The effect of tidal range on the flushing of ammonium from intertidal sediments of the Tagus estuary,Portugal

The time-course evolution of ammonium concentration has been examined in the flood water during the first 25 min of tidal inundation. The way this transport fluctuates with the tidal ranges and wind conditions was investigated. Flood water was collected at three sites, located along a transect from the lower to the upper intertidal area of the Tagus estuary. At spring and intermediate tides, the periods of air exposure vary slightly along the transect due to the high tidal amplitude and the flatness of the area, but the upper site remains uncovered at neap tide over the entire tidal cycle. At each site, sampling was performed at different tidal ranges covering the neap-spring tidal cycle and wind conditions. Ammonium was determined in the flood water at short time intervals: 1, 2, 3, 4, 5, 10, 15, 20 and 25 min. A clear pattern was observed along the transect: considerable quantities of ammonium were exported from the sediment to the water column at the beginning of the inundation, ranging from 0.2 to 4.8 mmol m⁻² d⁻¹. The highest transport was recorded at the lower intertidal site under spring tide conditions, which corresponds to the higher energetic situation and shorter emersion period. The lowest transport was observed at the upper intertidal site during the first inundation that followed three days of neap tide and continuous exposure of the sediment to the air. The value rates (0.2–4.8 mmol m⁻² d⁻¹) were one order of magnitude higher than those calculated from molecular diffusion (0.07 – 0.16 mmol m⁻² d⁻¹). This study points to the importance of the tidal flushing of ammonium from the intertidal sediments, and its spatial and tidal fluctuation.     

大小潮作用对潮滩沉积物层理影响的数值模拟研究

潮滩垂向沉积韵律层的形成主要取决于周期性的潮汐条件,包括涨落潮、大小潮、季节性及更长时间尺度的潮汐特征,为探究大小潮周期对潮滩沉积物垂向层理形成机制的影响,应用一维潮流泥沙与底床分层数学模型,对周期性潮汐条件作用下潮滩垂向沉积韵律层形成机制进行了数值模拟研究。结果表明,大小潮的周期性是模型中沉积层理表现韵律性的主要原因之一,韵律层中单个层理结构对应于1个大小潮周期过程,层理结构由形成于小潮期间的泥质层及形成于大潮期间的砂质层组成,层理的厚度也呈旋回性变化,大潮时层理较厚而小潮时层理较薄。水体边界含沙量是影响潮汐层理结构的重要因子,边界含沙量中粉砂占比增大会使潮汐韵律层整体粗化且砂质层厚度增大,当边界含沙量整体显著增大时,潮滩上的垂向潮汐韵律层会更加完整且厚度明显增大。潮汐层理的形成与特征是多种因子共同作用的结果,后续需进一步探究包括波浪、风暴潮、潮滩生物等其他因子的作用。     

长江口北支悬沙浓度及输移的时空变化

本文基于4次洪枯季同步水文观测资料,着重分析了长江口北支悬沙浓度的潮周期变化、垂向分布、纵向分布和悬沙输移及其时空差异。研究结果显示,悬沙浓度的潮周期变化过程在大中潮期以M型(双峰型)为主,下段主槽内在大潮期多出现V型,上段在枯季可出现涨潮单峰型;小潮期可出现无峰、单峰或双峰型。涨、落潮悬沙浓度峰值及均值,在枯季多涨潮大于落潮,洪季中小潮特别是小潮期易出现落潮大于涨潮;下段主槽内在大潮期易出现落潮大于涨潮。悬沙浓度的垂向分布及其变化特点,在大中潮期与悬沙的潮周期变化型式有关,其中M型存在显著的洪枯季差异。纵向上,最高悬沙浓度在枯季出现于中段灵甸港至三和港之间及附近河段,洪季则在下段三条港附近。潮周期悬沙净输移,枯季大多向陆特别是大中潮期,洪季中上段大多向海,下段大潮期多向陆、中小潮易出现向海;下段主槽内在大潮期易出现向海。     

