A key issue in the implementation of the Water Framework Directive is the classification of streams and rivers using biologicalquality parameters and type-specific reference conditions. Four groups of stream types were defined in NE Spain on the basisof 152 diatom samples by means of detrended correspondence analysis and classification techniques. Diatom analysis was restrictedto epilithic taxa, and the sites included gradients ranging from near-natural streams to sites with poor ecological quality.The main gradient shows a clear separation of sites in relation to the degree of human influence: polluted streams (mainly locatedin the lowlands) differ from streams in mountainous areas and in the Pyrenees. A second gradient is related to physiographicalfeatures. Headwater streams can be distinguished by their catchment geology. The type-specific diatom taxa for the streamtypes studied were determined by using indicator species analysis (IndVal). The type-specific taxa from near-natural streams arecoincident with the indicator taxa for high ecological status. Human impact reduced the typological heterogeneity of the diatomcommunity composition. Overall, the diatom communities in NE Spain exhibit a regional distribution pattern that closely correspondswith that observed in river systems elsewhere. Physiographical differences are only evident in undisturbed sites, whilenutrient enrichment and other human disturbances may mask the regional differences in the distribution of diatom communities.

Salinity is a serious threat to freshwater ecosystems, particularly those near coastal areas. An increase in salinity producesdrastic changes in community structure of freshwaters, sometimes in an irreversible fashion. Thus, freshwater species must copewith salinity stress in a manner proportional to their degree of tolerance. Bearing this in mind, we studied the acute and chroniceffects of different salinity concentrations in two species of cladocerans: Daphnia magna Straus, a standard test organism, andDaphnia longispina O. F. Müller, an autochthonous species. Salinity experiments were based on successive dilutions of a stocksolution of NaCl in a synthetic medium. The results showed that D. magna is more tolerant than D. longispina, both in acute(EC50 5.9 and 2.9 g/L, respectively) and chronic (EC50 5.0 and 2.2 g/L, correspondingly) exposures. In the chronic exposure,salinity caused a significant reduction in fecundity and a developmental delay (increase in age at first reproduction), as well asa decrease in the growth rate of daphnids. However, these effects were mainly observed at salinity concentrations where mortalityoccurred.

Phytoplankton dynamics and morphological plasticity were studied in an oligo-mesotrophic lake from late spring to earlyautumn in 2004 on a weekly to bi-weekly basis. This study aimed to evaluate the effect of environmental constraints on morphologicalplasticity and size structure of dominant species through the stratified period of the lake. While centric diatoms developedmainly in the epilimnion, Fragilaria crotonensis, Synedra sp. and Synedra acus were very well distributed through thewhole water column, as was the cryptophyte Plagioselmis nannoplanctica. A filamentous cyanobacterium, Planktothrix rubescens,was stratified in the metalimnion throughout the sampling period, while Mougeotia sp. was entrained through the wholewater column during the early autumn. Surface area / volume (S/V) ratios were calculated for the dominant species on each samplingdate. The minimum S/V ratio was found with centric diatoms, while maximal values measured were for Synedra sp. andAsterionella formosa. The S/V ratio of the only dominant cryptophyte, Plagioselmis nannoplanctica was also high; variationswere negatively correlated with NO3-N and PO4-P (-0.62 and -0.61, respectively) and positively correlated with euphotic depth(r=0.57) and temperature (r=0.82). On the other hand, the S/V ratios of Fragilaria crotonensis and Cyclotella ocellata each showedstrong negative correlation with silica concentrations (-0.55 and -0.62, respectively). It is concluded that allometric relationshipsshowed significant differences among species according to depth and season.

