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1.
Biodeposition rates were studied for a fouling community with a biomass of 6–10 kg per m2 dry wt including shells in which the barnacle Balanus eburneus was a dominant species. The fouling community filtered Indian River lagoon water containing 2–15 mg per 1 mud-size particles and deposited them as sand-size fecal pellets. Measurements of the fecal pellet flux by sediment traps indicated seasonal variations between 16.7 and 74.8 g per m2 per day. A significant correlation was found between fecal pellet flux and temperature (r=0.90; p<0.001). The average flux of fecal pellet deposition was four times greater than the average flux of suspended particle settling without biological influence. Suspended sediment concentration did not significantly affect the rate of biodeposition. Annual biodeposition was 18 kg per m2.  相似文献   

2.
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   

3.
In situ ingestion rates of some infaunal deposit feeders can be determined without collecting feces by labeling the sediment with fluorescent particles and using these to trace ingested material through the gut of the animals. This technique was applied to the polychaeteNereis succinea and showed that ingestion rate, expressed as material ingested per body weight, increased with temperature and decreased with body size. Total annual ingestion of sediment and detritus for aN. succinea population in a salt marsh near Beaufort, N.C., was estimated to be 5 kg of dry material m?2, more than 4 times that reported for salt marsh epifaunal deposit feeders. *** DIRECT SUPPORT *** A01BY009 00005  相似文献   

4.
The environmental impacts of salmon net-pen aquaculture on the benthic environment were investigated at a commercial fish farm located in coastal Maine waters. This site has a sandy mud bottom and low current velocities, is subjected to episodic sediment resuspension, and way in production for 3 yr prior to this study: We examined both the increase in carbon flux to the benthos caused by the net-pen and the effects of the elevated flux on sediment biogeochemistry and the microbenthic communities. The experimental design involved the establishment of two study sites, an ambient site ca. 100 m from the net-pen and a treatment site around the pen. Sediment traps deployed 1 m above the sediment-water interface indicated that carbon flux to the benthos was increased 1-fold to 6-fold (to a maximum of 5 g m?2d?1) at the edge of the net-pen with little or no increase in carbon flux 10 m from the pen. Unlike carbon flux rates, sediment organic matter inventories showed a complex pattern of change over time. Mineral surface area, organic carbon and nitrogen, digestible protein, and sterol content were initially (April 1991) lower beneath the pen than in ambient sediments. During 1991 ambient sediment accumulated organic matter until July after which it decreased, to a low during November. In contrast, organic matter inventories of sediment beneath the pen remained low until July and then increased to a high during November. These latter gains were associated with the development of bacterial mats at the sediment-water interface. Beneath the pen, microbial and macrofaunal communities were shifted toward those commonly associated with organic enrichment but seasonal trends and storm-related resuspension events also significantly affected these sediment communities. When abundant, most epibenthic organisms were more numerous near the pen than in adjacent ambient areas. These results suggest that net-pen aquaculture can alter the benthic ecosystem in Maine Coastal waters but indicate that the effects are spatially limited.  相似文献   

5.
In situ carbon flux measurements and calculated burial rates are utilized to construct an organic carbon budget for the upper meter of sediment at a single station in Cape Lookout Bight, a small marine basin located on the Outer Banks of North Carolina, U.S.A. (34°37′N, 76°33′W). Of 149 ± 20 mole · m?2 · yr?1 of total organic carbon deposited, 35.6 ± 5.2 mole · m?2 · yr?1 is recycled to overlying waters, 84 ± 18% as ∑CO2 and 16 ± 8% as CH4. Approximately 68 ± 20% of the upward carbon flux is supported by sulfate reduction while 32 ± 16% takes place as the result of underlying methanogenesis. Measured ∑CO2 and CH4 sediment-water fluxes range seasonally from 1900–6300 and 50–2500 μmole · m?2 · hr?1 respectively.The mean residence time of metabolizable organic carbon in the upper 80 cm of sediment is approximately four months with greater than 98% of the calculated total remineralization taking place within three years. In spite of large upward fluxes of methane, larger molecules derived from metabolizable sedimentary organic carbon appear to be the dominant reductants for dissolved sulfate.  相似文献   

