Spatial Distribution Of Sediments Research Articles

Bottom sediment resuspension in the easternmost Gulf of Finland in the Baltic Sea: A case study based on three–dimensional modeling

A three-dimensional model of the Neva Bay, located in the eastern part of the Baltic Sea, was used to simulate the bottom sediment resuspension. The model takes into account the non-linear interaction of current-related and wave-related bed shear stress, sediment cohesion and packing effects, variable fall velocity of suspended particles due to hindered settling and flocculation, and also the influence of suspended particles upon the total stratification of the water column. Three main types of sediments in the Neva Bay were considered: gravel, sand and silt. The model SWAN was used to calculate the characteristics of wind waves. Satellite data was used to calibrate and validate the model. The present study has revealed that for the Neva Bay it is necessary to consider both current-related and wave-related bed shear stresses and spatial distribution of sediments, and also that taking into account the influence of suspended particles upon the total stratification in the Neva Bay leads to the damping of vertical turbulent mixing. The results have demonstrated that the model correctly simulates the patterns of high-turbidity events in the Neva Bay. Model runs for ice-free periods of 2004, 2008 and 2013 years have shown that significant sediment resuspension happened along the whole coastline from the town of Sestroretsk to the estuary of the Neva River and at the river sand bars during strong west and south-west winds. Sediment resuspension occurred most intensively during autumn months, with the peak of intensity being observed in November.

DISTRIBUCIÓN ESPACIAL DE SEDIMENTOS EN LA REGIÓN NORTE DEL CARIBE COLOMBIANO

The spatial distribution of sediments in the continental shelf, their granulometry (phi) and composition (content of calcium carbonate, CaCO3) is described, taking into account the localization (depth, latitude and longitude) to explain their source and distribution and to establish their relationship with the more productive areas in the northern Colombian Caribbean region. Sediment samples were collected in 68 stations during two surveys carried out in December 2005 and February 2006. Granulometry was determined with sieving separation method and medium grains values of sediment (PHI = F) were calculated. Additionally calcium carbonate (CaCO3) contents were determined. Cluster analysis was performed to characterize groups of similar stations in terms of sediment types and sediment type maps were made using geostatistical techniques. Analysis of relationship between sediment types, according to their PHI, with depth, latitude and longitude, and CaCO3 content with sediment types and depth, was made with Generalized Additive Models (GAM). According to spatial distribution of sediments was possible characterize three sectors in agreement with the values of PHI: 1) from Río Buritaca to Río Camarones with fine sands and muds, 2) from Riohacha to Cabo de la Vela with very coarse sands and sands, 3) from Cabo de la Vela to Puerto Estrella with fine sands and muds.

Evaluation of an Empirical Reservoir Shape Function to Define Sediment Distributions in Small Reservoirs

Understanding and defining the spatial distribution of sediment deposited in reservoirs is essential not only at the design stage but also during the operation. The majority of research concerns the distribution of sediment deposition in medium and large water reservoirs. Most empirical methods do not provide satisfactory results when applied to the determination of sediment deposition in small reservoirs. Small reservoir’s volumes do not exceed 5 × 106 m3 and their capacity-inflow ratio is less than 10%. Long-term silting measurements of three small reservoirs were used to evaluate the method described by Rahmanian and Banihashemi for predicting sediment distributions in small reservoirs. Rahmanian and Banihashemi stated that their model of distribution of sediment deposition in water reservoir works well for a long duration operation. In the presented study, the silting rate was used in order to determine the long duration operation. Silting rate is a quotient of volume of the sediment deposited in the reservoir and its original volume. It was stated that when the silting rate had reached 50%, the sediment deposition in the reservoir may be described by an empirical reservoir depth shape function (RDSF).

SOME REGULARITIES OF SEDIMENT REDISTRIBUTION IN THE EROSION-CHANNEL SYSTEMS OF CENTRAL RUSSIA

Drainage-areas of little and middle rivers in the Volga and Don basins were analyzed. The regularities of spatial sediment distribution and correlations between modulus of flow and sediment discharge in the different elements of erosion network are determined. River silt load and value of basin have low correlation, the causes of which may be the large spatial variability of accumulation processes outside the valley and significant importance of the riverbed erosion and accumulation for the formation of fluvial degradation sheet.

