莆田围填海工程对岸线变迁及海岸环境的影响研究

文章运用 ArcGIS10.5软件的DSAS模块的端点变化率、线性回归率等算法,以莆田市 1984年、1994年、2004年、2010年、2014年和2019年6个时期的google遥感影像图（Landsat卫星）为数据源,分析莆田30余年来围海、填海工程及其他岸线类型的变迁过程。结合历史文献资料研究发现:①1984—2004年,围填海工程基本以围海养殖和围海盐业生产为主,胜利、澄峰、后海、东峤围海垦区占围海工程90%以上;②2004—2014年,填海造地工程飞速发展,临港产业园、妈祖城、东吴港区、石门澳等大面积区域性填海面积约60 km2,约占全市填海面积的93%;③近5年来,大批围海工程转产转型,围海面积逐年减少,生态修复岸线和砂质岸线迅速增长,海岸保护能力不断升级。莆田围填海工程建设提升了莆田海洋经济社会的发展水平,增加了海洋经济产值,适应了城市发展需求,但海岸保护功能降低、纳潮量减少、生物多样性损伤、水质恶化等海洋生态环境问题日益突出。随着生态海堤、蓝色海湾等海洋修复工程的实施,改善了海岸防护工程的功能体系,提升了海岸带生态环境自适应能力,为推进海岸带生态修复工程的实施提供科学依据。     

连云港洪门古沙堤沉积特征及其意义

通过钻孔、年代地层、沉积物粒度和有孔虫组合综合分析,并配合探地雷达,对洪门古沙堤的成因类型以及古海岸环境进行了探讨。洪门古沙堤沉积物和海州湾现代沙滩、苏北平原贝壳堤相比较,颗粒集中在粗砂—极粗砂范围,分选性偏差,极有可能形成于靠近河口或受河口影响的环境。探地雷达揭示洪门古沙堤曾有过向海方向的进积和生长,指示当时沙源丰富。洪门古沙堤的浅钻地层反映了洪门地区在6400 aBP左右为滨海沼泽环境,此时期与青莲岗文化期的年代相吻合;湖沼沉积结束后,洪门地区迎来了中全新世的最大海侵,受周围地形的制约,洪门地区可能形成了河口浅海湾环境,普遍沉积了2 m左右的青灰色淤泥沉积,有孔虫组合反映当时的环境并非完全开敞,而是受到一定程度限制的近岸浅水环境,反映了洪门地区为浅海湾环境;6000 aBP左右,随着砂砾质沉积物供应的丰富以及相对海平面下降,洪门古沙堤开始发育,直到5000 aBP苏北和连云港地区普遍发生海退,古沙堤发育结束。     

海南岛三亚湾现代沉积环境

海南岛三亚湾海滩沉积物主要以中细砂为主,中值粒径在2.0~2.5Φ之间,为细砂质,少量样品在1.0~2.0Φ之间,属中砂质,适合于海滩旅游。近岸海底沉积物总体分布较细,为砂-粉砂-黏土的组合,仅仅在海湾西侧靠近岬角处,以中粗砂为主。近岸海底沉积物是低海平面时古河道的堆积物,能够为现代海滩提供很好的砂源,为确保海滩的稳定性提供了物质前提条件。但是,由于近20年的海岸开发,海滩东部受到人类开发活动的深刻影响,人为排放的有机物污染使海滩部分出现泥化和变黑,而且,由于人为的违规建筑物紧逼高潮线和大潮高潮线,破坏海滩的整体形态,改变海岸的动力条件,进而破坏了海滩旅游资源。     

CMIP6模式对中国近海气象要素模拟评估与预测

为了研究第六次国际耦合模式比较计划(CMIP6)中新提出的“情景模式比较计划”(ScenarioMIP)下中国近海气象要素的变化情况,本文选取了其中6个海气耦合模型,对其模拟的风速、气温、降水进行评估与预测。评估结果表明选取的模式对中国近海模拟效果整体都不错,但在菲律宾群岛附近模拟结果相对欠佳。模型平均预估结果表明未来21世纪中叶4个情景下渤黄海风速夏季增加、冬季减弱;至21世纪末,研究海域夏季15°N以北(南)风速主要呈增加(减小)的趋势,冬季25°N以北(南)风速主要呈减小(增加)的趋势。4个未来情景下的中国近海气温都将持续升高,高纬区域增幅大于低纬。可持续发展情景(SSP1-2.6)能有效减缓升温,其他放任温室气体大量排放的情景(如SSP5-8.5),则会加剧升温。未来中国近海降水变化总体上呈增加趋势,渤黄海与东海降水增幅在SSP5-8.5情景下最大,世纪末分别增加约15.87%与5.61%;南海降水增幅在SSP2-4.5情景下最大,世纪末增加约4.84%。     

南海北部甲烷渗漏活动存在的证据:近底层海水甲烷高浓度异常

用吹扫-捕集法对东沙群岛西南和西沙海槽附近海域5个站位水柱中的甲烷浓度进行了测定,在其中的3个站位发现了甲烷高浓度异常。在东沙群岛西南海域的E105A和E106两站位近底层海水中甲烷浓度均出现异常增加,其值分别为4.25和10.64 nmol/dm3。在西沙海槽附近的E413站位甲烷异常出现在1 750,1 900和2 050 m深的近底层水中,浓度分别达5.17,8.48和8.70 nmol/dm3。在近底层海水中出现的甲烷高浓度异常是由于沉积物下部甲烷渗漏活动造成的,结合前人在这两个海域沉积物的地球物理和化学调查资料,认为可能是与冷泉渗漏或天然气水合物分解有关。2007年5月在探测到甲烷高浓度明显异常的东沙群岛西南神弧海域,获得了天然气水合物的实物样品,但是西沙海槽附近海域近底层水的甲烷高浓度异常是来源于天然气水合物还是来源于冷泉需要进一步加以确认。     

