Abstract:We investigated the mode (active versus passive) of larval downstream dispersal and its influencing factors in the nase carp (Chondrostoma nasus). Marked larvae (early and later stages), together with equivalent numbers of passive particles, were released in the main channel of the River Danube (Austria) at different flow (low, high) and current (over-critical, under-critical) conditions. Larvae and particles were recaptured with stationary nets at varying distances from release. We assumed that differences in the spatial dispersal patterns between larvae and particles were due to fish activity. We hypothesized that river discharge, developmental stage, current speed, and distance from release would influence these differences. We found that activity was independent of developmental stage or current speed at release, although activity was higher during low flow conditions. It may be that larvae deliberately enter the current during low flow, because the hydraulic conditions facilitate active dispersal. Furthermore, activity was greatest near the release site. This might be due to an intrinsically greater activity when fish are placed into novel surroundings or a result of rheoreaction. The discharge-dependent dispersal patterns observed represent an important ecological link between flow and recruitment and demonstrate the importance of inshore conditions for the early life stages of fish in large rivers, especially with regard to river modification and restoration schemes.Résumé : Nous avons étudié le mode (actif ou passif) de dispersion des larves vers l'aval et les facteurs qui l'influencent chez le hotu (Chondrostoma nasus). Des larves marquées (stades précoces et plus avancés) et un nombre équivalent de particules passives ont été relâchées dans le chenal principal du fleuve Danube (Autriche) dans différentes conditions d'écoulement (débit faible, débit élevé) et de courant (supercritique, sous-critique). Des larves et des particules ont été capturées dans des filets stationnaires à différentes distances du lieu de lâcher. Nous sommes partis de l'hypothèse que les différences des motifs de dispersion spatiale entre les larves et les particules étaient dues à l'activité des poissons. Nous avons postulé que le débit du fleuve, le stade de développement, la vitesse du courant et la distance par rapport au lieu de lâcher influenceraient ces différences. Nous avons constaté que l'activité était indépendante du stade de développement ou de la vitesse du courant au lieu de lâcher, l'activité étant toutefois plus forte durant des conditions de faible débit. Il est possible que les larves entrent délibérément dans le courant quand le débit est faible, parce que ces conditions hydrauliques facilitent la dispersion active. En outre, l'activité était la plus forte près du lieu de lâcher. Cela pourrait être dû à une activité intrinsèquement plus forte quand les poissons sont placés dans un environnement nouveau ou en raison d'une rhéoréaction. Les motifs de dispersion dépendant du débit observés constituent u...

The surface chemistry and dispersion in poly(lactic-acid) of microfibrillated wood and microfibrillated lignocellulose prepared from untreated and partially delignified beech were compared with conventional microfibrillated cellulose produced from bleached pulp. High heterogeneity in fibril morphology and bulk chemical composition was observed. Also surface chemistry of the fibrils was highly variable, but not clearly correlated with bulk chemistry. Composite solution-cast films of poly(lacticacid) reinforced with 1 % fibrils were produced by adding fibrils dried from solvent into a polymer solution. Highly variable dispersion of fibrils correlated with varying mechanical performance was observed. Correlations were obtained between surface chemistry of fibrils as revealed by X-ray photoelectron spectroscopy and adhesion force microscopy on the one hand and the tensile performance of the fibril-reinforced polymer composites on the other hand. Overall, certain variants of fibrillated material with residual lignin and hemicellulose content showed reduced surface polarity, improved dispersion in poly(lactic-acid) and improved reinforcement efficiency compared to conventional MFC produced from bleached pulp.

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