Field study of the potential for winter precipitation enhancement in the Australian Snowy Mountains     

Joseph A. Warburton  Melanie A. Wetzel 《Atmospheric Research》1992,28(3-4)

A research program was initiated in 1988 to investigate the potential for winter snowpack enhancement in the Snowy Mountains of Australia. Field studies were conducted during the austral winters of 1988 and 1989 in order to characterize the water and ice composition of clouds passing over these mountains. We utilized a dual-channel microwave radiometer and a Ka-band (8.6 mm wavelength) radar in a coordinated observational program to document the distribution of supercooled liquid water, ice phase precipitation and water vapor in the winter storm systems. The vertical temperature, humidity and wind profiles were obtained at high temporal resolution from local rawinsonde launches. Ground-based sampling of the snow crystal types and the stable isotopic composition of the snow provided information on the processes of crystal formation and riming during these storms. A precipitation trajectory model was used to simulate ice crystal growth for snow which precipitates within the study region. Analysis of these data indicate buildup of supercooled liquid water during certain storm periods, while during other periods the ice crystal growth processes efficiently remove cloud liquid. Several aspects of the cloud seeding potential are discussed in this paper and the overall conclusion is that winter precipitation enhancement is scientifically feasible, based upon the World Meteorological Organization criterion of supercooled liquid water availability.  相似文献   

Cyanobacterial influence on diatom community lifeform dynamics in shallow subtropical lakes of Florida USA     

Thomas J. Whitmore  Melanie A. Riedinger-Whitmore  Francesca M. Lauterman  Jason H. Curtis 《Journal of Paleolimnology》2018,60(2):223-246

Fragilarioid diatom taxa are often deemed ubiquitous in shallow lake systems. Their presence has been described as contributing to statistical noise in paleolimnological studies of cold-temperate lakes. In shallow, warm-temperate lakes of Florida, long-term transitions from assemblages dominated by Aulacoseira spp. to fragilarioid taxa, particularly Pseudostaurosira brevistriata, Staurosira construens var. venter, and Staurosirella pinnata, often occur. Distinctly higher limnetic nutrient optima are demonstrated by these fragilarioid taxa than by planktonic Aulacoseira spp. Community successions occur during eutrophication, and progressive replacement of Aulacoseira spp. and other planktonic taxa by fragilarioid taxa is concurrent with and apparently related to the onset of cyanobacterial dominance. We examine successions from Aulacoseira-dominated to fragilarioid-dominated assemblages in sediment cores from subtropical Florida lakes that have undergone eutrophication. Diatom profiles are compared with sedimented pigments, nitrogen stable isotopes of organic matter, and with silica accumulation rates. These study lakes have little if any macrophyte presence. Their light-extinction depths are extremely shallow, yet diatom communities are dominated by bottom-dwelling rather than planktonic taxa. Frequent wind-generated mixing, sometimes to lake bottoms, is sufficient to sustain the light needs of benthic and tychoplanktonic taxa. We conclude that assemblage changes generally are not caused by reduced water depths, silica limitation, nor increased incipient stratification, but that cyanobacteria are responsible for reducing planktonic Aulacoseira in favor of fragilarioid taxa. Cyanobacteria blooms persist over a wide seasonal range because of warm climate and high limnetic nutrient concentrations in Florida lakes. Cyanobacteria progressively displace and outcompete Aulacoseira and other planktonic taxa as eutrophication proceeds. Reduced light availability, changes in mineral/nutrient availability, and other aspects of competitive exclusion, such as cyanobacterial allelotoxins, might contribute to observed changes. Climate warming is not likely to account for Aulacoseira reduction as in colder regions because it is less pronounced in this subtropical district. Lakes with low nutrient levels and less cyanobacteria still sustain large Aulacoseira populations, and decreases in limnetic nutrients sometimes lead to the return of planktonic Aulacoseira. Rather than simply representing statistical noise for paleolimnological reconstructions, shifts to certain fragilarioid taxa indicate when subtropical Florida lakes progressed to hypereutrophic conditions that were marked by cyanobacterial proliferation.  相似文献   

Tidal Freshwater Marshes Harbor Phylogenetically Unique Clades of Sulfate Reducers That Are Resistant to Climate-Change-Induced Salinity Intrusion     

Patrick J. Kearns  Nathaniel B. Weston  Jennifer L. Bowen  Tatjana Živković  Melanie A. Vile 《Estuaries and Coasts》2016,39(4):981-991

