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Water Transport in Brick, Stone and Concrete

Scaling is an integral component of ecology and earth science. To date, the ability to determine the importance of air – water gas exchange across large spatial scales is hampered partly by our ability to scale the gas transfer velocity and stream hydraulics. Here we report on a metadata analysis of 563 direct gas tracer release experiments that examines scaling laws for the gas transfer velocity. We found that the gas transfer velocity scales with the product of stream slope and velocity, which is in alignment with theory on stream energy dissipation. In addition to providing equations that predict the gas transfer velocity based on stream hydraulics, we used our hydraulic data set to report a new set of hydraulic exponents and coefficients that allow the prediction of stream width, depth, and velocity based on discharge. Finally, we report a new table of gas Schmidt number dependencies to allow researchers to estimate a gas transfer velocity using our equation for many gasses of interest.

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Scaling the gas transfer velocity and hydraulic geometry in streams and small rivers

Nitrous oxide generation in full-scale biological nutrient removal wastewater treatment plants

Cultivation-independent techniques were applied to assess the succession and phylogenetic composition of bacterial communities in a vertical oxygen gradient in flooded, unplanted paddy soil microcosms. Microsensor measurements showed that within 6 h of flooding, oxygen was depleted from 200 microM at the floodwater-soil interface to undetectable amounts at a depth of approximately 2 mm and below. The gradient was quite stable over time, although the oxygen depletion was less pronounced 84 days than 6 h after flooding. Community fingerprint patterns were obtained by terminal restriction fragment length polymorphism (T-RFLP) analysis from the oxic, transition, and anoxic zones of triplicate soil microcosms at 0, 1 and 6 h, and 1, 2, 7, 21, 30, 42, 84, and 168 days after flooding. Correspondence analyses revealed that T-RFLP patterns obtained using either community DNA or RNA were affected by time and oxygen zone, and that there was a significant interaction between the effects of time and oxygen zone. The temporal dynamics of bacterial populations were resolved more clearly using RNA than using DNA. At the RNA level, successional community dynamics were most pronounced from 1 h to 2 days and less pronounced from 2 to 21 days after flooding, for both oxic and anoxic zones. No effect of time or oxygen zone on the community dynamics was observed from 21 to 168 days after flooding. Dominant early successional populations were identified by cloning and comparative sequence analysis of environmental 16S rRNA and 16S rRNA genes as members of the Betaproteobacteria (oxic zone) and the clostridial cluster I (anoxic zone). Dominant late successional populations belonged to the Verrucomicrobia and Nitrospira (detected mainly in the oxic zone), and to the Myxococcales (detected mainly in the anoxic zone). In conclusion, the bacterial community developed through successional stages, leading at the RNA level to almost stable community patterns within 21 days after flooding. This principal finding, in combination with the phylogenetic identity of early- and late-appearing populations, suggests that the community dynamics can be explained by the principles of r- and K-selection.

Succession of bacterial community structure and diversity in a paddy soil oxygen gradient.

The diffusion coefficient of O2 in H2O and D2O has been determined as a function of temperature from −0.5 to 95 °C, using the Taylor dispersion technique with optical absorbance detection at 200 nm. Over this temperature range, significant deviation from both Arrhenius and Stokes−Einstein behavior is found. A practical interpolation formula for the H2O solvent is (T in Kelvin) log10[D/cm2 s-1] = −4.410 + 773.8/T − (506.4/T)2 and, for the D2O solvent, log10[D/cm2 s-1] = −4.706 + 903.6/T − (526.6/T)2. As a test of the apparatus, the diffusion coefficient of nitrobenzene in water was carefully measured and found to be 1.04 × 10-5 cm2 s-1 at 26 °C and 2.14 × 10-5 cm2 s-1 at 60.1 °C.

Ralph T. Ferrell

Papers

Diffusion coefficients of nitrogen and oxygen in water