Rivers of North-Rhine Westphalia revisited: Tracing changes in river chemistry   总被引：1，自引：0，他引：1  

Andrea Stgbauer  Harald Strauss  Julia Arndt  Victoria Marek  Florian Einsiedl  Robert van Geldern 《Applied Geochemistry》2008,23(12):3290-3304

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Decadal changes in distribution and frequency of wood in a free meandering river,the Ain River,France     

Neil S. Lassettre  Herv Pigay  Simon Dufour  Anne‐Julia Rollet 《地球表面变化过程与地形》2008,33(7):1098-1112

This study examined the temporal dynamics and longitudinal distribution of wood over a multi‐decadal timescale at the river reach scale (36 km) and a meander bend scale (300–600 m) in the Ain River, a large gravel‐bed river flowing through a forested corridor, and adjusting to regulation and floodplain land‐use change. At the 36 km scale, more wood was recruited by bank erosion in 1991–2000 than since the 1950s. The longitudinal distribution of accumulations was similar between 1989 and 1999, but in both years individual pieces occurred homogeneously throughout the reach, while jam distribution was localized, associated with large concave banks. A relationship between the mean number of pieces and the volume recruited by bank erosion (r² = 0·97) indicated a spatial relationship between areas of wood production and storage. Wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends. Sinuosity was related to wood mass recruited by bank erosion during the previous decade (r² = 0·73) and both of these parameters were correlated to the mean mass of wood/plot (r² = 0·98 and 0·69 respectively), appearing to control wood storage and delivery at the bend scale. This suggests a local origin of wood stored in channel, not input from upstream trapped by preferential sites. The increase in wood since 1950 is a response to floodplain afforestation, to a change from braided to meandering channel pattern in response to regulation, and to recent large floods. We observed temporal stability of supply and depositional sectors over a decade (on a reach scale). Meander bends were major storage sites, trapping wood with concave banks, also delivering wood. These results, and the link between sinuosity and wood frequency, establish geomorphology as a dominant wood storage and recruitment control in large gravel‐bed rivers. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Accessing adaptation: Multiple stressors on livelihoods in the Bolivian highlands under a changing climate     

Julia Z. McDowell  Jeremy J. Hess 《Global Environmental Change》2012,22(2):342-352

Smallholder farmers continuously confront multiple social and environmental stressors that necessitate changes in livelihood strategies to prevent damages and take advantage of new opportunities, or adaptation. Vulnerability, meaning susceptibility to harm, is attributable to social determinants that limit access to assets, leading to greater exposure and sensitivity to stressors and a limited capacity to adapt. Stressors and adaptation are intertwined because stressors deplete resources available for adaptation, while adaptation may erode resources available to respond to future stressors. We present empirical evidence demonstrating the interactions of multiple stressors and adaptations over time through a case study of indigenous farmers in highland Bolivia. We examine how farmers perceive the stress on their livelihoods, their strategies for adapting to these threats, and the influence of past adaptation and exposure on vulnerability under increasing climatic change. We find that vulnerability changes over time as multiple stressors, such as land scarcity and delayed seasonal rainfall, compound, simultaneously reducing access and demanding the expenditure of household assets for adaptation, including natural capital (water and land), human capital (including labor), and financial, physical, and social capital. To reduce vulnerability over time, constraints on access to key resources must be addressed, allowing households the flexibility to reduce their exposure and improve their adaptive capacity to the multiple stressors they confront.  相似文献   

Surface and groundwater pollution by organochlorine compounds in a typical soybean system from the south Pampa,Argentina   总被引：3，自引：0，他引：3  

Mariana Gonzalez  Karina S. B. Miglioranza  Valeria M. Shimabukuro  Orlando M. Quiroz Londoño  Daniel E. Martinez  Julia E. Aizpún  Víctor J. Moreno 《Environmental Earth Sciences》2012,65(2):481-491