We studied the influence of lotic and lentic stretches on zooseston flux in the karstic barrage Plitvice Lakes (Croatia). Threesampling stretches were selected: 1) a channel with low inclination; 2) water flow through a deep lake (retention), and 3) a channelwith cascades and sharp inclination. At all sampling points of the three stretches, zooseston reached maximum abundance inSeptember (up to 147.39 ind/m3). Rotifers dominated in both zooseston abundance (58 to 80%) and diversity (66 taxa), followedby crustaceans (23 taxa), predominantly Cladocera and Copepoda. Kruskal-Wallis test suggest statistically significant differencesbetween the lentic and both lotic stretches in the biomass net flux of euplanktonic organisms. The net flux of benthicorganism biomass and changes in the biodiversity index were significantly different between the lentic stretch and lotic stretchwith high inclination. Lotic stretches had a greater influence on the increase of abundance and biomass of benthic and semiplanktonicorganisms than on the decrease of euplanktonic organisms. Principal Components Analysis of the species environmentrelationship explained 66% of the variance by the two first axes, where axis 1 accounted for 39% and axis 2 accounted for27% of the variance. Oligochaets, insect larvae, nematodes and total zooseston were associated with component 1, showing thattheir biomass was negatively correlated with discharge and dissolved oxygen concentration and positively correlated with temperature.Other taxa showed a similar correlation with component 1. Biomass of Cladocera, Copepoda, T. birostris, Polyarthraspp., K. cochlearis and rotifers was associated with component 2, and positively correlated with food resources such as chl-a,POM and DOM. The inference is that zooseston flux through Plitvice Lakes is a function of the hydrological and physiographicalfeatures of the stretches, as well as food resources from the lakes.

Recent publications suggest that in large watersheds a large proportion (20 to 70%) of the net nitrogen input to the aquaticenvironment may be removed during water’s downstream path towards the outlet. In small watersheds there are few to no evaluationsof the importance of in-stream processes in the overall nitrogen budget due in part to the lack of simple and robustmethods for measuring in-stream nitrate uptake. We propose a comparative study for laboratory and field measurements on openmesocosms, 30 cm in diameter. Nitrate uptake was evaluated from the kinetics of disappearance of nitrate in water overlyingundisturbed sediment cores, both in the laboratory and in-situ. Using both laboratory and in-situ mesocosms was an effort todetermine whether the methods were comparable and applicable on a routine basis. Nitrate disappearance kinetics in the laboratoryyielded expected results, which are that nitrate uptake rates are linearly correlated to nitrate concentration in the watercolumn. In such conditions, our results show that the potential for nitrate uptake in streams can be calculated from the mass transfercoefficient. Our comparative study shows that incubations conducted in the laboratory intrinsically limit hyporheic exchanges,associated with small water level fluctuations, which may in fact prevail in the field as the in-situ incubations have shown.In-situ experiments yielded unexpected results, such as the succession of disappearance and gain of nitrate in the mesocosmsthrough time. This was attributed to hyporheic exchanges, both natural and artificially induced by the design of the mesocosms.Both methods should be considered for future nitrate uptake studies as they yield complementary results, provided that somesimple changes are made in the design of in-situ mesocosms.

Lithoglyphus naticoides was observed for the first time in the north of France at the beginning of the 19th century, but sincethen this gastropod has only succeeded in colonising the eastern half of this country. A map showing its distribution in Franceis proposed. In the Saône river, L. naticoides is an annual species: spawning occurs from March to June and the juveniles thatgenerally appear in May grow rapidly during the summer then spawn and disappear in the spring of the following year. Differentobservations suggest that increased water temperatures occurring in the context of global warming and potential/possible interspecificcompetition are the main reasons for the disappearance of L. naticoides in the Saône river at Lyon since November 2004.

The aquatic larvae of the Diptera are often the most abundant and most diverse group of the benthic macroinvertebrate fauna.They are able to survive in and colonise practically all freshwater habitats, and some species can tolerate harsh environmentalconditions. They are therefore both a qualitatively and quantitatively important group of biological indicators for assessing freshwatersystems. On the other hand their determination at the species level is very difficult. This is in part due to a lack of taxonomicwork in the group, but also the absence of comprehensive determination keys, that meet the needs of water managers. Asa result, the aquatic larvae of the Diptera often play a subordinate role in water management. In light of the EU Water FrameworkDirective the present work is a first step in improving the integration of the important group of the Diptera in water managementpractice: a comprehensive determination key, which is geared at water managers. The key includes 60 taxa, largely at the familyand genus level. In contrast to already existing keys the present work tries to differentiate the taxa on the basis of simple anduser-friendly characters. Numerous figures allow for easy checking of determination results. The key is applicable in Germany,Scandinavia, Great Britain and the Benelux states. Mainly taxa from running water systems are considered, but the key can alsobe used at the family level to determine taxa from standing water bodies.