. Conclusions The variations in amounts of sediment trapped in the Rhine delta during the past 6,000 years are largely attributed to changes in land use in the upstream basin. At present, the sediment trapping efficiency of the floodplains is low and heavily influenced by river regulation and engineering works. Upstream changes in climate and land use, and direct measures for flood reduction in the lower floodplains, may again change the amounts of sediments trapped by the lower floodplains in the forthcoming decades.

Fluxes of particulate organic carbon (POC) through the oxygen deficient waters in the eastern tropical North Pacific were found to be relatively less attenuated with depth than elsewhere in the eastern North Pacific. The attenuation coefficient (b) for the flux was found to be 0.40 versus the composite value of 0.86 determined by . To examine this further, sinking POC was collected using sediment traps and allowed to degrade in oxic and suboxic experiments. Using a kinetic model, it was found that degradation proceeded at similar rates (roughly 0.8 day Ϫ1 ) under oxic and suboxic conditions, but a greater fraction of bulk POC was resistant to degradation in the suboxic experiments (61% vs. 23%). Amino acids accounted for 37% of POC collected at 75m, but following degradation the value dropped to 17% and 16% in the oxic and suboxic experiments respectively. POC collected from 500m was 10% amino acids. The non-AA component of POC collected at 75m was not degraded under suboxic conditions, while under oxic conditions it was. These results suggest that microbes degrading OC under suboxic conditions via denitrification preferentially utilize nitrogen-rich amino acids. This preferential degradation of amino acids suggests that 9% more nitrogen may be lost via water column denitrification than is accounted for when a more "Redfieldian" stoichiometry for POC is assumed.

In this paper, we develop and apply a framework for estimating the potential global-scale impact of reservoir construction on riverine sediment transport to the ocean. Using this framework, we discern a large, global-scale, and growing impact from anthropogenic impoundment. Our study links information on 633 of the world's largest reservoirs (LRs) ( z 0.5 km 3 maximum storage capacity) to the geography of continental discharge and uses statistical inferences to assess the potential impact of the remaining >44,000 smaller reservoirs (SRs). Information on the LRs was linked to a digitized river network at 30V (latitude  longitude) spatial resolution. A residence time change (Ds R ) for otherwise free-flowing river water is determined locally for each reservoir and used with a sediment retention function to predict the proportion of incident sediment flux trapped within each impoundment. The discharge-weighted mean Ds R for individual impoundments distributed across the globe is 0.21 years for LRs and 0.011 years for SRs. More than 40% of global river discharge is intercepted locally by the LRs analyzed here, and a significant proportion ( c 70%) of this discharge maintains a theoretical sediment trapping efficiency in excess of 50%. Half of all discharge entering LRs shows a local sediment trapping efficiency of 80% or more. Analysis of the recent history of river impoundment reveals that between 1950 and 1968, there was tripling from 5% to 15% in global LR sediment trapping, another doubling to 30% by 1985, and stabilization thereafter. Several large basins such as the Colorado and Nile show nearly complete trapping due to large reservoir construction and flow diversion. From the standpoint of sediment retention rates, the most heavily regulated drainage basins reside in Europe. North America, Africa, and Australia/Oceania are also strongly affected by LRs. Globally, greater than 50% of basin-scale sediment flux in regulated basins is potentially trapped in artificial impoundments, with a discharge-weighted sediment trapping due to LRs of 30%, and an additional contribution of 23% from SRs. If we consider both regulated and unregulated basins, the interception of global sediment flux by all registered reservoirs 0921-8181/03/$ -see front matter D Global and Planetary Change 39 (2003) 169 -190 (n c 45,000) is conservatively placed at 4 -5 Gt year À 1 or 25 -30% of the total. There is an additional but unknown impact due to still smaller unregistered impoundments (n c 800,000). Our results demonstrate that river impoundment should now be considered explicitly in global elemental flux studies, such as for water, sediment, carbon, and nutrients. From a global change perspective, the long-term impact of such hydraulic engineering works on the world's coastal zone appears to be significant but has yet to be fully elucidated. D

