The effects of beach nourishment on the sandy-beach amphipod Exoediceros fossor: impact and recovery in Botany Bay, New South Wales, Australia     

Alan R. Jones  Anna Murray  Theresa A. Lasiak  & Robin E. Marsh 《Marine Ecology》2008,29(S1):28-36

Beach nourishment is increasingly being implemented to address problems of erosion. However, the ecological consequences of nourishment are poorly understood, especially in Australia. In Botany Bay, sand was piped from an intertidal borrow area at Elephant's Trunk to nourish the nearby eroding beach at Towra Point. The effects on an intertidal exoedicerotid amphipod, Exoediceros fossor (Stimpson, 1856), were examined using a beyond-BACI (Before–After, Control–Impact) sampling design. Sampling was conducted before and after engineering operations at sites within the borrow and nourishment locations and multiple control locations. Hypotheses concerning impact and recovery were tested using asymmetrical ANOVAs and two-tailed F-tests. These examined the effects on abundance and spatial variability, respectively. The impact of the engineering operations on abundance was very large at both borrow and nourishment locations. However, recovery started within several weeks and, using space × time interactions as a criterion, appeared to be complete within a year. This conclusion is made cautiously because of low statistical power and because other criteria for recovery suggest that it was not complete at some sites. As beach erosion is likely to increase in severity with rising sea levels and greater storm surges associated with climate change, management authorities will need a better understanding of the ecological effects of beach nourishment.  相似文献   

Assessing the extent of mangrove change caused by Cyclone Vance in the eastern Exmouth Gulf, northwestern Australia   总被引：1，自引：1，他引：0  

E.I. Paling  H.T. Kobryn  G. Humphreys   《Estuarine, Coastal and Shelf Science》2008,77(4):603-613

Changes in mangal area were quantified in the eastern Exmouth Gulf over six years (1999–2004) after Cyclone Vance using Landsat TM satellite imagery and aerial photography. Vance was the strongest tropical cyclone ever to impact the Australian mainland before 2006 and produced wind gusts of more than 280 km h⁻¹. Image data were processed using ENVI™ and IDRISI™ software. Three sets of Landsat TM images from 1999 (a few days before the cyclone), 2002 and 2004 were used, along with 2004 digital aerial photography. A ‘common’ subset of 904 km² was selected from all images and classification was developed using ISODATA™ unsupervised classification to identify spectrally distinct areas followed by principal component analysis (PCA), vegetation indices and supervised classification. Some 12,800 ha of mangrove habitat was present before the cyclone and approximately 5700 ha (44%) was removed by it. Most mangroves lost (74%) between 1999 and 2004 were converted either to bare sediment or to live saltmarshes and this occurred mostly between 1999 and 2002. Five basic categories of damage were conspicuous from imagery and field observations, and evidence suggests that much of the loss was due to the longer term consequences of sediment deposition or smothering, rather than the immediate effects of wind or waves. Mangroves exhibited accelerated recovery between 2002 and 2004, and around 1580 ha regenerated during this time, amounting to a return of 68% of their former coverage. At this recovery rate we estimate that they should have returned to their pre-cyclone area by 2009. Over half of the saltmarsh habitats (54%) were removed by the cyclone (4060 ha) but their recovery has been far more rapid than mangroves. After 5 years, saltmarshes had returned to 87% of their previous area. The 5700 ha of mangrove habitat damaged by Cyclone Vance exceeds any anthropogenic impact that has ever taken place in Western Australia by several orders of magnitude.  相似文献   

Climate change and coral reef bleaching: An ecological assessment of long-term impacts,recovery trends and future outlook   总被引：2，自引：0，他引：2  

Andrew C. Baker  Peter W. Glynn  Bernhard Riegl 《Estuarine, Coastal and Shelf Science》2008

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.  相似文献   

正理庄高89-1区块CO2混相驱参数优化数值模拟研究     

史华 《海洋地质译丛》2008,(1):68-73

为了确保高89-1区块CO2混相驱项目的顺利实施,依据该区块的精细油藏描述成果,在优化适于CO2混相驱模型基础上,建立了符合油藏地质特点的三维地质模型。在此基础上对开发指标进行计算,对五个参数（井网、开发方式、压力水平、注入量和采油速度）进行优化,并提出了推荐方案,预测采收率可达23.10%,比弹性开采方式提高15.16%。  相似文献   

提高机采水平的配套技术及应用     

张健泉  吴凤英  师清磊 《海洋地质译丛》2008,(4):70-72

随着濮城油田的持续性高速开发,油田综合含水逐渐上升,油水井井况进一步恶化,作为油田生产主体的机械采油井躺井频繁、管杆泵使用寿命缩短。近几年中原油田采油二厂濮城油田年平均躺井数达560井次之多,导致机械采油井维护费用增加,管杆泵投入增大,严重制约着油田的生产和经营。通过加缓蚀剂在油管内壁形成保护油膜,起到润滑作用;应用特殊抽油杆防腐止磨;应用尼龙扶正器对抽油杆体扶正,避免了钢体与钢体的硬磨;应用旋转井口通过地面人力转动改变油管与抽油杆的偏磨面;配合合理生产参数;各种配套技术的合理应用,使濮城油田躺井减少,避免了频繁作业,增加长寿井,管杆泵投入节约了19.3%。  相似文献   

