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1.
This paper addresses temporal variability in bottom hypoxia in broad shallow areas of Mobile Bay, Alabama. Time-series data collected in the summer of 2004 from one station (mean depth of 4 m) exhibit bottom dissolved oxygen (DO) variations associated with various time scales of hours to days. Despite a large velocity shear, stratification was strong enough to suppress vertical mixing most of the time. Bottom DO was closely related to the vertical salinity gradient (ΔS). Hypoxia seldom occurred when ΔS (over 2.5 m) was <2 psu and occurred almost all the time when ΔS was >8 psu in the absence of extreme events like hurricanes. Oxygen balance between vertical mixing and total oxygen demand was considered for bottom water from which oxygen demand and diffusive oxygen flux were estimated. The estimated decay rates at 20°C ranging between 0.175–0.322 d−1 and the corresponding oxygen consumption as large as 7.4 g O2 m−2 d−1 fall at the upper limit of previously reported ranges. The diffusive oxygen flux and the corresponding vertical diffusivity estimated for well mixed conditions range between 8.6–9.5 g O2 m−2 d−1 and 2.6–2.9 m2 d−1, respectively. Mobile Bay hypoxia is likely to be associated with a large oxygen demand, supported by both water column and sediment oxygen demands, so that oxygen supply from surface water during destratification events would be quickly exhausted to return to hypoxic conditions within a few hours to days after destratification events are terminated.  相似文献   

2.
To validate a resuspension model of particulate material (salmonid farm wastes), a UV fluorescent particle tracer was selected with similar settling characteristics. Tracer was introduced to the seabed (water depth ≈30 m) and sediment samples taken on days 0, 3, 10, 17 and 30 to measure the horizontal and vertical distribution of tracer in sediments. A concentric sampling grid was established at radii of 25, 50, 100, 150, 200, 400, 700 and 1, 000 m from the source on transects 30° apart. The bulk of the deployed tracer was initially concentrated in an area 25 m radius from the release point; tracer was observed to steadily decrease to zero over a period of 30 days. In a 200 m region measured from the release point in the direction of the residual current, the redeposition of tracer was low. A Lagrangian particle tracking model was validated using these observed data by varying resuspension model parameters within limits to obtain the best agreement between spatial and temporal distributions. The validated model generally gave good predictions of total mass budgets (±7% of total tracer released), particulary where tracer concentrations were high near the release point. Best fit model parameters (critical erosion shear stress=0.018 N m−2, erodibility constan=60 g m−2 d−1) are at the low end of reported parameters for coastal resuspension models. Such a low critical erosion shear stress indicates that the frequency of resuspension and deposition events for freshly deposited material is high.  相似文献   

3.
The temporal and spatial variations in the rate of sedimentation and sediment resuspension in Lake Rehtijärvi (southern Finland) were studied by sediment traps deployed in the stratifying and non‐stratifying regions of the lake. Both the gross sedimentation rate and the resuspension rate recorded by near‐bottom traps were significantly higher in the stratifying region (>20 m depth) than in the shallow part of the lake (2 m depth). These rate changes were caused by temporarily elevated hypolimnetic resuspension rates exceeding 40 g dry weight m?2 day?1 in July 2005, whereas in the shallow station no such peak was observed and the resuspension rate remained below 30 g dry weight m?2 day?1 throughout the study. The elevated resuspension rate in the hypolimnion could not be attributed to surface wave action or sediment disturbance by fish, but was due to the occurrence of internal seiches. The seiche amplitude was on average the highest in July, although the wind velocities were low; this was because winds temporarily were blowing along the longitudinal axis of the lake. Due to the steep slopes, the sediments of Lake Rehtijärvi are prone to redistribution and sediment focusing towards the accumulation areas also affected trap catches in the deep stations.  相似文献   

