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291.
ABSTRACTLand science has generated critical knowledge about how humans modify Earth’s surface and has advanced our understanding of land as a coupled human–environment system. However, to date, most work has been in frontier environments with less attention – both conceptually and empirically – on how urban land systems affect the carbon cycle. Much of what is known about urban areas and the carbon cycle is limited to aggregate levels of activities within urban areas, usually by sector, with little focus on how the spatial configuration of urban land systems affects carbon-emitting activities. Given that urban areas produce about 70% of global energy-related CO2 emissions, it is crucial to understand the relationship between urban environments, the activities they influence, and the resulting carbon emissions. This paper summarizes the current state of knowledge of how urban land systems affect carbon emissions and vulnerability, and identifies research gaps and opportunities for urban land science to contribute to climate change science, particularly through land architecture. We argue that more attention to urban land science conceptualization, measurement, and analysis would contribute to both fundamental knowledge about urban systems, as well as help identify policies and strategies for mitigation and adaptation to climate change at the urban scale. 相似文献
292.
Ernstson H van der Leeuw SE Redman CL Meffert DJ Davis G Alfsen C Elmqvist T 《Ambio》2010,39(8):531-545
Urbanization is a global multidimensional process paired with increasing uncertainty due to climate change, migration of people,
and changes in the capacity to sustain ecosystem services. This article lays a foundation for discussing transitions in urban
governance, which enable cities to navigate change, build capacity to withstand shocks, and use experimentation and innovation
in face of uncertainty. Using the three concrete case cities—New Orleans, Cape Town, and Phoenix—the article analyzes thresholds
and cross-scale interactions, and expands the scale at which urban resilience has been discussed by integrating the idea from
geography that cities form part of “system of cities” (i.e., they cannot be seen as single entities). Based on this, the article
argues that urban governance need to harness social networks of urban innovation to sustain ecosystem services, while nurturing
discourses that situate the city as part of regional ecosystems. The article broadens the discussion on urban resilience while
challenging resilience theory when addressing human-dominated ecosystems. Practical examples of harnessing urban innovation
are presented, paired with an agenda for research and policy. 相似文献
293.
Nitrogen Subsidies from Hillslope Alder Stands to Streamside Wetlands and Headwater Streams,Kenai Peninsula,Alaska 下载免费PDF全文
Michael K. Callahan Dennis F. Whigham Mark C. Rains Kai C. Rains Ryan S. King Coowe M. Walker Jasmine R. Maurer Steven J. Baird 《Journal of the American Water Resources Association》2017,53(2):478-492
We examined nitrogen transport and wetland primary production along hydrologic flow paths that link nitrogen‐fixing alder (Alnus spp.) stands to downslope wetlands and streams in the Kenai Lowlands, Alaska. We expected that nitrate concentrations in surface water and groundwater would be higher on flow paths below alder. We further expected that nitrate concentrations would be higher in surface water and groundwater at the base of short flow paths with alder and that streamside wetlands at the base of alder‐near flow paths would be less nitrogen limited than wetlands at the base of long flow paths with alder. Our results showed that groundwater nitrate‐N concentrations were significantly higher at alder‐near sites than at no‐alder sites, but did not differ significantly between alder‐far sites and no‐alder sites or between alder‐far sites and alder‐near sites. A survey of 15N stable isotope signatures in soils and foliage in alder‐near and no‐alder flow paths indicated the alder‐derived nitrogen evident in soils below alder is quickly integrated downslope. Additionally, there was a significant difference in the relative increase in plant biomass after nitrogen fertilization, with the greatest increase occurring in the no‐alder sites. This study demonstrates that streamside wetlands and streams are connected to the surrounding landscapes through hydrologic flow paths, and flow paths with alder stands are potential “hot spots” for nitrogen subsidies at the hillslope scale. 相似文献
294.
295.
Introduction: Crashes involving roadway objects and animals can cause severe injuries and property damages and are a major concern for the traveling public, state transportation agencies, and the automotive industry. This project involved an in-depth investigation of such crashes based on the second Strategic Highway Research Program (SHRP 2) Naturalistic Driving Study (NDS) data including detailed information and videos about 2,689 events. Methods: The research team conducted a variety of logistic regression analyses, complemented by Support Vector Machine (SVM) analyses and detailed case studies. Results: The logistic regression results indicated that driver behavior/errors, involvement of secondary tasks, roadway characteristics, lighting condition, and pavement surface condition are among the factors that contributed significantly to the occurrence and/or increased severity outcomes of crashes involving roadway objects and animals. Among these factors, improper turning movements (odds ratio = 88), avoiding animal or other vehicle (odds ratio = 38), and reaching/moving object in vehicle (odds ratio = 29) particularly increased the odds of crash occurrence. Factors such as open country roadways, sign/signal violation, unfamiliar with roadway, fatigue/drowsiness, and speeding significantly increased the severity outcomes when such crashes occurred. The sensitivity analysis of the three SVM classifiers confirmed that driver behavior/errors, critical speed, struck object type, and reaction time were major factors affecting the occurrence and severity outcomes of events involving roadway objects and animals. Practical Applications: The study provides insights on risk factors influencing safety events involving roadway objects, including their occurrence and the severity outcomes. The findings allow researchers and traffic engineers to better understand the causes of such crashes and therefore develop more effective roadway- and vehicle- based countermeasures. 相似文献
296.
