Effects of Oxygen Loss on Carbon Processing and Heterotrophic Prokaryotes from an Estuarine Ecosystem: Results from Stable Isotope Probing and Cytometry Analyses

Many aquatic ecosystems are experiencing a decline in their oxygen (O₂) content and this is predicted to continue. Implications of this change on several properties of bacterioplankton (heterotrophic prokaryotes) remain however are poorly known. In this study, oxic samples (～170 μM O₂?=?controls) from an oligohaline region of the Scheldt Estuary were purged with N₂ to yield low-O₂ samples (～69 μM O₂?=?treatments); all were amended with ¹³C-glucose and incubated in dark to examine carbon incorporation and cell size of heterotrophic prokaryotes, and relationships between organic matter (OM) degradation and phosphate (P) availability in waters following O₂ loss. Stable isotope (¹³C) probing of phospholipid fatty acids (PLFA) and flow cytometry were used. In samples that have experienced O₂ loss, PLFA biomass became higher, prokaryotic cells had significantly larger size and higher nucleic acid content, but P concentrations was lower, compared to controls. P concentration and OM degradation were positively related in controls, but uncoupled in low-O₂ samples. Moreover, the dominant PLFA 16:1ω7c (likely mainly from Gram-negative bacteria) and the nucleic acid content of heterotrophic prokaryotic cells in low-O₂ samples explained (62–72 %) differences between controls and low-O₂ samples in P amounts. Shortly after incubations began, low-O₂ samples had consistently lower bacterial PLFA ¹³C-enrichments, suggesting involvement of facultatively anaerobic metabolism in carbon incorporation, and supporting the view that this metabolic pathway is widespread among pelagic bacteria in coastal nutrient-rich ecosystems. Estimates based on ¹³C-enrichment of PLFAs indicated that grazing by protozoa on some bacteria was stronger in low-O₂ samples than in controls, suggesting that the grazing pressure on some heterotrophic prokaryotes may increase at the onset of O₂ deficiency in nutrient-rich aquatic systems. These findings also suggest that physiological responses of heterotrophic prokaryotes to O₂ loss in such ecosystems include increases in cell activity, high carbon incorporation, and possibly phosphorus retention by cells that may contribute to reduce phosphate availability in waters.     

Toxic volatile organic air pollutants across Canada: multi-year concentration trends,regional air quality modelling and source apportionment

A Unified Regional Air-quality Modelling System, AURAMS, was expanded to predict six toxic volatile organic compounds (VOCs) within a continental domain and two nested domains covering eastern and western Canada. The model predictions were evaluated against Environment Canada’s National Air Pollution Surveillance (NAPS) data set to assess the predictive capability of the model at daily and seasonal time scales. The predictions were also evaluated with satellite-derived column total maps for formaldehyde, carbon monoxide, and nitrogen dioxide. In general, the model showed fair to good predictive skill in terms of both correlation (R) and normalized mean bias (NMB) for benzene (R = 0.53 NMB = 26 %), formaldehyde (R = 0.73, NMB = ?15 %) and acetaldehyde (R = 0.55, NMB = 29 %). For the other toxics VOCs, the model showed less predictive skill in the order 1,2,4-trimethylbenzene (R = 0.50, NMB = ?41 %), 1,3-butadiene (R = 0.26, NMB = 40 %) and acrolein (R = 0.052, NMB = ?51 %). The goal of this study was to apply an air quality model to assess the contribution of mobile sources to ambient levels of toxic VOCs at urban locations across Canada. The mobile source contribution varied in a complex manner for each species for different regions. For benzene and 1,2,4-trimethylbenzene, the mobile source contribution was in the range 40–65 % for major Canadian cities. The model predicted considerably lower mobile source contributions for rural locations in the Canadian Prairies, where other area sources dominate, such as the petrochemical industry. Measured concentration trends in toxics are also presented from 2004 to 2010. The primary emitted toxics declined gradually (13–16 % over 6 yr) whereas the toxic aldehydes showed no trend.     

Extensive degradation and fractionation of organic matter during subsurface weathering

Organic carbon, sulphur, ¹³C_org, iron, manganese and calcium have been measured across a subsurface-weathering front in Pliocene sediments in southern Sicily. The results show an almost quantitative removal of C_org and sulphur and an increase in iron and manganese oxides over the weathering front, accompanied with a significant shift of the ¹³C_org to lower values. These data are among the first to support the rapid, extensive weathering of sedimentary organic matter and sulphur, a basic assumption made in global biogeochemical models on a Phanerozoic timescale.     

