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101.
Duarte CM Agustí S Wassmann P Arrieta JM Alcaraz M Coello A Marbà N Hendriks IE Holding J García-Zarandona I Kritzberg E Vaqué D 《Ambio》2012,41(1):44-55
The Arctic marine ecosystem contains multiple elements that present alternative states. The most obvious of which is an Arctic Ocean largely covered by an ice sheet in summer versus one largely devoid of such cover. Ecosystems under pressure typically shift between such alternative states in an abrupt, rather than smooth manner, with the level of forcing required for shifting this status termed threshold or tipping point. Loss of Arctic ice due to anthropogenic climate change is accelerating, with the extent of Arctic sea ice displaying increased variance at present, a leading indicator of the proximity of a possible tipping point. Reduced ice extent is expected, in turn, to trigger a number of additional tipping elements, physical, chemical, and biological, in motion, with potentially large impacts on the Arctic marine ecosystem. 相似文献
102.
Amber Spackman Jones Jeffery S. Horsburgh Nancy O. Mesner Ronald J. Ryel David K. Stevens 《Journal of the American Water Resources Association》2012,48(6):1258-1275
Abstract: The determination of sediment and nutrient loads is typically based on the collection and analysis of grab samples. The frequency and regularity of traditional sampling may not provide representation of constituent loading, particularly in systems with flashy hydrology. At two sites in the Little Bear River, Utah, continuous, high‐frequency turbidity was used with surrogate relationships to generate estimates of total phosphorus and total suspended solids concentrations, which were paired with discharge to estimate annual loads. The high frequency records were randomly subsampled to represent hourly, daily, weekly, and monthly sampling frequencies and to examine the effects of timing, and resulting annual load estimates were compared to the reference loads. Higher frequency sampling resulted in load estimates that better approximated the reference loads. The degree of bias was greater at the more hydrologically responsive site in the upper watershed, which required a higher sampling frequency than the lower watershed site to achieve the same level of accuracy in estimating the reference load. The hour of day and day of week of sampling impacted load estimation, depending on site and hydrologic conditions. The effects of sampling frequency on the determination of compliance with a water quality criterion were also examined. These techniques can be helpful in determining necessary sampling frequency to meet the objectives of a water quality monitoring program. 相似文献
103.
Candice Stevens 《Natural resources forum》2010,34(1):16-23
Achieving sustainable development depends on comprehensive approaches which integrate consumption and production initiatives. At present, sustainable consumption is being overemphasized to the neglect of the more important production side. This paper examines the role of governments in promoting sustainable consumption and production to identify gaps in national schemes which reduce their overall effectiveness. Public policy tools promoting sustainable consumption and production are discussed in terms of whether they are aimed at correcting: 1) market failures (regulations, taxes, subsidies); or 2) systems failures (labels, communications, education, public procurement). The challenge for governments is to link sustainable consumption initiatives to policies aimed at increasing the sustainability of production in the private sector in both their national and international dimensions. In this way, governments can enlist the aid of consumers in pushing producers towards sustainability and to achieve the ultimate goal of sustainable development. 相似文献
104.
Francesca Maria Russo Anne-Gael Cordier Luc De Catte Julien Saada Alexandra Benachi Jan Deprest 《黑龙江环境通报》2018,38(9):629-637
Congenital diaphragmatic hernia is a rare disease associated with high mortality and morbidity. Antenatal ultrasound screening identifies more than 70% of cases, providing the opportunity for in utero referral to a tertiary care center for expert assessment and perinatal management. Additional genetic and morphologic assessment may be used to rule out associated anomalies. In isolated cases, the outcome may be predicted prenatally by medical imaging. The combination of lung size and liver herniation is a widely accepted method to stratify fetuses into groups with an increasing degree of pulmonary hypoplasia and corresponding mortality rates. Ultrasound measurement of the observed to expected lung-to-head ratio (o/e LHR) is most widely used. The o/e LHR is an independent predictor of survival and short-term morbidity. Finally, evaluation of stomach position has recently been introduced as an indirect method to estimate severity of the disease in left-sided defects, as it has been shown to correlate with the proportion of intrathoracic liver. Herein, we propose a protocol for the standardized ultrasound assessment of fetuses with isolated CDH and individualized prediction of neonatal outcome. 相似文献
105.
