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1.
《Marine pollution bulletin》2011,62(7-12):399-412
In order to quantify the spatial and seasonal variations of sediment oxygen consumption and nutrient fluxes, we performed a spatial survey in the south west lagoon of New Caledonia during the two major seasons (dry and wet) based on a network of 11 sampling stations. Stations were selected along two barrier reef to land transects representing most types of sediments encountered in the lagoon. Fluxes were measured using ex-situ sediment incubations and compared to sediment characteristics. Sediment oxygen consumption (SOC) varied between 500 and 2000 μmol m−2 h−1, depending on season and stations. Nutrient effluxes from sediment were highly variable with highest fluxes measured in muddy sediments near the coast. Inter-sample variability was as high as seasonal differences so that no seasonally driven temperature effect could be observed on benthic nutrient fluxes in our temperature range. Nutrient fluxes, generally directed from the sediment to the water column, varied between −5.0 and 70.0 μmol m−2 h−1 for ammonia and between −2.5 and +12.5 μmol m−2 h−1 for PO4 and NO2+3. SOC and nutrient fluxes were compared to pelagic primary production rates in order to highlight the tight coupling existing between the benthic and pelagic compartments in this shallow tropical lagoon. Under specific occasions of low pelagic productivity, oxygen sediment consumption and related carbon and nutrient fluxes could balance nearly all net primary production in the lagoon. These biogeochemical estimates point to the functional importance of sediment biogeochemistry in the lagoon of New Caledonia. 相似文献
2.
《Continental Shelf Research》2007,27(10-11):1465-1476
Core sediment samples were collected from the middle shelf of the East China Sea (ECS) to study the phosphorus forms, P accumulation rate (PAR), P burial efficiency and the burial flux in the ECS. The sediment samples were sequentially extracted and directly extracted to analyze different forms of sedimentary P: lossely sorbed P and iron-bound P (PCDB); inorganic P associated with francolite (carbonate fluorapatite, CFA), biogenic hydroxyapatite, smecite, and CaCO3 (PCFA); detrital P (PDetrital); organic P (POrganic); and total P. In addition, the Fe contents in the citrate-dithionite-bicarbonate (CDB) extracted solution were also measured.The total concentrations of P in the surface sediments in the study area ranged from 13.5 to 22.3 μmol g−1. Inorganic P was the major form and accounted for 72–93% of the total P pool. The average percentage of each fraction of P followed the sequence: PDetrital (70%)>POrganic (15.5%)>PCDB (8.4%)>PCFA (5.8%). The distribution pattern of total P in the surface sediment was similar to that of PDetrital and POrganic, but different from that of PCDB and PCFA. The profile variation of POrganic was the most significant among the phosphorus forms at the study stations. The concentrations of PCDB and PCFA showed minor variation with depth. These results may suggest that transformations of POrganic, PCFA and PCDB occurred at the study stations during sedimentary P burial.Based on the concentrations of total P, PCDB and FeCDB obtained in the present study and the mass accumulation rate (MAR) reported in the literature, the values of the PAR, the P diffusion flux (JPFe) supplied by reducible iron hydroxides and the P burial efficiency were calculated. The calculated results for PAR and JPFe in the study area ranged from 1.02 to 24.23 μmol cm−2 yr−1 and from 0.1 to 2.11 μmol cm−2 yr−1, respectively. The phosphorus burial efficiency (PBE) was approximately 90%. The ECS is a phosphorus sink, and the average annual P burial flux has been reasonably estimated to be in the range of 20–25×109 mol yr−1. 相似文献
3.
《Continental Shelf Research》2007,27(10-11):1584-1599
Historic data from the Russian-American Hydrochemical Atlas of Arctic Ocean together with data from the TRANSDRIFT II 1994 and TUNDRA 1994 cruises have been used to assess the spatial and inter-annual variability of carbon and nutrient fluxes, as well as air–sea CO2 exchange in the Laptev and western East Siberian Seas during the summer season. Budget computations using summer data of dissolved inorganic phosphate (DIP), dissolved inorganic nitrogen (DIN) and dissolved inorganic carbon (DIC) gives that the Laptev Sea shelf is a net sink of DIP and DIN of 2.5×106, 23.2×106 mol d−1, respectively, while it is a net source of DIC (excluding air–sea exchange) of 1249×106 mol d−1. In the East Siberian Seas the budget computations give 0.5×106, −11.4×106 and −173×106 mol d−1 (minus being a sink) for DIP, DIN, and DIC, respectively. In summers, the Laptev Sea Shelf is net autotrophic while the East-Siberian Sea Shelf is net heterotrophic, and both systems are weak net denitrifying. The Laptev Sea Shelf takes up 2.1 mmol CO2 m−2 d−1 from atmosphere, whereas the western part of the East-Siberian Sea Shelf loose 0.3 mmol CO2 m−2 d−1 to the atmosphere. The variability of DIP, DIN and DIC fluxes during summer in the different regions of the Laptev and East Siberian Seas depends on bottom topography, river runoff, exchange with surrounding seas and wind field. 相似文献
4.
