Physical control of sediment carbon content in an estuarine tidal flat system (Nanakita River, Japan): A mechanistic case study

Temporal variations in sediment carbon content were tracked by sampling every 2 weeks for 6 to 33 months at 6 tidal flat stations with different carbon content levels (0.05–1.64%) in a single estuary. Three temporal series of current velocity at 5 cm above the sediment were also obtained. Non-cohesive and cohesive sediment stations differed in patterns of temporal variation in sediment carbon content, suggesting the difference in processes controlling sediment carbon content. In the stations of non-cohesive sandy sediment with relatively low carbon content (0.05–0.15%), sediment carbon content fluctuated within ranges specific to each station. In these stations, current velocity data suggested that frequency of sand resuspension washing out sediment carbon controls sediment carbon content level. In the stations of cohesive sediment with relatively high carbon content (0.77–1.64%), sediment carbon contents showed some unusual upward and downward peaks, recovered to usual levels specific to the stations, and was always kept higher than that in the non-cohesive sediment stations. We speculate that in the cohesive sediment stations, sand inputs may significantly control processes establishing the consolidated sediments with various carbon content levels. Spatial transitions from non-cohesive to cohesive sediments and from low to high sediment carbon contents likely occur as sand resuspension at spring tides become more irregular and less frequent. Based on these results, conceptual models describing physical processes controlling sediment carbon content at the studied stations were proposed.     

The sediment-water interface increment due to the complex burrows of macrofauna in a tidal flat

The architecture of macrofaunal burrows and the total area of the sediment-water interface created by biogenic structure were investigated in the Donggeomdo tidal flat on the west coast of Korea. Resin casting methods were applied to recover burrows of four dominant species, Macrophthalmus japonicus, Cleistostoma dilatatum, Perinereis aibuhitensis, and Periserrula leucophryna, and whole burrows within the casting area at three sites in different tidal levels.P. leucophryna excavated the largest burrow in terms of a surface area among them. In the case of whole burrow casting, the space occupied by the biogenic structure was extended into deeper and expanded more greatly at the higher tidal level. In the uppermost flat, the burrow wall surface area within sediment was more extensive than the sediment surface area. Increased oxygen supply through the extended interface could enhance the degradation rates of organic carbon and also change the pathways of degradation. Quantifying the relationship between the extended interface and mineralization rate and pathway requires more extensive study.     

Enzyme variation in marine and estuarine populations of a mud crab,Macrophthalmus hirtipes (Ocypodidae)

Protein and enzyme variation in 2 populations of the mud crab Macrophthalmus hirtipes (Jacquinot, 1853) (Ocypodidae) from 1 marine and 1 estuarine habitat were investigated by poly‐acrylamide gel electrophoresis. A survey of 24 loci revealed that 22 were common to both populations; 20 were monomorphic and 2 were highly polymorphic. Two alleles were detected for each of the polymorphic loci, esterase‐2 (EST‐2) and ester‐ase‐3 (EST‐3). The frequencies of the EST‐3 alleles were similar in the 2 populations. However, the frequencies of the 2 EST‐2 alleles in the estuarine population were significantly different from those for the marine population. Expression of 1 locus, esterase‐4 (EST‐4) was confined to the estuarine population. Two alkaline phosphatase loci (AKPH‐1 and AKPH‐2) were detected in the estuarine population, but only AKPH‐1 was found in the marine population. EST‐4 and AKPH‐2 were neither sex nor age specific. These interpopulational genetic differences may reflect differences in environmental conditions measured between the 2 habitats.     

