Sedimentation rates in the Wanggang salt marshes, Jiangsu

Coastal salt-marshes represent an important coastal wetland system. The total area of coastal wetlands exceeds 5000 km2 in Jiangsu Province, China, but it is decreasing rapidly in response to the intense reclamation activities and coastal erosion along a part of the coastline. Hence, two types of plants, Spartina angelica and Spartina alterniflora, were introduced successively into the Jiangsu coastal areas, in order to protect the coastline from erosion and to increase the accumulation rate. Pb-210 and Cs-137 analyses were carried out for sediment samples from the salt-marshes of Wanggang to determine the sedimentation rate, on the basis of an evaluation of the background activity values and the factors affecting the enrichment of Pb-210. Analysis of a typical sediment column of the tidal flat shows that there is weak absorption of Pb-210 in the silt-dominated sediment. Because of the influences of factors such as storm events, bioturbation, material sources and analytical error, some abnormal data points appear in the Pb-210 record. After ignoring these data the calculated sedimentation rate was 3.3 cm yr-1 on average. Based upon analysis of the Cs-137 dating, the rate since 1963 was 3.1 cm yr-1 on average, similar to the data by Pb-210 dating and the previous studies. The dating results show that there were three stages of sedimentation, with the most rapid accretion being taking place after Spartina angelica was introduced into the area. The study also shows that at the stage of Spartina alterniflora growth, the accretion rate was higher than on the flat surface with the same elevation without the cover of this plant.     

江苏王港盐沼的现代沉积速率

Coastal salt-marshes represent an important coastal wetland system. The total area of coastal wetlands exceeds 5000 km2 in Jiangsu Province, China, but it is decreasing rapidly in response to the intense reclamation activities and coastal erosion along a part of the coastline. Hence, two types of plants, Spartina angelica and Spartina alterniflora, were introduced successively into the Jiangsu coastal areas, in order to protect the coastline from erosion and to increase the accumulation rate. Pb-210 and Cs-137 analyses were carried out for sediment samples from the salt-marshes of Wanggang to determine the sedimentation rate, on the basis of an evaluation of the background activity values and the factors affecting the enrichment of Pb-210. Analysis of a typical sediment column of the tidal flat shows that there is weak absorption of Pb-210 in the silt-dominated sediment. Because of the influences of factors such as storm events, bioturbation, material sources and analytical error, some abnormal data points appear in the Pb-210 record. After ignoring these data the calculated sedimentation rate was 3.3 cm yr-1 on average. Based upon analysis of the Cs-137 dating, the rate since 1963 was 3.1 cm yr-1 on average, similar to the data by Pb-210 dating and the previous studies. The dating results show that there were three stages of sedimentation, with the most rapid accretion being taking place after Spartina angelica was introduced into the area. The study also shows that at the stage of Spartina alterniflora growth, the accretion rate was higher than on the flat surface with the same elevation without the cover of this plant.     

江苏王港盐沼的现代沉积速率

江苏海岸湿地总面积超过5000km^2，但围垦活动的加剧使盐沼湿地面积迅速减少；为了达到海岸防护、保滩促淤的目的，先后引种了大米草和互花米草。通过采集江苏王港潮滩盐沼湿地9处柱状样和挖取探槽剖面，以及对沉积剖面样品进行^210Pb和^137Cs测年分析，探讨了^210Pb的本底及影响^210Pb富集的因素，估算了王港盐沼湿地的现代沉积速率。王港潮滩盐沼沉积物对^210Pb的吸附作用较弱；受风暴潮、生物扰动、物源变化及实验误差等因素的影响，在^210Pbex剖面上出现了数据异常点，将这些数据点剔除后计算得到的沉积速率为33cm yr^-1，^137Cs测年显示，该地区1963年以来的平均沉积速率3．1cm yr^-1，与^210Pb法及前人研究结果相一致。根据一个典型剖面的^137Cs测年数据分析，王港潮滩盐沼的沉积过程根据地貌特征的不同可分3个阶段，大米草覆盖阶段滩面高程迅速增加，互花米草的生长提高了滩面淤积速率。     

