瑞典森林中不同地区的林下植被情况与氮沉积的关系

在557块针叶林分中进行调查,以图了解欧洲越桔(Vacciniummyrtillus)、越桔(V.vitis-idaea)和曲芒发草(Deschampsiaflexuosa)与氮沉积率的相互联系.欧洲越桔在高氮地区比在低氮地区发生频度、丰富度都较少并且易感染叶部病原(Valdensiaheterodoxa),越桔的发生与氮沉积的增加呈明显的负相关,曲芒发草却没有这种趋势.在高氮沉积地区,欧洲越桔在优势种为欧洲赤松的林分中比在挪威云杉为优势种的林分中更为最普遍.在氮沉积较低水平的地区不是这种情形.调查的情况与增施氮素实验的结果一致,氮沉积对植被显示了巨大的效应.数据表明即使是较低的氮沉积也可能减少针叶林分林下植被最优势种的丰富度.     

减少农田硝酸盐淋溶的可能性

农业土壤对自然水体中的硝酸盐含量有影响.从土壤中排出的高浓度的硝酸盐溶液关系到饮用水中硝酸盐的高浓度,同时,过量的硝酸盐还会改变河流、湖自的生态平衡.本文对通过改善农业措施减少硝酸盐淋溶这个重大环境问题进行了讨论.对农业土地硝酸盐淋溶的原因做了简略的解释,对于减少硝酸盐淋溶的现有措施做了描述、分析和评价.减少养分淋溶不是实施有机农业或传统农业所能解决的问题,而是应该通过引进和使用适当的对策来加以解决.为此,本文提出了最大限度地降低农业土壤养分淋溶的下述指导性原则,在某种程度上实施这些指导性原则需要一种新的观念:①在分析一个小流域内的养分淋溶时,应考虑到农田的环境指数和空间变异性对其的影响;②通过减少氮肥使用量和降低动物饲养密度,将土壤中的氮肥施用量降低到某一合理的水平,这一水平应稍低于土地预期最适产量的氮需求量;③依据不同地区耕作系统、土壤和气候对硝酸盐淋溶的敏感性,采取相应的对策来控制硝酸盐的淋溶,如作物间作、土地少耕或免耕、调节生物过程等.     

"21世纪的食物":寻找增进食物链可持续性的措施和工具的研究计划

"21世纪的食物",是一项包括整个农业食物链的跨学科研究计划,于1997～2004年在瑞典实施.该研究所面临的挑战是为整个食物链中存在的不可持续的活动提出环境分析工具和解决方案.这需要科学家和食物链利益相关人紧密合作.本文提出了一整套以可持续食物生产为特征的目标方案.综合和系统分析是用来分析拟定变化的可持续性的主要工具.在本文中我们对"21世纪的食物"的概念进行概述,同时着重说明一些结论.例如,我们发现:就环境影响和产品质量而言,总体上来说,有机农业及其产品并不比常规的产品和方法优越.项目所采用的一些管理经验非常独特,这也是项目成功完成的重要原因,所以本文中我们对此也进行了总结.     

提高农业种植体系有机物质中氮利用的可能性研究

土壤有机养分源中的氮释放受许多因子的影响,如土壤温度和水分、有机物质的化学组成.在某种程度上,控制有机物质的化学组成可以增加氮释放和植物需求的同步性,而气候因子是不能控制的,因此在计划管理措施时要考虑这些因素.本文通过调节新鲜或预处理过的植物材料和牲畜粪肥的化学组成、施用时间以及有意分配,来探讨影响氮释放的不同途径.最后阐述提高氮利用率需要实施的农场外的(off-farm)的选择,尤其是对氮过剩的农业体系.     

Past changes in Arctic terrestrial ecosystems, climate and UV radiation

At the last glacial maximum, vast ice sheets covered many continental areas. The beds of some shallow seas were exposed thereby connecting previously separated landmasses. Although some areas were ice-free and supported a flora and fauna, mean annual temperatures were 10-13 degrees C colder than during the Holocene. Within a few millennia of the glacial maximum, deglaciation started, characterized by a series of climatic fluctuations between about 18,000 and 11,400 years ago. Following the general thermal maximum in the Holocene, there has been a modest overall cooling trend, superimposed upon which have been a series of millennial and centennial fluctuations in climate such as the "Little Ice Age spanning approximately the late 13th to early 19th centuries. Throughout the climatic fluctuations of the last 150,000 years, Arctic ecosystems and biota have been close to their minimum extent within the most recent 10,000 years. They suffered loss of diversity as a result of extinctions during the most recent large-magnitude rapid global warming at the end of the last glacial stage. Consequently, Arctic ecosystems and biota such as large vertebrates are already under pressure and are particularly vulnerable to current and projected future global warming. Evidence from the past indicates that the treeline will very probably advance, perhaps rapidly, into tundra areas, as it did during the early Holocene, reducing the extent of tundra and increasing the risk of species extinction. Species will very probably extend their ranges northwards, displacing Arctic species as in the past. However, unlike the early Holocene, when lower relative sea level allowed a belt of tundra to persist around at least some parts of the Arctic basin when treelines advanced to the present coast, sea level is very likely to rise in future, further restricting the area of tundra and other treeless Arctic ecosystems. The negative response of current Arctic ecosystems to global climatic conditions that are apparently without precedent during the Pleistocene is likely to be considerable, particularly as their exposure to co-occurring environmental changes (such as enhanced levels of UV-B, deposition of nitrogen compounds from the atmosphere, heavy metal and acidic pollution, radioactive contamination, increased habitat fragmentation) is also without precedent.     

