The summertime net transport of dissolved oxygen,salt and heat in a salt marsh basin,North Inlet,S.C.

This study addresses the impact marshes have on the dissolved oxygen content of tidal waters, particularly during summer when respiratory demand for oxygen in adjacent coastal waters is at a maximum and the solubility of oxygen is lowest. The net transports of dissolved oxygen, salt and heat have been measured for 65 tidal cycles during late spring and summer for a small (0·14 km²) salt marsh basin near North Inlet, S.C. The results indicate that export of dissolved oxygen occurs only on tidal cycles that begin between 2:00 am and 10:00 am such that high tide occurs within 4 h of noon. The largest exports of oxygen and heat are produced by spring tides beginning near sunrise. Although the time window for oxygen export is only about 8 h in duration, there is a more or less overall long-term balance between export and import because the magnitude of oxygen export is about 25% greater than import. The magnitude of heat export similarly exceeds heat import but because the time windows for heat export and import are equal, there is an overall export of heat. This study thus suggests that in summer salt marshes of the Atlantic coast export heat and are in balance with respect to the export and import of dissolved oxygen. However, because of the interaction of the diurnal tide with the daily cycle of solar radiation, transient dissolved oxygen concentrations in tidal waters can range from 1.5 to 10.0 ppm. Thus loading of additional oxygen consuming materials to these waters possibly could lead to significant periods of anoxia.     

Marsh topography and hypsometric characteristics of a South Carolina salt marsh basin

A detailed topographic map of a portion of the North Inlet salt marsh system in South Carolina was constructed from aerial overflights, surveying, and tidal measurements. Water storage curves were computed from both (1) hypsometric considerations, and (2) direct measurements of stream and marsh sheet flow. The shape of the hypsometric curve for the basin suggests an immature marsh, which has not yet reached equilibrium in its development.     

Response of a hypersaline salt marsh to a large flood and rainfall event along the west coast of southern Africa

The Orange Estuary lost 27% (276 ha) of its wetland area near the mouth as a result of bad management practices during the 1980s. The salt marsh has been unable to recover over the last 20 years because of the persistently high soil and groundwater salinity. In 2006, a 1 in 5 year flood occurred that completely covered the desertified salt marsh and floodplain with freshwater. The flood was followed by an above average (>45 mm) winter rainfall. Soil and groundwater sampled in April and August 2004 were compared with 2006 data to quantify the impact of the flood and rainfall event. It was hypothesised that the two freshwater events would significantly reduce the soil and groundwater salinity. However, the results showed no significant difference in sediment electrical conductivity throughout the soil profile over the four sampling periods. Soil moisture and organic content however increased significantly after these events in the surface soil layer. The flood deposited silt and scoured sand from the surface layers in significant quantities. The depth to groundwater in the desertified marsh retained a similar pattern after the flood despite 15 cm changes in depth in places. In 2004 a clear groundwater electrical conductivity gradient was present extending from the less saline north part of the marsh (0–15 mS cm⁻¹) to the central part (120–135 mS cm⁻¹) and decreasing again towards the south (60–75 mS cm⁻¹). The flood served to even out the groundwater salinity across the desertified marsh (60–90 mS cm⁻¹). The flood and high rainfall had a limited impact on the soil and groundwater characteristics. The few significant changes that were recorded were mostly restricted to the surface soil layers and on a small spatial scale. The rainfall did however create numerous pools of low salinity (<60 mS cm⁻¹) water on the marsh surface that provided a brief opportunity for salt marsh seeds to germinate. A further benefit of the flood was the increased tidal reach into the desertified marsh importing freshwater from the river mouth and exporting salt. Despite these responses it is unlikely that the hypersaline salt marsh will revegetate naturally. Human intervention is needed to ensure the rehabilitation of this important Ramsar site.     