The high resolution sedimentary filling in Qiongdongnan Basin, Northern South China Sea

Abstract The high density (2 km × 6 km), high resolution (19 sequence boundaries) seismic reflection profiles and 42 industrial wells (including VSP data, gamma ray, sonic and density logs) are now available in Qiongdongnan Basin to the northwest of South China Sea. Then we explored the time–depth relationships of strata, obtained the compaction curves of shale and sand, and recovered the original sediment thickness. Furthermore, we calculated the sediment budget and analyzed the deepwater sedimentation processes. The thickest sediment of Qiongdongnan Basin is more than 16 km. The temporal–spatial distribution of sedimentation is characterized by three stages i.e. syn-rift stage (45–21 Ma), early post-rift stage (21–10.5 Ma) and late post-rift stage (10.5–0 Ma). The distribution of sedimentation in deepwater is mainly controlled by the sediment source and transportation routes. The NE trended, S-shaped central canyon is ~ 430 km in length and inferred to firstly develop at 10.5 Ma in the east of Qiongdongnan Basin, then evolve westwards and form at ~ 5.5 Ma in the west. The canyon was significantly filled by sediment in 5.5–4.2 Ma and 4.2–3.8 Ma, during which the sediment can be transported from west to the Baodao and Changchang Sags in the east. Four stages of sedimentary accumulation in Qiongdongnan Basin were identified. They are 86 m/myr in 45–36 Ma, 200–300 m/myr in 36–15.5 Ma, 90–130 m/myr in 15.5–5.5 Ma and 150–630 m/myr since 5.5 Ma. It is markedly different from that of Yinggehai–Song Hong basin in some periods, i.e. the early Oligocene (36–30 Ma) and the early to middle Miocene (21–10.5 Ma), which suggest the Qiongdongnan Basin may have other provenances besides the Red River, such as Hainan Island and Indochina.

History of benthic research in the English Channel: From general patterns of communities to habitat mosaic description

Benthic studies in the English Channel (EC), a shallow megatidal and epicontinental sea, began in the 1960s and 1970s with the work of teams led by Norman Holme (UK) and Louis Cabioch (F). During this period, benthic sampling was mainly qualitative, i.e. using a device such as the ‘Rallier du Baty’ dredge in the case of the French team and a modified anchor dredge in the case of the British team. Studies were focused on acquiring knowledge of the main distributions of benthic communities and species. Surveys on the scale of the whole EC led to the recognition of general features and two main patterns were identified: 1) the role of hydrodynamics on the spatial distribution of sediment, benthic species and communities; 2) the presence of a west–east climatic gradient of faunal impoverishment. Benthic studies in the 1980s–1990s were focused on the beginning of the implementation of long-term survey at a limited number of sites to identify seasonal and multi-annual changes. In the first decade of the 2000s, the implementation of the European Water Framework Directive and the Marine Strategy Framework Directive to define the Ecological Quality Status of marine environments increased the need to acquire better information of the structure and functioning of benthic communities, since benthic species and habitats were recognised as good indicators of human pressure on marine ecosystems. Faced with the increase of human maritime activities, the appearance of invasive species and the need to preserve sensitive marine habitats, benthic studies have been focused on developing a ‘toolkit’ to help in the decision-making and planning for both sound governance and sustainable management of marine resources and human activities in the English Channel. Multidisciplinary approaches were used to differentiate habitats in a more precise detail. Both indirect (side-scan sonar, ROV) and direct (grab sampling with benthos identification and grain-size analyses) approaches were used and combined to allow the description of benthic habitats using numerous descriptors. These approaches were mainly applied on a local scale, leading to the identification of habitat mosaics mainly in coarse sands, gravels and pebbly areas which cover 80% of the EC seabed. They also allowed the enrichment of the EUNIS habitat classification for infralittoral and circalittoral zones taking into account the scale of observations of benthic habitats. Moreover, several recommendations for future benthic studies are proposed within a HABITAT approach.

