Nutrient enrichment of inshore waters is considered the ultimate cause of the island mass effect of Barbados, and other tropicalislands. The present study is an evaluation of the three principal causative mechanisms of enrichment of Barbados coastal waters, i.e. run-off from land, a nutrient exchange between the benthos and overlying waters and internal waves of lunar periodicity. Attempts to link high precipitation to high primary production rates or low salinity with high nutrient levels were unsuccessful. This suggested that land-drainage was not an important factor. Comparisons of nutrient concentrations and C14 fixation rates in waters overlying two contrasting (sand and coral) benthic situations showed trends rather than statistically valid differences in these production variables. A simple calculation of potential nutrient supply versus actual demand showed that internal waves represent a potential source of enrichment. It is suggested that internal waves contribute to the observed high levels of standing crop and production which are characteristic of an island mass effect. 相似文献
ABSTRACTHuman activity has led to widespread chemical alteration of natural environments. Aquatic ecosystems are especially susceptible to chemical changes, including those caused by runoff and invasive species. Here, we examined the effects of water chemistry, specifically sodium chloride as well as three metals (Ca, K, and Mn) known to differ between native and invasive wetland plant species’ leaf tissues, on the development of two model amphibians: the native Northern leopard frog, Lithobates pipiens, and the non-native African clawed frog, Xenopus laevis. We exposed frog eggs to metal treatment solutions and measured time to hatching (TTH), and following hatching, we exposed tadpoles to a lethal concentration of sodium chloride and recorded time to death (TTD). We found that increasing metal concentrations generally resulted in acceleration of TTH for Xenopus tadpoles, but had no effect on leopard frogs. However, increasing metal concentrations (Ca, Mn) increased leopard frog tadpole susceptibility to NaCl (decreased TTD), while increasing metal concentrations (Ca, K) generally resulted in decreased Xenopus tadpole susceptibility to NaCl. Overall, our data suggest that invasive amphibians may be more tolerant to chemical changes than native amphibians, including those driven by the introduction of invasive plant species. 相似文献
A model capable of quantifying the potential environmental impacts of agricultural application of composted or anaerobically digested source-separated organic municipal solid waste (MSW) is presented. In addition to the direct impacts, the model accounts for savings by avoiding the production and use of commercial fertilizers. The model is part of a larger model, Environmental Assessment of Solid Waste Systems and Technology (EASEWASTE), developed as a decision-support model, focusing on assessment of alternative waste management options. The environmental impacts of the land application of processed organic waste are quantified by emission coefficients referring to the composition of the processed waste and related to specific crop rotation as well as soil type. The model contains several default parameters based on literature data, field experiments and modelling by the agro-ecosystem model, Daisy. All data can be modified by the user allowing application of the model to other situations. A case study including four scenarios was performed to illustrate the use of the model. One tonne of nitrogen in composted and anaerobically digested MSW was applied as fertilizer to loamy and sandy soil at a plant farm in western Denmark. Application of the processed organic waste mainly affected the environmental impact categories global warming (0.4-0.7 PE), acidification (-0.06 (saving)-1.6 PE), nutrient enrichment (-1.0 (saving)-3.1 PE), and toxicity. The main contributors to these categories were nitrous oxide formation (global warming), ammonia volatilization (acidification and nutrient enrichment), nitrate losses (nutrient enrichment and groundwater contamination), and heavy metal input to soil (toxicity potentials). The local agricultural conditions as well as the composition of the processed MSW showed large influence on the environmental impacts. A range of benefits, mainly related to improved soil quality from long-term application of the processed organic waste, could not be generally quantified with respect to the chosen life cycle assessment impact categories and were therefore not included in the model. These effects should be considered in conjunction with the results of the life cycle assessment. 相似文献
Objective: The probability of crash occurrence on horizontal curves is 1.5 to 4 times higher than that on tangent sections. A majority of these crashes are associated with human errors. Therefore, human behavior in curves needs to be corrected.
Methodology: In this study, 2 different road marking treatments, optical circles and herringbone patterns, were used to influence driver behavior while entering a curve on a 2-lane rural road section. A driving simulator was used to perform the experiment. The simulated road sections are replicas of 2 real road sections in Flanders.
Results: Both treatments were found to reduce speed before entering the curve. However, speed reduction was more gradual when optical circles were used. A herringbone pattern had more influence on lateral position than optical circles by forcing drivers to maintain a safe distance from opposing traffic in the adjacent lane.