Gravity field of Mars from Mariner 9 tracking data

Further reduction of Doppler tracking data from Mariner 9 confirms our earlier conclusion that the gravity field of Mars is considerably rougher than the fields of either the Earth or the Moon. The largest positive gravity anomaly uncovered is in the Tharsis region which is also topographically high and geologically unusual. The best determined coefficients of the harmonic expansion of the gravitational potential are: J₂ = (1.96 ± 10.01) × 10^?3 ; C₂₂ = ?(5.1 ± 0.2) × 10^?5; and S₂₂ = (3.4 ± 0.2) × 10^?5. The other coefficients have not been well determined on an individual basis, but the ensemble yields a useful model for the gravity field for all longitudes in the vicinity of 23° South latitude which corresponds to the periapse position for the orbiter.The value obtained for the inverse mass of Mars (3 098 720 ± 70 M⊙^?1) is in good agreement with prior determinations from Mariner flyby trajectories. The direction found for the rotational pole of Mars, referred to the mean equinox and equator of 1950.0, is characterized by α = 317°.3 ± 0°.2, δ = 52°.7 ± 0°.2. This result is in excellent agreement with Sinclair's recent value, determined from earth-based observations of Mars' satellites, but differs by about 0°.5 from the previously accepted value. Other important physical constants that have either been refined or confirmed by the Mariner 9 data include: (i) the dynamical flattening, f = (5.24 ± 0.02) × 10^?3; (ii) the maximum principal moment of inertia, C = (0.375 ± 0.006) MR²; and (iii) the period of precession of Mars' pole, P ? (1.73 ± 0.03) × 10⁵ yr, corresponding to a rate of 7.4 sec of arc per yr.     

Comparison of P- and S-wave velocity profiles obtained from surface seismic refraction/reflection and downhole data

High-resolution seismic-reflection/refraction data were acquired on the ground surface at six locations to compare with near-surface seismic-velocity downhole measurements. Measurement sites were in Seattle, WA, the San Francisco Bay Area, CA, and the San Fernando Valley, CA. We quantitatively compared the data in terms of the average shear-wave velocity to 30-m depth (V_s30), and by the ratio of the relative site amplification produced by the velocity profiles of each data type over a specified set of quarter-wavelength frequencies. In terms of V_s30, similar values were determined from the two methods. There is <15% difference at four of the six sites. The V_s30 values at the other two sites differ by 21% and 48%. The relative site amplification factors differ generally by less than 10% for both P- and S-wave velocities. We also found that S-wave reflections and first-arrival phase delays are essential for identifying velocity inversions. The results suggest that seismic reflection/refraction data are a fast, non-invasive, and less expensive alternative to downhole data for determining V_s30. In addition, we emphasize that some P- and S-wave reflection travel times can directly indicate the frequencies of potentially damaging earthquake site resonances. A strong correlation between the simple S-wave first-arrival travel time/apparent velocity on the ground surface at 100 m offset from the seismic source and the V_s30 value for that site is an additional unique feature of the reflection/refraction data that could greatly simplify V_s30 determinations.     

Pyrolysis-combustion C dating of soil organic matter

Radiocarbon (¹⁴C) dating of total soil organic matter (SOM) often yields results inconsistent with the stratigraphic sequence. The onerous chemical extractions for SOM fractions do not always produce satisfactory ¹⁴C dates. In an effort to develop an alternative method, the pyrolysis-combustion technique was investigated to partition SOM into pyrolysis volatile (Py-V) and pyrolysis residue (Py-R) fractions. The Py-V fractions obtained from a thick glacigenic loess succession in Illinois yielded ¹⁴C dates much younger but more reasonable than the counterpart Py-R fractions for the soil residence time. Carbon isotopic composition (δ¹³C) was heavier in the Py-V fractions, suggesting a greater abundance of carbohydrate- and protein-related constituents, and δ¹³C was lighter in the Py-R fractions, suggesting more lignin- and lipid-related constituents. The combination of ¹⁴C dates and δ¹³C values indicates that the Py-V fractions are less biodegradation resistant and the Py-R fractions are more biodegradation resistant. The pyrolysis-combustion method provides a less cumbersome approach for ¹⁴C dating of SOM fractions. With further study, this method may become a useful tool for analyzing unlithified terrestrial sediments when macrofossils are absent.     

Institutional frameworks for the study of mountain environments and development

During the two decades since the 1972 Stockholm Conference the concern for mountain environments coalesced under an institutional framework involving several organizations and many scholars and scientists. The evolution of the progress of these interested individuals, institutions, and their scholarly journal is outlined with benchmarks noted. An appraisal of the past two decades is given here in recognition of the UNCED-92 conference, the Earth Summit.     

Dissipative and reflective beaches in a large lake and the physical effects of lake level regulation

Nearshore environments in Flathead Lake, Montana, USA, were described as dissipative or reflective on the basis of: the surf similarity parameter , grain size, morphology, number of breaking waves and angle of wave incidence. The relative resistance to foreshore and backshore erosion caused by anthropogenic lake level regulation was compared between these two nearshore configurations. Reflective systems were characterized by dynamic gravel beach faces and steep inshore shelves armored by wave-washed cobble. In contrast, dissipative systems were characterized by sand-sized substratum, broad flat inshore shelves and the presence of multiple linear bars approximately 350 m offshore. Five decades of regulated lake levels have resulted in extensive shoreline erosion (970 ha on the north shore of the lake) and a general reshaping of both types of nearshore environments, although dissipative shorelines eroded faster (5.7 m/year maximum and 2.0 m/year average). The presence of docks and other man-made structures on reflective beaches accelerated erosion by intercepting longshore gravel transport. This analysis provided a physical basis for understanding the effects of lake level regulation on shoreline ecology and management.