Videos by Yakov Pachepsky
Drones to help in microbial water quality monitoring
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Papers by Yakov Pachepsky
Frontiers in Water, 2021
Phytoplankton functional groups and their influence on water quality have been studied in various... more Phytoplankton functional groups and their influence on water quality have been studied in various types of water bodies but have yet to be studied in agricultural irrigation ponds. Freshwater sources (e.g., lakes, rivers, and reservoirs) have been previously shown to exhibit high spatial and temporal variability in phytoplankton populations. Improvements in the monitoring of phytoplankton populations may be achieved if patterns of stable spatial variability can be found in the phytoplankton populations through time. The objective of this work was to determine if temporally stable spatial patterns in phytoplankton communities could be detected in agricultural irrigation ponds using a functional group approach. The study was performed at two working agricultural irrigation ponds located in Maryland, USA over two summer sampling campaigns in 2017 and 2018. Concentrations of four phytoplankton groups, along with sensor-based and fluorometer based water quality parameters were measured. ...
Temporal stability of E. coli concentration patterns in two irrigation ponds in Maryland
EGUGA, Apr 1, 2017
Editorial for the special issue on “Advances in soil scaling: Theories, techniques and applications”
European Journal of Soil Science, Mar 1, 2021
Scale is an essential concept in the description of soils. The bulk of empirical information on s... more Scale is an essential concept in the description of soils. The bulk of empirical information on soils is obtained at fine scales, whereas assessment of environmental trends and scenarios requires information and decisions at much larger scales. The quest to discover how soil information can be linked across scales is an important focal point of soil science. Relating soil properties and processes at different scales has been the focus of the series of PEDOFRACT conferences organized by the Group of Fractal Studies at the Technical School of Agronomic, Food and Biosystem Engineering at the Universidad Politécnica de Madrid (UPM). The PEDOFRACT IX conference took place in Barco de Avila, Spain, in July 2019. Scientists from 15 countries participated. The conference theme was “Advances in soil scaling: theories, techniques, and applications”. This special issue of EJSS presents selected contributions to the meeting programme and related work. The conference encompassed research at various hierarchical scales, including pore, aggregate, horizon, pedon and coarser scales. Within these hierarchical scales, researchers varied the measurement scale (i.e., size of the support, the distance between measurement locations, and the total extent of the measurement domain). Some works addressed the classical question of whether there exist dependencies of soil properties on scale that are valid within a range of scales, and if they exist, whether coefficients in those dependencies can be related to soil genesis and management. Other authors were more interested in observing and interpreting differences in the manifestation of soil processes, appearing as scale changes. Research at the pore and aggregate scale mostly addressed the characterization of soil structure. The classical approach relies on 2D soil imaging and the use of the multifractal model. The latter model assumes that the statistical moments of the measurement follow the power-law dependence on the measurement scale. A comprehensive summary of the multifractal modelling is presented by Perrier, Baveye, and Garnier (2020), who applied it to the two-dimensional image of a soil thin section. The authors concluded that this model is applicable in a range of scales but creates artifacts if applied outside of this range. The onset of X-ray computer tomography (X-ray CT) provided new opportunities for quantifying scale dependencies of soil properties in three dimensions. Gerke and Karsanina (2020) observed substantial differences in scaling when the scale was defined in terms of the support size or the spacing size. These authors imaged samples from Ah and B horizons of the Haplic Greyzems. They computed porosities and simulated flow in the complex pore space for a set of progressively increasing subsamples of their original samples. They observed the emergence of the representative elementary volume (REV). The increase of the subsample size beyond REV did not lead to a significant change in saturated hydraulic conductivity of porosity. The authors also defined correlation functions that showed the features of the pore space as functions of spacing. As they changed the subsample size, they discovered that correlation functions depended on scale and continued to change beyond the representative elementary volume scale threshold. Somewhat similar differences in the scale dependence of structural metrics were observed by Lucas, Vetterlein, Vogel, and Schlüter (2020). They used data from X-ray CT imaging of samples of three distinctly different sizes to observe the scaling behaviour of two pore connectivity metrics: the Euler number and gamma indicator. The former reflects the degree of pore connectivity irrespective of how far the connections are, whereas the latter is sensitive to long-range connectivity. The increase in the sample size did not affect the Euler number but critically modified the long-range connectivity because the larger samples had long pores created by root systems and tillage. Segmentation of images (i.e., separation of pore space from solids) has been and remains a necessary preprocessing operation before any study of scale dependencies at the pore or aggregate scale. This operation with X-ray CT imagery can lead to additional uncertainty, especially if parts of the pore space are filled with loose organic material (Gerke & Karsanina, 2020) or include incompletely saturated pores (Guber, Kutlu, Rivers, & Kravchenko, 2020). The latter authors proposed an elegant solution for the segmentation problem based on saturating the soil sample with a salt solution that Received: 6 October 2020 Accepted: 7 October 2020
