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221.
In an earlier article, we discussed the effects of dissensus and low paradigm development on the lives and scholarly successes of junior scholars. Our analysis painted a somewhat bleak picture, but our advice for moving forward was simple, actionable, and therefore hopeful. Based on the bleak picture that was painted, one particular aspect of our work, career‐level evaluation reliability, was recently critiqued. We respond to that critique here. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
222.
Nitrous oxide emissions from a Northern Great Plains soil as influenced by nitrogen management and cropping systems 总被引:1,自引:0,他引:1
Dusenbury MP Engel RE Miller PR Lemke RL Wallander R 《Journal of environmental quality》2008,37(2):542-550
Field measurements of N2O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N2O emission-time profiles for cropping systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N2O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha(-1) available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N2O emissions were modest in contrast to reports from more humid regions. Greatest N2O flux activity occurred following urea-N fertilization (10-wk) and during freeze-thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N2O emissions during the post-N fertilization period, while denitrification was more important during freeze-thaw cycles. Cumulative 2-yr N2O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha(-1)) than wheat-fallow (CT and NT) (0.48 kg N ha(-1)), and wheat-pea (0.71 kg N ha(-1)) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha(-1)). Tillage did not affect N2O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%). 相似文献
223.
Sharon E. Clarke Kelly M. Burnett Daniel J. Miller 《Journal of the American Water Resources Association》2008,44(2):459-477
Abstract: Managers, regulators, and researchers of aquatic ecosystems are increasingly pressed to consider large areas. However, accurate stream maps with geo‐referenced attributes are uncommon over relevant spatial extents. Field inventories provide high‐quality data, particularly for habitat characteristics at fine spatial resolutions (e.g., large wood), but are costly and so cover relatively small areas. Recent availability of regional digital data and Geographic Information Systems software has advanced capabilities to delineate stream networks and estimate coarse‐resolution hydrogeomorphic attributes (e.g., gradient). A spatially comprehensive coverage results, but types of modeled outputs may be limited and their accuracy is typically unknown. Capitalizing on strengths in both field and regional digital data, we modeled a synthetic stream network and a variety of hydrogeomorphic attributes for the Oregon Coastal Province. The synthetic network, encompassing 96,000 km of stream, was derived from digital elevation data. We used high‐resolution but spatially restricted data from field inventories and streamflow gauges to evaluate, calibrate, and interpret hydrogeomorphic attributes modeled from digital elevation and precipitation data. The attributes we chose to model (drainage area, mean annual precipitation, mean annual flow, probability of perennial flow, channel gradient, active‐channel width and depth, valley‐floor width, valley‐width index, and valley constraint) have demonstrated value for stream research and management. For most of these attributes, field‐measured, and modeled values were highly correlated, yielding confidence in the modeled outputs. The modeled stream network and attributes have been used for a variety of purposes, including mapping riparian areas, identifying headwater streams likely to transport debris flows, and characterizing the potential of streams to provide high‐quality habitat for salmonids. Our framework and models can be adapted and applied to areas where the necessary field and digital data exist or can be obtained. 相似文献
224.
One aspect of describing contamination in an alluvial aquifer is estimating changes in concentrations over time. A variety of statistical methods are available for assessing trends in contaminant concentrations. We present a method that extends trend analysis to include estimating the coefficients for the exponential decay equation and calculating contaminant attenuation half-lives. The conceptual model for this approach assumes that the rate of decline is proportional to the contaminant concentration in an aquifer. Consequently, the amount of time to remove a unit quantity of the contaminant inventory from an aquifer lengthens as the concentration decreases. Support for this conceptual model is demonstrated empirically with log-transformed time series of contaminant data. Equations are provided for calculating system attenuation half-lives for non-radioactive contaminants. For radioactive contaminants, the system attenuation half-life is partitioned into the intrinsic radioactive decay and the concentration reduction caused by aquifer processes. Examples are presented that provide the details of this approach. In addition to gaining an understanding of aquifer characteristics and changes in constituent concentrations, this method can be used to assess compliance with regulatory standards and to estimate the time to compliance when natural attenuation is being considered as a remediation strategy. A special application of this method is also provided that estimates the half-life of the residence time for groundwater in the aquifer by estimating the half life for a conservative contaminant that is no longer being released into the aquifer. Finally, the ratio of the half-life for groundwater residence time to the attenuation half-life for a contaminant is discussed as a system-scale retardation factor which can be used in analytical and numerical modeling. 相似文献
225.
Yann Devos Pieter Maeseele Dirk Reheul Linda Van Speybroeck Danny De Waele 《Journal of Agricultural and Environmental Ethics》2008,21(1):29-61
Via a historical reconstruction, this paper primarily demonstrates how the societal debate on genetically modified organisms
(GMOs) gradually extended in terms of actors involved and concerns reflected. It is argued that the implementation of recombinant
DNA technology out of the laboratory and into civil society entailed a “complex of concerns.” In this complex, distinctions
between environmental, agricultural, socio-economic, and ethical issues proved to be blurred. This fueled the confusion between
the wider debate on genetic modification and the risk assessment of transgenic crops in the European Union. In this paper,
the lasting skeptical and/or ambivalent attitude of Europeans towards agro-food biotechnology is interpreted as signaling
an ongoing social request – and even a quest – for an evaluation of biotechnology with Sense and Sensibility. In this (re)quest, a broader-than-scientific dimension is sought for that allows addressing the GMO debate in a more “sensible”
way, whilst making “sense” of the different stances taken in it. Here, the restyling of the European regulatory frame on transgenic
agro-food products and of science communication models are discussed and taken to be indicative of the (re)quest to move from
a merely scientific evaluation and risk-based policy towards a socially more robust evaluation that takes the “non-scientific”
concerns at stake in the GMO debate seriously. 相似文献
226.
