Evaluation of high-resolution simulations of daily-scale temperature and precipitation over the United States   总被引：1，自引：0，他引：1  

Megan D. Walker  Noah S. Diffenbaugh 《Climate Dynamics》2009,33(7-8):1131-1147

Extreme climate events have been increasing over much of the world, and dynamical models predict further increases in response to enhanced greenhouse forcing. We examine the ability of a high-resolution nested climate model, RegCM3, to capture the statistics of daily-scale temperature and precipitation events over the conterminous United States, using observational and reanalysis data for comparison. Our analyses reveal that RegCM3 captures the pattern of mean, interannual variability, and trend in the tails of the daily temperature and precipitation distributions. However, consistent biases do exist, including wet biases in the topographically-complex regions of the western United States and hot biases in the southern and central United States. The biases in heavy precipitation in the western United States are associated with excessively strong surface and low-level winds. The biases in daily-scale temperature and precipitation in the southcentral United States are at least partially driven by biases in circulation and moisture fields. Further, the areas of agreement and disagreement with the observational data are not intuitive from analyzing the simulated mean seasonal temperature and precipitation fields alone. Our evaluation should enable more informed application and improvement of high-resolution climate models for the study of future changes in socially- and economically-relevant temperature and precipitation events.  相似文献   

Postglacial vegetation, climate, and fire history along the east side of the Andes (lat 41-42.5°S), Argentina     

Cathy Whitlock  Maria Martha Bianchi  Vera Markgraf  Megan Walsh 《Quaternary Research》2006,66(2):187-201

The history of the low-elevation forest and forest-steppe ecotone on the east side of the Andes is revealed in pollen and charcoal records obtained from mid-latitude lakes. Prior to 15,000 cal yr BP, the vegetation was characterized by steppe vegetation with isolated stands of Nothofagus. The climate was generally dry, and the sparse vegetation apparently lacked sufficient fuels to burn extensively. After 15,000 cal yr BP, a mixture of Nothofagus forest and shrubland/steppe developed. Fire activity increased between 13,250 and 11,400 cal yr BP, contemporaneous with a regionally defined cold dry period (Huelmo/Mascardi Cold Reversal). The early-Holocene period was characterized by an open Nothofagus forest/shrubland mosaic, and fire frequency was high in dry sites and low in wet sites; the data suggest a sharp decrease in moisture eastward from the Andes. A shift to a surface-fire regime occurred at 7500 cal yr BP at the wet site and at 4400 cal yr BP at the dry site, preceding the expansion of Austrocedrus by 1000-1500 yr. The spread of Austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late Holocene. The change to a surface-fire regime is consistent with increased interannual climate variability and the onset or strengthening of ENSO. The present-day mixed forest dominated by Nothofagus and Austrocedrus was established in the last few millennia.  相似文献   

Molecular and compound-specific isotopic characterization of monocarboxylic acids in carbonaceous meteorites     

Yongsong Huang  Yi Wang  Taewoo Lee  Megan Fuller 《Geochimica et cosmochimica acta》2005,69(4):1073-1084

Low molecular weight monocarboxylic acids are the most abundant water soluble organic compounds in the Murchison and many other CM type carbonaceous chondrites. In this study, we examined the monocarboxylic acids in Murchison and EET96029.20 carbonaceous meteorites using a new sample preparation and introduction technique for gas chromatograph recently developed for volatile, water-soluble organic compounds: solid phase micro-extraction (SPME). We identified more than 50 monocarboxylic acids from Murchison compared with the 18 compounds reported previously. Formic acid, a known interstellar molecule, has been fully analyzed in these carbonaceous meteorites, with its δD value suggesting an interstellar origin. We determined both carbon and hydrogen isotopic ratios of individual monocarboxylic acids in Murchison, to better define the origins and genetic relationships of these compounds. The compound-specific isotopic data reveal a large enrichment in ¹³C (δ¹³C up to + 32.5‰) and particularly D (δD up to + 2024‰). The branched acids are substantially enriched in both ¹³C and D relative to the straight chain acids, with those branched acids containing a quaternary carbon showing the greatest isotopic enrichment. The isotopic difference may be attributed to variations in the different synthetic regimes or terrestrial input of straight chain acids.  相似文献   

Inhibition of coral photosynthesis by the antifouling herbicide Irgarol 1051   总被引：1，自引：0，他引：1  

Owen R  Knap A  Toaspern M  Carbery K 《Marine pollution bulletin》2002,44(7):623-632

