太湖波浪与湖流对沉积物再悬浮不同影响的研究

基于有关太湖湖流、波浪和水化学指标的实测资料，对太湖中由于风强迫作用和底层湖流分别产生的湖底切应力进行了计算，发现二之间量级相差很大，得出了在风扰动情况下，由于波动而产生的湖底切应力对沉积物的再悬浮起着主导作用的结论，并估算了其临界值。     

Sediment dynamics of turbidity maximum in Changjiang River mouth in dry season

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.     

高浑浊度河口沉积物的沉积机理评述

该文主要介绍了潮流对沉积作用的影响，沉积物的再悬浮和最大浑浊带的形成机制以及影响沉积物絮凝沉降的因素。潮流是搬运河口泥沙的主要动力，沉积在河口拦门沙的泥沙会在潮流的作用下向河口外继续搬运。沉积物的再悬浮和最大浑浊带密不可分，正是由于沉积物在周期性潮流的作用下引起再悬浮，为最大浑浊带的形成提供了条件。影响沉积物絮凝沉降的因素很多，有内因，也有外因。内因是颗粒物自身的性质；外因如盐度、流速、pH值等。     

Particle flux through the Huanghai Sea cold water mass

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value.     

菲律宾蛤仔(Ruditapes philippinarum)对潮间带水层-沉积物界面颗粒通量影响的研究

研究利用中型生物扰动系统 (AFS)对胶州湾薛家岛潮间带菲律宾蛤仔 (Ruditapesphilippinarum)养殖断面和非养殖断面的中潮和低潮 4个站位的生物沉降和沉积物的再悬浮过程进行测定。结果表明生物沉降作用与大型滤食性双壳类动物 -菲律宾蛤仔的丰度呈显著的正相关关系 (r=0 .984 ,P<0 .0 5 ) ,养殖断面的生物沉降作用要明显地大于非养殖断面。在菲律宾蛤仔的低密度区 ,生物沉降的作用小于自然沉降 ,而在其养殖的高密度区 ,生物沉降率约为自然沉降率的4倍。薛家岛潮间带沉积物的临界侵蚀速率为 17.4～ 2 0 .4 cm/ s。沉积物的稳定性与所测生物因子的关系不密切 (P>0 .0 5 )。作者推测两个断面中潮站位沉积物的相对易侵蚀性 ,可能是由于此处环境受到某些大型动物及高潮带人工养殖带来的扰动所致     

Fine Sediment Resuspension Dynamics in Moreton Bay

A comprehensive field study has been undertaken to investigate sediment resuspension dynamics in the Moreton Bay, a large semi-enclosed bay situated in South East Queensland, Australia. An instrumented tripod, which housed three current meters, three OBS sensors and one underwater video camera, was used to collect the field data on tides, currents, waves and suspended sediment concentrations at four sites (Sites 1, 2, 4, and 5) in the bay. Site 1 was located at the main entrance, Site 2 at the central bay in deep water, and Sites 4 and 5 at two small bays in shallow water. The bed sediment was fine sand (d50=0.2 mm) at Site 1, and cohesive sediment at the other three sites. Based on the collected field data, it is found that the dominant driving forces for sediment resuspension are a combination of ocean swell and tidal currents at Site 1, tidal currents at Site 2, and wind-waves at Sites 4 and 5. The critical bed shear stress for cohesive sediment resuspension is determined as 0.079 Pa in unidirectional flow at Site 2, and 0.076 Pa in wave-induced oscillatory flow at Site 5.     

Contribution of benthic and epiphytic diatoms to clam and oyster production in the Akkeshi-ko estuary

The species composition and dynamics of phytoplankton in the water column and its contribution to clam, Ruditapes philippinarum, and oyster, Crassostrea gigas, production were studied in the Akkeshi-ko estuary, eastern part of Hokkaido, Japan. A total 128 taxa of diatoms were identified, with 103 and 102 species occurring on the surface sediments and in the water column, respectively. Amphora sp., Bacillaria paradoxa var paxilifer, Cocconeis scutellum, Navicula sp., Nitzschia sigma, Paralia sulcata, Rhoicosphenia curvata, Synedra ulna and Thalassiosira sp. were most common and dominant in all stations in both water column and surface sediment. Benthic diatoms were most dominant in both water column and surface sediment. The species composition of epiphytes was, in part, similar to diatom assemblage of the water column and also to that of the surface sediment. The benthic and pelagic ratio in the diatom assemblage of the water column was very high. Benthic diatoms were able to resuspend into water column by turbulence stimulated by wind. Chlorophyll a concentration in the water column increased as wind speed increased. Seventy and 67% of the gut contents oysters consisted of benthic diatoms in 2003 and 2004 and also 78 and 87% of clams in 2003 and 2004, respectively. The availability of benthic and epiphytic diatom assemblages contributes significantly to food resources for clam and oyster mariculture due to resuspension by disturbance in the Akkeshi-ko estuary.     

Horizontal and vertical variations in sedimentation and resuspension rates in a stratifying lake – effects of internal seiches

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.     

波浪作用下浮泥悬扬浓度特性研究

为研究不同波浪环境下,水底浮泥层产生泥沙悬扬后其浓度的分布特性,使用浊度计测定浊度的方法确定水体中泥沙的浓度,并在水槽实验中改变水深、浮泥厚度及造波机的频率和振幅,观察水槽中悬浮泥沙浓度的变化情况,获得水深、波浪频率、波幅以及浮泥厚度对底床泥沙悬扬的影响,分析泥沙浓度的垂向分布特征等。实验结果显示,水深对底床泥沙悬扬的影响最为显著,其他实验参数的影响均不十分显著。同时,通过垂向输沙平衡的分析,得到一个可描述泥沙垂向浓度分布的理论公式,并利用水槽实验结果进行验证。对比结果显示,理论公式所得曲线与实验结果曲线变化趋势一致,部分工况下,理论值稍稍偏大。     

Modelling of resuspension due to fish activity:Mathematical modeling and annular flume experiments

A spatially averaged numerical model was developed to describe the erosion of cohesive sediment. Together with known empirical relations, the model comprises a new formulation for resuspension due to fish activity. Experiments on erosion of natural sediments in the annular flume at Aachen University are used for model calibration. Empirical coefficients were evaluated with genetic algorithms to achieve the best agreement between the model results and the experimental data. The presented model shows sufficient flexibility to account for various sediment properties, including different sediment sources, natural and artificial contaminants, presence or absence of aquatic organisms, and results in an average coefficient of determination, R2 = 90.5% between the model results and the experimental data. Model validation allows it to be assumed that different contaminants affect bed properties differently. Fish activity plays an essential role in correct resuspension prediction. Further sediment erosion experiments with carefully chosen conditions will allow a more comprehensive model evaluation. The presented model is intended to serve as a building block in the development of a hydraulic-sediment-biota model within the W3-Hydro: Water Quality Event Detection for Urban Water Security and Urban Water Management Based on Hydrotoxicological Investigations project that aims to improve the knowledge concerning bioavailability, transport, fate, and effects of contaminants on the aquatic environment.