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941.
Sarah B. Gewurtz Nilima Gandhi Guttorm N. Christensen Anita Evenset Dennis Gregor Miriam L. Diamond 《Environmental science and pollution research international》2009,16(2):176-190
Background, aim, and scope
Lake Ellasjøen, located in the Norwegian high arctic, contains the highest concentrations of polychlorinated biphenyls (PCBs) ever recorded in fish and sediment from high arctic lakes, and concentrations are more than 10 times greater than in nearby Lake Øyangen. These elevated concentrations in Ellasjøen have been previously attributed, in part, to contaminant loadings from seabirds that use Ellasjøen, but not Øyangen, as a resting area. However, other factors, such as food web structure, organism growth rate, weight, lipid content, lake morphology, and nutrient inputs from the seabird guano, also differ between the two systems. The aim of this study is to evaluate the relative influence of these factors as explanatory variables for the higher PCB fish concentrations in Ellasjøen compared with Øyangen, using both a food web model and empirical data.Methods
The model is based on previously developed models but parameterized for Lakes Ellasjøen and Øyangen using measured data wherever possible. The model was applied to five representative PCB congeners (PCB 105, 118, 138, 153, and 180) using measured sediment and water concentrations as input data and evaluated with previously collected food web data.Results
Modeled concentrations are within a factor of two of measured concentrations in 60% and 40% of the cases in Lakes Ellasjøen and Øyangen, respectively, and within a factor of 10 in 100% of the cases in both lakes. In many cases, this is comparable to the variability associated with the data as well as the efficacy of the predictions of other food web model applications.Discussion
We next used the model to quantify the relative importance of five major differences between Ellasjøen and Øyangen by replacing variables representing each of these factors in the Ellasjøen model with those from Øyangen, in separate simulations. The model predicts that the elevated PCB concentrations in Ellasjøen water and sediment account for 49%–58% of differences in modeled fish PCB concentrations between lakes. These elevated sediment and, to a lesser extent, water concentrations in Ellasjøen are due to PCB loadings from seabird guano. However, sediment–water fugacity ratios of PCBs are consistently greater in Ellasjøen compared with Øyangen, which suggests that internal lake processes also contribute to differences in sediment and water concentrations. We hypothesize that the nutrients associated with guano influence sediment–water fugacity ratios of PCBs by increasing the stock of pelagic algae. As both these algae and the guano settle, their organic carbon content is degraded faster than PCBs, which causes an extra magnification step in Ellasjøen before these detrital particles are consumed by benthic organisms, which are in turn consumed by fish. The model predicts that the remaining ~50% of the differences in PCB concentrations observed between the fish of these lakes are due to other subtle differences in their food web structures.Conclusions
In conclusion, based on the results of a food web model, we found that the most dominant factors influencing the higher PCB fish concentrations in Lake Ellasjøen compared with Øyangen are the higher sediment and water concentrations in Ellasjøen, caused by seabird guano. Together, sediment and water are predicted to account for 49%–58% of differences in fish concentrations between lakes. Although seabird guano provides a source of nutrients to the lake, in addition to contaminants, empirical data and indirect model results suggest that nutrients are not leading to decreased bioaccumulation, in contrast to what has been observed in temperate, pelagic food webs.Recommendations and perspectives
The results of this study emphasize the importance of considering even small differences in food web structure when comparing bioaccumulation in two lakes; although the food web structures of Ellasjøen and Øyangen differ only slightly, the model predicts that these differences account for most of the remaining ~50% of the differences in PCB fish concentrations between the two lakes. This study further demonstrates the utility of food web models as we were able to predict and tease apart the influence of various factors responsible for the elevated concentrations in the fish from Lake Ellasjøen, which would have been difficult using the field data alone. 相似文献942.