6.
Throughflow marsh flumes were used to measure total sediment exchanges (TSS) between the marshes and water column of two Louisiana estuaries. One, the Barataria Basin estuary, is isolated from significant riverine sediment input. There were significant (p<0.05) imports of 33.9 to 443 mg TSS m?2 h?1 at the Barataria Basin brackish marsh (BM) site. The Barataria Basin saltmarsh (SM) site exported TSS in two summer samplings, but significant uptake was measured in April (166 mg m?2 h?1) and November (45 mg m?2 h?1) during a winter frontal passage event. The other estuary, Fourleague Bay, receives large sediment inputs from the Atchafalaya River, and TSS imports of 22.5 to 118.5 mg m?2 h?1 were measured at the BM site here. We calculated sediment accumulation from fluxes quantified in marsh flumes using site-specific sedimentological data and flooding regimes at each site. Water level records from May 1987 to April 1989 showed an extended period of unusually low flooding frequencies. As a result, calculated accretion rates were low, with monthly rates of 0.02 to 0.11 mm and ?0.06 to 0.06 mm at the Barataria BM and SM sites, respectively, and ?0.18 to 0.08 mm at the Fourleague Bay marsh flume site. Actual net sediment deposition, determined by feldspar marker horizon analysis, was 0.7–1.6 mm mo?1 at the Barataria SM and 0.2–1.3 mm mo?1 at the Fourleague Bay BM. Even the highest calculated accretion rates, based on flume measurements, were half to one order of magnitude lower than actual measured sediment deposition. This discrepancy was probably because: 1) most sedimentation occurs during episodic events, such as Hurricane Gilbert in September 1988, which deposited 3.5–15.5 mm of sediment on the Barataria Basin saltmarsh, or 2) most vertical accretion in Louisiana marshes occurs via deposition of in situ organic matter rather than by influx of allochthonous sediment. Our results affirm the variability of short-term sediment transport and depositional processes, the close coupling of meteorologic forcing and flooding regime to sediment dynamics, and the importance of understanding these interrelated mechanisms in the context of longer term measurements.  相似文献   

7.
Benthic macroinvertebrate biomass and ammonium excretion rates were measured at four stations in the Gulf of Mexico near the Mississippi River mouth. Calculated areal excretion rates were then compared to sediment-water nitrogen fluxes measured in benthic bottom lander chambers at similar stations to estimate the potential importance of macroinvertebrate excretion to sediment nitrogen mineralization. Excretion rates for individual crustaceans (amphipods and decapods) was 2–21 nmoles NH4 + (mg dry weight)?1 h?1. The mean excretion rates for the polychaetes, Paraprionaspio pinnata [6–12 nmoles NH4 + (mg dry weight)?1h?1] and Magelona sp. [27–53 nmoles NH4 + (mg dry weight)?1h?1], were comparable or higher than previous measurements for similar size benthic or pelagic invertebrates incubated at the same temperature (22±1°C). Although the relatively high rates of excretion by these selective feeders may have been partially caused by experimental handling effects (e.g., removal from sediment substrates), they probably reflected the availability of nitrogen-rich food supplies in the Mississippi River plume. When the measured weight-specific rates were extrapolated to total areal biomass, areal macroinvertebrate excretion estimates ranged from 7 μmole NH4 + m?2h?1 at a 40-m deep station near the river mouth to 18 μmole NH4 + m?2h?1 at a shallower (28-m deep) station further from the river mouth. The net flux of ammonium and nitrate from the sediments to the water measured in bottom lander chambers in the same region were 15–53 μmole NH4 + m?2h?1 and ?25–21 μmole NO3 ? m?2h?1. These results suggest that excretion of NH4 + by macroinvertebrates could be a potentially important component of benthic nitrogen regeneration in the Mississippi River plume-Gulf shelf region.  相似文献   

8.
This work focuses on the direct measurement of the vertical flux of appendicularian houses in order to assess their importance as a component of vertical carbon flux in coastal areas. For this purpose, arrays of cylindrical sediment traps were deployed for 5 to 8 days at two depths in a coastal area of the northern Aegean Sea (inner Thermaikos Gulf) during spring. The data support the contention that resuspension was minimal. Fecal pellet (FP) production and grazing experiments with the dominant copepods (Acartia clausi) were conducted to provide additional information on the potential FP contribution to the total carbon flux. The magnitude of the vertical flux of particulate organic carbon (POC) ranged between 310 and 724 mg C m?2 day?1. The proportion of phytoplankton carbon in the POC vertical flux was up to 45 %. The contribution of zooplankton FPs to the total carbon never exceeded 5 %. On the contrary, appendicularian houses were an essential component of the biogenic carbon flux contributing up to 55.3 % of the total vertical carbon flux. Consequently, both phytoplankton and appendicularian houses contributed equally to the biogenic carbon flux exceeding 80 % of the total sinking POC. Taking into account the sinking speed of the particles and the environment in the area, all this carbon probably reaches the seafloor, thus indicating a strong pelagic–benthic coupling.  相似文献   

