Denitrification potential of intermittently saturated floodplain soils from a subtropical perennial stream and an ephemeral tributary     

Christine S. Fellows  Heather M. Hunter  Claire E.A. Eccleston  David W. Rassam  Philip M. Bloesch 《Soil biology & biochemistry》2011,43(2):324-332

Denitrification has the potential to remove excess nitrogen from groundwater passing through riparian buffers, thus improving water quality downstream. In regions with markedly seasonal precipitation, transient stream flow events may be important in saturating adjacent floodplain soils and intermittently providing the anaerobic conditions necessary for denitrification to occur. In two experiments we characterised the denitrification potential of soils from two contrasting floodplains that experience intermittent saturation. We quantified under controlled laboratory conditions: 1) potential rates of denitrification in these soils with depth and over time, for a typical period of saturation; and 2) the influences on rates of nitrate and organic carbon. Treatments differed between experiments, but in each case soil-water slurries were incubated anaerobically with differing amendments of organic carbon and nitrate; denitrification rates were measured at selected time intervals by the acetylene-block technique; and slurry filtrates were analysed for various chemical constituents. In the first experiment (ephemeral tributary), denitrification was evident in soils from both depths (0-0.3 m; 0.3-1.1 m) within hours of saturation. Before Day 2, mean denitrification rates at each depth were generally comparable, irrespective of added substrates; mean rates (Days 0 and 1) were 5.2 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m) and 1.6 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.1 m). Rates generally peaked on Days 2 or 3. The availability of labile organic carbon was a major constraint on denitrification in these soils. Acetate addition greatly increased rates, reaching a maximum in ephemeral floodplain soils of 17.4 ± 1.8 mg N kg dry soil⁻¹ day⁻¹ on Day 2: in one deep-soil treatment (low nitrate) this overcame differences in rates observed with depth when acetate was not added, although the rate increase in the other deep-soil treatment (high nitrate) was significantly less (P ≤ 0.01). Without acetate, peak denitrification rates in this experiment were 6.9 ± 0.4 and 2.8 ± 0.2 mg N kg dry soil⁻¹ day⁻¹ in surface and deep soils, respectively. Differences in rates were observed with depth on all occasions, despite similar initial concentrations of dissolved organic carbon (DOC) at both depths. Levels of substrate addition in the second experiment (perennial stream) more closely reflected natural conditions at the site. Mean denitrification rates were consistently much higher in surface soil (P ≤ 0.001), while the source of water used in the slurries (surface water or groundwater from the site) had little effect on rates at any depth. Mean rates when all treatments retained nitrate were: 4.5 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0-0.3 m depth); 0.8 ± 0.3 mg N kg dry soil⁻¹ day⁻¹ (0.3-1.0 m); and 0.6 ± 0.1 mg N kg dry soil⁻¹ day⁻¹ (1.8-3.5 m). For comparable treatments and soil depths, denitrification potentials at both sites were similar, apart from higher initial rates in the ephemeral floodplain soils, probably associated with their higher DOC content and possibly also their history of more frequent saturation. The rapid onset of denitrification and the rates measured in these soils suggest there may be considerable potential for nitrate removal from groundwater in these floodplain environments during relatively short periods of saturation.  相似文献   

Contrasting Observation and Transect-Based Models of Cattle Distribution on Lincoln National Forest,New Mexico     

Heather Halbritter  Louis C. Bender 《Strength and Conditioning Journal》2011,64(5):514-520