EGU General Assembly Conference Abstracts, Apr 1, 2018
Journal of Hydrology, 1998
Fractal scaling laws of water transport were found for soils. A water transport model is needed t... more Fractal scaling laws of water transport were found for soils. A water transport model is needed to describe this type of transport in soils. We have developed a water transport equation using the physical model of percolation clusters, employing the mass conservation law, and assuming that hydraulic conductivity is a product of a local component dependent on water content and a scaling component depending on the distance traveled. The model predicts scaling of water contents with a variable x/t v(2dJ) wherefl deviates from the zero value characteristic for the Richards equation. A change in the apparent water diffusivity with the distance is predicted if the apparent diffusivity is calculated using the Richards equation. An equation for the time and space invariant soil water diffusivity is obtained. Published data sets of five authors were used to test the scaling properties predicted by the model. The value offl was significantly greater than zero in almost all data sets and typically was in the range from 0.05 to 0.5. This exponent was found from regression equations that had correlation coefficients from 0.97 to 0.995. In some cases a dependence offl on water content was found indicating changes in scaling as the water transport progressed.
Applied and Environmental Microbiology, May 15, 2007
Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particle... more 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.
Uncertainty in Climatology-Based Estimates of Shallow Groundwater Recharge
AGU Fall Meeting Abstracts, Dec 1, 2007
Assessing and Reducing Hydrogeologic Model Uncertainty
AGUSM, May 1, 2009
The accuracy-based model performance metrics not necessarily reflect the qualitative corresponden... more The accuracy-based model performance metrics not necessarily reflect the qualitative correspondence between simulated and measured streamflow time series. The objective of this work was to use the information theory-based metrics to see whether they can be used as complementary tool for hydrologic model evaluation and selection. We simulated 10-year streamflow time series in five watersheds located in Texas, North Carolina, Mississippi, and West Virginia. Eight model of different complexity were applied. The information theory based metrics were obtained after representing the time series as strings of symbols where different symbols corresponded to different quantiles of the probability distribution of streamflow. The symbol alphabet was used. Three metrics were computed for those strings -mean information gain that measures the randomness of the signal, effective measure complexity that characterizes predictability and fluctuation complexity that characterizes the presence of a pattern in the signal. The observed streamflow time series has smaller information content and larger complexity metrics than the precipitation time series. Watersheds served as information filters and and streamflow time series were less random and more complex than the ones of precipitation. This is reflected by the fact that the watershed acts as the information filter in the hydrologic conversion process from precipitation to streamflow. The Nash Sutcliffe efficiency metric increased as the complexity of models increased, but in many cases several model had this efficiency values not statistically significant from each other. In such cases, ranking models by the closeness of the information theory based parameters in simulated and measured streamflow time series can provide an additional criterion for the evaluation of hydrologic model performance. Hydrologic modeling plays the critical role in hydrologic response prediction for the applications such as water resources management activities, flood control, and water quality evaluation
Solid Earth, Feb 22, 2018
The soil texture representation with the standard textural fraction triplet "sand-silt-clay" is c... more The soil texture representation with the standard textural fraction triplet "sand-silt-clay" is commonly used to estimate soil properties. The objective of this work was to test the hypothesis that other fraction sizes in the triplets may provide a better representation of soil texture for estimating some soil parameters. We estimated the cumulative particle size distribution and bulk density from an entropy-based representation of the textural triplet with experimental data for 6240 soil samples. The results supported the hypothesis. For example, simulated distributions were not significantly different from the original ones in 25 and 85 % of cases when the sand-silt-clay and "very coarse+coarse + medium sand fine + very fine sand -silt+clay" were used, respectively. When the same standard and modified triplets were used to estimate the average bulk density, the coefficients of determination were 0.001 and 0.967, respectively. Overall, the textural triplet selection appears to be application and data specific.
