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1.
In unpolluted areas the log-normal distribution of individuals per species fits well data from many benthic communities. Using a simple plotting method, under slight pollution the data show a distinct break in the normally straight line log-normal plot and the plot covers more geometric classes than data from unpolluted areas. Under more severe pollution stress the data show a return to a log-normal distribution, but with a shallower slope, and span more geometric classes than data from less polluted areas. The above-mentioned patterns are consistent for spatial effects of pollution in Oslofjord and for temporal effects in data from a Scottish sea loch and also apply to other communities. An explanation of the reasons for such patterns is given and consideration given to the robustness of and application of the methods described.  相似文献   

2.
The paper presents a study of the effect of excessive amounts of organic matter (OM) on Arctic benthos. The source of nontoxic OM is from the mariculture of blue mussels in the White Sea (north-western area of Russia). The use of multivariate analysis procedures made it evident that in the Arctic conditions benthos is incapable of annual utilization of more than 1.5 kg dry OM m−2 from an external source. Mineralization of OM accumulated in sediments will deteriorate the oxygen regime. The critical concentration of OM in sediments is 9–10%. An excess over this threshold leads to the formation of oxygen-free zones at the bottom, and degradation of benthos community.  相似文献   

3.
Nazarova  L. B.  Semenov  V. F.  Sabirov  R. M.  Efimov  I. Yu. 《Water Resources》2004,31(3):316-322
Present-day quantitative and qualitative characteristics of the Cheboksary Reservoir have been investigated, and data on the biological diversity of benthic organisms have been compared to those of hydrobiological studies carried out in the region prior to the reservoir construction. The reservoir bottom communities include 75 species and forms of benthos. The reservoir water quality has been evaluated using different methods, including the determination of the degree of morphological structure abnormalities in chironomid larvae, regarded as sublethal indicators of bottom sediment pollution with toxic substances.  相似文献   

4.
Multidisciplinary studies were carried out in the Lower Don River in the low-water November of 2012. The studies showed relatively low concentrations of oil products (up to 2 MAC) and heavy metals (up to 1 MAC), which were likely due to the cessation of navigation in the river. However, copper concentration was found to be in excess of its MAC. The most polluted were found to be the port water areas of the cities of Volgodonsk, Ust’-Donetsk, and Semikarakorsk. The distribution of nutrients over streams is uneven: the Don water is poorer in nutrients than the waters of the Severskii Donets and the Manych are. Oxbows can serve as depots of organic matter, where it accumulates over longer periods than in the river. The residual manifestations of the summer–autumn blooming of blue-green algae, observed in shallows, the predominance of algae of divisions Cryptophyta and Bacillariophyta (typical representatives of winter planktonic algacenosis), and their low abundance suggest the transitional state of phytoplankton communities to autumn–winter season (pre-winter period). The species diversity and biomass of zooplankton were largest in the Don R. and lowest in the Severskii Donets R. The formation of zooplankton species composition shows the effect of the runoff from the Tsimlyanskoe Reservoir. An increase in the proportion of oligochaetes and invading species was recorded in the Don. The decrease in the diversity of benthos is attributed to natural factors, i.e., the decay of imago and thicket forms in autumn. The biomass of the soft (food) benthos is low because of the predominance of its small-size forms.  相似文献   

5.
Specific features of polychlorinated biphenyl (PCB) distributions in bottom sediments, benthos, and fish of the Sheksninskii Pool of the Rybinsk Reservoir are discussed. It is shown that 95% of the total PCB is accumulated in bottom sediments. Mapping of PCB-polluted bottom sediments with allowance for the sediment type and bed relief is proposed. The obtained data along with coefficients of accumulation in the bottom sediments–benthos–fish chain were used to evaluate the maximum concentration of PCB in bottom sediments at which the environmental risk of fish metabolism disturbance will be minimum. It is shown that once the PCB discharge into the water body is completely eliminated, their presence in the system will still be an ecological hazard for 25–30 years.  相似文献   

6.
Bottom sediment was analysed, via grab, trawl and underwater photography in 1991–1992 in the Barents, White, Kara, Norwegian and Greenland Seas, and the large scale features of macrobenthos distribution are described. The maps of alpha-diversity, biomass and trophic zone distribution on the investigated shelf are presented. Statistical assessment of the bottom community structure changes during the last 60–70 years for the Barents Sea area is presented. It is shown that on regional and transregional levels the researched communities are of natural undisturbed character and that the revealed changes may be both the result of natural processes or sampling errors. Local disturbances of benthos composition and structure, supposedly caused by man, are found to be rare not far from the Novaya Zemlya and Murman coasts.  相似文献   