Gizzard shad put a freeze on winter mortality of age-0 yellow perch but not white perch.

Four decades of observations on the limnology and fishes of Oneida Lake, New York, USA, provided an opportunity to investigate causes of mortality during winter, a period of resource scarcity for most juvenile fishes, in age-0 yellow perch (Perca flavescens) and age-0 white perch (Morone americana). This time series contains several environmental (e.g., winter severity) and biological (e.g., predator abundance) signals that can be used to disentangle multiple effects on overwinter mortality of these fishes. A multiple regression analysis indicated that age-0 yellow perch winter mortality was inversely related to fish length in autumn and to the abundance of alternative prey (gizzard shad [Dorosoma cepedianum] and white perch). However, no length-selective predation of yellow perch by one of the main predators, adult walleye (Sander vitreus), was detected. In contrast, white perch mortality was directly associated with total predator biomass and abundance of white perch in autumn, and inversely related to yellow perch abundance as a potential buffer species, but not to the abundance of gizzard shad. Winter severity was not a significant predictor of mortality for either perch species. Predicted winter starvation mortality, from a model described in the literature, was much lower than observed mortality for yellow perch. Similar models for white perch were correlated with observed mortality. These results collectively suggest that predation is the main mechanism shaping winter mortality of yellow perch, while both predation and starvation may be important for white perch. This analysis also revealed that gizzard shad buffer winter mortality of yellow perch. Although winter duration determines the northern limit of fish distributions, in mid-latitude Oneida Lake and for these species, predator-prey interactions seem to exert a greater influence on winter mortality than starvation.     

Measurements and comparisons of gamma radiation doses in a high and a low (137)Cs deposition area in Sweden

Sweden is one of the countries affected by the Chernobyl fallout. The aim of the present study was to investigate the average radiation dose to people living in a high-deposition area (the parish of Hille) in Sweden for comparison with dose rates previously measured in a low-deposition area in western Sweden. Individual measurements (personal and dwelling dose rates) were performed using thermoluminescence dosimeters in 24 randomly chosen individuals. Dwelling and personal dose rates in Hille were 0.12 and 0.11 microSv/h, respectively. The dose rates in Hille were slightly higher than in western Sweden (difference for detached houses=0.024 microSv/h for personal and 0.030 microSv/h for dwelling dose rates), partly because of the higher (137)Cs deposition. In wooden houses, the difference was somewhat greater. Our results indicate a current contribution to personal gamma radiation in this area of about 0.2 mSv per year from the Chernobyl fallout.     

A new general dynamic model predicting radionuclide concentrations and fluxes in coastal areas from readily accessible driving variables

This paper presents a general, process-based dynamic model for coastal areas for radionuclides (metals, organics and nutrients) from both single pulse fallout and continuous deposition. The model gives radionuclide concentrations in water (total, dissolved and particulate phases and concentrations in sediments and fish) for entire defined coastal areas. The model gives monthly variations. It accounts for inflow from tributaries, direct fallout to the coastal area, internal fluxes (sedimentation, resuspension, diffusion, burial, mixing and biouptake and retention in fish) and fluxes to and from the sea outside the defined coastal area and/or adjacent coastal areas. The fluxes of water and substances between the sea and the coastal area are differentiated into three categories of coast types: (i) areas where the water exchange is regulated by tidal effects; (ii) open coastal areas where the water exchange is regulated by coastal currents; and (iii) semi-enclosed archipelago coasts. The coastal model gives the fluxes to and from the following four abiotic compartments: surface water, deep water, ET areas (i.e., areas where fine sediment erosion and transport processes dominate the bottom dynamic conditions and resuspension appears) and A-areas (i.e., areas of continuous fine sediment accumulation). Criteria to define the boundaries for the given coastal area towards the sea, and to define whether a coastal area is open or closed are given in operational terms. The model is simple to apply since all driving variables may be readily accessed from maps and standard monitoring programs. The driving variables are: latitude, catchment area, mean annual precipitation, fallout and month of fallout and parameters expressing coastal size and form as determined from, e.g., digitized bathymetric maps using a GIS program. Selected results: the predictions of radionuclide concentrations in water and fish largely depend on two factors, the concentration in the sea outside the given coastal area and/or adjacent coastal areas and the ecological half-life of the radionuclide in the sea. Uncertainties in these factors generally dominate all other uncertainties, e.g., concerning the surface water retention time, the settling velocity of the particulate fraction, the distribution coefficient regulating the fluxes in dissolved and particulate phases, the catchment area influences and the factors regulating biouptake and excretion of the radionuclide in fish. This means that the conditions in the sea are of paramount importance for the conditions in the coastal area, even for relatively enclosed coastal areas. This coastal model may be regarded as a tool for testing working hypotheses on the relative roles of different processes in different coastal areas. Such information is essential for getting realistic expectations of various remedial measures, such as coastal dredging discussed in this work.