《Continental Shelf Research》2006,26(17-18):2125-2140
Sediment delivered to coastal systems by rivers (15×109 tons) plays a key role in the global carbon and nutrient cycles, as deltas and continental shelves are considered to be the main repositories of organic matter in marine sediments. The Mississippi River, delivering more than 60% of the total dissolved and suspended materials from the conterminous US, dominates coastal and margin processes in the northern Gulf of Mexico. Draining approximately 41% of the conterminous US, the Mississippi and Atchafalaya river system deliver approximately 2×108 tons of suspended matter to the northern Gulf shelf each year. Unlike previous work, this study provides a comprehensive evaluation of sediment accumulation covering majority of the shelf (<150 m water depth) west of the Mississippi Delta from 92 cores collected throughout the last 15 years. This provides a unique and invaluable data set of the spatial and modern temporal variations of the sediment accumulation in this dynamic coastal environment.Three types of 210Pb profiles were observed from short cores (15–45 cm) collected on the shelf. Proximal to Southwest Pass in 30–100 m water depths, non-steady-state profiles were observed indicating rapid accumulation. Sediment accumulation rates in this area are typically >2.5 cm yr−1 (>1.8 g cm−2 yr−1). Kasten cores (∼200 cm in length) collected near Southwest Pass also indicate rapid deposition (>4 cm yr−1; >3 g cm−2 yr−1) on a longer timescale than that captured in the box cores. Near shore (<20 m), profiles are dominated by sediments reworked by waves and currents with no accumulation (the exception is an area just south of Barataria Bay where accumulation occurs). The remainder of the shelf (distal of Southwest Pass) is dominated by steady-state accumulation beneath a ∼10-cm thick mixed layer. Sediment accumulation rates for the distal shelf are typically <0.7 cm yr−1 (<0.5 g cm−2 yr−1). A preliminary sediment budget based on the distribution of 210Pb accumulation rates indicates that 40–50% of the sediment delivered by the river is transported out of the study region. Sediment is moved to distal regions of the shelf/slope through two different mechanisms. Along-isobath sediment movement occurs by normal resuspension processes west of the delta, whereas delivery of sediments south and southwest of the delta may be also be influenced by mass movement events on varying timescales. 相似文献
5.
《Limnologica》2015
To investigate the interaction between cyanobacteria and heterotrophic bacteria under gradients of glucose and nitrate, a cyanobacterial strain of Microcystis aeruginosa was grown in microcosms with and without a freshwater bacterial mixture, which was collected from Lake Taihu. Concentrations of glucose (1350, 975, 600, 300, 150, and 37.5 μmol C L−1) and nitrate (150, 300, and 9000 μmol N L−1) were used in a range of combinations giving 9 different treatments of glucose:nitrate. In the microcosm without the bacterial mixture, M. aeruginosa abundance gradually increased with days in all treatments. However, M. aeruginosa had much lower density in some treatments with the bacterial mixture. The difference in M. aeruginosa growth could be explained by competition with bacteria in the cultures in which these were added. The abundance of M. aeruginosa and bacteria when grown together was nearly equal and the number of the bacterial species was highest in the treatment with 300 μmol C L−1 and 150 μmol N L−1. Our results suggest that at this glucose:nitrate ratio M. aeruginosa and the bacterial mixture maintain a balance, and bacteria maintain diversity. In conclusion, we propose that dissolved organic carbon and nitrate availability fundamentally affects the structure as well as stoichiometry of pelagic associations. 相似文献
6.
《Marine pollution bulletin》2009,58(6-12):349-356
This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) ≈ P) being the dominant P fraction. Given the considerable average Fe(OOH) ≈ P concentration of 912 μg g−1, Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m−2 d−1 recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642–3582 mg kg−1), the high zero equilibrium P concentrations (0.02–0.51 mg L−1) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes. 相似文献
7.