9.
Methane produced in anoxic organic-rich sediments of Cape Lookout Bight, North Carolina, enters the water column via two seasonally dependent mechanisms: diffusion and bubble ebullition. Diffusive transport measured in situ with benthic chambers averages 49 and 163 μmol · m ?2 · hr ?1 during November–May and June–October respectively. High summer sediment methane production causes saturation concentrations and formation of bubbles near the sediment-water interface. Subsequent bubble ebullition is triggered by low-tide hydrostatic pressure release. June–October sediment-water gas fluxes at the surface average 411 ml (377 ml STP: 16.8 mmol) · m?2 per low tide. Bubbling maintains open bubble tubes which apparently enhance diffusive transport. When tubes are present, apparent sediment diffusivities are 1.2–3.1-fold higher than theoretical molecular values reaching a peak value of 5.2 × 10?5 cm2 · sec?1. Dissolution of 15% of the rising bubble flux containing 86% methane supplies 170μmol · m?2 · hr?1 of methane to the bight water column during summer months; the remainder is lost to the troposphere. Bottom water methane concentration increases observed during bubbling can be predicted using a 5–15 μm stagnant boundary layer dissolution model. Advective transport to surrounding waters is the major dissolved methane sink: aerobic oxidation and diffusive atmospheric evasion losses are minor within the bight.  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.
Trends in the spatial distribution of chlorophylla (chla) and colloidal and total carbohydrates on the Molenplaat tidal flat in the Westerschelde estuary, Netherlands, reflected spatial differences in physical properties of the sediment. Results from a Spearman Rank Order Correlation indicated that many of the physical and biological measures covaried. Multiple regression analyses describing the relationship between colloidal carbohydrates and sediment properties resulted in several highly significant equations, although in all cases chla was able to predict colloidal carbohydrate content. Relationships between sediment surface chla and colloidal carbohydrate, and sediment erodibility (i.e., critical erosion threshold, Ucrit, and mass of sediment eroded at a velocity of 30 cm s?1) determined in annular flume experiments were examined. Overall sediment erodibility was lowest (i.e., high thresholds, low mass eroded) for the siltiest sediments in June 1996 when chla and colloidal carbohydrates were high (56.9 μg gDW?1 and 320.6 μg gluc.equ. gDW?1, respectively), and greatest (i.e., low thresholds, high mass eroded) at the sandier sediments in September 1996, when chla and colloidal carbohydrates were low (1.0 μg gDW?1 and 5.7 μg gluc.equ. gDW?1, respectively). When sediments were grouped according to relative silt content, the most significant relationships were found in muddy sand with a finegrained fraction (<63 μm) of 25–50%. Thresholds of erosion increased, while mass of sediment eroded decreased, with increasing chla and colloidal carbohydrate. A similar trend was observed for the sand-muddy sand (63 μm 10–25%). In the sand (63 μm 0–10%), there were no relationships for Ucrit, whereas mass eroded appeared to increase with increasing chla and colloidal carbohydrate. The increased carbohydrate may stick sand grains together, altering the nature of erosion from rolling grains to clumps of resuspension.  相似文献   

12.
The release of remineralized N and P from the organic-rich anoxic sediments of Cape Lookout Bight is controlled by processes occurring within the sediment column and at the sediment-water interface. The relatively rapid rates of temperature dependent microbial degradation of organic matter support seasonally varying nutrient fluxes ranging from 20 to 1200 μmol·m?2·hr?1 for dissolved ammonium and from ? 20 to 120 μmol·m?2·hr?1 for total dissolved phosphate (measured in situ over the period October, 1976 to October, 1978). Molecular diffusion along steep vertical pore water concentration gradients measured simultaneously cannot explain the high fluxes observed during warmer months. Gradients for ammonium and phosphate ranged from 0.33 to 1.10 and from 0 to 0.29 μmol·cm?3pw·cm?1s respectively. These high summertime fluxes appear to result from increased sediment-water transport associated with bubble tubes created and maintained by low-tide methane gas bubble ebullition. When these tubes are present, apparent bulk sediment diffusivities calculated from concurrent studies of methane and radon-222 sediment-water exchange are 1.0–3.1 times greater than molecular diffusivities. Nutrient fluxes calculated via Fick's first law taking into account this enhanced transport and the differential diffusive mobilities of dissolved ammonium, phosphate and phosphate ion pairs indicate that removal by aerobic adsorption and/or biological uptake at the sediment-water interface plays an important role in controlling nutrient exchange in these sediments.  相似文献   

