Andrey K. Guber

Survival of manure-borne E. coli in streambed sediment: effects of temperature and sediment properties.

Escherichia coli bacteria are commonly used as indicator organisms to designate of impaired surface waters and to guide the design of management practices to prevent fecal contamination of water. Stream sediments are known to serve as a reservoir and potential source of fecal bacteria (E. coli) for stream water. In agricultural watersheds, substantial numbers of E. coli may reach surface waters, and subsequently be deposited into sediments, along with fecal material in runoff from land-applied manures, grazing lands, or wildlife excreta. The objectives of this work were (a) to test the hypothesis that E. coli survival in streambed sediment in the presence of manure material will be affected by sediment texture and organic carbon content and (b) to evaluate applicability of the exponential die-off equation to the E. coli survival data in the presence of manure material. Experiments were conducted at three temperatures (4 degrees C, 14 degrees C, and 24 degrees C) in flow-through chambers using sediment from three locations at the Beaverdam Creek Tributary in Beltsville, Maryland mixed with dairy manure slurry in the proportion of 1000:1. Indigenous E. coli populations in sediments ranged from ca. 10(1) to 10(3)MPNg(-1) while approx 10(3) manure-borne E. coli MPNg(-1) were added. E. coli survived in sediments much longer than in the overlaying water. The exponential inactivation model gave an excellent approximation of data after 6-16 days from the beginning of the experiment. Slower inactivation was observed with the increase in organic carbon content in sediments with identical granulometric composition. The increase in the content of fine particles and organic carbon in sediments led not only to the slower inactivation but also to lower sensitivity of the inactivation to temperature. Streambed sediment properties have to be documented to better evaluate the role of sediments as reservoirs of E. coli that can affect microbiological stream water quality during high flow events.

Effect of Bovine Manure on Fecal Coliform Attachment to Soil and Soil Particles of Different Sizes

ABSTRACT Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particles, and cells attached to manure particles. The objectives of this work were to compare the attachment of fecal coliforms (FC) to different soils and soil fractions and to assess the effect of bovine manure on FC attachment to soil and soil fractions. Three sand fractions of different sizes, the silt fraction, and the clay fraction of loam and sandy clay loam soils were separated and used along with soil samples in batch attachment experiments with water-FC suspensions and water-manure-FC suspensions. In the absence of manure colloids, bacterial attachment to soil, silt, and clay particles was much higher than the attachment to sand particles having no organic coating. The attachment to the coated sand particles was similar to the attachment to silt and clay. Manure colloids in suspensions decreased bacterial attachment to soils, clay and silt fractions, and coated sand fractions, but did not decrease the attachment to sand fractions without the coating. The low attachment of bacteria to silt and clay particles in the presence of manure colloids may cause predominantly free-cell transport of manure-borne FC in runoff.

Comparison of release and transport of manure‐borne Escherichia coli and enterococci under grass buffer conditions

Aim:  To test the hypothesis that Escherichia coli and enterococci bacteria have similar release rates and transport characteristics after being released from land‐applied manure.

Properties of soil pore space regulate pathways of plant residue decomposition and community structure of associated bacteria

Physical protection of soil carbon (C) is one of the important components of C storage. However, its exact mechanisms are still not sufficiently lucid. The goal of this study was to explore the influence of soil structure, that is, soil pore spatial arrangements, with and without presence of plant residue on (i) decomposition of added plant residue, (ii) CO2 emission from soil, and (iii) structure of soil bacterial communities. The study consisted of several soil incubation experiments with samples of contrasting pore characteristics with/without plant residue, accompanied by X-ray micro-tomographic analyses of soil pores and by microbial community analysis of amplified 16S–18S rRNA genes via pyrosequencing. We observed that in the samples with substantial presence of air-filled well-connected large (>30 µm) pores, 75–80% of the added plant residue was decomposed, cumulative CO2 emission constituted 1,200 µm C g-1 soil, and movement of C from decomposing plant residue into adjacent soil was insignificant. In the samples with greater abundance of water-filled small pores, 60% of the added plant residue was decomposed, cumulative CO2 emission constituted 2,000 µm C g-1 soil, and the movement of residue C into adjacent soil was substantial. In the absence of plant residue the influence of pore characteristics on CO2 emission, that is on decomposition of the native soil organic C, was negligible. The microbial communities on the plant residue in the samples with large pores had more microbial groups known to be cellulose decomposers, that is, Bacteroidetes, Proteobacteria, Actinobacteria, and Firmicutes, while a number of oligotrophic Acidobacteria groups were more abundant on the plant residue from the samples with small pores. This study provides the first experimental evidence that characteristics of soil pores and their air/water flow status determine the phylogenetic composition of the local microbial community and directions and magnitudes of soil C decomposition processes.