《Journal of Geodynamics》2007,43(1):170-186
Stratigraphic and sedimentological studies indicate that Iceland has experienced over 20 glaciations during the last 4–5 Myr, in reasonable agreement with the number of glaciations reconstructed from the ∂18O record in deep-sea sediment. The pattern of glacial erosion was to a large part controlled by constructive volcanic processes resulting in increased topographic relief after 2.5 Myr. Between 2.5 and 0.5 Ma valleys up to 400 m deep were excavated into the Tertiary basalts of eastern and south Iceland with an average erosion rate of 10–20 cm ka−1. During the last 0.5 million years rates of erosion increased to 50–175 cm ka−1, with an additional 200 to over 1000 m of valley excavation. Previous estimates of the rate of landscape erosion during the Holocene vary widely, from 5 to 70,000 cm ka−1. We present new studies that define the rates of landscape denudation during the major part of the Holocene (the last 10,200 years): one based on the Iceland shelf sediment record, the other from the sediment record in the glacier-fed lake, Hvítárvatn. Both studies indicate average Holocene erosion rates of about 5 cm ka−1 similar to our erosion rate estimate for 4–5 Ma old strata that has not been subjected to regional glaciation. 相似文献
8.
《Continental Shelf Research》2006,26(17-18):2178-2204
Continental-shelf lithofacies are described from a series of cores collected in the northern Gulf of Alaska, a high-energy paraglacial shelf experiencing rapid rates of sediment accumulation. Short-lived tracers (234Th and chlorophyll-a) indicate that during the annual peak in fluvial sediment input (summer), biologic sediment mixing coefficients in the surficial seabed are generally lower than other coastal environments (<20 cm2 yr−1) and mixing extends downward <10 cm.210Pb geochronology indicates that sediment accumulation rates (time scales of 10–100 yr) are 0.1–3 cm yr−1. The measured bioturbation and accumulation rates lead to predictions of moderate to bioturbated lithofacies, as observed. Primary depositional fabric is preferentially preserved where sediment accumulation rates >2 cm yr−1 and non-steady sediment deposition occurs. Depositional fabric is also observed in strata at 50–100 m water depths and is similar in appearance to beds that may form through deposition of wave-induced fluid-mud flows, which have been observed forming on other shelves with moderate to high wave energy. Five general lithofacies can be identified for the study area: inner-shelf sand facies, interbedded sandy mud facies, moderate-to-well-bioturbated mud facies, gravelly mud facies, and Tertiary bedrock facies. The moderate-to-well-bioturbated mud facies is areally dominant, representing over 50% of the shelf area, although roughly equal volumes (∼0.4 km3) of strata with some preservation of primary fabric are annually accumulating. Lithofacies on this paraglacial shelf generally resemble mid- and low-latitude allochthonous shelf strata to a much greater degree than Holocene glacimarine strata formed on shelves dominated by icebergs and floating ice shelves. Paraglacial strata may be differentiated from non-glacial shelf strata by lower organic carbon concentrations, a relatively lower degree of bioturbation, and increased preservation of primary depositional fabric. 相似文献
9.
《Continental Shelf Research》2007,27(3-4):489-505
Sediment accumulation over the past century on the continental shelf near the Po delta varies with distance from the most active distributary channels. Near the Pila and Goro distributaries, sediment accumulation is rapid (1–4 cm yr−1) and occurs in pulses. In these areas, the seabed is dominated by physical sedimentary structures that can be related to flood sedimentation. Between the two distributaries and in the southern portion of the dispersal system, sediment accumulation is slower (rates reach a minimum of 0.23 cm yr−1 at ∼50 km from the Pila mouth) and steady-state, reflecting more continuous dispersal of sediment during non-flood periods. Sedimentary strata in these locations are composed of finer (clayey silt), mottled sediment. The similarity in the spatial distribution of long-term (100-yr) sediment accumulation to deposition resulting from the 2000 flood event suggests that the Po shelf is flood-dominated.About half of the sediment delivered by the Po River on a 100-yr time scale can be accounted for in the seabed deposit within ∼50 km of the Pila mouth. The remaining sediment is likely transported southward by the prevailing circulation, and this sediment coalesces with inputs from the Apennine Rivers. 相似文献
10.
Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LEd = Rnd + A − B(Ts − Ta)). LEd has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rnd) from a linear equation derived from the instantaneous net Radiation (Rnd = CRni + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rnd, A, B, and surface and air temperatures has been calculated. Results showed that Rnd had good performance (nonbias and low RMSE). LEd errors for pasture and soybean were ±28 W m−2 and ±40 W m−2 respectively. 相似文献
11.