Near-bed hydrodynamic conditions were recorded for almost one year in the Viosca Knoll area (lease block 826), one of the most well-developed cold-water coral habitats in the Gulf of Mexico. Here, a reef-like cold-water coral ecosystem, dominated by the coral Lophelia pertusa, resembles coral habitats found off the southeastern US coast and the North East Atlantic. Two landers were deployed

Purpose The sediments of Torch Lake, located in Houghton County, MI, USA, have been impacted by copper mining activity. Remediation of the site has focused on immobilizing shoreline tailing deposits. However, a large amount of copper remains in the mining-sourced sediment, and high copper concentrations persist in surface sediments. This study analyzes sediment core and sediment trap data to determine the source of copper in the surface sediments. Materials and methods Sediment cores were retrieved from the lake, sectioned into 0.5-cm to 1.0-cm slices, and analyzed for Cu (atomic absorption spectrophotometry), bulk density, and organic matter content (loss on ignition). Sedimentation rates were determined using radioisotope dating. Sediment traps were deployed throughout the lake, and the collected material was analyzed for Cu and other metals (ICP-MS). Results and discussion Radioisotope-and sediment trapderived sedimentation rates agree well. Copper concentrations in the post-mining sediment are significantly (approximately 1.5 to 2 times) greater than those in the underlying mine tailings. Current copper deposition rates, calculated from sediment trap data, are lower (∼1.5 to 2 times) than accumulation rates measured in the surface sediment of the cores.

The regional water quality of the Humber catchment was mapped for key inorganic chemical determinands using a GIS system and an extensive Environment Agency and LOIS monitoring database. The resultant maps revealed the major factors affecting the general characteristics of regional water quality. Sewage inputs from industrial and domestic sources account for the high concentration of many determinands in urban areas. The concentrations of particulate components increase in tidal zones because of sediment trapping and tidal re-suspension effects. Some determinands also exhibit localized high concentrations related to coal mine drainage, soil pollution caused by past ore mining, bedrock geology, the agricultural use of fertilizers and the ingression of seawater into the estuary. ᮊ

This review describes various studies of marine plutonium distributions, behaviour and transfer carried out at the Marine Environment Laboratory of IAEA. Plutonium in sea water is primarily present in solution as Pu(V), probably as PuO+2, and on particles in reduced form as Pu(IV), most likely as species such as adsorbed Pu(OH)4. In nearshore sediments and coastal soils, plutonium is complexed with high molecular weight humic and low molecular weight fulvic compounds. Results of oxidation state studies in the Black Sea and Norwegian fjords show that major reduction of dissolved Pu(V) occurs [to Pu(III)] in anoxic waters in association with complexation of reduced plutonium with these dissolved and colloidal humics and fulvics. The IAEA-MEL has also been active in developing and applying laboratory radiotracer methods to study rates and pathways of plutonium flux through marine organisms, particularly using the),-emitting tracer, 237Pu. Plutonium concentration factors spanning five orders of magnitude have been observed, with no significant dependence on oxidation state. Almost complete excretion of ingested plutonium by zooplankton makes their defecation an extremely important mechanism in the scavenging of plutonium from surface waters. This phenomenon has been well documentated in many field studies using time-series sediment traps to quantify and characterize elemental flux. Plutonium fluxes in the northwestern Mediterranean have recently been shown to correlate well with mass flux and suggest residence times of 24 and 3.5 years, respectively, for 239' 24°pu and 24'Am in the upper mixed layers, values which are rather longer than those measured previously. The IAEA-MEL has recently studied plutonium distributions in the vicinity of former waste dumpsites in the NE Atlantic Ocean and in the Kara Sea. The results of these surveys provide evidence of radiologically negligible but measurable leakage at the former site and of no leakage whatsoever at the latter. Computer predictions of potential future dispersion of plutonium-containing wastes from the Kara Sea suggest that the maximum possible global collective dose (30 manSv) would be extremely low. Finally, the review notes the increasing analytical contribution to environmental plutonium studies which can be made by mass-spectrometric techniques. At IAEA-MEL, the ETV-ICPMS technique along with low-level radiometric methods is being refined in order to maximize the possibility of using aquatic isotopic signals to characterize and identify nuclear source-terms.

