摘要:

AbstractMarine mining of manganese nodules will affect the deep sea benthos in a harmful and longterm way. The near complete removal of manganese nodules will result in a change of the megabenthic community from one that is rich in both diversity and density to a soft bottom community with greatly reduced diversity.Pre‐pilot mining tests and pilot mining operations, which have to demonstrate the feasibility of deep‐sea mining, should be accompanied by environmental impact studies before commercial mining begins.The photographic assessment of megabenthic communities represents one cost‐effective possibility of monitoring large‐scale impacts on the deep sea floor. A method based on the analysis of video and photomaterial was used to obtain basic data on community structure and density of the abyssal megabenthos of undisturbed manganese nodule sites in the North (Clarion‐Clipperton Fracture Zone) and South (Peru Basin) Pacific Ocean.A comparison of the results with data from the literature demonstrates that the different methods used result in different density values.Total density varied between less than 300 to more than 1600 individuals/10000 m2.There is a clear need for standardization of methods. A system which combines video and photographic capabilities is useful. It will give the best results when the distance of the camera to the sea floor is between 2 and 3 m, and the area covered by one photograph is within

ISSN:1052-7613    

DOI:10.1002/aqc.3270040302

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractLight spatfalls of the Pacific oyster,Crassostrea gigas, have occurred in the estuaries of the Rivers Exe, Teign and Dart (Devon) and in the Menai Strait (Gwynedd), near to sites of commercial cultivation of this species.Comparisons of the sizes of the naturally settled oysters with hatchery oysters suggests that the spat from the River Teign and Menai Strait settled in 1989 and 1990. The springs and summers of these years were exceptionally warm with mean monthly air temperatures 0.8°‐1.3°C above the 1951–1980 average for the period April to August.Although sitings of Pacific oyster spat were made in Loch Sween and Emsworth Harbour over 20 years ago, there is no evidence that self‐sustaining populations have developed.The spatfalls which occurred in some coastal waters of Devon and Gwynedd in 1989 and 1990 are unlikely to sustain natural fisheries and are likely to die out as did the Portuguese oysters which occasionally settled in the River Blackwater

ISSN:1052-7613    

DOI:10.1002/aqc.3270040303

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe classification of river corridors may simply aim to describe what is there in a concise form or it may form a tool to support the assessment of conservation or enhancement potential and management decision‐making.An analysis of 140 international publications on river corridor classification illustrates temporal trends towards (i) multidisciplinary bases for classification related to (ii) increasingly small spatial units and spatially hierarchical structures, with (iii) the majority of the schemes being developed in North America and most of the remainder generated within Europe.An operational classification scheme that is robust and widely applicable will be based on a wide range of information types with a hierarchical structure incorporating different types and resolutions of information suitable to support classifications for different applications.In developing an operational scheme, spatial units for data handling must be defined which present a compromise between the natural boundaries representative of the character of the river corridor, and the environmentally arbitrary boundaries which often define the spatial units against which environmental data sets have been collected.A variety of data sources may support classification, including routine field surveys and laboratory determinations, thematic maps and remotely sensed information. Different sources present different problems of spatial resolution, generalization, age and changing data standards.Problems arise when data from different sources are integrated to derive a classification. GIS provides a flexible technology for such integration but the results may be misleading if GIS functions are not used intelligently. Data handling should (i) maintain separation between raw data and their derivatives, (ii) apply spatial aggregation or smoothing of data to a consistent spatial resolution prior to integration, and (iii) the spatial resolution selected should be appropriate for the hierarchical level to which it applie

ISSN:1052-7613    

DOI:10.1002/aqc.3270040304

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper summarizes research on the uses of marine reserves for fisheries management. Examples emphasize temperate marine reserves.Marine reserves commonly support higher densities and larger sizes of heavily fished species than are found outside reserves.‘Spillover’ of individuals across reserve borders is likely to augment local catches. There are good reasons to expect such spillover, and there is limited direct evidence for it. However, the magnitude of any resulting increase in local catches will be difficult to predict.‘Larval export’ from reserves has potential to augment recruitment over large regions, but its success will depend upon many factors that are difficult to predict. No studies have clearly tested the effects of larval export.To design more effective marine reserves, studies are needed of the movement patterns and habitat requirements of all life stages (larval, settlement, juvenile, adult, feeding, and breeding) of targeted species.To determine clearly the effects of marine reserves on fisheries requires replicated before/after

