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891.
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   
892.
Athabasca and Marte Valles lie on the Cerberus plains, between the young, lava-covered plains of Elysium Planitia and Amazonis Planitia. To test pre-MGS (Mars Global Surveyor) suggestions of extremely young volcanic and fluvial activity, we present the first crater counts from MGS imagery, at resolutions (∼2-20 m/pixel) much higher than previously available. The most striking result, based on morphologic relations as well as crater counts from different stratigraphic units, is to confirm quantitatively that these channel systems are much younger than most other major outflow channels. The general region has an average model age for lava and fluvial surfaces of ≤200 Myr, and has possibly seen localized water releases, interspersed with lava flows, within the past 20 Myr. The youngest lavas may be no more than a few megayears old. Access of lava and liquid brines to the surface may be favored by openings of the Cerberus Fossae fracture system, but, as shown in the new images, the fractures appear to have continued developing more recently than the most recent lavas or fluvial activity. The Cerberus Fossae system may be an analog to an early stage of Valles Marineris, and its youthful activity raises questions about regional tectonic history. Large-volume water delivery to the surface of young lava flows in recent martian history puts significant boundary conditions on the storage and history of water on Mars.  相似文献   
893.
Petrological, faunal and floral information derived from a new drill core taken in the Yangtze delta, coupled with data from borings recovered earlier, record a marked transition to warmer, wetter conditions which resulted in widespread inundation of the delta about 4000 years ago. Also identified for that time on the delta plain is a major discontinuity between the Neolithic Liangzhu and Bronze age Maqiao cultures. The cultural discontinuity is indicated by: (1) absence of in situ material between the two at ∼4000 yr B.P.; (2) missing Maqiao material in strata above many Liangzhu sites; (3) less sophisticated Maqiao material than in the older Neolithic phase; and (4) notably fewer Maqiao sites in more restricted areas of the delta plain. It is of note that the change from the Liangzhu to the younger Maqiao does not show an increasingly complex cultural advancement of the type generally associated with the foundation of Chinese civilization. We propose that this cultural discontinuity was caused by the interplay of increased environmental stress and new population migrations into the delta. © 1999 John Wiley & Sons, Inc.  相似文献   
894.
Many oases(wet interdunes)are sedimentary systems characterized by high-frequency water-level oscillations,marked changes in salinity and intense biological activity at their margins.They are considered to be one of the most challenging environments on Earth for ecosystem development.These dynamic,depositional settings are usually unfavourable for fossilization and subsequent preservation of vegetal remains.This paper describes bryophyte(liverwort)assemblages occurring in three successive horizons interpreted to represent(i)recurrent early successional phases of biological soil crust colonization of wet interdune margins or(ii)exceptional preservation of floating or riparian liverworts in oasis pond waters associated with a progressive fall of the interdune water level.The record of in situ colonization surfaces characterized by delicate(e.g.lignin-free)three-dimensional structures represents an exceptional type of preservation herein associated with a rapid variation in phreatic interdune water level and the subsequent establishment of anoxic and reducing conditions.The occurrence of exceptionally preserved liverwort colonies coincides with the sedimentary record of,at least,three seismite levels in the oasis.Data gathered from the site suggests that the water table of the oasis was controlled by a combination of(i)a positive creation of accommodation space due to subsidence associated with movement on syn-sedimentary extensional faults,and(ii)the rise and fall of the oasis water table controlled by the oscillations of the groundwater system due to orbital changes which appear to drive the variability of the climate system.Rising groundwater levels flooded the oasis soil crusts and lead to the exceptional recurrent preservation of liverwort colonies at the oasis margins.Alternatively,considering the hypothesis of floating or riparian liverworts in the oasis pond waters,the fall in the level of the oasis water table placed the floating liverworts in contact with the oasis bottom sediments.This fall in the level of the oasis water table could indicate a cessation of accommodation space by syn-sedimentary extensional faults and/or a regional lowering of the groundwater system level associated with drought periods.Preliminary results indicate that oasis lamination between liverwort colonies records decadal and sub-decadal cyclicity,related with 11-year Schwabe sunspot and sub-decadal NAO cyclicities,conferring for every sedimentary cycle between liverwort colonies a duration of approximately 200 years,that otherwise matches the expected recurrence period for the De Vries cycle of solar activity.  相似文献   
895.