长江口北支悬沙浓度在潮周期内和大小潮周期尺度的变化特征及输运研究

Profiles of tidal current and suspended sediment concentration(SSC) were measured in the North Branch of the Changjiang Estuary from neap tide to spring tide in April 2010. The measurement data were analyzed to determine the characteristics of intratidal and neap-spring variations of SSC and suspended sediment transport. Modulated by tidal range and current speed, the tidal mean SSC increased from 0.5 kg/m3 in neap tide to 3.5 kg/m3 in spring tide. The intratidal variation of the depth-mean SSC can be summarized into three types: V-shape variation in neap tide, M-shape and mixed M-V shape variation in medium and spring tides. The occurrence of these variation types is controlled by the relative intensity and interaction of resuspension, settling and impact of water exchange from the rise and fall of tide. In neap tide the V-shape variation is mainly due to the dominant effect of the water exchange from the rise and fall of tide. During medium and spring tides, resuspension and settling processes become dominant. The interactions of these processes, together with the sustained high ebb current and shorter duration of low-tide slack, are responsible for the M-shape and M-V shape SSC variation. Weakly consolidated mud and high current speed cause significant resuspension and remarkable flood and ebb SSC peaks. Settling occurs at the slack water periods to cause SSC troughs and formation of a thin fluff layer on the bed. Fluxes of water and suspended sediment averaged over the neap-spring cycle are all seawards, but the magnitude and direction of tidal net sediment flux is highly variable.     

崇明东北潮滩泥沙输运过程的研究

潮滩泥沙的输运过程是河口近岸泥沙输运的重要组成部分,也是诊断潮滩侵蚀-淤积的重要动力指标,特别是在地貌演变过程显著的区域更具指示意义.本研究选择长江口崇明岛东北部潮滩,在2018年3月30日-4月10日进行三脚架多参数观测,获取了高分辨率的流速、含沙量等剖面数据,运用机制分解法分析了连续21个潮周期的泥沙输运过程.结果...     

Tidal,diel and semi-lunar changes in the faunal assemblage of an intertidal salt marsh creek

The utilisation of a brackish estuarine marsh by nekton was investigated over a semi-lunar cycle in August 1994. Nekton migrating in and out of the intertidal creeks of the marsh ‘Het Verdronken Land van Saeftinghe’ in the Westerschelde estuary, SW Netherlands, was sampled passively during seven complete tidal cycles. Sampling one tidal cycle yielded three consecutive flood samples and four consecutive ebb samples. Sampling occurred every 2–3 days, covering diel, tidal and semi-lunar situations, thus allowing comparison of tidal, diel and semi-lunar influences on the composition of the intertidal fauna.Two different tidal-migration modes were observed. The mysid shrimp, Mesopodopsis slabberi, showed maximum abundance around high tide. For the remaining common species, the mysid (Neomysis integer), the shrimp (Palaemonetes varians), the crab (Carcinus maenas) and the goby (Pomatoschistus microps) and the amphipod (Corophium volutator), highest densities were recorded during lower water heights. The faunal assemblage shifts between the different tidal stages.On two occasions, consecutive day and night samples were taken. Total densities were higher during the night samples. During spring tide, difference in community composition was noticed between the night and the day samples. During neap tide, day–night differences were less clear. Recorded total densities were highest during spring tide and lowest during neap tide. At maximum water levels, a drop in total density was observed. A shift in community composition occurred between spring and neap tides.     

