The distribution and overall fish abundance, and biomass of fish populations in the open water of meso-eutrophic Lake Balatonwere studied in 2003-2007 using hydroacoustics and gill nets. Gillnet catches revealed that bleak (53-76 %) common bream (8-42%), white bream and razor fish (2-18 %) dominated in the open water of the lake. Comparisons of target strength distribution fromhydroacoustics and length distribution from the gillnets showed that the fishing gear did not quantitatively catch the smallest andlargest size groups of fish. Mean acoustic fish abundance and biomass fluctuated significantly between both basins and years. Thebiomass of fish populations reflects the trophic gradient along the longitudinal axis of the lake (min-max.: 89-181 kg ha-1) showinga decreasing trend with years. The mean acoustic fish biomass was significantly higher in the eutrophic western basin, comparedwith mesotrophic eastern and middle ones.

The population dynamics and life cycle of two mollusc species Pisidium amnicum and Valvata piscinalis of the Saône river werestudied for nine years. The newborn of the former species appeared in April each year. The latter species produced two cohorts peryear until 2003. Spawning in spring led to the birth of the early cohort, which generally appeared in May, while spawning in thesummer led to the birth of the late cohort, which appeared from July to November. The increase of the mean annual temperature by1.9°C from 1998 to 2000 was followed by an increase in the density of mollusc populations, possibly triggering or amplifying interand intra specific competition for food. However, the 2003 heatwave was responsible for the sudden decline of the P. amnicumpopulation, then the more progressive decline of that of V. piscinalis after having strongly modified its demographic structure andits life cycle. In 2004 and 2005 V. piscinalis only produced one cohort per year. The observations carried out strongly suggest thatthe insufficiency of available resources was one of the possible causes of their failure to recover in 2004 and 2005. The increase ofglobal warming predicted by different models could result in the gradual disappearance of P. amnicum from the potamon and ofV. piscinalis from the freshwater systems most directly exposed to climatic warming, such as the Saône River.

Mediterranean Temporary Ponds (MTPs) are priority habitats (Natura 2000) of great importance according to the EuropeanLegislation (Habitats Directive 92/43/EEC). They are being destroyed mostly because of public ignorance of their significantvalue. Today, MTPs are subject to high pressures from several human activities (agriculture, livestock, tourism etc.). In this work,the “Drivers-Pressures-State-Impacts-Responses” (DPSIR) model has been used, because it allows to evaluate the impact of thehuman socioeconomic pressure. We estimated the present condition of West Crete’s MTPs, in order to propose managementpractices for their restoration. A comparison with the Greek and European MTPs is also developed.

Without human intervention, ponds progressively fill up with aquatic vegetation, so that the structure and age of the vegetalformations show great contrasts within a given set of water bodies. We hypothesized that the biological traits of pond invertebratecommunities differed significantly among ponds having different vegetal formations. To test this hypothesis, we selected threeneighbouring ponds showing a gradient of vegetation cover and type (sparse bryophytes on rocky substrata (pond 1), extensivesubmerged Chara beds (pond 2), aerial Typha stands (pond 3)), and we studied between-ponds variations in the combinations ofspecies traits. Taxa biomass was monthly recorded in each pond over one year, to take into account species’ seasonality. Speciestraits were described using a fuzzy-coding method and a simultaneous analysis of the two matrices (co-inertia analysis) was usedto investigate changes in biological trait composition. Biomass increased from pond 1 to pond 3, and was higher in vegetal than inmuddy mesohabitats. Among 25 biological traits, 10 were significantly correlated to the distribution of samples: number of generationsper year, cohort production interval, adult longevity, adult size, number of eggs per female, dispersal ability, dispersal mode,consumer level, ingested food type, and feeding group. Invertebrates in pond 1 species allocated much energy to reproduction,while in pond 3 resource use was favoured by larger body size, long-lived organisms, and a higher diversity of feeding groups.Our results suggest that the structure and age of the vegetal formation play role in selecting species traits related to populationdynamics and feeding habits.

Sediment-water interactions play an important role in influencing the water quality of aquatic systems. Water quality managementof freshwater systems needs to take into account this behaviour, which depends largely on early diagenetic processes thatcondition the physical and biogeochemical properties of the sediment. Among these processes, the redox transformations resultingfrom the oxidation of organic matter by the microbial activity have a major influence on the biogeochemical properties of sediments.In particular, these reactions condition the vertical profiles of nutrient concentrations, pH and metals along the sedimentarycolumn. This paper presents a method which couples both experimental and modelling approaches in order to characterise andanalyse the biogeochemistry of freshwater sediments. The modelling approach is based on a coupling between biogeochemicalprocesses and interstitial diffusion. As pore water pH influences the behaviour of the biogeochemical species, we have extendedthese models to allow for the calculation of pH by taking into account the inventory of protons consumed or produced by differentbiogeochemical reactions. In parallel, an analytical protocol has been developed to obtain vertical distributions of the main physicochemicalparameters in natural sediments cores. To illustrate this approach, we apply our method to sediments cores sampled inthe Durance, a river in the south-east of France.