长江口潮沼植物对动力沉积过程的影响

为探讨潮沼植物对动力沉积过程的影响,在长江口南汇东滩沼泽和邻近的光滩上进行了近底层流速、波浪、悬沙浓度、沉积物粒径和滩面淤积速率等对比实验,并在九段沙潮沼中做了两种先锋植物黏附悬沙的实验.结果表明,沼泽和同高程的邻近光滩近底层平均流速的比值为0.16～0.84;两种环境平均波周期、平均波高和平均悬沙浓度的比值分别为1.4,0.43,和0.71.波浪传入沼泽后,一方面波高大大降低,另一方面变得规则有序.海三棱草和草两种先锋植物群落黏附的悬沙分别达到298和40g/m2.由于水动力降低和植物的捕沙功能,细颗粒泥沙易于在沼泽中沉积下来,导致沼泽环境沉积物明显较相邻光滩细;沼泽中沉积速率加快,侵蚀受到抑制.     

A numerical study of tidal asymmetry in Okatee Creek,South Carolina

The Okatee River, South Carolina is characterized by a narrow tidal channel and an extensive area of intertidal salt marshes. Current measurements in the upstream portion Okatee Creek show that tidal flow features an asymmetric pattern: ebb current is stronger than flood current. The ebb dominance is mainly caused by deformation of the dominant astronomical tidal constituent M₂. An unstructured grid, finite volume coastal ocean model (FVCOM) with wet-dry point treatment method is applied to examine physical mechanisms of M₄ overtide generation. Model experiments show that mean absolute amplitude and phase errors are 3.1 cm and 1.7^° for M₂ elevation, 2.4 cm s⁻¹ and 0.8^° for M₂ current major axis, 2.1 cm and 1.8^° for M₄ elevation, and 2.1 cm s⁻¹ and 24.6^° for M₄ current major axis. The overall pattern of tidal asymmetry is qualitatively reproduced. Various sensitivity experiments suggest that the generation of M₄ overtide is a result of nonlinear interaction of tidal currents with irregular creek geometry and bottom topography. Consistent with the classical view, the large volume of intertidal water storage is the major reason for ebb dominance in the creek. However, the zero-inertia assumption (i.e., negligible advective terms) is probably not valid for the entire tidal cycle. Besides the pressure gradient force and the bottom friction force, terms related to lateral shear of the along-estuary velocity (i.e., advective inertia and horizontal eddy viscosity) may also contribute in horizontal momentum balance. Exclusion of the flooding-draining processes over the intertidal zone will severely underestimate tidal currents in the river channel and make the tidal asymmetry less prominent.     

Seasonal distribution of bacteria in salt marsh sediments in North Carolina

The number and size of bacteria at four depths (0–1, 5–6, 10–11 and 20–21 cm) in a North Carolina salt marsh were minotored by direct counts for 13 months. The number of bacteria reached a maximum of about 1·4 × 10¹⁰ cells cm^?3 at the sediment surface in October, corresponding to the period of Spartina alterniflora die-back. Cell numbers were lowest and most consistent throughout the year at the 20 cm depth of sediment. Cell volumes averaged 0·2 μm³ at the marsh surface and decreased with depth. Mean standing crop of bacteria to a depth of 20 cm of sediment was about 14 g bacterial carbon m^?2. In surface sediments bacteria contribute up to 15% and algae up to 10% of total living microbial biomass as estimated by adenosine triphosphate (ATP). Bacteria were the major biomass component at sediment depths of 5, 10 and 20 cm. At all depths the microbial community contributes < 4% total organic carbon and < 8% of total nitrogen.     