Perceptions of cattle distribution and resource conflicts are often based upon qualitative observations of cattle by managers or the general public. Such information on cattle presence and inferred habitat preferences may not reflect true habitat correlates of cattle because observations do not include any sampling design. We documented cattle presence and used presence data to model distribution of cattle with respect to landscape features on the Lincoln National Forest (LNF) of south-central New Mexico, an area of conflict with regard to cattle herbivory. We recorded cattle presence both from visual observations of cattle while conducting other research activities and from randomized pellet-group transects during the spring–autumn period when cattle grazed the high-elevation habitats. Distribution of cattle differed for several habitat variables between datasets, although distribution models from both datasets indicated that elevation, slope, distance to water and roads, and vegetation cover type most influenced cattle presence. Cattle presence was associated with a variety of cover types, and cattle were generally within 500 m of water and on slopes of < 15–20%. Observation-based models showed positive associations with open cover types, including the strongest positive association with montane meadows, the area of conflict in LNF. In contrast, transect-based models showed positive associations with more cover types (11) than did observation-based (6). Observation-based models also showed higher association with areas closer to roads. Inferred habitat preferences based on casual observations of cattle may not accurately reflect true distribution or use, as transect-based models predicted much broader distribution throughout LNF and higher overall probabilities of cattle presence. Because cattle distribution included many other vegetation cover types in addition to montane meadows, management to enhance positive correlates of cattle distribution on LNF may be useful to alter cattle distribution away from areas of perceived conflict.  相似文献   

Deoxynivalenol biosynthesis-related gene expression during wheat kernel colonization by Fusarium graminearum     

Hallen-Adams HE  Wenner N  Kuldau GA  Trail F 《Phytopathology》2011,101(9):1091-1096

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Mercury Concentrations in Largemouth BASS (Micropterus Salmoides) from Five South Carolina Reservoirs     

John D. Peles  Travis C. Glenn  Heather A. Brant  Angela K. Wall  Charles H. Jagoe 《Water, air, and soil pollution》2006,173(1-4):151-162

Mercury concentrations in largemouth bass (Micropterus salmoides) bass were compared among five reservoirs in South Carolina. Three of these reservoirs (Lake Russell, Lake Thurmond, and Lake Marion) are accessible to the public and two (L-Lake and Par Pond) are located on the U.S. Department of Energy's Savannah River Site (SRS), which is closed to public access. Age-adjusted mercury concentrations were significantly higher in SRS bass compared to the offsite reservoirs. In addition, mercury concentrations were significantly higher in bass from Par Pond compared to L-Lake and in bass from Lakes Russell and Thurmond compared to Lake Marion. No mercury concentrations in excess of the U.S. Food and Drug Administration action level (1.0 mg?kg^?1) were found in any bass from the public-accessible reservoirs. However, the majority of fish from these reservoirs had mercury concentrations that fall into or exceed the U.S. Environmental Protection Agency consumption category of “no more than one per week". In addition, most fish from these reservoirs had mercury levels in excess of those believed to be detrimental to sensitive avian species.  相似文献   

Avian encephalomyelitis virus. II. Pathogenesis in chickens     

M O Braune  R F Gentry 《Avian diseases》1971,15(4):648-653

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Competency of blood coagulation in the newborn calf     

P.A. Gentry  M.L. Ross  H. Hayatgheybi   《Research in veterinary science》1994,57(3):1176

This study evaluated the haemostatic profiles of a group of 11 female and seven male calves from the day of birth until they were 60 days of age. Similar results were found for both sexes. At birth the plasma activity of the procoagulant proteins, Factors VII, VIII:C, IX, X and XI and fibrinogen were all close to the adult values. Factors VII, VIII:C and fibrinogen increased transiently during the first seven days of life but the increases were not sufficient to influence routine coagulation screening assays such as the activated partial thromboplastin time and the prothrombin time. At birth, the plasma concentration of the protease inhibitor, α₂-macroglobulin, was approximately 50 per cent of adult values and increased slowly during the first seven days of life; the plasma concentration of antithrombin III was higher than that of α₂-macroglobulin. The changes in the plasma concentration of fibronectin paralleled the changes in fibrinogen and Factor VIII:C from birth to 60 days of age; the concentrations of total plasma protein and plasma albumin remained stable and within the adult ranges throughout the 60 days. The plasma concentration of glucose increased transiently during the first 48 hours after birth.  相似文献   