Vetiver grass is a tall perennial tussock grass from Asia which has been used in a variety of soil conservation applications in that region. Interest in this grass outside Asia is increasing but its application is handicapped by a lack of quantitative knowledge of its flow-retarding and sediment-trapping capability. In this paper, trials aimed at a quantitative description of the hydraulic characteristics of stiff vetiver grass hedges are described. Three hedges were planted across a large outdoor flume, perpendicular to the flow. Trials were conducted at various discharges and depths. The discharge and the depths upstream and downstream of each hedge were recorded. From these data a hydraulic relationship was developed between the depths and the discharge. Finally, this relationship was used to calculate the maximum vetiver grass hedge spacing required to control soil erosion on a cultivated flood plain of low slope subject to overland flow.

Seagrass beds have traditionally been considered to act as sinks for particles due to the reduction of flow velocities by the plant canopy. Yet, there is a paucity of measurements to confirm this role. In this work we illustrate changes in flow in the presence and absence of Posidonia oceanica using an ADV, and provide direct measures of particle trapping by the use of sediment traps. We also describe a model to estimate sediment resuspension after measuring particle flux at different distances from the bottom. Measurements of particle flux are conducted parallel to the study of structural parameters of the Posidonia meadow potentially involved in both particle trapping and retention. Data obtained on velocity profiles confirm previous findings that seagrass canopies slow down current velocities with intensities proportional to the canopy height of the plants. The projected surface area of the plants (LAI) significantly correlated with the total amount of particles trapped within the Posidonia meadow, thus indicating seagrass canopy slightly increased particle trapping in the absence of resuspension. The trapping capacity of the canopy was not linearly correlated to LAI but significantly decreased at LAI above four, thus suggesting that other factors such as bending of the leaves and particle attachment to the surface may interfere with particle free sinking within the canopy at high projected surface area. The model proposed to estimate resuspension allowed to measure the retention capacity of the P. oceanica meadow, this being up to 15 times higher compared to a barren bottom during situations of high energy (large eddies reaching the bottom). The results obtained provide direct quantitative support to seagrass beds promoting sediment accretion and demonstrate a promising avenue to provide the needed empirical support for the effect of seagrasses on depositional processes.

The North Water, a large polynya in northern Baffin Bay, has an extensive period of continuous primary production lasting up to 6 months. The well-known richness of this polynya in higher trophic levels, including numerous marine mammals and birds, must be based on the magnitude and duration of that production. As part of the International North Water Polynya Study, we observed that two groups of phytoplankton were responsible for most of the primary production in 1997-1999: the large centric diatoms, Thalassiosira spp., and the smaller, colonial centric diatom, Chaetoceros socialis Lauder. We studied the phytoplankton community assemblage in the North Water

This paper presents a multiple linear regression model developed for describing global river export of sediments (suspended solids, TSS) to coastal seas, and approaches for estimating organic carbon, nitrogen, and phosphorous transported as particulate matter (POC, PN, and PP) associated with sediments. The model, with river-basin spatial scale and a 1-year temporal scale, is based on five factors with a significant influence on TSS yields (the extent of marginal grassland and wetland rice, Fournier precipitation, Fournier slope, and lithology), and accounts for sediment trapping in reservoirs. The model generates predictions within a factor of 4 for 80% of the 124 rivers in the data set. It is a robust model which was cross-validated by using training and validation sets of data, and validated against independent data. In addition, Monte Carlo simulations were used to deal with uncertainties in the model coefficients for the five model factors. The global river export of TSS calculated thus is 19 Pg yr À1 with a 95% confidence interval of 11-27 Pg yr À1 when accounting for sediment trapping in regulated rivers. Associated POC, PN, and PP export is 197 Tg yr À1 (as C), 30 Tg yr À1 (N), and 9 Tg yr À1 (P), respectively. The global sediment trapping included in these estimates is 13%. Most particulate nutrients are transported by rivers to the Pacific ($37% of global particulate nutrient export), Atlantic (28-29%), and Indian ($20%) oceans, and the major source regions are Asia ($50% of global particulate nutrient export), South America ($20%), and Africa (12%).