Rainfall trends in twentieth century over Kerala,India 总被引:1,自引:0,他引:1
K.N. Krishnakumar G.S.L.H.V. Prasada Rao C.S. Gopakumar 《Atmospheric environment (Oxford, England : 1994)》2009,43(11):1940-1944
Attempts were made to study temporal variation in monthly, seasonal and annual rainfall over Kerala, India, during the period from 1871 to 2005. Longterm changes in rainfall determined by Man-Kendall rank statistics and linear trend. The analysis revealed significant decrease in southwest monsoon rainfall while increase in post-monsoon season over the State of Kerala which is popularly known as the “Gateway of summer monsoon”. Rainfall during winter and summer seasons showed insignificant increasing trend. Rainfall during June and July showed significant decreasing trend while increasing trend in January, February and April. Hydel power generation and water availability during summer months are the concern in the State due to rainfall decline in June and July, which are the rainiest months. At the same time, majority of plantation crops are likely to benefit due to increase in rainfall during the post-monsoon season if they are stable and prolonged. 相似文献
943.
Chromosomal and nuclear characteristics of deep-sea hydrothermal-vent organisms: correlates of increased growth rate 总被引:2,自引:0,他引:2
A range of tissue and cell types from adult and juvenile stages of vent- and non-vent-dwelling deep-sea and shallow-water organisms were compared for signs of cell division, in preparation for a cytogenetic study of the different groups. Virtually all the Mid-Atlantic Ridge (MAR) vent species (bresiliid shrimp, bathymodiolid mussel, branchipolynoid polychaete, and a range of small gastropods) showed an abundance of metaphase chromosome spreads, indicating a generally high intrinsic rate of cell division, irrespective of their phylogenetic group. In comparison, similar tissues and life-history stages (i.e. gonad, developing eggs and gill) from two deep-sea bathypelagic crustaceans, Hymenodora and Gnathophausia, failed to yield any convincing evidence of cell division. This indicated that rates of growth and reproduction in the rest of the deep sea are extremely low. While much has been written about the contrasting growth rates of vent versus non-vent organisms, this is the first direct evidence of differences in cell-division rate between vent and non-vent species, which undoubtedly reflects contrasting conditions relating to food availability and temporal stability in these two deep-sea environments. The cells of shallow-water marine invertebrates (Mytilus, Nucella, Littorina, Pomatoceros and Crangon), based on the results of previous cytogenetic investigations, occupy an intermediate position with respect to their cell-division kinetics. When chromosome numbers, DNA content and nuclear diameters were compared between vent and non-vent species, this showed that no change had occurred in these characters since the time of vent colonisation. Representative chromosome spreads from hydrothermal-vent organisms are shown here for the first time. 相似文献
944.
945.
946.
X. Qu V.A. Vavilin L. Mazéas M. Lemunier C. Duquennoi P.-J. He T. Bouchez 《Waste management (New York, N.Y.)》2009,29(6):1828-1837
Utilizing stable carbon isotope data to account for aceticlastic and non-aceticlastic pathways of methane generation, a model was created to describe laboratory batch anaerobic decomposition of cellulosic materials (office paper and cardboard). The total organic and inorganic carbon concentrations, methane production volume, and methane and CO2 partial pressure values were used for the model calibration and validation. According to the fluorescent in situ hybridization observations, three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H2/H2CO3 as well as acetate-oxidizing syntrophs, were considered. It was shown that temporary inhibition of aceticlastic methanogens by non-ionized volatile fatty acids or acidic pH was responsible for two-step methane production from office paper at 35 °C where during the first and second steps methane was generated mostly from H2/H2CO3 and acetate, respectively. Water saturated and unsaturated cases were tested. According to the model, at the intermediate moisture (150%), much lower methane production occurred because of full-time inhibition of aceticlastic methanogens. At the lowest moisture, methane production was very low because most likely hydrolysis was seriously inhibited. Simulations showed that during cardboard and office paper biodegradation at 55 °C, non-aceticlastic syntrophic oxidation by acetate-oxidizing syntrophs and hydrogenotrophic methanogens were the dominant methanogenic pathways. 相似文献
947.