Thickness distribution of quaternary deposits in the formerly glaciated part of the East European plain

A thickness map of Quaternary deposits in the south-eastern sector of the last Scandinavian Ice Sheet (SIS) and in areas of Middle Pleistocene Moscow (Warthe) and the Dniepr (Drente) stages of the Late Saalian glaciation on the East European Plain is presented (Main Map). The map of the thickness and related statistics of the Quaternary deposits were calculated from the difference between the current digital terrain model and the bedrock surface topography model. The distribution of Quaternary deposits shows that 29% of the mapped territory has sediments less than 25 m thick, 16% more than 100 m and 1.2% more than 200 m. Within the SIS area, the thickness of sediments in the southern sector exceeds threefold the sediment thickness in the eastern flank. This difference is attributed to the bedrock depression in the south-east of the Baltic Syneclise rather than to glacial dynamics. The calculated average thickness of the sediments within the SIS area is ca 50 m, in the formerly glaciated area outside the LGM it is ca 61 m and outside the glaciated area ca 14 m. Our study confirms that, in formerly glaciated areas, the spatial distribution of sediments did amplify the differences in glacial bed topography with the exception of the southern and eastern flanks of the Moscow glaciation area where exceptionally thick Quaternary deposits have inverted bedrock depressions into elevated areas in recent terrain. We suggest that the map presented improves existing knowledge of this area by adding detail and thus contributing to the on-going development of numerical ice-sheet models.

象山港网箱养殖区沉积物的古菌空间分布

PDF HTML阅读 XML下载 导出引用 引用提醒 象山港网箱养殖区沉积物的古菌空间分布 DOI: 10.5846/stxb201212041745 作者: 作者单位: 宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41101234）；浙江省教育厅科研项目（Y201121499）；宁波大学学科项目（xkl11090）；国家863资助项目（2012AA092001） The archaeal spatial distribution in sediments of cage culture area in Xiangshan Bay, Zhejiang, China Author: Affiliation: School of Marine Science, Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:对象山港网箱养殖区及其周边沉积物中古菌群落的空间分布进行研究，应用基于16S rRNA基因的T-RFLP（末端限制性片段多态性分析）技术分析象山港网箱养殖区及其周边不同深度沉积物中古菌的群落结构和多样性，并构建克隆文库进行系统发育学分析。测定沉积物各项理化因子，通过PCA和RDA分析了古菌群落分布及其与环境因子之间的关系。结果表明，泉古菌是港口沉积物中的优势古菌群，占古菌群落的50%以上。网箱养殖区沉积物的古菌群落结构较非养殖区简单，多样性降低。非养殖区古菌群落随深度呈现有规律的变化。营养盐类和pH是造成养殖区域古菌群落结构区别于非养殖区域的主要环境因素。 Abstract:Archaea was distributed widely in marine environments. It plays an important role in nutrient and energy cycling in marine ecosystems. For studying the archaeal spatial distribution in sediment of cage culture area, archaeal community structures in sediments were investigated in July 2011, in Xiangshan Bay, Zhejiang Province, China. Sediments used in this paper were as the same as described previously[1]: a control or check site (CK), an intersection site 6-8 km from the aquaculture site (IS), and a cage culture site (AC). For sub-sampling, sediments were cut into several sections throughout their depth: a (0-5 cm), b (5-10 cm), c (10-15 cm), d (15-20 cm), e (20-25 cm) and f (50-55 cm). Physiochemical factors (NH4+, NO2-, NO3-, SiO32- and P) of sediments were analyzed in laboratory after transport with liquid nitrogen. Based on 16S rRNA gene, the structure and diversity of archaeal communities in sediments were analyzed by T-RFLP (Terminal Restriction Fragment Length Polymorphism), which was conducted after amplification of the archaeal 16S rRNA partial gene using a fluorescent primer pair 109F /934R-FAM and digestion by TaqI (T^CGA). Archaeal 16S rRNA gene clone library was constructed using DNA extracted from layer 0-5 cm sediment of the CK site, and the following phylogenetic analysis was carried out using ARB software. In agreement with other studies, Crenarchaeota is the dominant archaea in marine sediment. T-RFLP profiles showed that the dominant T-RF of 188 bp, affiliated to Crenarchaeota, occupied 80.3% in the cage culture site, more than it in the check site (61.2%). While, the kingdoms Euryarchaeota and Crenarchaeota were present equally in clone library and methanogens constituted a small proportion of the archaeal community. Because the check site is near to East Sea with a higher salinity, T-RF of 78 bp, belonged Halobacteriales, emerged in its upper layers (0-20 cm) sediments and was more abundant than it in other sites. Principal component analysis for the archaeal 16S rRNA gene T-RFLP using R software indicated a complete separation of archaeal communities of the cage culture sit from the check site. And archaeal communities of the intersection site were in the middle. An obvious difference of archaeal communities in the check site sediments at various depths was indicated by PCA. T-RFs of 78 bp, 88 bp, 383 bp and 188 bp related archaea may be the main microorganisms who made the difference among horizontal and vertical distribution. Although calculation of Shannon diversity index H' and evenness index E' showed large errors in parallels, comparing with the check site, the diversity of archaeal communities in cage culture sediments displayed a dropping tendency. Redundancy analysis of archaeal community compositions and environmental factors of sediments in different sites and depths suggested that nutritive salt and pH mainly affected the distribution of archaeal in horizontal by aquaculture. Eh and ammonium were tend to have a relation with archaeal vertical distribution, especially in the check site. In short, aquaculture affected the spatial distribution of uncultivated archaea. 参考文献 相似文献 引证文献