P. J. Murray D. J. Hatch E. R. Dixon S. Granger C. O’Prey R. J. Stevens R. J. Laughlin S. C. Jarvis 《Water, Air, & Soil Pollution: Focus》2005,4(6):45-52
Much work has been done on gaseous emissions and leaching of nitrogenous compounds from whole soil profiles and also from soil surface measurements which are assumed to be mainly due to topsoil activity. In soils with an impervious clay subsoil, the boundary between the topsoil and subsoil may provide an interface for microbial activity, including N transformations. In this study, we investigated movement and transformations of two reactive N species (nitrate and urea) at the subsoil interface using a series of replicate, intact soil blocks, under two contrasting watering regimes. We measured fluxes in both liquid and gaseous phases and demonstrated that nitrate reaching the subsoil interface does not necessarily leach into water systems, but may denitrify immediately and could, therefore, add to atmospheric pollution through N2O production. On the other hand, ammonium reaching the subsoil interface either directly, or after mineralization, appears to be more mobile than expected and has the potential to pollute watercourses. 相似文献
106.
/ Adaptive ecosystem management seeks to sustain ecosystems while extracting or using natural resources. The goal of endangered species management under the Endangered Species Act is limited to the protection and recovery of designated species, and the act takes precedence over other policies and regulations guiding ecosystem management. We present an example of conflict between endangered species and ecosystem management during the first planned flood on the Colorado River in Grand Canyon in 1996. We discuss the resolution of the conflict and the circumstances that allowed a solution to be reached. We recommend that adaptive management be implemented extensively and early in ecosystem management so that information and working relationships will be available to address conflicts as they arise. Though adaptive management is not a panacea, it offers the best opportunity for balanced solutions to competing management goals. 相似文献
107.
Ahmed?SaidEmail author David?K.?Stevens Gerald?Sehlke 《Environment, Development and Sustainability》2005,7(4):453-464
A new approach for evaluating water sustainability is introduced by comparing physical and economic sustainability. To achieve
physical sustainability, water should be available in sufficient quantity and of good quality and used efficiently. The economic
sustainability can be achieved by balancing between costs and values of water. The objectives of this study were to estimate
the physical and economic sustainability of surface water in the Big Lost River, south–central Idaho. The study used a Bayesian
network by building a graphical diagram of nodes representing all significant variables related with the sustainability, such
as water demand, water quality, and the different costs and values of water. The study showed that the likelihood of the physical
sustainability is less than that of the economic sustainability, which is attributed to the scarcity of water in the Big Lost
River.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
108.
Kaluzhnaya OV Belikov SI Schröder HC Rothenberger M Zapf S Kaandorp JA Borejko A Müller IM Müller WE 《Die Naturwissenschaften》2005,92(3):128-133
In ancient Lake Baikal (East Siberia), freshwater sponges have diversified to an extraordinary degree. The skeleton of Lubomirskia baicalensis, which attains a size of up to 1 m, is constructed from spicules, which are cemented into longitudinal bundles. Our X-ray analysis revealed that the architecture of the specimens follows a highly ordered radiate accretive growth pattern. The spicules have a central axial canal with an axial filament inside. This organic filament is composed of silicatein, the major enzyme involved in silica formation of the spicules. We found that the specific activity of silicatein in samples from the non-growing (basal) zone is much lower than in those from the growth zone (tips) and that even the composition of this molecule differs in these regions. The present study shows for the first time that the turnover of silicatein, the major element of the axial canal of sponge spicules, changes within a sponge specimen depending on the region in which it is found. 相似文献
109.
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