13.
Direct measurements of groundwater seepage show the importance of subaqueous discharges as sources of fresh water and of dissolved chemicals to lakes and the coastal ocean. The rate of seepage decreases rapidly offshore; an analytical solution was developed that describes the discharge as Ki(In(coth πxk/4l))/k where i is the hydraulic gradient, K is the vertical hydraulic conductivity,l is the aquifer thickness, x is the distance from the shoreline, and k2 is K divided by the horizontal hydraulic conductivity. In addition to variations due to the inhomogeneities in the aquifer, seepage into the coastal ocean involves some recirculation of the salt water. In Great South Bay, New York measured fluxes were as great as 150 I m?2 d?1. The discharge near the shore was typically 50 I m?2 d?1, decreasing to 30 1 m?2 d?1 at a distance of 100 m offshore. Secondary convection due to an unstable density structure at the sediment-water interface may also be superimposed on the seepage distribution. Fingers of salt should be capable of carrying marine water many decimenters downward against the fresh groundwater advection. As a result, care must be exercised in interpreting direct measures of seepage flux to recognize the contribution of recirculated seawater.  相似文献   

14.
Long time-series studies are critical to assessing impacts of climate change on the marine carbon cycle. A 27-year time-series study in the abyssal northeast Pacific (Sta. M, 4000 m depth) has provided the first concurrent measurements of sinking particulate organic carbon supply (POC flux) and remineralization by the benthic community. Sediment community oxygen consumption (SCOC), an estimate of organic carbon remineralization, was measured in situ over daily to interannual periods with four different instruments. Daily averages of SCOC ranged from a low of 5.0 mg C m?2 day?1 in February 1991 to a high of 31.0 mg C m?2 day?1 in June 2012. POC flux estimated from sediment trap collections at 600 and 50 m above bottom ranged from 0.3 mg C m?2 day?1 in October 2013 to 32.0 mg C m?2 day?1 in June 2011. Monthly averages of SCOC and POC flux correlated significantly with no time lag. Over the long time series, yearly average POC flux accounted for 63 % of the estimated carbon demand of the benthic community. Long time-series studies of sediment community processes, particularly SCOC, have shown similar fluctuations with the flux of POC reaching the abyssal seafloor. SCOC quickly responds to changes in food supply and tracks POC flux. Yet, SCOC consistently exceeds POC flux as measured by sediment traps alone. The shortfall of ~37 % could be explained by sediment trap sampling artifacts over decadal scales including undersampling of large sinking particles. High-resolution measurements of SCOC are critical to developing a realistic carbon cycle model for the open ocean. Such input is essential to evaluate the impact of climate change on the oceanic carbon cycle, and the long-term influences on the sedimentation record.  相似文献   

15.
Sediment oxygen uptake and net sediment-water fluxes of dissolved inorganic and organic nitrogen and phosphorus were measured at two sites in Fourleague Bay, Louisiana, from August 1981, through May 1982. This estuary is an extension of Atchafalaya Bay which receives high discharge and nutrient loading from the Atchafalaya River. Sediment O2 uptake averaged 49 mg m?2 h?1. On the average, ammonium (NH4 +) was released from the sediments (mean flux =+129 μmol m?2 h?1), and NO3 ? was taken up (mean flux =?19 μmol m?2h?1). However, very different NO3 ? fluxes were observed at the two sites, with sediment uptake at the upper, river-influenced, high NO3 ? site (mean flux =?112 μmol m?2 h?1) and release at the lower, marine-influenced low NO3 ? site (mean flux =+79 μmol m?2 h?1). PO4 3? fluxes were low and often negative (mean flux =?8 μmol m?2 h?1), while dissolved organic phosphorus fluxes were high and positive (mean flux =+124 μmol m?2 h?1). Dissolved organic nitrogen fluxes varied greatly, ranging from a mean of +305 μmol m?2 h?1 at the lower bay, to ?710 μmol m?2 h?1 at the upper bay. Total dissolved nitrogen and phosphorus fluxes indicated the sediments were a nitrogen (mean flux =+543 μmol m?2 h?1) and phosphorus source (mean flux =+30 μmol m?2 h?1) at the lower bay, and a nitrogen sink (mean flux =?553 μmol m?2 h?1) and phosphorus source (mean flux =+17 μmol m?2 h?1) in the upper bay. Mean annual O∶N ration of the positive inorganic sediment fluxes were 27∶1 at the upper bay and 18∶1 at the lower bay. Based on these data we hypothesize that nitrification and denitrification are important sediment processes in the upper bay. We further hypothesize that Atchafalaya River discharge affects sediment-water fluxes through seasonally high nutrient loading which leads to net nutrient uptake by sediments in the upper bay and release in the lower bay, where there is less river influnces.  相似文献   