The central plain of Thailand was formed over the last 8-7 kyr mainly by the deltaic processes of two major rivers, the Chao Phraya and the Mae Klong. The delta plain is the third largest delta plain in Southeast Asia after that of the Mekong and the Irrawaddy. On the basis of sedimentological and paleontological analyses of samples from three boreholes and an open-pit survey, the evolution of the delta was clarified with high-resolution 14 C dating.

Borehole data from the Ganges-Brahmaputra delta system unveil an intriguing Late Quaternary history controlled by immense sediment discharge, tectonics, and eustasy. Sea level first intersected a major portion of the lowstand surface ϳ10,000-11,000 cal yr BP, marking the onset of sediment trapping and delta growth. Despite rapid sea-level rise (Ͼ1 cm/yr), sediment load was sufficient to maintain relative shoreline stability during this time. By ϳ7000 cal yr BP, accommodation was quickly infilled with slowed sea-level rise, leading to upstream channel migration and widespread dispersal of sands. This forced coastal progradation along the western delta front where the Ganges was situated, and much of the river's fine-grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf. Concurrently, Brahmaputra sediments were sequestered to an inland tectonic basin, thus starving the adjacent shoreline and leading to transgression along the eastern delta. By ϳ5000 cal yr BP, the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river-mouth estuary. Present delta configuration appears to have developed by ϳ3000 cal yr BP. Evolution of the tectonically active Ganges-Brahmaputra (G-B) system reveals important similarities and differences with other deltas. Overall facies succession follows that of basic models, progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain. However, the timing, thickness, and controls of these deposits differ. Immense sediment discharge from the Ganges and Brahmaputra rivers allowed initial delta growth 2000-3000 yr earlier than the global average, despite debouching onto a canyon-incised, high-energy margin. Subsequently, a thick (ϳ50 m) transgressive systems tract was formed during the early Holocene phase of delta aggradation, contrasting with extensive shoreline retreat documented along most margins. Highstand progradation of coastal and shelf sequences ensued by the middle Holocene, but subsiding inland basins also favored accumulation of a thick (to 40 m) highstand sequence in the lower floodplains. Unlike many other delta systems, subsidence in the subaerial G-B delta is not dominated by compaction, but rather by plate-driven tectonic processes that generate rates up to 4 mm/year. Overall, the huge sediment load, tectonic subsidence, major seismic events, and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta, shelf, and deep-sea Bengal Fan throughout the Late Quaternary. ᭧

