Seasonal phytoplankton composition, productivity and biomass in the Neuse River estuary, North Carolina

Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m⁻², mean chlorophyll a was 11·8 mg m⁻³, and mean phytoplankton density was 1·56 × 10³ cells ml⁻¹. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m⁻².     

Water level variations in the Neuse and Pamlico Estuaries,North Carolina due to local and remote forcing

Water level time series records from the Neuse and Pamlico River Estuaries were statistically compared to local and distant wind field data, water level records within the Pamlico Sound and also coastal ocean sites to determine the relative contribution of each time series to water levels in the Neuse and Pamlico Estuaries. The objectives of this study were to examine these time series data using various statistical methods (i.e. autoregressive, empirical orthogonal function analysis (EOF), exploratory data analysis (EDA)) to determine short- and long-time-scale variability, and to develop predictive statistical models that can be used to estimate past water level fluctuations in both the Neuse Estuary (NE) and Pamlico Estuary (PE). Short- and long-time-scale similarities were observed in all time series of estuarine, Pamlico Sound and subtidal coastal ocean water level and wind component data, due to events (nor'easters, fronts and tropical systems) and seasonality. Empirical orthogonal function analyses revealed a strong coastal ocean and wind field contribution to water level in the NE and PE. Approximately 95% of the variation was captured in the first two EOF components for water level data from the NE, sound and coastal ocean, and 70% for the PE, sound and coastal ocean. Spectral density plots revealed strong diurnal signals in both wind and water level data, and a strong cross correlation and coherency between the NE water level and the North/South wind component. There was good agreement between data and predictions using autoregressive statistical models for the NE (R² = 0.92) and PE (R² = 0.76). These methods also revealed significant autoregressive lags for the NE (days 1 and 3) and for the PE (days 1, 2 and 3). Significant departures from predictions are attributed to local meteorological and hydrological events. The autoregressive techniques showed significant predictive improvement over ordinary least squares methods. The results are considered within the context of providing long time-scale hindcast data for the two estuaries, and the importance of these data for multidisciplinary researchers and managers.     

长江口北港口门海域悬沙输运机制分析

根据2012年10月24日至11月1日在长江口北港口门海域获取的沉积动力学数据,采用输运通量分解方法分析水沙输运机制。结果表明,长江口北港口门附近海域涨、落潮期间底部悬沙浓度与近底部流速呈显著线性相关,存在显著的再悬浮作用;潮周期内的悬沙输运具不对称特征,涨潮悬沙浓度大于落潮悬沙浓度,悬浮泥沙有向陆输运的趋势。拉格朗日平流输运是影响悬沙输运的主要贡献项;潮泵效应(尤其是潮汐捕捉效应)以及河口垂向环流作用是两个次要影响因素,在影响程度上前者比后者略大。观测发现,长江口北港口门海域潮流除了具有涨落潮流速、历时等不对称现象外,还具有流速结构不对称的特征,进而导致涨、落潮底部湍流混合程度不对称与输沙不对称,这可能是造成悬沙向河口内输运形成最大浑浊带的重要因素。     

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.     

Decadal-scale sediment dynamics and environmental change in the Albemarle Estuarine System, North Carolina

During the summer of 2001, several short cores (<50 cm) were collected in the Albemarle Estuarine System (AES). Down-core measurements for radiochemical tracers (²¹⁰Pb, ¹³⁷Cs) and organic matter signatures (δ¹³C, δ¹⁵N, C:N ratio, and LOI) have been used to elucidate potential temporal changes in fluxes and cycles of organic matter in the AES. Pb-210 geochronology indicates temporal and spatial variations in sediment deposition rates (0.08–0.57 cm y⁻¹) with highest rates near the AES western limit relative to the rest of the estuary. Low accumulation rates, deficient excess ²¹⁰Pb inventories, and near linear ¹³⁷Cs profiles throughout the AES suggest that sediments are resuspended by wind-generated waves and currents and flushed from the system by river discharge and wind-tides, probably to Pamlico Sound to the south. Sediments in the AES are accumulating at rates less than the current rate of relative sea-level rise for this region except in protected portions of the estuary. Thus sediment accumulation in the AES is controlled in the short term by storm wave-base and in the long term by the creation of accommodation space by basin subsidence and sea-level rise. The geochemical and sedimentological data characterize the evolution of the Albemarle Sound and associated tributaries over the past 200–300 years. The majority of cores collected throughout the system show a significant decrease in ¹³C and increase in ¹⁵N isotopic signatures up-core. Thus, the estuarine system of eastern North Carolina has changed from a marine-influenced, high brackish environment to the modern-day system, which is a highly variable, terrestrially influenced, low brackish environment.     

