Headwater streams: neglected ecosystems in the EU Water Framework Directive. Implications for nitrogen pollution control

The European Union Water Framework Directive (WFD) aims to achieve the “good status” of waters by 2015, through monitoring and control of human impacts on “bodies of surface water” (BSWs), discrete elements for quality diagnosis and management. Headwater streams, however, are frequently neglected as they are not usually recognised as BSW. This poses limitations for the management of river catchments, because anthropogenic impacts on headwaters can constrain the quality of downstream rivers. To illustrate this problem, we compared nitrate levels and land use pressures in a small agricultural catchment with those recorded in the catchment in which it is embedded (Ega), and in the Ebro River Basin (NE Spain) comprising both. Agriculture greatly influenced water nitrate concentration, regardless of the size of the catchments: R² = 0.91 for headwater catchments (0.1–7.3 km²), and R² = 0.82 for Ebro tributary catchments (223–3113 km²). Moreover, nitrate concentration in the outlet of a non-BSW small river catchment was similar to that of the greater downstream BSW rivers. These results are of interest since, despite representing 76% of the length of the Ega catchment hydrographical network, only 3.1% of the length of the headwater streams has been identified as BSWs. Human activities affecting headwater streams should therefore be considered if the 2015 objective of the WFD is to be achieved.     

Glass buildings on river banks as “polarized light traps” for mass-swarming polarotactic caddis flies

The caddis flies Hydropsyche pellucidula emerge at dusk from the river Danube and swarm around trees and bushes on the river bank. We document here that these aquatic insects can also be attracted en masse to the vertical glass surfaces of buildings on the river bank. The individuals lured to dark, vertical glass panes land, copulate, and remain on the glass for hours. Many of them are trapped by the partly open, tiltable windows. In laboratory choice experiments, we showed that ovipositing H. pellucidula are attracted to highly and horizontally polarized light stimulating their ventral eye region and, thus, have positive polarotaxis. In the field, we documented that highly polarizing vertical black glass surfaces are significantly more attractive to both female and male H. pellucidula than weakly polarizing white ones. Using video polarimetry, we measured the reflection-polarization characteristics of vertical glass surfaces of buildings where caddis flies swarmed. We propose that after its emergence from the river, H. pellucidula is attracted to buildings by their dark silhouettes and the glass-reflected, horizontally polarized light. After sunset, this attraction may be strengthened by positive phototaxis elicited by the buildings' lights. The novelty of this visual-ecological phenomenon is that the attraction of caddis flies to vertical glass surfaces has not been expected because vertical glass panes do not resemble the horizontal surface of waters from which these insects emerge and to which they must return to oviposit.     

Nest site selection and induced response in a dominant arboreal ant species

It is well known that arboreal ants, both territorially dominant species and plant ants (e.g., species associated with myrmecophytes or plants housing them in hollow structures), protect their host trees from defoliators. Nevertheless, the presence of an induced defense, suggested by the fact that the workers discovering a leaf wound recruit nestmates, is only known for plant ants. Based on the results from a field study, we show here (1) that colonies of Azteca chartifex, a territorially dominant, neotropical arboreal ant species, mostly selected Goupia glabra (Goupiaceae) trees in which to build their principal carton nests and (2) that plant signals induced workers to recruit nestmates, which patrol the leaves, likely providing the plant with a biotic defense. Furthermore, the number of recruited workers was clearly higher on G. glabra, their most frequently selected host tree species, than on other tree species. These results show that contrary to what was previously believed, induced responses are also found in territorially dominant arboreal ants and so are not limited to the specific associations between myrmecophytes and plant ants.     

Mantophasmatodea now in the Jurassic

The Mantophasmatodea is the most recently discovered insect order. The fossil records of all other ‘polyneopteran’ orders extend far in the past, but the current absence of pre-Cenozoic fossils of the Mantophasmatodea contradicts a long evolutionary history, which has to be assumed from the morphological distinctness of the group. In this paper, we report the first Mesozoic evidence of a mantophasmatodean from the Middle Jurassic of Daohugou, Inner Mongolia, China. Furthermore, the new fossil shares apomorphic characters with Cenozoic and recent Mantophasmatodea, suggesting a longer evolutionary history of this order.     

Prediction of thermal hazards from fireballs

Various models of fireball diameter have been evaluated by statistical techniques. The model of Gayle for fireball diameter estimation showed good agreement between the predicted and experimental data. The models relating to fireball duration, transmissivity and view factor have been selected based on their relative merits. A user interactive computer program has been developed to predict thermal hazards from fireballs in chemical process industries.     

A drop in the bucket: when is a pay raise a pay raise?

Although merit pay continues to receive much theoretical and practical attention, little systematic effort is devoted to determining how large a pay raise must be before employees see it as a pay raise. This study uses psychophysical reasoning and techniques in a sample of 192 student ‘employees’ to establish the size of pay raise thresholds in a relatively controlled setting. Results indicate that, below about the 7 per cent level, increases in pay amounts are unlikely to evoke positive perceptual and attitudinal reactions among employees. Theoretical, methodological, and practical implications of these results are highlighted. © 1997 by John Wiley & Sons, Ltd.