Transport of salt and suspended sediments in a curving channel of a coastal plain estuary: Satilla River, GA

This study describes the transport of salt and suspended sediment in a curving reach of a shallow mesotidal coastal plain estuary. Circulation data revealed a subtidal upstream bottom flow during neap tide, indicating the presence of a gravitational circulation mode throughout the channel. During spring tide, landward bottom flow weakened considerably at the upstream end of the channel and changed to seaward in the middle and downstream areas of the reach, suggesting the importance of tidal pumping. Salt flux near-bottom was landward at both ends of the channel during neap tide. At spring, however, the salt flux diverged along the bottom of the thalweg suggesting that tidal pumping caused a transfer of salt vertically and laterally into the intertidal zone. Thus, landward flux of salt is maintained even in the presence of subtidal seaward flow along the bottom at the downstream end of the channel.Landward bottom stress is greater than seaward stress, preferentially transporting suspended sediments upstream. Compared with salt, however, the weight of the suspended sediments causes less upward transfer of sediments into the intertidal zone. Flood flow carried more suspended sediments landward at the upstream end compared with the downstream end. We speculate that secondary flow in the curving channel picks up increasing amounts of suspended sediments along the sides during flood and adds them to the axial flow in the thalweg. Since the landward flow along the bottom of the thalweg weakens and even reverses during spring tide, there appears to be a complex re-circulation system for sediments re-suspended in curving channels that complicates the picture of a net transport of sediments landward.     

The chenier plain coastal system of Guyana

The low chenier coast of northeastern of South America bears Holocene cheniers which are considered as useful features because they protect the coast against marine erosion as sites for human settlement, and the transportation network.

The relationship between chenier formation and the morphology of the coast is striking. Most cheniers in Guyana are old features. It is believed that clusters of cheniers were formed when large quantities of sand were available during periods of dry climatic conditions.

When fine particles were transported by the streams towards the sea during pluvial climates, chenier formation naturally decreased. A similar cycle of shorter duration based on the movements of mud shoals in the nearshore area of the continental shelf affects the coastal process, resulting in the formation or destruction of cheniers. On the Guyana coast chenier formation is not as active as on the Suriname coast. Much research is necessary to survey and protect these important features.     

Cheniers on the east coastal plain of China

Three to four cheniers are found in the coastal areas of the Bohai Sea and west Yellow Sea. They are formed in the sheltered low tidal flat coast with low to medium wave energy, large quantity of fine sediment supply and shells, and a coastal slope of 0.9–3.0 ‰. The Huanghe River played a major role in controlling the chenier development by either providing sediment supply or cutting off the supply through shifting of its course. Cheniers may be used to determine the coastal development and dynamic processes.     

Plankton dynamics due to rainfall,eutrophication, dilution,grazing and assimilation in an urbanized coastal lagoon

After a prolonged summer dry period, the effects of a distinctive and continuing rainfall on the nutrients and plankton of an urban coastal lagoon were investigated over 2 months. The lagoon filled up over 5 weeks from <10% of its maximum volume until it broke open to the sea. Nutrients (ammonia and oxidised nitrogen) significantly increased the day after initial rainfall, before returning to pre-rainfall conditions within 5 days. Phytoplankton biomass grew 10 fold within a week after initial rainfall in the 25–30 °C water and declined to near initial levels 2 weeks later. The assemblage of phytoplankton and zooplankton changed dramatically after 1 day and again by 6 days later, gradually returning to the original community by 2 weeks after the initial rainfall. Zooplankton responded within a day with a two fold increase in the adult stages of the calanoid copepod Oithona sp., followed a week later by nauplii and adult Acartia bispinosa. The influx of adult Oithona indicates resting populations that were previously under sampled by our plankton net. The plankton community returned to the initial state by 2 weeks, to being dominated by a centric diatom and A. bispinosa after 5 weeks. Dilution of the lagoon reached a maximum of 0.25 d⁻¹, while growth rates of the phytoplankton population reached a maximum of 1 d⁻¹, and A. bispinosa nauplii growth of 2.5 d⁻¹. Declines in chlorophyll biomass from the maximum 10 μg l⁻¹, at a rate of approximately 10% d⁻¹ are consistent with the modelled uptake by zooplankton. The nutrients from runoff, growth and the influx of new zooplankton into the water column, resulted in a depleted δ¹³C and δ¹⁵N stable isotope signature of A. bispinosa by 2–4 ppt within 1–2 weeks, consistent with diatom growth and the terrestrial supply of depleted nutrients. δ³⁴S of A. bispinosa was enriched by 2 ppt for 1–2 weeks after rainfall, but unlike C and N, returned to pre-rainfall levels by the end of the study period. We suggest that plankton studies in coastal lakes with variable water levels that are not tidally driven, should account for the influence of changes in water levels to help explain data variability.     