Rates of sea level rise associated with climate change are predicted to increase in the future, potentially altering ecosystems at all ecological levels. Sea level rise can increase the extent of brackish water intrusion into freshwater ecosystems, which in turn can affect the structure and function of resident microbial communities. In this study, we performed a year-long mesocosm experiment using intact tidal freshwater marsh sediment cores to examine the effect of a 5-part per thousand (ppt) salinity increase on the diversity and community composition of sulfate-reducing prokaryotes. We used a clone library approach to examine the dsrA gene, which encodes an important catalytic enzyme in sulfate reduction. Our results indicate that tidal freshwater marshes contain extremely diverse communities of sulfate-reducing bacteria. Members of these communities were, on average, only 71 % similar to known cultured sulfate reducers and 81 % similar to previously sequenced environmental clones. Salinity and associated increases in sulfate availability did not significantly affect the diversity or community composition of sulfate-reducing prokaryotes. However, carbon quality and quantity, which correlated with depth, were found to be the strongest drivers of sulfate-reducing community structure. Our study demonstrates that the sulfate-reducing community in tidal freshwater marsh sediments appears resistant to increased salinity in the face of sea level rise. Additionally, the microorganisms that comprise this sulfate-reducing community appear to be unique to tidal freshwater marsh sediments and may represent novel lineages of previously undescribed sulfate reducers.  相似文献   

Participatory research supporting community-based fishery management   总被引：3，自引：0，他引：3  

Melanie Wiber  Fikret Berkes  Anthony Charles  John Kearney   《Marine Policy》2004,28(6):353

This paper reports on a project to engage researchers and fishers together in adapting social science approaches to the purposes and the constraints of community-based fisher organizations. The work was carried out in the Scotia–Fundy Region of Atlantic Canada (the Bay of Fundy and Scotian Shelf). Its rationale reflects arguments that (1) effective community-based management requires that managers are able to pose and address social science questions, (2) participatory research, involving true cooperation in all stages, can support this process, and (3) there is a need to overcome practical and methodological barriers faced in developing participatory research protocols, to serve the needs of community-based management while not demanding excessive transaction costs. In this paper, we report on work with fisher organizations, both aboriginal and non-aboriginal, in which social science priorities were set by each organization, and small-scale research projects designed and carried out to meet these needs. This work identified interests among fishers in research on three different levels of meaning: (1) practical livelihood concerns, including what, when and where to fish, and with what intensity of effort, (2) social, economic and political issues (e.g., on institutional structures, politics of access and allocation, overlap and conflict between regulatory regimes), and (3) values and ethics that implicitly or explicitly guide policy development and implementation. Several research themes proved crucial, including those of power sharing, defining boundaries of a community-based group, access and equity, designing effective management plans, enforcement, and scaling up for effective regional and ecosystem-wide management. The research results demonstrate the effectiveness of extending participatory methods to challenge traditional scientific notions of the research process.  相似文献   

A combined IR and XRD study of natural well crystalline goethites (α-FeOOH)     

Kaufhold  Stephan  Ufer  Kristian  Hein  Melanie  Götze  Niko  Dohrmann  Reiner 《中国地球化学学报》2022,41(5):794-810

Acta Geochimica - Goethite (α-FeOOH) is one of the most abundant minerals on the Earth surface, occurring in temperate, tropical and equatorial climates. Fe in goethite can be substituted by...  相似文献   

A Monograph of the Fossil Reptilia of the Liassic Formations by Richard Owen. Cambridge University Press,Cambridge, 2015. No. of pages: 249. Price: UK£25‐00. ISBN: 9781108081351 (paperback).     

Melanie A. D. During 《Geological Journal》2016,51(6):971-971

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中国不同气候区基于火险气象指数的火险概率模型   总被引：2，自引：0，他引：2  

李晓炜  傅国斌  于秀波  赵刚  Derek EAMUS  于强 《资源与生态学报(英文版)》2012,3(2):105-117

目前,森林火险气象指数被广泛用于世界多个国家和地区.本研究目的为,基于火险气象指数,在中国不同气候区建立火险概率模型.本文在中国4个气候区,使用1998-2007年的气象及火灾数据,以位置变量、月份、海拔、加拿大、美国及澳大利亚的气象火险指数、植被指数为自变量,建立了半参数化Logistic回归模型,分析各自变量与着火概率及大火发生概率之间的非线性关系.在不同区域,模型所选自变量组合不同,这与各气候区不同气象及植被状况有关.通过模型模拟数据和实际观测数据散点图、火险概率图、大面积火灾数量预报曲线图,分析了模型的预测能力.研究结果表明,在4个气候区,海拔和NDVI指数对着火概率影响显著.模拟可燃物含水量的气象火险指数由于反映出了植被的季节变化特征,在中国北部成为火险概率模型中的重要因子.模拟土壤有机层可燃物状况的火险气象指数在中国南部(东南、西南)成为火险概率模型的重要因子.在中国4个气候区,应用半参数化Logistic回归模型,可以有效模拟月时间尺度着火概率及大火发生概率,并为分析火险气象指数的预报能力提供了有效途径.本研究为进一步分析气候与火险之间的动态关系提供了理论基础.  相似文献   

Plant root traits affecting the resistance of soils to concentrated flow erosion   总被引：5，自引：0，他引：5  

Melanie Burylo  Freddy Rey  Nicolle Mathys  Thierry Dutoit 《地球表面变化过程与地形》2012,37(14):1463-1470

