Biodegradation of riverine dissolved organic carbon in five estuaries of the southeastern United States

The biological turnover of riverine dissolved organic carbon (DOC) discharged into five southeastern United States estuaries was examined in long-term respiration bioassays. Measures of bacterial oxygen consumption indicated surprisingly large differences in the inherent biodegradability of DOC among the five estuaries, despite their close geographic proximity. Differences of up to 13-fold in biodegradation rates were also found temporally within a single estuary. For most of the southeastern United States estuaries, measured rates of riverine DOC biodegradation were low relative to rates reported for other freshwater and marine environments. This was particularly true for the coastal plain (“blackwater”) rivers that contribute about 35% of the riverine DOC exported to coastal marine environments in this region; extrapolation of biodegradation rates to the adjacent continental shelf predict biodegradation of a maximum of 11% of exported blackwater DOC within the estuary-shelf system (with transit times of up to 140 d). DOC from Piedmont rivers was more biologically labile, with maximum losses of 30% predicted within the estuary and adjacent shelf. Short exposures to natural sunlight increased the lability of the riverine DOC and enhanced biodegradation rates by over 3-fold in some cases, although significant inter-estuary differences in susceptibility of riverine DOC to photolysis were also evident. *** DIRECT SUPPORT *** A01BY085 00007     

Evaluation of anthropogenic and biogenic inputs into the western Mediterranean using molecular markers

Aliphatic hydrocarbons (AHs), sterols (ST), and lipid classes were determined in suspended particles collected in the Catalan Sea, northwestern Mediterranean. Principal Component Analysis of the data set revealed a clustering of samples depending on the sources of organic matter, i.e., coastal influenced, open sea and frontal zone. Terrestrial inputs were recognized in particles collected in the surface waters, at the vicinities of river outflow (i.e., Rhône and Ebro), by a predominance of C₂₉ and C₃₁ n-alkanes, 24-ethylcholest-5-en-3β-ol (S12), and the anthropogenic 5β(H)-cholestan-3β-ol, coprostanol (S1). Phytoplanktonic molecular markers (n-C₁₇, 27-nor-24-methylcholesta-5,22E-dien-3β-ol, cholesta-5,22-dien-3β-ol and 24-methylcholest-5-en-3β-ol) were widespread but relatively more apparent in the open sea and frontal zones. A similar distribution was observed for lipid classes, with higher concentrations of phospholipids, and an enrichment in free fatty acids in the areas influenced by river discharges. Total sterol, the unresolved complex mixture of hydrocarbons and the pristane–phytane ratio were highest at a persistent frontal zone, possibly reflecting the combination of a higher primary productivity and fossil hydrocarbon absorption on to suspended particles. Moreover, vertical profiles exhibited a subsurface concentration maximum at 20–30 m water depth, concurrently with the chlorophyll.     

Biliary fluorescent aromatic compounds (FACs) measured by fixed wavelength fluorescence (FF) in several marine fish species from the NW Mediterranean

The fixed wavelength fluoresce (FF) method was used to estimate the levels of fluorescent aromatic compounds (FACs) in the bile of fourteen fish species of commercial and/or ecological interest. Sampling was carried out in the NW Mediterranean at depths ranging from 50 to 1000 m during four seasonal cruises. During the summer sampling period, some species were also collected from another site (Vilanova fishing grounds) for comparison. Baseline levels of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, phenanthrene, pyrene and benzo[a]pyrene were measured. Some seasonality was observed, with reduced FF levels in summer and no differences among sites, consistent with sediment PAH levels. We discuss our results in relation to fish phylogeny, season, depth, diet, trophic level and swimming capacity. Overall FF levels indicated differences among species; the suprabenthic feeders from shallow and deep communities, and Mullus barbatus in particular, displayed elevated FF values and are potential candidates for additional monitoring studies.     

Explosive felsic volcanism on El Hierro (Canary Islands)

The Canary Islands consist of seven basaltic shield volcanoes whose submerged portion is much more voluminous than the subaerial part of each island. Like so many other volcanic oceanic islands, the indicative deposits of explosive felsic volcanism are not a common feature on the Canary archipelago. Hitherto, they have only been documented from the central islands of Gran Canaria and Tenerife, which are the largest volcanic complexes of the islands. On the other Canary Islands, the presence of felsic rocks is mostly restricted to intrusions and a few lava flows, generally within the succession in the oldest parts of individual islands. In this paper, we present a detailed stratigraphic, lithological and sedimentological study of a significant felsic pumice deposit on the island of El Hierro, referred here as the Malpaso Member, which represents the only explosive episode of felsic volcanism found on the Canary Islands (outside of Gran Canaria and Tenerife). The products of the eruption indicate a single eruptive event and cover an area of about 15 km². This work provides a detailed stratigraphic and chronological framework for El Hierro, and four subunits are identified within the member on the basis of lithological and granulometric characteristics. The results of this study demonstrate the importance of an explosive eruption in a setting where the activity is typified by effusive basaltic events. Given the style and the spatial distribution of the Malpaso eruption and its products, a future event with similar characteristics could have a serious impact on the population, infrastructure and economy of the island of El Hierro.     