7.
Changes in the log-normal distribution in general have been found to give promising results in the detection of pollution-induced changes in communities. Recently Preston has proposed a similar idea based on deviation from a special variant, the canonical log-normal, as an index of disturbance. Yet wide variation in the canonical log-normal occurs in data from unpolluted communities and thus the technique is not likely to be sensitive. Preston also proposed another method based on lack of fit to the log-normal. Under heavily polluted conditions Gray & Mirza have shown that a good fit to the log-normal nevertheless occurs. Lack of fit, therefore, cannot expect to be a reliable method for detecting pollution-induced changes.It is shown that the initial changes induced by pollutants are in skewness and progressive increases in the standard deviation of the log-normal plot follow increased pollution stress. Exact methods of fitting the log-normal and comparative data on standard deviations and skewness are recommended, therefore, for detecting pollution-induced changes.  相似文献   

8.
Ecosystem effects of fishing activities in the North Sea   总被引：2，自引：0，他引：2  
The North Sea harbours an intensive fishery which removes between 30 and 40% of the biomass of exploited fish species each year. In addition fishing causes mortality of non-target species of benthos, fish, seabirds and mammals. Heavy towed gears disturb the uppermost layer of the seabed and cause mortality of benthos, while gillnets accidentally entangle seabirds and marine mammals. Unwanted catch is usually returned to the sea where it is eaten by scavenging species, such as seabirds. Since the North Sea ecosystem is highly complex and exhibits a high natural variability, it has proved difficult to isolate the longer term consequences of these impacts. Until more is known about the environmental impact of fisheries management, action (or no action) will have to be agreed upon in the light of considerable scientific uncertainty.  相似文献   

9.
The quantitative characteristics and biomass distribution of plankton and benthos in the Southern Barents Sea are estimated by using geographic information system technologies. A database from a computer atlas of the Barents Sea is used to calculate the summary, total, and mean biomass. The quantitative parameters of plankton are estimated via creating a synthetic digital map, reflecting the joint distribution of phytoplankton, meso-and macrozooplankton in a raster format. The total and mean biomass of benthos is calculated via digitizing published cartographic data with subsequent processing of the digital cartogram. The obtained results are compared with estimates made earlier by other researchers. Generalizing characteristics, such as biomass production, P/B-coefficient, and ecological efficiency are calculated.  相似文献   

10.
The determination of the probability distribution of recurrence times is the most important problem in the calculation of long-term conditional probabilities for the recurrence of large and great earthquakes.The principle of maximum entropy in conjunction with a goodness-of-fit test (chi-square or Kolmogorov-Smirnov test) may be employed to obtain estimates of these densities using recurrence data for some seismic regions.Four different distributions are characterized by the property of maximum entropy, as possible laws for recurrence times of the largest earthquakes: uniform, exponential, Gaussian and log-normal. To discriminate among these different probability distributions we use the probability theory and the chi-square test to check the goodness-of-fit to the distribution of recurrence time of shocks of magnitude 6.5 and largest occurred in the west-northwestern zone of the Hellenic arc from 1791 to 1983.It is found that the recurrence times data for the west-northwestern zone of the Hellenic arc cannot be represented by the uniform and the Gaussian probability densities. The recurrence times data for the west-northwestern zone of the Hellenic arc can be described accurately by the exponential and log-normal probability densities, which were predicted from the principle of maximum entropy. In other words, the principle of maximum entropy does not necessarily lead to a unique solution. In turn, the mathematical properties of these distributions could be used to derive different physical properties of the earthquake process in the west-northwestern zone of the Hellenic arc.  相似文献   

11.
Mainly from the trends of fish yield four stages of fish succession in European lakes under cultural eutrophication are described. Trends of transparency, phosphorus, weed, benthos, and plankton are included. Supplementary interrelated effects of eutrophication on fish biology (growth, fat content, condition, distribution, reproduction, parasites, fish kills, introgression, feeding) have been collected from literature. The effects, mainly observed on planktivores, are not specific for species or localities.  相似文献   

