Channel response to a dam-removal sediment pulse captured at high-temporal resolution using routine gage data

In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr⁻¹) and peak (~2.6 km yr⁻¹) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later. The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow. In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service-indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period. This study captured a two-signal response from the sediment pulse: (1) short- to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales.     

Deformation and mineralisation in the Scotty Creek Basin,Agnew district,Eastern Goldfields,Western Australia: evidence for D1- and D3-related gold mineralisation

Gold deposits in the Agnew district display markedly different structural styles. The Waroonga and Songvang deposits are hosted in layer-parallel extensional shears formed under highly ductile conditions. In contrast, the New Holland–Genesis deposits are shallow-dipping quartz-filled brittle fractures and breccia zones that cut across the tightly folded bedding and formed during east–west compression. It is difficult to attribute their formation to a single compressive event. The Waroonga and Songvang deposits formed during D₁ extension, uplift and exhumation of the Agnew granitic complex and formation of the Scotty Creek Basin at ca 2670–2660?Ma. The New Holland–Genesis deposits formed during east–west D₃ compression at about ca 2650–2630?Ma. An S₁ foliation wraps around the Agnew granitic complex and L₁ stretching lineations form a radial pattern around the granite, consistent with formation during D₁ uplift of the composite granite body. Uplift and erosion of granite bodies in the surrounding area provide a source for the granite clasts in the upper parts of the Scotty Creek Basin. As clasts in the basin are undeformed, no significant deformation occurred prior to the uplift and erosion of the source granites in this area. Syn-tectonic emplacement of the Lawlers Tonalite during formation of the Scotty Creek Basin at ca 2665?Ma may have provided a good heat/fluid source for the mineralising systems during the first gold event. The distribution of the large deposits along the western edge of the Agnew granitic complex indicates that the extensional shear along the granite contact is a first-order control on gold deposition by providing a conduit for rising hydrothermal fluids. The northerly trend of high-grade shoots in the Waroonga deposit coincides with early north-trending growth faults, which are also likely fluid conduits.     

Landowner Attitudes Toward Conservation Easements: Balancing the Private and Public Interest in Land

Private land conservation provides an opportunity to address problems of habitat fragmentation and biodiversity loss caused by an increase in the development and parcelization of private land. Conservation easements (CEs) are used to protect significant natural qualities of private land. In this study, we explore landowner attitudes toward CEs through the implementation of a mixed-mode survey to private landowners in the Whychus Creek Watershed (Deschutes County, Oregon). The results of an exploratory factor analysis suggest there are two dimensions to landowner attitudes toward CEs, an internal dimension and an external dimension. We found that positive external attitudes are primarily influenced by environmental beliefs, whereas positive internal attitudes are influenced by a suite of factors, including financial beliefs and perceived risk to private ownership. Awareness of CEs may also play a role in attitude development. Through this research, we argue that CEs may be beneficial in reintegrating the public good into private property.     

Combining Geography,Math, and Science to Teach Climate Change and Sea Level Rise

This study examines the effectiveness of integrating geography into existing math and science curriculum to teach climate change and sea level rise. The desired outcome is to improve student performance in all three subjects. A sample of 120 fifth graders from three schools were taught the integrated curriculum over a period of two to three weeks. They were given a pretest and posttest comprised of questions measuring knowledge relevant to the lesson in terms of geography, math, science, and spatial skills. Paired-samples t-tests were conducted to determine significant differences in student performance. These t-tests indicate statistically significant improvements in all but one instance across all subjects, at all schools for both boys and girls. No statistically significant results were observed for a control group of an additional twenty-seven fifth graders. These results demonstrate the value of combining geography with math and science to improve student performance in STEM knowledge.     