How to Invert Multi-Band,Regional Phase Amplitudes for 2-D Attenuation and Source Parameters: Tests Using the USArray

We inverted for laterally varying attenuation, absolute site terms, moments and apparent stress using over 460,000 Lg amplitudes recorded by the USArray for frequencies between 0.5 and 16 Hz. Corner frequencies of Wells, Nevada, aftershocks, obtained by independent analysis of coda spectral ratios, controlled the tradeoff between attenuation and stress, while independently determined moments from St. Louis University and the University of California constrained absolute levels. The quality factor, Q, was low for coastal regions and interior volcanic and tectonic areas, and high for stable regions such as the Great Plains, and Colorado and Columbia Plateaus. Q increased with frequency, and the rate of increase correlated inversely with 1-Hz Q, with highest rates in low-Q tectonic regions, and lowest rates in high-Q stable areas. Moments matched independently determined moments with a scatter of 0.2 NM. Apparent stress ranged from below 0.01 to above 1 MPa, with means of 0.1 MPa for smaller events, and 0.3 MPa for larger events. Stress was observed to be spatially coherent in some areas; for example, stress was lower along the San Andreas fault through central and northern California, and higher in the Walker Lane, and for isolated sequences such as Wells. Variance reduction relative to 1-D models ranged from 50 to 90 % depending on band and inversion method. Parameterizing frequency dependent Q as a power law produced little misfit relative to a collection of independent, multi-band Q models, and performed better than the omega-square source parameterization in that sense. Amplitude residuals showed modest, but regionally coherent patterns that varied from event to event, even between those with similar source mechanisms, indicating a combination of focal mechanism, and near source propagation effects played a role. An exception was the Wells mainshock, which produced dramatic amplitude patterns due to its directivity, and was thus excluded from the inversions. The 2-D Q plus absolute site models can be used for high accuracy, broad area source spectra, magnitude and yield estimation, and, in combination with models for all regional phases, can be used to improve discrimination, in particular for intermediate bands that allow coverage to be extended beyond that available for high frequency P-to-S discriminants.     

Minor Constituent Concentrations Measured from a High Altitude Aircraft Using High Resolution Far-Infrared Fourier Transform Spectroscopy

Far-infrared emission spectroscopy has beendemonstrated to be a valuable method for remotesensing of trace species in the stratosphere, with theability to simultaneously detect a number of keychemical species. SAFIRE-A is a new far-infraredFourier Transform (FT) spectrometer which has beenspecifically designed to operate on board of a highaltitude aircraft in the lower stratosphere and uppertroposphere regions where relatively few remotesensing measurements have been made. Using newtechnology, the sensitivity of the FT spectrometermethod has been substantially improved for the longwavelength region. Results are reported formeasurements of O₃, HNO₃ and N₂O at 17and 19 km using a detection window near 23 cm^-1.Geographical and altitude variability of the volumemixing ratio of these constituents and their relativecorrelation are discussed. Ozone measurements agreewell with in situ measurements, except in regions ofstrong stirring and mixing associated with deformationof the northern vortex edge. Whilst SAFIREmeasurements of trace gases do not capture all of thelocal variability seen by rapid in-situ techniques,they can indicate horizontal variability close to, butnot intercepted by, the aircraft's flight path. Apossible detection of ClO at the low background levelsexpected outside the polar vortex is also reported.     

Ground deformation in a viscoelastic medium composed of a layer overlying a half-space: a comparison between point and extended sources

We obtain and compare analytical and numerical solutions for ground displacement caused by an overpressurized magma chamber placed in a linear viscoelastic medium composed of a layer over a half-space. Different parameters such as size, depth and shape of the chamber, crustal rheology and topography are considered and discussed. Numerical solutions for an axisymmetric extended source are computed using a finite element method (FEM). Analytical solutions for a point source are obtained using the dislocation theory and the propagator matrix technique. In both cases, the elastic solutions are used together with the correspondence principle of linear viscoelasticity to obtain the solution in the Laplace transform domain. Viscoelastic solutions in the time domain are derived inverting the Laplace transform using the Prony series method. The differences between the results allow us to constrain the applicability of the point source and the flat surface hypothesis, which are usually implicitly assumed when analytical solutions are derived. The effect of the topography is also considered. The results obtained show that neglecting the topographic effects may, in some cases, introduce an error greater than that implicit in the point-source hypothesis. Therefore, for an adequate modelling and interpretation of the time-dependent displacements, topography must be considered.