Autogenic dynamics of alluvial fans in endorheic basins: Outcrop examples and stratigraphic significance

AbstractAlluvial fans are relatively simple depositional systems, due to the direct coupling of sediment sources and adjacent accumulation areas. Nonetheless, general models of alluvial‐fan evolution and stratigraphy remain elusive, due to the great sensitivity of such systems to allogenic controls and their strongly case‐specific responses. Autogenic processes intrinsic to alluvial‐fan dynamics can complicate stratigraphic architectures, with effects not easily distinguishable from those of allogenic forcing. A distinction is made here between lateral autogenic dynamics, tied to spatial sediment distribution over fan surfaces, and vertical autogenic dynamics, related to independent incision‐aggradation cycles. Autogenic mechanisms have been highlighted recently by modelling studies, but remain poorly constrained in field‐based studies. Examples are presented here from the margins of the Cenozoic Teruel and Ebro basins (Spain), where alluvial fans accumulated thick successions during phases of basin topographic closure and endorheic drainage which promoted forced aggradation. Fan successions consist of conformable architectures of stacked clastic sheets, laterally continuous and with no evidence of internal unconformities, inset architectures, fan segmentation or preserved incised channels. Continuous aggradation in these closed basins strongly inhibited ‘vertical’ autogenic dynamics in the form of fan head and through fan incision, due to the forced rise in geomorphic base level and the creation of positive accommodation. Furthermore, the lack of incised channels favoured widespread sediment transport and aggradation over broad fan sectors in relatively short time spans, in contrast to the typical occurrence of active lobes and abandoned fan surfaces caused by ‘lateral’ autogenic dynamics. Stratigraphic records of alluvial fans developed in endorheic basins are essentially complete and largely unaffected by autogenic processes. The latter characteristic implies that they can be more unambiguously interpreted in terms of allogenic forcing, because stratigraphic signatures are not complicated by the effects of complex fan autodynamics.

Sedimentation monitoring including uncertainty analysis in complex floodplains: a case study in the Mekong Delta

Abstract. Quantity and quality of sediment deposition in complex floodplains are affected by many processes that are typically highly spatially and temporally variable and hard to quantify exactly. The main processes in this context are suspended sediment transport dynamics in rivers, floodplain channel interactions, and internal floodplain processes. In consequence, any point measurement of sedimentation in floodplains contains a high degree of uncertainty, both stemming from measurement errors and from the lack of representativeness for a larger area. However, up to now, uncertainty analyses have not been performed as part of publications on floodplain sedimentation data. Therefore the present work illustrates a field sampling strategy aiming at the monitoring of floodplain deposition and spatial variability on a large scale and at the quantification of uncertainties associated to sediment deposition data. The study was performed in the Mekong Delta, being an example for a large and complex floodplain with a high degree of anthropogenic disturbances. We present a procedure for the quantification of the uncertainty associated to the data, based on the design of the monitoring campaign, sampling procedures, and floodplain characteristics. Sediment traps were distributed strategically over the floodplain in clusters of three mat traps representing one monitoring point. The uncertainty originating from collection of the traps from still ponding water is quantified by lab experiments. The overall uncertainty of the deposition samples and the associated nutrient content is quantified in a Monte Carlo simulation and illustrated by uncertainty bounds. For the study area the results show a very high variability of the annual floodplain deposition (2.2–60 kg m−2) with uncertainty bounds ranging from −61 to +129% relative to overall mean deposition of 11.4 kg m−2. No correlations in the spatial distribution of sedimentation in the floodplains could be found. This is caused by the highly complex channel and dike system and the high number of hydraulic structures. Also, no differences in deposition between floodplain compartments protected with high and low dikes could be detected. However, it can be shown that within single floodplain compartments the spatial deposition variability depends on the dike levels and operation and location of hydraulic structures.