Uncertainty evaluation of coliform bacteria removal from vegetated filter strip under overland flow condition.

Vegetated filter strips (VFS) have become an important component of water quality improvement by reducing sediment and nutrients transport to surface water. This management practice is also beneficial for controlling manure-borne pathogen transport to surface water. The objective of this work was to assess the VFS efficiency and evaluate the uncertainty in predicting the microbial pollutant removal from overland flow in VFS. We used the kinematic wave overland flow model as implemented in KINEROS2 coupled with the convective-dispersive overland transport model which accounts for the reversible attachment-detachment and surface straining of infiltrating bacteria. The model was successfully calibrated with experimental data obtained from a series of simulated rainfall experiments at vegetated and bare sandy loam and clay loam plots, where fecal coliforms were released from manure slurry applied on the top of the plots. The calibrated model was then used to assess the sensitivity of the VFS efficiency to the model parameters, rainfall duration, and intensity for a case study with a 6-m VFS placed at the edge of 200-m long field. The Monte Carlo simulations were also performed to evaluate the uncertainty associated with the VFS efficiency given the uncertainty in the model parameters and key inputs. The VFS efficiency was found to be <95% in 25%, <75% in 23%, and <25% in 20% of cases. Relatively long high-intensity rainfalls, low hydraulic conductivities, low net capillary drives of soil, and high soil moisture contents before rainfalls caused the partial failure of VFS to retain coliforms from the infiltration excess runoff.

Protection of soil carbon within macro-aggregates depends on intra-aggregate pore characteristics.

Soil contains almost twice as much carbon (C) as the atmosphere and 5–15% of soil C is stored in a form of particulate organic matter (POM). Particulate organic matter C is regarded as one of the most labile components of the soil C, such that can be easily lost under right environmental settings. Conceptually, micro-environmental conditions are understood to be responsible for protection of soil C. However, quantitative knowledge of the specific mechanisms driving micro-environmental effects is still lacking. Here we combined CO2 respiration measurements of intact soil samples with X-ray computed micro-tomography imaging and investigated how micro-environmental conditions, represented by soil pores, influence decomposition of POM. We found that atmosphere-connected soil pores influenced soil C’s, and especially POM’s, decomposition. In presence of such pores losses in POM were 3–15 times higher than in their absence. Moreover, we demonstrated the presence of a feed-forward relationship between soil C decomposition and pore connections that enhance it. Since soil hydrology and soil pores are likely to be affected by future climate changes, our findings indicate that not-accounting for the influence of soil pores can add another sizable source of uncertainty to estimates of future soil C losses.

Modeling transport of Escherichia coli in a creek during and after artificial high-flow events: Three-year study and analysis

