The responses of 32 Hydraenidae and Elmidae species to six chemical parameters -alkalinity, CI", S0 4 " ", COD, N0 3 \ and total P have been analysed in the Orbigo river basin. The study of the distribution in relation to these factors by means of elaborating their ecological profiles pointed out the indicator species for each one of these parameters, according to their reciprocal species-factor information.

-Complete inventories of the fauna at a given place, for a specific community or geographical area are often exceedingly hard to get. In recent years a number of estimation techniques have emerged that can be used to extrapolate from these samples to the true number of species in an area. These estimation models are based on different mathematical approaches and can be classified as either species accumulation curves or nonparametric estimators (Brose et al., 2003, Ecology, 84, 2364-2377. In this paper, we have tested the performance of some of the richness estimators on nineteen mountain ponds in Castilla y Leo´n (Spain) in order to provide guidance on their potential use in future researches. We collected benthic macroinvertebrate of these ponds from the littoral zone with a pond net by kicking and sweeping. Ten-second samples were collected in each pond up to a total time of 3 to 5 minutes per pond, depending on the pond size. In addition, two of the ponds, were sampled in 2004, 2006 and 2007 providing a three-year time series. The results of this study showed that Jackknife 2 was the best of the evaluated methods based on all chosen criteria and also performed well across all studied ponds. Jackknife 1, Chao 1 and Chao 2 also presented good results and they were inferior to Jackknife 2 mainly because of the requirement for larger sub-sample sizes.

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We built a classification system for lentic ecosystems and groundwaters in South-East León based on degree of mineralization and composition of major ions. In the ponds with the softest water (< 5 mEq/L), chlorides and bicarbonates were the main mineralizing anions. In contrast, in more highly mineralized ponds (> 5 mEq/L), all major ions were at comparable proportions. In these more mineralized shallow lakes, more sulphates could be found compared to less mineralized waters in the region. Independently of the level of mineralization, calcium was the predominant cation, although shallow lakes with lower mineral content favoured sodium over magnesium. The intense summer evaporation and the filling in autumn of ponds which had completely dried out and remained dry during the summer triggered changes not only in the mineral content, but also in the ionic composition of the water, with an increase in the concentrations of all ions in autumn. Overall mineralization and alkalinization were the two chief factors shaping the chemical variability of groundwater in our region. The length of flows discharging into groundwater-influenced areas shaped the general features of the wetlands studied, so that the degree of mineralization of the water in any given lake was determined in large measure by the geographical position. Thus, the greater length of flows in southerly areas of the study zone led to an increase in the more highly mineralized shallow lakes of the salinity of groundwater and of surfacing groundwater. Nonetheless, a substantial number of the ponds investigated are apparently linked to the aquifers under the "raña" formations. The chemical make-up of the water in these bodies is to some extent related to precipitation in the form of rain or in other forms and is apparently little influenced by groundwater. Hence the ponds are made up of slightly mineralized sheets of water, and can be tracked to discharges from brief surfacing groundwater flows. A link to deeper regional flows can be identified by the presence of comparatively more mineralized water bodies. Overall, outflows do not correspond to the chemical pattern of groundwaters, suggesting a more complex explanation for the hydrology of the study area.

The chemical composition of the river Bernesga has been evaluated throughout four seasonal sampling studies at twelve sampling points. The tendency towards an increase in mineralization all along the river can be observed when using a principal component analysis to the complete data gathered. A temporal differentiation based on the variations which affect the flow rate through out the year is also established.The spatial organization defined by the second component enables us to use the scores as the starting point in order to determine the value of the chemical distance between the different sampling stations. The contrast between the chemical and actual distance gives an overall view of the river, which is a reflection of what happens on its course with regard to its chemical processes.VariaUons spatio-temporelle de la composition physico-ehimique de la rivière Bernesga (Leon, Espagne).Mots clés : Physico-chimie, rivières.12 stations ont été échantillonnées aux 4 saisons pour étudier la composition chimique des eaux de la rivière Bernesga. L'analyse de l'ensemble des données par une méthode en composantes principales révèle une augmentation de la minéra-lisation le long de la rivière. Des différences temporelles liées aux variations qui affectent le volume d'eau au cours des saisons sont également établies.L'organisation spatiale définie par la seconde composante nous permet de déterminer une distance chimique entre les différentes stations. La comparaison entre la distance chimique et la distance réelle donne un reflet général des processus chimiques qui se déroulent sur le cours de la rivière.