Importance of tropical coastal environments

On a global basis, a very large fraction (>50%) of the mass flux from land to the marine environment enters from tropical rivers. A broad range of processes active in the adjacent coastal ocean determines the fate of this material. The tropical setting causes many of the coastal processes to be fundamentally distinct from those operating in temperate and polar regions. Therefore, their operation cannot necessarily be understood by extrapolation from empirical observations at higher latitudes. Other coastal processes are influenced by the extremely large water, particulate, and solute discharges from tropical rivers. Further complexity is added by the diverse range of geographic settings through which tropical rivers flow and into which they empty. In summary, coastal—ocean processes in the wet tropics are: globally important, fundamentally different than at higher latitudes, and diverse in operation. Many recent advances have been made in the understanding of the tropical coastal ocean, and it is hoped these will continue into the future. Such understanding is important for predicting processes of river—ocean interaction and terrestrial fluxes to the global ocean, which affect and are affected by human populations. It also can be combined with knowledge of temperate and polar settings to provide a comprehensive understanding of the coastal ocean.     

Zooplankton responses to sandbar opening in a tropical eutrophic coastal lagoon

The effects of a disturbance by sandbar opening on the zooplankton community were evaluated through a long-term study in an eutrophic and oligohaline system, Imboassica Lagoon, Rio de Janeiro, Brazil. Zooplankton samples and limnological data were collected monthly from March 2000 to February 2003. Before the sandbar was opened in February 2001, the lagoon showed eutrophic conditions, with high mean nutrient concentrations and low salinity (total nitrogen – TN = 190.28 μM, chlorophyll a content – Chl. a = 104.60 μg/L and salinity = 0.87′). During this period, the zooplankton species present, such as the rotifers Brachionus calyciflorus and Brachionus havanaensis, were typical of freshwater to oligohaline and eutrophic environments. After the sandbar opening, the lagoon changed to a lower trophic status and increased salinity (TN = 55.11 μM, Chl. a = 27.56 μg/L and salinity = 19.64′). As a result, the zooplankton community came to consist largely of the rotifer Brachionus plicatilis, marine copepods and meroplanktonic larvae, mainly Gastropoda. Salinity was the main force structuring the zooplankton community after the sandbar opening. Two years after this episode, the prior zooplankton community had not reestablished itself, indicating a low resilience to this disturbance. The conditions developed prior to a sandbar opening can be crucial to the community responses in the face of this disturbance and for the capacity of the original zooplankton community to re-establish itself.     

The case for restoration of tropical coastal ecosystems

At no time have humans so altered their natural environment than the present. Marine ecosystems have not been spared, and the degradation of coastal habitats has reached severe proportions in many parts of the world. The mere setting aside of areas for protection may not be enough to ensure adequate production and provision of services for a growing global human population. Hence, the active restoration of habitats, in addition to protection and preservation, is probably the more desirable conservation strategy. Accumulated experience over several decades has demonstrated that the rehabilitation or even restoration of damaged coastal ecosystems is feasible. However, the degree of difficulty and expense involved vary, with coral reefs being the most complicated habitats to restore, followed by seagrass beds and then mangrove forests. In ecosystem restoration, a comprehensive strategy based on sound biological and ecological principles, and proven techniques must be developed. A concrete, achievable goal must be articulated. Because of the dynamic nature of ecosystems, and the inability to accurately predict pathways of succession after a community is established through artificial means, subsequent modifications to a project must proceed within a flexible framework of adaptive management. Finally, for restoration efforts to be successful, local communities must participate actively in cooperation with local governments in accordance with the principle of co-management.     

210Pb in a tropical coastal lagoon sediment core

Excess ²¹⁰Pb in a core from a Mexican Coastal Lagoon, which has no connection with the sea shows a small but measurable decay over the length of the core, when different approaches were compared (excess and corrected ²¹⁰Pb activity with depth, total and inorganic cumulative weights) significant differences in the values for the sedimentation rate are obtained. The best coefficient correlation was calculated when corrected ²¹⁰Pb activity for the uneven distribution of organic matter and cumulative inorganic weight is considered ($\text{ω}\text{= 0·93 cm yr}{}^{\mathrm{?1}}$, R = ?0·86; ω = 0·51 cm yr^?1 for the top 13 cm, R = ?0·90 and 1·52 cm yr^?1 for the interval 14–46 with R = ?0·96).Time frames in the sedimentary column were in agreement between the ²¹⁰Pb calculated time and the appearance of shells fragments probably associated with the disturbances caused by the 1961 hurricane Tara.The surface accumulation rate is equivalent to a mean deposition of 262·5 g m^?2 yr^?1 or organic matter which is minor but comparable to some salt marshes of United States.     