Distribution and retention of Petrolisthes armatus in a coastal plain estuary: The role of vertical movement in larval transport

Since transport of planktonic larvae is essential to the maintenance and expansion of many marine species, we examined the spatial and temporal distribution of green porcelain crab Petrolisthes armatus (Gibbes, 1850) larvae and the possible underlying physical and behavioral mechanisms using a combination of field observations and numerical modeling. The field study consisted of observations of larval abundance and distribution as well as hydrographic surveys of the Satilla River estuary on the east coast of the USA in August 2006. Larvae were found throughout the water column within the tributaries but primarily at depth in the main river. A numerical model was used to examine the effect of flow and possible larval behavior responsible for the observed distribution and the consequences for larval retention in the estuary. Model results that included downward larval movement are consistent with the field observations, supporting the hypothesis that P. armatus larvae vertically migrate within the water column, which aids in their retention within the estuary.     

Potential rates and environmental controls of denitrification and nitrous oxide production in a temperate urbanized estuary

Denitrification may play a major role in inorganic nitrogen removal from estuarine ecosystems, particularly in those subjected to increased nitrate and organic matter loads. The Douro estuary (NW Portugal) suffers from both problems: freshwater input of nitrate and organic load from untreated wastewater discharges. To assess how these factors might control sediment denitrification, a 12-month survey was designed. Denitrification potential and nitrous oxide (N₂O) production were measured at different locations using the slurry acetylene blockage technique. Denitrification rate ranged from 0.4 to 38 nmol N g⁻¹ h⁻¹, increasing towards the river mouth following an urban pollution gradient. N₂O production, a powerful greenhouse gas implicated on the destruction of the ozone layer, was significantly related with sediment organic matter and accounted for 0.5–47% of the N gases produced. Additional enrichment experiments were consistent with the results found in the environment, showing that sediments from the upper less urban stretch of the estuary, mostly sandy, respond positively to carbon and, inversely, in organic rich sediments from the lower estuary, the denitrification potential was limited by nitrate availability. The obtained results confirmed denitrification as an important process for the removal of nitrate in estuaries. The presence of wastewater discharges appears to stimulate nitrogen removal but also the production of N₂O, a powerful greenhouse gas, exacerbating the N₂O:N₂ ratio and thus should be controlled.     

Study of colloidal phosphorus variation in estuary with salinity

The variation of colloidal phosphorus with salinity in estuary was studied in this paper, which was compared with those of particle and truly dissolved phosphorus with the purpose of ˉnding out the similarities and di?erences between their behaviors in the estuary. Distribution patterns of phospho- rus in particle, colloidal and truly dissolved phase at di?erent salinities and their relationships with suspended particulate matter were also studied to understand the transformation and transporta- tion of colloidal phosphorus in estuarine area. The result showed that the concentrations of total colloidal phosphorus, organic colloidal phosphorus and inorganic colloidall phosphate all descended from river-end to sea-end, illustrating their terrigenous source. Ratios of organic to total colloidal phosphorus decreased with salinity's increment, indicating that organic phosphorus was in°uenced by scavenging process of colloid more signiˉcantly as compared with inorganic phosphate. Both of the phosphorus variation tendencies and the proportion between organic and inorganic phosphorus in colloidal phase was similar with that in truly dissolved phase while di?erent from that in particle phase.     

胶体磷在河口区随盐度变化的研究

研究了胶体磷在河口海区随盐度变化的趋势,并将其与颗粒态、真溶解态磷随盐度的变化趋势进行对比,分析胶体态磷在河口的行为与颗粒态磷和真溶解态磷二者的异同。探讨磷在颗粒相、胶体相和真溶液相之间的分配及其与悬浮颗粒物浓度的关系,研究胶体磷在河口海区中的迁移转化作用。研究结果表明,胶体相中总磷、有机磷和活性磷浓度由河端向海端降低,表明陆源输入是其主要来源。胶体有机磷占总磷比例随盐度增加而下降,表明有机磷受胶体去除过程的影响较明显,胶体磷在河口海区的浓度变化趋势及胶体中有机磷和活性磷的比例都与真溶解相接近而与颗粒相差别较大。     