Along channel flow and sediment dynamics at North Inlet, South Carolina

In May of 2005, an observational program was carried out to investigate the along channel hydrodynamics and suspended sediment transport patterns at North Inlet, South Carolina. Along channel variability, which is important in establishing sediment transport pathways, has not been characterized for this system. Measurements of water column currents, salinity, bed sediment, suspended sediment concentration, and particle size distribution were obtained over a complete tidal cycle along the thalweg of the inlet entrance. Along channel currents, shear stress and bed sediment distributions vary significantly in space and time along a 3 km section bracketing the inlet throat. Most of the variability is consistent with geomorphic controls such as bed elevation variability and channel width. The highest velocities, shear stresses, suspended sediment concentration and bed sediment grain size are observed in the narrowest section of the inlet throat. Magnitudes systematically decrease along the channel toward the marsh as changes in channel geometry and branching reduces flow energy. Due to tidal asymmetry, the ebb phase contains significantly higher currents and associated sediment transport. Over the complete tidal cycle, depth integrated transport is directed towards the marsh landward of the intersection of Town and Debidue Creek. In contrast, net transport is out of the inlet seaward of this intersection. Sediment grain size distributions show 35% more material less than 63 μm on flood, suggesting net landward transport of fines.     

长江口盐沼滩面演化的沉积和地球化学特征

选择长江口盐沼典型高程部位(高潮滩上部、中潮滩下部、光滩)柱状样,采用小间隔(1 cm)取样,通过粒度、颗粒有机碳(POC)含量与碳稳定同位素组成(δ13C)分析,研究盐沼滩面发育的沉积和地球化学特征,结果表明,盐沼沉积物的粒度参数、POC含量与δ13C值随深度变化明显;在盐沼典型高程部位沉积物的颗粒组成与地球化学特征差异显著,有明显的滩面趋势,这与滩面的规律性演化密切相关.柱样有限深度内有明显的相对淤积期与冲刷作用相对较强时期的交替,表明长江口盐沼滩面发育过程并不是线性的.盐沼沉积物黏粒含量对POC含量和δ13C值的垂向变化及滩面趋势影响显著,表明流域来水来沙明显制约河口盐沼的发育.对于沉积动力环境复杂、冲淤过程频繁、厚度为毫米级的砂质纹层和泥质纹层发育的河口盐沼,在沉积和地球化学研究中采用小间隔取样的效果明显,有助于揭示盐沼发育过程的更多信息,为年际滩面冲淤演变研究提供新途径.     

Analysis of characteristics of time-frequency correlations between runoff, tidal range and salinity in the Changjiang Estuary

Power spectrum and cross-wavelet transform analysis was adopted to study the time-frequency characteristics and multiscale correlations between runoff, tidal range and salinity in the Changjiang Estuary based on the runoff data collected at the Datong Station, the tidal range measured at the Baozhen Station, and the salinity at the Baogang Station from 2008 to 2009. The variations of the salinity showed significant periodicity at scales of 2-3, 7-8, 14-15 and 26-30 d. The correlation between the salinity and the runoff and the tidal range were found to be significantly related to shock at scales of 5-7, 14-15, 26-30 d and 0.5 a. The correlation between the runoff and the salinity was mainly in the same phase, while the correlation between the tidal range and the salinity was in the antiphase. Different frequency bands were related to different degrees, and their relevance increased as the resonance frequency decreased. In addition, changes of the seasonal runoff were obvious. Specifically, a point of discontinuity was reached in early June with a cycle of 7-8 d, which coincided with the periodicity of plum rains in the Changjiang-Huaihe region. High-frequency changes (8-16 d period) of the salinity corresponded to the time domain in January-April 2008, February-April 2009 and October-December 2009 and exhibited an approximately 0.5 a (184 d) long frequency oscillation. Short-period changes were found to be stronger than long-period changes. Cross-wavelet transforms for the salinity, the runoff and the tidal range revealed local features in the time domain, while the significant levels of different periodic oscillations were observed in the frequency domain. The correlation characteristics of the salinity and the runoff were significant in the 80-90 d frequency domain, indicating that the major impact of the runoff on the salinity was reflected in seasonal changes. The tidal range on the small scale of 14-15 and 30-32 d was more obvious than the runoff.     

