A simple model for forecasting the effects of nitrogen loads on Chesapeake Bay hypoxia   总被引：1，自引：0，他引：1  

Donald Scavia  Emily L. A. Kelly  James D. Hagy 《Estuaries and Coasts》2006,29(4):674-684

The causes and consequences of oxygen depletion in Chesapeake Bay have been the focus of research, assessment, and policy action over the past several decades. An ongoing scientific re-evaluation of what nutrient load reductions are necessary to meet the water quality goals is needed. While models can provide insights and advice for public policy on load reduction goals, they are caricatures of nature, and it is wise to use independent modeling approaches. In this paper, we describe our simple, biophysically based model that offers a middle ground between statistical models and complex dynamic models. Our model suggests that the target total nitrogen load reduction of 35% will reduce hypoxic volumes by 36–68%, which, on average (53% or 3.4 km³) is lower than values reported for 1950–1970 (4.2 km³), and roughly half of the values reported for 1980–1990 (7.2 km³). By pursuing a simple model construct, we were able to quantify uncertainty to a greater extent than is possible with the more complex numerical models. Yet, by retaining some mechanistic detail we could validate the model against state variables and process rates, an advantage over simple regressions.  相似文献   

Farmer Identity in Multifunctional Landscapes: using a collective identity construct to explore the nature and impact of occupational identity     

Theresa M. Groth  Emily Mendham  Eric Toman 《The Australian geographer》2014,45(1):71-86

The use of multifunctionalism to conceptualise contemporary rural landscapes has focused attention on the increased extent and impact of non-farmers in traditionally agriculture-based rural communities. Typologies of rural landholders have been developed as part of that research effort. However, those typologies are not grounded in established theory, including collective identity theory that could provide an important foundation for the study of occupational identity. Indeed, most quantitative studies may be flawed in drawing on only one of the seven elements contributing to collective identity. This paper examines the efficacy of relying on self-declared occupational identity through the analysis of rural landholder survey data in an Australian region. Tests for expected relationships between self-declared identity of farmer/non-farmer and social and farming variables expected to be correlated with occupation, such as property size, profitability, hours worked on- and off-property, enterprise type and membership of farming-related local organisations found that the expected relationships existed. It seems that self-declared occupational identity is a valid and cost-effective way to explore occupational identity amongst rural landholders. Collective identity, however, is complex and it is unlikely that important research questions can be adequately explored without a more holistic approach to the study of farmer identity in multifunctional landscapes. The paper concludes with a discussion of the potential benefits of moving beyond self-declared occupation to include other elements in the collective identity construct.  相似文献   

The model minority stereotype in Arizona’s anti-immigrant climate: SB 1070 and discordant reactions from Asian Indian migrant organizations     

Emily Skop 《GeoJournal》2017,82(3):553-566

This research explores the discordant reactions of local Asian Indian migrant organizations to the passage of Arizona Senate Bill 1070. The objective is to illustrate how migrants from India to Arizona negotiate their identities in the context of this anti-immigrant climate. The research draws insight largely from local records and publications of Asian Indian migrant organizations, including monthly newsletters, board meeting minutes, and other materials found on organizational websites. The analysis chronicles how various Asian Indian migrant organizations shape public discourse about migrant identity, belonging, and citizenship through their reactions to Arizona Senate Bill 1070. The place-based approach provides a way to re-think traditional migration theories and explore the role of racialization in better understanding the consequences of migration from India to the U.S.  相似文献   

Thermal Monitoring of Natural Source Zone Depletion          下载免费PDF全文

Kayvan Karimi Askarani  Emily B. Stockwell  Keith R. Piontek  Tom C. Sale 《Ground Water Monitoring & Remediation》2018,38(3):43-52

Natural depletion of subsurface petroleum liquids releases energy in the form of heat. The rate of natural source zone depletion (NSZD) can be derived from subsurface temperature data. An energy balance is performed to resolve NSZD‐generated energy in terms of W/m². Biodegradation rates are resolved by dividing the NSZD energy by the heat of reaction in joules/mol. Required temperature data are collected using data loggers, wireless connections, and automated data storage and analysis. Continuous thermal resolution of monthly NSZD rates at a field site indicates that apparent monthly NSZD rates vary through time, ranging from 10,000 to 77,000 L/ha/year. Temporal variations in observed apparent NSZD rates are attributed to processes governing the conversion of CH₄ to CO₂, as opposed to the actual rates of NSZD. Given a year or more of continuous NSZD rate data, it is anticipated that positive and negative biases in apparent NSZD rates will average out, and averaged apparent NSZD rates will converge to true NSZD rates. An 8.4% difference between average apparent NSZD rates over a 31‐month period using the thermal monitoring method and seven rounds of CO₂ efflux measurements using CO₂ traps supports the validity of both CO₂ trap and thermal monitoring methods. A promising aspect of thermal monitoring methods is that continuous data provide a rigorous approach to resolving the true mean NSZD rates as compared to temporally sparse CO₂ trap NSZD rate measurements. Overall, a vision is advanced of real‐time sensor‐based groundwater monitoring that can provide better data at lower costs and with greater safety, security, and sustainability.  相似文献   

Using the commons to understand the Dutch elm disease epidemic in Syracuse,NY     

Emily Bukowski 《Geographical review》2019,109(2):180-198

Prior to the arrival of Dutch elm disease to the United States in 1930, American elm (Ulmus americana) had become one of the most beloved and commonly planted urban trees throughout the country, especially in the Northeastern United States. The trees were revered for their beauty, hardiness, and the corridor‐like shade provided to city streets. Syracuse, NY stands as an example of this popularity: in 1951, when the disease first arrived in the city, over 50,000 elms grew in the city. But over the course of twenty years, nearly all elms in the city had become infected and succumbed to the disease. Although efforts to control the fungus in Syracuse ultimately failed to stop elm loss, the case study can be used to better inform contemporary urban forest management practices today by highlighting the effects of mixed property ownership in cities and its effects on pest management.  相似文献   

