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21.
Successful natural resource management increasingly requires collaboration across boundaries and between diverse stakeholder groups, and trust is a key ingredient of successful collaboration. This study represents an early qualitative empirical attempt to understand how different forms of trust develop, function, and interact in collaborative natural resource management initiatives. We conducted case studies of four landscape-level initiatives in the Collaborative Forest Landscape Restoration Program (CFLRP). Our results suggest that three forms of trust, affinitive, rational, and procedural trust, were all important for successful collaboration, but different forms of trust appeared to function more powerfully during convening, recruitment, retention, and ongoing collaboration of stakeholders, with affinitive trust particularly important for convening, and rational and procedural trust gaining importance for recruiting and retention of members. We discuss the implications of the findings in both theoretical and practical terms.  相似文献   
22.
Massachusetts Bay, a semi-enclosed embayment (50×100 km) in the Northwest Atlantic, is the focus of a monitoring program designed to measure the effects of relocating the Boston Harbor sewage outfall to a site 15 km offshore in Massachusetts Bay. The Massachusetts Water Resources Authority (MWRA) in situ monitoring program samples selected stations up to 17 times per year to observe seasonal changes in phytoplankton biomass and other water quality variables. We investigated the feasibility of augmenting the monitoring data with satellite ocean color data to increase the spatial and temporal resolution of quantitative phytoplankton measurements. In coastal regions such as Massachusetts Bay, ocean color remote sensing can be complicated by in-water constituents whose concentrations vary independently of phytoplankton and by inaccurate modeling of absorbing aerosols that tend to be concentrated near the coast. An evaluation of in situ and sea-viewing wide field-of-view sensor (SeaWiFS) measurements from 1998 to 2005 demonstrated that SeaWiFS overestimated chlorophyll a mainly due to atmospheric correction errors that were amplified by absorption from elevated concentrations of chlorophyll a and colored dissolved organic matter. Negative water-leaving radiances in the 412 nm band, an obvious artifact of inadequate atmospheric correction, were recorded in approximately 60–80% of the cloud-free images along the coast, while the remaining portions of the Bay only experience negative radiances 35–55% of the time with a clear nearshore to offshore decrease in frequency. Seasonally, the greatest occurrences of negative 412 nm radiances were in November and December and the lowest were recorded during the summer months. Concentrations of suspended solids in Massachusetts Bay were low compared with other coastal regions and did not have a significant impact on SeaWiFS chlorophyll a measurements. A regional empirical algorithm was developed to correct the SeaWiFS data to agree with in situ observations. Monthly SeaWiFS composites illustrated the spatial extent of a bimodal seasonal pattern, including prominent spring and fall phytoplankton blooms; and the approximate 115 cloud-free scenes per year revealed interannual variations in the timing, magnitude and duration of phytoplankton blooms. Despite known artifacts of SeaWiFS in coastal regions, this study provided a viable chlorophyll a product in Massachusetts Bay that significantly increased the spatial and temporal synoptic coverage of phytoplankton biomass, which can be used to gain a comprehensive ecosystem-wide understanding of phytoplankton dynamics at event, seasonal and interannual timescales.  相似文献   
23.
New high-resolution spectra in the 0.33 to 0.92 μm range of Iapetus, Hyperion, Phoebe, Dione, Rhea, and three D-type asteroids were obtained on the Palomar 200-inch telescope and the double spectrograph. The spectra of Hyperion and the low-albedo hemisphere of Iapetus can both be closely matched by a simple model that is the linear admixture of the spectrum of a medium-sized, high-albedo icy saturnian satellite and D-type material. Our results support an exogenous origin to the dark material on Iapetus; furthermore, this material may share a common origin and a similar means of transport with material on the surface of Hyperion. The recently discovered retrograde satellites of Saturn (Gladman et al., Nature412, 163-166) may be the source of this material. The leading sides of Callisto and the Uranian satellites may be subjected to a similar alteration mechanism as that of Iapetus: accretion of low-albedo dust originating from outer retrograde satellites. Phoebe does not appear to be related to either Iapetus or Hyperion. Separate spectra of the two hemispheres of Phoebe show no identifiable global compositional differences.  相似文献   
24.