江苏海岸带盐沼潮滩在小尺度下的沉积变化过程

在小尺度范围内,潮滩沉积的研究一般都是基于几个站位或断面进行短时日的调查和监测来获取数据,或多或少地存在数据的连续性不足等问题。基于此,本文在潮滩地貌典型的江苏平原海岸选取了约160 000 m²的盐沼潮滩作为研究对象,在多年的野外连续观测下,分析了人类围垦活动对盐沼潮滩沉积过程及变化的影响。结果表明：人类围垦活动（如堤坝建设等）对潮滩沉积和盐沼植被覆盖的变化有重要影响。围垦堤坝修建之前,研究区向陆一侧为盐沼植物（现为养殖池）,向海一侧为光滩,岸线形态比较平直。在2006年围垦堤坝修建后,研究区变为“凹岸”型的人工岸线,沉积环境变得更有利于泥沙的淤积。根据2007-2012年对滩面高程的野外观测,在风暴潮的影响下,潮滩最大淤积率高达23 cm/a。盐沼植被在泥沙快速淤积的基础上不断发育生长,盐沼植物覆盖面积不断扩张。同时外部的沙嘴也在不断增长,潮汐风浪侵蚀携带沙嘴外部泥沙进入盐沼滩地,盐沼植物在泥沙的覆盖下,出现萎缩退化,覆盖面积减少,但是对潮滩上的泥沙而言还是不断堆积增厚。柱状样岩芯的粒度垂向剖面特征也记录了盐沼潮滩沉积环境的变化。小尺度下盐沼潮滩沉积表现出的阶段性变化规律,揭示出合理的围垦活动有利于堤坝前的潮滩淤积和盐沼植被的扩张。     

Cross-shore suspended sediment flux in the salt marsh pioneer zone of Chongming eastern beach in the Changjiang Estuary in China

Between April 2002 and April 2003, in situ measurements of water depth, current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang (Yangtze) Estuary under different weather conditions. Cross-shore suspended sediment flux was calculated and analyzed. The results show that under calm weather conditions, the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles. Owing to current velocity asymmetry, mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase. As a result, net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting. There was significant positive correlation between total sediment flux and quartic power of maximum water depth. It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition. The sedimentation rate on the adjacent mudflat was higher than the salt marsh, which induced stable accreting of salt marsh towards the sea. The wind events enhanced SSC and current velocity during the semidiurnal tides. And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.     

长江口崇明东滩盐沼前缘地带悬浮泥沙横向通量的潮周期变化

对长江口崇明东滩盐沼边缘及邻近光滩处的水深、流速和悬沙含量的潮周期变化过程进行了现场实测,并对横向悬沙通量进行了计算和分析。研究结果表明,在平静天气条件下光滩和盐沼上的流速过程有明显差异,植被缓流作用在落潮期更为显著,流速在涨潮由光滩向盐沼不断增大。与涨潮流速优势相对应,涨潮期平均悬沙含量是落潮期的1.8倍。横向悬沙通量以向岸输移为主,悬沙总通量与潮次内最大水深的四次方呈显著正相关。在平静天气条件下潮汐作用控制着盐沼前缘地带泥沙输移水平,盐沼滩面保持稳定淤积,前缘光滩淤积速率高于盐沼处的,盐沼逐渐向海延伸。在大风天气条件下潮次内的流速和悬沙含量水平提高了数倍,悬沙输移量大增,净输移仍以向岸方向为主,在盐沼上部和前缘光滩均可能在短期内发生大量淤积。     

Fish utilization of a salt marsh intertidal creek in the Yangtze River estuary, China

The structure and temporal variations of the fish community in salt marshes of Chinese estuaries are poorly understood. Fish utilization of a salt marsh intertidal creek in the Yangtze River estuary was studied based on quarterly sampling surveys in July and November, 2004, and February and May, 2005. Fishes were collected by consecutive day and night samplings using fyke nets during the ebbing spring tides. A total of 25,010 individuals were caught during the study. 17 families and 33 species were documented, and the most species-rich family was Gobiidae. Three species, Synechogobius ommaturus, Chelon haematocheilus and Lateolabrax maculatus together comprised 95.65% of the total catch, which were also the most important commercial fishery species in the Yangtze River estuary. The fish community was dominated by juvenile individuals of estuarine resident species. Time of year significantly affected fish use of salt marshes, but no significant effects of diel periodicity on the fish community were found except for fish sampling in July. These findings indicate that salt marshes in the Yangtze River estuary may play important nursery roles for fish community.     

