Bacterial degradation of acetone in an outdoor model stream

Diurnal variations of the acetone concentration in an outdoor model stream were measured with and without a nitrate supplement to determine if the nitrate supplement would stimulate bacterial degradation of the acetone. Acetone loss coefficients were computed from the diurnal data using a fitting procedure based on a Lagrangian particle model. The coefficients indicated that bacterial degradation of the acetone was occurring in the downstream part of the stream during the nitrate addition. However, the acetone concentrations stabilized at values considerably above the limit of detection for acetone determination, in contrast to laboratory respirometer studies where the acetone concentration decreased rapidly to less than the detection limit, once bacterial acclimation to the acetone had occurred. One possible explanation for the difference in behavior was the limited 6-hour residence time of the acetone in the model stream.     

Assessing the construct validity and utility of two new influence tactics

Progress in developing theories of interpersonal influence depends on the identification of meaningful and measurable constructs for classifying influence behavior. We assessed the construct validity and relative effectiveness of two new influence tactics with a field survey study, an incident study, and a laboratory experiment. The confirmatory factor analysis of data from the survey study indicated that collaboration and apprising were distinct from nine proactive tactics identified in earlier research. Additional evidence for construct validity was provided by a comparison of tactics in terms of expected differences in influence outcomes, frequency of use, and differential use with subordinates and peers. Managers who understand the differences among the tactics will be more effective in influencing people in organizations. Copyright © 2005 John Wiley & Sons, Ltd.     

Food resource utilization among five species of embiotocids at King Harbor,California, with preliminary estimates of caloric intake

The diets of 5 species of embiotocids (Rhacochilus vacca, Embiotoca jacksoni, Hypsurus caryi ryi, Phanerodon furcatus and Micrometrus minimus) from King Harbor, Redondo Beach, California, USA, are examined by means of a dietary survey, field feeding observations and bomb calorimetry of prey items. Each species is shown to have statistically different diets from all others, with the exception of H. caryi which apparently is a dietary intermediate between E. jacksoni and P. furcatus. Dietary overlap between E. jacksoni and H. caryi appears to have resulted in some competitive exclusion along other niche parameters. Estimated caloric intakes suggest that R. vacca has the highest caloric yield per bite and the lowest feeding rate of the species studied. Possible energetic advantages are found for diet specialization in R. vacca.     

Arsenic remobilization in a shallow lake: the role of sediment resuspension

Oxic resuspension occurs regularly in shallow lakes, yet its role as a mechanism for contaminant remobilization remains ill defined. This study investigated contaminant remobilization during sediment resuspension and determined whether changes in contaminant sediment partitioning reflected the mechanisms controlling remobilization. Arsenic-contaminated sediment from a shallow wetland was subjected to simulated resuspension under a range of differing initial pH conditions. The effect of resuspension on As partitioning was evaluated using a fractionation scheme targeting the dissolved, ion exchangeable, carbonate, organic, amorphous iron oxide, crystalline iron oxide, and apatite fractions. Rate investigations demonstrated that arsenic remobilization occurred on timescales similar to resuspension events, with concentrations reaching steady state within 24 h. The sediment also buffered slurry pH to 8.3 in experiments where the initial pH was between 4 and 10. This pH regulation was attributed to carbonate dissolution or acid-base equilibria of surface base functional groups, although iron oxide and organic matter dissolution did occur in experiments with an initial pH outside this range. Remobilization caused losses in arsenic associated with the ion exchangeable, organic, and amorphous iron fractions but changes in initial pH have a negligible effect on arsenic remobilization or partitioning within the well-buffered region. Resuspension released approximately 20% of the total sediment arsenic, although calculations indicated that a single resuspension event would not significantly change water column arsenic concentrations. While not conclusively proving the mechanisms of remobilization, fractionation gave valuable insight into the effect of sediment resuspension on contaminant remobilization.     

Temporal and spatial variation in the δ<Superscript>15</Superscript>N and δ<Superscript>13</Superscript>C values of fish and squid from Alaskan waters

To test the hypothesis that stable isotope ratios from marine organisms vary, the δ¹⁵N and δ¹³C values from fish and squid collected in Alaskan waters were measured across years (1997, 2000, and 2005), seasons, geographic locations, and different size/age classes, and between muscle tissue and whole animals. Temporal, geographic, and ontogenetic differences in stable isotope ratios ranged from 0.5–2.5‰ (δ¹⁵N) to 0.5–2.0‰ (δ¹³C). Twenty-one comparisons of stable isotope values between whole organisms and muscle tissue revealed only four small differences each for δ¹⁵N and δ¹³C, making costly and space prohibitive collection of whole animals unnecessary. The data from this study indicate that significant variations of stable isotope values from animals in marine systems necessitates collection of prey and predator tissues from the same time and place for best interpretation of stable isotope analysis in foraging ecology studies.     

Calculated physical properties of polychlorinated dibenzo-p-dioxins and dibenzofurans

The modified neglect of diatomic overlap (MNDO) method, a semi-empirical molecular orbital calculation, has been used to calculate the heats of formation, ionization potentials, dipole moments, and LUMOs (lowest unoccupied molecular orbitals) for all of the tetra, penta, hexa, hepta, and octa-chlorinated dibenzo-p-dioxins and dibenzofurans. These data have been used to predict gas chromatographic retention indexes.