Nepheloid and suspended particulate matter in south-eastern Lake Michigan*

A persistent benthic nepheloid layer with high total suspended matter (TSM) and high total particulate surface area was observed in south-eastern Lake Michigan. The layer thickens from a few metres near the shelf-slope boundary to greater than 10 m at the base of the slope. When compared to the hypolimnion, TSM increases by a factor of 2-20 at 1 m above the bottom, the greatest increase detected at the slope-basin boundary. Sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom, suggesting that a large fraction of the collected material came from resuspension. A nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period, apparently through the action of weak but persistent currents. This layer is supplemented by lakeward transport of fine particles resuspended near the shelf-slope boundary due to impingement of the thermocline on the bottom, or during higher energy events.     

Geochemistry of suspended matter and sinking material in the eastern Norwegian Sea

This paper reports the results of a geochemical study of suspended particulate matter and particle fluxes in the Norwegian Sea above the Bear Island slope. The concentrations of suspended particles and the main components of suspended matter were determined in the euphotic, intermediate (“clean water”), and bottom nepheloid layers. It was shown that biogenic components are predominant in the water above the nepheloid layer, whereas the suspended matter of the nepheloid layer is formed by the resuspension of the lithogenic components of bottom sediments. The chemical compositions of suspended matter and material collected in sediment traps are identical.     

Iron and Manganese Minerals in Suspended Matter from the Barents Sea

The mineralogy of suspended matter from surface and bottom waters is studied at two sites in the Barents Sea. Along with terrigenous minerals, the suspended matter samples contain authigenic mineral phases of iron and manganese oxyhydroxides. Mn-feroxyhite, Fe-vernadite, goethite, and proto-ferrihydrite were identified in samples from surface waters, whereas birnessite and nonferruginous vernadite were registered in samples from bottom waters. The formation of suspended manganese minerals in bottom waters is explained by an additional Mn supply from underlying reduced sediments during their early diagenesis and oxygen depletion in the near-bottom nepheloid layer. Bacteria are supposed to take part in the authigenic mineral formation.     

Organic geochemistry of suspended and settling particulate matter in Lake Michigan

Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by $\text{C}\text{N}$ ratios and by distributions of biomarker fatty acids, alkanols, sterols, and aliphatic hydrocarbons. Differences in organic constituents of particulate matter from various depths and distances from shore indicate a complex interaction of production, transformation, and destruction of the organic matter contained in sinking particles. Near-surface material contains important contributions of landderived organic matter, presumably of eolian input. Midwater particles have predominantly aquatic organic material of algal origin. At the sediment-water interface, selective suspension of the finer fractions of surficial sediments enriches bottom nepheloid layers with these sediment size classes. As a result, near-bottom particulate matter has an aquatic biomarker character. Organic matter associated with sinking particles undergoes substantial degradation during passage to the bottom of Lake Michigan, and aquatic components are selectively destroyed relative to terrigenous components.     

Modeling diagnosis of suspended sediment transport in tidal estuarine system

A three-dimensional, time-dependent hydrodynamic and suspended sediment transport model was performed and applied to the Danshuei River estuarine system and adjacent coastal sea in northern Taiwan. The model was validated with observed time-series salinity in 2001, and with salinity and suspended sediment distributions in 2002. The predicted results quantitatively agreed with the measured data. A local turbidity maximum was found in the bottom water of the Kuan-Du station. The validated model then was conducted with no salinity gradient, no sediment supply from the sediment bed, wind stress, and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the Danshuei River estuarine system. The results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the Kuan-Du station. Without bottom resuspension process, the estuarine turbidity maximum zone at the Kuan-Du station vanishes. This suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum. The wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration. When the freshwater discharges increase at the upstream boundaries, the limits of salt intrusion pushes downriver toward river mouth. Suspended sediment concentrations increase at the upriver reaches in the Danshuei River to Tahan Stream, while decrease at Kuan-Du station.     