河口潮滩地貌和沉积物对人类工程的响应特征

河口潮滩受径潮流的共同作用,在自然环境与人类活动的影响下处于不断的动态调整中,其中大型人类工程往往对其短期地貌变化和沉积物特征产生巨大影响。2013年底至2014年5月,长江口崇明东滩北部开展大规模互花米草治理工程,本文基于地面三维激光扫描技术、植被点云数据滤除算法、沉积物取样以及室内粒度分析等手段,对比了工程前后潮滩地貌与沉积物特征。研究发现:（1）完工后研究区域靠海及南侧区域出现明显冲刷,北侧虽出现淤积,但整个区域平均冲刷幅度仍达4 cm;（2）工程前研究区域沉积物平均中值粒径为29 μm,工程完工后沉积物平均中值粒径则增大到38 μm;（3）工程完工后沉积物靠海及南侧区域明显粗化,北侧沉积物则变细。结果表明,围垦工程会造成邻近潮滩大幅冲刷以及表层沉积物粗化,但潮滩不同区域地貌和沉积物特征对工程的响应仍存在空间差异性。研究揭示尽管河口潮滩长期演变过程受流域来沙条件影响,但围垦工程等局部影响因素会短期内显著改变潮滩动力地貌过程。     

Effect of environmental conditions on variation in the sediment-water interface created by complex macrofaunal burrows on a tidal flat

We quantified the increase in the sediment-water interface created by the burrowing activities of the resident macrofaunal community and its variation with respect to the physical conditions of the habitat on a tidal fat. We investigated environmental factors and dimensions of macrofaunal burrows with respect to tidal height and vegetation during spring and summer at three sites. A resin-casting method was used to quantify the dimensions of all burrows at each site. The dimensions of macrofaunal burrows varied both temporally and spatially and the increase in the sediment-water interface reached a maximum of 311%, ranging from 20 to 255% under different habitat conditions. The sediment-water interface depended on the duration of exposure resulting from tidal height, increased temperatures resulting from seasonality, and marsh plant density. Burrows were deeper and more expansive at both higher tidal levels and higher temperatures in summer. Burrow dimensions were sharply reduced with the disappearance of adult macrofauna in areas where the roots of the marsh plant Suaeda japonica were dense. The significance of this study lies in quantifying the burrow dimensions of the entire macrofaunal community, rather than just a single population, and confirming their spatial and temporal variation with respect to physical conditions of the habitat. Environmental factors responsible for variation in burrow dimensions are discussed.     

Effect of environmental conditions on variation in the sediment-water interface created by complex macrofaunal burrows on a tidal flat

We quantified the increase in the sediment-water interface created by the burrowing activities of the resident macrofaunal community and its variation with respect to the physical conditions of the habitat on a tidal fat. We investigated environmental factors and dimensions of macrofaunal burrows with respect to tidal height and vegetation during spring and summer at three sites. A resin-casting method was used to quantify the dimensions of all burrows at each site. The dimensions of macrofaunal burrows varied both temporally and spatially and the increase in the sediment-water interface reached a maximum of 311%, ranging from 20 to 255% under different habitat conditions. The sediment-water interface depended on the duration of exposure resulting from tidal height, increased temperatures resulting from seasonality, and marsh plant density. Burrows were deeper and more expansive at both higher tidal levels and higher temperatures in summer. Burrow dimensions were sharply reduced with the disappearance of adult macrofauna in areas where the roots of the marsh plant Suaeda japonica were dense. The significance of this study lies in quantifying the burrow dimensions of the entire macrofaunal community, rather than just a single population, and confirming their spatial and temporal variation with respect to physical conditions of the habitat. Environmental factors responsible for variation in burrow dimensions are discussed.     

The effect of a tidal cycle on the dynamics of nutrients in a tidal estuary in the Seto Inland Sea, Japan

A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH₄ ⁺−N, (NO₃ ⁻+NO₂ ⁻)−N, PO₄ ³⁻−P and Si (OH)₄−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r ²=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r ²=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.     

Citrate-dithionite-bicarbonate extractable phosphorus (CDB-P) pool in the suspended and surface sediments of the tidal flat area in inner Ariake Bay,Japan

CDB-P (phosphorus extractable by the citrate-dithionite-bicarbonate extraction procedure) was used as the indicator of bio-available inorganic P in the suspended and surface sediments in the inner part of Ariake Bay. The CDB-P pool of suspended and surface sediments in the tidal flat area was estimated to be 10 ton and 90 ton, respectively (total of 100 ton), which corresponds to 1.5 times the average dissolved inorganic phosphorus standing stock. During the summer periods of hypoxia, the CDB-P concentration in the surface sediments decreased with the decline of Eh, losing 43–47% of the CDB-P observed in April. These results suggest that the phosphorus dynamics have been affected by the decrease of resuspended sediment concentrations brought about by the reduction of the tidal currents and phosphate release from the surface sediments during frequently occurring summer hypoxia events.     