The Florida Keys National Marine Sanctuary (FKNMS) developed a zoning plan as part of its overall management plan, fully implemented as of 1997. The plan created several closed areas or harvest refugia in which consumptive activities are prohibited. This research reports results of surveys that we conducted with members of three stakeholder groups in the Florida Keys: commercial fishers, dive operators, and members of local environmental groups. Surveys requested responses regarding the information sources individuals tapped when learning of the zoning plan and the FKNMS; their degree of public participation; their perceptions and acceptance of the zoning strategy and the process of its design; and the expected outcomes of the zoning strategy. Many responses show significant differences among the three groups. Fishers felt highly alienated from the process of zone designation and displayed a sense of anger and powerlessness with respect to what they considered to be an attempt to exclude their group from the harvest refugia. Dive operators demonstrated the highest levels of participation in the designation process, but were concerned that refugia regulations could limit their activities in the future. Members of environmental groups were the strongest supporters of the harvest refugia concept and the FKNMS. This research suggests numerous ways in which marine resource managers could improve their public outreach and information dissemination strategies when developing future harvest refugia and marine protected areas.  相似文献   
896.
Agricultural land management requires strategies to reduce impacts on soil and water resources while maintaining food production. Models that capture the effects of agricultural and conservation practices on soil erosion and sediment delivery can help to address this challenge. Historic records of climatic variability and agricultural change over the last century also offer valuable information for establishing extended baselines against which to evaluate management scenarios. Here, we present an approach that combines centennial‐scale reconstructions of climate and agricultural land cover with modelling across four lake catchments in the UK where radiometric dating provides a record of lake sedimentation. We compare simulations using MMF‐TWI, a catchment‐scale model developed for humid agricultural landscapes that incorporates representation of seasonal variability in vegetation cover, soil water balance, runoff and sediment contributing areas. MMF‐TWI produced mean annual sediment exports within 9–20% of sediment core‐based records without calibration and using guide parameter values to represent vegetation cover. Simulations of land management scenarios compare upland afforestation and lowland field‐scale conservation measures to reconstructed historic baselines. Oak woodland versus conifer afforestation showed similar reductions in mean annual surface runoff (8–16%) compared to current moorland vegetation but a larger reduction in sediment exports (26–46 versus 4–30%). Riparian woodland buffers reduced upland sediment yields by 15–41%, depending on understorey cover levels, but had only minor effect on surface runoff. Planting of winter cover crops in the lowland arable catchment halved historic sediment exports. Permanent grass margins applied to sets of arable fields across 15% or more of the catchment led to further significant reduction in exports. Our findings show the potential for reducing sediment delivery at the catchment scale with land management interventions. We also demonstrate how MMF‐TWI can support hydrologically‐informed decision making to better target conservation measures in humid agricultural environments. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   
897.
The potential for rising groundwater is an important consideration in any coastal resiliency assessment. Unlike other groundwater modeling that focuses mostly on contaminant tracking, coastal groundwater resiliency assessments are primarily concerned with the potential for groundwater emergence induced by sea level rise. This provides more options for modelers that range from simplified water table elevation models to fully integrated groundwater and storm water models. The selection is dependent on available data and project needs. However, despite the relative simplicity of some of the techniques, all the methods benefit from a professional with hydrogeological training.  相似文献   
898.