低渗油藏采收率确定新方法     

黄小亮  ;唐海  ;吕栋梁  ;李仲  ;吕浙江  ;余贝贝 《海洋地质译丛》2008,(3):74-77

通过对油藏相渗曲线的归一化处理,利用达西定律理论,建立采油指数与含水率的关系;再通过油藏确定的单井经济极限采油量和油藏极限生产压差求出极限采油指数,从而得到极限含水率;最后以最终水驱体积波及系数与储层退汞效率计算出采收率。并以低渗透油藏为实例验证了该方法的正确与适用性,说明该方法对油田开发中确定低渗油藏采收率具有科学的指导意义。  相似文献   

海岸波浪多次破碎波能耗散模型   总被引：1，自引：0，他引：1  

闫圣  邹志利 《海洋学报》2020,42(9):30-37

在坡度很缓(接近或小于1∶100)的海岸,波浪在向海岸传播的过程中,可能经历多次破碎,而在两次波浪破碎之间将伴随着波浪恢复(波浪恢复到不破碎状态)。在现有海岸波高计算模型中,波浪破碎是通过波能耗散来模拟的,但所采用的波能耗散模型都不能自动考虑波浪出现多次破碎的过程,特别精确模拟这一过程中出现的波浪恢复。本文提出了解决这一问题的新的波能耗散模型,模型的建立是通过在Dally模型中重新建立稳定波能、饱和波高水深比和波能耗散系数,并引入了波浪恢复的判断条件实现的。该模型的波能耗散在波浪恢复区的值很小故能描述波浪恢复区的波浪运动。与实验结果的对比表明,新模型可以适合缓坡情况波浪多次破碎的波高模拟,而且对不同坡度的平坡和沙坝海岸(1∶100～1∶10)的破碎波模拟都可以给出与实验结果符合的结果,并且可以自动识别多次波浪破碎的存在和波浪恢复的发生。  相似文献   

Study on the negative bias temperature instability effect under dynamic stress     

马晓华  曹艳荣  郝跃 《海洋学报(英文版)》2010,29(11)

This paper studies negative bias temperature instability (NBTI) under alternant and alternating current (AC) stress. Under alternant stress, the degradation smaller than that of single negative stress is obtained. The smaller degradation is resulted from the recovery of positive stress. There are two reasons for the recovery. One is the passivation of H dangling bonds, and another is the detrapping of charges trapped in the oxide. Under different frequencies of AC stress, the parameters all show regular degradation, and also smaller than that of the direct current stress. The higher the frequency is, the smaller the degradation becomes. As the negative stress time is too small under higher frequency, the deeper defects are hard to be filled in. Therefore, the detrapping of oxide charges is easy to occur under positive bias and the degradation is smaller with higher frequency.  相似文献   

Reef status in the Rasfari region (North Malé Atoll,Maldives) five years before the mass mortality event of 1998     

Carla Morri  Stefano Aliani  Carlo Nike Bianchi 《Estuarine, Coastal and Shelf Science》2010

The Maldives was severely hit by massive coral bleaching and subsequent mortality in 1998. The results of reef monitoring in the following years have supported contrasting views about their recovery potential, partly because of the scarcity of information on the situation before 1998. Quantitative data on coral assemblages collected in 1993 in the Rasfari region (North Malé Atoll) may provide a base-line for the evaluation of the present status of the Maldivian reefs. Five years before the 1998 mortality, most coral communities appeared to be similar, in terms of both coral cover and growth-form composition, to those described in 1958 and 1964, notwithstanding increased human pressure and local events such as minor bleaching episodes in 1987 and crown-of-thorns starfish (COTS) attacks in 1989. Three lessons can be learnt from these results to help to understand the present situation, some ten years after the 1998 mass mortality. First, Maldivian reefs proved in the past to be capable of maintaining flourishing coral life despite various disturbances. Second, four years had been sufficient for complete reef recovery after a (minor) bleaching event. Third, recovery after both COTS attack and bleaching follows a predictable path suggesting that the presence of a three-dimensional community structure, which should reduce post settlement mortality of coral recruits, is essential for rapid coral recovery. As coral recruitment remains high and large tabular Acropora colonies are now reappearing, it is expected that Maldivian reefs should return to their original condition within the next few years.  相似文献   

Effects of different types of mechanical disturbances on a charophyte dominated macrophyte community     

Kaire Torn  Georg MartinJonne Kotta  Maarit Kupp 《Estuarine, Coastal and Shelf Science》2010

Charophytes are unique and endangered macroalgae. Mechanical stress is known to damage charophyte communities, however, virtually nothing is known how such disturbance affect seasonal succession and recovery of charophyte communities. We examined the response of a shallow water charophyte community to different types and timing of disturbances by conducting seasonal in situ field experiment in a brackish water ecosystem. The disturbances associated with mechanical removal of vegetation or sediment had the largest impact on the charophyte community. Disturbances that only partly damaged the plants had minor effects and communities were characterized by fast recovery. The timing of disturbance had significant effects on the charophyte community with stronger effects when disturbed at the early stage compared to mid-stage of seasonal succession.  相似文献