Acoustic measurements of the spatial distribution of suspended sediment at three sites on the Lower Mekong River

The Mekong River spans thousands of kilometers, flows through six countries, and its basin is one of the world’s richest in terms of biodiversity. However, land-use changes, dredging of the river bed, and the construction of dams are changing its sediment dynamics and morphology. The resultant increases in bank erosion and reduction in sediment supply to floodplains may have adverse effects on the economical and biological productivity of the region. In order to monitor these changes, the current conditions must be well understood. Comprehensive measurements of the spatial distribution of sediment (both suspended and bed load) were made at three locations in different physiographic regions of the Lower Mekong at the end of the 2012 rainy season. Acoustic Doppler Current Profilers and a multifrequency acoustic backscatter system, the AQUAscat, were used in combination with water sampling to provide high resolution measurements of concentration and grain size. The AQUAscat consisted of four monostatic transducers operating at 0.5, 1, 2.5, and 4 MHz. At each site, it was deployed horizontally at five across-stream positions and 5–10 depths per vertical; a 10 m profile was recorded at each point. The spatial distribution of particle size and concentration were determined using multifrequency inversions of (1) backscattered intensity and (2) attenuation calculated from the intensity profiles. This data set provides a baseline to which to compare future measurements at these sites.

化学組成および粒度分布に基づいた東京湾の底質分布

The deposition and transport of sediments should be managed properly in ports not only for the maintenance of port channels, but also from an environment perspective. Our focus in this study was to create maps of sediment spatial distributions in Tokyo Bay by using chemical composition. We collected sediments from 449 stations in the bay and analyzed particle-size distribution and chemical composition. Sediments were grouped by chemical compositions using k-means clustering and maps of the spatial distribution of sediments were drawn up. These maps enable determination of spatial distributions of sediments from each main river that enters the bay.

Estimating floodplain sedimentation in the Laguna de Santa Rosa, Sonoma County, CA

We present a conceptual and analytical framework for predicting the spatial distribution of floodplain sedimentation for the Laguna de Santa Rosa, Sonoma County, CA. We assess the role of the floodplain as a sink for fine-grained sediment and investigate concerns regarding the potential loss of flood storage capacity due to historic sedimentation. We characterized the spatial distribution of sedimentation during a post-flood survey and developed a spatially distributed sediment deposition potential map that highlights zones of floodplain sedimentation. The sediment deposition potential map, built using raster files that describe the spatial distribution of relevant hydrologic and landscape variables, was calibrated using 2 years of measured overbank sedimentation data and verified using longer-term rates determined using dendrochronology. The calibrated floodplain deposition potential relation was used to estimate an average annual floodplain sedimentation rate (3.6 mm/year) for the ~11 km2 floodplain. This study documents the development of a conceptual model of overbank sedimentation, describes a methodology to estimate the potential for various parts of a floodplain complex to accumulate sediment over time, and provides estimates of short and long-term overbank sedimentation rates that can be used for ecosystem management and prioritization of restoration activities.

Analysis of Sediment Distribution in a Typical Irrigation District Along the Lower Yellow River

Sediment diverted from the Lower Yellow River is crucial for irrigation district sustainable development. As a complex problem, spatial distribution of sediment in district is related with natural geographical environment, incoming water amount and sediment concentration, methods of treatment, engineering facilities. Analysis of sediment distribution is the precondition for sediment utilization, transportation and treatment. As Bojili irrigation district for example, the paper analyzed sediment siltation characteristics in desilting branch, main canal, branch canal and field ditch with long term observed data from 1985 to 2009. Proportions of sediment siltation in different parts of irrigation system were calculated and difference of seasonal siltation in desilting branch was discussed. Besides, the paper proposed effective suggestions about reducing sediment siltation and improving transportation with long distance.