长江口北槽黏性细颗粒泥沙特性的试验研究

选用长江口北槽黏性细颗粒泥沙,在不同盐度的人工海水中通过静水沉降、动水沉降等各种试验手段了解其基本特性。在静水沉降管中观测了胶粒的电化学絮凝过程和重力碰并过程,于不同盐度条件下找出最佳絮凝盐度;并通过黏性细颗粒泥沙在流动海水中絮凝的试验研究,揭示其在动水中絮凝的机理和规律,及不同条件下的起动流速、不淤流速、沉降速度等特征值,从而分析其落淤情况。研究结果表明,长江口北槽细颗粒黏性泥沙的最佳絮凝盐度约为15,起动流速为15~20 cm/s,这与泥沙的淤积固结时间有关,而不淤流速约为60 cm/s。并由试验得到了挟沙力与流速之间的经验关系,以及用于估算不同流速条件下泥沙沉降速度及淤积量的经验公式。这些结果可用于长江口航道的疏浚、整治工作中,具有一定的理论指导意义。     

Faunal characteristics and sediment accumulation processes in the James River estuary,Virginia

This study was designed to relate fauna characteristics and sediment accumulation processes in the James River, VA and was conducted during June 1981. Physical sedimentary and benthic biological parameters, as well as sediment structure and radionuclide profiles, were evaluated for 11 stations. Faunal distribution patterns reflected species' response to salinity changes along the estuarine gradient, but not to differences in sediment accumulation rates. Levels of bioturbation could not be predicted easily on the basis of faunal characteristics alone. Results suggest that the physical processes of erosion and deposition strongly influence the ability of macrobenthos to bioturbate sediments in this estuary. Areas of rapid deposition (>3 cm y⁻¹) exhibit little evidence of bioturbation, as do areas where erosion, or relatively constant physical reworking of sediments, dominate. Areas with low sediment accumulation rates (0·5-3 cm y⁻¹) exhibit the highest levels of mixing as evidenced in X-radiographs. Estuarine organisms inhabiting soft bottoms are typically ‘opportunistic’, shallow-living and short-lived species, and the composition of their communities is not strongly influenced by rates of deposition. Physical reworking of sediments is most likely to occur near to the sediment-water interface where reworking by shallow-living organisms is most intense. Sediment-mixing processes should be characterized using a range of approaches. The phasing of interactions among erosion, physical transport, deposition and biological mixing must be resolved on the appropriate time scales if the mechanics of processes governing the formation of the sedimentary record are to be elucidated.     

The importance of bioturbation to continental slope sediment structure and benthic processes off Cape Hatteras, North Carolina

Even though the continental slope off Cape Hatteras has sediment accumulation rates on the order of 1 cm/year, large areas of soft sediment are intensively reworked by infaunal organisms. Primary sedimentary structures have been completely replaced with biogenic structures. Surface sedimentary structures are dominated by the bioturbational activities of a deep burrowing infauna (to at least 30 cm). The layer actively mixed by the benthos, as evidenced by sediment profile and X-ray images, is estimated to range from 5 to 20 cm, with the residence time for particles within the surface mixed layer ranging from about 4.5 to 18 years. The biological mixing parameter (G) ranges from 0.4 to 5.5, which indicates moderate to strong biological mixing relative to accumulation and strata formation. Bioturbation contributes to the dynamic forces affecting the surface sediments by decreasing compaction of sediment layers and dilating sediment fabrics by sediment mixing, and introducing large water-filled burrows and voids to subsurface sediments. The sediment profile images captured numerous subsurface feeding voids, and worms in the process of making deep burrows, many of which extended below the 5 to 10 cm average depth of the apparent color redoxpotential discontinuity layer. High rates of accumulation of organic-rich sediment lead to high standing stocks of benthos and intensive feeding/burrowing activity that result in organic rich stratagraphic sequences that are thoroughly mixed. Cape Hatteras is a apparent focusing point for the transport of shallow water sediments to the deep sea. Sediments across other areas of the continental slope just 100's of kilometers south of Cape Hatteras are not as thoroughly mixed or biologically active.     