Suspended sediment transport,sedimentation, and resuspension in Lake Houston,Texas: Implications for water quality

Lake Houston is a man-made reservoir located northeast of Houston, Texas. The purpose of this investigation was to document suspended sediment transport, sedimentation, and resuspension in the lake with a view towards estimating the influence of sedimentation on water quality. Sediment traps were placed in strategic locations in the lake to collect suspended sediments. Samples were analyzed for bulk density, grain size, organic carbon, and a number of trace elements. These data were analyzed along with meteorological data to examine those factors which regulate suspended sediment input and dispersal, and the role of suspended sediments in controlling water quality within the lake. Sediment input to the lake depends primarily on the intensity of rainfall in the watershed. Sediment movement within the lake is strongly influenced by wave activity, which resuspends sediments from shallow areas, and by wind-driven circulation. The increased residence time of suspended sediments due to resuspension allows greater decomposition of organic matter and the release of several trace elements from sediments to the water column. Virtually all samples from sediment traps suspended between 1 and 5 m above the lake bottom contain medium to coarse silt, and even some very fine sand-sized material. This implies that circulation in Lake Houston is periodically intense enough to transport this size material in suspension. During winter, northerly winds with sustained velocities of greater than 5 m/sec provide the most suitable condition for rapid (<1 d) transport of suspended sediment down the length of the lake. Fluctuations in current velocities and the subsequent suspension/deposition of particles may explain variations in the abundance of coliform bacteria in Lake Houston.     

A decade of sedimentation in ice-contact, proglacial lakes, Bering Glacier, AK

Bathymetric surveys during the 1991–2000 decade in two ice-contact, proglacial lakes on the eastern sector of Bering piedmont lobe captured the buildup effects of the 1993–1995 surge. Following ice-front advance of 1.0–1.5 km into Tsivat and Tsiu Lakes, the basins were significantly altered by surge-related sedimentation including the impact of a subglacial outburst into Tsivat Lake. The subsequent changes in basin shape, size, and morphology were monitored by six bathymetric surveys. Measured changes in water depth serve as a proxy for determining increments of sediment accumulation.

Upwelling, ice-front vents fed by subglacial tunnels transported suspended fine sediment directly into the lake system. The rate of suspension settling within both lakes varied from 0.6 to 1.2 m year⁻¹ prior to the surge. Suspended load during surge years increased sixfold from 1.7 to 13.9 g l⁻¹, accompanied by increased sediment accumulation of 2.2–3.1 m year⁻¹. Vent-related aggradation and subsequent filling of Tsivat Lake caused sediment bypassing to Tsiu Lake, where encroachment by delta growth contributed to a postsurge rate of bottomset accumulation of 3.0 m year⁻¹.

The total sediment influx from subglacial sources is represented by the sum of bathymetrically determined accumulation, plus an estimated volume of sediment that remained suspended, thus passing through the lake system. Total sediment flux along the eastern Bering piedmont lobe from 1991 to 2000 is approximately 227 million cubic meters.     

Interaction of the Western Boundary Undercurrent with the continental margin off Newfoundland

Sedimentation on the Newfoundland rise is strongly influenced by the Western Boundary Undercurrent (WBU). The upper rise (2600-2800 m) is swept by a rapid (ū= 8·5 cm sec^?1), south-flowing core of the WBU which has generated a sandy contourite facies characterized by coarse gravelly, sandy sediments; current-induced bedforms such as scour moats, lineations and lee drifts; ferro-manganese-stained gravel clasts; a high proportion of broken foraminiferal tests and a diagnostic benthic foraminiferal assemblage. The overlying nepheloid layer, when compared to adjacent waters, is thickest (800 m), most sediment laden (80 μg 1^?1), contains the highest proportion of terrigenous sediment and exhibits the best developed bottom mixed layer (～ 15 m thick). Comparisons with earlier data from the same area imply the dimensions and sediment load of the nepheloid layer vary with time. Empirical considerations, based on near-bottom current meter records from Labrador and Newfoundland, suggest the WBU is capable of transporting bedload with threshold friction velocities (u*) of around 0·87-1·14 cm sec^?1 for between 1 and 15% of the time. The prevailing transport direction is southwards along the rise, but this may be punctuated periodically by brief incursions to the north. The erosional regime of the upper rise is bordered by a regime of fine-grained deposition typified by muddy contourites. Both the lower slope and lower rise are mantled by bioturbated muds, the former zone having terrigenous mud and the latter, biogenic calcareous mud. The accompanying nepheloid layer is thin, biogenic-rich and devoid of an identifiable mixed layer.     