4.
Sediment trap deployments in estuaries provide a method for estimating the amount of organic material transported to the sediments from the euphotic zone. The amino acid composition of suspended particles, benthic sediment, and sediment-trap material collected at 2.4 m, 5.8 m, and 7.9 m depths in the Potomac Estuary was determined in stratified summer waters, and in well-mixed oxygenated waters (DO) in late fall. The total vertical flow, or flux, of material into the top traps ranged from 3 g m?2 d?1 in August to 4.9 g m?2 d?1 in October. The carbon and nitrogen fluxes increased in the deepest traps relative to the surface traps during both sampling periods, along with that of the total material flux (up to 47.3 g m?2 d?1 in the deepest trap), although the actual weight percent of organic carbon and organic nitrogen decreased with depth. Amino acid concentrations ranged from 129 mg g?1 in surface water particulate material to 22 mg g?1 in particulate material in 9-m-deep waters and in the benthic sediment. Amino acid concentrations from 2.4-mg-depth sediment traps averaged 104±29 mg g?1 in stratified waters and 164±81 mg g?1 in well-mixed waters. The deep trap samples averaed, 77.3±4.8 mg g?1 amino acids in summer waters and 37±16 mg g?1 in oxygenated fall waters. Amino acids comprised 13% to 39% of the organic carbon and 12% to 89% of the orgnaic nitrogen in these samples. Analysis of the flux results suggest that resuspension combined with lateral advection from adjacent slopes can account for up to 27% of the material in the deep traps when the estuary was well-mixed and unstratified. When the estuary was stratified in late summer, the amino acid carbon produced by primary productivity in the euphotic zone decreased by 85% (86% for total organic carbon) at the pycnocline at 6 m depth, leaving up to 15% of the vertical organic flux available for benthic sediment deposition.  相似文献   

5.
Water quality and criculation in Florida Bay (a shallow, subtropical estuary in south Florida) are highly dependent upon the development and evolution of carbonate mud banks distributed throughout the Bay. Predicting the effect of natural and anthropogenic perturbations on carbonate sedimentation requires an understanding of annual, seasonal, and daily variations in the biogenic and inorganic processes affecting carbonate sediment precipitation and dissolution. In this study, net calcification rates were measured over diurnal cycles on 27 d during summer and winter from 1999 to 2003 on mud banks and four representative substrate types located within basins between mud banks. Substrate types that were measured in basins include seagrass beds of sparse and intermediate densityThalassia sp., mud bottom, and hard bottom communities. Changes in total alkalinity were used as a proxy for calcification and dissolution. On 22 d (81%), diurnal variation in rates of net calcification was observed. The highest rates of net carbonate sediment production (or lowest rates of net dissolution) generally occurred during daylight hours and ranged from 2.900 to −0.410 g CaCO3 m−2d−1. The lowest rates of carbonate sediment production (or net sediment dissolution) occurred at night and ranged from 0.210 to −1.900 g CaCO3 m−2 night−1. During typical diurnal cycles, dissolution during the night consumed an average of 29% of sediment produced during the day on banks and 68% of sediment produced during the day in basins. Net sediment dissolution also occurred during daylight, but only when there was total cloud cover, high turbidity, or hypersalinity. Diurnal variation in calcification and dissolution in surface waters and surface sediments of Florida Bay is linked to cycling of carbon dioxide through photosynthesis and respiration. Estimation of long-term sediment accumulation rates from diurnal rates of carbonate sediment production measured in this study indicates an overall average accumulation rate for Florida Bay of 8.7 cm 1000 yr−1 and suggests that sediment dissolution plays a more important role than sediment transport in loss of sediment from Florida Bay.  相似文献   

6.
Biogeochemical processes occurring near the sediment-water interface of shallow (≈20 m) water sediments lying beneath the Mississippi River plume on the Louisiana shelf were studied using benthic chambers and sediment cores. Three sites were chosen with distinctly different characteristics. One was overlain by oxic water where aerobic respiration dominated organic matter remineralization. The second site was overlain by oxic water but organic matter remineralization was dominated by sulfate reduction. The third site was overlain by hypoxic water and aerobic remineralization was of minor significance. Major differences were observed in the fluxes of CO2(17–56 mmol m−2 d−1), O2(2–56 mmol m−2 d−1) and nutrients (e.g., NH4 +, 2.6–4.2 mmol m−2 d−1) across the sediment-water interface, and the relative importance of different electron acceptors, even though the sites were in close proximity and at nearly the same water depth. Large variations in the efficiency of organic-C burial (3%–51%) were also calculated based on a simplified model of the relationships between the fraction of organic matter remineralized by sulfate reduction and the fraction of sulfide produced that is buried as pyrite. These observations demonstrate the high degree of spatial heterogeneity of benthic biogeochemistry in this important near-deltaic environment.  相似文献   