影响广西沿海的热带气旋分析

应用《台风年鉴》1953—2012年热带气旋(TC)最佳路径资料,统计分析了影响广西沿海TC和易引发广西沿海显著增水的TC的时空分布特征以及年际变化特征。结果表明:影响广西沿海的TC主要集中于7、8、9三个月份,以南海为主要源地,而引起广西沿海显著增水的TC多源于菲律宾以东大洋洋面。从影响广西沿海的TC在近60年频数和强度变化来看,广西沿海TC最大强度存在下降趋势,但每年的平均强度存在上升趋势。     

The effects of tropical storm Dennis on coastal phytoplankton

The effects of tropical storm Dennis were documented in the coastal waters of South Carolina during August 1981. Phytoplankton photosynthesis vs. irradiance curves showed initial depression of the parameter a followed by three- to five-fold increase of both a and the asymptotic maximum rate of photosynthesis P_m^B. Productivity rates were depressed in most samples immediately after the storm. Surface samples at the inshore stations were around 50 mg C m^?3 h^?1 at saturating light intensities, while the offshore station rates were around 10 mg C m^?3 h^?1. After a 10-day lag these rates had increased to about 200 mg C m^?3 h^?1 inshore and 75 mg C m^?3 h^?1 offshore. These changes are thought to be primarily caused by changes in species composition. Some of the dominant diatom species changed and dinoflagellate species were introduced. No significant changes in nutrient concentrations were observed. Transient depressions of water temperature, salinity and light intensity may have contributed to the observed changes.     

Benthic boundary layer processes in coastal environments: An introduction

This special issue ofGeo-Marine Letters Benthic Boundary Layer Processes in Coastal Environments includes 20 papers devoted to results of recent near-shore experiments supported by the Coastal Benthic Boundary Layer (CBBL) program. Experiments were conducted in gas-rich muddy sediments of Eckernförde Bay of the Baltic Sea and on relict sandy sediments of the West Florida Sand Sheet. In this introductory paper we present scientific justification for experiments and summarize preliminary results.     

中国东部近海现代沉积环境

东海近岸海域岛屿、入海河流众多,大量陆源物质随沿岸流自长江口向东迁移,是海陆相互作用最为强烈的区域之一。对2016和2017年夏季采集的570个东海近岸表层沉积物样品进行了沉积物物理化学性质、粒度特征、有机质含量等测试分析。结果表明,这些特征参数明显受区域沉积环境的控制。杭州湾区域沉积物偏弱碱性, 氧化还原电位(Eh)＜0, 有机质含量北部偏高, 沉积物组成以黏土质粉砂为主,抗剪强度较低(普遍＜0.5kpa),各指标无明显分布规律,相关性较强。浙江东部沿海区域沉积物近中性至弱酸性,Eh较高(＞0),Eh与pH自陆向海降低,象山港、乐清湾海域有机质含量较高; 舟山至台州海域以粉砂为主,台州以南分布斑块状泥质区,抗剪强度比杭州湾区域偏高,各指标无明显相关性。整体来看,杭州湾与浙江东部沿海属于两个完全不同的沉积环境体系,主要是因杭州湾物质来源较为稳定,区域水动力较强,导致沉积物分布相对均一; 而浙江东部海域河流、岛屿较多,各个区域物质来源和水动力环境都存在较大差异。     

有机污染物在不同沿海沉积环境中积累的差异性

以浙江沿海水域为研究区域,在系统地测定水体与沉积物中有机污染物种类的基础上,研究了表层沉积物中有机污染物的积累与沉积环境、沉积物矿物组成和排放环境因素之间的相互关系.结果显示,沿海水体和表层沉积物中主要存在的有机污染物有石油烷烃类化合物、邻苯二甲酸酯化合物、有机硅氧链类化合物、氯代苯酚类、苯醚类和胺类化合物等6大类,它们在表层沉积物中的积累强度呈现出河口大于沿岸大于强潮汐河沉积环境的趋势,但在相同沉积环境的沉积物中有机污染物的积累强度存在一定的差异,这说明有机污染物在沿海沉积物中的积累除与沉积环境有关外,还与区域有机污染物的排放特点有关.     

