Fe(III)-reducing isolates were recovered from two aquifers in which Fe(III) reduction is known to be important. Strain BemT was enriched from subsurface sediments collected in Bemidji, MN, USA, near a site where Fe(III) reduction is important in aromatic hydrocarbon degradation. Strains P11, P35T and P39 were isolated from the groundwater of an aquifer in Plymouth, MA, USA, in which Fe(III) reduction is important because of long-term inputs of acetate as a highway de-icing agent to the subsurface. All four isolates were Gram-negative, slightly curved rods that grew best in freshwater media. Strains P11, P35T and P39 exhibited motility via means of monotrichous flagella. Analysis of the 16S rRNA and nifD genes indicated that all four strains are δ-proteobacteria and members of the Geobacter cluster of the Geobacteraceae. Differences in phenotypic and phylogenetic characteristics indicated that the four isolates represent two novel species within the genus Geobacter. All of the isolates coupled the oxidation of acetate to the reduction of Fe(III) [iron(III) citrate, amorphous iron(III) oxide, iron(III) pyrophosphate and iron(III) nitrilotriacetate]. All four strains utilized ethanol, lactate, malate, pyruvate and succinate as electron donors and malate and fumarate as electron acceptors. Strain BemT grew fastest at 30 °C, whereas strains P11, P35T and P39 grew equally well at 17, 22 and 30 °C. In addition, strains P11, P35T and P39 were capable of growth at 4 °C. The names Geobacter bemidjiensis sp. nov. (type strain BemT=ATCC BAA-1014T=DSM 16622T=JCM 12645T) and Geobacter psychrophilus sp. nov. (strains P11, P35T and P39; type strain P35T=ATCC BAA-1013T=DSM 16674T=JCM 12644T) are proposed.

The time-averaged concentration of hydrocarbon and oxygen vapors were measured in the unsaturated zone above the residually contaminated capillary fringe at the U.S. Coast Guard Air Station in Traverse City, Michigan. Total hydrocarbon and oxygen vapor concentrations were observed over a 13-month period. Supplementary grain size, porosity, and moisture content data support the assumption of a uniform, homogeneous site geology which, in view of the planar hydrocarbon source term, abundant oxygen, and sparse data base, is suitable for simple analytical modeling. In the assumed absence of advection, leaching, and transience, the analysis is a straightforward balance of gaseous diffusion and biological degradation coupled stoichiometrically in the two reacting constituents. Volatilization is shown to be a significant transport mechanism for hydrocarbons at Traverse City, and biodegradation prevents the escape of appreciable contamination to the atmosphere for most locations at this site. Little oxygen is expected to reach the water table because of the aerobic biodegradation process in the unsaturated zone. Traverse City, Michigan. This work bears upon the larger problem of organic contamination of the subsurface environment, a phenomenon of emerging importance due to the widespread use of organic fluids arid solutions in post Word War II America [National Academy of Sciences, 1984; Wise and Fahrenthold, 1981]. Pesticides, herbicides, solvents, gasoline, heating oil, creosote, and transmission fluid are typical examples, and their eventual distribution in waste lagoons, agricultural runoff, landfills, spills, and buried drum sites commonly leads to subsurface pollution [Schwille, 1967; Jury et al., 1986; Reinhard et al., 1984; Kitunen et al., 19871. Gaseous transport of volatile compounds has been identified as a potentially important mechanism in mathematical, laboratory, and field investigations of the unsaturated zone. Baehr [1987], Falta et al. [1989], Sleep and Sykes [1989], Mendoza and McAlary [1990], and Jury et al. [1990] all model the gaseous hydrocarbon transport process in the vadose zone. Baehr's [1987] work is a useful analytical balance of transience, sorption, and diffusion which highlights the influence of air/water partitioning on the release of hydrocarbon vapors to the surface and subsurface environments. Falta et al. [ 1989] feature density-driven advection in their finite difference model of chlorinated hydrocarbon vapor transport, as do the finite element codes of Sleep and Sykes [1989] and Mendoza and McAlary [1990], which include leaching of trichloroethylene into an underlying water table. Jury et al. [1990] put forward an analytical model of gaseous diffusion and dissolved advection of vola-Copyright 199! by the American Geophysical Union. Paper number 9 ! WR001 ! I. 0043-1397/91/91WR-00111 $05.00 tile organic chemicals through the vadose zone, subject to sorption and first-order decay. These simulations provide sensitivity studies for various transport mechanisms but are typically not calib...

