Janine Ryburn

Microbial and chemical tracer movement through two Southland soils, New Zealand

There has been a recent, rapid increase in both land application of dairy shed effluent in Southland, New Zealand, and the microbial load in ground and surface waters. We investigated the fate of faecal coliforms, a host-specific Salmonella bacteriophage, and a non-reactive chemical tracer (Br–), when applied to large intact lysimeter soil cores (500 mm diam. by 500 mm high), to determine the pattern of microbial transport through typical Southland soils. The soils were a poorly drained Fragic Perch-gley Pallic Soil, and a well-drained Typic Firm Brown Soil. A depth of 25 mm of dairy shed effluent containing faecal coliforms and spiked with bacteriophage and Br– was applied to the soil at a rate of 5 mm/h followed by ~1 pore volume of simulated rainfall applied at 5 mm/h. Resulting leachates, collected continuously over ~1 pore volume, were analysed for the microbial and bromide tracers. The microbial tracers moved rapidly through both soils, peaking early in the leachate at ~0.15 pore volume and then tailing off in a pattern indicative of bypass flow. Bromide moved more uniformly through the soils but peaked at ~0.5–0.8 pore volume. The microbial flow pattern observed indicates that the structure in these soils makes them vulnerable to leaching of microbes into local surface and ground water. The large difference between the rate of microbial and chemical tracer transport indicates chemical tracers should only be used with caution to model microbial transport parameters.

Regionalizing Potential for Microbial Bypass Flow through New Zealand Soils

Microbial breakthrough curves of 12 soils, generated by the application of dairy shed effluent followed by continuous artificial rainfall for one pore volume at 5 mm h(-1) onto large undisturbed soil cores, have been ranked as high, medium, or low potential for microbial bypass flow. The ranking is based on the position of the peak in the breakthrough curve. Knowledge of soil properties that affect microbial transport through soil gained from the microbial breakthrough curves was linked to soil classes, or to their accessory properties, of the New Zealand Soil Classification. Spatial depiction of the ratings has been achieved via the national 1:50,000 scale soil map. Soils with a drainage impediment or those with well developed soil structure have a high potential for microbial bypass flow, whereas soils from tephra and Recent Soils with less developed, porous, soil structure have a low potential for microbial bypass flow. The risk rankings should be considered as maxima because management may change some rankings.

Atrazine mineralisation rates in New Zealand soils are affected by time since atrazine exposure

To understand more clearly the groundwater contamination potential of herbicides applied to New Zealand soils, experimental field plots were established on 2 different soil types: Himatangi, a sandy dune soil, and Kiripaka, a silty clay derived from basalt. A mix of triazine herbicides, containing atrazine, terbuthylazine, and hexazinone, was applied to the plots at 10 kg a.i./ha. At various times after application, soil was removed from the plots and analysed for residual levels of herbicides, in vitro rates of mineralisation of 14C-ring-labelled atrazine, and numbers of atrazine-degrading microbes. Atrazine and terbuthylazine were below detectable levels (<0.01 mg/kg) in Himatangi topsoil 18 months after pesticide application but still detectable in topsoil from the Kiripaka site. Hexazinone was detectable in topsoil from both soil plots 18 months after application. Atrazine adsorption isotherms were constructed for topsoil and subsoil from both plots, with estimated Kf values ranging from 0.53 to 4.69 μg1–n mLn/g. A single application of atrazine was sufficient to enhance the rate of 14C-atrazine mineralisation in vitro by topsoil from both plots, and subsoil from the Kiripaka site. Rates of mineralisation of atrazine in the soil from the plots increased 1–6 months after pesticide application and remained elevated for 18–24 months. The numbers of atrazine degraders detected did not correlate with atrazine mineralisation rates. An atrazine-degrading bacterium, identifed as Arthrobacter nicotinovorans, was isolated from Himatangi soil exhibiting enhanced rates of atrazine-mineralisation activity.