杭州湾枯季水沙若干特征分析

根据2014年1月及2017年2月杭州湾大、小潮水沙资料,计算了流速、含沙量、单宽潮量、单宽输沙量,进而分析了潮周期断面净潮量、净输沙量和区域冲淤分布。研究发现杭州湾涨、落潮平均流速比值整体较20世纪八九十年代增大,绝大部分区域大于1.0,涨潮流相对增强,澉浦南岸和金山北岸尤为显著。含沙量平面上分布澉浦、杭州湾南岸两个高值区(大潮大于3 kg/m³,小潮大于1.3 kg/m³)以及北岸湾口至乍浦之间的低值区(大潮小于2 kg/m³,小潮小于0.9 kg/m³),随潮汛变化显著,最大含沙量浓度通常滞后于急流时刻。各测站涨、落潮量和输沙量呈现“大涨大落”和“大进大出”的特征,造成杭州湾短时间尺度内的“大冲大淤”。大潮两涨两落金山与乍浦、乍浦与澉浦之间区域净输沙量可达几千万吨,净冲淤则在几百万吨。     

Hydrology of Okarito Lagoon and the inferred effects of selective logging in Okarito Forest

Okarito Lagoon (43° 11′S, 170° 14′E) is a small (20 km²) shore‐parallel, predominantly subtidal estuary, deepest near the landward end, and linked to the sea by two subtidal channels incised through shallow subtidal and intertidal flats which occupy the southern third of the lagoon. Tides at sea vary from 2.1m (spring) to 1.2 m (neap), but in the lagoon the tidal range is constant through the lunar cycle and varies from 0.80 m at the entrance to 0.17 m in the upper lagoon. Tidal water level and flow asymmetries in the subtidal channels are separated by a 1.7 h phase difference. Variations in the net discharge through the inlet result from changing flow cross‐sections rather than from variations in current velocities. Both the tidal‐averaged volume and the tidal compartment of the lagoon vary through the lunar cycle, from maxima at spring tides to minima at neap tides.

Freshwater inflows vary from less than 11 m³.s^‐1 to more than 750 m³.s^‐1. During storms, water level in the lagoon rises rapidly by 2–3 m, then declines to normal over several days. Three water masses, two with salinity and turbidity largely controlled by antecedent rainfall, normally occur in the lagoon. Suspended sediment concentrations in both freshwater inflows and lagoon waters are normally low but increase during floods. Most sediment is supplied by the Waitangi‐taona River or by erosion of tidal channel margins. The lagoon is floored with organic‐rich mud and sandy mud, deposited predominantly from suspension. Surface sediment is consistently muddier than subsurface sediment, probably reflecting an increase in the mud supply since diversion of the Waitangi‐taona River in 1967.

Comparisons of the estimated sediment yield and water inflow effects of the 1967 river diversion with short‐term observations during selective logging suggest that the effects of logging on sediment yield, water balance of the lagoon, and dissolved solids inputs will be small compared with changes caused by diversion of the Waitangi‐taona River.     

特大洪水期间长江口浑浊带分粒级输沙特征

基于2020年7月特大洪水期间长江口浑浊带南槽、北槽和北港多站位同步实测水沙动力数据,研究了河口浑浊带分粒级输沙时空特征及其对泥沙来源响应的指示意义,结果表明：1）北港和北槽是流域泥沙净向口外输移的主要输沙通道,南槽是海域泥沙净向口内输移的主要输沙通道,主槽内粉砂是主要输沙组分,占比63.2%,口外粉砂和黏土是主要输沙组分,分别占43.2%、40.9%;2）大潮粉砂输运占比高于小潮,黏土输运占比低于小潮,口外测站砂组分在大小潮期间在横沙浅滩和九段沙间沿岸输移,横沙浅滩附近大、小潮离岸输沙分别是北港口外的1.7倍和8倍,不利于横沙浅滩淤涨;3）当前流域减沙高达70%,此次特大洪水期间黏土、粉砂和砂三组分近底净向口内输移为减沙背景下的口外供沙提供了有力的佐证。     