7.
High-resolution current velocity and suspended sediment concentration (SSC) data were collected by using an Acoustic Doppler Current Profiler (ADCP) at two anchor stations and a cross-section in the South Channel of the Changjiang River mouth during meso and neap tides on Nov. 16, 2003. In addition, tidal cycle (13-hour) observation at two stations was carried out with traditional methods during the spring tide. Results indicated that resuspension occurred not only at the flood and ebb maximum, but also in the early phase of ebb in the meso and neap tide. When tidal current transited from high to ebb phase, current speed accelerated. Subsequently, fine-grained sediment with low critical threshold was resuspended and increased concentration. The river mouth area remained in siltation in the meso and neap tidal phase during the observation season, with calculated resuspension flux in the order of magnitude of 10−4–10−7 kg·m−2/s. Suspended sediment transport in the South Channel was dominated by freshwater discharge, but the Storks drift, vertical circulation and vertical shear effect due to tidal oscillation also played an important role in resuspension and associated sediment transport. In contrast, resuspension sediment flux in the spring tide was larger than that in meso and neap tide, especially at the ebb maximum and flood maximum. The present study revealed that intensive resuspension corresponded well with the larger current velocity during winter. In addition, the ‘tidal pumping’ effect and tidal gravity circulation were also vital for forming the turbidity maximum in the Changjiang River estuary.  相似文献   

8.
The high permeability of sediments and strong near-bottom currents cause seawater to infiltrate the surface layers of Middle Atlantic Bight shelf deposits. In this study, sandy sediment cores from 11 to 12 m water depth were percolated with filtered seawater on shipboard. Sedimentary oxygen consumption (SOC) increased non-linearly with pore water flow, approaching maximum rates of 120 mmol m−2 d−1 (May 2001) or 75 mmol m−2 d−1(July 2001). The addition of acetate to the inflowing water promptly enhanced the release of dissolved inorganic carbon (DIC) from the cores. DIC production rates were a linear function of acetate concentration, ranging from 100 to 300 mmol m−2 d−1 without substrate addition to 572 mmol m−2 d−1 with 100 mM acetate. The sediments also hydrolyzed a glucose pseudopolymer, and the liberated glucose prompted an increase of SOC. Our results suggest that decomposition rates of organic matter in permeable sands can exceed those of fine-grained, organic-rich deposits, when water currents cause advective interstitial flow, supplying the subsurface microbial community with degradable material and electron acceptors. We conclude that the highly permeable sand beds of the Middle Atlantic Bight are responsive within minutes to hours and efficiently operate as biocatalytical filters.  相似文献   

9.
Resuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m−2 dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m−2. The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind-exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m−2 and 4971 g m−2, respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short.  相似文献   

10.
Tidal currents and the spatial variability of tidally-induced shear stress were studied during a tidal cycle on four intertidal mudflats from the fluvial to the marine part of the Seine estuary. Measurements were carried out during low water discharge (<400 m3 s−1) in neap and spring tide conditions. Turbulent kinetic energy, covariance, and logarithmic profile methods were used and compared for the determination of shear stress. The cTKE coefficient value of 0.19 cited in the literature was confirmed. Shear stress values were shown to decrease above mudflats from the mouth to the fluvial part of the estuary due to dissipation of the tidal energy, from 1 to 0.2 N m−2 for spring tides and 0.8 to 0.05 N m−2 for neap tides. Flood currents dominate tidally-induced shear stress in the marine and lower fluvial estuary during neap and spring tides and in the upper fluvial part during spring tides. Ebb currents control tidally-induced shear stress in the upper fluvial part of the estuary during neap tides. These results revealed a linear relationship between friction velocities and current velocities. Bed roughness length values were calculated from the empirical relationship given by Mitchener and Torfs (1996) for each site; these values are in agreement with the modes of the sediment particle-size distribution. The influence of tidal currents on the mudflat dynamics of the Seine estuary was examined by comparing the tidally-induced bed shear stress and the critical erosion shear stress estimated from bed sediment properties. Bed sediment resuspension induced by tidal currents was shown to occur only in the lower part of the estuary.  相似文献   

11.
Venice Lagoon, Italy, rests on a series of aquifers that are 1,000 m thick. Measurements of submarine groundwater discharge (SGD) were made in Venice Lagoon using benthic chambers vented to a plastic collection bag. Two hundred measurements taken in a pristine northern lagoon site (Isola la Cura) revealed flow rates as high as 200 cm d−1 with an average of 30 cm d−1. Over 100 measurements taken adjacent to a bulkhead shoreline in the Porto Marghera industrial zone (Fusina) showed flow rates as high as 30 cm d−1 and averaging 6 cm d−1. These flow rates, if representative of even a fraction of the lagoon floor, are easily able to account for the 15% deficit previously calculated between precipitation and runoff for the entire Venice Lagoon drainage basin. Land elevation surrounding the Venice Lagoon is < 10 m within 20 km of the shoreline and is unable to support any substantial onshore water table. Submarine groundwater discharge most likely represents upward artesian discharge from deeper partially confined aquifers. Over 60 samples were collected in total from both sites for nutrient analysis. Ammonium concentration was found to be 2–8 fold higher in the device water than in the lagoon water at the northern site depending on season, and 10–30 times higher at the industrial zone site. These numbers suggest that SGD may be the primary pathway for nutrients and perhaps other contaminants to enter Venice Lagoon.  相似文献   