12.
There are different sulfur forms in the black shales from the Early Cambrian of the Yangtze platform. With its emphasis on pyrite and organosulfur, this paper discusses their distribution and formation. The research shows that sulfur phases take regular variations laterally as well as vertically in the research areas. In western researched profile with high terrigenous supply at the time it formed, there exists a larger amount of pyrite and less organosulfur, and pyrite amount declines while organosulfur content increases upwards along the profile. This black shale profile is characterized by relatively light sulfur isotope composition with evolution trend of becoming heavier both for pyrite and organosulfur from bottom to top along the profile. Opposite situation occurs in eastern profiles which were located farther away from terrigenous land. Here pyrite amount obviously decreases and organic matter has combined more sulfur, although these two kinds of sulfur species take similar trend in content variation along profiles to that for western profile. At the same time more34S is accumulated in sulfur species of black shale samples from eastern profile, and sulfur isotope composition gradually turns lighter from bottom to top. In combination with other information of iron, organic carbon contents and petrographic features, it can be established that sea-level change, supply of terrigenous matters, tectonic background and natures of paleoceanic chemistry have exerted great influence on the distribution of sulfur species in these black shales.  相似文献   

13.
Self-similar cataclasis in the formation of fault gouge   总被引：1，自引：0，他引：1  
Particle-size distributions have been determined for gouge formed by the fresh fracture of granodiorite from the Sierra Nevada batholith, for Pelona schist from the San Andreas fault zone in southern California, and for Berea sandstone from Berea, Ohio, under a variety of triaxial stress states. The finer fractions of the gouge derived from granodiorite and schist are consistent with either a self-similar or a logarithmic normal distribution, whereas the gouge from sandstone is not. Sandstone gouges are texturally similar to the disaggregated protolith, with comminution limited to the polycrystalline fragments and dominantly calcite cement. All three rock types produced significantly less gouge at higher confining pressures, but only the granodiorite showed a significant reduction in particle size with increased confining pressure. Comparison with natural gouges showed that gouges in crystalline rocks from the San Andreas fault zone also tend to be described by either a self-similar or log-normal particle distribution, with a significant reduction in particle size with increased confining pressure (depth). Natural gouges formed in porous sandstone do not follow either a self-similar or a log-normal distribution. Rather, these are represented by mixed log-normal distributions. These textural characteristics are interpreted in terms of the suppression of axial microfracturing by confining pressure and the accommodation of finite strain by scale-independent comminution.  相似文献   

14.
Macrobenthos recovery after hypoxia-induced mass mortality was assessed in an estuarine tidal mudflat during 3 years. During the first 2 years, a Pearson-Rosenberg type of community recovery took place along with the improving bottom water oxygen conditions. After 3 months, spionid polychaetes became superabundant (i.e. opportunistic peak), followed rapidly by a steep decline (i.e. ecotone point). Subsequently, a moderate increase in species richness and a steep increase in biomass, related to the growth of long-lived species occurred (i.e. transition region). Afterwards, however, the recovering community diverged again from the ambient, undisturbed, sediments due to enhanced recruitment success of long-lived species presumably resulting from the lowered interference from bioturbation during early recovery stages in the disturbed plots. Hence, despite early community recovery may be more or less deterministic, lagged divergent community reassembling may occur at the longer-term, thereby contributing to benthos patchiness in areas which are frequently subjected to disturbances.  相似文献   

15.
Seabed impacted by settling solids from a turbidity plume can be surveyed by submersible using a ‘bounce’ technique to determine depth of the turbidity front, and hence depth above which benthos observations are practical. The protocol adopted was that after frontal depth was determined by a preliminary dive, the site for the benthic survey was selected. On arrival on the seabed a reconnaisance was made for the observers to agree on the identification of visible benthos. Then 100 × 1 m2 transects were surveyed using a 1 m2 quadrat attached to the submersible in view of the port-side observer. At the site investigated, two shallow water stations (depths 13–15 m, and 16–18 m) showing light deposits of mine tailings were seen to support associations of large epifauna and infauna. The first station had an almost single-species stand of the burrowing anenome Pachycerianthus fimbriatus at approximately 100 · 100 m?2, and the second a diverse species association with several starfish and other species at 1–2 · 100 m?2. Burrow holes (up to 3–5 cm diameter) of various sizes indicated that large infaunal species were present. At a deeper station (36–27 m) with heavy tailings and almost no burrow holes, a single Dungeness crab, Cancer magister, and an unidentified shrimp were seen in the 100 m2 transect. Each dive site was inshore (shallower) from a routinely monitored benthos station shown repeatedly to support a population of small infauna in the tailings. Burrow holes have the potential for determining the identity and abundance of large infaunal species present if an identification system can be developed. The technique of epifaunal and burrow hole surveys (by submersible and scuba diver), combined with infaunal and sediment core surveys and contemporary theory on infaunal succession, provides the potential for a procedure to map the distribution in shallow water of tailings impact and benthic recovery (succession).  相似文献   