Carleton R. Bern Michael J. Holmberg Zachary D. Kisfalusi 《Journal of the American Water Resources Association》2020,56(4):647-668
Salinity, selenium, and uranium pose water‐quality challenges for the Arkansas River in southeastern Colorado and other rivers that support irrigation in semiarid regions. This study used 31 years of continuous discharge and specific conductance (SC) monitoring data to assess interannual patterns in water quality using mass balance on a 120‐km reach of river. Discrete sampling data were used to link the SC records to salinity, selenium, and uranium. Several important patterns emerged. Consumptive use reduced discharge by a median value of 33% and drove corresponding increases in salinity and uranium concentrations. Increased water availability for irrigation from rainfall and upstream snowpack in 1995–1999 flushed additional salinity and uranium into the river in 1996–2000; average annual total dissolved solids (salinity) concentrations increased 25%, and loads increased 131%. Smaller flushing events have occurred, sometimes lagging an increase in water availability by about one year. The pattern indicates flushing of salts temporarily stored, evaporatively concentrated, or of geologic origin. Mobilization of selenium from the reach was minor compared to salinity and uranium, and net selenium removal from the river was suggested in some years. Several processes related to irrigation could be removing selenium. The results provide context for efforts to improve water quality in the Arkansas River and rivers in other semiarid regions. 相似文献
297.
Jun Wang Wei Xi Yonghua Xiao Chenjiang Ying Jia Long Hui Zhang Xi Chen Congda Mao Xiumin Li Lin Wang Shunqing Xu 《环境科学学报(英文版)》2014,26(10):2131-2137
Food has been documented as one of major routes for human exposure to environmental estrogens(EEs), but information on the occurrence of EEs in animal foodstuffs is still scarce.This study analyzed estrogenic activity in 16 types of animal foodstuffs(n = 142) collected from four cities(Wuhan, Guangzhou, Wenzhou and Yantai) of China by combined yeast estrogen screen(YES) bioassay and chemical analysis. By bioassay, all samples' extracts were found to induce estrogenic activities and the bioassay-derived 17β-estradiol equivalent(EEQbio) ranged from 8.29 to 118.32 ng/g. In addition, the samples were analyzed by liquid chromatography coupled to tandem mass spectrometry for further chemical analysis. 17β-Estradiol was found in all samples in this survey at levels of 0.44 to 15.04 ng/g.All samples had 33.1% detection rate of 17α-ethinylestradiol(EE2), and the maximum concentration was 2.80 ng/g. Bisphenol A and 4-nonylphenols were detected in 83.8% and83.1% of samples, with concentrations up to 12.56 ng/g and 35.76 ng/g, respectively.However, the concentrations of estrone, diethylstilbestrol and 4-t-octylphenol were found to be below the limit of detection. A comparison of EEQbiomeasured from the YES assay and EEQchemcalculated from chemical analysis showed good correlation(R2= 0.84). Based on the results, the YES assay can be used as a rapid pre-screening method for monitoring the levels of estrogenic activity in large numbers of animal foodstuffs, and chemical analysis used in combination can be used for the identification of specific EEs. 相似文献
298.
299.
The mechanism of flow turbulence, sediment supply conditions, and sediment transport patterns that affect the adsorption of cadmium ions onto sediment particles in natural waters are experimentally simulated and studied in this study both in batch reactors and in a turbulence simulation tank. By changing the agitation conditions, the sediment transport in batch reactors can be categorized into bottom sediment-dominated sediment and suspended sediment-dominated sediment. It is found that the adsorption rate of bottom sediment is much less than that of suspended sediment, but the sediment transport pattern does not affect the final (equilibrium) concentration of dissolved cadmium. This result indicates that the parameters of an adsorption isotherm are the same regardless of the sediment transport pattern. In the turbulence simulation tank, the turbulence is generated by harmonic grid-stirred motions, and the turbulence intensity is quantified in terms of eddy diffusivity, which is equal to 9.84F(F is the harmonic vibration frequency) and is comparable to natural surface water conditions.When the turbulence intensity of flow is low and sediment particles stay as bottom sediment, the adsorption rate is significantly low, and the adsorption quantity compared with that of suspended sediment is negligible in the 6 h duration of the experiment. This result greatly favors the simplification of the numerical modeling of heavy metal pollutant transformation in natural rivers. When the turbulence intensity is high but bottom sediment persists, the rate and extent of descent of the dissolved cadmium concentration in the tank noticeably increase, and the time that is required to reach adsorption equilibrium also increases considerably due to the continuous exchange that occurs between the suspended sediment and the bottom sediment.A comparison of the results of the experiments in the batch reactor and those in the turbulence simulation tank reveals that the adsorption ability of the sediment, and in particular the adsorption rate, is greatly over-estimated in the batch reactor. 相似文献
300.
Zhang W 《Environmental monitoring and assessment》2007,124(1-3):253-261
Both direct and indirect ecological interactions may occur in an ecosystem with large numbers of taxa. Traditional food web
technique is a popular tool to measure the quality and health of the environment. Much of works must be done before constructing
a food web for an ecosystem especially with many taxa. This food web is generally specific for some ecological interactions
and fixed for a set of given species. It is therefore not an effective method for dynamic and prompt assessment of environment.
Ecological interactions and their interactive intensity may be detected by sampling biological taxa in the field and by detecting
various between-taxa distances or similarities. Network may clearly exhibit the complex interactions among biological taxa.
Statistic tests on various distance or similarity measures and computer designs are required to infer the {network. We develop
an algorithm and software to infer the network of direct or indirect ecological interactions in ecosystem. It is a prompt
and effective tool in monitoring and assessment of the environment. A redundant network may be inferred and drawn by computer
based on the statistic tests on sampling data or the pathway information given in HTML file. Dominant taxa may be found in
the network. In total of 16 distance and similarity measures, including Euclidean distance, Manhattan distance, Pearson correlation,
partial correlation, point correlation, linkage coefficients, Jaccard coefficient etc., are provided to detect taxa pairs
with significant parametric or nonparametric similarities, based on randomization tests and ordinary statistic tests. Criteria
to use distance and similarity measures are discussed. 相似文献