江苏沿海互花米草盐沼动态变化及影响因素研究

收集1988～2001年12个时相的江苏盐城幅卫星影像，提取双洋河口至梁垛河闸之间的互花米草盐沼，统计不同时期的分布信息。分析表明：互花米草盐沼在江苏扩张非常迅速，到2001年7月互花米草盐沼分布面积达129．28km^2,从射阳河口至梁垛河闸之间的潮间中上带泥滩大部分已被互花米草盐沼所覆盖；由于生态位的影响，互花米草盐沼沿平行于海岸线方向扩张速度快于垂直于海岸线方向的扩张速度；依据野外调查和卫星影像分析，互花米草盐沼扩张可分为立地、快速扩张及成熟3个阶段。此外，还对互花米草盐沼的影响因素进行了探讨。     

人类活动对苏北潮滩发育的影响

江苏北部潮滩宽阔而平坦,历史上就是人类活动比较频繁的地区。随着对潮滩开发利用强度和深度的增加,人类对潮滩发育的影响越来越显著。潮滩剖面自然发育的均衡形态为上凸型;潮滩被围垦并建堤后,改变了原有的水沙动态平衡关系,潮滩剖面形态发生了调整,海堤附近的潮水沟则不断被淤积。大米草和互花米草等植被的引种改变了潮滩生态结构,由于植被能降低水流流速和波浪能量,起到捕捉沉积物的作用,因此能增加潮间带滩面的淤积速率,改变潮滩分带结构;此外,植被的存在还影响到滩面潮水沟的形态。港口工程的建设改变了沉积物的输运方向。     

近期长江北支口门圆陀角附近潮滩地貌动态变化

圆陀角位于长江北支岸线与江苏海岸线的交会处,独特的互花米草潮滩、淤泥质光滩环境和复杂的河海沉积动力,决定了潮滩地貌对海洋环境变化的响应具有敏感性。由于大规模的围垦,圆陀角附近过去40年来海岸线向东推进了6km。根据2006年以来多次的野外调查和室内粒度与钻孔岩芯的¹³⁷Cs分析, 2006年以来圆陀角附近潮滩淤积明显加强,由¹³⁷Cs时标估算的互花米草滩多年平均沉积速率为2.3cm/a, 2006~2008年观测到的互花米草滩淤积速率>4cm/a,粉砂淤泥质光滩的淤积速率更高;圆陀角风景区内互花米草滩前缘陡坎在风暴潮影响下侵蚀后退,并因粉砂淤泥质光滩的快速淤长而消亡,圆陀角附近潮滩地貌动态是对人类围垦活动、风暴潮与潮汐海洋动力的综合响应,互花米草与光滩快速淤积是近期圆陀角附近潮滩地貌演化的主要特点。     

互花米草引种对苏北潮滩湿地 TOC 、TN和TP分布的影响

分析了TOC、TN和TP在苏北潮滩湿地不同生态带沉积物和植被中的分布状况,结果表明:TOC和TN的水平和垂向平均含量以互花米草滩为最高,其次分别为盐蒿滩、芦苇滩和光滩。TP的平均含量以光滩为最高,依次由海向陆逐渐减小。在生物量最大期间(秋季),单位面积上互花米草体内TOC、TN和TP的累积量远大于盐蒿和芦苇。互花米草主要通过以下4个方面对研究区潮滩湿地TOC、TN和TP的分布产生影响:(1)互花米草滩面较高的沉积速率;(2)互花米草对整个潮滩湿地不同植被分布格局的改变;(3)互花米草有着高生产力以及巨大的地下生物量;(4)互花米草的生长特性使其在生长过程中对磷的需求量很大。     

基于影像间潮滩地形修正的海岸线监测研究——以黄河三角洲为例

针对潮滩环境中潮汐和坡度变化对海岸线变化监测的影响,提出一种通过两景影像计算潮滩坡降进而准确获得海岸线的方法,并利用坡降值估算潮滩体积。以岸线变化较剧烈的黄河三角洲南部的甜水沟口至小清河口的粉砂淤泥质潮滩为例进行应用研究。结合遥感影像、实测固定断面数据和水深测量数据分析表明,影像间的潮差对坡降估算值虽有较大影响,但选择合适潮位估算潮滩坡降是可行的,估算坡降的最小相对误差可达0.2%,均方根误差小于实测坡降一个数量级。1973-2009 年甜水沟口至小清河口14 个年份的岸线变化分析显示,黄河改道对本区的直接淤积影响在甜水沟向南3 km范围内,最大淤积区位于甜水沟口附近,年均淤积率31 m/a,而后在1989-2002 年海区南部出现较大幅度淤积,主要为黄河入海水沙直接或间接淤积造成的;研究时段内岸滩总体演化趋势为蚀退,最大年均蚀退速率51 m/a,黄河改道造成的海洋动力变化是影响本区海岸冲刷的主要因素。验证表明,本文方法计算的潮滩体积用于指示海滩冲淤变迁是合理可行的。     