Observed fluxes of water,salt and suspended sediment in a partly mixed estuary

Observations of the residual fluxes of water, salt and suspended sediment are presented for seven stations along the Tamar Estuary. The data include measurements over single spring and neap tidal cycles, and are generally applicable to medium or high run-off conditions.Surface to bed differences in salinity are typically of the order of several parts per thousand. Gravitational circulation is an important component of residual flow in the deep, lower reaches of the estuary. Here, Stokes drift is insignificant. In the shallow upper reaches, the major residual currents are generated by Stokes drift and freshwater inputs. Data are compared with predictions from Hansen and Rattray's (1966) model of estuarine circulation.Salt fluxes due to tidal pumping and vertical shear are directed up-estuary at spring tides, tidal pumping being dominant. Tidal pumping of salt is also directed up-estuary at neap tides, although it is insignificant in the lower reaches, where vertical shear dominates.Tidal pumping of suspended sediment is directed up-estuary near the head at spring tides, and probably contributes to the formation of the turbidity maximum. The existence of the turbidity maximum is predicted using a simplified model of the transport of water and sediment. The model shows that an additional mechanism for the existence of the turbidity maximum is an up-estuary maximum in the tidal current speeds (and thus resuspension). In the lower reaches, transport of suspended sediment is directed down-estuary at both spring and neap tides, and sediment is essentially flushed to sea with the fresh water.     

Growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea

To examine the growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea, we surveyed environmental factors such as water temperature, underwater irradiance, tidal exposure, and nutrient concentrations in the water column and sediment pore water in relation to the shoot density, biomass, morphological characteristics, and growth of Z. marina inhabiting the upper and lower intertidal zones. The survey was conducted monthly from January 2003 to December 2004. The water temperature of the two areas displayed seasonal fluctuations. Underwater irradiance was significantly higher in the upper intertidal zone than in the lower intertidal zone. Tidal exposure was also markedly longer in the upper intertidal zone than in the lower intertidal zone, whereas tidal exposure was highest in the spring and lowest in the summer in both areas. Water column NH₄ ⁺ and sediment pore water NO₃ ^?+NO₂ ^? concentrations were significantly higher in the upper intertidal zone than the lower intertidal zone. The eelgrass shoot density, biomass, morphology, and leaf productivity were significantly higher in the lower intertidal zone than in the upper intertidal zone. Both areas displayed a clear seasonal variation depending on changes in water temperature. However, leaf turnover time was significantly shorter in the upper intertidal zone than in the lower intertidal zone, with a higher turnover rate in the upper intertidal zone. Compared to the seagrasses in the lower intertidal zone, those in the upper intertidal zone showed more effective adaptations to the stress of long tidal exposure through downsizing and increased turnover time. These results suggest that tidal exposure, coupled with desiccation stress, can be a limiting factor for seagrass growth in the intertidal zone, along with underwater irradiance, water temperature, and nutrient availability.     

基于浊度计和ADCP的悬沙浓度估计与分析

作者采用浊度计和声学多普勒流速剖面仪(ADCP)在近海区域连续、定点观测的应用中,利用浊度与悬沙浓度之间良好的线性关系,对潮汐半月周期内的浊度和ADCP后向散射声强数据进行相关性分析,讨论了小、中、大潮期间利用ADCP后向散射声强反演悬沙浓度的可靠性,反演过程中综合考虑了声学近场非球面扩散和本底噪声的影响。结果表明,在实验海域中,小潮情况下,各水层内悬浮泥沙成分较为稳定,ADCP后向散射声强与浊度变化相关性较高,达到0.91;而在大潮情况下,ADCP后向散射声强与浊度变化的相关性降低,悬沙浓度及成分容易在海流的影响下发生变化。     

The effects of semi-lunar spring and neap tidal change on nitrification, denitrification and N2O vertical distribution in the intertidal sediments of the Yangtze estuary, China