黄河河口泥沙输移分布特性及其回归计算

在分析黄河河口泥沙输移和分布影响因素的基础上,分径流区域、径流潮汐区域和外海区域3个不同区域对黄河河口泥沙的输移和分布规律进行了系统探讨总结;利用实测资料对河口清水沟流路的泥沙分布特征进行了分析,并据此得出了河口泥沙沉积分配的回归计算式。     

Sedimentation and morphological changes at Yuantuojiao Point,estuary of the North Branch,Changjiang River

The North Branch, separated by the Chongming Island, was once the main channel in the estuary of the Changjiang River. Reclamation and a decrease in runoff to the North Branch had led to the narrowing and shallowing of the channel. The Yuantuojiao Point is located at the intersecting point connecting the North Branch of the Changjiang River and the Jiangsu coastline. Erosion cliffs are developed between the typical silty-muddy tidal flat and the salt marsh occupied by Spartina alterniflorea, and this has changed rapidly over the past few years. The sediment grain size analysis results of the surficial and two core samples indicate that the Yuantuojiao Point tidal flat experienced continuous accretional processes. Based upon 137 Cs analysis results of the YT and YY Cores sampled from the tidal flat at the Yuantuojiao Point, the average sedimentation rate of the YT Core was 2.30 cm/a from 1963 to 2007, and 2.38 cm/a from 1954 to 2007 for the YY Core. The sedimentation rates of both core locations have declined since the 1960s corresponding to the seaward reclamation at the Yuantuojiao Point. The average sedimentation rates at the Yuantuojiao Point were similar to that of the silty-muddy tidal flat at the northern Jiangsu coast, but lower than that of the south of the Changjiang River Estuary. According to field morphological investigations from 2006 to 2008 on the salt marsh at the Yuantuojiao Point, cliffs retreated markedly by storm surges and disappeared gradually because of the rapid sedimentation on the silty-muddy tidal flat. The maximum annual retreat reached 10 m. The recent sedimentation and morphological changes of the Yuantuojiao Point tidal flat not only displayed the retreat of the salt marsh and the disappearance of cliffs, but also was accompanied by rapid sedimentation of the silty-muddy tidal flat and the salt marsh, indicating the responses to the tidal currents, storm surges, Spartina alterniflorea trapping sediments and large-scale reclamation. The sediment grain size and their trends, southward coastal flow, and sandspits of the longshore bars suggest that the main sediment source at the Yuantuoijao Point, estuary of the North Branch was possibly from the Changjiang River before 1958, since then, it has been from the south of the submarine radial sand ridges of the southern Huanghai Sea (Yellow Sea).     

长江口南部赤潮区春季表层沉积物中色素组成、含量与分布状况

为剖析长江口邻近海域春季硅藻藻华后期藻类沉降与底层水体缺氧现象之间的关系,作者于2011年春季,在长江口南部赤潮区采集了表层沉积物样品,并通过高效液相色谱法(HPLC),对浮游植物色素进行了分析。结果表明,硅藻藻华发生后,表层沉积物中叶绿素a(Chl a)、岩藻黄素(Fuco)和19’-丁酰氧基岩藻黄素(But-Fuco)含量有显著增加,高值区主要分布在调查海域东南侧50 m等深线外侧,与底层低氧水体分布区基本吻合。因此,硅藻藻华后沉降的藻类对于该海域夏季缺氧区的形成应具有一定作用,其具体过程和机制仍有待于研究。     

黄河口挑河河口悬沙分布与输移特征研究

基于实测资料对黄河废弃河道挑河河口段的悬沙分布及输移特点进行了研究。结果表明:挑河河口段悬沙浓度与潮流流速正相关,风浪作用则导致悬沙质量浓度大大提高;在空间尺度上悬沙浓度呈河口高、河道上游低的特点;挑河河口附近,涨潮流输沙明显占优势,向河道内侧,悬沙输移率有所降低,且逐渐转变为落潮输沙占优势。结合河口外侧海域冲淤演变趋势以及悬沙输运动力机制,认为河口段河道总体处于弱淤积状态,而风浪作用可以加速河道淤积。本研究可为挑河的河口演变和航道整治等提供参考。     

Sources and transport of particulate organic carbon in the Amazon River and its estuary

Stable carbon isotope ratios have been used to study the sources of particulate organic carbon(POC) in the Amazon River and its tributaries, and to examine the transport of the riverine POC intothe oceanic environment. POC in the upper reaches of the Amazon River has more positive δ ~(13)C values(--24.5‰ to -- 28.0‰) than that in the middle and lower reaches (--27.9‰ to -- 30.1‰). Theδ ~(13)C of POC from the tributaries is generally more negative than that observed in the Amazon mainchannel. This δ ~(13)C datum shows that the POC in the Amazon main channel is predominantly of terres-trial origin rather than a result of in situ production. A large range of δ ~(13)C values (--17.5‰ to -28.4‰) is observed in the Amazon Estuary and plume. and is considered as the result of the mixing     

A sediment budget for the Choptank River estuary in Maryland,U.S.A.

