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Streams and rivers metabolize dissolved organic matter (DOM). Although most DOM compounds originate from natural sources, recreational use of rivers increasingly introduces chemically distinct anthropogenic DOM. So far, the ecological impact of this DOM source is not well understood. Here, we show that a large music festival held adjacent to the Traisen River in Austria increased the river’s dissolved organic carbon (DOC) concentration from 1.6 to 2.1 mg L–1 and stream ecosystem respiration from −3.2 to −4.5 mg L–1. The DOC increase was not detected by sensors continuously logging absorbance spectra, thereby challenging their applicability for monitoring. However, the fluorescence intensity doubled during the festival. Using parallel factor analysis, we were able to assign the increase in fluorescence intensity to the chemically stable UV-B filter phenylbenzimidazole sulfonic acid, indicating organic compounds in sunscreen and other personal care products as sources of elevated DOC. This observation was confirmed by liquid chromatography coupled with mass spectrometry. The elevated respiration is probably fueled by anthropogenic DOM contained in beer and/or urine. We conclude that intense recreational use of running waters transiently increases the anthropogenic DOM load into stream ecosystems and alters the fluvial metabolism. We further propose that chemically distinct, manmade DOM extends the natural range of DOM decomposition rates in fluvial ecosystems.

The recent discovery of a new lyotropic liquid crystal phase, the structure and properties of which are analogous to the chiral ferroelectric smectic C-phase (SmC*) in thermotropics, was based on a tailored amphiphile structure in which a tilt-promoting mesogenic core was linked to a chiral diol-headgroup via a hydrophilic ethylene glycol spacer [J. R. Bruckner et al., Angew. Chem., Int. Ed., 2013, 52, 8934–8937]. However, so far there is only one example of this general amphiphile structure known to form the new lyotropic SmC* phase in mixtures with water and with formamide. In an attempt to systematically elucidate the underlying structure–property relations we now report two new amphiphiles leading to lyotropic SmC* phases. These amphiphiles are derived from the parent amphiphile structure by (i) an elongation of the hydrophilic ethylene glycol spacer and (ii) an exchange of the original 2-phenylpyrimidine core by an even more tilt-promoting fluorenone core. Our investigations also reveal that the formation of the lyotropic SmC* phase is highly sensitive to exchanging or enlarging a building block of the primary material.

Hydrology is the main driver of dissolved organic matter (DOM) dynamics in intermittent rivers and ephemeral streams. However, it is still unclear how the timing and the spatial variation in flow connectivity affect the dynamics of DOM and inorganic solutes. This study focuses on the impact of flow cessation on the temporal and spatial heterogeneity of DOM quantity and quality along an intermittent stream. We monitored a headwater intermittent stream at high spatial and temporal frequencies during a summer drying episode and analysed dissolved organic carbon (DOC) and its spectroscopic properties, inorganic solutes and dissolved CO2. The drying period determined the disruption of the fluvial continuum with a recession of stream continuum at a rate of ~60 m/d and the gradual formation of a patched system of isolated pools of different sizes. Our results showed that the period of time that had elapsed since isolated pool formation (CI-days) was an essential factor for understanding how drying shaped the biogeochemistry of the fluvial system. Overall, drying caused a high DOC concentration and an increase in the humic-like fluorescence signal. Additionally, solutes showed contrasting responses to hydrological disconnection. Electrical conductivity, for instance, is a clear “sentinel” of the fragmentation process because it starts to increase before the hydrological disruption occurs. In contrast, DOC, most spectroscopic DOM descriptors and CO2 showed delayed responses of approximately 5–21 days after the formation of isolated pools. Furthermore, the spatial location and volume of each isolated pool seemed to exert a significant impact on most variables. In contrast, the temperature did not follow a clear pattern. These findings indicate that the fragmentation of longitudinal hydrological connectivity does not induce a single biogeochemical response but rather stimulates a set of solute-specific responses that generates a complex biogeochemical mosaic in a single fluvial unit.

1. Microbial heterotrophic activity is a major driver of nutrient and organic matter processing in the hyporheic zone of headwater streams. Additionally, the hypor‐ heic zone might provide refuge for microbes when surface flow ceases during drought events. 2. We investigated chemical (organic and inorganic nutrients) and microbiological parameters (bacterial cell concentration, live–dead ratios, and extracellular en‐ zyme activities) of surface and interstitial pore water in a period of progressive surface-hyporheic disconnection due to summer drying. The special situation of the chosen study reach, where groundwater mixing is impeded by the bedrock forming a natural channel filled with sediment, allowed as to study the transfor‐ mation of these parameters along hyporheic flow paths. 3. The chemical composition of the hyporheic pore water reflected the connectivity with the surface water, as expressed in the availability of nitrate and oxygen. Conversely, microbiological parameters in all hyporheic locations were different from the surface waters, suggesting that the microbial activity in the water changes rapidly once the water enters the hyporheic zone. This feature was prin‐ cipally manifested in higher live–dead ratios and lower leucine aminopeptidase (an activity related to nitrogen acquisition) in the hyporheic pore waters. 4. Overall, bacterial cell concentration and extracellular enzyme activities increased along hyporheic flow paths, with a congruent decrease in inorganic nutrients and dissolved organic matter quantity and apparent molecular size. 5. Our findings show two important functions of the hyporheic zone during drought: (1) deeper (−50 cm) water-saturated layers can act as a refuge for microbial activity; and (2) the hyporheic zone shows high rates of carbon and nitrogen turnover when water residence times are longer during drought. These rates might be even enhanced by an increase in living microbes in the remaining moist locations of the hyporheic zone FP7 People: Marie-Curie Actions, Grant/ Award Number: 607150; FP7 Environment, Grant/Award Number: 603629-ENV-6.2.1