胶体磷在河口IX随盐度变化的研究

研究了胶体磷在河口海区随盐度变化的趋势,并将其与颗粒态、真溶解态磷随盐度的变化趋势进行对比,分析胶体态磷在河口的行为与颗粒态磷和真溶解态磷二者的异同.探讨磷在颗粒相,胶体相和真溶液相之间的分配及其与悬浮颗粒物浓度的关系,研究胶体磷在河口海区中的迁移转化作用.研究结果表明,胶体相中总磷、有机磷和活性磷浓度由河端向海端降低,表明陆源输入是其主要来源.胶体有机磷占总磷比例随盐度增加而下降,表明有机磷受胶体去除过程的影响较明显,胶体磷在河口海区的浓度变化趋势及胶体中有机磷和活性磷的比例都与真溶解相接近而与颗粒相差别较大.     

Sedimentation of terrigenous red soils in coastal area adjacent to an estuary and coral reefs,the Okkubi River estuary,Okinawa Island,Japan

Sedimentation process of fine-grained terrigenous red soils was observed on the seafloor by coral reefs near an estuary using a paired mooring of turbidity meter and sediment trap or a mooring of sediment trap and current meter. Silty clays contained in the bottom calcareous sands were mainly resuspended and trapped in both surface and bottom layer traps, at noncatastrophic normal sedimentation periods. In addition, silty clays were supplied to this mooring site by inflowing river. Turbidity and the flux rate determined by sediment traps show certain relationship accompanied with the coefficient, which is changed by precipitation, current, and other conditions. Resuspension process caused by a typhoon was recorded as both core sequence of sediment trap and time-series data of bottom current. Maximum velocity of 49.5 cm/s was recorded from bottom currents resulting from the passing of attyphoon at the mooring site. A graded sand layer is interbedded in dark-gray, silty clay and considered to be a resuspended sediment resulting from the passing of the typhoon. Flux of the resuspended sediments by the typhoon was estimated from this core sequence and compared to the flux observed at the normal sedimentation.     

Influence of intermittent estuary outflow on coastal sediments of adjacent sandy beaches

Outflows from estuaries potentially contribute to the productivity of adjacent coastal waters, although most previous work has been on estuaries with considerable river discharge. We investigated the influence of estuary outflow on aspects of coastal sediments adjacent to two seasonally intermittent estuaries, the Curdies and Anglesea Rivers, in southwest Victoria, Australia. For each estuary, we measured sediment organic matter, microphytobenthic chlorophyll a and microbial utilization of carbon sources at three locations associated with each estuary: (1) inside estuary mouth, (2) estuary swash and (3) control swash (an open beach distant from any estuarine influences). Sampling occurred one week before and at one and nine weeks after both an artificial mouth opening and a separate natural flood at both estuaries. Significant temporal changes were detected for all three variables at the estuary mouth and estuary swash but the direction of change was inconsistent across the two estuaries and between the artificial mouth opening and natural flood. Organic matter in both estuaries showed no difference after the artificial mouth openings. Only Anglesea showed an increase in organic matter in the estuary mouth and estuary swash after the floods. Microphytobenthic chlorophyll a concentrations were highest when the estuary mouths were closed. Concentrations decreased at all locations at Curdies after the mouth was artificially opened. The estuary mouth at Anglesea sustained high chlorophyll concentrations and the estuary swash increased one week post artificial opening. The flood event resulted in an increase in chlorophyll a at the estuary mouth and swash at both estuaries, one week post flood. At Curdies, the microbial utilization of different carbon sources changed after both mouth events; estuary mouth and estuary swash showed similar patterns at one and nine weeks post opening. At Anglesea, the bacteria utilized different carbon sources between locations and the only significant interaction between location and time was post flood with change in carbon sources utilized by bacteria in the estuary mouth and estuary swash for one and nine weeks post flood. The southern coastline of Australia is characterized by estuaries with small catchments. This study highlights the spatial and temporal variability in the effects of the output of relatively small, intermittent estuaries on coastal sediment of adjacent beaches, particularly during prolonged periods of drought.     