Snowmelt detection from QuikSCAT and ASCAT satellite radar scatterometer data across the Alaskan North Slope     

Emily J. Sturdivant  Frank E. Urban 《地理信息系统科学与遥感》2019,56(1):87-108

The timing of seasonal snowmelt in high-latitude tundra has implications ranging from local biological productivity to global atmospheric circulation, yet remains difficult to quantify, particularly at large spatial scales. Snowmelt detection in such remote polar environments is possible using satellite-based microwave scatterometers, such as NASA’s QuikSCAT. QuikSCAT measured scattering in Ku-band, which is sensitive to snowmelt signals, from 1999 until the antenna failed in 2009. The Advanced Scatterometer (ASCAT) (2006–2021 (projected) operational), which operates at C-band, may be able to extend the QuikSCAT record, but existing techniques fail to adequately monitor tundra environments. Here, we designed a departure threshold algorithm to produce a consistent 15-year time series of melt onset for the tundra of the Alaskan North Slope, using the overlap period for the enhanced resolution datasets to calibrate the ASCAT melt detection record against QuikSCAT. We produced a time series of day of year of melt onset for 4.45 km x 4.45 km grid cells on the Alaskan North Slope from 2000–2014. Time series validation with in situ mean daily air temperature produced mean R² values of 0.75 (QuikSCAT) and 0.72 (ASCAT). We qualitatively observed a difference between early-season melt, which occurred rapidly and was driven by strong wind events, and more typical melt, which occurred gradually along a latitudinal gradient. We speculate that future melt timing will have greater frequency of early-season onset as climate change destabilizes the high-latitude atmosphere.  相似文献   

Erratum to: Tidal decay and stable Roche-lobe overflow of short-period gaseous exoplanets     

Brian Jackson  Emily Jensen  Sarah Peacock  Phil Arras  Kaloyan Penev 《Celestial Mechanics and Dynamical Astronomy》2017,129(4):553-554

  相似文献   

Middle Pleistocene environments,landscapes and tephrostratigraphy of the Armenian Highlands: evidence from Bird Farm 1, Hrazdan Valley     

Jenni E. Sherriff  Keith N. Wilkinson  Poppy Harding  Hayley Hawkins  Rhys G. O. Timms  Daniel S. Adler  Emily J. Beverly  Simon P. E. Blockley  Boris Gasparyan  Christina J. Manning  Darren Mark  Samvel Nahapetyan  Katie J. Preece 《第四纪科学杂志》2022,37(1):6-27

The significance of the southern Caucasus in understanding Pleistocene hominin expansions is well established. However, the palaeoenvironments in which Palaeolithic occupation of the region took place are presently poorly defined. The Hrazdan river valley, Armenian Highlands, contains a rich Palaeolithic record alongside Middle Pleistocene volcanic, fluvial and lacustrine strata, and thus offer exciting potential for palaeoenvironmental reconstruction. We present the first results of sedimentological, geochemical, tephrostratigraphical and biological (diatoms) study of the sequence of Bird Farm 1, located in the central part of the valley. These data show six phases of landscape development during the interval 440–200 ka. The sequence represents the first quantitative Pleistocene diatom record from the Armenian Highlands and the southern Caucasus, and indicates the persistence of a deep, stratified lacustrine system, with evidence for changing lake productivity that is tentatively linked to climate. Furthermore, major element chemical characterization of visible and crypto-tephra horizons in the sequence enables the first stages of the development of a regional tephrostratigraphy. Together, the evidence from Bird Farm 1 demonstrates the importance of lacustrine archives in the region for palaeoenvironmental reconstruction and highlights the potential for linkages between archives on both a local and regional scale.  相似文献   

Chemical and genetic characterization of the ungrouped pallasite Lieksa     

Emily M. Chiappe  Richard D. Ash  Arto Luttinen  Sari Lukkari  Jukka Kuva  Connor D. Hilton  Richard J. Walker 《Meteoritics & planetary science》2023,58(12):1747-1759

The meteorite Lieksa was found in 2017 in Löpönvaara, Finland, and later donated to the Finnish Museum of Natural History. Here, we report siderophile element concentrations, genetic isotopic data, and a metal–silicate segregation age for the meteorite. The ~280 g Lieksa is ~80% metal and ~20% silicate and oxide inclusions by volume, with the inclusions consisting primarily of Fe-rich olivine. Due to Lieksa's silicate content, coupled with a texture characterized by metal enclosing the silicates, it has been classified as a pallasite. Lieksa's olivine and bulk chemical characteristics are distinct from those of the known pallasite and iron meteorite groups, consistent with its classification as ungrouped. The meteorite exhibits a flat, chondrite-normalized highly siderophile element pattern, consistent with an origin as an early crystallization product from a metallic melt with chondritic relative abundances. Molybdenum, Ru, and ¹⁸³W isotopic data indicate that Lieksa formed in the non-carbonaceous (NC) domain of the solar nebula. Radiogenic ¹⁸²W abundances for Lieksa yield a model metal–silicate segregation age of 1.5 ± 0.8 Myr after calcium-aluminum-rich inclusion formation, which is within the range established for other NC-type pallasite and iron meteorite parent bodies.  相似文献