我国海洋滩涂主要污染物的研究概况

随着经济的发展和生活水平的提高,海洋滩涂因其资源丰富且易开发,受到了越来越多的关注。然而,由于过度开发、环境污染及异常海况变动造成海洋滩涂生态正在恶化并日趋加剧。在介绍海洋滩涂主要污染物类型的基础上,本文对海洋滩涂沉积物中污染物的组成、来源、空间分布及污染水平进行概述,列举滩涂污染生态风险评估主要方法,剖析滩涂污染引发的主要问题,总结近年来滩涂治理的思路和措施,旨在为新型沿海滩涂管理及资源开发提供一定的理论基础。     

海洋浮游细菌在碳循环中的作用

由于海洋浮游细菌(marine bacterioplankton)在全球碳循环中非常重要,浮游细菌的生物学和生态学研究成为当前生物海洋学最活跃的前沿领域之一。浮游细菌主要包括异养细菌(heterotrphic bacteria)和超微型光合原核生物(picoprokaryotes)蓝细菌(Synechococcus,聚球菌属,细胞粒径为0．5-1．5μm)     

江苏大丰中潮滩大小潮周期沉积特征研究

于2007年7月28日至8月14日期间对江苏大丰海岸中潮滩进行了连续半个月的大小潮周期沉积的现场观测与采样,对采集的沉积物样品在室内进行了粒度、沉积通量和质量磁化率等的测试,结果表明:研究区中潮滩沉积物颗粒的粗细、沉积通量等与潮汐的周期变化关系不明显,而与波浪之间有着较为密切的关系;从中潮滩的上部到中部,再到下部,沉积物颗粒由细变粗,沉积通量由低变高,质量磁化率由小变大。此外,研究区的中潮滩沉积物质量磁化率与粒径组分中的细砂和极细砂关系密切。本项研究结果为微观尺度上潮滩沉积差异的分析以及潮汐韵律层作为高分辨率测年工具的适用性评价提供了参考。     

Sediment transport on an estuarine intertidal flat: Measurements and conceptual model of waves, rainfall and exchanges with a tidal creek

Sediment (silt) transport on a wave-dominated estuarine intertidal flat dissected by a tidal creek that connects to the watershed freshwater network is investigated by analysing field data from Waikopua, New Zealand, and by applying simple models. The intention is to expand understanding beyond the case of the idealised, two-dimensional wave-dominated flat. During fairweather (no waves), there is a continuous exchange of silt between the bed of the tidal creek and the upper flat, and that exchange is controlled by the elevation of the flat with respect to the creek bed. Rainfall in the watershed does not fundamentally alter the way the intertidal flat and the creek interact, but it does increase silt loads in the creek, which in turn increases the amount of silt exchanged with the upper flat. Waves on the flat are fetch-limited, and frictional dissipation causes waves to reduce in height at the edge of the water body. Under some circumstances, a frictional-dissipation zone may occupy the entire middle-plus-upper flat. There is a maximum in wave-orbital speed at the bed (U_sigb) in the middle reaches of the flat, which arises from the particular balance between down-fetch wave growth, wave dissipation by bottom friction, and attenuation through the water column of wave-orbital motions under the short-period waves. There is a progressive decoupling of suspended-silt concentration (SSC) from U_sigb moving from the bottom to the top of the flat, such that SSC is highest towards the top of the flat, where U_sigb is virtually zero. We suggest that this is due to wave activity retarding the settling of suspended silt, and explore that idea with a simple model that is capable of reproducing the essential features of the data set. The results are assimilated in a conceptual model of the system, which shows the balances that control net silt transport in the creek and on the different parts of the flat, three different silt sources, and the role of waves and rainfall. The conceptual model also points at the feedbacks between sediment-transport processes and morphology that are inherent in the system. Implications of those feedbacks to long-term morphodynamics are essentially unexplored.     