互花米草盐沼潮沟地貌特征

互花米草是我国从国外引进的能在淤泥质潮滩的高潮带下部和中潮带上部生长的禾木科植物,由于其植株高大、群落盖度高、根系发达等生物学特性,其对潮流动力特征有显著的影响。本文通过对江苏省东台市笆斗垦区外互花米草盐沼地的潮沟形态调查,发现互花米草盐沼潮沟具有以下一些特征:潮沟密度大,可达50km/km²以上;潮沟的宽深比小,大多在8以下;沿岸堤发育,且多呈不对称状;一级主潮沟与主潮沟接头处普遍呈逆弧形;盐沼外侧边缘发育有明显的陡坎冲沟。分析认为这些特征主要与互花米草发达的根系和致密的植株等生物学特性有关,发达的根系增加了盐沼滩面的稳定性,而互花米草高大的植株增加了对潮水运动的阻力,提高了滩面落潮水的归槽水位,改变了潮流的泥沙沉积地点和涨、落潮流的流向,从而形成比较特别的互花米草盐沼潮沟特征。     

Assessing the utility of 210Pb geochronology for estimating sediment accumulation rates on river floodplains in Fiji

Low‐energy gamma ray spectroscopy has been employed to estimate floodplain sedimentation rates using measurements of ²¹⁰Pb in floodplain alluvium. The utility of the technique is assessed through the analysis of excess (unsupported) ²¹⁰Pb profiles in three sediment cores taken from the floodplain of the Labasa River on Vanua Levu in northern Fiji. A low‐energy germanium spectrometer (LEGe) was used for the nondestructive determination of excess ²¹⁰Pb in a region cultivated intensively with sugarcane. Measured average historical (c. 25 years) vertical accretion rates are between 2.2 and 4.4 cm yr^?1. The findings are broadly comparable with published sedimentation rates from analyses of radionuclide profiles elsewhere in the tropical South Pacific Islands, but the rates are higher than those measured previously at the same Labasa River sites using ¹³⁷Cs profiles. Accelerated soil erosion owing to cane burning and land tillage seems to be largely responsible for sediment production, although flood‐related effects such as channel accretion by coarse bedload and the emplacement of large organic debris also influence floodplain sedimentation. However, application of the ²¹⁰Pb technique in Fiji (and perhaps neighbouring island countries) is found to have serious drawbacks compared to the more robust ¹³⁷Cs method, owing principally to the low ²¹⁰Pb concentrations in the sandy alluvial sediment tested.     

基于淤积量的崇明东滩促淤围垦合理性评价

精准围垦的生态预警研究,需要从较短的时间尺度上和较集中的空间尺度上及时精准地监测滩涂的淤积量和淤积位置,这是滩涂围垦工程规划和实施的参考依据。以崇明东滩为例,结合滩涂湿地淤积量的直接测定和滩涂微地貌调查,尝试基于淤积量长期累积的相对高程评价促淤围垦的合理性。淤积量的测定结果表明:1微地形下的植被群落分带差异大到足以掩盖高程逐渐下降的梯度趋势;2潮间带和高潮滩的年均淤积速度均不足1 cm,而低潮滩的年均淤积速度达到了7 cm左右;3微地貌高程与淤积量之间呈极显著的负相关关系,呈现出两种不同的淤积机制。在此基础上,对目前以"生物促淤+物理围垦"的模式治理互花米草外来种入侵的促淤围垦进行了评价:1在快速淤涨的崇明东滩湿地中,生态系统工程师效应起着重要作用;2尽管在本研究实验区的围垦边界高程选择是合理的,但在实验区以外的围垦边界高程甚至延展到了0 m线以下,这是滩涂湿地过度围垦的直接证据之一;3与过去几次大围垦所不同的是,本次围垦范围选择的留一半、围一半的模式,一方面可以有效治理互花米草,另一方面可以预留足够的生态栖息地保留区。总之,淤积量的长期定点观测,为长江三角洲滩涂资源的动态管理和科学围垦提供了参考依据,可更客观地协调滩涂湿地保护和开发利用之间的矛盾。     

Reconstructing recent sedimentation in two urbanised coastal lagoons (NSW,Australia) using radioisotopes and geochemistry