Organochlorine pesticides (OCPs) use has been restricted or forbidden in Argentina since 1998 and technical endosulfan is the last currently used OCPs on the soybean-wheat production. As they persist in soil for several years after application, OCPs constitute a source of environmental pollution. This work aims to assess OCPs contamination of groundwater (Gw) and streamwater (Sw) in the Quequén Grande River watershed from south Argentinean Pampas in relation to the hydrogeological characteristics. OCPs were analyzed in Sw, Gw, surface bottom sediments, soils and borehole cutting sediments (Cs) by gas chromatograph-electron capture detector. Pesticide distribution in Cs was dependent on the characteristic of the non-saturated zone. Leached pesticides over 3 m in Cs showed the pattern: HCHs = endosulfan > chlordanes > DDTs, and from 3 to 6 m heptachlor was the main group as a consequence of the past use of this compound in the area, mainly on potato crops. Endosulfan reaches Gw during application season as well as during flooding events while a retard effect was observed for Sw. Levels of α- and β-isomers were in certain cases above national (7 ng L⁻¹) and international (3 ng L⁻¹) limits for aquatic biota protection. As the endosulfan sulfate metabolite was present in Gw and Sw and due to its high toxicity, it should be considered in the establishment of water quality criteria for human and environmental protection.  相似文献   

Origin and sustainability of the population of asteroids captured in the exterior resonance 1:2 with Mars     

Tabaré Gallardo  Julia Venturini  Ricardo Gil-Hutton 《Icarus》2011,214(2):632-644

At present, approximately 1500 asteroids are known to evolve inside or sticked to the exterior 1:2 resonance with Mars at a ? 2.418 AU, being (142) Polana the largest member of this group. The effect of the forced secular modes superposed to the resonance gives rise to a complex dynamical evolution. Chaotic diffusion, collisions, close encounters with massive asteroids and mainly orbital migration due to the Yarkovsky effect generate continuous captures to and losses from the resonance, with a fraction of asteroids remaining captured over long time scales and generating a concentration in the semimajor axis distribution that exceeds by 20% the population of background asteroids. The Yarkovsky effect induces different dynamics according to the asteroid size, producing an excess of small asteroids inside the resonance. The evolution in the resonance generates a signature on the orbits, mainly in eccentricity, that depends on the time the asteroid remains captured inside the resonance and on the magnitude of the Yarkovsky effect. The greater the asteroids, the larger the time they remain captured in the resonance, allowing greater diffusion in eccentricity and inclination. The resonance generates a discontinuity and mixing in the space of proper elements producing misidentification of dynamical family members, mainly for Vesta and Nysa-Polana families. The half-life of resonant asteroids large enough for not being affected by the Yarkovsky effect is about 1 Gyr. From the point of view of taxonomic classes, the resonant population does not differ from the background population and the excess of small asteroids is confirmed.  相似文献   

Integrating the effects of flood experience on risk perception with responses to changing climate risk     

Judy Lawrence  Dorothee Quade  Julia Becker 《Natural Hazards》2014,74(3):1773-1794

Flood management decision-makers face significant challenges as the climate changes. The perceptions of those affected by floods are critical to the successful implementation of adaptation responses; risk perceptions are affected by how information is communicated and, in turn, perceptions influence expectations on flood risk managers to respond. The links between flood experience, risk perception, and responses by individual households were examined in the Hutt Valley, New Zealand, through a household survey, a workshop and interviews with local government practitioners. Two propositions were tested: (1) that flood experience can influence flood risk perceptions; and (2) that flood experience can stimulate increased risk reduction and adaptation actions where changing climate risk is likely. Perceptions of responsibility for flood management were also examined. The study found that previous flood experience contributes to heightened perception of risk, increased preparedness of households, greater willingness to make household-level changes, greater communication with councils, and more advocacy for spatial planning to complement existing structural protection. Flood-affected households had a stronger preference for central government and communities having flood risk responsibilities, in addition to local government. Those who lacked experience were more likely to be normalised to their prior benign experiences and thus optimistic about flood consequences. These results suggest that harnessing positive aspects of experience and communication of changing risk through engagement strategies could help shift the focus from citizens’ expectation that governments will always provide protection, to a citizen–local government–central government dialogue about the changing character of flood risk and its implications, and build a ‘risk conscious’ society in which ‘sharing and bearing’ is considered desirable.  相似文献   

Leaching and dilution of fertilizers in the Yucatan karstic aquifer     

Roger Gonzalez-Herrera  Eden Martinez-Santibañez  Julia Pacheco-Avila  Armando Cabrera-Sansores 《Environmental Earth Sciences》2014,72(8):2879-2886