Tidal time-scale variation in nutrient flux across the sediment–water interface of an estuarine tidal flat

We determined the range of the tidal variations in nutrient flux across the sediment–water interface and elucidated mechanisms of the flux variation in two estuarine intertidal flats (one sand, one mud) in northeastern Japan. Nutrient flux was measured using in situ light and dark chambers, which were incubated for 2 h, 2–6 times per day. Results showed that nutrient concentration in overlying water varied by tide and was also affected by sewage-treated water inflow. The nutrient fluxes responded quickly to the tidal variation in overlying water chemistry and the range of the variation in flux was as large as the seasonal-scale variation reported in previous studies. In the sand flat, salinity increase likely enhanced benthos respiration and led to increases in both O₂ consumption and PO₄³⁻ regeneration under low illumination, while benthic microalgae were likely to actively generate O₂, uptake PO₄³⁻ and suppress PO₄³⁻ release under high illumination (>900 μmol photons m⁻² s⁻¹). Also in the mud flat, PO₄³⁻ flux was related with O₂ flux, although the range of temporal variation in PO₄³⁻ flux was small. In both the flats, NH₄⁺ flux was always governed by NH₄⁺ concentration in the overlying water; either an increase in NH₄⁺ uptake or a decrease in NH₄⁺ release was observed as the NH₄⁺ concentration rose due to inflow of river water or input of sewage-treated water. Although NO₃⁻ tended to be released in both tidal flats when low NO₃⁻ concentration seawater dominated, their relationship was likely to be weakened under conditions of low oxygen consumption and suppressed denitrification. It is likely that tidal variation in nutrient flux is governed more by the nutrient concentration than other factors, such as benthic biological processes, particularly in the case where nutrient concentration in the overlying water is relatively high and with wide amplitude.     

菲律宾蛤仔垦区三联人工育苗技术

2017年9月至2018年1月,在福清东壁岛三联垦区(A、B、C)开展了菲律宾蛤仔垦区人工育苗技术研究,其中A、B垦区用于育苗,C垦区用于饵料培育,并于2017年9月开始分两批次共向A、B垦区投放菲律宾蛤仔亲贝1670 t。结果显示,育苗期间菲律宾蛤仔亲贝共出现4次大规模产卵。亲贝精卵排放率为32.0%~84.0%,孵化率为45.00%~68.54%;浮游幼虫生长速度为4.73~7.14μm/d,变态率为28.37%~59.67%;稚贝壳长生长速度为7.08~25.10μm/d,共培育砂粒苗7580亿粒,育苗成活率为50.23%。因此,采用垦区三联方法可保障菲律宾蛤仔苗种的生物饵料供给,从而提高砂粒苗的生长速度和成活率。     

Facies and architecture of an estuarine tidal bar (the Trompeloup bar, Gironde Estuary, SW France)

This study describes the sedimentary facies and internal architecture of a modern estuarine tidal bar present in the bay-head delta of a wave- and tide-dominated estuary, the Gironde Estuary, in southwest France. Based on 51 cores (2 to 5 m long), this work demonstrates that such bars are composite sedimentary bodies made up of individual sigmoidal sand units isolated from one another by thick muddy layers. The bar appeared in the study area around 1874. Since then, its evolution has been characterized by phases of rapid downstream bar migration alternating with periods of bar abandonment. During the periods of active bar progradation, which commonly last between 10 and 20 years, the bar progrades up to 7 km seaward and forms a narrow (200–800 m wide) sand ridge up to 6 m thick. During abandonment phases which also last around 10–20 years, the bar is starved of sand and a mud layer (1 to 3 m thick) is deposited. The vertical succession formed by the seaward progradation of the tidal bar records these alternating phases of growth and abandonment. A typical vertical succession in the bar system is 8 m thick and comprises several superimposed, upward-coarsening units of cross-stratified sand, deposited during phases of seaward progradation, separated by a thick layer of thinner-bedded mud and sand laminae deposited during phases of bar abandonment. When a tidal bar builds up to the supratidal zone, marshes accumulate and the bar becomes a permanent island in the estuary. The large-scale architecture of the bar is thus made of an alternation of potential sandy reservoir units and muddy internal seals. The reservoir units are characterized by a sigmoidal shape. The muddy layer, which is deposited between the two sigmoidal units, is a thick, continuous potential internal seal. This complex internal architecture is due to the fact that there is a considerable amount of mud present in the bay-head delta of the Gironde Estuary. It is thought to be representative of the architecture of tidal bars in the inner part of wave- and tide-dominated estuaries.     