The effect of plant species on erosion processes may be decisive for long‐term soil protection in degraded ecosystems. The identification of functional effect traits that predict species ability for erosion control would be of great interest for ecological restoration purposes. Flume experiments were carried out to investigate the effect of the root systems of three species having contrasted ecological requirements from eroded marly lands of the French Southern Alps [i.e. Robinia pseudo acacia (tree), Pinus nigra austriaca (tree) and Achnatherum calamagrostis (grass)], on concentrated flow erosion rates. Ten functional traits, describing plant morphological and biomechanical features, were measured on each tested sample. Analyses were performed to identify traits that determine plant root effects on erosion control. Erosion rates were lowest for samples of Robinia pseudo acacia, intermediate in Achnatherum calamagrostis and highest in Pinus nigra austriaca. The three species also differed strongly in their traits. Principal components analysis showed that the erosion‐reducing potential of plant species was negatively correlated to root diameter and positively correlated to the percentage of fine roots. The results highlighted the role of small flexible roots in root reinforcement processes, and suggested the importance of high root surface and higher tensile strength for soil stabilization. By combining flume experiment to plant functional traits measurements, we identified root system features influencing plant species performance for soil protection against concentrated flow erosion. Plant functional traits related to species efficiency for erosion control represent useful tools to improve the diagnosis of land vulnerability to erosion, plant community resistance and the prediction of ecosystem functioning after ecological restoration. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Diatom habitats,species diversity and water-depth inference models across surface-sediment transects in Worth Lake,northwest Ontario,Canada     

Kathleen R. Laird  Melanie V. Kingsbury  Brian F. Cumming 《Journal of Paleolimnology》2010,44(4):1009-1024

We analyzed surface-sediment samples collected along transects from three sub-basins of a relatively large (~115 ha), bathymetrically complex lake, in northwest Ontario, Canada, to assess the reproducibility of diatom species habitats and diversity along a water-depth gradient. Transects displayed different orientations with respect to prevailing wind direction and varied in complexity and degree of slope along the lake bottom. Each transect consisted of three replicate samples at a resolution of ~1 m water depth from ~1 to 30 m for the two deep-basin transects and from ~1 to 18 m in the shallower basin. Distinct diatom assemblages were identified in all transects: (1) a near-shore community composed largely of attached life-forms and some motile benthic taxa, (2) a mid-depth community composed largely of motile life-forms and other benthic taxa that are adapted to lower light conditions (e.g. Staurosirella pinnata), and (3) a deep-water community dominated by planktonic taxa. Species richness was highest in the benthic zones (<9 m), with greatest species evenness in the mid-depth zone (~3–9 m). Species richness and evenness were highly correlated across the three transects (r = 0.89–0.93, p < 0.01). Diatom-inferred depth models were developed from the individual transects to assess reproducibility and applicability for down-core analyses using modern analog (MAT) and weighted-averaging (WA-PLS) approaches. Coefficients of determination (r ²) for these models ranged from 0.80 to 0.98, and RMSEP ranged from 1.2 to 4.2 m. The models developed from the transect with the highest resolution sampling, gentlest non-complex slope and shallowest maximum depth were the strongest ( r_\textMAT² = 0.97 r_{\text{MAT}}^{2} = 0.97 ; r_{\textWA - PLS}² = 0.98 r_{\text{WA - PLS}}^{2} = 0.98 ) and had the lowest RMSEP (MAT = 1.2 m, WA-PLS = 1.3 m). These inference models can be used to infer past fluctuations in the depth of the benthic/planktonic boundary from cores retrieved near this ecotone and provide a sensitive record of the past change in location of the benthic zone. These types of data can be used to assess past variability in droughts and lake levels to better plan for potential future extremes. Such records incorporate more realistic estimates of natural variability than the ~100-year instrumental records currently used by water resource managers.  相似文献   

Entanglements of marine mammals and seabirds in central California and the north-west coast of the United States 2001-2005     

Emma Moore  Shannon Lyday  Kate Litle  Hannah Nevins  Joe Mortenson  Melanie Piazza  Derek Lee  Sarah Allen 《Marine pollution bulletin》2009,58(7):1045-1051

Entanglement records for seabirds and marine mammals were investigated for the period 2001-2005. The entanglement records were extracted from databases maintained by seven organizations operating along the west coast of the United States of America. Their programmes included beach monitoring surveys, rescue and rehabilitation and regional pinniped censuses. Records of 454 entanglements were documented in live animals and in carcasses for 31 bird species and nine marine mammal species. The most frequently entangled species were Common Murres, Western Gulls and California sea lions. The entanglement materials identified were primarily fishing related. Entanglements were recorded every year suggesting that although the incidence level differs annually, entanglement is a persistent problem. It is recommended that each programme records details in standardized categories to determine entanglement material sources. Numbers of entanglements observed during these surveys are likely to be a conservative view of the actual entanglement rate taking place at sea.  相似文献