Serum and tissue concentrations of erythromycin in calves with induced pneumonic pasteurellosis   总被引：1，自引：0，他引：1  

G E Burrows  M Gentry  P Ewing 《American journal of veterinary research》1989,50(7):1166-1169

The effects of pneumonia on the pharmacokinetics of erythromycin administered IM and the tissue concentration changes with time were evaluated in 2-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures through the thoracic wall into each lung. Six days prior to induction of pneumonia, erythromycin (15 mg/kg) was administered in a single IM dose. Erythromycin was administered again 48, 72, and 96 hours after injection of P haemolytica. On the third day of erythromycin administration (96 hours), the calves were serially euthanatized in groups of 4 calves each at 2, 5, 8, 12, 18, and 24 hours after the final dose was given. Tissue concentrations of erythromycin in kidney, liver, lung, muscle, CSF, and serum were determined. Neither the serum concentrations nor the overall pharmacokinetic values were significantly (P less than or equal to 0.05) changed by pneumonia. The concentrations of erythromycin were maximal at 5 hours for liver, muscle, and serum and at 8 hours for CSF, kidney, and lung. Serum and muscle concentrations were similar, whereas concentrations in CSF were lower than in serum and higher in kidney, liver, and lung. The lung/serum ratios were approximately 2.5 to 3 at 8 through 24 hours after IM administration. The peak concentration in lung was approximately 6 micrograms/g at 8 hours.  相似文献   

65Zn tissue distribution in lactating Holstein cows fed normal and low-zinc practical diets     

M W Neathery  W J Miller  D M Blackmon  R P Gentry 《Journal of animal science》1974,38(4):854-859

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Chromatographic separation and characterization of Pasteurella haemolytica cytotoxin   总被引：5，自引：0，他引：5  

D A Mosier  B A Lessley  A W Confer  S M Antone  M J Gentry 《American journal of veterinary research》1986,47(10):2233-2241

Biochemical and immunologic properties of the cytotoxin (leukotoxin) produced by Pasteurella haemolytica were examined. Crude, bacteria-free supernatants from logarithmic phase P haemolytica were fractionated, using a series of column chromatographic techniques. Sequential anion exchange chromatography, gel-filtration chromatography, and chromatofocusing resulted in a cytotoxic substance (cytotoxin-C) of approximately 160 kilodaltons (kD), as determined by use of gel-filtration chromatography. Polyacrylamide-gel electrophoresis of cytotoxin-C yielded 3 protein bands with relative mobilities of 0.37, 0.42, and 0.63. On the basis of immunoblotting with a cytotoxin-neutralizing bovine immunoglobulin for antigen detection, the 2 low-mobility bands shared a strong region of immunogenicity. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, principal protein constituents of cytotoxin-C were found at 160, 66, 57, and 23 kD. Using immunoblotting with cytotoxin-neutralizing immunoglobulin, strong, distinct reactions with the 66- and 57-kD bands were detected. Immunization of rabbits and mice with cytotoxin-C resulted in sera that reacted strongly with cytotoxin-C in enzyme-linked immunosorbent assays and immunodiffusion assays. The major immunogenic proteins also were detected by use of immunoblotting with anticytotoxin-C sera from rabbits and mice. Postinoculation rabbit sera neutralized crude cytotoxin.  相似文献   

Ovine platelet function and its inhibition by T-2 toxin     

P. A. Gentry  A. S. Socha  M. L. Ross 《Veterinary research communications》1987,11(5):457-466

Ovine platelets suspended in homologous plasma aggregated effectively in response to adenosine-diphosphate, acid-soluble collagen and aggregated moderately to serotonin and arachidonic acid. Ovine platelet aggregation, in response to each agent, was inhibited in a concentration dependent fashion by T-2 toxin. The platelet aggregates which formed in the presence of T-2 toxin appeared to be less stable than aggregates in comparable control platelet suspensions.  相似文献