Microbial Transport Processes in the Environment: Cells and Solutes III Posters
Presiding: K Searcy, Northwestern University; S Findlay, Institute of Ecosystem Studies; A Packman, Northwestern University
B33C-01 1330h
Revisiting the Cape Cod Bacteria Injection Experiment Using a Stochastic Modeling Approach
Colloid filtration models developed in the 1970s for application to homogeneous sand filters used in water treatment have been coupled with the advection-dispersion equation and successfully applied to transport of microorganisms through lab-scale sand columns. Application of this approach to field-scale problems requires adjustment of the model formulation to address the realistic complexity posed by spatial variability of geologic materials known to affect flow and transport processes in aquifers. Representation of geologic heterogeneity as a three-dimensional random permeability field has been incorporated analytically and numerically into mathematical models of colloid transport. In both cases applications to hypothetical field-scale scenarios have shown significant effects of aquifer heterogeneity on the colloid transport process compared to equivalent homogeneous systems. We have applied a particle-tracking technique implementing several different colloid filtration models to a previously-published data set from Cape Cod, Massachusetts, where non-growing, non-motile stained bacteria were injected into an aquifer and recovered 7 meters away in multiple observation wells. The parameters of the heterogeneous hydraulic-conductivity field (mean, variance, and correlation scales of the ln K field) were calibrated based on bromide breakthrough curves from the bacteria/bromide injection test, in addition to independent hydraulic conductivity measurements from a nearby plot. Application of the particle-tracking model to the bacteria data illustrates the robustness of the modeling approach and the sensitivity of transport parameters to the physical heterogeneity representation and the colloid filtration model chosen. In addition, because the distribution diameter sizes of the injected bacteria was known in this case, we show that utilizing a size distribution rather than a mean bacteria diameter as input gives a much more realistic prediction of the composite bacteria breakthrough curve. Results of the simulations also point to needs for quantifying the correlation of local-scale colloid transport parameters (single collector efficiency factor, collision efficiency, detachment) to hydraulic conductivity variability, as well as mathematical incorporation of the effects of geochemical heterogeneity on the three-dimensional transport process.
B33C-02 1330h
Role of extra-polymeric substances (EPS) on the microbial activity in unsaturated porous media
Microbes form colonies to pool resources and better cope with changes in environmental conditions including nutrient availability and hydration status. The excretion of extracellular polymeric substances (EPS) plays an important role in forming colony structure, anchoring to solid surfaces, nutrient entrapment and many other functions. In this study we focus on the micro-hydrological functions of EPS enabling microbial activity in the presence of large spatial and temporal variations in hydration status common to the shallow vadoze zone. We will review key hydraulic and transport properties and postulate mechanisms conferring advantage to microbial colonies embedded in EPS. Relationships between pore space geometry, physical constraints and, EPS production and morphology will be studied. The morphology of EPS and, its effect on the internal arrangement of microbial colonies (typical sizes) will be evaluated under diffusion constraints imposed by conditions in unsaturated soil pores.
B33C-03 1330h
Biogeochemistry of phosphorus exchange in magnetic bacteria
Magnetotactic bacteria swim at high relative speeds (5 mm/min) and cross the sediment water interface in an apparent diurnal pattern. We hypothesized that this is part of a migratory life cycle across the oxic anoxic transition zone at the water sediment interface. If true, this migration has important consequences on the exchange of phosphorous, sulfur and iron between water and sediments. Magnetotactic bacteria may also influence biomineralization and the magnetization of sediments. Our results show that the exchange of phosphorus between magnetic bacteria and water is consistent with a periodic life cycle, during which cells accumulated large amounts of phosphate under oxidizing conditions. Under reducing and anaerobic conditions (i.e. sulfidic sediments) cells release phosphorus. This research shows the importance of magnetic bacteria in the exchange of materials across redox interfaces.
