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Small headwater streams interlink catchment soils with the river network. Recent studies have identified small streams as 'critical reservoirs' of microbial diversity, but the origin of this diversity is not well understood. Here we present first results from the HYDRO-DIVERSITY project which aims to investigate the dynamic transfer of dissolved organic matter (DOM) and microbial life from catchment soils into streams. We hypothesize that increased soil saturation enhances the lateral inflow of microbial life and DOM into streams and that these lateral inflows shape stream biofilm community composition and diversity. To address these hypotheses, we sampled six first-order streams and three soil transects with two depth located within the pre-alpine Oberer Seebach (OSB) catchment in Austria over a duration of 18 month. We found a strong variation in dissolved organic carbon (DOC) concentrations (range: 0.4 to 4.7 mg L-1) and bacterial counts (range: <500 to 3862 counts µL-1) measured by flow-cytometry. The highest values of DOC and counts occurred during high flow events. Also, DOC concentration and bacterial abundance were strongly correlated across all streams and seasons. In soils, ranges were higher and a similar correlation between DOC and bacterial abundance was found, but DOC concentrations were ~10 times higher per bacterial count than in streams. To further investigate the role of newly transferred soil microbes on stream microbial communities we also performed a large scale flume experiment, in which the relative importance of biofilm successional age (5 to 35 days) for soil microbial inoculation was investigated. Overall our results show that soils provide a dynamic and relevant influx of microbes to first order streams and that streams are able to maintain higher bacterial abundances as soils. We propose that the dynamic and repeatedly occurring inoculation of small streams by soils is relevant for microbial community dynamics of downstream fluvial networks. [ABSTRACT FROM AUTHOR]

Hydraulic modeling for flood risk management requires amongst others Digital Terrain Models (DTMs) and river axes as inputs. These spatial datasets often suffer from positional discrepancies due to (i) different data sources, (ii) different acquisition techniques, and (iii) temporal decorrelation as a result of physical changes between the respective acquisition times. It is thus necessary to ensure spatial consistency of the datasets. We developed an automatic procedure to adapt a given river axis to the river bed represented in a high resolution DTM. The original or densified nodes of the axis are sequentially corrected with a cross-section-based weighting function. The multiplicative weight composition enables the introduction of several criteria concerning river bed geometry, river axis height profiles and water flow behavior. Practical application of the procedure shows good results as long as the assumptions concerning river bed or water surface representation in the DTM are met. While narrow, alpine river beds can be detected very well, wide lowland rivers pose certain challenges especially in case of a poor water surface representation. For the latter, the resulting corrected axis still remains in the river bed but tends to have a visually less appealing zig-zag course. Evaluating the results in a study area of about 6000 km² in Austria showed that at most a few per cent of a river's automatically corrected nodes needed manual editing, mainly in the upper reach where no clear river bed can be identified. Exceptionally, this value exceeds 3 % for rivers where significant parts are conducted underground. [ABSTRACT FROM AUTHOR]

The Frequency Music Festival attracts more than 200 000 visitors every summer. Most visitors camp in close proximity to the Traisen River, a tributary to the Danube River in Austria. The campers typically stay for four days and make intensive recreational use of the Traisen. To quantify the effects of this distinct human activity on water quality and stream ecosystem functioning, we established a stream sampling campaign and deployed continuously measuring UV-Vis and oxygen probes upstream and downstream of the festival area. With our design, we aimed to evaluate the impact of the Festival on river biogeochemistry, namely dissolved organic matter (DOM) dynamics, nitrate concentrations and stream ecosystem metabolism. Analysis of stream samples revealed an increase in dissolved organic carbon (DOC) concentration by up to 1 mg L-1 which corresponds to a mean increase of 30 % during the festival, as compared to upstream (1.6 mg/L). Fluorescence intensity doubled as a result of the festival, indicating a potential change in DOM sources. Interestingly, the UV-Vis sensors neither detected changes in DOC nor nitrate concentrations during the festival, suggesting that the additional DOM was outside the detection range and was likely different from natural sources. At the contrary, laboratory analysis confirmed that nitrate and total nitrogen concentrations did not change significantly; ecosystem respiration was slightly enhanced. Using parallel factor analysis (PARAFAC) on Excitation-Emission Matrices we were able to assign the increase in DOC to a distinct PARAFAC-component that was neither present in the river before or after the festival, nor upstream the festival area. A laboratory experiment of absorbance and fluorescence of various sources of human associated DOM (sunscreen, beer, human urine, toothpaste, plastics...) indicated that sunscreen was the most probable source. Further, back-of-the-envelope calculations showed that at least 2 tons of sunscreen had to be dissolved into river water to cause the observed gain in DOC concentration during the festival. Overall we conclude that large cultural and recreational events may artificially increase carbon load to river ecosystems. This carbon may modify stream ecosystem functioning, as indicated by the transient increase in ecosystem respiration. As the world's population rises, human induced, man-made synthetic DOM may become more relevant for streams and rivers in the future. [ABSTRACT FROM AUTHOR]