Optical and near-IR signatures of water ice on the Moon's surface were sought in the permanently shadowed regions near its poles. Significant amounts of multiply-scattered radiation partly illuminate primary shadows cast by craters and other features. If there is water ice in the permanently shadowed regions of the Moon's surface, its spectral signature should appear in this multiply-scattered light. This investigation can be done most effectively with observations obtained by spacecraft, because most selenocentric positions occupied by the Earth will also be occupied by the Sun at some point in time, and because the lunar poles are seen only obliquely to a terrestrial observer. Images obtained by Clementine are particularly well-suited to this task, because the spacecraft's polar orbit allowed images of the poles to be acquired on nearly every orbit, resulting in literally thousands of images taken within a few degrees of each pole, and because the filters on the ultraviolet-visual camera (UVVIS) and the near infrared camera (NIR) occur at major absorption bands or within important continuum features of water ice. Approximately 5800 images obtained by the UVVIS camera and 1800 images obtained by the NIR camera were calibrated and combined into coadded mosaics to create multispectral maps of the lunar poles with the highest possible signal-to-noise. Unfortunately, analysis of our UVVIS mosaics indicates that any possible signal from multiply-scattered light in primary shadows was overwhelmed by instrumental stray light. For the NIR camera, we were able to determine the normalized reflectance of several regions that were identified by Margot et al. (1999, Science284, 1658-1660) as permanent shadows. We have identified one permanently shadowed crater with a 1.5-μm band spectral signature indicative of between 2.5 and 21% fractional coverage of H2O frost. However, the same region shows a 2.0 μm spectral signature that is inconsistent with the presence of any water.  相似文献   
25.
Urban forest management is being increasingly recognized as a viable policy vehicle for improving community health, sustainable development, and well-being for city dwellers. To improve our understanding of public concern for the local urban forest, a theoretical framework employing concepts traditionally explored in social–psychological and environmental concern studies was tested using data from a public opinion survey of 800 homeowners living in a major urban area in Southern Appalachia, USA. Publicly available geographic information system (GIS) data were analyzed to measure tree canopy density around survey respondents’ properties. Structural equation modeling was used to test the validity of the hypothesized relationships among the survey-derived constructs and the spatial data as predictors of public support for urban forest protection policy. The results suggest that homeowners living around urban trees place greater importance on various attributes of trees, and that tree knowledge and experience are indirectly and positively related to support for urban forest protection.  相似文献   
26.
The mechanism by which olivine grains became embedded within iron‐nickel alloy in pallasite meteorites continues to be a matter of scientific debate. Geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals; however, little research attention has been devoted to their crystallographic orientations within the metal matrix. Using electron backscatter diffraction, we have collected crystallographic orientation data for 296 crystals within ~65 cm2 sample surface from Springwater. Though no global crystallographic preferred orientation exists, very low misorientations are observed among [100] axes of olivine crystals within specific texturally defined domains. Combined with a thorough characterization of large‐scale Springwater textures, the definitively nonrandom spatial distribution of olivine orientations provides clues regarding the nature of the olivine's initial formation environment as well as the sequence of events subsequent to metal incorporation.  相似文献   
27.
The efficacy of water quality policies aiming to reduce or prevent nitrate contamination of waterbodies may be constrained by the inherent delay or “time lag” of water and solute transport through unsaturated (soil) and saturated (groundwater) pathways. These delays must be quantified in order to establish realistic deadlines, thresholds and policy expectations, and to design effective best management practices. The objective of this review is to synthesise the current state of research on nitrate-related time lags in both the European and North American environmental and legislative contexts. The durations of time lags have been found to differ according to climatic, pedological, landscape and management scenarios. Elucidation of these driving factors at a watershed scale is essential where water quality is impaired or at risk. Finally, the existence of time lags is increasingly being acknowledged at a policy level and incorporated into the development of environmental legislation. However, the full impact of these time lags is not yet fully understood or appreciated, and continued outreach and education in scientific, public and policy venues is still required.  相似文献   
28.
We measured the effects of a plant invasion (Phragmites australis) on resident fish (Fundulus heteroclitus) in New England salt marshes by assessing diet quality at the food web base and by quantifying the importance of primary producers to secondary production using a recently developed Bayesian mixing model (Stable Isotope Analysis in R, “SIAR”). Spartina alterniflora, the dominant native plant, exhibited significantly greater leaf toughness and higher C/N ratios relative to P. australis. Benthic microalgae and phytoplankton (as suspended particulate matter) exhibited the lowest C/N indicating higher diet quality. We conducted a sensitivity analysis in SIAR by modeling F. heteroclitus at three separate trophic levels (1.5, 2.0, and 2.5) using species-specific discrimination factors to determine basal resource contributions. Overall, the best-fitting models include those that assume F. heteroclitus resides approximately 2.0 trophic levels above primary producers. Using discrimination factors from a range of data sources reported in the literature, our analyses revealed that consumers rely less on benthic microalgae and phytoplankton in restricted marshes (7–23 % and 11–44 %, respectively) relative to reference marshes (5–34 % and 23–48 %, respectively), resulting in a shift in diet toward invasive plant consumption (0–27 %). This is likely due to increased P. australis cover and marsh surface shading leading to decreased microalgal biomass, combined with reduced flooding of the marsh surface that favors terrestrial invertebrate assemblages. Restoration decreased the quantity of P. australis in the food web (0–15 %) and increased the importance of microalgae (1–30 %), phytoplankton (19–48 %), and native plants (23–63 %), indicating a shift in ecological recovery toward reference conditions.  相似文献   
29.