B33C-04 1330h
Geomicrobiology of Phreatic Caves Associated With Central Florida Springs
Phreatic (underwater) limestone caves are common in Florida in association with the numerous springs that issue from the karst landscape. Extensive microbial mats and diverse communities of invertebrates have been observed by cave divers, but, as ecosystems, the caves are not well studied. Four aphotic aquatic caves were identified in which to investigate relationships between microbial communities and their geochemical surroundings, and to evaluate the potential for chemolithoautotrophic microbial activity to support higher-order consumers. The caves were associated with the discharge sites of four different second-magnitude springs (flow: 0.3 to 3 m3 s-1) in central Florida in which communities containing microbial mats, isopods, amphiphods, and cave crayfish have been observed. Samples of bulk water and microbial mat were collected along the flow path in each cave; depths ranged from 0.5 to 15 m below the ground surface, and penetration distance extended up to 250 m from each cave entrance. Microscopic examination of the mats revealed the presence of sulfur-granule-containing, filamentous morphologies consistent with Thiothrix and Beggiatoa and an unidentified filamentous iron bacteria. The bacteria were found in all four springs, but H2S was detected in water samples from only one of the caves. In many cases, the morphology of the organisms changed along the flow path within an individual spring, although there was little change in the associated water chemistry (pH, dissolved oxygen, conductivity, total Fe, NH4+, NO3-, HS-, SO42-, PO4-, Cl-, Fl-, Ca2+, Na+, and Mg2+). The overall water chemistry of the four caves/springs was distinct (principal components analysis), and the major differences were due to Ca2+, K+, and Cl- concentrations, pH (range: 7.3 to 8.4), and sulfur and iron availability. Efforts to culture the dominant organisms in each set of mats (using media prepared with cave or spring water) and community-level genetic analyses (T-RFLP) demonstrated that the communities are composed of a diverse mixture of both chemoautotrophic and heterotrophic bacteria. Elemental analysis (C, N, and S) of the mats revealed a high sulfur content (> 10 %), and low C:N ratios. The latter suggests the material would be a high quality food source for other members of the ecosystem. The results suggest that bacterial production from reduced inorganic compounds in these springs may provide a plentiful source of energy and nutrition to support the higher forms endemic there. Additionally, the microbes likely play an active role in speleogenesis in these phreatic caves, given that sulfuric acid is produced as a metabolic by-product of microbial sulfur oxidation. Additional work is needed to determine the influence of these bacterial communities on the rate and extent of cave formation.
B33C-05 1330h
The Longitudinal Effects of Impoundment on Periphyton Biomass and Δ13C in a Northern Michigan Stream
Autochthonous production is often altered upstream of small impoundments, such as beaver dams, but few studies have examined how such impoundments affect downstream production. A better understanding is needed of how production and organic matter dynamics are affected by natural impoundments. In this study we examined the effects of a beaver impoundment on periphyton biomass and Δ13C in a low-order, forested stream. Periphyton samples were cultured at locations every 200 meters starting at a beaver dam and continuing 800 meters downstream. Samples were analyzed for biomass and carbon and nitrogen stable isotopes. By using additions of macrophyte biomass, the system was manipulated in an attempt to alter natural production levels and isotopic signatures of periphyton. Statistically significant effects were not detected; however, the results did indicate trends. Production decreased with distance from the impoundment, and detrital additions increased production. The amount of increase, however, was inversely related to distance from the impoundment. A shift in isotopic ratios of periphyton was detected, suggesting effects on the inorganic carbon pool, and perhaps shortening of carbon turnover lengths.
B33C-06 1330h
Effects of Periodic Substrate Scouring on Scraper-Algae Interactions in a Small Idaho Stream.
Our objective was to examine how a stream benthic community would organize under periodic scouring events occurring at two different time intervals. We conducted our study in a small, 2nd ordered, mountain stream. We divided a series of stream segments into 3 treatment sections: 1) substrate was manually scoured twice a month, 2) the substrate was scoured once a month, and 3) the substrate was left undisturbed (control). We sampled algal biomass, benthic invertebrates and measured physiochemical variables (DO, water temperature, conductivity, pH, discharge) once every two weeks from June 1 to August 31. We found that scraping invertebrates (primarily Baetis, Cinygmula, Epeorus, Glossosoma) decreased with increased scouring, while algal biomass was positively related to scouring frequency. The algae recovered quickly between scouring intervals, the scraping invertebrates did not. By keeping scraper numbers low, scouring dampened grazing activity on the algae resulting in an increase in its biomass. Scouring may also have removed senescent algae, allowing metabolically active cells more access to nutrient, sunlight, etc.
B33C-07 1330h
Physical Factors Influencing Periphyton Accrual in a Prairie Stream
Physical characteristics can constrain periphyton colonization and accumulation. Unglazed tiles set at three orientations (0°, 45°, and 90° from horizontal) and six substrata of varying surface roughness (glass, glazed tiles (2), unglazed tile, brick, and natural stone) were deployed in a Kansas prairie stream for three weeks. Substrata were analyzed for loosely attached, tightly attached, and total periphyton chlorophyll a. 90° substrata averaged 80 mg chl a m-2, 34% and 37% less periphyton than 0° and 45° tiles respectively. Additionally, variability among 0° and 45° tiles was more than twice that of 90° tiles (SD = 18.6, 25.3, and 8.8 respectively). Periphyton biomass increased with increasing surface roughness, ranging from 47 mg chl a m-2 on glass, to 130 mg chl a m-2 on stones. Linear regression analysis of surface roughness versus chl a showed a better correlation for tightly attached (R2 = 0.85, p = <.001) than total (R2 = 0.76, p = <.001), or loosely attached (R2 = 0.34, p = .001) periphyton. The physical characteristics of stream substrata (roughness and proportion vertical area) should be considered when designing stream periphyton studies, particularly when artificial substrata are used to sample biomass accrual rates.