海南陵水沙坝潟湖海岸近26年地貌类型空间格局演化

通过对海南陵水县黎安、新村两个沙坝潟湖海岸地貌的野外踏勘, 构建研究区地貌类型分类标准, 据此采用德国智能影像分析软件eCognition提供的随机森林法模块, 对1987~2013年26年间6期Landsat卫星遥感影进行地貌类型分类与空间分布位置图斑提取, 结合ArcGIS软件据实测地形数据生成数字高程模型以及地貌类型转移矩阵数理分析技术, 对研究区地貌格局演化特征及地貌类型转化趋势展开研究。结果表明, 上述野外测量、随机森林遥感影像分类提取、GIS空间分析及矩阵转换数理统计等多技术方法结合用于沙坝潟湖海岸地貌长周期演化研究是可行、有效的, 此方法弥补了传统采用钻孔及沉积柱状样采集分析中以点代面、难以全域覆盖的海岸带沉积地貌分析方法的不足。研究发现, 近26年间, 陵水双潟湖海岸地貌发生了显著变化, 地貌类型转化趋势为海积平原、水下浅滩、海积阶地向养殖池及盐田转化, 自然地貌间的相互转化不明显; 大范围的潮滩围垦及海积平原挖掘改造, 形成了一条人工地貌带, 打破了原有自然地貌空间格局, 改变了海积平原与水下浅滩之间的沉积动力作用方式以及物质能量交换模式, 不断加强的人类活动已成为研究区海岸地貌改造的主要驱动力。     

Beach face and berm morphodynamics fronting a coastal lagoon

This study documents two different modes of berm development: (1) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode 1 sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth.     

Variance estimate and taxonomic resolution: An analysis of macrobenthic spatial patterns at different scales in a Western Mediterranean coastal lagoon

The effects of taxonomic resolution on the variance estimates of macrobenthic assemblages were studied at four spatial scales in a Mediterranean coastal lagoon. The assemblages exhibited significant differences at all the investigated scales; however, spatial variability was mainly associated with the smallest and the largest scales. The decrease of taxonomic resolution (from species to family) was not related to a decrease of the overall variability and similar estimates of variance components were obtained using species and family resolution levels. The ordination models derived from species and family abundances were very similar both in terms of location and dispersion effect, while further aggregation to the class level began to alter the observed spatial patterns. In future studies aimed at assessing changes in the lagoon, resources derived from the cost reductions achieved using family level could be employed to plan more frequent surveys and/or to adopt complex spatial sampling designs with a high number of replicates.     

Enhancement of regional variations in salinity and temperature in a coral reef lagoon, New Caledonia

The variability in salinity and temperature in the southwest lagoon of New Caledonia (2100 km²) under non-storm conditions is analysed using a 4-year dataset (1997–2001). Seasonal and interannual variations in salinity are amplified nearshore. Temperature is larger in bays than in the open lagoon during summer, the reverse is true in winter. El Niño Southern Oscillation (ENSO) related nearshore temperature variations parallel those at regional scale, but with seasonal variations amplified. Haline stratification, if any, is enhanced in coastal areas. To cite this article: S. Ouillon et al., C. R. Geoscience 337 (2005).     

The role of benthic macrophytes and their associated macroinvertebrate community in coastal lagoon resistance to eutrophication

Eutrophication is widely recognised as one of the major menaces to coastal environments, particularly enclosed bays and lagoons. Although there is a general understanding of the consequences of eutrophication in these systems, there is a lack of sufficient knowledge concerning biotic feedbacks that influence eutrophication patterns and the resistance capacity of coastal environments.In this paper, the isotope ratios of main producers and consumers of a Mediterranean lagoon were examined in order to elucidate the fate of anthropogenic inputs from the main watercourse flowing into the lagoon.The results of the study of stable isotope data in the Mar Menor lagoon reflected that the whole benthic community plays an important role as a natural ‘filter’ that removes excess nutrients from the water column and stores them in the sediments, thereby enhancing lagoon resistance to eutrophication.     