《Limnologica》2017
Currently, nanotechnology has gained much interest due to the unique properties of nanomaterials in science and technology. Different types of metallic nanoparticles are routinely synthesized. However, their release into the aquatic environments is a major ecotoxicological concern. In this scenario, it is important to study the potential impact of engineered nanoparticle in aquatic organisms especially freshwater microcrustaceans, such as Ceriodaphnia cornuta. In this study, ZnO NPs were synthesized using the aqueous leaf extracts of Musa paradisiaca and physico-chemically characterized by UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infra red (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). UV–Vis spectroscopy recorded the absorbance peak of ZnO NPs at 338 nm. XRD analysis showed the various Bragg’s reflection peaks at 100, 002, 101, 102, 110, 103, 200, 112, 201, 004 and 202 lattice planes. FTIR spectroscopy outlined sharp intense peaks at 3416 cm−1, 1388 and 1416 cm−1. SEM showed the spherical shape of ZnO NPs with mean particle size of 23.3 nm. AFM confirmed the spherical shape, nanosize and 3D topography of NPs. The ecotoxicity of ZnO NPs was tested on the freshwater crustacean C. cornuta. ZnO NPs were comparatively less toxic than zinc acetate. ZnO NPs caused 42% mortality of C. cornuta at 50 μg mL−1. However, 80% mortality was observed at 50 μg mL−1 of zinc acetate after 24 h. Light and confocal laser scanning microscopic images evidenced the uptake and accumulation of ZnO NPs in the gut of C. cornuta at 50 μg mL−1 after 24 h. Structural deformities were observed on C. cornuta after treatment with 50 μg mL−1 of ZnO NPs. Overall, this study describes the potential impact of the biologically synthesized ZnO NPs in comparison with zinc acetate in the freshwater crustacean C. cornuta. 相似文献
12.
《Marine pollution bulletin》2012,65(12):2857-2859
Baseline Hg concentration in bycatch fish from the SE Gulf of California were determined in muscle and liver of 19 species. Levels of Hg in muscle were compared with legal limits of this element in national and international legislation. Considering all fish species, mean concentrations in liver (2.458 ± 1.997 μg g−1) were significantly higher (p < 0.05) than in muscle (0.993 ± 0.670 μg g−1). The sequence of averaged Hg concentrations in most ichthyofauna was liver > muscle. Highest level of Hg in muscle (2.556 μg g−1) and liver (7.515 μg g−1) corresponded to Diapterus peruvianus and Ophioscion strabo, respectively. Considering muscle samples, none of the species had levels of Hg above the limit (1.0 μg g−1 wet weight) in the Mexican legislation; with respect to the Japanese (0.4 μg g−1 wet weight) and British (0.3 μg g−1 wet weight) legislations, 26.3% and 31.6% of the species respectively, were above the corresponding limits. 相似文献
13.
The diffusion behavior of HA and Nd in the presence of HA in compacted bentonite was investigated experimentally by means of the through-diffusion method. Breakthrough of HA is observed in 1 and 0.1 mol dm−3 NaCl solution and is more significant with a lower dry density such as 1.2 Mg m−3. The one dimensional diffusion model taking parallel complexation equilibrium into account was fitted to the experimentally obtained breakthrough curves and concentration profiles, and the diffusion parameters, such as effective diffusivity and rock capacity factor, were evaluated. The obtained effective diffusivity, around 10−11 m2 s−1, for HA and Nd–HA is comparable to the previously reported value. Using these parameters, predictive calculations were performed to evaluate the effect of HA concentration and sorption distribution coefficient. It is indicated that the effect of sorption distribution coefficient is significant only for a short period and that relatively low HA concentrations might bring higher diffused mass depending on the diffusion behavior of dominant species. 相似文献
14.
《Marine pollution bulletin》2013,77(1-2):411-416
The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in mullet (Liza klunzingeri), water and sediment from northern part of Hormuz strait (Persian Gulf). The concentration levels of total PAHs in L. klunzingeri, water and sediment were 133.99–268.57 ng g−1 dry weight, 3.12–5.88 ng l−1 and 42.29–228.9 ng g−1 dry weight, respectively. Based on isomer ratios, analysis of the PAHs source in the sediment demonstrated that the PAHs come from pyrogenic and petrogenic origin. Risk assessment showed PAHs threshold concentrations to occasionally be exceeded in the study area. 相似文献
15.
