排序方式： 共有44条查询结果，搜索用时 15 毫秒
11.
Environmental assessments generate and/or collect individual research efforts to answer policy-relevant questions and otherwise provide technical advice to decision-makers, typically legislators, international negotiators and regulators. Though one might think first of assessments in terms of the reports that they often produce, the implications of scientific assessment are better understood by viewing assessments as a social processes, rather than principally as a document. Assessment processes are embedded in different sorts of institutional settings, within which scientists, decision-makers, and advocates communicate to define relevant questions for analysis, mobilize certain kinds of experts and expertise, and interpret findings in particular ways. This social process perspective on assessment directs attention beyond the content of assessment reports to encompass questions the design of the social process. In this paper, we focus on four elements of assessment design that are too frequently under-appreciated: assessment context and initiation, science–policy interaction, participation in assessment processes, and assessment capacity. We show how widely these elements vary across five different assessments and discuss the implications of this variation. 相似文献
12.
The tidally inundated marsh surface is an importnat site for energy exchanges for many resident and transient species. In
many areas along the East Coast of the U.S. the dominant vegetation,Spartina alterniflora, has been replaced by the common reed (Phragmites australis). This shift has caused concern about the impact ofPhragmites on marsh fauna but research in this area has been limited. During 1997 and 1998, we examined the effect ofPhragmites on fish and decapod crustacean use of the marsh surface in the brackish water reaches of the Mullica River, in southern New
Jersey, U.S. Fish and decapod crustaceans were sampled with an array of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7
cm) and with flumes (1.3 m wide×10 m long of 3.2-mm mesh). Fish (2–60 mm TL) dominated pit trap collections withFundulus heteroclitus andFundulus luciae significantly more abundant atSpartina sites.Fundulus heteroclitus was also the dominant fish (15–275 mm TL) collected in flumes but collections with this gear, including a number of species
not collected in pit traps, showed no distinct preferences for different marsh vegetation types. Decapod crustaceans (1–48
mm CW) collected in pit traps were generally less abundant than fishes withCallinectes sapidus andPalaemonetes spp. most abundant inSpartina, whileRhithropanopeus harrisii was most abundant inPhragmites. The same decapod crustacean species (2–186 mm CW) dominanted the flume collections and, similar to the pattern of fish collected
by the flumes, there were no distinct habitat preferences for different marsh vegetation types. As a result of these observations,
with different sampling techniques, it appears there is an overall negative effect ofPhragmites on larval and small juvenile fish but less or no effect on larger fish and decapods crustaceans. 相似文献
13.
Stacy D. Jupiter Graham Epstein Natalie C. Ban Sangeeta Mangubhai Margaret Fox Michael Cox 《社会与自然资源》2017,30(9):1096-1111
Locally managed marine areas (LMMAs) are often recommended as a strategy to achieve conservation and fisheries management, though few studies have evaluated their performance against these objectives. We assessed the effectiveness of eight periodically harvested closures (PHCs), the most common form of management within Fijian LMMAs, focusing on two outcomes: protection of resource units and biodiversity conservation. Of the eight PHCs, only one provided biodiversity benefits, whereas three were moderately successful in protecting resource units (targeted fish biomass). Protection of resource units was more likely when PHCs were harvested less frequently, less recently, and when total fish biomass in open areas was lower. Our findings further suggest that monitoring, enforcement, and clearly defined boundaries are critical, less frequent harvesting regimes are advised, and culturally appropriate management incentives are needed. Although PHCs have some potential to protect resource units, they are not recommended as a single strategy for broad-scale biodiversity conservation. 相似文献
14.