Particulate organic carbon (POC) is vertically transported to the oceanic interior by aggregates and their ballasts, mainly CaCO 3 and biogenic opal, with a smaller role for lithogenic aerosols through the mesopelagic zone. Diel migrating zooplankton communities effect vertical transport and remineralization of POC in the upper layers of the ocean. Below 1.5 km, the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport. We normalized the fluxes of POC, CaCO 3 , and biogenic opal from data published on samples collected at 134 globally distributed, bottom-tethered, time-series sediment trap (TS-trap) stations to annual mole fluxes at the mesopelagic/bathypelagic boundary (m/b) at 2 km and defined them as F m/b C org , F m/b C inorg , and F m/b Si bio . Using this global data set, we investigated (1) the geographic contrasts of POC export at m/b and (2) the supply rate of P CO 2 to the world mesopelagic water column. F m/b C org varies from 25 (Pacific Warm Pool) to 605 (divergent Arabian Sea) mmolC m À2 yr À1 ; F m/b C inorg varies from >8 (high latitude Polar Oceans) or 15 (Pacific Warm Pool) to 459 (divergent Arabian Sea) mmolC m À2 yr À1 ; and F m/b Si bio , the most spatially/temporally variable flux, ranges from 6 (North Atlantic Drift) to 1118 (Pacific Subarctic Gyre) mmolSi m À2 yr À1 . The oceanic region exhibiting the highest POC flux over a significantly large region is the area of the North Pacific Boreal Gyres where the average F m/b C org = 213, F m/b C inorg = 126, and F m/b Si bio = 578 mmol m À2 yr À1 . F m/b C org and F m/b C inorg are particularly high in large upwelling margins, including the divergent Arabian Sea and off Cape Verde. One of the data sets showing the lowest flux over a significant region/basin is F m/b C org = 39, F m/b C inorg = 69, and F m/b Si bio = 22 mmol m À2 yr À1 in the North Pacific subtropical/tropical gyres; Pan-Atlantic average fluxes are similar except F m/b Si bio fluxes are even lower. Where C org /C inorg and Si bio /C inorg are <1 defines the ''Carbonate Ocean", and where these ratios are P1 defines the ''Silica Ocean". The Carbonate Ocean occupies about 80% of the present world pelagic ocean between the two major oceanographic fronts, the North Pacific Polar Front and the Antarctic Polar Front, and the Silica Ocean is found on the polar sides of these fronts. The total global annual fluxes of F m/b C org , F m/b Based on our global F m/b C inorg and recently estimated global primary production of PIC, 36-86 teramolC yr À1 of PIC is assumed to be dissolved within the upper 2 km of the water column.

Sediment traps in the northern and north central Bay of Bengal are characterized by highly seasonal fluxes and unusually high efficiency of organic carbon export. However, the mechanism for high export production remains under debate. To evaluate the relationships between production in the photic zone and export processes responsible for the fluxes into the traps, over an annual cycle we examine a series of indicators of production regime set in surface waters. These indicators include communities of planktic foraminifera and coccolithophores, stable isotopic chemistry of foraminifera and coccoliths, and the Sr/Ca ratios in coccoliths. Coccolith and foraminiferal assemblages confirm that the Bay of Bengal is a region of high productivity. Coccolithophore communities are dominated to an unusually high degree (90%) by the lower photic zone dweller Florisphaera profunda, a species adapted to high-nutrient and low-light conditions typical of stratified waters like those induced by the strong halocline in the Bay of Bengal. Cyclonic eddy pumping and strong winds during the southwest monsoon (SWM) increase the relative abundance of upwelling indicator species like foraminifera Globigerina bulloides and the upper photic coccolithophores Globigerina oceanica and Emiliania huxleyi. However, while upwelling and eddy pumping do coincide with high opal and coccolith export, in both traps peak organic carbon export precedes the onset of eddy pumping and upwelling indicators. These data suggest an alternate mode of production in the Bay of Bengal, which is not driven by upwelling but rather high production deeper in the water column, probably by taxa adapted to lower light levels. In both traps, the pulses of organic carbon export coincide with elevated fluxes of planktonic foraminifera, which likely reflect increased primary production. Consequently, while major export pulses of organic carbon coincide with pulses of lithogenic export, the pulses of organic carbon export are not likely to reflect simple scavenging of suspended organic carbon by lithogenic pulses. Rather, they reflect increased organic carbon production. Nonetheless, some seasonal changes increase in coccolith export efficiency during the SWM are suggested by coccolith Sr/Ca ratios. In the northern trap, coccolith carbonate export is decoupled from the main pulse of organic carbon export. Consequently, ballasting of organic carbon aggregates by coccolith carbonate does not play a major role in the seasonal cycle of organic carbon export from the photic zone to shallow (800-m) traps. r