12.
Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (So), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol−1) than at station A (Ea=110 kJ mol−1). The maximum SRR values observed equalled 14 μmol cm−3 d−1 at station B and 1 μmol cm−3 d−1 at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and So were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m−2 yr−1, and at station A of the order of 12 mol m−2 yr−1. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment.  相似文献   

13.
In a large (8 ha) salt marsh restoration site, we tested the effects of excavating tidal creeks patterned after reference systems. Our purposes were to enhance understanding of tidal creek networks and to test the need to excavate creeks during salt marsh restoration. We compared geomorphic changes in areas with and without creek networks (n = 3; each area 1.3 ha) and monitored creek cross-sectional areas, creek lengths, vertical accretion, and marsh surface elevations for 5 yr that included multiple sedimentation events. We hypothesized that cells with creeks would develop different marsh surface and creek network characteristics (i.e., surface elevation change, sedimentation rate, creek cross-sectional area, length, and drainage density). Marsh surface vertical accretion averaged 1.3 cm yr−1 with large storm inputs, providing the opportunity to assess the response of the drainage network to extreme sedimentation rates. The constructed creeks initially filled due to high accretion rates but stabilized at cross-sectional areas matching, or on a trajectory toward, equilibrium values predicted by regional regression equations. Sedimentation on the marsh surface was greatest in low elevation areas and was not directly influenced by creeks. Time required for cross-sectional area stabilization ranged from 0 to > 5 yr, depending on creek order. First-order constructed creeks lengthened rapidly (mean rate of 1.3 m yr−1) in areas of low elevation and low vegetation cover. New (volunteer) creeks formed rapidly in cells without creeks in areas with low elevation, low vegetation cover, and high elevation gradient (mean rate of 6.2 m yr−1). After 5 yr, volunteer creeks were, at most, one-fourth the area of constructed creeks and had not yet reached the upper marsh plain. In just 4 yr, the site’s drainage density expanded from 0.018 to reference levels of 0.022 m m−2. Pools also formed on the marsh plain due to sediment resuspension associated with wind-driven waves. We conclude that excavated creeks jump-started the development of drainage density and creek and channel dimensions, and that the tidal prism became similar to those of the reference site in 4–5 yr.  相似文献   

14.
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.  相似文献   

15.
This paper characterizes major ion distributions and investigates whether groundwater exerts a major control on the chemical functioning of Mangueira Lagoon, a large (90 km long), shallow (∼4–5 m deep), and fresh coastal lagoon in southern Brazil. Water volumes equivalent to ∼80% of the total annual input are used in the summer for irrigating nearby rice plantations, the most important regional economic activity. While Na+ and Cl− are the major ions in local groundwater, Na+ and HCO3− are the most enriched ions in lagoon water. The ion concentrations measured in Mangueira Lagoon were homogeneous, except for a few samples affected by rainwater and groundwater inputs. A shore-normal transect starting at the pump house of a rice irrigation canal indicated strong groundwater input at this canal. In spite of the small volume contribution (∼2% of precipitation), groundwater discharge accounts for 50–70% of major ion inputs into the lagoon, with ∼70% of the groundwater inputs being anthropogenically derived (e.g., from the rice irrigation canals). This may have serious implications for the management of the coastal water resources from Mangueira Lagoon and other similar areas as groundwater associated with agricultural systems may be contaminated by fertilizers and pesticides. The results imply that groundwater should not be neglected in dissolved species’ budgets even when its volume contribution is small.  相似文献   

16.
Time-series Mark VII sediment trap was deployed at 72°58.55′E, 62°28.63°S (north of the Prydz Bay, Antarctica) during the cruise of CHINARE-15 in cooperation with University of Marine of America. Seasonal variability of deep ocean particle fluxes and biogenic components were investigated in order to reveal the fluxes and biogeochemistry of sinking particles in the deep ocean. The results show that the total mass flux of sinking particles at a water depth of 1000 m ranges from 13.00 to 334.59 mg⋅d−1⋅m−2). A marked seasonal variability exists in the fluxes of all particle components reflecting the seasonal changes in upper water productivity. Biogenic material was a significant component and biogenic silica represented more than 80% of the biogenic matter, reflecting a diatom dominated system, but a lithogenic fraction is always present. The fact that the POC dominated over particulate inorganic carbon (as CaCO3) and Cinorg/Corg was always greater than 1, indicate a net removal of CO2 from surface water by biological activity. __________ Translated from Acta Oceanologica Sinica, 2006, 5: 49–55 [译自:海洋 学报]  相似文献   

