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131.
Metachronal swimming, in which adjacent appendages stroke in sequence, is widespread among crustaceans inhabiting the transitional
flow realm in which both viscosity and inertia effects are important. However, the design and operation of this propulsion
system in response to various hydrodynamic, energetic, and behavioral needs have not been well investigated. We examine free-swimming
Antarctic krill (Euphausia superba) as a model species and identify three distinct behavioral swimming gaits. The pleopod kinematics of these gaits, hovering,
fast-forward swimming, and upside-down swimming, are quantified via image analysis of high-speed video. Pleopod stroke amplitude
and frequency were found to vary significantly among these swimming modes. In order to increase swimming speed, krill were
found first to increase stroke amplitude and secondarily to increase beat frequency. The kinematics of these distinct swimming
modes provide insight as we consider multi-appendage metachronal swimming from a design standpoint. The ratio of the distance
between adjacent appendage bases and appendage length is identified as a key parameter in metachrony, the value of which is
constrained to a narrow range for a wide variety of species. 相似文献
132.
Amundsen PA Kashulin NA Terentjev P Gjelland KØ Koroleva IM Dauvalter VA Sandimirov S Kashulin A Knudsen R 《Environmental monitoring and assessment》2011,182(1-4):301-316
Metallurgic industry is a source of serious environmental pollution related to the emission of heavy metals. Freshwater systems are focal points for pollution, acting as sinks for contaminants that may end up in fish and humans. The Pasvik watercourse in the border area between Finland, Norway and Russia is located in the vicinity of the Pechenganickel metallurgic enterprises, and the lower part of the watershed drains the Nikel smelters directly through Lake Kuetsjarvi. Heavy metal (Ni, Cu, Cd, Zn, Pb and Hg) concentrations in environment (water and sediments) and whitefish Coregonus lavaretus tissue (gills, liver, kidney and muscle) were contrasted between five lake localities situated along a spatial gradient of increasing distance (5-100 km) to the smelters. The heavy metal concentrations, in particular Ni, Cu and Cd, were highly elevated in Kuetsjarvi, but steeply declined with increasing distance to the smelters and were moderate or low in the other four localities. The study demonstrates that the majority of metal emissions and runoffs are deposited near the pollution source, and only moderate amounts of the heavy metal contaminants seem to be transported at further distances. Bioaccumulation of Hg occurred in all investigated tissues, and higher Hg concentrations in planktivorous versus benthivorous whitefish furthermore indicated that pelagic foraging is associated with higher levels of Hg biomagnification. Potential population ecology impacts of high heavy metal contaminations where mainly observed in whitefish in Kuetsjarvi, which showed depletions in growth rate, condition factor and size and age at maturation. 相似文献
133.
Objective
To examine the impact of the fetal fraction (FF) on the screen-positive rate in screening for microdeletion 22q11.2.Methods
This study is based on samples that were analyzed using the Harmony® Prenatal Test (Roche Inc). The study cohort comprised samples from women with singleton pregnancies who were at least 16 years old and at least at 11 weeks' gestation. Logistic regression analysis was used to determine significant covariates that carry an impact on the screen-positive rate.Results
The study population consisted of 52,019 pregnancies, including 309 pregnancies with a high-risk result for microdeletion 22q11.2. Thus, the overall screen-positive rate was 0.59%. In the low-risk group, the FF was 10.1%, and in the high-risk group, it was 7.3%. Regression analysis indicated a strong correlation between the FF and the screen-positive rate. In the cases with an FF of <11.0%, the screen-positive rate was 0.92%, while it was 0.13% in the group with a higher FF.Conclusion
The screen-positive rate depends on the FF. In order to keep the rate low, we recommend restricting the analysis to samples with a FF of 11% and more. 相似文献134.
Sport and commercial fishing conflicts: A theoretical analysis 总被引:1,自引:0,他引:1
Richard C Bishop Karl C Samples 《Journal of Environmental Economics and Management》1980,7(3):220-233
A recreational sector is added to a standard commercial fishing optimal control model to identify public decision variables which should be considered when determining optimal population levels and allocating harvestable fish between sport and commercial users. Both linear and nonlinear models are presented. A predator-prey relationship is also considered. Results derived from the models indicate that shortcomings exist with current economic inputs to policy making because of failure to consider relevant bioeconomic relationships. Future research topics to remedy this are discussed. 相似文献
135.
Global emissions trading allows for agricultural measures to be accounted for the carbon sequestration in soils. The Environmental Policy Integrated Climate (EPIC) model was tested for central European site conditions by means of agricultural extensification scenarios. Results of soil and management analyses of different management systems (cultivation with mouldboard plough, reduced tillage, and grassland/fallow establishment) on 13 representative sites in the German State Baden-Württemberg were used to calibrate the EPIC model. Calibration results were compared to those of the Intergovernmental Panel on Climate Change (IPCC) prognosis tool. The first calibration step included adjustments in (a) N depositions, (b) N2-fixation by bacteria during fallow, and (c) nutrient content of organic fertilisers according to regional values. The mixing efficiency of implements used for reduced tillage and four crop parameters were adapted to site conditions as a second step of the iterative calibration process, which should optimise the agreement between measured and simulated humus changes. Thus, general rules were obtained for the calibration of EPIC for different criteria and regions. EPIC simulated an average increase of +0.341 Mg humus-C ha−1 a−1 for on average 11.3 years of reduced tillage compared to land cultivated with mouldboard plough during the same time scale. Field measurements revealed an average increase of +0.343 Mg C ha−1 a−1 and the IPCC prognosis tool +0.345 Mg C ha−1 a−1. EPIC simulated an average increase of +1.253 Mg C ha−1 a−1 for on average 10.6 years of grassland/fallow establishment compared to an average increase of +1.342 Mg humus-C ha−1 a−1 measured by field measurements and +1.254 Mg C ha−1 a−1 according to the IPCC prognosis tool. The comparison of simulated and measured humus C stocks was r2 ≥ 0.825 for all treatments. However, on some sites deviations between simulated and measured results were considerable. The result for the simulation of yields was similar. In 49% of the cases the simulated yields differed from the surveyed ones by more than 20%. Some explanations could be found by qualitative cause analyses. Yet, for quantitative analyses the available information from farmers was not sufficient. Altogether EPIC is able to represent the expected changes by reduced tillage or grassland/fallow establishment acceptably under central European site conditions of south-western Germany. 相似文献
136.
