Job-related mobility and plant performance in Sweden

This paper uses a Swedish micro-dataset containing 2,696,909 hires during the period 2002–2006 to assess the impact of job-related mobility on plant-level performance. The analysis classifies new recruits according to their work experience and level of formal qualification, as well as by the region of origin and of destination. New hires are divided into graduates and experienced workers and between high- and low-educated. The results point towards the importance of acknowledging both the experience and the skills of new recruits. The greatest benefits are related to hiring new workers from outside the region where the plant is located. The analysis also stresses the importance of geography, with plants in metropolitan regions gaining the most from labour mobility, while the benefits of mobility for plants in smaller, more peripheral regions are more diverse and dependent on both the type and origin of new workers.     

空间分辨率对总初级生产力模拟结果差异的影响

利用模型分析气候变化对陆地生态系统功能的影响,是当前全球变化生态学的研究热点,然而模型模拟不确定性来源之一就是空间异质性的问题。空间异质性是尺度的函数,基于气象和遥感数据驱动的生态系统过程模型（BEPS模型）,分别模拟2003-2005年中国生态系统通量观测与研究网络（ChinaFLUX）长白山站、千烟洲站、海北站及当雄站在1 km和8 km空间分辨率下的总初级生产力（GPP）的时间动态变化,并结合土地覆盖类型及叶面积指数(LAI)的差异,探讨两种空间分辨率输入数据对GPP模拟结果的影响。结果表明：① 差异性主要是由于8 km范围内混合像元导致LAI的不同,4个站点月均差异值分别为0.85、1.60、0.13及0.04;② 两种空间分辨率均能较好地反映各站点GPP的季节动态变化,与GPP观测值的相关性R²为0.79~0.97 (1 km)、0.69~0.97(8 km),月均差异值为11.46~29.65 gC/m²/month (1 km)、11.87~24.81 gC/m²/month (8 km);③ 4个通量站点在两种空间分辨率下的GPP月均差异值分别为14.43,12.05,4.79,3.22 gC/m²/month,不同空间分辨率的模拟结果在森林站的差异大于草地站,且生长季的差异大于非生长季。因此,模型在模拟大尺度、长时间序列GPP时,为了提高模型模拟效率,适度降低空间分辨率是可行的,但应尽量减小低空间分辨率对于森林生态系统以及生长季GPP模拟上的误差。     

无线传感器网络和遥感技术结合监测煤矿环境地质

针对矿区环境地质监测面临的主要问题,本文探讨了结合无线传感器网络技术和遥感技术对矿区进行环境地质监测的方案,并针对该方案面临的问题与难点,提出了运用这两种技术在矿区建立植被净初值生产力(NPP)动态模型来实时监测矿区的环境地质状况的设想。     

How is organic farming performing agronomically and economically in sub-Saharan Africa?

The potential of organic agriculture and agroecological approaches for improving food security in Africa is a controversial topic in global discussions. While there is a number of meta-analyses on the environmental, agronomic and financial performance of organic farming, most of the underlying data stems from on-station field trials from temperate regions. Data from sub-Sahara Africa in particular, as well as detailed real-farm data is scarce. How organic farming is implemented in sub-Saharan Africa and how it performs in a smallholder context remains poorly understood. We applied a novel observational two-factorial research design, which allowed to evaluate the impacts of i) interventions for introducing organic agriculture and ii) specific organic management practices on 1,645 farms from five case studies in Ghana and Kenya, which we closely monitored for 24 months. Among the farmers who have been exposed to the interventions, we found heterogeneous adoption of organic agriculture principles, depending on the intervention. Furthermore, we found rather passive than active organic management among farmers. Most yields and gross margins under organic management remained at similar levels as the conventional values in four of the case studies. In one case study, however, coffee, maize and macadamia nut yields increased by 127–308% and farm-level gross margins over all analysed crops by 292%. Pooling our data across all case studies, we found significantly higher (+144%) farm-level gross margins on organically managed farms than on conventional farms. This indicates the potential of organic and agroecological approaches if implemented well. Based on our observations, we argue for improving the implementation of organic agriculture projects in settings with smallholder farmers. Limited capacities, lack of appropriate inputs and market access are major agronomic and institutional challenges to be addressed. Furthermore, we argue for supporting a differentiated debate about which types of organic farming are really desirable by classifying approaches to organic farming according to i) their intention to work organically and ii) the degree of following the organic principles. This will support the design and implementation of targeted policy interventions for stimulating sustainability of farming systems and rural development.     

Productivity,carbon assimilation and intra-annual change in tropical reef platform seagrass communities of the Torres Strait,north-eastern Australia

Detailed data on seagrass distribution, abundance, growth rates and community structure information were collected at Orman Reefs in March 2004 to estimate the above-ground productivity and carbon assimilated by seagrass meadows. Seagrass meadows were re-examined in November 2004 for comparison at the seasonal extremes of seagrass abundance. Ten seagrass species were identified in the meadows on Orman Reefs. Extensive seagrass coverage was found in March (18,700 ha) and November (21,600 ha), with seagrass covering the majority of the intertidal reef-top areas and a large proportion of the subtidal areas examined. There were marked differences in seagrass above-ground biomass, distribution and species composition between the two surveys. Major changes between March and November included a substantial decline in biomass for intertidal meadows and an expansion in area of subtidal meadows. Changes were most likely a result of greater tidal exposure of intertidal meadows prior to November leading to desiccation and temperature-related stress.     