International regulation of organotin compounds for use in antifouling paints has led to the development and increased use of replacement compounds, notably the s-triazine herbicide Irgarol 1051. Little is known about the distribution of Irgarol 1051 in tropical waters. Nor has the potential impact of this triazine upon photosynthesis of endosymbiotic microalgae (zooxanthellae) in corals been assessed. In this study Irgarol 1051 was detected in marinas, harbours and coastal waters of the Florida Keys, Bermuda and St. Croix, with concentrations ranging between 3 and 294 ng 1(-1). 14C incubation experiments with isolated zooxanthellae from the common inshore coral Madracis mirabilis showed no incorporation of H14CO3- from the sea water medium after 4-8 h exposure to Irgarol 1051 concentrations as low as 63 ng 1(-1). Reduction in net photosynthesis of intact corals was found at concentrations of l00 ng 1(-1) with little or no photosynthesis at concentrations exceeding 1000 ng 1(-1) after 2-8 h exposure at all irradiances. The data suggest Irgarol 1051 to be both prevalent in tropical marine ecosystems and a potent inhibitor of coral photosynthesis at environmentally relevant concentrations.  相似文献   

Integrated,Regional, Natural Resource and Environmental Planning and the Natural Heritage Trust Phase 2: a case study of the Northern Agricultural Catchments Council,Western Australia     

Megan Farrelly 《The Australian geographer》2007,38(3):309-333

Since 2002, the Australian Natural Heritage Trust Phase 2 (NHT2) has required community groups seeking funds for natural resource management projects to have developed nationally accredited regional strategies and investment plans. This case study reports on the progress of one such regional (and sub-regional) group, examining in particular the perceptions of the community group members and other stakeholders of the overall process. Through interviews, participant observation and document analysis in 2004–05, the process of developing a regional strategy and an investment plan by the Northern Agricultural Catchments Council in Western Australia, and the involvement of regional stakeholders in the process, were examined. While the concept of regional-scale management was perceived favourably by community interviewees, their concerns related to increasing bureaucracy, the need for further local involvement, more on-ground action instead of further planning, the relevance of the regional Council to local communities, and the motives of Council members. Communication with regional stakeholders was extensive in preparing the regional strategy, but fell short during the development of the investment plan. The success of the regional planning process will be evidenced by whether members of the regional community actively implement regional priorities, and whether long-term funding and support from the State and Australian governments are provided.  相似文献   

Assessing functional equivalency of nekton habitat in enhanced habitats: Comparison of terraced and unterraced marsh ponds     

Megan K. La Peyre  Bryan Gossman  John A. Nyman 《Estuaries and Coasts》2007,30(3):526-536

A primary goal of many coastal restoration programs is to increase nekton habitat in terms of both quantity and quality. Using shallow water ponds rehabilitated with a technique called marsh terracing, we examined the quality of nekton habitat created, using and comparing several metrics including nekton density and diversity, functional group composition, and weight-length relationships as indirect measures of habitat quality. We examined three paired terraced and unterraced marsh ponds in southwest Louisiana. Nekton, submerged aquatic vegetation (SAV), and soil and water quality variables were sampled bimonthly from April 2004 through April 2005 at four subtidal habitat types: terraced nearshore, terraced open water, unterraced nearshore, and unterraced open water. Results indicate that terraced ponds had increased the habitat value of degrading unterraced ponds over open water areas for estuarine nekton; nekton density and richness were similar between terraced and unterraced nearshore habitat types, but greater at all nearshore as compared to open water sites. Analysis of the distribution of nekton functional groups and weight:length ratios indicates the terraced and unterraced pond habitats were not functioning similarly: distribution of nekton functional groups differed significantly between habitat types with greater percentages of benthic-oriented species at unterraced open water habitats and higher percentage of open water species in terraced ponds as compared to unterraced ponds, and two of the six numerically dominant fish species had greater weight-length relationships in unterraced ponds as compared to terraced ponds. This lack of functional equivalency may be attributed to environmental differences between terraced and unterraced ponds such as water depth or SAV biomass, or the relatively young age of the terraces studied, which may not have allowed for the development of some critical habitat variables, such as soil organic matter that was found to be significantly lower in terraced versus unterraced ponds (p < 0.05). To properly assess the ecological equivalency of restored or rehabilitated sites for nekton requires that we move beyond measures of nekton density, biomass, and diversity and incorporate measures of functional equivalency, including habitat measures.  相似文献   

A 14,300-year-long record of fire-vegetation-climate linkages at Battle Ground Lake, southwestern Washington   总被引：1，自引：0，他引：1  

