Comparison of marine and river water humic substances in a Patagonian environment (Argentina)

Structural aspects of humic substances (HSs) in marine waters of Engaño Bay (Atlantic Ocean) and water from the Chubut River (Patagonia, Argentina) were compared. The HSs were isolated, purified, and analyzed using a multiple-method approach for structural characterization: elemental analysis, nuclear magnetic resonance (¹³C and ¹H NMR), infrared spectroscopy (FTIR), UV-visible absorption and fluorescence. Similarities between the marine and freshwater components were evaluated on the basis of N and O contents, H/C and C/N atomic ratios, infrared bands from nitrogen-containing and carboxylic groups, percentage of functional groups obtained from NMR spectra, spectral slope coefficient of absorption spectra, absorbance ratios at 250 and 365 nm (E ₂/E ₃), aromaticity, excitation–emission matrices and fluorescence quantum yield. Both the Engaño Bay and Chubut River waters have HSs that are mainly composed of fulvic acids (FAs); although they are very similar, they may be distinguished from one another. Similarities include the predominance of aliphatic carbon content (low aromatic content); however, the water bodies differed in their content of proteins and carboxylic acids. The Engaño Bay FAs have mainly an aquatic origin; although the Chubut River FAs suggest a similar aquagenic origin, there is also evidence of contributions from pedogenic FAs.     

Ichthyoplankton spatial pattern in the inner shelf off Bahía Blanca Estuary, SW Atlantic Ocean

This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m⁻³ (eggs) and 4000 per 10 m⁻³ (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it.     

A methodological approach to water quality assessment in an ungauged basin,Buenos Aires,Argentina

The Reconquista River is one of the most polluted rivers in Latin America. This paper aims at identifying the dynamics of water quality in an area with low or “background” concentrations of pollutants within the Reconquista River system in order to better define levels of pollution in the main system. In order to describe the dynamics of water quality in the background area, we propose a methodology based on flow estimation with the instantaneous unit hydrograph model and on measurements of physical and chemical water variables under different hydrological conditions. Because of high dissolved oxygen and low ammonium and o-phosphate concentrations, the Arroyo Durazno, a tributary stream of the Reconquista River, is defined as a background area. When a storm event begins, the concentration of nitrates and the electrical conductivity diminish. An increase in dissolved organic carbon suggests an important input of carbon from hillslope runoff. The proportion of fulvic and humic acids also increases. On the receding limb of the hydrograph, nitrate concentration was lower than during maximum flow and organic carbon concentration remained high. This behavior, known as the “flushing effect”, suggests that the soluble material accumulated in the drainage area during dry periods is transported to the stream by leaching or “lixiviation” and surface runoff, thus raising solute concentrations during the first few hours of the storm. Water quality changes rapidly, even in background areas, due to its dependence on the flow. The methodology followed in this paper can also be applied to other basins with similar characteristics. Due to the difficulty in defining baseline areas for surface waters, a knowledge of background water quality and its dynamics is essential for understanding pollution trends and anthropogenic impacts on rivers.     

Long-term variation of the semiannual amplitude in the aa index

The long-term variation of the semiannual amplitude in the geomagnetic activity index aa is analyzed with the purpose of contributing to the understanding of solar variability, directly linked to geomagnetic variability. The time series of the semiannual oscillation amplitude, obtained through a wavelet analysis of the daily aa series, presents a long-term variation similar to that shown by solar and geomagnetic indices, like aa itself or Dst. However, the maximum in the semiannual amplitude series occurs around 1947, almost 10 years before it occurs in solar and geomagnetic indices time series. The phase of the semiannual oscillation fluctuates around the values predicted by the equinoctial and Russell–McPherron models, with a predominance of the equinoctial mechanism during the period of maximum semiannual amplitude. A possible source of changes in the equinoctial mechanism would be the secular variation of the Earth's dipole tilt. But, since it does not follow the semiannual amplitude trend, at first sight, it seems not to be responsible for the equinoctial predominance around 1947. The analysis of quiet and disturbed days separately indicates that only disturbed days present the semiannual annual amplitude maximum around 1947, so the 10 year time shift could be due to the mechanism responsible for the semiannual variation in geomagnetically active periods.     

Asteroid (101955) 1999 RQ36: Spectroscopy from 0.4 to 2.4 μm and meteorite analogs