Stacy A. Fleenor Christopher J. Biagi Kenneth L. Cummins E. Philip Krider Xuan-Min Shao 《Atmospheric Research》2009,91(2-4):333-352
In July 2005, a field campaign was conducted in the Central Great Plains to obtain 60-field/s video imagery of lightning in correlation with reports from the U.S. National Lightning Detection Network (NLDN) and broadband electric field waveforms from the Los Alamos Sferic Array (LASA). A total of 342 GPS time-stamped cloud-to-ground (CG) flashes were recorded in 17 different sessions, and 311 (91%) of these were correlated with reports from the NLDN. Only 6 of the 17 recording sessions were dominated by flashes that lowered negative charge to ground, and 11 were dominated by positive CG flashes. A total of 103 flashes recorded on video were correlated with at least one NLDN report of negative CG strokes, 204 video flashes were correlated with one or two positive stroke reports, and 4 had bipolar reports. In this paper, we will give distributions of the estimated peak current, Ip, as reported by the NLDN, of negative and positive first strokes that were recorded on video, the multiplicity of strokes that were recorded on video, and the number of ground contacts per flash that were resolved on video. 41 (40%) of the negative flashes produced just a single-stroke on video, and 62 (60%) showed two or more strokes. The observed multiplicity of negative flashes averaged 2.83, which becomes about 3.14 after correcting for the finite time-resolution of the video camera. 195 (96%) of the positive flashes produced just a single-stroke on video, and 9 (4%) showed two strokes; therefore, the observed multiplicity of positive flashes averaged 1.04. Five out of 9 (56%) of the positive subsequent strokes re-illuminated a previous channel, and 4 out of 9 (44%) created a new ground contact. Simultaneous video, LASA, and NLDN measurements also allowed us to examine the classification of NLDN reports during 3 single-cell storms (one negative and two positive). Based on the LASA waveforms, a total of 204 out of 376 (54%) NLDN reports of CG strokes were determined to be for cloud pulses. The misclassified negative reports had |Ip| values ranging from 3.8 kA to 29.7 kA, but only 58 (24%) of these had |Ip| > 10 kA, and only one misclassified positive report had Ip > 20 kA. Radar analyses showed that most of the negative and positive CG strokes that were recorded on video were produced within or near the convective cores of storms. The radar imagery also showed that single-cell storms tended to produce one polarity of CG flashes at a time, and that such storms could switch rapidly from negative to positive CG flashes when the reflectivity was near maximum. Multiple-cell storms produced both negative and positive flashes over a broad region, but each polarity tended to cluster near regions of high-reflectivity. 相似文献
15.
Ronald?GoldbergEmail author Beth?Phelan Jose?Pereira Stacy?Hagan Paul?Clark Allen?Bejda Anthony?Calabrese Anne?Studholme Kenneth?W.?Able 《Estuaries and Coasts》2002,25(2):215-226
We compared distribution and abundance by habitat for age-0, young-of-the-year (YOY) winter flounder,Pseudopleuronectes americanus, in three estuaries (Hammonasset River, Navesink River, and Great Bay-Little Egg Harbor) in the northeastern United States to better define essential fish habitat (EFH). Two replicates of five representative habitats were sampled in most estuaries: eelgrass (Zostera marina), unvegetated areas adjacent to eelgrass, macroalgae, (primarilyUlva lactuca), unvegetated areas adjacent to macroalgae, and tidal marsh creeks. Fish were sampled every two weeks, May through October 1995 and 1996, with a beam-trawl (1-m width, 3-mm mesh net). Abundance of YOY winter flounder was highest in the Navesink River estuary and similar between years, but was significantly lower and differed between years in the Great Bay-Little Egg Harbor and Hammonasset River estuaries. Annual temperature differences appear to influence estuary use by YOY. In the years and estuaries studied, where habitat-related differences in abundance were significant, YOY were found in higher densities in unvegetated areas adjacent to eelgrass. The exception was in the Hammonasset River in 1995 when densities were higher in eelgrass. We conclude that the type of habitat most important to YOY winter flounder varies among estuaries and as a result, care should be taken in defining EFH, based only on limited spatial and temporal sampling. 相似文献
16.
17.
Jennifer Elizabeth Miller Stacy A. C. Nelson George R. Hess 《The Professional geographer》2013,65(2):250-264
Detailed land cover maps provide important information for research and decision-making but are often expensive to develop and can become outdated quickly. Widespread availability of aerial photography provides increased accessibility of high-resolution imagery and the potential to produce high-accuracy land cover classifications. However, these classifications often require expert knowledge and are time consuming. Our goal was to develop an efficient, accurate technique for classifying impervious surface in urbanizing Wake County, North Carolina. Using an iterative training technique, we classified 111 nonmosaicked, very-high-resolution images using the Feature Analyst software developed by Visual Learning Systems. Feature Analyst provides object extraction classifications by analyzing spatial context in relation to spectral data to classify high-resolution imagery. Our image classification results were 95 percent accurate in impervious surface extraction, with an overall total accuracy of 92 percent. Using this method, users with relatively limited geographic information system (GIS) training and modest budgets can produce highly accurate object-extracted classifications of impervious and pervious surface that are easily manipulated in a GIS. 相似文献
18.