In thermotropic chiral $\mathrm{Sm}\text{\ensuremath{-}}{A}^{*}$ phases, an electric field along the smectic layers breaks the ${D}_{\ensuremath{\infty}}$ symmetry of the $\mathrm{Sm}\text{\ensuremath{-}}{A}^{*}$ phase and induces a tilt of the liquid crystal director. This so-called electroclinic effect (ECE) was first reported by Garoff and Meyer in 1977 and attracted substantial scientific and technological interest due to its linear and submicrosecond electro-optic response [S. Garoff and R. B. Meyer, Phys. Rev. A 19, 338 (1979)]. We now report the observation of an ECE in the pretransitional regime from a lyotropic chiral lamellar ${L}_{\ensuremath{\alpha}}^{*}$ phase into a lyo-$\mathrm{Sm}\text{\ensuremath{-}}{C}^{*}$ phase, the lyotropic analog to the thermotropic $\mathrm{Sm}\text{\ensuremath{-}}{C}^{*}$ phase which was recently discovered by Bruckner et al. [Angew. Chem. Int. Ed. 52, 8934 (2013)]. We further show that the observed ECE has all signatures of its thermotropic counterpart, namely (i) the effect is chiral in nature and vanishes in the racemic ${L}_{\ensuremath{\alpha}}$ phase, (ii) the effect is essentially linear in the sign and magnitude of the electric field, and (iii) the magnitude of the effect diverges hyperbolically as the temperature approaches the critical temperature of the second order tilting transition. Specific deviations between the ECEs in chiral lamellar and chiral smectic phases are related to the internal field screening effect of electric double layers formed by inevitable ionic impurities in lyotropic phases.

Hydrological conditions are key drivers of dissolved organic matter (DOM) processing in intermittent streams. However, there still exist major gaps in knowledge regarding the temporal dynamics of DOM processing during drought periods, as well as the role of the hyporheic zone (HZ). We conducted weekly sampling of surface water and hyporheic pore water during a drying/rewetting cycle and characterized DOM by fluorescence and absorbance properties. Overall, the contribution of allochthonous and humic-like DOM increased during base flow in early summer (pre-drought) and continued increasing throughout the drought period, which covered three phases: contraction, fragmentation and dry. The contribution of autochthonous DOM during this period was restricted to very specific points in time (the transition from contraction to fragmentation phase) and space (the HZ). Hydrological connectivity between the HZ and the surface water was a driver of DOM composition by supplying terrestrial, aromatic DOM to the HZ. The disconnection of the stream from the riparian groundwater enabled us to quantify the DOM retention/release in the HZ. DOM mass balance at the stream-hyporheic interface revealed the occurrence of two time periods with disproportionately high rates for DOM processing (hot moments) during the study period: (1) a short pulse of protein-like, autochthonous DOM net release at the beginning of the disconnection; and (2) a longer time period of increasing net dissolved organic carbon (DOC) retention up to 30% along 25 m of HZ length during fragmentation and dry phase. Remarkably, the net carbon retention was coupled to a decrease of aromatic and high molecular weight compounds, while protein-like, autochthonous DOM was released. This result evidenced that under drought conditions, the HZ becomes a sink for DOM compounds previously assumed to be recalcitrant in aquatic ecosystems and therefore highlights the importance of hydrological drivers on DOM processing.

24 páginas, 9 figuras, 1 tabla., Protecting or restoring aquatic ecosystems in the face of growing anthropogenic pressures requires an understanding of hydrological and biogeochemical functioning across multiple spatial and temporal scales. Recent technological and methodological advances have vastly increased the number and diversity of hydrological, biogeochemical, and ecological tracers available, providing potentially powerful tools to improve understanding of fundamental problems in ecohydrology, notably: 1. Identifying spatially explicit flowpaths, 2. Quantifying water residence time, and 3. Quantifying and localizing biogeochemical transformation. In this review, we synthesize the history of hydrological and biogeochemical theory, summarize modern tracer methods, and discuss how improved understanding of flowpath, residence time, and biogeochemical transformation can help ecohydrology move beyond description of site-specific heterogeneity. We focus on using multiple tracers with contrasting characteristics (crossing proxies) to infer ecosystem functioning across multiple scales. Specifically, we present how crossed proxies could test recent ecohydrological theory, combining the concepts of hotspots and hot moments with the Damköhler number in what we call the HotDam framework., This project has been funded by the European Union's Seventh Framework Program for research, technological development and demonstration under grant agreement no. 607150 (FP7-PEOPLE-2013-ITN – INTERFACES - Ecohydrological interfaces as critical hotspots for transformations of ecosystem exchange fluxes and biogeochemical cycling). B. Abbott and G. Pinay were also supported by the French EC2CO grant “Caractérisation hydrologique et biogéochimique de la dénitrification dans les paysages.” C. Mendoza-Lera and T. Datry were supported by the French National Agency for Water and Aquatic Environments (ONEMA, Action 13, “Colmatage, échanges nappe-rivière et processus biogéochimiques”).