Effect of forest harvesting on hydrogeomorphic processes in steep terrain of central Japan

Forest harvesting activities affect various hydrogeomorphic processes in forest terrain, including increases in occurrence of mass movements (i.e., landslides and debris flows), and changes in sediment transport rate in channels. Thus, the influence of harvesting on these processes needs to be assessed to protect aquatic ecosystems. In steep terrain with frequent mass movement, relationships between rainfall magnitude and frequency of mass movements associated with forest harvesting are needed to develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of mass movements in the steep Sanko catchment (central Japan) using aerial photographs for six different years covering 1976 to 2003. We also investigated the spatial distribution of sediment stored in the system as well as sediment transport rate in selected subcatchments by field surveys. Landslides occur during moderate rainfall events (return period of daily rainfall<10years) in younger forests (<25years after harvesting), whereas the threshold magnitude of rainfall for landslides is higher in older forests (>25years after harvesting). The occurrence of mass movements substantially altered the volume of sediment storage in the channel that links sediment supply from hillslopes with sediment yield downstream. However, the volume and spatial distribution of sediment deposits in headwater channels were not clearly related to forest age because of the redistribution and evacuation of sediment by debris flows. Bedload transport rate was highly affected by sediment storage volume, whereas suspended sediment concentration was affected by the area of exposed sediment along channels that was carved by debris flows. Thus, the effect of harvesting on hydrogeomorphic processes cannot be estimated simply by the elapsed time after forest harvesting; rainfall magnitude and the history of mass movements need to be considered to better understand these linkages.

Bed load transport in bedrock rivers: The role of sediment cover in grain entrainment, translation, and deposition

[1] Bedrock rivers exert a critical control over landscape evolution, yet little is known about the sediment transport processes that affect their incision. We present theoretical analyses and field data that demonstrate how grain entrainment, translation and deposition are affected by the degree of sediment cover in a bedrock channel. Theoretical considerations of grain entrainment mechanics and sediment continuity each demonstrate that areas of exposed bedrock and thin sediment depths cause sediment transport to be size-independent, albeit excluding extreme grain sizes. We report gravel and cobble magnetic tracer data from three rivers with contrasting sediment cover: the bedrock River Calder (20% cover), the bedrock South Fork Eel River (80%) and the alluvial Allt Dubhaig (100%). These data sets show that: 1) transport distances in the River Calder are controlled by sediment patch location, whereas in the other rivers transport distances are described by gamma distributions representing local dispersion; 2) River Calder transport distances are size-independent across all recorded shear stresses, whereas the other rivers display size-selectivity; 3) River Calder tracers are entrained at a dimensionless shear stress of 0.038, which is relatively low compared to alluvial rivers; and, 4) virtual grain velocities in the River Calder are higher than in a comparable reach of the Allt Dubhaig. These contrasts result from differences in the thicknesses and spatial distribution of sediment in the three rivers, and support the theoretical analysis. Sediment processes in bedrock rivers systematically vary along a continuum between bedrock and alluvial end-members. Citation: Hodge, R. A., T. B. Hoey, and L. S. Sklar (2011), Bed load transport in bedrock rivers: The role of sediment cover in grain entrainment, translation, and deposition, J. Geophys. Res., 116, F04028, doi:10.1029/2011JF002032.

The Zoning of Semi-Enclosed Bodies of Water According to the Sediment Pollution: The Bay of Algeciras as a Case Example

This paper reports a study of the occurrence and levels of polycyclic aromatic hydrocarbons (PAHs) in a bay characterised by a chronic persistent impact. A total of 55 sediment samples were taken at different depths up to 111 m in two sampling campaigns. Chemical analyses were carried out by gas chromatography-mass spectroscopy. The results indicate that: (1) significant spatial variations exist, (2) levels of PAHs are related more strongly to the spatial distribution of sediments than to mineralogy/granulometry, (3) the sediments are slightly-to-moderately contaminated by PAHs, and (4) these PAHs derive from pyrolytic and petrogenic sources. Through use of an innovative data classification system (proposed according to depth and spatial location of sampling points), and using factorial and cluster techniques, five zones have been differentiated depending on the contamination level and source.