Rachel F. S. Massaro Eric Heinen De Carlo Patrick S. Drupp Fred T. Mackenzie Stacy Maenner Jones Katie E. Shamberger Christopher L. Sabine Richard A. Feely 《Aquatic Geochemistry》2012,18(4):357-386
In this paper, we present the results of the first automated continuous multi-year high temporal frequency study of CO2 dynamics in a coastal coral reef ecosystem. The data cover 2.5?years of nearly continuous operation of the CRIMP-CO2 buoy spanning particularly wet and dry seasons in southern Kaneohe Bay, a semi-enclosed tropical coral reef ecosystem in Hawaii. We interpret our observational results in the context of how rapidly changing physical and biogeochemical conditions affect the pCO2 of surface waters and the magnitude and direction of air–sea exchange of CO2. Local climatic forcing strongly affects the biogeochemistry, water column properties, and gas exchange between the ocean and atmosphere in Kaneohe Bay. Rainfall driven by trade winds and other localized storms generates pulses of nutrient-rich water, which exert a strong control on primary productivity and impact carbon cycling in the water column of the bay. The “La Ni?a” winter of 2005–2006 was one of the wettest winters in Hawaii in 30?years and contrasted sharply with preceding and subsequent drier winter seasons. In addition, short-term variability in physical forcing adds complexity and helps drive the response of the CO2–carbonic acid system of the bay. Freshwater pulses to Kaneohe Bay provide nutrient subsidies to bay waters, relieving the normal nitrogen limitation of this system and driving phytoplankton productivity. Seawater pCO2 responds to the blooms as well as to physical forcing mechanisms, leading to a relatively wide range of pCO2 in seawater from about 250 to 650?μatm, depending on conditions. Large drawdowns in pCO2 following storms occasionally cause bay waters to switch from being a source of CO2 to the atmosphere to being a sink. Yet, during our study period, the southern sector of Kaneohe Bay remained a net source of CO2 to the atmosphere on an annualized basis. The integrated net annual flux of CO2 from the bay to the atmosphere varied between years by a factor of more than two and was lower during the wet “La Ni?a” year, than during the following year. Over the study period, the net annualized flux was 1.80?mol?C?m?2?year?1. Our CO2 flux estimates are consistent with prior synoptic work in Kaneohe Bay and with estimates in other tropical coral reef ecosystems studied to date. The high degree of climatological, physical, and biogeochemical variability observed in this study suggests that automated high-frequency observations are needed to capture the short-, intermediate-, and long-term variability of CO2 and other properties of these highly dynamic coastal coral reef ecosystems. 相似文献
19.
Kenneth W. Able Deborah N. Vivian Gina Petruzzelli Stacy M. Hagan 《Estuaries and Coasts》2012,35(3):743-753
We examined connectivity among marsh subhabitats to determine the structural limits and important components of a polyhaline
salt marsh by studying the patterns of abundance, residency, and movement of a numerically and ecologically dominant nektonic
fish (mummichog, Fundulus heteroclitus). We captured, tagged (n = 14,040 individuals, 30–110 mm), and recaptured from Feb 2001 to Jul 2002, although most recaptures (75–95% by tagging location)
occurred within 150 days. Seasonal residency and movements were common among most subhabitats based on catch per unit effort
and recapture per unit effort. Thus, these (marsh pools, intertidal and subtidal creeks, and marsh surface) should be considered
natural subhabitats within New England type salt marshes. Further, all these subhabitat types should be included in studies
of salt marsh nekton and marsh restoration and creation activities. 相似文献
20.
Tara R. Clark Jian-xin Zhao Yue-xing Feng Terry J. Done Stacy Jupiter Janice Lough John M. Pandolfi 《Geochimica et cosmochimica acta》2012
The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 (230Th0), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the 230Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial 230Th/232Th (230Th/232Th0) variability. In these living Porites corals, the majority of 230Th/232Th0 values fell within error of the conservative bulk Earth 230Th/232Th atomic value of 4.3 ± 4.3 × 10?6 (2σ) generally assumed for 230Th0 corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of 230Th ages can be further improved by using locally determined 230Th/232Th0 values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in 230Th/232Th0 between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 230Th/232Th0 atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10?6, with a weighted mean of 5.76 ± 0.34 × 10?6 (2σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more conservative assigned error of 25% (i.e. 5.8 ± 1.4 × 10?6) that encompasses the full variation of the 39 230Th/232Th0 measurements is recommended as a more appropriate value for initial 230Th corrections for U-series dating of most Porites samples from inshore regions of the GBR. This will result in significant improvement in both the precision and accuracy of the corrected 230Th ages related to those based on the assumed bulk Earth 230Th/232Th0 value of 4.3 ± 4.3 × 10?6. However, several anomalously high 230Th/232Th0 values reaching up to 28.0 ± 1.6 × 10?6 occasionally found in some coral annual bands coinciding with El Niño years imply high 230Th/232Th0 sources and highlight the complexities of understanding 230Th/232Th0 variability. For U-series dating of young coral samples from such sites where anomalous 230Th/232Th0 values occur, we suggest replicate dating of multiple growth bands with known age difference to verify age accuracy. 相似文献