排序方式： 共有117条查询结果，搜索用时 203 毫秒
81.
Duke NC Bell AM Pederson DK Roelfsema CM Bengtson Nash S 《Marine pollution bulletin》2005,51(1-4):308-324
Herbicides, particularly diuron, were correlated with severe and widespread dieback of the dominant mangrove, Avicennia marina (Forsk.) Vierh. var. eucalyptifolia (Val.) N.C. Duke (Avicenniaceae), its reduced canopy condition, and declines in seedling health within three neighbouring estuaries in the Mackay region of NE Australia. This unusual species-specific dieback, first observed in the early 1990s, had gotten notably worse by 2002 to affect >30 km(2) of mangroves in at least five adjacent estuaries in the region. Over the past century, agricultural production has responded well to the demands of increasing population with improvements in farm efficiency assisted by significant increases in the use of agricultural chemicals. However, with regular and episodic river flow events, these chemicals have sometimes found their way into estuarine and nearshore water and sediments where their effects on marine habitats have been largely unquantified. Investigations over the last three years in the Mackay region provide compelling evidence of diuron, and possibly other agricultural herbicides, as the most likely cause of the severe and widespread mangrove dieback. The likely consequences of such dieback included declines in coastal water quality with increased turbidity, nutrients and sediment deposition, as well as further dispersal of the toxic chemicals. The implications of such findings are immense since they describe not only the serious deterioration of protected and beneficial mangrove habitat but also the potential for significant direct and indirect effects on other highly-valued estuarine and marine habitats in the region, including seagrass beds and coral reefs of the Great Barrier Reef lagoon. This article reviews all key findings and observations to date and describes the essential correlative and causative evidence. 相似文献
83.
对流岩浆混合是热液和组分作用于熔融体密度引起的。我们通过二维数字模拟研究了组分浮力在对流岩浆混合中的作用。在我们的模拟中,观察到了两种自组织作用现象:(1)与流动逆转相伴随的局部暂时未混合事件;(2)在对流单元中心延续很久的分异作用(眼球状构造)。分异作用的级序统计量、级序比率与强度、对于使混合与自组织现象定量化,是组分场的有益抽象。级序比率和强度的轨迹揭示了吸引子的行为,并提供了控制混合和自组织作用演化的简洁方式。组分浮力与热液浮力之比由参数Rr给出:当Rr=0时,意味着被动混合;当Rr>0时,意味着动力混合。既形成于被动混合也形成于动力混合中的眼球状构造趋向于使混合率减小。流动逆转和仅存在于动力混合中的未混合事件进一步减慢了混合。然而,因为一个强而持久的眼球状构造形成于被动混合中,被动混合比以小的Rr值混合更慢。在高的Rr(Rr>1)情况下,由于始态的重力稳定性,混合一般被组分浮力所妨碍。 相似文献
84.
85.
We coordinated a collaborative research project to investigate environmental conditions in Vancouver Harbour, British Columbia, Canada, between 23 May and 7 June 1999. This special volume of Marine Environmental Research presents a collection of papers giving results of these studies. The project was part of a practical workshop sponsored by the Marine Environmental Quality (MEQ) committee of the North Pacific Marine Science Organization (PICES). Twenty-four scientists from PICES countries (USA, Canada, Russia, Japan, Korea, and China) participated. A wide variety of data was collected, including community structure of benthic invertebrates and fish, evaluation of fish health using biological markers and exposure data, evaluation of contaminant exposure in inter-tidal invertebrates, imposex in gastropods, and information about natural toxins produced by algae. The workshop provided an opportunity for PICES participants to gain an improved appreciation of the approaches and techniques used by other member countries to assess the effects of marine pollution. The purpose of this introductory paper is to briefly describe the project, provide background information on how it was organized, and give an overview of our knowledge about the harbour's environment. 相似文献
86.
Bolton JL Stehr CM Boyd DT Burrows DG Tkalin AV Lishavskaya TS 《Marine environmental research》2004,57(1-2):19-36
As part of a multinational workshop on marine environmental quality, sediments were collected from seven sites in Vancouver Harbour and analyzed for polynuclear aromatic hydrocarbons (PAHs) and organochlorines (OCs), and for trace metals. English sole were collected from five sites, and muscle was analyzed for trace metals and liver for OCs. As expected, sediment PAH and OC concentrations and tissue OC concentrations were higher at sites east of the First Narrows, compared to the outer harbor and reference sites. Sediment PAH concentrations east of the First Narrows were similar to concentrations at moderately contaminated sites in Puget Sound, south of Vancouver Harbour. In contrast, concentrations of OCs in sediments and tissue were low to moderate, even at relatively contaminated sites within Vancouver Harbour. Although several trace metals in sediments were higher than in contaminated sediments from Puget Sound, trace metals measured in fish muscle were lower. 相似文献
87.
Mascaró O Bennett S Marbà N Nikolić V Romero J Duarte CM Alcoverro T 《Marine pollution bulletin》2012,64(5):926-931
Uncertainty analyses allow the identification and quantification of the factors that contribute to the potential misclassification of the ecological status of water bodies, helping to improve the sampling design used in monitoring. Here we used a Posidonia oceanica multivariate index (POMI) bio-monitoring dataset covering a total of 81 sites distributed throughout 28 water bodies from the coast of Catalonia, Balearic Islands and Croatia to determine the levels of uncertainty associated with each region and how they change according to the quality status of water bodies. Overall, variability among sites (meadows) within water bodies was the factor that generated the greatest risk of misclassification among the three regions, within which the Balearic Islands had the lowest uncertainty, followed by Croatia and Catalonia. When water bodies classified in good/high quality were separated from those in moderate/poor status classes, we found that the latter displayed higher levels of uncertainty than the former. 相似文献
88.
Díaz-Almela E Marbà N Alvarez E Santiago R Holmer M Grau A Mirto S Danovaro R Petrou A Argyrou M Karakassis I Duarte CM 《Marine pollution bulletin》2008,56(7):1332-1342
Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities. 相似文献
89.
90.
Metal accumulation by Juncus maritimus and the effect this plant might have on the physico-chemical composition of sediments, from Douro river estuary (NW Portugal), were investigated through one year of plant's life. The contents of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined (by atomic absorption spectrophotometry) in sediments, rhizosediments (those among plant roots and rhizomes) and different tissues of J. maritimus. Two estuarine sites with different characteristics were studied, one a sandy sediment with relatively low organic matter content, the other a muddy site. The role of the plant seemed to be markedly dependent on the sediment composition. At the sandy site, significant variations throughout the year (a decrease from winter to summer and an increase in autumn) either in rhizosediment and sediment or in J. maritimus roots were only observed in Cd and Cu levels. These variations were the same in both compartments, probably caused by tidal water movements and the activity of the plant. At the muddy site, variations throughout the year were observed for all studied elements but Pb. Changes in the Cd and Zn contents of roots were opposite to those in the rhizosediment (uptake of Cd and Zn by J. maritimus roots in summer may have caused a decrease in rhizosediment levels). Fe and Mn showed similar patterns of variation in both roots and rhizosediment (contents significantly increasing in summer). Higher contents of Fe and Mn in roots in summer could be related to changes in mass, higher availability of the elements, or accumulation at the surface of the root in (hydr)oxides forms. For the remaining elements no significant correlations between rhizosediment and roots variations were observed, indicating that their uptake and release by roots were not based on single exchanges with the sediment. J. maritimus showed capacity to accumulate Cu, Zn and particularly Cd, thus appearing to be useful for the phytostabilization of these metals. 相似文献