The effect of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off Perth, Western Australia

Submarine groundwater discharge (SGD) into a coastal lagoon off Perth, Western Australia, contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters. This discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days. The delivery rate of nitrate nitrogen by SGD is equal to about 48% of that required for observed growth rates of lagoon macrophytes. Surface salinity is lower close to the shore as a result of SGD. During calm conditions a salinity front was observed in the lagoon, with a nearshore pool of nutrient-enriched water floating above the more saline ocean water.     

Nitrogen and phosphorus concentrations within North Inlet,South Carolina—Speculation as to sources and sinks

The daily concentrations of $\text{NH}{}_4{}^{\mathrm{+}}$, $\text{NO}{}_3{}^{\mathrm{?}}$, and $\text{NO}{}_3{}^{\mathrm{?}}\text{+ NO}{}_2{}^{\mathrm{?}}$ within the North Inlet system are all negatively associated with tidal stage during the late summer, this association breaking down during the winter. The high concentrations of these constituents during low tide coupled with the lack of streamflow during the late summer suggests that there is an internal source for these species. Ammonium and orthophosphate most likely have their source in sediment diffusion from tidal creek sediments and/or seepage from the vegetated marsh surface during tidal exposure. It is hypothesized that high nitrate plus nitrite values at low tide are caused by nitrification within the tidal water or tidal creek sediments. During the summer there is evidence for a source of dissolved organic nitrogen and dissolved organic phosphorus within the North Inlet system, probably via diffusion from creek sediments. In general the main source of dissolved organic nitrogen is via stream-flow from the adjacent watershed. Particulate nitrogen and phosphorus concentrations are a function of: (1) wind and rain events which cause resuspension of particulate material from the tidal creek banks, (2) rain events which scour the marsh surface during tidal exposure, and (3) high tidal velocities which scour the creek bottoms.     

Sedimentary facies and paleoenvironmental interpretation of a Holocene marsh in the Gironde Estuary in France

1Introduction Since the last glacial maximum, the Holocenehas been marked by a rapid rise in sea level. After6 000 a BP, the present-day level was reached andthe rate of sea-level rise (SLR) decreased rapidly(Morzadec -Kerfourn, 1974; Kidson, 1986 ).These…     

潮沟系统水沙输运研究——以长江口崇明东滩为例

本研究以崇明东滩2015年4月实测潮间带水沙数据为基础,分析了潮沟、盐沼及光滩的水沙特征,重点研究了潮沟系统及邻近潮滩潮周期内悬沙通量情况。结果表明:（1）潮沟表层沉积物比潮滩细,二者平均中值粒径分别为21.7 μm和33.0 μm,悬沙粒径由海向陆逐渐变小;（2）大、小潮沟潮周期内潮流均以往复流为主,垂向平均流速分别为15.4 cm/s和34.6 cm/s;盐沼界和光滩则以旋转流为主,平均流速分别为11.3 cm/s和28.9 cm/s;（3）潮沟中的高悬沙浓度出现在涨潮初期,最大可达7.5 kg/m3,而潮滩高悬沙浓度则出现在潮落潮中期和高水位时刻;大、小潮沟和盐沼界站涨潮阶段平均悬沙浓度大于落潮阶段,光滩站则相反。潮沟悬沙主要来自邻近水域,而潮滩悬沙则与滩面表层沉积物密切相关;（4）潮沟在潮周期内净输沙方向均指向滩地,大潮沟潮周期单宽净输沙量可达4.0 t/m;盐沼界处垂直岸线和沿岸输沙强度相近,净输沙由海向陆,潮周期离岸输沙强度为1.0 t/m;光滩沿岸输沙强度远大于垂直岸线输沙,光滩净输沙由陆向海。研究揭示了潮间带潮沟系统的强供沙能力以及研究区域光滩冲蚀,盐沼植被带淤积的动力地貌过程。     

Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium

Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.     

