We investigated factors that contribute to isotopic carbon fractionation in periphytic biofilms in a human-altered headwater stream with a flashy hydrograph. Water velocity had an important effect on periphyton ␦ 13 C, explaining both temporal and spatial variation. We found that water velocity averaged over a certain period before sampling, rather than the instantaneous water velocity, explained a high percentage of both temporal and spatial variation of the periphyton ␦ 13 C signature. The relationship between water velocity and periphyton ␦ 13 C signature was particularly influenced by individual flow events during the recent flow history. A simple model based on a flow history of 3-4 weeks reliably estimated the ␦ 13 C signature of periphyton from distinct reaches. The model clearly identified signature shifts caused by the deposition of activated sludge particles from a wastewater treatment plant onto the periphytic biofilms. We highlight the high spatial and temporal variability of periphyton ␦ 13 C signatures (i.e., up to 3-6‰) in a heterogeneous flow environment with inputs from a wastewater treatment plant, and we explore its implications for food web analysis.

Pelagic food web processes with focus on phyto-and bacterioplankton dynamics were followed in a high Arctic lake on Ziegler Island, Franz Joseph Land archipelago, during July and August 1996. The oligotrophlc, permanently ice-covered lake is characterized by a rather short pelagic food web with rotifers representing the highest trophic level. Phytoplankton biomass and net primary production averaging 1.8 pg chl a 1-' and 22 pg C 1-' d-', respectively, decreased dunng the investigation period. Photosynthetic extracellular release (P,,) corrected for bacterial uptake was high and contributed between 31 % (July) and 96% (August) of total primary production. The abundance of bacteria (9.3 to 17.3 X 10' ml-l) and flagellates (7.8 to 17.3 X 10' ml-l) varied within a narrow range. Bacterioplankton production ranging from 1.2 to 3.9 pg C 1-' d-' and bacterial growth rates (0.1 to 0.3 d-') increased with increasing % P,,, indicating that algal exudates are the major carbon source for bacterioplankton. Bacterial carbon demand (assuming a 50% growth efficiency) amounted to 19% of gross pelagic primary production (P,,,, + P,,) and 31 % of P,, during the investigation period. Evidence was found that bacterioplankton metabolism responds quickly to slight increases in temperature (1.2 to 2.0°C) with increased growth. Overall, production rates of phyto-and bacterioplankton in this high Arctic lake are simdar to other Arctic lakes studied thus far, and the food web structure is even simpler than in most lakes at similar latitudes.

The effect of solar radiation (photosynthetically active radiation and ultraviolet radiation [UVR]) on the photosynthetic extracellular release (PER) of phytoplankton and its utilization by bacterioplankton were studied in an alpine lake (Gossenköllesee, Austria) over a seasonal cycle. For comparison, 2 Arctic lakes on the Taymir Peninsula (Siberia) were investigated as well. The contribution of PER to primary production (% net PER) ranged between 0 and 95% (mean 32%) in Gossenköllesee (May 1999 to July 2000) following a seasonal trend that was inversely related to phytoplankton biomass. PER was released only under light conditions and was positively related to the intensity of solar radiation. During the ice-covered period, the % net PER increased, while total primary production (P tot ) decreased with experimentally increasing irradiance, indicating radiationinduced stress with dark-adapted phytoplankton. During the ice-free period, the increase of % net PER with increasing irradiance was independent of photoinhibition. The fraction of PER not immediately incorporated by bacteria (~60% of total PER) may be an important contribution to the generally low pool of dissolved organic carbon (DOC) in Gossenköllesee. At the Arctic site, net PER amounted to 21% of P tot in an ice-free lake and 51% in the ice-covered Lake Nyagamya. In all lakes, the amount of PER was sufficient to meet the bacterial carbon demand. The UVR-induced inhibition of primary production in the investigated lakes was inversely related to the DOC concentration of the water column, with the lowest effect in the ice-free Arctic lake (3.5% reduction of P tot ) and the highest impact in the alpine lake (56% reduction of P tot, 61% reduction of PER); the percentage of net PER was apparently not controlled by UVR. This suggests that the investigated alpine lake is more sensitive to changes in UVR than the Arctic lakes are. KEY WORDS: Primary production · PAR · UVR · Exudates · Carbon fluxResale or republication not permitted without written consent of the publisher

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<p>According to various recent studies, Austrian citizens have a lower interest in science and are less likely to belief in the benefits of science and technology than the average EU citizen. Limited trust and interest in science are closely linked to a lack of knowledge of the research process and scientifically generated data. Projects and networks at the interface of science and education provide an excellent opportunity to develop innovative ways of science communication, raise scientific literacy and influence the attitude towards scientific findings positively. Thus, scientists from several disciplines, educators, and administrative authorities teamed up to form the partnership “Interdisciplinary network for science education Lower Austria (INSE)”, led by WasserCluster Lunz and funded by GFF NÖ. Our partnership aims at (i) raising school students’ and the public’s understanding of science by demonstrating and involving them into the scientific process of different scientific disciplines, (ii) increasing the interest in science by using innovative forms of science communication, and (iii) strengthening the belief in the benefits of science by highlighting the contributions of science to existing and emerging societal and ecological challenges.  We will present our partnership project, show examples of concepts for science education and science communication, and hope to initiate contact with other (inter)national partners (e.g. interested scientists from other disciplines, existing networks for science communication…) to strengthen and expand our partnership network.</p>