Suspended Sediment Transport in the Freshwater Reach of the Hudson River Estuary in Eastern New York

Deposition of Hudson River sediment into New York Harbor interferes with navigation lanes and requires continuous dredging. Sediment dynamics at the Hudson estuary turbidity maximum (ETM) have received considerable study, but delivery of sediment to the ETM through the freshwater reach of the estuary has received relatively little attention and few direct measurements. An acoustic Doppler current profiler was positioned at the approximate limit of continuous freshwater to develop a 4-year time series of water velocity, discharge, suspended sediment concentration, and suspended sediment discharge. This data set was compared with suspended sediment discharge data collected during the same period at two sites just above the Hudson head-of-tide (the Federal Dam at Troy) that together represent the single largest source of sediment entering the estuary. The mean annual suspended sediment–discharge from the freshwater reach of the estuary was 737,000 metric tons. Unexpectedly, the total suspended sediment discharge at the study site in November and December slightly exceeded that observed during March and April, the months during which rain and snowmelt typically result in the largest sediment discharge to the estuary. Suspended sediment discharge at the study site exceeded that from the Federal Dam, even though the intervening reach appears to store significant amounts of sediment, suggesting that 30–40% of sediment discharge observed at the study site is derived from tributaries to the estuary between the Federal Dam and study site. A simple model of sediment entering and passing through the freshwater reach on a timescale of weeks appears reasonable during normal hydrologic conditions in adjoining watersheds; however, this simple model may dramatically overestimate sediment delivery during extreme tributary high flows, especially those at the end of, or after, the “flushing season” (October through April). Previous estimates of annual or seasonal sediment delivery from tributaries and the Federal Dam to the ETM and harbor may be high for those years with extreme tributary high-flow events.     

Sediment dynamics in the lowermost Mississippi River

There is much to be gained from investigating sediment dynamics in the lower Mississippi system, the largest river in terms of discharge and sediment load in North America. Such work can improve conceptual knowledge concerning downstream changes at the lower end of large river systems and can be applied to manage sediment diversions for wetland restoration in south Louisiana. Suspended sediment dynamics in the lowermost Mississippi River system in Louisiana are characterized using three approaches: (1) temporal changes in discharge-suspended sediment relationships showing interannual variations and the effects of floods over short timescales; (2) empirical relationships between discharge and suspended sediment variables at various locations; and (3) downstream changes in discharge-suspended sediment relationships. Interpretation of this data set is enhanced with other secondary data regarding processes, morphology, and bed materials.

Upstream, near Old River, LA, empirical relationships show nonlinearity, particularly in fine sediments, with decreased concentrations at highest discharges. During high discharge years, suspended sediment concentration peaks precede discharge crests by 40–85 days. The lead generally decreases with decreasing discharge maxima so that in low discharge years sediment peaks and discharge crests closely coincide in time. Downstream, near Belle Chasse, LA, fine bottom materials are resuspended and the timing of sediment peaks and discharge crests is coincident, regardless of flow magnitude. Conceptually, results suggest caution when generalizing about the relative timing of the sediment wave and flood wave and their downstream progression. These phenomena are influenced by local bed material and hydraulic conditions, and depend on the causative factors of sediment peaks. From an applied perspective, diversions should be managed differently depending upon where they are constructed along the river and upon the magnitude of the annual maximum flow. During high discharge years, when concerns for navigation and water supply are minimal, flow should be diverted on the rising limb upstream, near Old River, and during the discharge crest downstream near New Orleans.     

Sedimentation of particulate matter in the Dona Paula Bay, West Coast of India during November to May 1995–1997

Data on hydrography, nutrients, suspended particles, and sedimented particles were collected at weekly intervals from November to May during 1995 to 1997 at a station in the coastal waters of Dona Paula Bay, India. Suspended and sedimented particles were analyzed for total suspended matter (SPM), total sedimented particulate matter (TPM), particulate organic carbon (POC), particulate organic nitrogen (PON), chlorophylla (chla), and diatom abundance. Variations in hydrography and nutrients influenced the quantity and composition of sedimented particles. The TPM, POC, PON, and chla fluxes showed small-scale seasonal variations and were higher in the summer (February to May) than in the winter (November to January). Resuspension of carbon accounted for approximately 25% of the gross POC and was highest in April 1997 (45%). The mean net POC flux was 197±90 mg C m⁻² d⁻¹ and accounts for 4.6% of the TPM. The average C∶N (w∶w) ratio of the sedimented material was 13.2±6.6. The POC:chla ratio was relatively higher in the sedimented material as compared to the suspended material. The particulate carbon reaching the bottom sediment was 39% of the primary production. The low organic carbon concentration (approximately 0.1% of dry sediment) in the sediments implies that about 98% of the sedimented carbon was either consumed at the sedimentwater interface or resuspended/advected before it was finally buried into the sediments.     

