Short-term changes in C and N distribution in soil particle size fractions induced by agricultural practices in a cultivated volcanic soil from Mexico   总被引：6，自引：0，他引：6  

Sara Covaleda  Silvia Pajares  Juan F. Gallardo  Jorge D. Etchevers   《Organic Geochemistry》2006,37(12):1943

The purpose of this study was to assess the effect of agricultural practices on the characteristics of soil organic carbon (SOC). The study area is located in the Central Volcanic Belt (Michoacán) in Mexico. The soil is an Acrisol, acidic and rich in clays and sesquioxides. Experimental plots were treated with four different agronomic management systems between 2002 and 2003: traditional, improved traditional, organic and fallow. Each treatment was replicated twice. Samples were taken at depths of 0–10 and 10–20 cm and were subjected to a physical fractionation process by way of particle size. SOC was fractionated into fulvic acids, humic acids and humin. After two years of cultivation, the SOC content increased significantly with the organic management (2.2 mg g⁻¹ at 0–10 cm and 5.8 mg g⁻¹ at 10–20 cm). The C content of the soil fine particle fraction increased with the traditional and organic managements. The organic C and N contents of the silt + clay particle-size fraction were mainly concentrated as humin, indicating that this SOM should be stable and have a low risk of mineralization. The humin C content only decreased significantly under the traditional and fallow treatments. The N content of the humin fraction decreased significantly under the traditional management system (from 69% to 54%), indicating the low sustainability of this soil management. The C/N ratio of the soil increased significantly under all treatments, but mainly under the traditional and organic treatments (from 12.1 and 12.8 to 13.7 and 14.0, respectively). This indicates a decrease in humus quality. In addition, the C/N of the humin increased significantly (from 13.3 and 12.7 to 19.2 and 16.0, respectively).  相似文献   

Alkyl nitrate formation from the reaction of a series of branched RO2 radicals with NO as a function of temperature and pressure     

Roger Atkinson  Sara M. Aschmann  Arthur M. Winer 《Journal of Atmospheric Chemistry》1987,5(1):91-102

Alkyl nitrate yields from the NO _x photooxidations of neopentane, 2-methylbutane and 3-methylpentane have been determined over the temperature and pressure ranges 281–323 K and 54–740 torr, respectively. The formation of the alkyl nitrates is attributed to the reaction pathway (1b) $${\text{RO}}_{\text{2}} + {\text{NO}}^{{\text{ }}\underrightarrow {\text{M}}} {\text{ RONO}}_{\text{2}}$$ and rate constant ratios k _1b/(k _1a+k _1b) are estimated, where (1a) is the reaction pathway (1a) $${\text{RO}}_{\text{2}} + {\text{NO}} \to {\text{RONO}}_{\text{2}} .$$ A method for estimating this rate constant ratio for primary, secondary and tertiary alkyl peroxy radicals is presented.  相似文献   

Far from Being "Home Alone": The Dynamics of Accompanied Fieldwork     

Julie Cupples  Sara Kindon 《Singapore journal of tropical geography》2003,24(2):211-228

Despite persistent images to the contrary, most fieldworkers are accompanied. Yet, there has been limited discussion on the nature of accompanied fieldwork, particularly by geographers. Drawing on our experiences in three countries in the tropics, we discuss the dynamics of being accompanied in “the field” by our children and female co‐researchers. Specifically, we focus on issues of access and rapport; the impacts of their presence on our positionality; and the implications these have for power relations and research outcomes. We demonstrate how being accompanied entangles our personal and professional selves and can result in more egalitarian power relations as we become “observers observed”. We argue that by paying attention to the dynamics of accompanied fieldwork, there is the potential to enhance the conceptual focus of our methodological concerns and to provide a more theoretically sophisticated mode of exploring the ways in which our multiple identities intersect while in “the field”.  相似文献   

Predicting fine sediment dynamics along a pool-riffle mountain channel   总被引：1，自引：0，他引：1  

Sara Rathburn  Ellen Wohl   《Geomorphology》2003,55(1-4):111

Fine sediment dynamics in mountain rivers are of concern because of implications for aquatic habitat, channel stability, and downstream sediment yields. Many mountain river systems have episodic fine sediment transport because of infrequent, point-source sediment inputs from landslides; basin instability triggered by land uses such as logging; or infrequent mobilization of the coarse surface layer in channels. Dam removal, which is now more likely along mountain rivers, may also provide a substantial fine sediment input to downstream channel reaches.Fine sediment storage in the interstices of spawning gravels and within pools along mountain rivers is of particular interest because of impacts to aquatic organisms. In this study we focus on sediment dynamics within pools of the North Fork Poudre River in Colorado as an example of the processes controlling fine sediment deposition, storage, and transport within laterally constricted pools. The 1996 release of 7000 m³ of silt-to gravel-sized sediment from a reservoir on the North Fork provided an opportunity to develop a field data set of fine sediment dynamics and to test the predictions of three different one- or two-dimensional sediment transport and hydraulic models against the field observations.The models were calibrated against quantitative measurements of pool scour and fill. One-dimensional HEC-6 results indicate that robust simulations yield the greatest agreement between predicted and measured pool bed elevation change. Model calibration on two pools and validation on one pool indicate that at least 58% of observed bed changes after the sediment release were predicted by HEC-6. Modeling accuracy using quasi-two-dimensional GSTARS 2.0 was considerably more variable, and no pool-wide trends were obtained. The two-dimensional model RMA2 substantially improved the representation of eddy pool hydraulics within a compound pool of the North Fork. Results from the hydraulic modeling, coupled with bed load and total load computations, delineate areas of scour and deposition which are consistent with observations in the field.A conceptual model of sediment delivery and storage for laterally confined pools suggests that persistent deposition of fine sediment within eddies distal from the sediment source may result from sediment releases. The original loss of channel capacity facilitated additional deposition within eddies as sediment within upstream proximal pools became mobilized. At high discharges, the development of a strong shear zone prevents degradation of sediment deposits within the eddy. Central portions of these proximal pools may clear according to existing models, whereas deposition within recirculating zones may be long-term. Water managers could use these models to estimate minimum pool volume for overwinter habitat and residence time of pool sediment.  相似文献   