Sediment size and supply exert a dominant control on channel structure. We review the role of sediment supply in channel structure, and how regional differences in sediment supply and landuse affect stream restoration priorities. We show how stream restoration goals are best understood within a common fluvial geomorphology framework defined by sediment supply, storage, and transport. Landuse impacts in geologically young landscapes with high sediment yields (e.g., coastal British Columbia) typically result in loss of instream wood and accelerated sediment inputs from bank erosion, logging roads, hillslopes and gullies. In contrast, northern Sweden and Finland are landscapes with naturally low sediment yields caused by low relief, resistant bedrock, and abundant mainstem lakes that act as sediment traps. Landuse impacts involved extensive channel narrowing, removal of obstructions, and bank armouring with boulders to facilitate timber floating, thereby reducing sediment supply from bank erosion while increasing export through higher channel velocities. These contrasting landuse impacts have pushed stream channels in opposite directions (aggradation versus degradation) within a phase-space defined by sediment transport and supply. Restoration in coastal British Columbia has focused on reducing sediment supply (through bank and hillslope stabilization) and restoring wood inputs. In contrast, restoration in northern Fennoscandia (Sweden and Finland) has focused on channel widening and removal of bank-armouring boulders to increase sediment supply and retention. These contrasting restoration priorities illustrate the consequences of divergent regional landuse impacts on sediment supply, and the utility of planning restoration activities within a mechanistic sediment supply-transport framework.

The endorheic Lake Van in eastern Anatolia (Turkey) is the world's largest soda lake and it is an important site in paleoclimate studies to understand past continental conditions in western Asia. In order to gain further insights into the biomarker signatures in Lake Van's sediments we have analyzed particulate material in sediment traps deployed between August 2006 and July 2007. The biomarkers used were long chain alkenones (LCAs C 37 -C 39 , haptophyte lipids), isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs, Archaea membrane lipids) and pigments (chlorins and fucoxanthin). The biomarker fluxes indicate a strong seasonality in export primary productivity and the phytoplankton community structure. The highest total mass and organic carbon fluxes were found in summer, coupled to strong stratification while the lowest mass fluxes occurred in winter at the time of water column mixing. With increasing temperatures in early spring, phytoplankton export productivity grew, coupled with an increase of total mass flux and organic carbon, which might be associated to enhanced nutrient input from snowmelt runoff. The percentage of C 37:4 shows some correspondence with observed seasonal changes in Lake Van's stratification structure. We also evaluated the potential applicability of molecular temperature proxies derived from Archaea and haptophyte lipids. The use of the TEX 86 proxy was precluded by low GDGT abundances. Estimated LCA temperatures were consistent with temperatures in the photic zone but no seasonality changes were observed despite the wide annual temperature range measured at Lake Van.

The trace elements Re and MO both behave conservatively in seawater yet are strongly enriched in reducing sediments. Their potential for authigenic enrichment above crustal concentrations is greater than for many other elements, due to the high ratio of [metal],,/[metal],,,,.

A study of radiolarian fluxes collected during 1991-93 from time-series sediment traps deployed at 1071 and 3010 m water depth in the southern Bay of Bengal (SBBT) yielded 40 species/groups of radiolarians. Among the order Polycystina, the species of sub-order Spumellaria were by far the most abundant (~95%) followed by sub-order Nassellaria (5%). This is contrary to reports from the Atlantic and Pacific Oceans and is attributed to the prevailing hyposaline condition resulting from the monsoonal rainfall. Higher radiolarian fluxes occurred during March-May, when moderate salinity and a high sea surface temperature (SST) regime prevailed at the trap site. R-mode cluster analysis of the radiolarian flux data revealed three assemblages represented by the cooler (A) and warmer (C) surface dwelling fauna (0-50 m) dominated by spumellarians, and a deeper dwelling (B) sub-surface fauna (50-100 m) associated with deep dwelling (>100 m) nassellarian species. Spongaster tetras tetras, a surface water radiolarian species, exhibited its preference for high SST and moderate salinity conditions during the pre-monsoon season (March-May). Radiolarian fluxes responded to seasonal changes in SST and salinity variations due to the monsoonal precipitation, and the freshwater runoff from the Indian rivers causing a hyposaline condition in the Bay of Bengal. Results imply that the radiolarian assemblages in the down core data may reveal the monsoonal history in the geological past. r

Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18-22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach.