ISSN:1052-7613    

DOI:10.1002/aqc.3270040305

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractVerlorenvlei, a dryland aquatic ecosystem in South Africa, has been identified as having enormous conservation importance. Although the system has Ramsar status and is widely regarded as being in ‘pristine' condition, neither statutory control nor any form of management is currently in existence.Based on the analysis of fossil pollen derived from the sediments of Verlorenvlei, a sequence of rapid changes within the riparian and aquatic vegetation is identified. Synchronous changes in the rate of sedimentation suggest a threefold increase in annual sediment deposition since the mid‐18th century—the onset of colonial settlement.The pollen spectra prior to the arrival of colonial settlers suggest that abundant Poaceae (grasses) and rooted aquatic plants dominated the vegetation of the site. Radical changes in the pollen record become evident after the time of European colonization. Aquatic vegetation, including Gentianaceae (water lilies) and Potamogetonaceae, show a marked decrease while riparian vegetation, particularly reed elements such as Cyperaceae, Typhaceae and Juncaceae, are seen to increase progressively. Terrestrial pollen indicators reveal an expansion in the vegetation of classic disturbance indicators such as Asteraceae, Oxalidaceae and Scrophulariaceae.As the wetland has already endured rapid ecological adjustments in the face of colonial (and more recent) occupation of the broader landscape, it cannot be regarded as being in a ‘pristine’ state. Indeed, Verlorenvlei is interpreted as having reached a state of ‘transitional’ ecological equilibrium in which it continues to endure a number of rapid ecological changes; nonetheless, it is still worthy of conservation and management, not least because of its role as a strategic wetland in a dryland environment.Failing the timely implementation of remedial action in the form of an integrated conservation and management plan, Verlorenvlei appears destined to become irreversibly altered.Dryland aquatic ecosystems are vital aquatic resources in so called ‘Third World’ regions of the world yet, paradoxically, scientific research on, and the conservation of, these environments in the Southern Hemisphere are rare by comparison to wetland environments in the northern temperate zones. Although many dryland aquatic systems may already be altered, most are worthy of urgent management and conservation action, bearing in mind the fundamental question: ‘What is it that we wish to conserve?’.A number of recommendations for the management of dryland aquatic ecosystems such as Ve

ISSN:1052-7613    

DOI:10.1002/aqc.3270040306

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper demonstrates the possibility of quantifying sub‐catchment nutrient budgets from routinely monitored hydrological and hydrochemical data. The relative importance of a number of potential anthropogenic nutrient sources was quantified for a small catchment in Scotland. Within the catchment there are two Sites of Special Scientific Interest, including two lochs and a floodplain mire. The study was undertaken to provide information for prescribing strategies to safeguard the conservation interests of these aquatic systems.The principal source of nitrate was found to be groundwater. Phosphate and ammonium loadings were greatest in surface run‐off. The evidence indicates that the greatest contributor towards these nutrient sources is agriculture. Even when conservative estimates of losses were applied, current fertilizer and animal inputs could account for present day nutrient loadings. In addition, changes in the area under arable farming and under individual crops during the past 30 years are consistent with trends in nitrate and phosphate loads.Nutrient inputs from sewage works overflows and septic tanks within the catchment were estimated to be small. Leachate from a landfill site within the catchment was also not considered to be a major source of nutrients, but a more intensive water quality monitoring programme would be needed to confirm the absence of leachate plumes.The only long‐term solution to reducing nutrient loadings to the aquatic systems is a reduction in agricultural activities within the catchment and avoidance of fertilizer and slurry applications near water sources. Diversion of drainage ditch waters supplying the floodplain mire is also a possibility but the hydrological consequences of such an action could induce more severe degradation than that due to nutrient enric

ISSN:1052-7613    

DOI:10.1002/aqc.3270040307

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270040301

出版商:John Wiley&Sons, Ltd    

年代:1994

数据来源: WILEY