Dissolved organic carbon in the freshwater tidal reaches of the Schelde estuary

To unravel the factors that regulate DOC dynamics in the freshwater tidal reaches of the Schelde estuary, DOC concentration and biodegradability were monitored in the upper Schelde estuary and its major tributaries. Although the Schelde estuary possesses a densely populated and industrialized catchment, our data suggest that the bulk of DOC in the freshwater tidal reaches is not derived from waste water. This was concluded from the low biodegradability of DOC (on average 9%), DOC concentrations that are close to the mean for European rivers (4.61 mg l⁻¹) and the absence of an inverse relationship between DOC and discharge. Most DOC originating from waste water being discharged in tributaries of the estuary appears to be remineralised before these tributaries reach the main estuary. Although dense phytoplankton blooms were observed in the upper estuary during summer (up to 700 μg chl a l⁻¹), these blooms did not appear to produce large quantities of DOC in the freshwater tidal reaches as DOC concentrations were low when phytoplankton biomass was high. The fact that DOC concentrations were high in winter and decreased in summer suggests a predominantly terrestrial source of DOC in the freshwater tidal reaches of the Schelde estuary.     

Chemical studies on organic matter and carbon cycle in the ocean

Chemistry of organic materials of the suspended and sinking particles, and the evaluation of the particulate materials for the carbon cycle of the ocean are described in this paper. Organic carbon (POC) and nitrogen (PON) of the suspended particles collected from various areas of the North through South Pacific were determined with considerably high variabilities in their concentration. Higher values of the POC and PON were obtained in the surface water of the higher latitudinal areas of both northern and southern hemispheres and the equatorial Pacific, while the lower values of these organic elements were measured in the middle latitudinal areas of the Pacific. These facts clearly indicate that inorganic nutrients supply to the surface water layers from the underlying water is primarily determinative factor to govern the concentration of the POC and PON in the surface water layer. POC and PON concentrations in the intermediate through deep waters, however, are much less variable in time and space. Carbohydrates, free and combined amino acids and lipid materials were major organic constituents of the suspended particles. The organic composition of the particles was extensively variable in region, time and depth. Such change in the organic composition was mainly caused by the production and decay of the free and combined amino acids, lipid materials and water extractable carbohydrate. Sinking particle which has high sinking rate over 100 m day⁻¹ and can be collected only by sediment trap, also consists of carbohydrates, free and combined amino acids and lipid materials. A detailed analysis of the particle indicate that the sinking particle was much different from the suspended particle from the intermediate through deep waters in terms of the abundance of the biologically susceptible organic materials such as unsaturated hydrocarbon, fatty acid and water extractable carbohydrate often found in phytoplankton. These facts clearly indicate that the sinking particle plays an important role on the vertical transport of the biologically susceptible organic materials from the surface water to the deep water. Vertical flux of organic materials in various water depths was extensively measured in the North Pacific and Antarctic Ocean using the depth-series sediment trap system to collect the sinking particles from various depths of the waters. Regional and seasonal variabilities of the organic carbon flux at the various depths were obviously observed, however the attenuation rate of the organic carbon flux in the intermediate through deep water was not changed so much irrespective of the sampling time and region. The time-series sediment trap system was also using to determine the seasonal variation of the organic carbon flux. An average organic carbon flux at 1 km depth from this trap system was almost comparable to the amount of organic carbon degraded in the water deeper than 1 km depth, which was calculated from oxygen consumption rate of the deep water. Thus, it is clear that the sinking particle must play an important role in the carbon cycle of the deep water.     