137.
Reestablishing Naturally Functioning Dunes on Developed Coasts 总被引:2,自引:0,他引:2
Common beach management practices reduce the ecological values of coastal dunes. Mechanical beach cleaning eliminates incipient
dunes, habitat for nesting birds, seed sources for pioneer dune colonizers and food for fauna, and artificially small, stabilized
foredunes reduce the variability in microenvironments necessary for biodiversity. Recent initiatives for reducing coastal
hazards, protecting nesting birds, and encouraging nature-based tourism provide incentive for the development of a restoration
program for beaches and dunes that is compatible with human use. Suggested changes in management practice include restricting
or rerouting pedestrian traffic, altering beach-cleaning procedures, using symbolic fences to allow for aeolian transport
while preventing trampling of dunes, and eliminating or severely restricting exotic species. Landforms will be more natural
in function and appearance but will be more dynamic, smaller and in a different position from those in natural areas. Research
needs are specified for ecological, geomorphological, and attitudinal studies to support and inform restoration planning. 相似文献
138.
Geoffrey N. Delin Richard W. Healy Matthew K. Landon John Karl Bhlke 《Journal of the American Water Resources Association》2000,36(6):1401-1416
ABSTRACT: Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7‐hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site‐specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the lowland site (annual average of all methods of 29 cm) exceeded those at the upland site (annual average of 18 cm). On an annual basis, estimates by the individual methods ranged from 12 to 44 percent of precipitation at the upland site and from 21 to 83 percent at the lowland site. The difference in recharge rates between the sites is primarily attributed to depression focusing of surface water runon at the lowland site. However, two other factors were also important: the presence of thin lamellae at the upland site, and coarser textured soils below a depth of 1.5 m at the lowland site. 相似文献
139.
Modeling carbon sequestration under zero tillage at the regional scale. I. The effect of soil erosion 总被引:3,自引:0,他引:3
Thomas Gaiser Karl Stahr Norbert Billen Mohammad Abdel-Razek Mohammad 《Ecological modelling》2008,218(1-2):110-120
Zero tillage is recognized as a potential measure to sequester carbon dioxide in soils and to reduce CO2 emissions from arable lands. An up-scaling approach of the output of the Environmental Policy Integrated Climate (EPIC) model with the information system SLISYS-BW has been used to estimate the CO2-mitigation potential in the state of Baden-Württemberg (SW-Germany). The state territory of 35,742 km2 is subdivided into eight agro-ecological zones (AEZ), which have been further subdivided into a total of 3976 spatial response units. Annual CO2-mitigation rates where estimated from the changes in soil organic carbon content comparing 30 years simulations under conventional and zero tillage. Special attention was given to the influence of tillage practices on the losses of organic carbon through soil erosion, and consequently on the calculation of CO2-mitigation rates. Under conventional tillage, mean carbon losses through erosion in the AEZ were estimated to be up to 0.45 Mg C ha−1 a−1. The apparent CO2-mitigation rate for the conversion from conventional to zero tillage ranges from 0.08 to 1.82 Mg C ha−1 a−1 in the eight AEZ, if the carbon losses through soil erosion are included in the calculations. However, the higher carbon losses under conventional tillage compared to zero tillage are composed of both, losses through enhanced CO2 emissions, and losses through intensified soil erosion. The adjusted net CO2-mitigation rates of zero tillage, subtracting the reduced carbon losses through soil erosion, are between 0.07 and 1.27 Mg C ha−1 a−1 and the estimated net mitigation rate for the entire state amounts to 285 Gg C a−1. This equals to 1045 Gg CO2-equivalents per year with the cropping patterns in the reference year 2000. The results call attention to the necessity to revise those estimation methods for CO2-mitigation which are exclusively or predominantly based on the measurements of differential changes in total soil organic carbon without taking into account the tillage effects on carbon losses through soil erosion. 相似文献
140.
The decomposition of leaf litter is controlled by several factors. One factor that may play an important role is the content
of condensed tannins (proanthocyanidins). Here we designed a combined method to isolate proanthocyanidins from leaf extracts,
to convert them to anthocyanidins, and to quantify individual anthocyanidins exactly with a new, simple, but sensitive high-performance
liquid chromatography method. We used this method to show composition of proanthocyanidins and to monitor degradation of proanthocyanidins
and individual constituents in leaf litter in an aquatic environment over time. Despite the rapid decrease in the initial
concentrations, a fraction of the proanthocyanidins remained detectable for several weeks. 相似文献