Escherichia coli is the leading indicator of microbial contamination of natural waters, and so its in-stream fate and transport needs to be understood to eventually minimize surface water contamination by microorganisms. To better understand mechanisms of E. coli release and transport from soil sediment in a creek the artificial high-water flow events were created by releasing 60-80 m(3) of city water on a tarp-covered stream bank in four equal allotments in July 2008, 2009 and 2010. A conservative tracer difluorobenzoic acid (DFBA) was added to the released water in 2009 and 2010. Water flow rate, E. coli and DFBA concentrations as well as water turbidity were monitored with automated samplers at three in-stream weirs. A one-dimensional model was applied to simulate water flow, and E. coli and DFBA transport during these experiments. The Saint-Venant equations were used to calculate water depth and discharge while a stream solute transport model accounted for release of bacteria by shear stress from bottom sediments, advection-dispersion, and exchange with transient storage (TS). Reach-specific model parameters were estimated by evaluating observed time series of flow rates and concentrations of DFBA and E. coli at all three weir stations. Observed DFBA and E. coli breakthrough curves (BTC) exhibited long tails after the water pulse and tracer peaks had passed indicating that transient storage (TS) might be an important element of the in-stream transport process. Comparison of simulated and measured E. coli concentrations indicated that significant release of E. coli continued when water flow returned to the base level after the water pulse passed and bottom shear stress was small. The mechanism of bacteria continuing release from sediment could be the erosive boundary layer exchange enhanced by changes in biofilm properties by erosion and sloughing detachment.

Effect of biofilm in irrigation pipes on microbial quality of irrigation water

Aims:  The focus of this work was to investigate the contribution of native Escherichia coli to the microbial quality of irrigation water and to determine the potential for contamination by E. coli associated with heterotrophic biofilms in pipe‐based irrigation water delivery systems.

Effect of soil aggregate size distribution on water retention

&NA; Quantitative information on soil water retention is in demand in hydrology, agrometeorology, agronomy, contaminant transport, and other soil‐related disciplines of earth and environmental sciences. Soil aggregate composition is an important characteristic of soil structure and, as such, is expected to affect soil water retention. Our objective was to determine whether and how aggregate size distributions affect soil water retention from saturation to the wilting point. Soil properties were studied for samples of Podzoluvisols, Planosols, Chernozems, Fluvisols, Calcisols, and Gleysols. Cumulative particle size and aggregate size distributions were used in regression trees to determine what fractions provide the least heterogeneous groups of samples as determined from values of water retention at matric potentials of −10, −33, and −1500 kPa as well as from van Genuchten parameters of the water retention curves, all on a gravimetric basis. Soil aggregate composition provided important grouping parameters for almost all water retention characteristics in this work. Contents of either small aggregates (<0.25 mm, <0.5 mm, <1 mm) or large aggregates (>7 mm, >10 mm) were the grouping variables in most cases for parameters of the van Genuchten equation. No aggregate size distribution parameters were included in the regression tree for the water content at −10 kPa, whereas contents of aggregates of medium sizes do affect water content at −33 and −1500 kPa. Aggregate size distribution parameters can be useful in estimating parameters of soil water retention from other soil properties. (Soil Science 2003;168:223‐233)

Loss of bioactive phosphorus and enteric bacteria in runoff from dairy manure applied to sod

Information on the concurrent release and interactions between manure-borne phosphorus (P) and enteric bacteria to runoff from a live or dead grass sod is limited. A study of simulated runoff and an enzyme-based fractionation of runoff P forms from dairy manure applied on grass-covered soil in runoff boxes was conducted to compare the detachment and potential edge-of-field movement of manure P, Escherichia coli, and enterococci in runoff. Concentrations and mass loads of bioactive P forms and bacteria in runoff were log-normally distributed over time during all simulations. Although P and enteric bacteria were simultaneously released to runoff, high correlations were found predominantly between water turbidity, concentrations of bacteria, and phosphohydrolase-labile P, a fraction associated with particulate manure. Delayed bacteria and particulate P concentrations and mass loads indicated live leaf and bacterial surface interactions that impeded their release to runoff. Resultant deviations in linearity between manure water-extractable P and bacteria distributions and the significant correlation between bacteria and the phosphohydrolase-labile P fraction suggested that manure-borne E. coli were released in association with manure particulates that contained organic P. The state of the grass cover determined the asymmetry of bacteria and bioactive P distributions. Given the micrometer size range of suspended particles, losses of colloidal particulate P and colloid-associated bacteria may extend well beyond the immediate vicinity of the deposited manure.