A sediment budget for the Choptank River, one of the three largest estuaries on the eastern shore of Chesapeake Bay, was developed from measurements of sediment carried in upland runoff, shore erosion, sedimentation, and levels of suspended sediments in estuarine waters. Shore erosion was the major source of sediment (340 × 10⁶ kg y^?1), contributing seven times more sediment than upland runoff. Low relief, the rural character of the Coastal Plain drainage basin, and the susceptibility of poorly consolidated shoreline materials to erosion contributed to the dominance of shore erosion over runoff as a sediment source. Box modelling indicated a net annual flux (14–44 × 10⁶ kg y^?1) of sediment from the Choptank River to Chesapeake Bay. A mass balance estimate of sedimentation, calculated as the difference between total inputs and loss at the mouth of the estuary, (350 × 10⁶ kg y^?1) agreed well with an estimate based on ²¹⁰Pb profiles (340 × 10⁶ kg y^?1) measured along the longitudinal axis of the estuary. Lead-210 sedimentation rates correspond to accumulation rates of 1·5–7·9 mm y^?1.     

Microplastic pollution and enrichment of distinct microbiota in sediment of mangrove in Zhujiang River estuary,China

The microbial communities colonized on microplastics(MPs) have attracted widespread attention. However, few studies focused on the MPs impacts on mangrove ecosystems, particularly on bacterial communities. We investigated the MPs pollution in mangrove of Zhujiang(Pearl) River estuary(ZRE). To study the potential risk posed by MPs to the mangrove ecosystems, the differences in bacterial communities, functions, and complexity between MPs and sediment samples were reported for the first time.Microp...     

长江河口北槽弯道横向次生流、混合与层化

2013年2月25至26日(枯季/大潮)、7月23至24日(洪季/大潮)分别在长江河口北槽弯道沿着3条横向测线CS6、CSW和CS3(每条测线上有北、中、南3个站位)测得水位、流速、盐度和含沙量的时间序列资料。通过这些资料的定量计算、分析,理解弯道横向次生流、混合与层化的时、空变化和各种物理机制及其相对重要性。3条横向测线均存在横向次生流,且横向测线CS3还出现横向次生环流。枯、洪季,仅在横向测线CS6、CS3出现环状欧拉余流。枯、洪季,沿着横向测线CS3,3个站位的横向斜压梯度比离心加速度和科氏加速度都大1~2个数量级,而后两项大小接近且数量级都是10-4,罗斯贝数在1左右。这些表明:横向次生流受横向斜压梯度、离心加速度和科氏加速度共同驱动,前一项相对于后两项更加重要。沿着3条横向测线:1)枯、洪季大潮,平均势能差异分别约为54.23、66.56 J/m3,表明洪季层化强于枯季;2)枯季涨潮,平均的势能差异普遍小于落潮,而洪季涨潮,平均的势能差异普遍大于落潮,表明枯、洪季湍流混合均存在潮汐不对称性;3)枯季,由横向、纵向水深平均应变(ΦS-y、ΦS-x)引起的势能差异变化率的范围分别是-67×10~(-3)~37×10~(-3)、-7×10~(-3)~11×10~(-3)W/m~3,而洪季,相应的范围分别是-45×10~(-3)~30×10~(-3)、-14×10~(-3)~13×10~(-3)W/m~3,表明枯、洪季差异不明显,横向水深平均应变(ΦS-y)均大于纵向水深平均应变(ΦS-x),前项对水体混合与层化的影响更大;4)枯季大潮,纵向平流(ΦA-x)、横向平流(ΦA-y)、纵向水深平均应变(ΦS-x)和横向水深平均应变(ΦS-y)的潮汐平均绝对值占四项总和之比例分别为26%、33%、18%和23%,而洪季大潮,相应的值的比例分别为13%、9%、22%和56%,表明枯季,平流项(ΦA-y最大)对混合与层化的控制可能占主导地位;洪季,应变项(ΦS-y最大)可能占主导地位。无量纲数(m)被用于判别横向平流(ΦA-y)、横向水深-平均应变(ΦS-y)的相对重要性。一个概念性模式被用于显示层化与横向次生流/环流的相互关系。     