Megan K. Walsh  Cathy Whitlock 《Quaternary Research》2008,70(2):251-264

High-resolution macroscopic charcoal analysis was used to reconstruct a 14,300-year-long fire history record from the lower Columbia River Valley in southwestern Washington, which was compared to a previous vegetation reconstruction for the site. In the late-glacial period (ca. 14,300-13,100 cal yr BP), Pinus/Picea-dominated parkland supported little to no fire activity. From the late-glacial to the early Holocene (ca. 13,100-10,800 cal yr BP), Pseudotsuga/Abies-dominated forest featured more frequent fire episodes that burned mostly woody vegetation. In the early to middle Holocene (ca. 10,800-5200 cal yr BP), Quercus-dominated savanna was associated with frequent fire episodes of low-to-moderate severity, with an increased herbaceous (i.e., grass) charcoal content. From the middle to late Holocene (ca. 5200 cal yr BP to present), forest dominated by Pseudotsuga, Thuja-type, and Tsuga heterophylla supported less frequent, but mostly large or high-severity fire episodes. Fire episodes were least frequent, but were largest or most severe, after ca. 2500 cal yr BP. The fire history at Battle Ground Lake was apparently driven by climate, directly through the length and severity of the fire season, and indirectly through climate-driven vegetation shifts, which affected available fuel biomass.  相似文献   

Recruitment of Estuarine-Dependent Nekton Through a New Tidal Inlet: the Opening of Packery Channel in Corpus Christi,TX, USA     

Megan M. Reese  Gregory W. Stunz  Amanda M. Bushon 《Estuaries and Coasts》2008,31(6):1143-1157

The US Army Corps of Engineers recently dredged and permanently reopened Packery Channel, historically a natural tidal inlet, to allow water exchange between the Gulf of Mexico and the Laguna Madre, TX, USA. The main objective of this study was to characterize estuarine-dependent recruitment and community structure in seagrass habitats adjacent to Packery Channel pre- and post-channel opening. We sampled fish and crustacean abundance using an epibenthic sled in Halodule wrightii seagrass meadows in both control and impact locations over 2 years, 1 year before the opening of Packery Channel (October 2004–May 2005) and 1 year after (July 2005–April 2006). Using the before–after control–impact design, we found significantly fewer nekton post-channel opening. However, we found significantly higher mean densities of newly settled estuarine-dependent species (Sciaenops ocellatus, Micropogonias undulatus, Lagodon rhomboides, Callinectes sapidus, and penaeid shrimp) post-opening. Multivariate analyses showed significant community assemblage changes post-opening with increased contribution of estuarine-dependent species post-opening. Our results show that estuarine-dependent nekton are using Packery Channel as a means of ingress into areas of the upper Laguna Madre’s seagrass meadows that were previously inaccessible, which may lead to higher fisheries productivity for some of these economically and ecologically important fishery species.  相似文献   

Pathways for Participatory Water Governance in Ashaiman,Ghana: Learning from Institutional Bricolage and Hydrosocial Perspectives   总被引：1，自引：0，他引：1  

Megan M. Peloso  Leila M. Harris 《社会与自然资源》2017,30(12):1491-1506

Coupling a hydrosocial perspective with institutional bricolage, this research considers possibilities for participatory water governance in Ashaiman, a peri-urban settlement of Accra, Ghana. We explore three questions: (1) How do people in Ashaiman evoke ideas or experiences of water in general and water governance in particular? (2) What possibilities currently exist for engaging the community in key water-related decisions? (3) What possibilities exist for enhanced participatory water governance in this context, including potential for and interest in new institutions and engagement processes? Results of qualitative interviews and semistructured observation suggest that a siloed, water-centric approach inadequately captures everyday realities of water as hydrosocial and of existing institutions in Ashaiman. In contrast to “modern water,” we propose that water issues may be more meaningfully addressed as bundled with social welfare. Potential implications and alternative ways of understanding socio-institutional arrangements for participatory water governance are explored.  相似文献   

The Impact of Climate Change on the Viticultural Suitability of Maipo Valley,Chile     

Megan Mills-Novoa  Philippo Pszczólkowski  Francisco Meza 《The Professional geographer》2016,68(4):561-573

This study uses the case of the Maipo Valley in Chile to examine how climate change will affect viticultural suitability. Using a geographic information system analysis of topographic, soil, land use, and climate data, a baseline assessment of viticultural suitability in the Maipo Valley was performed. The impact of climate change on viticultural suitability was modeled by overlaying downscaled global circulation model temperature data for two emission scenarios. The findings of this study suggest that the capacity of vineyard managers in the Maipo Valley to cultivate high-quality traditional grape varietals from cooler grape maturity classes might be limited in the future.  相似文献