An integrated geochemical and hydrodynamic model for tidal coastal environments

In this paper, the design, calibration and application of an integrated geochemical–hydrodynamic model are described. The model comprises three parts: A hydrodynamic submodel that was adopted from a depth-averaged, semi-implicit hydrodynamic model, a geochemical submodel based on equilibrium partitioning of chemicals between aqueous and particulate phases, and a particle dynamic submodel that simulates resuspension, transport and settling of suspended particulate matter (SPM). The integrated model was implemented in San Diego Bay (SDB), a heavily urbanized, semi-closed mesotidal embayment. A series of model calibrations were carried out based on observations on salinity, polychlorinated biphenyls (PCBs) and SPM. Salinity calibrations indicated that only 15% of precipitation in the drainage area of SDB could reach the bay, presumably due to the dams on the tributary rivers. Steady-state calibrations of PCBs based on fixed concentrations at known ‘hot spots’ have reproduced observed PCB concentrations in both the dissolved and particulate phases. SPM calibrations showed that shipping-induced resuspension produce more SPM than natural processes. Based on the calibrated model, the annual transport of PCBs out of SDB was estimated to be 3.85 kg (3.5 kg and 0.35 kg in the dissolved and particulate phases, respectively), much higher than the previous estimates based on steady-state assumptions. It was also found out that only a small portion of the fine sediment exported from SDB was derived from riverine input. This model can be applied to the studies of the transport and fate of other chemical species. It can be transplanted to other coastal areas as well. The integrated model represents a novel framework in which geochemical processes in coastal environments can be investigated on a truly dynamic basis.     

龙海—漳浦沿海第四纪地层及沉积结构特征

本文根据实际调查资料，对研究区的第四纪地层层序进行了较系统地划，并初步探讨了第四纪地层的沉积结构特征。     

Modelling of complex coastal environments: Some considerations for best practise

The numerical modelling of large-scale sediment transport and coastal morphology frequently requires significant model reduction and optimisation in order to achieve expedient conclusions. This study provides a detailed sensitivity analysis of various model ‘reduction’ techniques using the Bristol Channel, western U.K. as a case study. The work elucidates a number of the best practises for employment of state-of-the-art systems to complex coastal regions.     

Regional stratigraphic framework linking continental shelf and coastal sedimentary deposits of west-central Florida

A regional study of the Holocene sequence onlapping the west-central Florida Platform was undertaken to merge our understanding of the barrier-island system with that of the depositional history of the adjacent inner continental shelf. Key objectives were to better understand the sedimentary processes, sediment accumulation patterns, and the history of coastal evolution during the post-glacial sea-level rise. In the subsurface, deformed limestone bedrock is attributed to mid-Cenozoic karstic processes. This stratigraphic interval is truncated by an erosional surface, commonly exposed, that regionally forms the base of the Holocene section. The Holocene section is thin and discontinuous and, north or south of the Tampa Bay area, is dominated by low-relief sand-ridge morphologies. Depositional geometries tend to be more sheet-like nearshore, and mounded or ridge-like offshore. Sand ridges exhibit 0.5–4 m of relief, with ridge widths on the order of 1 km and ridge spacing of a few kilometers. The central portion of the study area is dominated nearshore by a contiguous sand sheet associated with the Tampa Bay ebb-tidal delta. Sedimentary facies in this system consist mostly of redistributed siliciclastics, local carbonate production, and residual sediments derived from erosion of older strata. Hardground exposures are common throughout the study area. Regional trends in Holocene sediment thickness patterns are strongly correlated to antecedent topographic control. Both the present barrier-island system and thicker sediment accumulations offshore correlate with steeper slope gradients of the basal Holocene transgressive surface. Proposed models for coastal evolution during the Holocene transgression suggest a spatial and temporal combination of back-stepping barrier-island systems combined with open-marine, low-energy coastal environments. The present distribution of sand resources reflects the reworking of these earlier deposits by the late Holocene inner-shelf hydraulic regime.     