《Journal of Hydrology》2006,316(1-4):213-232
The Magdalena River, a major fluvial system draining most of the Colombian Andes, has the highest sediment yield of any medium-sized or large river in South America. We examined sediment yield and its response to control variables in the Magdalena drainage basin based on a multi-year dataset of sediment loads from 32 tributary catchments. Various morphometric, hydrologic, and climatic variables were estimated in order to understand and predict the variation in sediment yield. Sediment yield varies from 128 to 2200 t km−2 yr−1 for catchments ranging from 320 to 59,600 km2. The mean sediment yield for 32 sub-basins within the Magdalena basin is ∼690 t km−2 yr−1. Mean annual runoff is the dominant control and explains 51% of the observed variance in sediment yield. A multiple regression model, including two control variables, runoff and maximum water discharge, explains 58% of the variance. This model is efficient (ME=0.89) and is a valuable tool for predicting total sediment yield from tributary catchments in the Magdalena basin. Multiple correlations for those basins corresponding to the upper Magdalena, middle basin, Eastern Cordillera, and catchment areas greater than 2000 km2, explain 75, 77, 89, and 78% of the variance in sediment yield, respectively. Although more variance is explained when dataset are grouped into categories, the models are less efficient (ME<0.72). Within the spatially distributed models, six catchment variables predict sediment yield, including runoff, precipitation, precipitation peakedness, mean elevation, mean water discharge, and relief. These estimators are related to the relative importance of climate and weathering, hillslope erosion, and fluvial transport processes. Time series analysis indicates that significant increases in sediment load have occurred over 68% of the catchment area, while 31% have experienced a decreasing trend in sediment load and thus yield. Land use analysis and increasing sediment load trends indicate that erosion within the catchment has increased over the last 10–20 years. 相似文献
16.
《Marine pollution bulletin》2014,78(1-2):77-84
The distributions of 41 polychlorinated biphenyls (PCBs) were determined in the aqueous phase, suspended particulate matter (SPM), and sediment of the Daliao River estuary in Liaodong Bay, Bohai Sea (China). The total PCB concentrations ranged from 5.51 to 40.28 ng L−1 in the surface water, from 6.78 to 66.55 ng L−1 dry weight in the SPM, and from 0.83 to 7.29 ng g−1 dry weight in the sediment. The PCB concentrations in water, SPM, and sediment were moderate relative to those reported for other estuary and marine systems around the world. Sedimentary PCB concentrations decreased offshore due to the active deposition of laterally transported river-borne particles. The predominance of the highly chlorinated congeners for the water, SPM, and sediment samples are an indication of either a lack of degradation or the presence of nearby or recent releases into the environment. 相似文献
17.
《Marine pollution bulletin》2014,78(1-2):55-62
In Brazil, where reefs occur in markedly turbid environments, the relationship between sedimentation/organic matter and corals is poorly known. Thus, the ex situ effects of sediment with and without organic matter over the ΔF/Fm and physical state of Mussismilia braziliensis were analyzed. The ΔF/Fm and coral physical state, evaluated through the susceptibility index to sedimentation (SI), were measured in seven colonies exposed to sedimentation (0–450 mg cm−2 day−1) free of organic matter after 45 days of exposure, and in 12 colonies exposed to sedimentation (0–500 mg cm−2 day−1) with organic matter content (10%), in which case ΔF/Fm was measured after 72 h and SI after 120 h. In both cases there were effects of increasing sedimentation on the SI with no effect on ΔF/Fm. Despite the tolerance to high sedimentation rates shown by this coral, we noted that the presence of organic matter might reduce its tolerance to sedimentation stress. 相似文献
18.
This work presents a solid phase extraction (SPE) method for simultaneous preconcentration of trace elements in water samples prior to their ICP-OES determination. Dowex 50W-x8 and Chelex-100 resins were used as SPE sorbent materials for preconcentration of trace Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn. The optimum sample pH, eluent concentration and sample flow rates were found to 6, 3.0 mol L−1 and 3.0 mL min−1, respectively. In terms of multi-element preconcentration capabilities, Dowex 50W-x8 appeared to be a better sorbent. The recoveries for all the tested analytes were >95%. However, Chelex-100 showed a better performance in terms of recovery (>95%) towards Cu, Fe and Zn. Under optimized conditions using Dowex 50W-x8, the relative standard deviations for different metals were <3%. The limits of detection and limits of quantification ranged from 0.01–0.39 μg L−1 and 0.05–0.1.3 μg L−1, respectively. The accuracy of the preconcentration method was confirmed by spike recovery test and the analysis of certified reference materials. The SPE method was applied for preconcentration of the analyte ions in tap water, bottled water and wastewater samples. 相似文献
19.
《Marine pollution bulletin》2009,58(6-12):575-586
Irgarol 1051 (2-methythiol-4-tert-butylamino-6-cyclopropylamino-s-triazine) is an algaecide commonly used in antifouling paints. It undergoes photodegradation which yields M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) as its major and most stable degradant. Elevated levels of both Irgarol and M1 have been detected in coastal waters worldwide; however, ecotoxicity effects of M1 to various marine autotrophs such as cyanobacteria are still largely unknown. This study firstly examined and compared the 96 h toxicities of Irgarol and M1 to the cyanobacterium Chroococcus minor and two marine diatom species, Skeletonema costatum and Thalassiosira pseudonana. Our results suggested that Irgarol was consistently more toxic to all of the three species than M1 (96 h EC50 values: C. minor, 7.71 μg L−1 Irgarol vs. >200 μg L−1 M1; S. costatum, 0.29 μg L−1 Irgarol vs. 11.32 μg L−1 M1; and T. pseudonana, 0.41 μg L−1 Irgarol vs. 16.50 μg L−1 M1). Secondly, we conducted a meta-analysis of currently available data on toxicities of Irgarol and M1 to both freshwater and marine primary producers based on species sensitivity distributions (SSDs). Interestingly, freshwater autotrophs are more sensitive to Irgarol than their marine counterparts. For marine autotrophs, microalgae are generally more sensitive to Irgarol than macroalgae and cyanobacteria. With very limited available data on M1 (i.e. five species), M1 might be less toxic than Irgarol; nonetheless this finding warrants further confirmation with additional data on other autotrophic species. 相似文献
20.
《Continental Shelf Research》2006,26(17-18):2050-2072
A 5-yr data set of near-bed current and suspended-sediment concentration measured within 2 m of the seabed in 60-m water depth has been analyzed to evaluate the interannual variability of physical processes and sediment transport events on the Eel River continental shelf, northern California. This data set encompasses a wide range of shelf conditions with winter events characterized as: Major Flood (1996/97), strong El Niño (1997/98), strong La Niña (1998/99), and Major Storm (1999/00). Data were collected at a site located 25 km north of the Eel River mouth, on the landward edge of the mid-shelf mud deposit. During the winter months sediment resuspension is forced primarily by near-bed oscillatory flows, and sediment transport occurs both as suspended load and as gravity-driven (fluid-mud) flows. Winter conditions that caused periods of increased sediment transport existed on average for 142 d yr−1 over the total record, ranging between 89 d in the Major Flood year (1996/97) and 171 d in the La Niña year (1998/99). Hourly averaged values of significant wave height varied between 0.5 and 10.7 m and hourly averaged values of near-bed orbital velocities ranged between 0 and 125 cm s−1. During the five winters, sediment threshold conditions were exceeded an average of 35% of the time, ranging from 19% in the Major Flood year (1996/97) to 52% in the La Niña year (1998/99). Mean concentration of suspended sediment, measured at 30 cmab, ranged from values close to 0–8 g l−1. Among winters, major sediment flux events exhibited different patterns due to varying combinations of physical processes including river floods, waves, and shelf circulation. Within winters, the major period of sediment flux varied from a 3-d fluid mud event (Major Flood winter) to a 50-d period of persistent southerlies (El Niño winter) and a winter of continuous storm cycles (La Niña winter). Winter-averaged suspended-sediment concentration appeared to vary in response to river discharge, while total sediment flux responded to storm intensity. The net sediment flux appeared to depend on timing of river discharge and shelf conditions. On the Eel River shelf, the mid-shelf mud deposit apparently is not emplaced by deposition from the river plume, but by secondary processes from the inner shelf including off-shelf transport of sediment suspensions and gravity-driven fluid-mud flows. Thus, these inner-shelf processes redistribute sediment supplied by the Eel River (a point source) making the inner shelf a line source of sediment that forms and nourishes the mid-shelf deposit. Large-scale shelf circulation patterns and interannual variability of the physical forcing are also important in determining the locus of the mid-shelf deposit, and both are influenced by climate variations. Post-depositional alteration of the deposit also depends on the subsequent shelf conditions following major floods. 相似文献