To explore the influences of semi-lunar spring and neap tidal changes on nitrogen cycling in intertidal sediments, a comparative study among waterlogged, desiccated and reflooded systems was carried out in August 2005 and February 2006 by analyzing nitrification, denitrification and N₂O depth profiles in the intertidal flats of the Yangtze estuary. Laboratory experiments showed that alternating emersion and inundation resulted in the significant changes in nitrification and denitrification rates in the intertidal sediment systems. Due to the desiccation-related effects, lowest nitrification and denitrification rates were observed in the desiccated sediment cores. Highest nitrification and denitrification rates were however detected in the waterlogged and reflooded systems, respectively. It is hypothesized that the highest nitrification rates in the waterlogged sediments were mainly attributed to higher nitrifier numbers and NH₄⁺ being more available, whereas the availability of NO₃⁻ might dominate denitrification in the reflooded sediments. In addition, the highest N₂O concentrations were detected in the reflooded sediment cores, and the lowest found in the dried sediment cores. It was also shown that N₂O in the intertidal sediments was mainly from nitrification under the desiccated condition. In contrast, N₂O in the intertidal sediments was produced mainly via denitrification under the waterlogged and reflooded conditions. It is therefore concluded that the semi-lunar tidal cycle has a significant influence on nitrification, denitrification and N₂O production in the intertidal sediment systems.     

Variability of sediment suspended in rotatory currents,Swansea Bay (Bristol Channel), Great Britain

Two separate current systems have been identified in Swansea Bay — a rotatory current system, located in the northern part of the embayment, and a rectilinear current system, offshore. The amount of fine-grained sediment suspended in the rotatory currents varies with both direction during a tide cycle and tidal range. Measurements of suspended sediment indicate that the suspended load is higher on neap tides than spring tides. This is due to a change in axial orientation of the rectilinear system, which directs ebb-tide currents towards the northern part of the embayment on neap tides, but “deflects” ebb-tide currents from the northern area on spring tides.     

Variabilité spatio-temporelle de la biomasse microphytobenthique en rade de Brest et en Manche occidentale

Microphytobenthic biomass was estimated in the Bay of Brest (1994) and the western English Channel (Trezen Vraz, 1993) using spectrophotometry. Best results (42 % difference) were obtained with an instantaneous extraction procedure at room temperature, compared with the cold extraction procedure. Chlorophyll biomass in sediment was higher in the western English Channel (65–215 mg Chl a m⁻²) than in the Bay of Brest (10–113 mg Chl a m⁻²), in contrast to total pigment biomass (Chl a + pheo a : 88–254 mg m⁻² at Trezen Vraz vs. 131–934 mg m⁻² in the Bay of Brest). This study emphasized decreasing pigment biomass from the estuary to the open sea. Low benthic pigment biomass in the Bay, compared to eutrophic ecosystems, agrees with previous studies on the pelagic system, suggesting that there is no eutrophication in the Bay of Brest. Microphytobenthic blooms were strongly correlated with environmental factors, such as river floods, light intensity, water temperature and the spring/neap tidal cycle. Turbidity and light could be limiting factors at Roscanvel, i.e. the deepest site facing gyre circulation. The latter would favour sedimentation of silt particles at the sediment-water interface. Microphytobenthos population dynamics would be also dependent on the spring/neap tidal cycle, since maximum chlorophyll biomass occurred at neap tides at all three sites in the Bay of Brest, in contrast to the western English Channel. Lower temporal variations of pigment biomass in sediment were observed in the Channel, compared with the Bay of Brest; maximum chlorophyll biomass in sediment was found to occur three to four weeks after the phytoplankton blooms.     

Tidal phase control of sediment discharge from the Yangtze River

Tidal phase plays a major role in controlling sediment discharge from the Yangtze River estuary in eastern China. Direct measurements indicate that during spring tide in mid-November 1981 approximately 3 times the sediment passed down the main channel of the river as during the next neap tide, 3 days later. The estuary presumably acts as a conduit for riverine sediment during spring tide but as a sink during neap tide. Tidal phase control of sediment discharge appears to be primarily dependent upon tidal range relative to estuarine depth rather than river discharge or absolute tidal range per se.     