17.
Sediment-bound polychlorinated biphenyls (PCBs) measured at several sites in the lower Hudson River Estuary are above equilibrium with the overlying water, providing a thermodynamic driving force for exchange from sediment to water. The fluxes of PCB congeners are estimated for a number potential processes: diffusive release of dissolved and colloidal PCBs from the bed, resuspension and subsequent desorption from resuspended particles, and sediment accumulation and burial. All processes are potentially significant, at least for some congeners. The sediment exchange fluxes of PCB solutes for five sites between Governors Island and Haverstraw Bay are estimated to be 20–860 μm m?2 d?1, which is between 2 and 100 times more than the flux of dissolved PCBs coming down the river at Haverstraw Bay. Much of the exchange from sediment to water may be balanced by burial of sorbed PCBs by sediment accumulation. Advection down the river and sediment exchange dominate other potential sources of PCBs to the lower estuary under current loading conditions. The magnitude of the calculated fluxes is consistent with the nonconservative behavior of PCBs in the same region but is higher than earlier modeling estimates that employed different assumptions.  相似文献   

18.
A simple and inexpensive sampler to measure bedload sediment transport in shallow subtidal or intertidal areas is described. The cylindrical sub-sediment trap with an aspect ratio of 20 (height: diameter) is an improvement over conventional bedload samplers which are difficult to use in shallow areas or fail to collect the biological material associated with bedload. Traps deployed on a low-energy intertidal sandflat for six months provided daily estimates of bedload transport (quartz grains: 0.001–40 kg m?1 d?1), passive infaunal transport (e.g., the bivalveMya arenaria, max: 800 ind m?1 d?1), and organic detrital flux (e.g., macrophyte fragments, max: 400 g dry wt m?1 d?1). Bedload rates estimated with traps were compared to predictions from a numerical bedload model to evaluate the trap’s collection and retention efficiency. A significant linear regression between observed (trap) and predicted (model) rates (r2=0.65, p<0.001, n=97) indicated that the traps were useful for the measurement of high- and low-frequency variability in bedload transport. Potential applications of the traps in benthic oceanography include recruitment and recolonization studies.  相似文献   

19.
 The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of P. This is only few percent of the supply from adjacent marine areas, as the yearly transport through the study area is 218 000 tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m–2 yr–1) and 477 ton of P (on average 0.9 g m–2 yr–1). Shallow-water parts of the study area have no net deposition because of frequent (>35% of the year) resuspension. Resuspension frequency in deep water is <1% of the year. Resuspension rates, as averages for the study area, are 10–17 times higher than net deposition rates. Because of resuspension, shallow-water sediments are coarse lag deposits with small amounts of organic matter (1.1%) and nutrients (0.04% N and 0.02% P). Deep-water sediments, in contrast, are fine grained with high levels of organic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive sediment water fluxes of nutrients, oxygen consumption, and penetration into the sediment. Fluxes of dissolved reactive phosphate from sediment to water after resuspension were negative in organic-rich sediments (13.2% organic matter) with low porosity (56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Fluxes of inorganic N after resuspension were reduced to 70% and 0–20% in relation to the rates before resuspension, respectively. Received: 10 July 1995 · Accepted: 19 January 1996  相似文献   

20.
Suspended sediment concentration is a major variable influencing soil erosion and loss, study on which at different spatial scales is of great meaning to understand soil erosion mechanism and sediment transport process. Based on data from 4 sloping surfaces and 7 basins ranging from 0.0003 to 187 km2 in area, the suspended sediment concentration in flood season (SSC) with drainage area is studied. With increasing drainage area on the slope surfaces, the mean suspended sediment concentration in flood season (MSSC) enhances continuously until a peak value of 685 kg m−3 occurs at the whole slope surface No. 7 runoff plot resulting from harder and harder erosion forms downslope. Entering basin systems, the diluted action of subsurface water on the toeslope on MSSC and small water flow power Ω make a minimum MSSC value of 568 kg m−3 occur in the first-order basin system Tuanshangou basin at an area of 0.18 km2, and then from Tuanshangou basin to larger basins, the positive feedback function among drainage density, water flow energy, and hyperconcentrated flow as well as its reduction of settling velocity of coarser particles generates continuously increasing MSSC with drainage area.  相似文献   

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