Assessment by microsatellite analysis of genetic diversity and population structure of Enhalus acoroides from the coast of Khanh Hoa Province, Vietnam

Seagrass beds degraded significantly since the last century on both, global and local scale. The seagrass species Enhalus acoroides (Linnaeus f.) Royle is a common species found in almost all marine ecosystems including bays, lagoons and around offshore islands in tropical regions of the West Pacific. It was shown that genetic diversity is an essential indicator of the conditions of ecosystems. In the present study, microsatellite markers were used to assess the genetic diversity and population structure of six distinct seagrass beds along the coast of the Khanh Hoa Province, Vietnam. The results indicate that the genetic diversity of the populations in the open sea is higher than in the lagoon. Seagrass beds occurring in disturbed sites show reduced genetic diversity. The fixing index value (F_ST) depicts a relatively high genetic structure among populations. Structure analysis clusters the populations into open sea and lagoon populations and cluster analysis and AMOVA indicate a significant difference between the two groups. There are low but non-significant positive correlations between geographic and genetic distances. The different habitats of the open sea and the lagoon are probably responsible for forming two groups.     

Pesticide and Herbicide Residues in Sediments and Seagrasses from the Great Barrier Reef World Heritage Area and Queensland Coast

Pesticides and herbicides including organochlorine compounds have had extensive current and past application by Queensland's intensive coastal agriculture industry as well as for a wide range of domestic, public health and agricultural purposes in urban areas. The persistent nature of these types of compounds together with possible continued illegal use of banned organochlorine compounds raises the potential for continued long-term chronic exposure to plants and animals of the Great Barrier Reef. Sediment and seagrass samples were collected from 16 intertidal and 25 subtidal sampling sites between Torres Strait and Townsville, near Mackay and Gladstone, and in Hervey and Moreton Bays in 1997 and 1998 and analysed for pesticide and herbicide residues. Low levels of atrazine (0.1–0.3 μg kg⁻¹), diuron (0.2–10.1 μg kg⁻¹), lindane (0.08–0.19 μg kg⁻¹), dieldrin (0.05–0.37 μg kg⁻¹), DDT (0.05–0.26 μg kg⁻¹), and DDE (0.05–0.26 μg kg⁻¹) were detected in sediments and/or seagrasses. Contaminants were mainly detected in samples collected along the high rainfall, tropical coast between Townsville and Port Douglas and in Moreton Bay. Of the contaminants detected, the herbicide diuron is of most concern as the concentrations detected have some potential to impact local seagrass communities.     

Changes in trace metals in Thalassia testudinum after hurricane impacts

Major hurricanes Emily and Wilma hit the Mexican Caribbean in 2005. Changes in trace metals in the seagrass Thalassiatestudinum prior to (May 2004, 2005) and following passage of these hurricanes (May, June 2006) were determined at four locations along a ∼130 km long stretch of coast. Before the hurricanes, essential metals were likely limiting and concentrations of potentially toxic Pb were high in a contaminated lagoon (27.5 μg g⁻¹) and near submarine springs (6.10 μg g⁻¹); the likely sources were inland sewage disposal or excessive boat traffic. After the hurricanes, Pb decreased to 2.0 μg g⁻¹ in the contaminated lagoon probably through flushing. At the northern sites, essential Fe increased >2-fold (from 26.8 to 68.3 μg g⁻¹ on average), possibly from remobilization of anoxic sediments or upwelling of deep seawater during Wilma. Thus, hurricanes can be beneficial to seagrass beds in flushing toxic metals and replenishing essential elements.     

Decline of the Jakarta Bay molluscan fauna linked to human impact

In 1937/38 representative mollusc collections were made in Jakarta Bay (West Java, Indonesia). New data from here and the adjacent offshore Thousand Islands archipelago (Kepulauan Seribu) became available in 2005. Although collecting efforts and sampling methods differed, a comparison of the molluscan fauna of Jakarta Bay between 1937/38 and 2005 reveals a distinct deterioration. From 1937 to 2005, Jakarta Bay received increasing amounts of sewage from the greater Jakarta area, as well as increased sediment input from the deforested West Java hinterland. Predatory gastropods and numerous mollusc species associated with carbonate (reef) substrate have vanished from Jakarta Bay, among which many edible species.