In this study, we combined grain size and geochemical analyses with radioisotope analysis of lead-210 (²¹⁰Pb), caesium-137 (¹³⁷Cs) and radiocarbon (¹⁴C) ages to reconstruct the sedimentation history of two urbanised coastal lagoons in south-east Australia. Towradgi and Fairy Lagoons were both found to exhibit slow initial sedimentation of less than 1 mm year⁻¹ prior to anthropogenic influences. Land clearing in the catchments increased runoff and erosion in the creeks feeding into the estuaries, and has resulted in progradation of fluvial material into the estuarine systems with a marked increase in sedimentation to between 2 and 7 mm year⁻¹. The upper 20–50 cm of the sediment column in both lagoons contained elevated concentrations of heavy metals such as Pb, Cu, Ni and Zn. This pollution trend was found to be consistent with the history of industrialisation and urbanisation in the region, which expanded rapidly post World War 2. The total metal concentrations were consistent with other urbanised/industrialised estuaries around the world. Despite the fairly disturbed nature of these coastal lagoons, the use of ²¹⁰Pb, ¹³⁷Cs and ¹⁴C dating in combination with bulk geochemical analyses allowed detailed reconstruction of sedimentation history.     

海平面上升对长江三角洲和苏北滨海平原海岸侵蚀的可能影响

本区海岸现有30％的岸段为侵蚀海岸,海平面上升将使海岸侵蚀加剧。海平面上升因素在海岸侵蚀诸因素中的比重较国外同类研究结论偏小,这与本区海岸的特殊演变原因有关。海平面上升通过潮流、波浪和风暴潮作用增强,海岸潮滩和湿地损失,岸滩消浪和抗冲能力减小等途径引起海岸侵蚀加剧。其结果是,侵蚀岸段扩大,淤涨岸段减少甚至转为侵蚀,潮间带宽度变窄,坡度加大,从而使沿岸海堤等挡潮工程的标准要相应提高。     

盐城滨海湿地退化评估及分区诊断

根据野外监测数据和遥感信息解译结果,分析了盐城滨海湿地生态特征,定量评估了湿地退化程度,分区探讨了导致湿地退化的主导因素。结果表明:①盐城滨海湿地的主要植物为盐地碱蓬(Suaeda salsa)、互花米草(Spartina alterniflora)和芦苇(Phragmitesau stralis)。受湿地基底稳定性和土壤盐度影响,湿地植被呈现出明显的东西分带、南北分区的特点,地带性分布规律明显。②盐城滨海湿地景观类型可以划分为河口水域、盐地碱蓬滩、芦苇沼泽、互花米草沼泽、耕地、建筑用地、养殖池、盐田和光滩9种类型。由于自然因素和人为活动影响,自1980年以后,研究区景观格局发生了巨大变化。自然景观面积减少了33%,人工景观增加了180%。自然湿地中,面积减少最大的是盐地碱蓬滩和芦苇沼泽。③1980～2008年,盐城滨海湿地的互花米草滩面积呈现出增长趋势,盐地碱蓬滩处于严重退化状态,芦苇沼泽处于退化状态,导致盐地碱蓬滩和芦苇沼泽退化的主要因素是人类开发活动。④对不同区域的导致湿地退化的主导因素进行了诊断,其中灌河口—射阳河口岸段湿地退化的主导因素为海岸侵蚀。射阳河口—斗龙港口岸段属于淤蚀过渡海岸,因处于盐城珍禽国家级自然保护区的核心区位置,人类干扰强度不大,湿地退化不严重。斗龙港口—弶港岸段湿地退化的主导因素为人类对湿地的围垦和开发利用活动。     

Distribution of 137Cs and 210Pb in sediments of tidal flats in north Jiangsu Province

Seven cores were collected from different sediment zones of tidal flats at Xinyanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of 137Cs and 210Pb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the 137Cs and 210Pb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. 137Cs and 210Pb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of 137Cs and 210Pb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of 137Cs and 210Pb in the upper depths. 137Cs and 210Pb chronology got the comparable average sediment rates on the tidal flat. The characteristics of 137Cs and 210Pb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.     