We investigated cloud properties of warm clouds in a tropical montane cloud forest at Pico del Este (1,051 m a.s.l.) in the northeastern part of Puerto Rico to address the question of whether cloud properties in the Caribbean could potentially be affected by African dust transported across the Atlantic Ocean. We analyzed data collected during 12 days in July 2011. Cloud droplet size spectra were measured using the FM-100 fog droplet spectrometer that measured droplet size distributions in the range from 2 to 49 µm, primarily during fog events. The droplet size spectra revealed a bimodal structure, with the first peak (D < 6 µm) being more pronounced in terms of droplet number concentrations, whereas the second peak (10 µm < D < 20 µm) was found to be the one relevant for total liquid water content (LWC) of the cloud. We identified three major clusters of characteristic droplet size spectra by means of hierarchical clustering. All clusters differed significantly from each other in droplet number concentration ( \(N_{\rm tot}\) ), effective diameter (ED), and median volume diameter (MVD). For the cluster comprising the largest droplets and the lowest droplet number concentrations, we found evidence of inhomogeneous mixing in the cloud. Contrastingly, the other two clusters revealed microphysical behavior, which could be expected under homogeneous mixing conditions. For those conditions, an increase in cloud condensation nuclei—e.g., from processed African dust transported to the site—is supposed to lead to an increased droplet concentration. In fact, one of these two clusters showed a clear shift of cloud droplet size spectra towards smaller droplet diameters. Since this cluster occurred during periods with strong evidence for the presence of long-range transported African dust, we hypothesize a link between the observed dust episodes and cloud characteristics in the Caribbean at our site, which is similar to the anthropogenic aerosol indirect effect.  相似文献   
30.
Explosive activity at Lathrop Wells volcano, Nevada, U.S.A. originated with weak Strombolian (WS) eruptions along a short fissure, and transitioned to violent Strombolian (VS) activity from a central vent, with lava effusion during both stages. The cause for this transition is unknown; it does not reflect a compositional change, as evidenced by the consistent bulk geochemistry of all the eruptive products. However, comparison of agglutinate samples from the early, WS events with samples of scoria from the later, VS events reveal differences in the abundance and morphology of groundmass phases and variable textures in the rims of olivine phenocrysts. Scanning electron microscope (SEM) examination of thin sections from the WS samples show euhedral magnetite microlites in the groundmass glass and olivine phenocrysts show symplectite lamellae in their rims. Secondary ion mass spectrometry (SIMS) depth profiles of these symplectites indicate they are diffusion-controlled. The calculated DFe-Mg allows an estimation of the oxygen fugacity (fO2) and indicates an increased fO2 during eruption of the WS products. Conversely, the VS samples show virtually no magnetite microlites in the groundmass glass, a lack of symplectites in the olivines, and a lower calculated fO2. These microtextural features suggest that the Lathrop Wells trachybasalt experienced increased oxidation during WS activity. As magma ascended through the original fissure, exsolved bubbles were concentrated in the wider part(s) (the protoconduit) and this bubble flux drove convective circulation that oxidized the magma through exposure to atmosphere and recirculation. This oxidation resulted in groundmass crystallization of magnetite within the melt and formation of symplectites within the olivine phenocrysts. Bubble-driven convection mixed magma vertically within the protoconduit, keeping it fluid and driving Strombolian bursts, while microlite crystallization in narrower parts of the fissure helped to focus flow. Development of a central conduit increased the magma ascent velocity (due to a greater product volume in the later eruptive stages) and caused the shift in eruption intensity. Consequently, variations in microtextures of the Lathrop Wells products reveal how a combination of fluid dynamic and crystallization processes in the ascending magma resulted in different styles of activity while the products maintained a consistent bulk composition.  相似文献   
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