ALBERT

Notes: 1. The impact of burrowing larvae of Ephoron virgo (Ephemeroptera, Polymitarcidae) on sediment microbiology has not been previously investigated because of difficulties in sampling the sediment of large rivers under in situ conditions. Therefore, we conducted experiments in the on-ship Ecological Rhine Station of the University of Cologne (Germany), in which ambient conditions of the River Rhine can be closely mimicked.2. In two consecutive seasons, experimental flow channels were stocked with Ephoron larvae and continuously supplied with water taken directly from the River Rhine. Sediment from the immediate vicinity of Ephoron burrows (i.e. U-shaped cavities reaching 10–80 mm deep into the sediment) and bulk sediment samples were analysed for (i) particulate organic matter content, (ii) microscale in situ distribution of O2, NO〈inlineGraphic alt="inline image" href="urn:x-wiley:00465070:FWB1258:FWB_1258_mu1" location="equation/FWB_1258_mu1.gif"/〉, and NH〈inlineGraphic alt="inline image" href="urn:x-wiley:00465070:FWB1258:FWB_1258_mu2" location="equation/FWB_1258_mu2.gif"/〉, and (iii) potential activities of exoenzymes.3. Sediment surrounding the Ephoron burrows had markedly higher organic matter contents and exoenzyme activities compared with the bulk sediment. Microsensor measurements demonstrated that local O2 and NO〈inlineGraphic alt="inline image" href="urn:x-wiley:00465070:FWB1258:FWB_1258_mu3" location="equation/FWB_1258_mu3.gif"/〉 penetration into the sediment were greatly enhanced by larval ventilation behaviour. Volumetric O2 and NO〈inlineGraphic alt="inline image" href="urn:x-wiley:00465070:FWB1258:FWB_1258_mu4" location="equation/FWB_1258_mu4.gif"/〉 turnover rates that were calculated from steady state concentration profiles measured directly in the burrow lining were considerably higher than at the sediment surface.4. In the sediment of the fast flowing River Rhine Ephoron burrows are preferential sites of organic matter accumulation and dissolved oxidant penetration. Our data suggest that the burrows are surrounded by a highly active microbial community that responds to the inputs from the water column with elevated O2 and NO〈inlineGraphic alt="inline image" href="urn:x-wiley:00465070:FWB1258:FWB_1258_mu5" location="equation/FWB_1258_mu5.gif"/〉 turnover, and release of exoenzymes into the sediment pore water. Especially during periods of mass occurrence, the larvae of E. virgo may thus significantly contribute (i) to the ecological connection between the water column and the sediment and (ii) to biogeochemical processing of organic matter in the riverbed.

Notes: Abstract Recently the fauna of the River Rhine (macrozoobenthos) has recovered, but the species composition has changed. Some formerly extinct species have returned, but new species, introduced from other regions, have successfully invaded the stream. These neozoans, mainly bivalves and crustaceans, obviously tolerate the changed conditions and the remaining pollution better than most of the original stream species

Notes: Summary 1. New methods for the observation of moulting-, pupation-, and emergence-rhythms under natural and experimental conditions are described. 2. The larvae feed during all hours of the day. Rhythmic changes in their behaviour were not observed. 3. The drift rate of medium and large larvae is very low, if the animals are not disturbed (0.05% per day,n=5,500). The drift rate of young larvae seems to be much higher, but could not be determined quantitativly. Drift rhythms must not be concerned with circadian rhythms in Simuliidae. 4. The larvae moult and pupate during all hours of the day. The number of moults and pupations reaches its maximum in the afternoon. 5. The duration of the pupal stage depends on temperature and the hour of pupation. In the stream Kaltisjokk it lasts about 6–7 days. 6. The seasonal emergence of 9 species is compared in two years. 7. All species (10) emerge during the daylight hours. The rhythm persists in the continous light of the subarctic summer and under artificial LL and DD. 8. Emergence is timed by changes in light and temperature. Within ecological limits light is the dominant Zeitgeber. 9. Under LL and DD the Simuliidae emerge two hours after a rise in temperature. 10. Under natural illumination and low temperatures the emergence is concentrated round noon. In relatively high temperatures the distribution becomes broader and sometimes biphasic. There were no specific differences between species and sexes. 11. Simuliidae fly mainly in the morning and evening to a CO2-trap.Helodon ferrugineus was caught in light traps during the night.

Notes: Zusammenfassung Die Ausdrift von Niphargus aquilex schellenbergi Karaman aus Quellen verläuft tagesperiodisch. Sie wind durch eine Aufwanderung kompensiert. Drift und Aufwanderung werden als regelmäßige Bewegungen zwischen Spaltenwasser und Quellbach angesehen. Durch Farbmarkierung wird nachgewiesen, daß sie Niphargen unterhalb des Quellabflusses Nahrung aufnehmen und zurückwandern. Extrem große Driftfänge, deren Zusammensetzung sich auch qualitativ von der normalen Drift unterscheidet, können bisher noch night zufriedenstellend erklart werden. Die Tagesperiodik der Ausdrift wird von LD-Wechsel gesteuert. Schwankungen von Temperatur, O2- und CO2-Gehalt des Wassers lassen keinen Einfluß erkennen. Es wird vermutet, daß die Tagesperiodik der Ausdrift auf einer Aktivitätsperiodik beruht.