The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes

Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred during deceleration in the atmosphere. The fusion crust of the Winchcombe meteorite closely resembles that of other stony meteorites, and in particular CM2 chondrites, since it is dominated by olivine phenocrysts set in a glassy mesostasis with magnetite, and is highly vesicular. Dehydration cracks are unusually abundant in Winchcombe. Failure of this weak layer is an additional ablation mechanism to produce large numbers of particles during deceleration, consistent with the observation of pulses of plasma in videos of the Winchcombe fireball. Calving events might provide an observable phenomenon related to meteorites that are particularly susceptible to dehydration. Oscillatory zoning is observed within olivine phenocrysts in the fusion crust, in contrast to other meteorites, perhaps owing to temperature fluctuations resulting from calving events. Magnetite monolayers are found in the crust, and have also not been previously reported, and form discontinuous strata. These features grade into magnetite rims formed on the external surface of the crust and suggest the trapping of surface magnetite by collapse of melt. Magnetite monolayers may be a feature of meteorites that undergo significant degassing. Silicate warts with dendritic textures were observed and are suggested to be droplets ablated from another stone in the shower. They, therefore, represent the first evidence for intershower transfer of ablation materials and are consistent with the other evidence in the Winchcombe meteorite for unusually intense gas loss and ablation, despite its low entry velocity.     

Is there a link between deep‐sea biodiversity and ecosystem function?

Studying the diversity‐ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity‐ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep‐sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity‐function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity‐ecosystem function relationship in the largest ecosystem on Earth.     

Mussel reefs on soft sediments: a severely reduced but important habitat for macroinvertebrates and fishes in New Zealand

Green-lipped mussels (Perna canaliculus) formed extensive reefs on soft sediments in sheltered embayments around northern New Zealand until overfishing and/or increased sediment input caused their virtual disappearance by 1980. To determine the role of mussel reefs as habitat for other animals, we located remnant soft-sediment reefs in five locations and compared the density, biomass, productivity and composition of mobile macroinvertebrate communities, and the density of small fishes associated with mussels, with fauna in the surrounding soft sediments. The mussel reefs had a distinct assemblage of macroinvertebrates, which had 3.5 times the density, 3.4 times the biomass and 3.5 times the productivity of surrounding areas. The density of small fishes was 13.7 times higher than in surrounding areas. These results show that soft-sediment mussel reefs support an abundant and productive fauna, highlighting the probable large loss of productivity associated with the historical decline in mussel habitat and the consequent desirability of restoration efforts.     

Saigon from the diaspora

In the wake of reform in Vietnam and the end of the cold war, overseas Vietnamese are returning to their former homeland in increasing numbers. For most of the first generation in the diaspora, memories of wartime Saigon are now being augmented by a touristic experience of contemporary Saigon/Ho Chi Minh City. This essay asks how the co-presence of these differently spatialized and temporalized ways of knowing the city affects the production and consumption of images of Saigon in overseas Vietnamese communities in the West. Based on media ethnography carried out in Vietnamese households in Sydney, the paper argues that changes in the way Saigon is represented in overseas Vietnamese popular culture reflect a shift in the larger politics of diasporic identity. While narratives of exile and refugeehood remain potent forms of affective (if not instrumental) politics in overseas Vietnamese contexts, transnational forms of consciousness and identification are beginning to enter into diasporic public culture, albeit in a highly contested way.     

Spatiotemporal analysis of residential flood exposure in the Atlanta,Georgia metropolitan area

Natural Hazards - This research examines changes in residential built-environment flood exposure within the current boundaries of the Atlanta, Georgia metropolitan statistical area, by estimating...     

磁相变与地壳地球物理异常

我们曾提出过一种可能导致地磁和地壳电导率异常的来源：地壳中的二级磁相变,即居里（尼尔）深度附近磁化率的显著提高.这一现象能很好地解释一些来源不明的地磁异常.本文总结了在中地壳深度处、薄且高磁导率异常体的一维和多维大地电磁特征.高磁导率层引起的异常与高电导率层导致的异常相比,大小上可相比拟,但符号相反.无论在什么情况下,经典的大地电磁解释容易导致一个不真实的极厚高阻层,并且在地磁异常附近有与之对应的空间波长,二级磁相变也被认为是这一现象的可能解释.尽管在地壳中是否存在二级磁相变还有一定争议,但最近的一些固体物理实验结果进一步表明它可能是地壳各种地球物理异常的来源之一.