Brigitte Lods-Crozet

Contrasting chironomid assemblages in two high Arctic streams on Svalbard

Chironomid communities were investigated twice in summer 1997 in a glacier-fed (Bayelva) and a non-glacial stream (Londonelva), fed by snowmelt and rainfall near Ny-Alesund (Svalbard Archipelago, 78°N). Environmental conditions (discharge, water temperature, suspended sediment) were harsher for the fauna in the glacial system than in the non-glacial one. In all, 29 chironomid species were identifi ed from larval, pupal and male adult material, including six species new to Svalbard. Diamesa was the best represented genus, showing contrasting distributional trends at the species level in the two streams: Diamesa aberrata and D. bohemani were more characteristic of the glacial stream, while D. arctica and D. bertrami colonised primarily the snowmelt-fed one. Total abundance of chironomid larvae was ten times greater in Londonelva than in Bayelva. The prevailing harsh conditions in glacial streams, such as high and fl uctuating discharge, high sediment transport and substrate instability, strongly infl uenced the abundance of the chironomid fauna, demonstrating the key importance of water source in Arctic streams.

Quantification of the daily dynamics of streamflow components in a small alpine watershed in Switzerland using end member mixing analysis

There is a growing need to improve our understanding of catchment flow generation processes, especially in alpine watersheds, where the aquatic biodiversity is dependent upon the types of water sources and their seasonal dynamics. In order to identify and quantify the potential sources that contribute to stream runoff, Water samples were collected and discharge was measured. Other physical variables like electric conductivity and water temperature were also collected twice a day, once in the morning and once in the evening. These measurements continued for two to four consecutive days. In situ measurements were done for temperature, electric conductivity and turbidity of water at different temporal scale. Mass spectrometry was done to analyze silica and sulfate along with chlorine. Three different water sources were identified based on their physiochemical characteristics: glacier melt water, quickly routed surface runoff, and slowly routed ground water. Principal component analysis was performed in order to reduce dimensionality of the chemistry data independently in two hydrological years. End member mixing analysis was carried out for morning and afternoon data to describe the daily variation of runoff components. Our study suggests that glacier melt component has a strong daily variation, which influences the magnitude and timing of peak flow. A sign of early melt and accumulation can be seen in this watershed based on the studied years.

La végétation macrophytique d'un lac hautement eutrophe du Plateau suisse: Le Baldegger See

The study of the qualitative and quantitative distribution of the Baldeggersee macrophytic vegetation is undertaken in 1980 with the help of colour aerial photographies and verification on the field. The comparison with old data allows then a short survey of the macrophytic evolution in relation to the eutrophication.