We present reflectance spectra from 0.4 to 2.4 μm of Asteroid (101955) 1999 RQ36, the target of the OSIRIS-REx spacecraft mission. The visible spectral data were obtained at the McDonald Observatory 2.1-m telescope with the ES2 spectrograph. The infrared spectral data were obtained at the NASA Infrared Telescope Facility using the SpeX instrument. The average visible spectrum is combined with the average near-infrared wavelength spectrum to form a composite spectrum. We use three methods to constrain the compositional information in the composite spectrum of Asteroid (101955) 1999 RQ36 (hereafter RQ36). First, we perform a least-squares search for meteorite spectral analogs using 15,000 spectra from the RELAB database. Three most likely meteorite analogs are proposed based on the least-squares search. Next, six spectral parameters are measured for RQ36 and their values are compared with the ranges in parameter values of the carbonaceous chondrite meteorite classes. A most likely meteorite analog group is proposed based on the depth of overlap in parameter values. The results of the least-squares search and the parametric comparisons point to CIs and/or CMs as the most likely meteorite analogs for RQ36, and COs and CHs as the least likely. RQ36 has a spectrally “blue” continuum slope that is also observed in carbonaceous chondrites containing magnetite. We speculate that RQ36 is composed of a “CM1”-like material. Finally, we compare RQ36 to other B-type asteroids measured by Clark et al. (Clark, B.E. et al. [2010]. J. Geophys. Res. 115, E06005). The results of this comparison are inconclusive. RQ36 is comparable to Themis spectral properties in terms of its albedo, visible spectrum, and near-infrared spectrum from 1.1 to 1.45 μm. However, RQ36 is more similar to Pallas in terms of its near-infrared spectrum from 1.6 to 2.3 μm. Thus it is possible that B-type asteroids form a spectral continuum and that RQ36 is a transitional object, spectrally intermediate between the two end-members. This is particularly interesting because Asteroid 24 Themis was recently discovered to have H₂O ice on the surface (Rivkin, A., Emery, J. [2010]. Nature 464, 1322–1323; Campins, H. et al. [2010a]. Nature 464, 1320–1321).     

Perspectives on being a field-based geomorphologist during pregnancy and early motherhood

Many geomorphologists who are mothers find it challenging to balance field research alongside pregnancy and caring for young children. We offer perspectives on the challenges to conducting fieldwork as mothers and possible solutions, as a means of promoting conversations and highlighting issues that are less commonly considered in field-based geomorphic research. Although every mother's experience and needs are different, we discuss strategies for conducting fieldwork, addressing childcare issues, and dealing with financial considerations. We call for our community to support geomorphologists who are pregnant or caring for young children in carrying out fieldwork to help enhance the diversity of voices and perspectives within our discipline.     

Effect of increasing temperatures on cooling systems. A case of study: European greenhouse sector

The work attempts to assess the effects of global warming on the efficacy of current greenhouse cooling methods following a methodology previously proved for other agricultural buildings. The cooling potential of four greenhouse cooling techniques (natural ventilation, forced ventilation, fogging and shading) were simulated by computer modelling for five European locations, calculating the greenhouse internal air temperature from measured external climate data. Four 2080s scenarios were analysed in these five locations. They were constructed as a combination of General Circulation Models (Had CM3 and ECHAM4) downscaled for Europe with the HIRHAM and RCA3 regional models and driven by the A2 and B2 socio-economic scenarios. The crop considered as reference was tomato. The results showed that, in locations in southern Europe, adding evaporative cooling methods to ventilation and/or shading will be indispensable. In some areas of northern Europe, natural ventilation will no longer be sufficient, and shading or fogging will also be necessary. The economic consequences will be important, over all in the southern locations where water consumption, investment and working costs will be higher and necessary to ensure the crop production.     

Biomarkers in croakers Micropogonias furnieri (Teleostei: Sciaenidae) from polluted and non-polluted areas from the Patos Lagoon estuary (Southern Brazil): evidences of genotoxic and immunological effects

Biomarkers of exposure and effect of pollutants were analyzed in croakers Micropogonias furnieri (Teleostei: Sciaenidae) captured in winter and summer in a polluted and in a non-polluted site at the Patos Lagoon estuary (Southern Brazil). Catalase and glutathione S-transferase activities (exposure biomarkers) and lipid peroxidation (effect biomarker) were analyzed in liver samples. Other two effect biomarkers were also studied: blood cells DNA damage (through comet assay and micronucleus test) and respiratory burst measurements. In a broad view, results point to an important seasonal variation of the biochemical biomarkers analyzed. However, data obtained clearly indicate that croakers collected in winter at the polluted site were subjected to a level of clastogenic agents sufficient to generate irreversible genetic damages (mutations) and impair the fish immune system.     

Was GRB 990123 a unique optical flash?

GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. Motivated by this currently favoured idea, we compute the prompt reverse shock emission to be expected for bursts in which multiwavelength observations allow the physical parameters to be constrained. We find that for reasonable assumptions about the velocity of source expansion, a strong optical flash  m_V≈9  was expected from the reverse shocks, which were usually found to be mildly relativistic. The best observational prospects for detecting these prompt flashes are highlighted, along with the possible reasons for the absence of optical prompt detections in ongoing observations.     

Variation in groundwater salinity in a tidal salt marsh basin,North Inlet Estuary,South Carolina

Groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales, including storm events, tidal fluctuations, seasonal variations in rainfall and evapotranspiration (ET). Groundwater salinity can be a useful first order indicator of the balance between these flow processes. A dipole-dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of Crabhaul Creek, a tidal salt marsh basin at the boundary of the upland forest and the North Inlet marsh in South Carolina. The monthly electrical resistivity surveys were designed to provide a detailed, spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity. Resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers. The freshwater-brackish water interface was clearly imaged by the resistivity. Movement of this interface occurs on a timescale of months rather than a regular seasonal variation. The average salinity in the marsh basin is highest in late Summer (July–August) when ET is highest, and lowest during the Winter (November–December). The position of the brackish-freshwater interface changes, but is not well correlated to local rainfall or tidal cycles except under specific circumstances. A steady-state hydrological model correctly predicts the average position of the freshwater-brackish interface and suggests a linear relationship between the height of the water table and the location of the interface. These results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh.