共查询到20条相似文献，搜索用时 343 毫秒
1.
Surface samples are used to determine onshore-offshore variations in heavy metal concentrations on tidal flats on Chongming and Hengsha Islands in the Yangtze Estuary, China. The Mann-Whitney U-Test suggests that proximity to the estuarine turbidity maximum does not result in significantly higher metal concentrations on tidal flats. Principal Components Analysis shows that grain-size is the primary control on metal concentrations, reflecting the occurrence of salt marsh and mud and sand flats. Sediment quality is comparable to that of pristine estuaries because of dilution by high river sediment loads. 相似文献
2.
The core of the turbidity maximum zone in the Saint-Lawrence Estuary is located in the North Channel and oscillates in front of the large (3×106 m2) intertidal flats and marshes of Cap Tourmente. It is shown that seasonal fluctuations in the intensity and the position of this core are mainly determined by suspended sediment exchanges between the channel and the marshes. Fine sediments, most of them found 20 km downstream in the channel off Cap Maillard in late winter and early spring, are advected upstream over the flats during the summer months by the tide. The deposition, favored by marsh plant growth, reaches 5×105 metric tons in three months. A period of intense erosion, at a mean rate of 4,500 metric tons per tide, coincides with the destruction of the plant cover by migratory geese. The material removed fills up the Chenal de l’Île d’Orléans upstream and is flushed back into the water column during the next spring freshette. This rotating seasonal sediment circulation, although very localized, exerts a major influence on the distribution and storage time of suspended particles in the upper estuary. 相似文献
3.
Heavy metals on tidal flats in the Yangtze Estuary, China 总被引：7，自引：0，他引：7
Five short cores were used to examine heavy metals on tidal flats in the Yangtze Estuary, China. Statistically insignificant
trends in lead-210 and most metals with core depth are primarily due to high sedimentation rates. Metal contents are correlated
with percent aluminum, which reflects the clay contents in the sediment, and they are also affected by proximity to sewage
outlets and local industry. National standards for copper are exceeded in four cores, zinc in one core, and arsenic in all
cores. Heavy metal contents are generally lower on the Yangtze tidal flats compared to most other estuaries because high sediment
loads dilute metal inputs.
Received: 1 June 1999 · Accepted: 15 August 2000 相似文献
4.
Jacco C. Kromkamp Edward P. Morris Rodney M. Forster Claire Honeywill Scott Hagerthey David M. Paterson 《Estuaries and Coasts》2006,29(2):183-196
Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence,
especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance
and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics.
At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation,
Fo
15), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal
flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes;
we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation
index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. Fo
15 was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between
NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially
for Fo
15. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment
analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries. 相似文献
5.
潮滩沉积的物源一直是沉积学领域重要的研究内容。近30年长江入海泥沙量持续减少,致使长江入海泥沙对浙闽潮滩沉积的物质贡献降低。在此背景下,探究浙闽沿岸潮滩沉积的物源具有重要的现实意义。对杭州湾至福州湾沿岸的泥质潮滩表层沉积开展了详细地磁学研究,结果显示,研究区沉积物的磁性主要受磁铁矿主导,但磁性矿物含量、磁畴和矫顽力等磁性特征存在一定差异,这可能意味着沉积物受到多物源影响。皮尔森相关性分析进一步表明,沉积物磁性特征受粒度效应影响有限,主要与物源差异有关。物源判别结果指示,浙闽泥质潮滩沉积的物源包括长江、海岸基岩和浙闽河流。杭州湾至福宁湾,沉积物普遍受到长江和浙江诸河混合物质的影响,且浙江诸河的物质贡献较大;隘顽湾和象山港沉积物还受到其附近海岸基岩的影响;福宁湾沉积物可能还受到闽江源物质和其附近海岸基岩的影响;罗源湾和福州湾沉积物的潜在物源是闽江和其附近海岸基岩,长江和浙江诸河的物质贡献相当有限。 相似文献
6.
In order to understand natural sea‐level variability, and to enhance future predictions, accurate and precise estimates of Holocene tidal levels are required. Although the application of diatom‐based transfer functions can yield such data, these work best when underpinned by local training sets. Urbanized estuaries offer little prospect of obtaining local training sets and, instead, the reliability of regional transfer functions has to be assessed. The performance of a published regional (UK) diatom‐based tidal‐level transfer function applied to fossil assemblages from two contrasting core sites in the Mersey Estuary, UK, is assessed using modern analogue techniques and sediment isotope data. We find that, although estimated tidal levels coincide with changes in organic matter source, the frequent lack of modern analogues mean that palaeotide estimates are without basis. This is likely a consequence of the site‐specific nature of diatom assemblages in higher intertidal and supratidal areas in particular, where local factors are expected to exert a greater control on their ecology. This situation may be partly resolved by constructing and applying much larger regional training sets from multiple higher intertidal and supratidal sites (where intact). Otherwise the application of alternative techniques, such as regional foraminiferal tidal‐level transfer functions, may be more appropriate. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
7.
Direct and Indirect Effects of Estuarine Reclamation on Nutrient and Metal Fluxes in the Global Coastal Zone 总被引：1，自引：1，他引：0
We demonstrate that land reclamation in estuaries is resulting in very large-scale loss of intertidal area and disconnection of stored sediment with the water column. This process is not just causing loss of estuarine ecosystem services, it is also having a major deleterious impact on the ability of estuaries to retain nutrients and trace metals. The global scale of loss of estuarine wetlands and subtidal sediments has reached the point where the impact of this loss of estuarine retention is likely to be affecting coastal seas worldwide and possibly global element cycles. 相似文献
8.
Kirstin K. Holsman David A. Armstrong David A. Beauchamp Jennifer L. Ruesink 《Estuaries and Coasts》2003,26(4):1155-1173
Complex intertidal habitats characteristic of northeastern Pacific coastal estuaries provide critical nursery environments for young-of-the-year Dungeness crab,Cancer magister, yet their role in supporting subsequent year classes remains unclear. SubadultC. magister (40–130 mm; 1+ and >1+ year classes), which reach densities as high as 4,300 crabs ha?1 in subtidal channels during low tides, migrate during flood tides from subtidal refuges into intertidal habitats to forage. As with other brachyuran species that undertake extensive tidally-driven migrations, intertidal foraging may contribute significantly to the energy budget of subadultC. magister. In order to explore the energetic incentive for intertidal migrations by subadult crabs, we developed an ontogenetically-based bioenergetics model for crabs within Willapa Bay, Washington. The model showed that energetic demand varied spatially across the bay, with the highest average energetic demand of a population of subadult crabs (2.13×106 kJ ha?1) occurring in a habitat stratum termed lower side channel (LSC) and characterized by relatively little subtidal area and extensive intertidal flats. Comparison of model results with subtidal prey production revealed that the latter could not satisfy subadultC. magister energetic demands, especially in LSC where modeled crab predation depleted subtidal prey biomass within 17 simulation days. We estimate that 1 ha of subtidal crabs from LSC would minimally require an additional 1.6 ha of intertidal area to satisfy energetic demands without depleting prey biomass. Our model results support the assertion thatC. magister make regular migrations to forage on productive intertidal flats, and suggest that intertidal foraging may contribute significantly to the diet of subadult crabs in coastal estuaries. 相似文献
9.
通过近年来对江苏沿海有影响的台风暴潮作用前后的滩面高程观测,结合台风浪资料分析,探究了江苏中部沿海潮滩对风暴潮的响应过程。结果显示:潮滩剖面在风暴潮期间呈现"低滩侵蚀、沿岸输运、高滩稳定",明显区别于沙质海岸在台风浪作用下"高滩侵蚀、离岸输运、低滩淤积"的演变特征。应用Delft3D平面二维水沙动力数学模型,模拟了正常天气和台风浪情况下的滩面演变,从动力学角度解释了潮滩间不同区域演变特征差异的原因,论证了台风浪对地貌演变的短历时"插曲式"作用,阐明了涨潮优势流是风暴侵蚀后泥沙沿岸向输运的主控因子。 相似文献
10.
Although the supply and fate of suspended sediment is of fundamental importance to the functioning and morphological evolution
of muddy estuaries, reliable sediment budgets have been established in only a few cases. Especially for smaller estuaries,
inadequate bathymetric surveys and a lack of intertidal sedimentation data often preclude estimation of the sediment budget
from morphological change, while instrument-derived residual fluxes typically lie well within the errors associated with measurement
of much larger gross tidal transports. Given suitably long-term records of continuously monitored suspended sediment concentration
(SSC), however, analysis of the major scales of variation in sediment transport and their relation to hydrodynamic and meteorological
forcing permits qualitative testing of hypotheses suggested by directly measured residual fluxes. This paper analyzes data
from a 1-year acoustic Doppler profiler deployment in the Blyth estuary, a muddy mesotidal barrier-enclosed system on the
UK east coast. Flux calculations indicate a small sediment import equivalent to just 1.5% of the gross flood tide transport.
Little confidence can be assigned to either the magnitude or direction of such a small residual when considered in isolation.
However, the inference that the sediment regime is finely balanced is qualitatively supported by the close similarity between
flood-tide and ebb-tide SSC values. Singular spectrum analysis of the SSC time series shows the expectedly large contributions
to the variance in SSC at intratidal and subtidal (semimonthly and monthly) scales but also picks out intermittent variability
that is initially attributed to a combination of non-tidal surge and wind stress forcing. Closer examination of the data through
cross-correlograms and event-scale analysis indicates that local meteorological forcing is the major factor. Acting through
the resuspension of intertidal mudflat sediments at times of strong westerlies, meteorological forcing is directly implicated
in episodic sediment export from the estuary. Thresholding of tide-averaged fluxes using a range of critical wind stress values
further indicates that ‘tide-dominated’ (i.e., low wind stress) and ‘wave-dominated’ (high wind stress) conditions are associated
with sediment import and export. Sediment balance is potentially sensitive to the frequency of high wind stress events, since
the associated sediment exports are several times larger than the average import under calm conditions. Intermittent meteorological
forcing may thus exert an important control on the sedimentary balance of otherwise tidally dominated muddy estuarine systems,
and the role of wind climate should not be overlooked in studies of estuary response to environmental change. 相似文献
11.
Florencia Botto Gabriela Palomo Oscar Iribarne Mariano M. Martinez 《Estuaries and Coasts》2000,23(2):208-215
Southwestern Atlantic estuaries (Southern Brazil to Northern Patagonia, Argentina) are characterized by the presence of an intertidal burrowing crab Chasmagnathus granulata. This crab species is an important bioturbator which lives in large assemblages and excavates semi-permanent burrows that affect sediment characteristics. Our observations showed that distribution of the crabs in the Mar Chiquita coastal lagoon, Argentina (37°45′S, 57°26′W) affected habitat use and feeding success of migratory shorebirds. During the migratory season the two-banded plover (Charadrius falklandicus) foraged more frequently inside crab beds, and yellowlegs (Tringa flavipes and T. melanoleuca) fed more freqeuntly outside crab beds. Focal observations on the feeding behavior of the white-rumped sandpiper (Calidris fuscicollis) and the two-banded plover inside and outside crab beds showed that the plover was a visual searcher and captured more prey inside crab beds, and the white-rumped sandpiper was a tactile feeder. Although consumption rates (prey min?1) did not differ between sites, their efficiency (prey probe?1) inside crab beds was less. These differences were probably related to changes in sediment characteristics and prey behavior, which vary with crab activity. Burrowing crabs alter the suitability of intertidal habitats used by shorebirds in southwestern Atlantic estuaries. We believe that the same process could be occurring with other burrowing curstaceans such as thalassinidean shrimps in other estuaries of the world and could have important implications for management of flats for shorebirds. *** DIRECT SUPPORT *** A01BY090 00007 相似文献
12.
鸭绿江河口西岸潮间带柱状沉积物中重金属的分布特征及其对流域变化的响应 总被引：1，自引：0，他引：1
2010年和2011年在鸭绿江西水道和西岸潮间带共采集4根柱状样,通过对2mPb测年、粒度、总有机碳、重金属元素等多指标综合分析,探讨了：（1）鸭绿江河口西水道和西岸潮间带柱状沉积物中重金属的垂向分布及其来源：（2）重金属分布的粒度控制作用：（3）不同时期的粒度和重金属分布变化及其对流域变化的响应。结果表明：f1）Cu和zn可能来源于有机质降解的内源释放：Cr和Ni表征了岩石风化剥蚀形成陆源碎屑的自然来源：Cd和Pb反映了人类活动的影响。（2）除西岸潮间带的Cd和Pb含量可能部分受来源影响外,研究区的粒度效应是控制鸭绿江地区重金属含量分布的最主要因素。（3）粒度变化与流域演变密切相关,重金属含量对流域变化和人类活动响应明显,大致以1940年、1970年、1995年为界分为四个沉积阶段：1940年以前,自然演变对鸭绿江河口西岸潮间带的重金属分布控制明显,而1940年来至今,人类活动的控制作用日益凸显。 相似文献
13.
为研究多因子共同作用下的潮滩演变机制,开发了基于植被生长和潮动力作用的潮滩剖面演变数学模型。在不考虑植被作用下,模拟得到了潮滩中长期演变后的上凸形剖面特征;泥沙供给是决定潮滩宽度的因素,供给越充分,潮滩宽度越大。模型考虑植被过程时,结果表明不同的植被生物量分布形式对潮滩水动力的影响程度不同,在潮间带上部,生物量抛物线分布时的减流效果强于生物量线性分布形式;而在潮间带下部则相反。模拟结果显示盐沼和光滩之间出现陡坎,且随着滩面的逐步淤高,陡坎逐步向海移动。 相似文献
14.
Contaminated and possibly hazardous ground represents a problem in all of the industrialized countries of the world. The
investigation of a site that is suspected of being contaminated differs somewhat from a routine site investigation. Sampling
of soils, groundwater and gas-producing material may be required. Various precautions may be necessary in doing this and operatives
may have to wear protective clothing. Four case histories have been chosen to illustrate different aspects of the rehabilitation
of abandoned contaminated land, namely, investigation, assessment, ground treatment and redevelopment. The first comes from
Leeds in West Yorkshire, England, and outlines how a site investigation was undertaken and the nature of the contamination
present, together with a note on the suggested redevelopment. The remaining three case histories are taken from the heavily
industrialized district of the Ruhr in Germany, where extensive mining of coal and associated industries were developed from
the mid-19th century onwards. The first considers the site of the former Graf Moltke mine near Essen. In this instance, the
somewhat novel methods of data assessment and ground treatment are dealt with. The Mont Cenis site at Herne-Sodingen is one
of the more notable old mining/industrial sites undergoing redevelopment in the state of North Rhine Westphalia. Hence, the
case history concentrates of this aspect of rehabilitation. This involves not only the construction of new and interesting
structures but an attempt to reduce energy consumption in an attempt to effect the concept of sustainable development of an
urban area. The last example deals with the abandoned site of the Minister Achenbach mine at Lünen, where the ground conditions
were further complicated by the presence of old bomb craters that had been filled with a variety of materials. In addition,
because of the suspected presence of former foundation structures in the ground an electromagnetic survey was carried out
across part of the site, the areas of high conductivity suggesting their presence.
Received: 15 September 1999 · Accepted: 14 March 2000 相似文献
15.
ABSTRACT The pattern of lateral accretion on an intertidal point bar is a response to the suspended sediment concentrations to which it is exposed. In summer, high sediment concentrations occur only during shallow (ebb) channel flows; deposition therefore takes place mainly on the point bar toe. In winter, high concentrations obtain at all depths and deposition therefore occurs on the upper point bar slopes. Accretion of the point bar toe is limited by scouring resulting from the high rainfall runoff of winter. High suspended sediment concentrations have little effect, however, if flow velocities are too high to allow deposition. Deposition is dependent on the non-uniformity of curved channel flow and is often confined to the downstream (ebb-sense) portion of the point bar. The lateral accretion deposits form a series of wedge-shaped units. Each unit represents one year's deposition, bounded by erosion scarps produced during successive winters. The base of the point bar deposit shows a gradual aggradation, keeping pace with the build-up of the adjacent interchannel flats. 相似文献
16.