Conclusion: The study concluded that among other low-cost speed reduction methods, optical circles are effective tools to reduce speed and increase drivers’ attention. Moreover, a herringbone pattern can be used to reduce crashes on curves, mainly for head-on crashes where the main problem is inappropriate lateral position. 相似文献
This paper aims to investigate the correlations between the concentrations of nine heavy metals in moss and atmospheric deposition within ecological land classes covering Europe. Additionally, it is examined to what extent the statistical relations are affected by the land use around the moss sampling sites. Based on moss data collected in 2010/2011 throughout Europe and data on total atmospheric deposition modelled by two chemical transport models (EMEP MSC-E, LOTOS-EUROS), correlation coefficients between concentrations of heavy metals in moss and in modelled atmospheric deposition were specified for spatial subsamples defined by ecological land classes of Europe (ELCE) as a spatial reference system. Linear discriminant analysis (LDA) and logistic regression (LR) were then used to separate moss sampling sites regarding their contribution to the strength of correlation considering the areal percentage of urban, agricultural and forestry land use around the sampling location. After verification LDA models by LR, LDA models were used to transform spatial information on the land use to maps of potential correlation levels, applicable for future network planning in the European Moss Survey.
Results
Correlations between concentrations of heavy metals in moss and in modelled atmospheric deposition were found to be specific for elements and ELCE units. Land use around the sampling sites mainly influences the correlation level. Small radiuses around the sampling sites examined (5 km) are more relevant for Cd, Cu, Ni, and Zn, while the areal percentage of urban and agricultural land use within large radiuses (75–100 km) is more relevant for As, Cr, Hg, Pb, and V. Most valid LDA models pattern with error rates of <?40% were found for As, Cr, Cu, Hg, Pb, and V. Land use-dependent predictions of spatial patterns split up Europe into investigation areas revealing potentially high (=?above-average) or low (=?below-average) correlation coefficients.
Conclusions
LDA is an eligible method identifying and ranking boundary conditions of correlations between atmospheric deposition and respective concentrations of heavy metals in moss and related mapping considering the influence of the land use around moss sampling sites.
ABSTRACT: The national and regional economic impact of the Bureau of Reclamation's Uncompahgre Project which was authorized in 1903 is assessed. Benefit-cost ratios for the project are calculated for a range of production cost estimates and discount rates. An economic base approach is used to estimate the project's regional economic impact. Although the project has been marginal in terms of an economic efficiency rationale it has been an important impetus to regional economic growth in the Uncompahgre Region over time. 相似文献
In this paper a compartment model of the highly vulnerable Arctic terrestrial food chain "lichen-reindeer-man" is outlined. Based upon an analysis of measured (137)Cs and (90)Sr contents in lichen and reindeer meat from 1961 up to 2001, site specific model parameters for two regions in north-western Arctic Russia and for Kautokeino municipality in Arctic Norway have been determined. The dynamics of radionuclide activity concentrations in the "lichen-reindeer-man" food chain for all areas was satisfactorily described by a double exponential function with short-term and long-term effective ecological half-lives between 1-2 and 10-12 years, respectively, for both (137)Cs and (90)Sr. Using parameter values derived from the model, life-time internal effective doses due to consumption of reindeer meat by reindeer-breeders after an assumed single pulse deposit of 1 kBq m(-2) of (137)Cs were estimated to be 11.4 mSv (Kola Peninsula), 5 mSv (Nenets Autonomous Area), and 2 mSv (Kautokeino, Norway). Differences in vulnerability to radiocaesium deposition were due to differences in transfer between lichen and reindeer and in diet between the three regions. 相似文献
In nautical literature, ‘dead-water’ refers to the obstructive effect encountered by ships moving in stratified water due
to the ship generating waves on an interface that separates different water masses. To investigate the hypothesis that open
water swimming may also be obstructed by an encounter of dead-water, possibly causing drowning, we performed two experiments
that assess the impact of stratified water on swimming. In the first experiment, subjects made a single front-crawl stroke
while lying on a carriage that was rolling just above the water surface. The gain in kinetic energy, as a result of the stroke,
was far less in stratified than in homogeneous water. In the second experiment, four subjects swam a short distance (5 m)
in homogeneous and in two different settings of stratified water. At the same stroke frequency, swimming in stratified conditions
was slower by 15%, implying a loss in propulsive power by 40%. Although in nature stratification will be less strong, extrapolation
of the results suggests that dead-water might indeed obstruct swimming in open water as well. This effect will be most pronounced
during fair weather, when stratification of a shallow surface layer is most easily established. Our findings indicate that
swimmers’ anecdotal evidence on ‘water behaving strangely’ may have to be taken more seriously than previously thought. 相似文献