Microbial and chemical tracer movement through Granular, Ultic, and Recent Soils

Abstract The ability of New Zealand soils to renovate dairy‐shed effluent following application to land is being evaluated. We investigated the pattern of transport of faecal coliforms, a host‐specific Salmonella bacteriophage and a non‐reactive chemical tracer (Br–), when applied to large, intact lysimeter soil cores (460 mm dia. × 520–700 mm high) of three contrasting soils. The soils were imperfectly drained Ultic and Granular Soils and a well‐drained Recent Soil. A depth of 25 mm of dairy‐shed effluent containing faecal coliforms and spiked with bacteriophage and Br− was applied to the soil at a rate of 5 mm h−1 followed by up to 1 pore volume of simulated rainfall applied at 5 mm h−1. This application rate is generally much slower than the soils saturated hydraulic conductivity except in the Ultic Soil where saturated hydraulic conductivity is slower. Resulting leachates, collected continuously, were analysed for the microbial and bromide tracers. The phage tracer moved rapidly through all soils, peaking early in the leachates and then tailing off in a pattern indicative of bypass flow. Faecal coliforms also moved rapidly through the Ultic and Granular Soils but numbers were much lower or not detectable in leachate from the Recent Soil. In contrast, bromide moved uniformly through Granular and Recent Soils but peaked early at about 0.5–0.8 pore volume. The microbial data suggest the soil structure in the Ultic and Granular Soils makes them vulnerable to leaching of microbes into shallow water bodies.

Hexadecane mineralization activity in ornithogenic soil from Seabee Hook, Cape Hallett, Antarctica

Ornithogenic soils that form in penguin rookeries contain high levels of organic carbon and nitrogen. On Seabee Hook, Cape Hallett, Antartica, ornithogenic soil was contaminated with hydrocarbons following establishment of a scientific research station. In these soils hydrocarbon biodegradation could be supported by available soil nitrogen. Hexadecane mineralization activity was detected in vitro in ornithogenic soil when incubated at 5 or 15°C. At 5°C the extent of hexadecane mineralization was higher in hydrocarbon-contaminated soil than in uncontaminated soil. Alkane-degrading bacteria isolated from Seabee Hook soil were identified as Rhodococcus or Gordonia spp. or an unclassified Corynebacterineae. The alkane degraders grew on n-alkanes from heptane (C8) to eicosane (C20) and pristane, and utilized uric acid or ammonium nitrate as nitrogen source. All of the isolates possessed urease activity. Results of this study indicate biodegradation of hydrocarbons may contribute to the natural attenuation of oil spills in ornithogenic surface soils in summer.

Soil type influences the leaching of microbial indicators under natural rainfall following application of dairy shed effluent

The ability of soil to function as a barrier between microbial pathogens in wastes and groundwater following application of animal wastes is dependent on soil structure. We irrigated soil lysimeters with dairy shed effluent at intervals of 3–4 months and monitored microbial indicators (somatic coliphage, faecal enterococci, Escherichia coli) in soil core leachates for 1 year. The lysimeters were maintained in a lysimeter facility under natural soil temperature and moisture regimes. Microbial indicators were rapidly transported to depth in well-structured Netherton clay loam soil. Peak concentrations of E. coli and somatic coliphage were detected immediately following dairy shed effluent application to Netherton clay loam soil, and E. coli continued to leach from the soil following rainfall. In contrast, microbial indicators were rarely detected in leachates from fine-structured Manawatu sandy loam soil. Potential for leaching was dependent on soil moisture conditions in Manawatu soil but not Netherton soil, where leaching occurred regardless. Dye studies confirmed that E. coli can be transported to depth by flow through continuous macropores in Netherton soils. However, in the main E. coli was retained in topsoil of Netherton and Manawatu soil.

Culturable microbes in shallow groundwater underlying ornithogenic soil of Cape Hallett, Antarctica.

The objective of this study was to investigate the culturable psychrotolerant microbial community in groundwater from Seabee Hook, Antarctica. Shallow groundwater can be present in coastal regions at higher latitudes during the Antarctic summer. Perched groundwater atop ice-cemented permafrost occurs on Seabee Hook, Cape Hallett, at depths from 5 to 80 cm below the soil surface. Compared with terrestrial water from other sites in Antarctica, the groundwater was high in salt and nutrients, reflecting proximity to the sea and ornithogenic soil. Microbial communities in groundwater samples from Seabee Hook exhibited aerobic metabolism of 14C-acetate at 5 degrees C. Numbers of culturable aerobic heterotrophs in the samples ranged from <10 to ca. 1 x 106 colony-forming units.mL-1, and similar numbers of microaerophiles and nitrate reducers were detected. In contrast, numbers of nitrifiers, sulfate reducers, and iron reducers were up to 1000-fold lower. All cultures were incubated at 5 degrees C. Aerobic heterotrophic bacteria isolated from the groundwater were assigned to Actinobacteria, Proteobacteria, or Bacteroidetes. The isolates were most similar to cultured bacteria from Antarctic soil or sediment and were cold, salt, and alkaline pH tolerant, indicating they are adapted to in situ conditions.