Yanama budyari gumada: reframing the urban to care as Darug Country in western Sydney     

Darug Ngurra  Lexodious Dadd  Paul Glass  Marnie Graham  Sara Judge 《The Australian geographer》2019,50(3):279-293

ABSTRACT

In non-urban places of Australia, caring-as-Country frames natural resource management (NRM) as a practice of reciprocal, more-than-human care-giving (S. Suchet-Pearson, S. Wright, K. Lloyd, and L. Burarrwanga. 2013. ‘Caring as Country: towards and ontology of co-becoming in natural resource management.’ Asia Pacific Viewpoint 54 (2): 185–197). Caring-as-Country is an idea that encapsulates the entangled, reciprocal relationships that people have with, and as part of, agentic more-than-human worlds. In more urbanised places, however, practices of caring-as-Country are often unrecognised, undervalued and undocumented. In this paper we make explicit practices of caring, healing and rejuvenation at Yellomundee Regional Park, Darug Country in western Sydney. Our discussion of care, entanglement and reciprocity at Yellomundee focuses on two specific activities that embody caring-as-Country: the return of cultural burns and sustained presence on Country in the form of Darug-led culture camps. The Darug principle of yanama budyari gumada, to ‘walk with good spirit’, embodies and invites new ways of thinking and practising intercultural caring-as-Country in heavily colonised, urban places like Yellomundee. As we document the practices arising from this invitation, we consider its far-reaching implications for NRM and planning, and we expand on the importance of geographies of care for unceded urban places.  相似文献   

Tigris River Sediments as Abrasive for Polishing Marble     

Awadh  Salih Muhammad  Khalid  Sara Ali 《Natural Resources Research》2019,28(4):1371-1383

Natural Resources Research - This study aims to evaluate the use of Tigris River sediments as abrasives for polishing marble surfaces to achieve a usable form as floor tiles, facing stones and...  相似文献   

Amelioration and retrofitting of educational buildings     

Fabio Casciati  Sara Casciati 《地震工程与工程振动(英文版)》2018,17(1):47-51

Following a seismic event that occurred years ago in Central Italy, the public opinion was growing and growing a concern on the adequacy of educational buildings all across Italy. This activated several political decisions and a consequent technical effort is in progress. Technically speaking one has to manage the classical problem of retrofitting existing buildings. However, the legal environment goes across national codes, targeted guidelines and the professional need of achieving pragmatic solutions based on ethical and social acceptation schemes.This paper introduces the topic in its worldwide exception and focuses then on some operative aspects in the Italian situation. It outlines the consolidated steps along this technical process and emphasizes the weak aspects one meets when going across the designers’ reports.  相似文献   

Phytoremediation Potential of Jack Bean Plant for Multi‐Element Contaminated Soils From Ribeira Valley,Brazil          下载免费PDF全文

Maíra da Silva  Sara Adrián López de Andrade  Alfredo Borges De‐Campos 《洁净——土壤、空气、水》2018,46(6)

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Nature-Based Remediation: Growing Opportunities in the Harnessing of Natural Systems     

John Horst  Sara Drane  Jessica Gattenby 《Ground Water Monitoring & Remediation》2020,40(1):14-23

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Form-based river restoration decreases wetland hyporheic exchange: Lessons learned from the Upper Colorado River     

Matthew S. Sparacino  Sara L. Rathburn  Timothy P. Covino  Kamini Singha  Michael J. Ronayne 《地球表面变化过程与地形》2019,44(1):191-203

Restoration of river–wetland systems to recover lost ecosystem services and restore consistent flood regimes is commonly directed at modifying in-channel storage and hyporheic exchange. Here, we monitored the hydrologic response to channel realignment in a montane river–wetland system by comparing pre- and post-restoration measurements. In 2015, an earthen berm and 190 m segment of the Upper Colorado River were constructed to consolidate flow from multiple channels into the historic thalweg. We injected a sodium chloride tracer during baseflow and used mass-balance calculations and electrical resistivity imaging to assess changes in near-channel hyporheic exchange. Results indicate a decrease in hyporheic exchange within the wetland due to lost complexity along the consolidated flow path. Subsurface complexity appears to control hyporheic exchange more than surface complexity. Flow consolidation increased the area-adjusted wetland water yield by 231 mm, indicating a loss of wetland water storage capacity. One year of post-restoration monitoring suggests that the form-based channel restoration directed at consolidating flow into a single thread adversely affected the hyporheic exchange functioning in the pre-restoration system. Results from this case study are applicable to restoration planners as they consider the effects of form-based projects on water storage capacity in similar systems. © 2018 John Wiley & Sons, Ltd.  相似文献