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191.
Potential salinity limitations on nitrogen fixation in sediments from Mono Lake, California 总被引:2,自引:0,他引:2
David B. Herbst 《International Journal of Salt Lake Research》1998,7(3):261-274
Mono Lake is a hypersaline alkaline lake in the high altitude Great Basin desert of eastern California. Algal productivity
of the lake is nitrogen-limited, and a contributing source is derived from benthic nitrogen fixation. Lake level and salinity
have fluctuated with natural climatic variations but have also been affected by the diversion of tributary streams. This research
examines the influence of varied salinity and lake level on the potential for benthic nitrogen fixation in Mono Lake. A sediment-surface
microbial mat community was exposed directly, and in acclimated cultures, to a range of Mono Lake salinities under anaerobic
incubations and the activity of nitrogenase assayed by acetylene reduction. Activity was stimulated in light, but also occurred
in darkness. Over an experimental salinity range from 50 to 150 g L−1 TDS, nitrogenase activity was reduced by 90 per cent, with the activity persisting at the highest salinity being attributable
to dark fixation alone. Between a salinity of 50 g L−1, occurring in Mono Lake over 50 years ago, and 100 g L−1, nitrogenase activity was reduced by nearly half. Changes in the area of the littoral zone at varied lake levels also affect
the total amount of potential benthic nitrogen fixation in the lake. An accounting of yearly inputs of nitrogen to Mono Lake
suggests N2-fixation could contribute as much as 76–81 percent of the total. Inhibition of nitrogen fixation rates by increased salinity
could limit the long-term nutrient supply and benthic primary productivity of this ecosystem. 相似文献
192.
文章分析当前海域管理面临的形势,并剖析当前存在的管理问题,提出管理的总体目标和改革意见措施,同时对当前海域使用管理法修订、新一轮国土空间规划制定、围填海管控、海岸线保护与利用管理、养殖用海管理等主要工作提出管理建议。建议包括:构建基于生态系统的海域综合管理机制,深入落实生态文明建设总要求;开展海域资源本底调查,为深化综合管理奠定基础;整合涉海规划,发挥陆海统筹作用;发挥指标调控作用,实施市场化配置;调控产业用海,充分发挥海域资源最大效益;加大整治修复力度,恢复区域生态功能;打破部门间壁垒,形成监管闭环。 相似文献
193.
194.
Nicola Morrison 《GeoJournal》2000,51(4):339-349
This paper provides an overview of the current literature on why difficulties are being experienced in letting social housing within England. The first part of the paper focuses on whether the management of the social housing stock, and in particular the current allocation system, has contributed to the growing number of difficult to let (DTL) properties in the social sector. Drawing on findings from in-depth interviews with twenty local authorities, the paper provides evidence to support this argument and also highlights a number of initiatives which authorities have adopted to fill DTL properties. However, the paper argues that these initiatives are likely to have limited value in the long run in stemming the fall in demand for social housing, particularly in the North of England. The second part of the paper focuses on the changing aspirations of tenants and the way that social housing is in competition with alternative forms to housing provision, such as private rented housing. It concludes by advocating that an appropriate response to difficulties in letting social housing has to go beyond internal housing management initiatives. Instead a more strategic approach needs to be adopted which builds up an understanding of the operation of the local housing market and the complex interaction of neighbourhoods. 相似文献
195.
基于ARP协议的网络主机地址的识别技术研究 总被引:3,自引:0,他引:3
从移动IPv6工作原理入手,IP地址管理器是针对越来越严重的IP地址盗用现象而设计的一套有效的监控和管理IP地址的方案。分析与研究IP地址管理器中的信息收集模块后,以Winpcap为开发工具,利用ARP,附等协议完成对网络中活动主机的扫描以及信息(主机名、MAC、操作系统)的收集和识别。模块实现了对网络的自动实时监控,有效地提高了管理效率。 相似文献
196.
基于3S技术的土地动态监管系统研究 总被引:1,自引:0,他引:1
研究目的:针对目前县级国土资源土地利用动态监管的现状和要求,探讨了采用信息化手段如移动执法和在线分析等工具辅助土地执法监察管理,建立土地动态监管新模式.研究方法:采用全B/S架构,ArcGIS Server Standard 9.3 GIS平台和ArcPad 7.1嵌入式GIS平台,建立土地动态监管系统.研究结论:利用3S技术建立的土地动态监管系统可以满足土地监管工作信息化需求,操作简单便捷,适合基层土地管理人员使用,同时有助于提高工作效率,降低调查成本,规范土地执法监察行为. 相似文献
197.
灌溉实时调度是农业水管理走向智能化、自动化和现代化的重要标志,综合应用地理信息系统、卫星遥感技术、全球定位系统、计算机、人工智能、信息技术,以及农业灌溉、气象学、系统工程等多学科的最新成果,提高调度的灵活性、可靠性、实用性,是灌溉实时调度今后的发展趋势。同时,也面临着基础设施落后、技术力量薄弱、信息处理费用过高、卫星传输周期长等多方面的困难。综述了国内外在实时灌溉预报、渠系动态配水、土壤墒情监测、计算机辅助决策支持系统以及灌区空间信息管理等方面的最新研究进展和主要成就,力求促进灌区用水管理研究的发展。 相似文献
198.
199.
In irrigated agricultural landscapes, land-use conversion may have landscape-level social, hydrological, and ecological effects. We used geographic information systems (GIS) and interviews to analyze development effects on irrigation in the Henry's Fork Watershed, Idaho. Farmers developed irrigation there in the 19th century, and incidental recharge from canal seepage and flood irrigation raised groundwater levels and expanded wetlands. Cohesive culture in agricultural communities sustained irrigation systems until amenity-driven demographic shifts beginning in the 1970s led to development approved by local governments with land-use planning but no water-management authority. Although only 5% of irrigated land has been converted, development has fragmented irrigated landscapes and made canal-system operation more difficult, potentially reducing groundwater levels, wetland extent, and return flows critical to downstream irrigators and fish and wildlife. We discuss future scenarios, highlighting the need for increased communication among local and state governments regarding land use and water management in irrigated landscapes across the West. 相似文献
200.
随着农业和农村经济的发展,特别是农业产业化经营的兴起和农村劳动力转移的推进,农村土地承包经营权流转速度明显加快,规模不断扩大.该文论述了我国农村土地承包经营权流转的现状,针对目前农村土地承包经营权流转过程中出现的问题,从现行的法律体系中寻找解决思路,并对现行法律中的不足之处,提出了改良建议. 相似文献