磨刀门河口水沙变化与地貌响应

以西江磨刀门河口为研究对象,应用马口站1960～2000年月平均流量及含沙量资料,1980、1981和2003年洪枯季实测水文及表层沉积物采样资料,分析磨刀门河口近几十年来的水沙变化,建立磨刀门河口水沙变化与纵、横断面及口门形态的响应模式.结论认为,西江磨刀门河口径流量年际变化不大;含沙量及输沙总量在1993年前后发生变异,有减少的趋势,悬浮泥沙中值粒径偏细;总体上形成了丰水少沙的水沙组合.磨刀门河口形态响应滞后于水沙变化,存在洪淤枯冲的年内变化.由于上游来沙量减少、人工护岸的作用下,河口口门断面趋于窄深.总体上,磨刀门河口深槽变浅,拦门沙在波浪作用下加高变薄;口门向外海延伸较快,使得河口口门动力相对强弱发生了较大变化,波浪动力及沿岸流对泥沙转运的作用增强,磨刀门河口正逐渐向河流-波浪型河口转变.     

基于神经网络的长江口深水航道海域悬浮泥沙浓度研究

航道治理和维护的核心问题为泥沙问题。在充分分析遥感和遥测数据的基础上,利用BP神经网络方法对长江口深水航道海域悬浮泥沙浓度进行了研究。当隐含层神经元个数为8时,预测效果最好,网络的RMSE仅为0.102,网络的拟合度达到0.899。预测的最大相对误差为28%,最小相对误差为6%,总的相对误差为21.5%。     

Foraminifera from the continental slope off Cape Hatteras, North Carolina

The recent benthic meiofaunal foraminiferal assemblage from the continental slope (590-2 003 m) off Cape Hatteras, North Carolina exhibits high species richness and evenness, moderate diversity values, and lacks numerically dominant species. The preserved planktic assemblage has relatively low species richness, high evenness, low diversity, and a few numerically dominant species. Approximately 9% of the benthic species are those that typically live within continental shelf depth ranges. The benthic assemblage abundances and diversities do not follow depth patterns or geophysical characteristics. No biogeographic boundary can be described within the study area for meiofaunal foraminifera. Oxygen limitation does not appear to be a factor affecting the benthos of the North Carolina continental slope based upon the community structure of the benthic foraminifera, if total assemblage is assumed to reflect the recently living community. The high carbonate content of sediments in the area may be explained by foraminiferal tests. Within the study area, the foraminiferal assemblages are uniform, and probably reflect relative consistency of primary environmental variables as well as dynamic downslope transport and high influx of material from the water column in the vicinity where the Gulf Stream and the Western Boundary Undercurrent cross.     

The hydrodynamic response of the York River estuary to Tropical Cyclone Isabel, 2003

Hurricane Isabel made landfall along the North Carolina coast on September 18, 2003 (UTC 17:00) and the storm surge exceeded 2.0 m in many areas of the Chesapeake Bay and in the York River estuary. River flooding occurred subsequently, and the peak river discharge reached 317 and 104 m³ s⁻¹ in the Pamunkey and Mattaponi rivers, respectively. The York River estuary experienced both storm surge and river flooding during the event and the estuary dynamics changed dramatically. This study investigates the hydrodynamics of the York River estuary in response to the storm surge and high river inflows. A three-dimensional model was used to investigate the changes of estuarine stratification, longitudinal circulation, salt flux mechanisms, and the recovery time required for the estuary to return to its naturally evolved condition without the storm. Results show that the salt flux was mainly caused by advection, which was induced by the barotropic gradient during the storm event. The net salt flux increased by a factor of 30 during the rise of the storm surge. However, the large amount of salt transported into the estuary was quickly transported out of the estuary as the barotropic gradient reversed during the descent of the storm surge. Subsequent high freshwater inflow influenced the estuarine circulation substantially. The estuary changed from a partially mixed estuary to a very stratified estuary for a prolonged period. The model results show that it will take about 4 months for the estuary to recover to its naturally evolved salinity distribution after the impacts of the storm surge and freshwater pulse.