排序方式: 共有19条查询结果,搜索用时 20 毫秒
1.
2.
The Science of Nature - 相似文献
3.
4.
The Science of Nature - 相似文献
5.
Howard BJ Beresford NA Gashchak S Arkhipov A Mayes RW Caborn J Strømann G Wacker L 《Journal of environmental radioactivity》2007,98(1-2):191-204
In summer 1993 we measured the transfer of (239/240)Pu to milk from herbage from a pasture located 5 km from the Chernobyl nuclear power plant. In one treatment cows were allowed to graze freely on the pasture. In a second treatment, cows were fed herbage collected from the pasture in stalls. The milk transfer coefficient; F(m) did not vary significantly between treatments and the mean value of 7.5x10(-6)d l(-1) was higher than previously reported values. Despite many values of F(m) for Pu in the literature we identified few relevant original data sets. Transfer coefficient values for Pu are only appropriate when used in conjunction with a specified time period or an appropriate model which allows for the biological half-life. We recommend for screening purposes an F(m) value of 1x10(-5)d l(-1) for Pu, with an order of magnitude lower value being appropriate for cows which are only exposed for one grazing season. 相似文献
6.
7.
Agricultural land use has shifted towards more intensified production because the prices of agricultural products have increased
during the past years. Just a few years ago, voluntary area set-aside was a lucrative alternative in some regions. But nowadays,
land is re-cultivated again, inter alia with biomass crops. Consequently, this affects the soil and nutrient balances in agriculture.
The global changes on the world markets influence agricultural production and thus the water cycle at the regional scale.
In this paper, the regional developments and policy alternatives are discussed for the Elbe River Basin. The paper concludes
that on average, no substantial effects of nitrogen surpluses are expected for the Elbe River Basin due to a continuing decline
in animal herds. However, at the county level, nitrogen surpluses are likely to exceed the maximum threshold of 60 kg nitrogen
per hectare (stipulated in the German Fertiliser Regulation) due to regional concentrations of animal production. A halving
of the threshold to 30 kg per hectare shows that the marginal costs of nitrogen surplus reduction regionally exceeded 10 Euros
per kilogram nitrogen. 相似文献
8.
9.
10.