Spatial distribution of sediments and transfer properties in soils in a stormwater infiltration basin

The aim of our study was to characterise the heterogeneity of sediment distribution in a stormwater retention/infiltration basin (Pont de Chevire, Nantes, France) and to determine the impact of this distribution on water transfer properties in the soil. Soil water retention curves and saturated hydraulic conductivity (K s) measurements were made at 11 points in the basin. A highly heterogeneous organic matter (OM) distribution ranging from 45 to 222 g kg−1 was observed in the surface layer (layer A), with a sediment thickness ranging from 5 to 26 cm. The sediment thickness of the underlying layer, primarily made up of sand (layer S), ranged from 7 to 32 g kg−1. We observed a significant influence of OM and fine mineral particles on the soil pore distribution and a negative correlation with the saturated hydraulic conductivity (values between 1.3e−5 and 7.2e−6 m s−1 in layer A and close to 3e−4 m s−1 in layer S). This study allowed define the soil physical parameters that account for the clogging phenomenon in this infiltration basin. Nevertheless, this study raises questions as to the contribution of clay in the mineralogical sense on the one hand and OM dynamics on transfer properties and the clogging phenomenon on the other.

Sedimentation within and among mangrove forests along a gradient of geomorphological settings

Coastal wetlands provide important ecological services to the coastal zone, one of which is sediment retention. In this study we investigated sediment retention across a range of geomorphological settings and across vegetation zones comprising coastal wetlands. We selected six coastal wetlands dominated by mangroves over a gradient from riverine to tidal settings in Southeast Queensland, Australia. Each site was comprised of three distinct vegetation communities distributed as parallel zones to the coast line: seaward fringe mangroves, landward scrub mangroves and saltmarsh/ cyanobacteria mat of the high intertidal zone. We measured suspended sediment retention and sedimentation rates. Additionally, in order to assess the origin of sediment transported and deposited in the mangroves, glomalin, a novel terrestrial soil carbon tracer, was used. Our results show a mean average sedimentation of 0.64 ± 0.01 mg cm −2 spring tide −1, which was variable within sites, regardless of geomorphological setting. However, geomorphological setting influenced spatial patterns of sediment deposition. Riverine mangroves had a more homogeneous distribution of sediments across the intertidal zone than tidal mangroves, where most sedimentation occurred in the fringe zone. Overall, the fringe zone retained the majority of sediment entering the coastal wetland during a tidal cycle with 0.90 ± 0.22 mg cm −2 spring tide −1, accounting for 52.5 ± 12.5% of the total sedimentation. The presence of glomalin in suspended sediments, and thus the relative importance of terrigenous sediment, was strongly influenced by geomorphological setting, with riverine mangroves receiving more glomalin in suspended solids than tidal mangroves. Glomalin was also differentially deposited within the vegetation zones at different geomorphological settings: primarily at the fringe zone of tidal mangroves and within the scrub zone of riverine mangroves. The differences we observed in the spatial distribution of sedimentation and the difference in the origin of the sediment deposited in riverine and tidal mangroves are likely to have an impact on ecological processes.

Detection of Cochlodinium polykrikoides and Gymnodinium impudicum (Dinophyceae) in sediment samples from Korea using real-time PCR

Recurring blooms of fish killing dinoflagellate Cochlodinium polykrikoides has resulted in large economic losses in fisheries industry in Korea. This species has been monitored in water column samples, but its spatial distribution in sediments is poorly understood. To address this area, geographic distribution of C. polykrikoides and morphologically similar species Gymnodinium impudicum in surface sediments of Korea was investigated using species-specific real-time PCR probes targeting the internal transcribed spacer 2 rRNA gene. PCR-inhibitory substances in sediment samples were removed by dilution of DNA extracts from the field samples for preventing false-negative detection. G. impudicum was widely distributed in sediments from East, South, and Yellow Seas. C. polykrikoides was prevalent in sediments from South Sea whereas it was not detected in sediments from East and Yellow Seas. These results indicate that these dinoflagellates may persist in surface sediment likely in the form of cyst and their “seed beds” may exist in sediments of South Sea where blooms of C. polykrikoides occur annually.