Norman D. Folmar Arthur C. Miller Donald E. Woodward 《Journal of the American Water Resources Association》2007,43(3):829-838
Abstract: Many of the hydrologic methods that are used in engineering practice today resulted from the Spring Flood of 1936, which blanketed the Northeastern portion of the United States. Because of the flood damage that was caused by this rainfall‐snowmelt event, many federal agencies including the U.S. Army Corp of Engineers and the Soil Conservation Service (SCS) implemented the hydrologic theories that were available in the literature at this time and developed hydrologic procedures for design flow estimation. Sherman had recently published his unit hydrograph theory in 1932, and later in 1938 Snyder, who had been charged by the Water Resource Council to develop a synthetic unit hydrograph, published his famous paper. The SCS unit hydrograph theory was developed by Victor Mockus in the late 1950s. Most if not all of the theories at that time reported the rainfall‐runoff process for floods as a surface phenomenon, and as such those theories all required some type of a timing parameter to estimate watershed response time. This article documents the development of the SCS lag equation. 相似文献
227.
A comparative study of the otolith microstructure and microchemistry of Anguilla marmorata glass eels in the western North Pacific (Japan, Taiwan, the Philippines, Indonesia) determined the timing of metamorphosis and age at recruitment to freshwater habitats with a view to learning about the early life history and recruitment of this species of tropical anguillid eel, which has a wide range throughout much of the western Pacific and parts of the Indian Ocean. Three new samples (from Japan, Taiwan, Indonesia) were analyzed and statistically compared along with two other previously published samples that were analyzed using the same techniques. Ages at metamorphosis and recruitment, respectively, were 123ᆡ.4 days (mean-SD) and 154ᆥ.0 days in specimens from Japan, 116ᆢ.6 days and 145ᆣ.6 days in those from Taiwan, 120ᆡ.0 days and 154ᆡ.5 days in the Philippines stock and 132Nj.7 days and 159ᆟ.7 days, and 120ᆣ.6 days and 152ᆣ.2 days in the Indonesian stock. The average duration of the period of metamorphosis estimated from otolith microstructure was very similar (15-17 days) in the specimens from all locations. A close linear relationship was found between the ages at metamorphosis and recruitment at all locations, suggesting that individuals that metamorphosed earlier were recruited to freshwater habitats at a younger age. Back-calculated hatching dates ranged over about 6 months of the year, suggesting that this species may spawn throughout much of the year. It is hypothesized that specimens from all four sites are from the same spawning population originating in a spawning area in the North Equatorial Current of the western North Pacific. 相似文献
228.
Acute toxicity and sublethal behavioral effects of copper on barnacle nauplii (Balanus improvisus) 总被引:1,自引:0,他引:1
This study documents the effects of short-term (24h) sublethal copper exposures on undirected swimming activity and photobehavior of Balanus improvisus stage II nauplii. All Cu treatments were static, with temperature and salinity conditions at 20°C and 15 or 30. The 24h LC 50 estimate for Cu is 88 ppb at 15 and >200 ppb at 30. Sub-lethal Cu concentrations cause reductions in swimming speed, which decrease progressively with increasing Cu dose. At 50 ppb Cu, this was significant primarily at light intensities below the phototactic threshold. At higher Cu concentrations, significant reductions in mean linear velocity occurred at most light intensities tested. At 30, 50 and 100 ppb Cu also reduce the positive phototactic response and 150 ppb Cu causes reversal of phototaxis at optimal intensities. Photokinesis is reduced at 100 ppb Cu and disappears at 150 ppb Cu. At 15, the behavioral effects of 50 ppb Cu resemble those occurring with 150 ppb Cu at 30. Swimming speed and photobehavior show promise as sensitive behavioral indicators of copper toxicity. Additional research is required to determine if these responses apply to a broad range of pollutants and to other planktonic organisms. There is also a need to further evaluate the significance of these behavioral effects ecologically.Contribution No. 181 from the EPA Environmental Research Laboratory, Narragansett, RI 02882, USA 相似文献
229.
Reproduction of meso- and bathypelagic chaetognaths, a major group of zooplankton and hermaphroditic animals, became clear after the microscopic examination of samples collected from the Pacific Subarctic Water. Species of the genus Eukrohnia carry their developing eggs in two marsupial sacs, one on each side, and the young are retained in these marsupia for at least some period after hatching. This is in line with a general trend for low fecundity, as care of the young increases. Almost all individuals are protandric, the testes maturing sooner than ovaries. These facts suggest that the reproduction of these species depends upon cross-fertilization. 相似文献
230.
Brye KR Morris TL Miller DM Formica SJ Van Eps MA 《Journal of environmental quality》2004,33(5):1937-1942
Despite many decades of education and refining land-use practices, accelerated stream bank erosion is still prevalent in the United States. Eroding stream banks produce a sediment load to the riverine system and can cause reduced water quality as a result of increased suspended sediment. As total maximum daily loads (TMDLs) for water bodies impaired by turbidity or suspended sediments become more numerous, a simple, in situ field technique will be needed to estimate the bulk density of readily erodible stream bank material so that reasonably accurate sediment loading rates can be estimated. In this study, the excavation/polyurethane-foam technique for estimating total bulk density was applied to vertically exposed alluvium with high coarse-fragment content. Though not previously attempted in vertically exposed alluvium with high coarse-fragment content, the excavation/polyurethane-foam technique appears to provide a reasonably accurate estimate of the total and soil (<2-mm size fraction) bulk density from vertically exposed, alluvial deposits with high coarse-fragment content (i.e., >70%) along eroding stream banks. Obtaining bulk density estimates using this method would facilitate calculation of sediment loading rates to riverine systems with actual field data. 相似文献