Seasonal variation and tidal influences on estuarine use by bottlenose dolphins (Tursiops aduncus)

In order to show that dolphins use estuary habitats differently depending on the season and tidal state, possibly in response to prey distribution, temperature, risk of stranding and accessibility, Indo-Pacific bottlenose dolphins (Tursiops aduncus) were observed year-round during a 3-year study in the Clarence River estuary (CR) and Richmond River estuary (RR) in northern New South Wales, Australia. Peak dolphin sightings occurred during the spring season and one or 2 h prior to high tide. The spatial distribution of the dolphins in each estuary was analysed using the distance in kilometres that the dolphins travelled upstream with seasons and tidal phase as determinants. A General Linear Model showed that in the CR the dolphin spatial distribution in the estuary was not determined by season (F = 0.434, df = 3, P = 0.729) but was by tidal phase (F = 9.943, df = 3, P < 0.001) and the interaction between season and tidal phase (F = 3.398, df = 9, P < 0.002). However, in the RR the spatial distribution of the dolphin use of the estuary was not determined by either season (F = 1.647, df = 3, P = 0.194) or tidal phase (F = 0.302, df = 3, P = 0.824). In the CR, the spatial distribution of the dolphins was largest on high and flood tides. This pattern of spatial distribution may occur because the CR is a relatively shallow estuary and this increased spatial distribution may reflect a lower stranding risk and an increase in accessibility of shallow areas during periods of higher tide. These areas could also provide access to their preferred prey items of sea mullet (Mugil cephalus) and sand whiting (Sillago ciliata).     

The role of various dissolved organic matter forms on chlorpyrifos bioavailability to the estuarine bivalve Mercenaria mercenaria

Dissolved organic matter (DOM) is comprised of a myriad of macromolecules with specific physical and chemical properties that may influence the bioavailability of hydrophobic pesticides to animals. This study was conducted to assess the role of various forms of DOM on the uptake and bioconcentration of the organophosphate insecticide chlorpyrifos (CHPY) to the bivalve Mercenaria mercenaria. Bivalves were exposed to DOM-free seawater (30 per thousand) or to seawater containing a single form of DOM. DOM forms included two filtrate fractions of natural salt-marsh sediment DOM (DOM-(<0.45 mum) and DOM-(<3 kDa)); natural purified humic (HA) and fulvic (FA) acids; and water soluble cyclic oligosaccharides alpha and beta cyclodextrins (CD-alpha and CD-beta). In (14)C-CHPY uptake and elimination experiments, juvenile bivalves were exposed to uniformly-labeled (14)C-CHPY and collected at time intervals during 48 h. The remaining bivalves were transferred to (14)C-CHPY-free elimination chambers with bivalve collection at time intervals over 144 h. Total uptake of (14)C-CHPY by bivalves in DOM-free seawater was >40% greater than in bivalves exposed to (14)C-CHPY in the presence of most DOM forms. These results are consistent with much faster (14)C-CHPY uptake rates estimated using a simple two parameter model. After the elimination period, bivalves exposed to DOM-free seawater had (14)C-CHPY body residue concentrations between 25% and 86% greater than bivalves in the presence of DOM forms. Experiments with larger bivalves showed that pulse-chase exposures with a 1.5 h exposure period to (14)C-CHPY was not long enough to detect differences in (14)C-CHPY tissue accumulation efficiencies across treatments. Our findings suggest that natural forms of DOM, at environmentally realistic organic carbon concentrations, reduced pesticide uptake and bioconcentration, consistent with much lower uptake rates relative to bivalves exposed to (14)C-CHPY in the absence of DOM. Interestingly, at the tested organic carbon concentrations CD-alpha and CD-beta did not reduce (14)C-CHPY bioconcentration in M. mercenaria.