Marsh expansion at Calaveras Point Marsh, South San Francisco Bay, California

Studies of shoreline progradation along low-energy vegetated shorelines have been limited, as these environments are generally experiencing erosion rather than deposition, with extreme erosion rates frequently found. This study examined yearly changes along a vegetated shoreline at Calaveras Point Marsh, South San Francisco Bay, California, using aerial photography, to determine the roles of climatic, watershed, and coastal process in driving shoreline changes. In addition, sediment accumulation was monitored on a yearly basis at 48 locations across the marsh to determine the role of geomorphic factors in promoting accumulation. Calaveras Point Marsh was found to have expanded from 49.26 ± 5.2 to 165.7 ± 4.7 ha between 1975 and 2005. Although the rate of marsh expansion was not positively correlated with yearly variability in precipitation, local streamflow, delta outflow, water level observations, population growth, or ENSO indices, marsh growth was greater during years of higher than average temperatures. Warmer temperatures may have promoted the recruitment and growth of Spartina foliosa, a C₄ grass known to be highly responsive to temperature. Other factors, such as the formation of a coastal barrier, a recent change in the location of the mouth of the Guadalupe River, and channel readjustment in response to diking are credited with driving the bulk of the marsh expansion. Sediment accumulation was found to be high closest to channels and to the shoreline, at low elevations and in recently vegetated marsh. Globally, the pace of sea level rise exerts the primary control on wetland development and persistence. However, at local geographic scales, factors such as tectonic events, modifications to natural sediment transport pathways or land use changes may overwhelm the effects of regional sea level rise, and allow for wetlands to develop, expand and persist despite rapid sea level rise.     

Fouling assemblages on offshore wind power plants and adjacent substrata

A significant expansion of offshore wind power is expected in the near future, with thousands of turbines in coastal waters, and various aspects of how this may influence the coastal ecology including disturbance effects from noise, shadows, electromagnetic fields, and changed hydrological conditions are accordingly of concern. Further, wind power plants constitute habitats for a number of organisms, and may locally alter assemblage composition and biomass of invertebrates, algae and fish. In this study, fouling assemblages on offshore wind turbines were compared to adjacent hard substrate. Influences of the structures on the seabed were also investigated. The turbines differed significantly from adjacent boulders in terms of assemblage composition of epibiota and motile invertebrates. Species number and Shannon–Wiener diversity were, also, significantly lower on the wind power plants. It was also indicated that the turbines might have affected assemblages of invertebrates and algae on adjacent boulders. Off shore wind power plant offer atypical substrates for fouling assemblages in terms of orientation, depth range, structure, and surface texture. Some potential ecological implications of the addition of these non-natural habitats for coastal ecology are discussed.     

Tidal and residual circulations in coupled restricted and leaky lagoons

Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled “restricted” and “leaky” coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a “restricted” nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a “leaky” nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.     

Seasonal observations of surface waters in two Gulf of Maine estuary-plume systems: Relationships between watershed attributes,optical measurements and surface pCO2

The partial pressure of carbon dioxide (pCO₂) in estuary-plume systems is related to the internal processes of net organic metabolism and physical mixing, but is also strongly influenced by biogeochemical inputs from the land and ocean. Surface layer pCO₂, stimulated fluorescence of chlorophyll (f-chl) and colored organic matter (f-com), and beam attenuation at 660 nm (c-660) were measured during three seasonal surveys of the Kennebec (ME) and Merrimack (MA) estuary-plume systems. These estuaries are both supplied by large New England Rivers and separated by less than 150 km, but significant differences were often observed in the distributions of surface pCO₂ and optical variables. High pCO₂ concentrations were generally associated with high f-com, while lower pCO₂ concentrations were associated with high f-chl and c-660. Using simple regression models, optical measurements were used to estimate chlorophyll and total organic carbon concentrations. Results suggest that labile riverine carbon is responsible for sustaining supersaturated pCO₂ conditions and that phytoplankton productivity, likely driven by inputs of riverine dissolved inorganic nitrogen, is responsible for pCO₂ undersaturation. Although optical variables are often related to surface pCO₂, the results suggest that efforts to retrieve pCO₂ in complex waters using optical data may be enhanced using a site-specific, multivariate approach.     

Probabilistic Assessment of Wave Overtopping of Nampo Dike in the West Coast of Korea

The Nampo dike, which is located at the west coast of Korea, was destroyed by wave overtopping during the storms on 30 August and 17 September in 1959. In this paper, is performed the probabilistic assessment of wave overtopping of Nampo dike by use of Owen model, Van der Meer ＆ Janssen model and Hedges ＆ Reis model for wave overtopping of seawall. Based on the available tidal and wave data for storm surges in 1989, the risk assessment of wave overtopping of the Nampo dike has been carried out by both Level Ⅱ and Level Ⅲ reliability methods. The calculated resuhs show the general agreement of failure probability between the two methods. By utilizing the rehabilitated cross section of Nampo dike, the failure probability of wave overtopping for the Nampo dike after rehabilitation will be rapidly reduced to that of initial design at crest level of 9.0 m with the improved slope from 1 ： 2 to 1 ： 4 at seaside. Since the sea level may only rise 1.0 m in the next few decades, the failure probability of Nampo dike will be still in the safe range.