The Asian monsoon is comprised of the Indian and East Asian subsystems. These two components are linked to one another in varying degrees by regions of strong sensible heating (Indo-Asian landmass) and strong latent heat export (the Western Pacific Warm Pool and the southern subtropical Indian Ocean). Variability within the Indian and East Asian subsystems, interactions among them, and the extent to which they interact with other climate phenomena (e.g., ENSO) are current topics of modern and paleoclimate research. This work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records. While past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales, additional efforts are required to make further progress in two critical areas.

This paper presents a review of the past decade's highlights of research on the isolation and characterisation of particulate organic matter (POM) in the world's oceans. The emphasis is on chemical studies but, in keeping with the growing interdisciplinary nature of marine science, advances in other disciplines are also discussed, particularly those in biological sciences. Increasing evidence for the importance of picoplankton, bacteria and viruses as POM constituents is highlighted, including the recent recognition of large populations of autotrophic bacteria able to harvest light for energy. The transport of POM to bottom waters was thought to be largely confined to large, rapidly sinking faecal pellets. However, recent studies have highlighted the importance of organic aggregates and flocs formed by diatoms such as Rhizosolenia and other microalgae. Ascending particles have also been discovered, many of which are lipid-rich. Several studies have shown that resuspension of bottom sediments and lateral advection of material from continental shelves can lead to anomalously high particle fluxes measured in sediment traps moored in deep water. Many new approaches for characterizing POM have emerged, such as pyrolysis gas chromatography-mass spectrometry and direct temperature-resolved mass spectrometry for analysis of higher molecular weight materials and biopolymers. Lipid biomarker techniques have also advanced, exciting new possibilities being raised by the ability to measure stable and radioactive carbon isotopes for individual compounds. The techniques of molecular biology, such as the polymerase chain reaction (PCR), are being increasingly applied to provide complementary information to more conventional microscopy and flow cytometry on the identity of organisms in the sea. The combination of these techniques with advanced chemical analysis methods promises to greatly increase our knowledge of the origins, transport and fate of organic matter in the oceans.

During a spring and a summer cruise, we determined the amounts of biogenic silica (bSi) and particulate organic carbon (POC) encapsulated into fecal pellets by the community of large copepods in the Antarctic Polar Front region, in order to estimate the potential contribution of sinking pellets to bSi and POC flux from the surface layer. Grazing by large copepods can be an important mechanism for enhancing vertical flux of POC and bSi because particles in the diatom size range are excellent foods for mesozooplankton, bSi is inert in copepod guts, and copepod fecal pellets (which have a chitinous membrane that retards dissolution of pellet contents) have sinking rates of 100s m d À1 . Rates of pellet production were measured in deck incubations with natural seawater as food medium. BSi and POC contents of pellets were measured in the laboratory. These data were applied to measured abundances of large copepods and the resultant rates of bSi and POC pellet production were compared to flux measurements made by other investigators. Comparison between pellet production by the community of large copepods and flux at 100 m determined by thorium isotopes indicated that pellet production was equivalent to 22-63% of POC flux and 42-107% of bSi flux during the spring cruise. The potential contribution of pellets to flux at 100 m in the summer was considerably smaller, between 2% and 7% for POC and between 1% and 5% for bSi (with one exception at the southernmost station where there was a diatom bloom). We conclude that, in the spring especially, fecal pellets can contribute significantly to the bSi and POC sinking from the surface layer within the Antarctic Polar Front region. However, sediment traps deployed at a depth of 1000 m during the spring cruise indicated total fluxes of both bSi and POC were less than pellet production in the upper 100 m, indicating consumption or degradation of sinking material is significant between 100 and 1000 m. Fecal pellet production of POC was 4-10 times greater than the flux of POC at 1000 m and pellet production of bSi was 0.4-5 times the flux of bSi at 1000 m. Although pellets can contribute significantly to total flux, a large fraction of pellet material must be remineralized during sinking. r

