Herbizide im Spannungsfeld zwischen Ökologie und Ökonomie

The Science of Nature - Effective weed control has always been one of the central problems in agriculture. With the increase in the size of farm units and the drop in the number of workers,...     

The rise and fall of new knowledge interests in the Dutch environmental movement

Summary Since the late 1960s concern about the pollution of our physical environment has grown into a social and political issue. In this process of increasing awareness, environmental activists have played a catalysing role in most Western countries. Moreover the environmentalists formulated an alternative set of ideas and strategies concerning the production and use of knowledge. These new knowledge interests were organised around three dimensions: cosmology, technology, and the organisation of knowledge production. On the basis of a case-study of Dutch environmentalism this paper tries to demonstrate how the articulation of these new knowledge interests of international scope actually occurred in the particular Dutch national setting. The analysis shows that many of the ideas brought forward in the course of time by Dutch environmentalists have been imported from abroad, especially from the United States, Great Britain and West Germany. However, the specific ways in which Dutch environmentalists have defined the content of their own knowledge interests have depended very much on the particularities of the political culture and socio-economic climate of the Netherlands, as well as the internal dynamics within the various environmental groups themselves.Dr Jacqueline Cramer was until very recently a member of staff in the Department of Science Dynamics at the University of Amsterdam. She has now moved to the TNO Centre for Technology and Policy Studies, P.O. Box 541, 7300 AM, Apeldoorn, The Netherlands. This paper forms part of a comparative study of the development of environmentalism in Sweden, Denmark and the Netherlands carried out in association with Ron Eyerman and Andrew Jamison of the University of Lund, Sweden.)     

Feeding frequency and parental division of labour in the double-brooded great tit Parus major

Summary We studied the relative contribution of each sex and total effort expended in feeding nestlings in the great tit Parus major in relation to artificially altered brood size. A recent model suggests that feeding frequency should reflect the optimal trade-off between parental and fledgling survival, the former being negatively, the latter positively, influenced by high feeding frequencies. In both sexes weight loss was linearly related to feeding frequency. Since fledgling survival increases with nestling weight, the conditions of this model are fulfilled. However, in contrast to the predictions of the model, the total feeding frequency for both sexes combined did not differ between control and enlarged broods, but was lower for reduced ones. This outcome was not the result of a physiologically related inability of the parents to increase their delivery rate. Instead, we suggest that parents with enlarged broods could not find sufficient amounts of prey large enough to be economically worth transporting to the nest. Differences in brood-provisioning rates between the sexes may arise because costs and benefits of feeding nestlings may differ. Females lost more weight than males during the nesting period, but maintained a relatively higher weight during the incubation period. The relationship between weight loss and feeding frequency was similar for both sexes. Male and female brood-feeding frequency was related to brood size in a similar way. This is discussed in light of the great tit's mating system and the fact that the great tit is facultatively double-brooded.     

Diffusion scrubber technique used for measurements of atmospheric ammonia

A diffusion scrubber (DS) was developed to measure trace levels of gaseous ammonia in ambient air. The sampling resolution time for this method is 10 min and the detection limit is estimated to be 0.01 ppbv. The response to the NI-I₃ concentrations is found to be dependent on the relative humidity in the ambient air and the temperature. The method is calibrated by using a diluted NH₃ cylinder gas, and the concentrations of the calibration gas were in the range 0.02–2 ppbv during the test. Sampling performed with the DS-method is compared to sampling performed by a filter pack and a continuous flow denuder (AMANDA). The DS-method shows good agreement with the continuous flow denuder and the filter pack.