Non-combustible suspended matter in surface waters off eastern Asia*

A total of about 1100 well-distributed samples of suspended matter in surface waters off the length of eastern Asia are available. From these samples, 180 were selected for detailed examination of the non-combustible fraction using optical and electron microscopy along with computer methods of particle measurement and counting. The results showed that, generally, all major components of the suspended matter are most abundant in the nearshore belt (combustible fraction, mineral grains of silt size, skeletal debris, and clay minerals), the result of mechanical transport of detrital sediment and chemical transport of nutrients from the land. Mineral grains of silt size average about 2%, skeletal debris plus clay minerals—23%, and combustible organic matter—75% of total sample weights, but the last two categories vary over a wide range depending upon geographical positions of the samples. Most evident is an oceanward decrease in percentage and concentration of the total noncombustible fraction and an oceanward increase in median diameter of the mineral grains.     

太湖水体后向散射特性模拟

为研究太湖水体后向散射系数的光学特性,利用太湖实测数据和半分析方法与光学闭合(Optical Closure)原理,对太湖水体的后向散射系数进行模拟,在此基础上对其光学特性和影响因子进行分析.研究结果表明:由于悬浮物浓度的差异,使得太湖水体后向散射系数具有明显的差异性,后向散射主要由无机悬浮物引起,浮游藻类对后向散射系数的贡献较小;由于悬浮物来源不同,使得悬浮物粒径分布、形状以及组成成分不同,导致太湖水体单位后向散射系数存在一定变化;以550 nm作为参考波段对太湖后向散射系数进行参数化,得出该波段后向散射系数与悬浮物浓度具有很好的线性关系,其指数在1.32~2.8之间变化,平均值为2.09.     

Suspended sediment transport effectiveness of three large impounded rivers, U.S. Gulf Coastal Plain

 Suspended sediment transport effectiveness was examined near the mouths of three large impounded rivers (Rio Grande, Brazos, and Pearl Rivers) in differing precipitation regimes in the U.S. Gulf Coastal Plain. Magnitude and frequency analysis of suspended sediment transport was performed by examining the effectiveness of both discharge and time in transporting suspended sediment. Bivariate plots of discharge with infrequent values of silt/clay and sand provide an insight into the relative proportion of coarse-versus fine-grained sediment transport for the three rivers. Despite the aridity of the Rio Grande and Brazos drainage basins, which is often associated with infrequent or episodic transport of sediment, the duration of the effective discharge is similar to humid basins described in the literature. The majority of sediment transport occurs during the moderate discharge events, having a duration of 2.4%, 1.5%, and 4.4% for the Rio Grande, Brazos, and Pearl Rivers, respectively. This may be due to the influence of scale or the influence of upstream dams and reservoirs on discharge and sediment transport. Findings from this research suggest that magnitude and frequency analysis of discharge and suspended sediment near the mouths of large rivers may provide a useful framework for understanding the timing and delivery of riverine sediments to the nearshore coastal environment from rivers draining a range of geologic and climatic settings. Received: 6 September 1996 · Accepted: 4 February 1997     

基于水体光学分类的鄱阳湖悬沙浓度反演方法研究

鄱阳湖是我国重要的湿地生态系统,对调节流域的水沙变化有着重要作用。由于鄱阳湖湖区面积广,内部差异大,单一的悬浮泥沙反演模型不足以准确反演出湖区的悬浮泥沙浓度。以实测的反射光谱数据、泥沙浓度数据为基础,提出一种基于分类后的反演模型,即根据实测数据的光谱形态特征分类出5种典型的水体类型。在此基础上,将分类后的各类水体分别建立各自合适的反演模型进行反演。结果表明基于水体分类的经验模型反演达到满意效果,平均绝对误差为0.00217g/L,平均相对误差为3.022%。基于分类后的经验反演模型适用于鄱阳湖悬沙浓度分布的监测研究,有助于更加宏观、准确的掌握鄱阳湖泥沙浓度的空间分布和变化,为保持鄱阳湖资源的可持续开发与利用提供决策依据。     

Phosphorus in suspended matter and sediments of a hypertrophic lake. A case study: Lake Dianchi,China