枯季长江口南汇东滩潮间带盐沼湿地冲淤变化对大型底栖动物功能群的影响

盐沼湿地的冲淤变化是影响大型底栖动物功能群组成及其分布特征的一个重要因素。本文选择长江口南汇东滩作为研究区域,设置固定样地,分别于2015年11月和2016年2月,进行了大型底栖动物和沉积物理化因子的季节性取样分析,并在期间内每月进行滩面冲淤变化的观测,分析了枯季长江口南汇东滩潮间带盐沼湿地冲淤变化对大型底栖动物功能群的影响及作用机理。调研期间共采集到大型底栖动物37种,从功能群组成来看,以杂食者居多,共25种;植食者次之,共7种;肉食者最少,仅为5种。3种食性功能群的物种数、密度和生物量的时空变化特征有所不同。调研期间,3个功能群物种数都略有下降;植食者密度显著增加（P<0.01）,而肉食者、杂食者密度变化不显著（P>0.05）;3个功能群的生物量变化均不显著（P>0.05）。植食者密度和生物量在样地间都存在极显著差异（P<0.01）;肉食者和杂食者仅密度在2016年2月的调研中存在样地间的显著差异（P<0.05）。不同样地月际冲淤变化特征有所不同,但总体均呈淤涨态势。多数环境因子存在显著的空间差异（P<0.05）,仅不同深度的沉积物中值粒径在样地间无显著差异（P>0.05）。滩面冲淤变化对沉积物理化指标的变化具有主导作用。通过非线性回归分析筛选出的与各功能群物种数、密度、生物量变化具有显著相关性（P<0.05）的环境因子组合存在差异。其中,对植食者密度、生物量的变化和肉食者物种数的变化有显著影响的环境因子组合中都包含绝对冲淤变化量。滩面冲淤变化除对大型底栖动物产生直接影响外,还会通过改变沉积物理化因子特征,间接对大型底栖动物产生影响。对于3种食性功能群来说,产生影响作用的主要生境因子存在明显差异。虽然各食性功能群的物种数均有下降,但相对另外两种功能群而言,沉积物中的营养环境还是更利于杂食者的生存,因此杂食者在竞争过程中更具优势。未来相关研究需要在多因子系统监测的基础上,结合洪季的观测结果,进行综合分析。     

Carbon balance in a salt marsh: Interactions of diffusive export, tidal deposition and rainfall-caused erosion

Studies of the concentrations of particulate and dissolved organic carbon in the Duplin River, of the tidal exchange of POC and DOC in the marsh, of the standing stock and movement of Spartina alterniflora wrack in the Duplin, and of the removal of carbon from the surface of the marsh by rain were conducted at Sapelo Island, Georgia in order to test three hypotheses about export of carbon from the Duplin River watershed. We found that the gradients in POC and DOC concentrations are such that carbon is being transported down the Duplin River throughout the year, although in smaller quantities than previously believed. In contrast, almost all tidal exchanges within the marsh result in deposition of carbon. Most of this deposited carbon is subsequently eroded as a result of rain falling on the exposed marsh surface, and is washed back into the tidal creeks. This cycle of deposition and erosion is a possible mechanism keeping POC in the thin aerobic surface layer of the marsh, thus increasing its availability to detritivores and aerobic microbes. The standing stock of wrack is only a fraction of the S. alterniflora produced each year, and its export is a negligible term in the carbon balance equation.