Two sediment traps were deployed in time series collection from November 1991 to August 1994 at 3000 and 3500 m, respectively, above and below the oxygenated sea water/anoxic brine interface in the Bannock Basin, central eastern Mediterranean. Here, the coccolithophore flux and its contribution to the carbonate particulate flux are presented for the 3000 m trap and compared with the record in eastern Mediterranean surface sediments. A marked seasonal variation is observed in the fluxes of total mass, total coccoliths and whole coccospheres, with flux maxima in late winter and spring. The annual coccolith flux of 1×1010 coccoliths m−2 year−1 measured in the deep waters of Bannock Basin is much lower than published data from most other oceanographic settings, even when corrected for the trap efficiency of~23% calculated from the 230Th flux. The biogenic and lithogenic fluxes are primarily controlled by coccolithophore production and Saharan dust input, respectively. The calculated coccolith and coccosphere settling rates, estimated from the comparison of maximum pigment concentration in the surface ocean and arrival of maximum flux at 3000 m water depth, ranged from 17 to 25 m day−1 for coccoliths and 100 m day−1 for coccospheres. At the study site, carbonate dissolution is a minor process at both the trap depth and at the sea floor in both oxic and anoxic conditions, and there is a high preservation of coccolith CaCO 3

The Pernambuco Lagoon is a hypersaline water body located in the Massambaba barrier-island, coastal plain of Rio de Janeiro State, southeastern Brazil. Its marginal environments are characterized by the development of microbial mats resulting from the organic activity produced by sediment trapping and binding in the matrix. The aim of this study is to characterize the cyanobacterial and sedimentary composition of these mats, mainly those with polygonal morphology, where a porous compact structure limits and forms polygonal fi ssures and cracks. The MEV and SED analysis show a calcitic and sodium chlorate composition and dominance of fi lamentous cyanobacteria Microcoleus chthonoplastes (Thuret) Gomont 1892 in the polygonal microbial mats. The disposition of fi lamentous forms on the surface level and the spherical ones in the deeper layers results in a stratifi cation of the mats. These observations are useful in the identifi cation of similar organic generated deposits in the fossil record.

Long-term data characterizing the oceans' biological carbon pump are essential for understanding impacts of climate variability on marine ecosystems. The "Bakun upwelling intensification hypothesis" suggests intensified coastal upwelling due to a greater land-sea temperature gradient influenced by global warming. We present long time series of bathypelagic (approximately 1,200-3,600 m) particle fluxes from a coastal (CBeu: 2003-2016) and an offshore (CBmeso: 1988-2016) sediment trap setting located in the Canary Current upwelling. Organic carbon (C org) and biogenic opal (BSi, diatoms) fluxes were twofold to threefold higher at the coastal upwelling site compared to the offshore site, respectively, and showed higher seasonality with flux maxima in spring. A relationship between winter and spring BSi fluxes to the North Atlantic Oscillation index was best expressed at the offshore site CBmeso. Lithogenic (dust) fluxes regularly peaked in winter when frequent low-altitude dust storms and deposition occurred, decreasing offshore by about threefold. We obtained a high temporal match of short-term peaks of BSi and dust fluxes in winter to spring at the inner site CBeu. We found synchronous flux variations at both sites and an anomalous year 2005, characterized by high BSi and C org fluxes under a low North Atlantic Oscillation. C org and BSi fluxes revealed a decreasing trend from 2006 to 2016 at the coastal site CBeu, pointing to coastal upwelling relaxation during the last two decades. The permanent offshore upwelling zone of the deflected Canary Current represented by the flux record of CBmeso showed no signs of increasing upwelling as well which contradicts the Bakun hypothesis.

To investigate the mechanisms underlying the transport of particles from the shelf to the deep basin, sediment traps and oceanographic sensors were moored from October 2003 to August 2004 over the 300- and 500-m isobaths on the slope of the Mackenzie Shelf (Beaufort Sea, Arctic Ocean). Seasonal variations in the magnitude and nature of the vertical particulate organic carbon (POC)

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set-ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. š20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on-site soil erosion.