From June 2004 to December 2004, Lake Dianchi, which had large scale of cyanobacterial blooms was investigated in order to study P-fractionation in the suspended matter and the sediment. The investigation improves our understanding of phosphorus in Lake Dianchi and the relationship between phosphorus and cyanobacterial blooms. It contributes to the available literature on the behavior of P in hypertrophic lakes. The distribution of P-fractions in Lake Dianchi was not uniform from northwest to south, but was closely related to the trophic status of the whole lake. The concentrations of total phosphorus, labile P (NH₄Cl-P), Organic P (NaOH-NRP) and loss on ignition in suspended matter were positively correlated with the strength of cyanobacterial blooms. Total phosphorus in suspended matter was relatively stable for almost half an year and closely related to Chl. a concentration. The main content of organic phosphorus is in the cyanobacterial blooms. The concentrations of phosphorus bound to metal oxides and carbonates (NaOH-SRP and HCl-P) in sediment were similar to NaOH-SRP and HCl-P in the corresponding suspended matter. The latter two forms of P in suspended matter were not affected by cyanobacterial blooms, indicating that the inorganic phosphorus is derived from the sediment after resuspension from the sediment due to wind and wave action. The contribution of the different P-fractions to TP in sediment and in suspended matter indicates that NH₄Cl-P in the suspended matter is an important buffer for maintaining dissolved phosphorus in water.     

Controls of variation in suspended sediment concentration in the River Rother, West Sussex, England

Suspended sediment concentrations were determined for samples collected from the River Rother, West Sussex, and rating loops constructed for several hydrographs. The rating loops often exhibit hysteresis with a greater suspended sediment concentration for a given discharge occurring on the rising limb than on the falling limb. A comparison of these loops indicates that the hysteresis, and the suspended sediment concentration (for a given discharge) become progressively reduced when storm events occur in rapid succession. Various types of rating curves can be identified, and a model of suspended sediment concentration and discharge constructed. Controlling factors of suspended sediment concentration are river discharge, duration and frequency of the storm event, the length of time between successive events, and the time of year.     

The prehistory and palaeogeography of the great Indian desert : Bridget Allchin, Andrew Goudie, and Karunakara Hegde. Academic Press, London/New York/San Francisco, 1978, 370 pp., 73 figs., 85 tables, 12 plates. Bibliography, Index, £25/-, U.S. $48.90

Seismic reflection profiles (3.5 kHz) were obtained along more than 3500 km of shiptrack in Lake Superior within the last 2 yr. The acoustic character of profiles is categorized as: (I) a single, strong reflector at the lake floor, (II) a thick, acoustically transparent layer overlying a strong reflector, and (III) relatively thick sediment with internal acoustic reflectors. These profiles, in conjunction with sediment cores from the area, reveal that varved glacial-lacustrine sediment settled out preferentially in a trough between Isle Royale and the north shore, and to a lesser extent in other topographic depressions; bottom currents generated by storm waves prevent clay accumulation on till or bedrock in the open lake wherever the bottom is shallower than 100 m; bottom currents prevent deposition or erode bottom sediment in certain deep-water (> 200 m) valleys; and lacustrine sediment is disturbed by creep or slumping off Grand Portage, Minnesota, and by other processes such as dewatering in many other areas. These factors complicate sedimentation in Lake Superior, and must be considered when investigating any aspect of the lake sediment.     

Late-glacial and postglacial sedimentation in Lake Superior based on seismic-reflection profiles

Seismic reflection profiles (3.5 kHz) were obtained along more than 3500 km of shiptrack in Lake Superior within the last 2 yr. The acoustic character of profiles is categorized as: (I) a single, strong reflector at the lake floor, (II) a thick, acoustically transparent layer overlying a strong reflector, and (III) relatively thick sediment with internal acoustic reflectors. These profiles, in conjunction with sediment cores from the area, reveal that varved glacial-lacustrine sediment settled out preferentially in a trough between Isle Royale and the north shore, and to a lesser extent in other topographic depressions; bottom currents generated by storm waves prevent clay accumulation on till or bedrock in the open lake wherever the bottom is shallower than 100 m; bottom currents prevent deposition or erode bottom sediment in certain deep-water (> 200 m) valleys; and lacustrine sediment is disturbed by creep or slumping off Grand Portage, Minnesota, and by other processes such as dewatering in many other areas. These factors complicate sedimentation in Lake Superior, and must be considered when investigating any aspect of the lake sediment.