The application of agrochemicals in crops can cause pollution of aquifers, especially those with a shallow water table and covered by thin soils; such is the case of Yucatan, Mexico. Information about the requirements and application of fertilizers to major irrigation and rainfed crops as well as the volume of water consumed in growing were used to determine the potential amount of nitrate delivered to groundwater. The research reported in this paper was conducted in the metropolitan area of the city of Merida, in Yucatán, Mexico, where groundwater plays an important role since it is the main source of supply, due to the lack of surface water in the region. In addition, the vulnerability of this aquifer is threatened by the various activities taking place in the municipalities, which emphasize agriculture, located within the groundwater basin. This activity is analyzed as a source of contamination given the concentration of NO₃ ^? present in groundwater intended for human consumption. The results show that the contribution of farming that enriches the presence of nitrates in the aquifer is different for each municipality in the study area. For the ZMM, the average nutrient leaching is 44 % of the original mass applied; it could be diluted approximately 12 times, in the groundwater.  相似文献   

巴布亚新几内亚Muller高原的大漏斗     

Julia M James  黄保健  张远海 《中国岩溶》2006,25(Z1):49-58

Muller高原位于巴布亚新几内亚南部高地,以发育大漏斗(giant doline)群而闻名.这些漏斗中许多具有可与新不列巅岛Nakanai山地的超级漏斗(megadoline)和中国南方喀斯特天坑相媲美的特大规模和形态,都属"岩盖(caprock)"型漏斗.Muller高原的地质、自然地理和水文环境可与Nakanai山地环境和中国南方喀斯特区环境相对比.本文讨论了Muller高原上三个大漏斗群(Rogorepo,Mamo和Atea)的形成机制.Muller高原的大漏斗,像Nakanai的超级漏斗和中国天坑一样,形成于更新世.Muller高原漏斗的形成环境与其它大漏斗有许多相似性.然而,它却不可能演化成像Nakanai超级漏斗一样壮丽,像中国天坑那样具有极高美学价值,其原因在于石灰岩地层中有不纯非石灰岩夹层.  相似文献   

Physical, chemical and microbiological characterization of the intertidal sediments of Pereque Beach, Guarujá (SP), Brazil     

de Oliveira AJ  Hollnagel HC  Lima Mesquita Hde S  Fontes RF 《Marine pollution bulletin》2007,54(7):921-927

Physical and chemical characteristics of intertidal sediments and their relationships with bacteria and cyanobacteria were analyzed at four stations at Pereque Beach. Granulometric analysis showed that Pereque beach has sediment that is classified as sand. The lowest value of the sediment C/N rates (6.08), mainly due to a higher concentration of organic nitrogen, was found at the northern part of Pereque Beach, where organic matter of marine source was more prominent. In this area, density (9.6x10(6)cells cm(-3)), biomass (1992.04ngC cm(-3)) and activity of bacteria were higher than at the southern end. In contrast, cyanobacteria density varied from 2.0 to 4.0x10(5)cells cm(-3), with biomass and total chlorophyll a of the sediment being higher at the southern part, where there are water input from Pereque River and higher organic matter of continental origin. The variability in the microbial population is discussed in the light of the sediment granulometry, organic matter quality, fresh water inflow and pollution.  相似文献   

Historical contamination and sources of organochlorine pesticides in sediment cores from Quanzhou Bay, Southeast China   总被引：8，自引：0，他引：8  

Gong X  Qi S  Wang Y  Julia EB  Lv C 《Marine pollution bulletin》2007,54(9):1434-1440

Three sediment cores were collected from the top to the mouth of Quanzhou Bay, Southeast China, in order to establish sources and historical trends of organochlorine pesticides (OCPs) in the region. The spatial distribution of OCPs in surface sediments implies that Quanzhou Bay received the contamination inputs not only from rivers near the shore, but also from outside the bay. The variation profiles of concentrations clearly showed that OCPs were widely used between 1960s and 1980s in China. A recent increasing trend was found in all cores despite their ban in China in 1983. Different ratios of (DDD+DDE)/DDTs indicated that DDTs at the top of the bay were mainly derived from long-term weather soils, while DDTs near the mouth of the bay were mainly derived from fresh inputs from outside the bay. Higher percentage of gamma-HCH in HCHs deposited after 1990 implies that lindane may have been used recently around Quanzhou Bay.  相似文献