16.
During the anaerobic decomposition of organic matter in sediments iodine is released into solution. Three techniques have been applied to independently estimate the resulting flux of soluble I from the sediments to the overlying water of Mud Bay, Georgetown, South Carolina. Flux estimates (summer) range between ~ 5 and 41 μmol/m2/day. The estimates predicted from either the pore water I concentration gradient across the sediment-water interface or the dissolved I production rate are higher than the apparent flux measured directly at the same site. This suggests that I which is released to the pore water under the anoxic conditions below the sediment surface reacts with a sedimentary component at or near the sediment water interface and is lost from solution.  相似文献   

17.
The western Arctic Shelf has long been considered as an important sink of nitrogen because high primary productivity of the shelf water fuels active denitrification within the sediments, which has been recognized to account for all the nitrogen (N) removal of the Pacific water inflow. However, potentially high denitrifying activity was discovered within the oxygenated Chukchi Shelf water during our summer expedition. Based on 15N-isotope pairing incubations, we estimated denitrification rates ranging from 1.8 ± 0.4 to 75.9 ± 8.7 nmol N2 L?1 h?1. We find that the spatial pattern of denitrifying activity follows well with primary productivity, which supplies plentiful fresh organic matter, and there was a strong correlation between integrated denitrification and integrated primary productivity. Considering the active hydrodynamics over the Chukchi Shelf during summer, resuspension of benthic sediment coupled with particle-associated bacteria induces an active denitrification process in the oxic water column. We further extrapolate to the whole Chukchi Shelf and estimate an N removal flux from this cold Arctic shelf water to be 12.2 Tg-N year?1, which compensates for the difference between sediment cores incubation (~ 3 Tg-N year?1) and geochemical estimation based on N deficit relative to phosphorous (~ 16 Tg-N year?1). We infer that dynamic sediment resuspension combined with high biological productivity stimulates intensive denitrification in the water column, potentially creating a nitrogen sink over the shallow Arctic shelves that have previously been unrecognized.  相似文献   

18.
The nature of flow, sediment transport and bed texture and topography was studied in a laboratory flume using a mixed size-density sediment under equilibrium and non-equilibrium (aggradational, degradational) conditions and compared with theoretical models. During each experiment, water depth, bed and water surface elevation, flow velocity, bed shear stress, bedload transport and bed state were continuously monitored. Equilibrium, uniform flow was established with a discharge of about 0.05 m3 s?1, a flow depth of about 0.01 m, a flow velocity of about 0.81–0.88 m s?1, a spatially averaged bed shear stress of about 1.7–2.2 Pa and a sediment transport rate of about 0.005–0.013 kg m?1 s?1 (i.e. close to the threshold of sediment transport). Such equilibrium flow conditions were established prior to and at the end of each aggradation or degradation experiment. Pebble clusters, bedload sheets and low-lying bars were ubiquitous in the experiments. Heavy minerals were relatively immobile and occurred locally in high concentrations on the bed surface as lag deposits. Aggradation was induced by (1) increasing the downstream flow depth (flume tilting) and (2) sediment overloading. Tilt-induced aggradation resulted in rapid deposition in the downstream half of the flume of a cross-stratified deposit with downstream dipping pebbles (pseudo-imbricated). and caused a slight decrease in the equilibrium mean water surface slope and total bedload transport rate. These differences between pre- and post-aggradation equilibrium flow conditions are due to a decrease in the local grain roughness of the bed. Sediment overloading produced a downstream fining and thinning wedge of sediment with upstream dipping pebbles (imbricated), whereas the equilibrium flow and sediment transport conditions remained relatively unchanged. Degradation was induced by (1) decreasing the downstream flow depth (flume tilting) and (2) cutting off the sediment feed. Tilt-induced degradation produced rapid downstream erosion and upstream deposition due to flow convergence with little change to the equilibrium flow and sediment transport conditions. The cessation of sediment feed produced degradation and armour development, a reduction in the mean water surface slope and flow velocity, an increase in flow depth, and an exponential decrease in bedload transport rate as erosion proceeded. A bedload transport model predicted total and fractional transport rates extremely well when the coarse-grained (or bedform trough) areas of the bed are used to define the sediment available to be transported. A sediment routing model, MIDAS, also reproduced the equilibrium and non-equilibrium flow conditions, total and fractional bedload transport rates and changes in bed topography and texture very well.  相似文献   

19.
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   

20.
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   

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