16.
Benthic macroalgal communities of the upper rocky sublittoral were studied in 1995-1996 in the vicinity of the Marseille (Mediterranean, France) sewage outfall, 8 years after the setting up of a wastewater treatment plant and compared to a previous study carried out in 1972-1974. The number of taxa has increased, a clear stational and seasonal gradient of differentiation of the vegetation appeared, and a turf of ephemeral species is taking place of Corallina elongata at sites close to the outfall. These changes may be due to a decrease in pollutant load, the discharge of ferric chlorates used in the treatment process. However, the overall change is much less conspicuous than that described for deeper soft bottom communities, in particular the Cystoseira amantacea community is not still restored. Biological traits of this species (short distance dispersal) and the nature of most pollutants removed from the effluent (solids and organic matter) may explain this phenomenon.  相似文献   

17.
Mollusc death assemblages were recovered in 98 subtidal sampling stations on the seafloor of the shallow Pertuis Charentais Sea (Atlantic coast of France). Taxonomic composition and spatial distribution of death assemblages were investigated, as well as their response to sediment grain size (field data), bottom shear stress (coupled tide and wave hydrodynamic modelling), and sediment budget (bathymetric difference map). Results showed that molluscs are likely to be reliable paleoenvironmental indicators since death assemblages were able to acquire ecological changes within years (decadal-scale taphonomic inertia), and live–dead agreement inferred from existing data on living benthic communities was high, except close to river mouths and intertidal mudflats that provide terrestrial and intertidal species to subtidal death assemblages, respectively. Taxonomic composition of these within-habitat death assemblages strongly depended on sediment grain size and bottom shear stress, similarly to living subtidal communities. Post-mortem dispersal of shells, owing to relatively low bottom shear stress in the area, was only of a few 10s to 100s of meters, which shows that death assemblages preserved environmental gradients even at a fine spatial scale. Sediment budget had also a significant influence on death assemblages. Thick-shelled epifaunal species were correlated with erosion areas on one side, and thin-shelled infaunal species with deposition on the other, showing that mollusc fossil assemblages could be used as indicators of paleo-sedimentation rate. This new proxy was successfully tested on a previously published Holocene mollusc fossil record from the same area. It was possible to refine the paleoenvironmental interpretation already proposed, in accordance with existing stratigraphic and sedimentological data.  相似文献   

18.
Residues of DDE, DDD, DDT and PCB were measured in different tissues of fourteen sperm whales caught in the waters off Spain's north-western coasts. Unlike what seems common in other marine mammal species, females appear to be more contaminated by organochlorine compounds than males. Pollutant levels in this species were found to be intermediate to other cetaceans, probably due to their feeding habits mainly based on squid and bottom fish. Concentrations of total DDT and PCB in blubber were similar to most of those determined in sperm whales from other areas of the northern hemisphere.  相似文献   

19.
The present study examines the benthos within western inner Swansea Bay (Wales, UK), for the period before, during and immediately after the cessation of a major, sewage discharge from Mumbles Head. There have been significant improvements in seawater quality and changes in the species composition of the benthic communities following the cessation of the sewage discharge. There has been an increase in the diversity of deposit feeders, especially the amphipods, and a decrease in the diversity of the filter feeders, especially the polychaetes. Changes are not attributable either to sediment organic matter content or to gross changes in sediment type, but are related to the significant reduction in suspended particulate organic material and sewage contaminants discharged to the Bay. A recovery model has been proposed to describe how soft sediment benthic communities in a shallow, sublittoral, high tidal energy environment respond to the abrupt cessation of a major sewage discharge.  相似文献   

20.
Abstract

For a long time now, the hydrologist has been faced with the problem of finding which of the many possible probability distribution functions can be used most effectively in flood frequency analyses. This problem has been mainly due to the insufficiency of the conventional goodness-of-fit procedures when used with the typically skewed flood probability distributions. In this study, the Akaike Information Criterion (AIC) goodness-of-fit test is used to identify more objectively the optimum model for flood frequency analysis in Kenya from a class of competing models. The class is comprised of (a) seven three-parameter density functions, namely, log-normal, Pearson, log-Pearson, Fisher-Tippet, log-Fisher-Tippet, Walter Boughton and log-Walter Boughton; and (b) two five-parameter density functions, namely, Wakeby and log-Wakeby. The AIC is also used in this study as a method of testing for the existence of outlier peak-flow values in the peak annual data used. A modified version of the chi-square goodness-of-fit test is also used, but only for the sake of comparison with the AIC.  相似文献   

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