Stramonita haemastoma as a bioindicator for organotin contamination in coastal environments

Stramonita haemastoma was investigated as a suitable bioindicator of TBT and TPhT contamination in the tropical Atlantic Ocean by: 1. Imposex induction in healthy females after inoculation with TBT and TPhT in the laboratory; and 2. Determining incidence of imposex in S. haemastoma collected from areas with various levels of tributyltin (TBT) and triphenyltin (TPhT) and determining the concentrations of these chemical in its tissues and that of its prey, the mussell Perna pernas. Imposex intensities and organotin concentrations in tissues showed good correlation, indicating S. haemastoma as a reliable bioindicator of TBT and TPhT contamination in coastal waters. Body burden threshold of TBT and TPhT for imposex induction was estimated to be 10-20 ng g(-1).     

Carbon disulfide in the estuarine, coastal, and oceanic environments

The concentration of carbon disulfide (CS₂) in surface water and relevant hydrographic parameters were determined in coastal waters of the eastern USA (Delaware Bay and Chesapeake Bay, including the Potomac River; 7–11 September 1986). The CS₂ concentration varied extensively along the cruise track, from 4 to 510 pmol S(CS₂) l⁻¹ (n = 103). The average values in estuarine, shelf, and oceanic waters were found to be 118 ± 100 pmol S(CS₂) l⁻¹ (n = 54), 51 ± 34 pmol S(CS₂) l⁻¹ (n = 14), and 28 ± 12 pmol S(CS₂) l⁻¹ (n = 35), respectively. To help interpret the geochemical behavior of CS₂, we analyzed the depth distribution of CS₂ in the North Atlantic Ocean during an earlier cruise (23 April–2 May 1986). In most cases, these depth profiles show a near-surface maximum at about 10–20 m depth and a relatively steep gradient below this maximum. Based on the distribution pattern in the water column and evidence provided by earlier workers, we propose that diffusion of CS₂ from bottom sediments may contribute to CS₂ levels in surface seawater. The atmospheric concentration of CS₂ was also investigated at some locations during the September cruise. Except during periods when there was a significant anthropogenic input, the concentration of CS₂ in air was generally in the range of 4–15 pptv (parts per trillion by volume) with a mean of 10.4 ± 4.0 pptv (n = 10). The calculated sea-to-air emission rates of CS₂ at each of our sampling stations show a decreasing trend across estuarine, shelf, and oceanic areas, in agreement with the trend in surface water concentrations.     

华南近海热带气旋活动的研究

根据国家气象局１９４９－１９９４年《热带气旋年鉴》资料，分析华南近海热带气旋活动的频率，强度，路径和登陆情况，并从中总结其活动的特征和规律。     

Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands

Numerous studies have shown that most beaches and coastal dune systems of the world are currently eroding but very few have investigated the combined sediment budgets of subaerial and nearshore submarine systems. In the case of the dune field of the Maspalomas Natural Special Reserve (in the south of Gran Canaria), the adjacent Maspalomas and El Inglés beaches and the adjacent submarine platform, the sediment budgets have been severely affected by erosion over the past few decades. The objectives of this study were to investigate the availability of sand within the modern sedimentary system, including the coastal dunes, the beaches and the submerged shelf, but also to assess local sediment sinks. An isopach map generated on the basis of topo-bathymetric data and seismic-reflection profiles revealed that sediment thickness varies from 0–22 m in the study area. Expanses of relatively low sediment thickness were identified in the south-western sector of the coastal dune field along Maspalomas beach, and in the nearshore region to the south of this beach. These localized sediment-deficit areas earmark Maspalomas beach as the most vulnerable shore strip threatened by erosion. The shallow seismic data also revealed that the submarine platform south of Maspalomas represents a marine terrace cut into an ancient alluvial fan, thus documenting an influence of the geomorphological heritage on the present-day morphodynamics. A side-scan sonar mosaic of this nearshore platform enabled the delimitation of areas covered by rock, boulders and gravel, vegetated sand patches and a mobile sand facies, the latter including ripple and megaripple fields. The megaripple field in a valley close to the talus of the marine terrace has been identified as a major sediment sink of the Maspalomas sedimentary system. It is fed by south-westerly storm-wave events. The sediment deficit in the coastal dune field and along Maspalomas beach can therefore only be explained by a currently faster loss of sediment to an offshore sink than can be compensated by the supply of sand from outside the system.