E. Hernandez Plaza M. Kozak L. Navarrete J.L. Gonzalez-Andujar 《Agriculture, ecosystems & environment》2011,140(1-2):102-105
This study investigated whether the choice of a tillage system (no-tillage, minimum tillage or traditional tillage) affected weed diversity in a 23 years cereal–leguminous rotation system in Spain. Weed diversity was assessed using common diversity indices: species richness, Shannon's index and Pieloús evenness. Linear mixed-effects models were employed to compare the tillage systems. It was found that after 23 years no large differences between tillage systems have arisen related to weed diversity. Only minimum tillage appeared to support, on average, more species than the two other tillage systems. Richness, Shannon diversity index and evenness varied largely through the years in all tillage systems but this variation was not related to type of crop sown (cereal or leguminous). Our results highlight that conservation tillage practices did not represent any concern for weed diversity conservation in cereal–leguminous rotations in the conditions of central Spain. 相似文献
948.
Assessing ecological risk on a regional scale 总被引:17,自引:0,他引:17
Carolyn T. Hunsaker Robin L. Graham Glenn W. Suter II Robert V. O'Neill Lawrence W. Barnthouse Robert H. Gardner 《Environmental management》1990,14(3):325-332
Society needs a quantitative and systematic way to estimate and compare the impacts of environmental problems that affect
large geographic areas. This paper presents an approach for regional risk assessment that combines regional assessment methods
and landscape ecology theory with an existing framework for ecological risk assessment. Risk assessment evaluates the effects
of an environmental change on a valued natural resource and interprets the significance of those effects in light of the uncertainties
identified in each component of the assessment process. Unique and important issues for regional risk assessment are emphasized;
these include the definition of the disturbance scenario, the assessment boundary definition, and the spatial heterogeneity
of the landscape.
Although the research described in this article has been funded wholly or in part by the United States Environmental Protection
Agency (EPA) through Interagency Agreement Number DW89932112-01-2 to the U.S. Department of Energy, it has not been subjected
to EPA review and therefore does not necessarily reflect the views of EPA and no official endorsement should be inferred. 相似文献
949.
D. L. DeAngelis P. J. Mulholland J. W. Elwood A. V. Palumbo A. D. Steinman 《Environmental management》1990,14(5):685-697
In systems where production is limited by the availability of a nutrient, nutrient input to and recycling within the system
is related to the resilience, or speed of recovery, of a system to its steady state following a disturbance. In particular,
it is shown that the return timeT
s
of the system to steady state, or the inverse of the resilience, is approximately equal to the mean turnover time of the
limiting nutrient in the system. From this relationship, it is possible to understand and predict how various properties of
food webs and their environments affect resilience. These properties include nutrient input rate, loss rate, size of the detritus
compartment, and trophic structure. The effects of these properties on resilience are described by using simple mathematical
models.
To test model predictions, experimental studies of the response of periphyton-dominated stream ecosystems to disturbance are
being conducted on a set of laboratory streams in which nutrient inputs and grazing intensity are regulated at different levels.
In streams without snail grazers (low-grazed streams), 90% recirculation of stream water to reduce nutrient inputs resulted
in longer turnover times (T
r
) of phosphorus within the stream compared with once-through flow. However, in streams with snail grazers (high-grazed streams),
there were no differences in phosphorus turnover time between once-through and partially recirculated treatments. Results
on the rate of recovery of periphyton from a flood/scour disturbance to each stream partially support the model prediction
of a positive relationship between ecosystem return time (T
s
) and nutrient turnover time (T
r
) within the streams. 相似文献
950.
Introduction and large-scale production of synthetic halogenated organic chemicals over the last fifty years has resulted in a group of contaminants that tend to persist in the environment and resist both biotic and abiotic degradation. The low solubility of these types of contaminants, along with their toxicity and tendency to accumulate in food chains, make them particularly relevant targets for remediation activities. Among the mechanisms that result in dehalogenation of some classes of organic contaminants are stimulation of metabolic sequences through introduction of electron donor and acceptor combinations; addition of nutrients to meet the needs of dehalogenating microorganisms; possible use of engineered microorganisms; and use of enzyme systems capable of catalyzing reductive dehalogenation. The current state of research and development in the area of reductive dehalogenation is discussed along with possible technological application of relevant processes and mechanisms to remediation of soil and groundwater contaminated with chlorinated organics. In addition, an overview of research needs is suggested, which might be of interest for development of in-situ systems to reduce the mass of halogenated organic contaminants in soil and groundwater. 相似文献