We combined water activity meters and fractal modeling to facilitate rapid, physically based characterization of the soil water retention curve. Desorption data (6 points per sample) were collected in the tension (h) range 2.0 × 102 to 1.5 × 105 kPa using the gravimetric method to measure water content (w) and water activity meters to measure h Thirty‐two disturbed samples from a long‐term nitrogen fertilization and tillage comparison study on a silt loam soil were analyzed. A new form of an established fractal equation was derived: w = ahD−3 − ρw/ρs, where a is a compound parameter including the bulk density (ρb) and air entry tension (ha), D is the mass fractal dimension, ρw is the density of water, and ρs is the particle density. This model was fitted to the measured water retention curves by nonlinear regression analysis. The a and D parameters were estimated, while ρw and ρs were fixed at 1.00 and 2.65 Mg m−3, respectively. Convergence was always achieved and the equation fitted the data extremely well; residual sums of squares ranged from 1.2 × 10−6 to 6.7 × 10−5, with a median value of 2.2 × 10−5 Estimates of a (0.62–0.74) and D (2.948–2.963) were physically reasonable, and sensitive to soil management practices. The a parameter increased, r = 0.80 (P < 0.01), (signifying decreasing ρb and/or ha) whereas D decreased, r = −0.75 (P < 0.01), (signifying more rapid capillary drainage) with increasing soil carbon content. Additional research is needed to test this approach on other soil types, and to assess the influence of soil disturbance and variations in ρs on the model's performance.
We investigated the effect of different flow conditions on the transport of bacteriophage phiX174 in Memphis aquifer sand. Virus transport associated with a wetting front moving into an initially unsaturated horizontal sand column was experimentally compared with that observed under steady-state saturated vertical flow. Results obtained by sectioning the sand columns showthattotal (retained and free) resident virus concentrations decreased approximately exponentially with the travel distance. The rate of decline was similar under both transient unsaturated flow and steady-state saturated flow conditions. Total resident virus concentrations near the inlet were an order of magnitude greater than the virus concentration of the influent solution in both experiments, indicating continuous virus sorption during flow through this zone. Virus retardation was quantified using the ratio of the centroids of the relative saturation and virus concentration versus relative distance functions. The mean retardation factors were 6.43 (coefficient of variation, CV = 14.4%) and 8.22 (CV = 8.22%) for the transient unsaturated and steady-state saturated flow experiments, respectively. Attest indicated no significant difference between these values at P < 0.05. Air-water and air-water-solid interfaces are thought to enhance virus inactivation and sorption to solid particles. The similar retardation factors obtained may be attributable to the reduced presence of these interfaces in the two flow systems investigated as compared to steady-state unsaturated flow experiments in which these interfaces occur throughout the entire column.
Agricultural plants and domestic animals are subject to mycotoxin contamination or infection, respectively, during unusually wet or dry growing seasons. This study was designed to assay mycotoxin levels in a major wildlife food source. Acorn and corn samples were collected at the Ames Plantation in Grand Junction, Tennessee, from both bottomland and upland regions. Samples were gathered during Fall 1998 after a droughty summer. Forty-eight acorn samples were tested, using thin-layer chromatography, for six different toxins at the Animal Disease Diagnostic Laboratory at Purdue University. This determined the concentrations and types of mycotoxins present in each sample. Two of the six toxins showed up regularly and at fairly high concentrations throughout the samples. Acorn samples closer to cornfields yielded higher frequencies of one of the toxins. Wildlife that eat these acorns are receiving levels of mycotoxins at least twice that of the recommended levels for any domestic animal. Further research needs to be conducted during a year when there is little or no environmental stress to see if the 1998 acorn samples showed unusually high levels of toxins. These toxins can pose a threat to wildlife, and more research should be carried out to test the extent to which wildlife are exposed to and damaged by these toxins.
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