《Applied Geochemistry》2003,18(2):327-338
The concept that total organic C (TOC) is the main factor dominating the sorption of PCBs to sediment is over simplified. Numerous discrepancies are found when trying to compare concentrations predicted from laboratory observations to field concentrations. Some studies show a lack of correlation between PCB and TOC or particle size, but state that it is the origin of the organic matter or the clay swelling that is most important in determining the partitioning to sediment. It may also be argued that the discrepancies are merely a reflection of localised inputs of PCBs. An evaluation of the influence of these factors was undertaken at an intertidal site in the Clyde Estuary, previously highlighted as being highly contaminated by PCBs. Analysis of a series of sediment samples failed to show a strong correlation of PCB content with TOC or particle size. Separation into grain-size fractions and subsequent analysis suggested that both variation in organic matter source and mineralogical composition exerts an influence on congener distribution with implications for the mobility of PCBs within intertidal sediments. 相似文献
17.
《Applied Geochemistry》2002,17(1):59-68
In the intertidal flats of Bohai Bay, China, the spatial distribution of the grain size of sediments becomes coarser from landward to seaward. To study the grain size effect on multi-element concentrations in sediments, samples along the coastline and 3 horizontal cross-sections were collected from the intertidal flats of Bohai Bay, China, in 1998. Total concentrations of 49 elements, including alkali, alkaline earth, trace metal, rare and rare earth elements, were measured by ICP–AES, ICP–MS and INAA. The results show that sediment texture plays a controlling role on the concentrations and their spatial distribution. Principal component analysis and cluster analysis were carried out based on the grain sizes of the sediments, and the samples were classified into 3 groups: mud, silt-mud and silt. Significant differences among the element concentrations in the 3 groups were observed, and the concentrations of the elements in each group are reported in this study. Most of the elements have their highest concentrations in the fine grained mud samples, in comparison with the silt and silt-mud samples, with clay minerals possibly playing an important role. In contrast, concentrations of Ba, Sr, Hf, and Zr are elevated in the coarse silt samples. Ba and Sr may reside in feldspars, while Zr and Hf are present in zircons. Landward to seaward spatial variation of element concentrations in the sediments is observed, which is in line with the spatial distribution of the grain size and is related to the seawater hydrological dynamics in the intertidal flats. 相似文献
18.
19.
Tidal flat macrofaunal communities and their associated environments in estuaries of southern California and northern Baja California, Mexico 总被引：1，自引：0，他引：1
Theresa Sinicrope Talley Paul K. Dayton Silvia E. Ibarra-Obando 《Estuaries and Coasts》2000,23(1):97-114
Several tidal flats in both Estero de Punta Banda and Bahia de San Quintín, Baja California, and one in Mission Bay, southern California, were sampled for macrofaunal properties (taxonomic composition, density, species richness, and functional groups for animals ≥0.3 mm) and associated environmental variables (sediment properties, salinity, plant belowground biomass, and cover ofZostera marina) in order to establish a benchmark data set for these areas. The grouping of macrofauna into higher taxonomic or functional groups for these comparisons reduced variability and revealed stronger relationships. Each estuary had a fairly distinct macrofaunal assemblage, with that of Estero de Punta Banda being different from Bahia de San Quintín and Mission Bay primarily due to dominance by a capitellid polychaete, lower proportions of surface deposit feeders, and higher proportions of fauna with a planktonic stage. The flats in Mission Bay and Bahia de San Quintín were dominated by peracarid crustaceans, oligochaetes and polychaetes and had higher proportions of direct developers and macrofauna with mobile adult stages than did Estero de Punta Banda. There was an overlap of the environmental characteristics among estuaries, with more variability of sediment and vegetation properties within than among estuaries. Within Bahia de San Quintín, there was an oceanic to back-bay distribution gradient of macrofauna that was similar to that found in estuaries in wetter climates, despite the lack of a salinity gradient in San Quintín. A decoupling of the benthos and the assumed anthropogenic stresses was observed with the degraded site, Mission Bay, being most similar to the relatively pristine Bahia de San Quintín. Selection of reference sites and sampling variables should be made cautiously because effects of disturbance factors on the benthos may be site-dependent, scale-dependent, or negligible. 相似文献