珠江口洪季最大浑浊带的大小潮变化与机制分析*

基于ROMS三维模型, 模拟了珠江口洪季最大浑浊带的轴、侧向分布和大、小潮变化。模拟结果表明, 珠江口伶仃洋最大浑浊带的轴向位置在22.3°—22.45°N之间, 并随着潮流变化而周期性上下游迁移。控制最大浑浊带形成的主要因素是余流作用下的底层泥沙辐聚, 决定最大浑浊带位置的主要因素是水平对流输沙, 泥沙来源主要是上游浅滩沉积物的再悬浮。小潮期间堆积在浅滩的细颗粒沉积物在大潮期间被悬浮, 搬运到下游的滞流点位置, 在中滩南部和西滩外缘落淤。“潮泵”作用在大潮期间将泥沙向下游输运, 在小潮期间向上游输运; 垂向剪切作用则有利于悬浮泥沙的陆向输运; 二者共同作用产生泥沙辐聚, 形成最大浑浊带。大、小潮期间余流结构差异不大, 主要由密度差和潮汐混合不对称共同导致, 其中前者贡献更大。     

椒江河口层化动力特性研究

基于椒江河口大、小潮期间水位、流速、盐度和悬沙浓度观测数据,研究了椒江河口主潮汐通道的水动力、盐度和悬沙浓度的时空变化特征,解释了高浊度强潮作用下的层化物理机制。椒江河口大潮期悬沙浓度和盐度均大于小潮期,主潮汐通道区域落潮期悬沙浓度大于涨潮期;盐度随潮变化,盐水锋面出现在S2测站,锋面附近出现最大浑浊带;自陆向海,悬沙浓度递减,盐度递增;随水深增加,悬沙浓度与盐度递增。Richardson数与混合参数显示,盐度和悬沙引起的层化现象,是随着潮汐的变化而变化,涨潮时的层化均强于落潮,小潮时的层化持续时间最长,区域更广。混合参数随潮周期变化,大潮期高于临界值1.0,小潮期低于临界值1.0。小潮期水体层化强于大潮期;潮汐应变项是影响势能差异变化率的重要因素;落潮期间层化向混合状态转化,涨潮相反。     

Classification of highly turbid Jiaojiang Estuary

ThisstudywassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49276274,theZhejiangProvinceNaturalScienceFoundationundercontractNo.490013,theChina-Australiabilateralscienceandtechnologyprogram,theAustralianInstituteofMarineScience,theModellingLaboratoryoftheMarineScienceintheSecondInstituteofOceanographyoftheStateOceanicAdministration.INTRODUCTIONTheJiaojiangEstuaryis1ocatedintheeasterncoastofChina,2OokmfromthesouthoftheChangjiangRiver(YangtzeRiver),linkedin…     

Observations of boundary layer parameters and suspended sediment transport over the intertidal flats of northern Jiangsu, China

A current-turbidity monitoring system (CTMS) was deployed on the intertidal flat at Wanggang, northern Jiangsu during October 16-17, 2000, to measure the tidal current speeds and seawater turbidities at 5 levels above the seabed. Based upon the logarithmic-prof‘de equation, the boundary layer parameters, i.e., u*, Z0 and C60, were obtained for 247 tidal flow velocity prof‘des. Around 90% of the profiles were logarithmic according to the critical correlation coefficient. Internal consistency analysis shows that these parameters derived by different methods are consistent with each other. In addition, the height of the bedforms observed is close to the seabed roughness lengths calculated from the velocity prof‘des, indicating that the boundary layer parameters obtained can reveal the conditions at the sedimentwater interface on the intertidal flats. Suspended sediment concentrations were obtained from the 5 CTMS turbidity meters using laboratory and in-situ calibrations. The results show that the in-situ calibrated SSCs have a much higher accuracy than the laboratory calibrated ones. Calculation of suspended sediment fluxes on the intertidal flats, with a magnitude of 104 kg/m per spring tidal cycle, indicates that suspended sediment moves towards the northwest, which is reversal to the transport pattern controlled by the southward Northern Jiangsu Coastal Current in the sub-tidal zone and adjacent shallow waters.