Helerotrophic (cetoenzymatic and respiratory activities) and autotrophic (photosynthetic activity) metabolism on epilithic strearn biofilms have been measured, analyzed and studied in this thesis.The main objective was to determine the role of the heterotrophs in organic matter use (autochthonous and allochthonous) in Mediterranean streams.In Riera Major, a siliceous forest Mediterranean stream, the capacity to cleave polysaccharides is more important in the epipsammon than in the epilithon. The heterotrophic activity in the surface sediment was higher than in the subsurface sediment. This has been related to the higher quantity and quality of the organic matter which accumulates in the surface sediment. A drastic increase in benthic algal biomass and ectoenzymatic activities was observed in a stream stretch where the riparian vegetation had been removed.The bedrock of La Solana, a calcareous Mediterranean stream, is covered by a thick cyanobacterial crust with a layered structure similar to a stromatolite where different algal patches developed. This structure has a great capacity for organic matter utilization and seems to be adapted to the drastic environmental changes characteristic of Mediterranean streams. Specially, the ectoenzymatic activities were immediately recovered after a dry period.The ectoenzyme kinetics in Riera Major and La Solana was investigated along a seasonal study. In La Solana Vmax values for the three enzymes studied were always higher and the turnover time of substrate hydrolysis was lower (faster) than in the Riera Major which might be related to the more labile substrates for the heterotrophs (organic compounds from the primary producers) while Riera Major is receiving a more recalcitrant material (Ieaf from the riparian vegetation).The ectoenzymatic activity in the epilithic biofiIm of a fourth-order river, the Ter, followed a markedly seasonal pattern, most activities and biomass showing a peak in spring and autumn. Discharge and nutrients were the most important factors for Ihe regulation of biofilm metabolism.The epilithic ectoenzymatic activities were also measured in a Central European mountain stream. Colonization studies (by using clay tiles as substrates for the epilithon) showed that algal material is used by the heterotrophs as an organic matter source. / METODOLOGIA: La tècnica principal utilitzada en aquest estudi és la mesura de les activitats ectoenzimàtiques en els diferents biofilms -epilítics. Epipsàmmícs, crosta cianobacteriana- de nus. En aquest capítol es descriu el desenvolupament d'aquesta metodologia (procés d'incubació, concentració dels substrats, temps d'incubació) i la seva alplicació en l'estudi dels biofilms. Així mateix són descrites les altres mesures metabóliques aplicades en aquest estudi (activitat respirotória, ETS, i activitat fotosintètica, incorporació de H(14)CO3) així com la densitat i biomassa algals (comptatge de cèl.lules, clorofil.la-a) i bacterianes (microscopia de fluorescència) i la mesura dels paràmetres físics i quimícs del riu.

La investigación analiza el proceso de integración económica internacional y la competitividad de los países en transición de la Europa central (PEC) desde una perspectiva global. Defiende que el modelo de inserción de estos países en la economía mundial ha cambiado sustancialmente, pasando a predominar los sectores de sofisticación tecnológica media y alta e intensivos en capital físico y humano, y encuentra como principales impulsores del cambio estructural la apertura exterior y el objetivo estratégico de integración en la UE. El año 1997 aparece como el punto de inflexión clave, vinculado al aumento de las inversiones extranjeras directas y al cambio estratégico de las empresas multinacionales. No obstante, el proceso de globalización también ha influido, por la fuerte irrupción de los países asiáticos y la recuperación de los mercados de los países ex CAEM. El estudio también evidencia una mejora en la posición competitiva de estos países, que se encuentra ya muy próxima a los países de la UE-Sur, y defiende que la competitividad internacional ya no descansa sólo en las ventajas de costes, sino también en variables distintas al precio. No obstante, la investigación pone de relieve que todavía existen importantes retos a superar como el fenómeno de la dualización industrial, las asimetrías territoriales, la escasa capacidad de innovación y la limitada presencia en las regiones emergentes más dinámicas. Aunque en los últimos años se están observando mejoras relativas en algunos de estos aspectos, se considera necesario un papel más activo de los gobiernos y una mayor voluntad de apoyo por parte de la Unión Europea. / "THE INSERTION MODEL AND COMPETITIVE POSITION OF THE CENTRAL-EASTERN EUROPEAN COUNTRIES WITHIN THE CURRENT WORLDWIDE CONTEXT". TEXT:This research looks into the process of international economic integration and competitiveness of the central-eastern European countries from a global perspective. It argues that the insertion model for bringing these countries into the mainstream of the world economy has undergone significant change, where sectors employing a medium to high level of technological sophistication, with a high physical and human capital are gaining the upper hand, finding the international openness and the strategic goal of EU membership as the core of the thrust which is leading structural changes. In this context, the year 1997 can be credited as being the watershed, linked to the rise in foreign direct investment and the strategic changes made by the major multinationals. Nevertheless, the process of globalisation has also born an influence, most notably for the great impact caused by the Asian countries on the international scene and the recovery of markets from states of the former Comecon block. This work also sheds light on the improvement in the competitive position of the central¬eastern European countries, now in a position not far removed from those of the southern EU countries, underlining the assertion that international competitiveness does not depend solely on cost advantage, but on a number of variables apart from just price. It should be pointed out though that research has brought to light a number of important challenges to be overcome, such as that of the phenomenon of the dualisation of industry, territorial imbalances, a shortage of innovational skills and a limited presence in some of the most dynamic emerging regions. Even if in recent years some of the above have experienced movement in the right direction, it is nevertheless felt that governments should be taking a more active role and a greater determination to support the region be expressed in real terms by the European Union.