Assessing the non-ideality of the CO2-CS2 system at molecular level: A Raman scattering study

The dense phase of CO2-CS2 mixtures has been analysed by Raman spectroscopy as a function of the CO2 concentration (0.02-0.95 mole fractions) by varying the pressure (0.5 MPa up to 7.7 MPa) at constant temperature (313 K). The polarised and depolarised spectra of the induced (nu(2), nu(3)) modes of CS2 and of the nu(1)-2 nu(2) Fermi resonance dyad of both CO2 and CS2 have been measured. Upon dilution with CO2, the evolution of the spectroscopic observables of all these modes displays a \"plateau-like\" region in the CO2 mole fraction 0.3-0.7 never previously observed in CO2-organic liquids mixtures. The bandshape and intensity of the induced modes of CS2 are similar to those of pure CS2 up to equimolar concentration, after which variations occur. The preservation of the local ordering from pure CS2 to equimolar concentration together with the non-linear evolution of the spectroscopic observables allows inferring that two solvation regimes exist with a transition occurring in the plateau domain. In the first regime, corresponding to CS2 concentrated mixtures, the liquid phase is segregated with dominant CS2 clusters, whereas, in the second one, CO2 monomers and dimers and CO2-CS2 hetero-dimers coexist dynamically on a picosecond time-scale. It is demonstrated that the subtle interplay between attractive and repulsive interactions which provides a molecular interpretation of the non-ideality of the CO2-CS2 mixture allows rationalizing the volume expansion and the existence of the plateau-like region observed in the pressure-composition diagram previously ascribed to the proximity of an upper critical solution temperature at lower temperatures. (C) 2013 AIP Publishing LLC

Effects of external nutrient sources and extreme weather events on the nutrient budget of a Southern European coastal lagoon

The seasonal and annual nitrogen (N), phosphorus (P), and carbon (C) budgets of the mesotidal Ria Formosa lagoon, southern Portugal, were estimated to reveal the main inputs and outputs, the seasonal patterns, and how they may influence the ecological functioning of the system. The effects of extreme weather events such as long-lasting strong winds causing upwelling and strong rainfall were assessed. External nutrient inputs were quantified; ocean exchange was assessed in 24-h sampling campaigns, and final calculations were made using a hydrodynamic model of the lagoon. Rain and stream inputs were the main freshwater sources to the lagoon. However, wastewater treatment plant and groundwater discharges dominated nutrient input, together accounting for 98, 96, and 88 % of total C, N, and P input, respectively. Organic matter and nutrients were continuously exported to the ocean. This pattern was reversed following extreme events, such as strong winds in early summer that caused upwelling and after a period of heavy rainfall in late autumn. A principal component analysis (PCA) revealed that ammonium and organic N and C exchange were positively associated with temperature as opposed to pH and nitrate. These variables reflected mostly the benthic lagoon metabolism, whereas particulate P exchange was correlated to Chl a, indicating that this was more related to phytoplankton dynamics. The increase of stochastic events, as expected in climate change scenarios, may have strong effects on the ecological functioning of coastal lagoons, altering the C and nutrient budgets.Portuguese Science and Technology Foundation (FCT) [POCI/MAR/58427/2004, PPCDT/MAR/58427/2004]; Portuguese Science and Technology Foundation (FCT

Photoacclimation strategies in northeastern Atlantic seagrasses: Integrating responses across plant organizational levels

Seagrasses live in highly variable light environments and adjust to these variations by expressing acclimatory responses at different plant organizational levels (meadow, shoot, leaf and chloroplast level). Yet, comparative studies, to identify species' strategies, and integration of the relative importance of photoacclimatory adjustments at different levels are still missing. The variation in photoacclimatory responses at the chloroplast and leaf level were studied along individual leaves of Cymodocea nodosa, Zostera marina and Z. noltei, including measurements of variable chlorophyll fluorescence, photosynthesis, photoprotective capacities, non-photochemical quenching and D1-protein repair, and assessments of variation in leaf anatomy and chloroplast distribution. Our results show that the slower-growing C. nodosa expressed rather limited physiological and biochemical adjustments in response to light availability, while both species of faster-growing Zostera showed high variability along the leaves. In contrast, the inverse pattern was found for leaf anatomical adjustments in response to light availability, which were more pronounced in C. nodosa. This integrative plant organizational level approach shows that seagrasses differ in their photoacclimatory strategies and that these are linked to the species' life history strategies, information that will be critical for predicting the responses of seagrasses to disturbances and to accordingly develop adequate management strategies.Fundacao para a Ciencia e Tecnologia (FCT), Portugal [PTDC/MAR-EST/4257/2014