Dryland rock detention structures increase herbaceous vegetation cover and stabilize shrub cover over 10 years but do not directly affect soil fertility

Rock detention structures (RDS) such as check dams, gabions, and one rock dams are commonly used to mitigate erosion impacts in dryland ephemeral stream channels. RDS increase local water infiltration and floodplain connectivity, reduce sediment transport, and enhance vegetation growth and establishment. In addition to increasing overall vegetation cover, RDS may also buffer against a cycle of vegetation growth and collapse during years of extremely variable precipitation, helping to maintain stable cover. Although widely employed by land managers, success as reported in scientific literature varies, especially with regard to RDS effects on vegetation and soil fertility. We present the results of a 10-year field experiment in southeastern Arizona, USA, designed in collaboration with local land practitioners to measure local in-channel effects of RDS. Over 10 years, cover of herbaceous vegetation (forbs and grasses) doubled from 11 % to 22 % in channels treated with RDS, but did not significantly increase in untreated control channels. Shrub cover in treated channels was significantly less variable than in control channels over time. We analyzed the complex relationships between RDS, vegetation cover, and soil fertility using structural equation modeling (SEM), which represented conditions of the tenth year alone. SEM revealed that RDS did not directly affect soil fertility, as measured by total soil nitrogen, total soil carbon, soil organic matter, microbial richness, and potential nutrient cycling capacity. Notably, SEM did not yield the same trends as temporal monitoring, possibly because our structural equation models could not capture change over time. This discrepancy highlights the need for long-term, frequent monitoring of aboveground and belowground conditions to evaluate treatment success on a management scale. Overall, installing rock detention structures in ephemeral channels in arid and semiarid regions is a low-cost, feasible way to increase channel sediment aggradation, forb, and grass cover; stabilize shrub cover; and combat dryland degradation.

Effects of antibiotic therapy on Pseudomonas aeruginosa-induced lung injury in a rat model

The effect of antibiotics on the acute lung injury induced by virulent Pseudomonas aeruginosa PA103 was quantitatively analyzed in a rat model. Lung injury was induced by the instillation of PA103 directly into the right lower lobes of the lungs of anesthetized rats. The alveolar epithelial injury, extravascular lung water, and total plasma equivalents were measured as separate, independent parameters of acute lung injury. Four hours after the instillation of PA103, all the parameters were increased linearly depending on the dose of P. aeruginosa. Next, we examined the effects of intravenously administered antibiotics on the parameters of acute lung injury in D-galactosamine-sensitized rats. One hour after the rats received 10(7) CFU of PA103, an intravenous bolus injection of aztreonam (60 mg/kg) or imipenem-cilastatin (30 mg/kg) was administered. Despite an MIC indicating resistance, imipenem-cilastatin improved all the measurements of lung injury; in contrast, aztreonam, which had an MIC indicating sensitivity, did not improve any of the lung injury parameters. The antibiotics did not generate different quantities of plasma endotoxin; therefore, endotoxin did not appear to explain the differences in lung injury. This in vivo model is useful to quantitatively compare the efficacies of parenteral antibiotic administration on Pseudomonas airspace infections.

Thermal mechanical analysis of frozen solutions of mannitol and some related stereoisomers: evidence of expansion during warming and correlation with vial breakage during lyophilization

The mechanical properties of frozen mannitol, L-iditol, dulcitol, and sorbitol solutions were measured as a function of temperature during warming (after freezing) using a thermal mechanical analyzer (TMA). The mannitol sample first underwent a contractive phase starting at 30 degrees C and ending at -25 degrees C. This was followed by an initially rapid, then less rapid expansive phase which continued until melting occurred. These events provide direct evidence that mannitol solutions undergo an expansion during warming after "fast" freezing and also corroborate the vial breakage observed when mannitol solutions are frozen and thawed or freeze-dried in glass vials. Of the other stereoisomers studied, only dulcitol had an expansive phase although at a slower rate than mannitol. Its solution was found to cause vial breakage also but only at fill volumes higher than mannitol fill volumes. TMA is a useful technique for studying dimensional changes in the frozen state, with important implications for solving vial breakage problems in freeze-drying.