Radiometric dating of recent sediments: beyond the boundary conditions

Most mathematical models for radiometric dating of recent sediments are particular solutions of a unique physical problem: the advective?Cdiffusive transport of a particle-bound radiotracer within a sediment profile that undergoes accretion. Regardless of the particular assumptions about fluxes, sedimentation rates and the diffusion term, all models assume ideal deposition as a boundary condition at the sediment water interface, i.e. new radioactive input will be deposited above the previously existing material. In sediments with very high porosities, this assumption may be unrealistic, because a fraction of the incoming flux may penetrate rapidly through the connected pore spaces. This process will be referred to as non-ideal deposition. This paper reviews evidence from literature data, discusses the basic processes involved, and establishes the mathematical basis to incorporate non-ideal deposition into one-phase radiometric dating models, as depth-distributed local sources. Through analytical and numerical solutions, this work demonstrates that such penetration patterns can explain excess ²¹⁰Pb subsurface maxima, often observed in sediment cores, as well as penetration of ¹³⁷Cs to depths greater than expected from sedimentation rates and diffusion. These ideas are illustrated using examples from the literature in which sediment porosities were >90?%. Implications for radiometric dating include: (1) spurious accelerations in sedimentation rate inferred when applying the constant rate of supply model, and (2) erroneous chronologies, developed when using the maximum depth at which ¹³⁷Cs can be measured as a chronostratigraphic marker.     

互花米草入侵和持续扩张下黄河三角洲滨海湿地潮沟的形态特征及其变化

为了探究互花米草(Spartina alterniflora)入侵下滨海湿地潮沟的发育特征及其变化,采用随机森林分类技术和统计学分析方法,研究了2004~2020年黄河三角洲湿地互花米草的入侵过程,揭示了互花米草持续扩张下潮沟的形态特征及其变化。研究结果表明,现行黄河入海口两侧区域的互花米草群落扩张迅速,截至2020年7月,研究区互花米草群落面积已经达到4406.95 hm²;2012~2016年期间,互花米草群落的扩张速度和扩张动态度都相对最大,分别为490.2 hm²/a和45.9%;在互花米草入侵和持续扩张的条件下,黄河三角洲滨海湿地潮沟的分支增多,平均面积减小,总长度变长,平均长度缩短,平均宽度变窄,景观连通度变差;互花米草的入侵使潮沟形态发生了显著变化,在互花米草入侵区,潮沟的分支增多,平均长度缩短,平均宽度变窄。     

闽江河口湿地互花米草与芦苇光合特性及适应性研究

互花米草在闽江河口鳝鱼滩湿地中潮滩的入侵及快速扩张,已严重威胁到鳝鱼滩湿地的生物多样性及土著种沼泽植物生态系统的结构与功能。为了从植物光合速率的角度分析互花米草入侵及快速扩张的生理生态学机制,利用Li-6400便携式光合作用仪测定了互花米草与土著种芦苇的光合速率日进程及光合光响应曲线。结果表明,互花米草净光合速率的日均值与最大值均大于芦苇,互花米草可积累更多的光合作用产物,使其具有更快的生长速率和初级生产力。根据两种植物的光合光响应曲线可以看出,互花米草利用光合有效辐射的能力更强,显示出互花米草的高适应性。     

江苏淤泥质潮滩对海平面变化的形态响应

通过对江苏滨海平原淤泥质潮滩1980年以来19个固定潮滩断面112个测次滩面高程测量的统计分析，探讨典型淤泥质潮滩剖面形态对海平面变化的形态响应过程。结果表明，典型淤涨岸段海平面上升，多年平均潮位线以上滩面仍将淤积加高，但淤高幅度除多年平均高潮线附近滩面相对较大外，其余均较小，表明随海平面上升该滩带总体淤积速率将趋于减小；与此相反，多年平均潮位线以下滩面则趋于蚀低，且侵蚀强度较大，表明该滩带的侵蚀有加剧趋向，最终滩面总体形态将因上带不断淤高和下带不断蚀低而逐渐变陡，剖面上凸形态的曲率不断加大。曲型侵蚀岸段，海平面上升的效应则相反，海平面上升，多年平均潮位线以上滩面强烈蚀低；而多年平均潮位线以下滩面则强烈淤积加高，剖面的上凹形态最终将因上带不断蚀低和下带不断淤高而趋于平直。     

外来种互花米草在广西海岸的入侵现状及防治对策

本文在分析外来种互花米草引入历史和入侵现状的基础上,结合国内外的研究进展,提出了防范对策,以保护好近海滩涂、原有红树植物及其他海洋生物资源,维持保护区生态系统的独特性和稳定性。同时也可为其它地区互花米草入侵防治提供借鉴。