Investigating changes in an aquifer system often involves comparison of observed heads from different synoptic measurements, generally with potentiometric surfaces developed by hand or a statistical approach. Alternatively, head‐specified MODFLOW models, in which constant head cells simulate observed heads, generate gridded potentiometric surfaces that explicitly account for Darcy's Law and mass balance. We developed a transient head‐specified MODFLOW model for the stratified Cambrian‐Ordovician sandstone aquifer system of northeastern Illinois to analyze flow within its 275 m deep cone of depression. Potentiometric surfaces were developed using static heads from production wells regardless of open interval; hence assuming no vertical head difference. This assumption was tested against steady‐state, head‐specified models of each sandstone strata for 1980 and 2014. The results indicate that the original conceptual model was appropriate in 1980 but not 2014, where a vertical head difference had developed at the center of the cone of depression. For earlier years, when the head difference was minimal, the transient head‐specified model compared well with a traditional, flow‐specified model. In later years, the transient head‐specified model overestimated removal of water from storage. MODFLOW facilitates the development of a time‐series of potentiometric surfaces and can easily be modified to test the impacts of different conceptual models, such as assumptions on vertical head differences. For this study of a deep confined aquifer, MODFLOW also offers advantages in generating potentiometric surfaces and flow fields over statistical interpolation techniques, although future research is needed to assess its performance in other settings.  相似文献   
899.
FxJj43 differs from most other archaeological sites preserved in the Okote Member of the Koobi Fora Formation in ways that make it especially suited to the problem of clarifying the behavioral information encapsulated in fine time‐lines. At this site in northern Kenya, a continuous strip of outcrops, preserving a set of interlocking landforms, can be traced around the modern erosion front for more than half a kilometer. The characteristics and three‐dimensional geometries of the beds making up these outcrops show that they have preserved the southern bank, levee, and floodplain of a westerly flowing sandy channel. Both stone tools and animal bones are strewn across the eroding surfaces of these outcrops, and excavations show that they are derived from a narrow stratigraphic horizon immediately overlying the volcanic ash at the base of the sequence. The blue tuff, and the archaeological horizon that overlies it, have been dated using the 40Ar‐39Ar method on single crystals of alkali feldspar. Although there is no direct measure of how long it took the archaeological horizon to accumulate, it probably accumulated over a time span of 102–103 years. Thus the locality may be used to test the proposition that the analysis of archaeological debris from fine‐time lines will help to resolve ambiguities in the interpretation of early Pleistocene archaeological assemblages. © 2002 Wiley Periodicals, Inc.  相似文献   
900.
Sewer inlet structures are vital components of urban drainage systems and their operational conditions can largely affect the overall performance of the system. However, their hydraulic behaviour and the way in which it is affected by clogging is often overlooked in urban drainage models, thus leading to misrepresentation of system performance and, in particular, of flooding occurrence. In the present paper, a novel methodology is proposed to stochastically model stormwater urban drainage systems, taking the impact of sewer inlet operational conditions (e.g. clogging due to debris accumulation) on urban pluvial flooding into account. The proposed methodology comprises three main steps: (i) identification of sewer inlets most prone to clogging based upon a spatial analysis of their proximity to trees and evaluation of sewer inlet locations; (ii) Monte Carlo simulation of the capacity of inlets prone to clogging and subsequent simulation of flooding for each sewer inlet capacity scenario, and (iii) delineation of stochastic flood hazard maps. The proposed methodology was demonstrated using as case study design storms as well as two real storm events observed in the city of Coimbra (Portugal), which reportedly led to flooding in different areas of the catchment. The results show that sewer inlet capacity can indeed have a large impact on the occurrence of urban pluvial flooding and that it is essential to account for variations in sewer inlet capacity in urban drainage models. Overall, the stochastic methodology proposed in this study constitutes a useful tool for dealing with uncertainties in sewer inlet operational conditions and, as compared to more traditional deterministic approaches, it allows a more comprehensive assessment of urban pluvial flood hazard, which in turn enables better-informed flood risk assessment and management decisions.  相似文献   
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