宁波镇海沿岸岸滩演变分析

基于1959、1979、2010、2013年4个年份的水深资料,采用地理信息技术,研究了1959—2013年间宁波镇海沿岸海域的岸线变化、特征等深线分布变化及剖面变化,并定量计算了水下岸坡的冲淤变化.结果表明,在这54 a间,岸线持续向海推进约3～5 km,0、3、5 m等深线总体上也向海推进,幅度约330～5 600 m;但由于0 m等深线的推进速率小于岸线,因此干出滩面积锐减.相应的,不同时段水下岸坡的淤积速率分别为0. 46、2. 82、14. 14 cm/a,说明该水下岸坡经历了冲淤基本平衡—轻微淤积—较快淤积的调整过程.结合实测水文泥沙资料,探讨了水下岸坡的冲淤原因和动态趋势,得到了杭州湾南岸大规模围垦工程会维持并加快水下岸坡淤积的结论.     

Holocene strata along the coastal area of eastern Guangdong

The data of about 1700 drill holes are correlated, of which 47 drill sections are discussed comprehensively for chronology and sedimentology, and the characteristics and changes of sporo-pollen are analysed. The authors consider that the Holocene strata along the coast of eastern Guangdong can be divided into five formations. The Holocene began 12 000 years ago; the fluvial facies gravel, the striped weathered clay and the "old red sand" serves as the boundary between the Holocene and the Pleistocene.     

福建中南部沿岸海域潮汐特征分析

利用2004、2007、2010年在福建中南部沿海长期验潮站和临时验潮站获取的实测逐时潮位资料,采用基于最小二乘原理的潮汐调和分析方法,分析了福建中南部沿岸海域18个验潮站的潮汐调和常数,并根据调和常数分析了沿岸海域潮汐特征.结果表明:福建中南部沿岸海域以向南传播的半日分潮为主,传播至浮头湾以南海域后衰减明显,对应平潭至浮头湾海域的潮汐性质为半日潮,古雷半岛以南海域为不规则半日潮混合潮;福建中南部沿岸海域自北部平潭向南至诏安,平均海平面升高约25 cm,潮差减小超过3 m,平均大潮差与平均小潮差之差也减小2 m左右,理论高潮位降低约1.5m,而理论低潮位升高约2 m,潮时推迟约2h.     

九龙江口秋茄红树林恢复对底质磷的影响

以光滩为对照,分别在白礁选取5、6、8a生秋茄(Kandelia candel)人工林以及天然秋茄林为样地,在草埔头选取20a生和44a生秋茄人工林为样地,比较分析了福建九龙江口秋茄红树林恢复对底质总磷和有效磷的影响.结果表明:白礁和草埔头秋茄人工红树林的总磷和有效磷含量随红树林恢复时间的增加而增高.白礁天然秋茄林和草埔头秋茄人工林的总磷随底质深度增加而减少,有效磷在中下层含量较高.潮位对草埔头总磷有显著影响,由外滩到内滩,其总磷含量逐渐增加.九龙江口秋茄红树林早期恢复阶段的底质总磷和有效磷缺乏,5a生秋茄人工林底质总磷和有效磷分别为0.68g/kg和2.99mg/kg.     

Shear stress variations in an estuary

Observations in 1929 of the tidal variation of surface gradients in the Tees estuary were combined with measurements of the velocity and density structure in 1975 to compute the internal and boundary shear stresses. Drag coefficients were generally higher on ebb than on flood tides and this inequality is explained using established boundary layer theory. The results suggest that the wide variation in drag coefficients in estuaries may depend, in addition to roughness changes, on the bed slope and the available kinetic energy of the mean flow.     

温州沿海平原晚更新世以来的海相地层特征及沉积环境

沿海地区的海相地层记录了极其丰富的环境信息,研究海相层的地层特征和沉积环境,对理解古环境演变的过程、探讨沉积记录对海陆变迁的响应机制具有重要意义。QTZ1孔位于温州瓯江口北侧平原,根据岩石地层和磁性地层资料,钻孔34 m处为Qh/Qp3界线,91.5 m处为Qp3/Qp2界线。综合考虑刺甲藻、环纹藻的环境意义,钻孔沉积物粒度及微体化石组合的分析结果表明,温州沿海平原晚更新世以来共识别出3套海相地层单元,第二海相层和第三海相层之间发育有完整的陆相沉积层。沉积动力条件经历了低能(Qp3)→中低能(Qp3)→中高能(Qp3)→低能(Qp3)→高能(Qp3)→中低能(Qp3)→中低能(Qp3)→低能(Qp3)→低能(Qh)的演化过程。受海平面变化影响,研究区晚更新世沉积相变化频繁,以海陆过渡相、陆相和局部的浅海相为主,全新世沉积相以浅海相为主,全新世末期逐渐转为滨海相。