Livestock production and the water challenge of future food supply: Implications of agricultural management and dietary choices

Human activities use more than half of accessible freshwater, above all for agriculture. Most approaches for reconciling water conservation with feeding a growing population focus on the cropping sector. However, livestock production is pivotal to agricultural resource use, due to its low resource-use efficiency upstream in the food supply chain. Using a global modelling approach, we quantify the current and future contribution of livestock production, under different demand- and supply-side scenarios, to the consumption of “green” precipitation water infiltrated into the soil and “blue” freshwater withdrawn from rivers, lakes and reservoirs. Currently, cropland feed production accounts for 38% of crop water consumption and grazing involves 29% of total agricultural water consumption (9990 km³ yr⁻¹). Our analysis shows that changes in diets and livestock productivity have substantial implications for future consumption of agricultural blue water (19–36% increase compared to current levels) and green water (26–69% increase), but they can, at best, slow down trends of rising water requirements for decades to come. However, moderate productivity reductions in highly intensive livestock systems are possible without aggravating water scarcity. Productivity gains in developing regions decrease total agricultural water consumption, but lead to expansion of irrigated agriculture, due to the shift from grassland/green water to cropland/blue water resources. While the magnitude of the livestock water footprint gives cause for concern, neither dietary choices nor changes in livestock productivity will solve the water challenge of future food supply, unless accompanied by dedicated water protection policies.     

山东近岸水域的初级生产力

近几年来,我们对山东近岸34个海岛和一些海湾进行了综合性调查,本文主要根据这些调查的实测资料.在综合分析整理的基础上.获得了山东近岸水域浮植物的现存量(叶绿素 a)为0.91mg/m~2,初级生产力水平为310.2mg/(m~2·d),基本接近温带海洋近岸水域标准;其分布特征是以莱州湾、渤海海峡、千里岩海区为最高,宫家岛、鸭岛海区为最低;季节变化显著,主要显示双峰型特征.根据初级生产力的测定结果,我们对山东近岸水域潜在的各级生物生产力做出了初步估算,旨在为山东近岸水域开展海水增养殖,合理开发海洋资源提供科学依据.     

Spatio-temporal distribution of dissolved inorganic carbon and net community production in the Chukchi and Beaufort Seas

As part of the 2002 Western Arctic Shelf–Basin Interactions (SBI) project, spatio-temporal variability of dissolved inorganic carbon (DIC) was employed to determine rates of net community production (NCP) for the Chukchi and western Beaufort Sea shelf and slope, and Canada Basin of the Arctic Ocean. Seasonal and spatial distributions of DIC were characterized for all water masses (e.g., mixed layer, halocline waters, Atlantic layer, and deep Arctic Ocean) of the Chukchi Sea region during field investigations in spring (5 May–15 June 2002) and summer (15 July–25 August 2002). Between these periods, high rates of phytoplankton production resulted in large drawdown of inorganic nutrients and DIC in the Polar Mixed Layer (PML) and in the shallow depths of the Upper Halocline Layer (UHL). The highest rates of NCP (1000–2850 mg C m⁻² d⁻¹) occurred on the shelf in the Barrow Canyon region of the Chukchi Sea and east of Barrow in the western Beaufort Sea. A total NCP rate of 8.9–17.8×10¹² g for the growing season was estimated for the eastern Chukchi Sea shelf and slope region. Very low inorganic nutrient concentrations and low rates of NCP (<15–25 mg C m⁻² d⁻¹) estimated for the mixed layer of the adjacent Arctic Ocean basin indicate that this area is perennially oligotrophic.     

IFQs and total factor productivity changes: The case of the Gulf of Mexico red snapper fishery

This study investigates changes in the total factor productivity (TFP) and identifies the main sources of TFP growth following the adoption of an individual fishing quota (IFQ) program in the Gulf of Mexico red snapper commercial fishery. Utilizing an unbalanced panel of 722 vertical line vessels Malmquist indices were derived from an output-oriented stochastic distance frontier. The analysis shows that the IFQ program had a positive impact on the productivity of the fleet and that most of the productivity gains were due to improvements in technical efficiency. The study also finds that changes in technical efficiency were time variant suggesting that the exit of the less efficient vessels and easing of command and control regulations such as trip limits and short fishing seasons were responsible for most of these gains. Changes in the exploitable biomass of red snapper were found to have a moderate impact on productivity growth whereas the impact of technological progress was minimal.     

New evidence for a glacioeustatic influence on deep water circulation, bottom water ventilation and primary productivity in the South China Sea

We provide new evidence for the development of a stable estuarine circulation characterized by stagnating water bodies, nutrient recycling and increased primary productivity in the South China Sea (SCS) during glacial intervals. This circulation was caused by the closure of the shallow and narrow straits connecting the SCS in the south and west. Our main evidence is derived from newly measured Mn concentrations and Mn/Al ratios in two sediment cores from the northern and southeastern SCS covering the last 500 ky. Concentrations and Mn/Al ratios of the redox sensitive element Mn show clear glacial–interglacial cycles with maxima during interglacial periods and minima during glacial periods. These cycles indicate ventilation cycles of the bottom water, and are connected to the glacial–interglacial changes in sea level. In contrast, total organic carbon (TOC) concentrations display an opposite pattern with pronounced maxima during glacial times, especially in the southern part of the basin. The variations in TOC can be ascribed to two factors. Firstly, variations in primary productivity are controlled by variations in the intensity of the winter monsoon. Secondly to the degree of preservation of TOC controlled by variations in ventilation, which in turn is ultimately controlled by sea level. Consequently, variations in TOC represent a superimposition of primarily sea level influenced preservation control and winter monsoon driven variations in primary productivity intensity. The decrease in Mn correspond to times when sea level dropped 40–60 m below the present level. The larger amplitude of the variations in TOC and Mn in the southern part of the basin compared to the northern site suggest that oxygen depletion and nutrient recycling was stronger in the parts of the basin situated the furthest away from the only remaining opening to the open Pacific, the Luzon Strait.