At‐many‐stations hydraulic geometry (AMHG), while useful for estimating river discharge from satellite data, remains empirical and has yet to be reconciled with the at‐a‐station hydraulic geometry (AHG) from which it was originally derived. Here we present evidence, using United States Geological Survey field measurements of channel hydraulics for 155 rivers, that AMHG can be hydraulically and geomorphically reconciled with AHG. Our results indicate that AMHG is rightly understood as an expression of a river‐wide model of hydraulics driven by changes in slope imposed upon AHG physics. The explanatory power of AHG and this river‐wide model combine to determine whether AMHG exists: if both AHG and the river‐wide model adequately describe hydraulics, then we show that AMHG is a necessary mathematical consequence of these two phenomena. We also orient these findings in the context of river discharge estimation and other applications.

We incorporate a linear estimate of casing friction into the analytical slug test theory of Springer and Gelhar (1991) for high permeability aquifers. The modified theory elucidates the influence of inertia and casing friction on consistent, closed form equations for the free surface, pressure, and velocity fluctuations for overdamped and underdamped conditions. A consistent, but small, correction for kinetic energy is included as well. A characteristic velocity linearizes the turbulent casing shear stress so that an analytical solution for attenuated, phase shifted pressure fluctuations fits a single parameter (damping frequency) to transducer data from any depth in the casing. Underdamped slug tests of 0.3, 0.6, and 1 m amplitudes at five transducer depths in a 5.1 cm diameter PVC well 21 m deep in the Plymouth-Carver Aquifer yield a consistent hydraulic conductivity of 1.5 x 10(-3) m/s. The Springer and Gelhar (1991) model underestimates the hydraulic conductivity for these tests by as much as 25% by improperly ascribing smooth turbulent casing friction to the aquifer. The match point normalization of Butler (1998) agrees with our fitted hydraulic conductivity, however, when friction is included in the damping frequency. Zurbuchen et al. (2002) use a numerical model to establish a similar sensitivity of hydraulic conductivity to nonlinear casing friction.

We use Monod kinetics to calibrate previously published data that documentthe aerobic biodegradation of hydrocarbon vapors in soil microcosms from a weathered petroleum spill site. Monod kinetics offer insight into biodegradation mechanics because they address biomass growth as well as substrate depletion. A blend of five aromatics and five alkanes dose the microcosm sets at four strengths, and a finite difference model describes the response superimposed across the constituent substrates. An observed initial biomass X0 of 125 g biomass/m(3) soil moisture and an endogendous decay rate b of 0.102 day(-1) calibrate all four dosages and agree with heterotrophic plate counts. Common maximum specific growth rates microMJ and half saturation constants KSJ calibrate each constituent across the four dosages. The biodegradable alkanes exhibit microMJ values ranging from 0.0190 to 0.0996 day(-1), while the aromatic rates vary from 0.0946 to 0.322 day(-1). One of the alkanes (2,2,4-trimethylpentane) is recalcitrant. The half saturation constants range from 0.000083 to 0.000355 g substrate/m(3) soil moisture for the biodegradable alkanes, which imply zero-order kinetics. The aromatic KSJ values vary from 5.02 to 14.3 g substrate/m(3) soil moisture, and suggest first-order kinetics. The yield YJ increases with dosage concentration for all the biodegradable constituents, varying from 0.0533 to 1.58 g biomass/g substrate.