Journal of Environmental Management, Mar 1, 2009
Manure and animal waste deposited on cropland and grazing lands serve as a source of microorganis... more Manure and animal waste deposited on cropland and grazing lands serve as a source of microorganisms, some of which may be pathogenic. These microorganisms are released along with particles of dissolved manure during rainfall events. Relatively little if anything is known about the amounts and sizes of manure particles released during rainfall, that subsequently may serve as carriers, abode, and nutritional source for microorganisms. The objective of this work was to obtain and present the first experimental data on sizes of bovine manure particles released to runoff during simulated rainfall and leached through soil during subsequent infiltration. Experiments were conducted using 200 cm long boxes containing turfgrass soil sod; the boxes were designed so that rates of manure dissolution and subsequent infiltration and runoff could be monitored independently. Dairy manure was applied on the upper portion of boxes. Simulated rainfall (ca. 32.4 mm h À1 ) was applied for 90 min on boxes with stands of either live or dead grass. Electrical conductivity, turbidity, and particle size distributions obtained from laser diffractometry were determined in manure runoff and soil leachate samples. Turbidity of leachates and manure runoff samples decreased exponentially. Turbidity of manure runoff samples was on average 20% less than turbidity of soil leachate samples. Turbidity of leachate samples from boxes with dead grass was on average 30% less than from boxes with live grass. Particle size distributions in manure runoff and leachate suspensions remained remarkably stable after 15 min of runoff initiation, although the turbidity continued to decrease. Particles had the median diameter of 3.8 mm, and 90% of particles were between 0.6 and 17.8 mm. The particle size distributions were not affected by the grass status. Because manure particles are known to affect transport and retention of microbial pathogens in soil, more information needs to be collected about the concurrent release of pathogens and manure particles during rainfall events.
Letters in Applied Microbiology, Jan 6, 2012
Aims: The focus of this work was to investigate the contribution of native Escherichia coli to th... more 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. Methods and Results: The aluminium pipes in the sprinkler irrigation system were outfitted with coupons that were extracted before each of the 2-h long irrigations carried out with weekly intervals. Water from the creek water and sprinklers, residual water from the previous irrigation and biofilms on the coupons were analysed for E. coli. High E. coli concentrations in water remaining in irrigation pipes between irrigation events were indicative of E. coli growth. In two of the four irrigations, the probability of the sample source, (creek vs sprinkler), being a noninfluential factor, was only 0AE14, that is, source was an important factor. The population of bacteria associated with the biofilm on pipe walls was estimated to be larger than that in water in pipes in the first three irrigation events and comparable to one in the fourth event. Conclusion: Biofilm-associated E. coli can affect microbial quality of irrigation water and, therefore, should not be neglected when estimating bacterial mass balances for irrigation systems. Significance and Impact of the Study: This work is the first peer-reviewed report on the impact of biofilms on microbial quality of irrigation waters. Flushing of the irrigation system may be a useful management practice to decrease the risk of microbial contamination of produce. Because microbial water quality can be substantially modified while water is transported in an irrigation system, it becomes imperative to monitor water quality at fields, rather than just at the intake. Letters in Applied Microbiology ISSN 0266-8254 ª No claim to US Government works Letters in Applied Microbiology 54, 217-224
Journal of Applied Microbiology, Oct 1, 2007
Aims: To compare survival of Escherichia coli and faecal coliforms (FC) in bovine faeces deposite... more Aims: To compare survival of Escherichia coli and faecal coliforms (FC) in bovine faeces deposited in a pasture or incubated in a controlled laboratory environment at temperatures within the same range. Methods and Results: Faecal samples from three cow herds were deposited as shaded and nonshaded cowpats in a field and incubated in a laboratory for one month at 21AE1, 26AE7 and 32AE2°C. Both FC and E. coli concentrations increased as much as 1AE5 orders of magnitude both in the field and in the laboratory during the 1st week and subsequently decreased. In shaded cowpats, the die-off of E. coli and FC was significantly slower, and the proportion of E. coli in FC was significantly larger as compared with nonshaded cowpats. The die-off was faster in the field than in the laboratory at similar temperatures. Conclusions: FC and E. coli die-off rates were substantially lower in laboratory conditions than in the field within the same range of temperatures. Significance and Impact of the Study: This study underscores the importance of field data on survival of manure-borne FC and E. coli, and indicates that laboratory die-off rates have to be corrected to be used for field condition simulations.
Is the Textural Classification Built on Sand
In 1967, the Committee of the Soil Science Society of America noted that the current system of pa... more In 1967, the Committee of the Soil Science Society of America noted that the current system of particle size boundaries arose due to geographic accident. The committee noted that there is "no narrowly defineable natural particle size boundaries that would be equally significant in all soil materials". Having three textural size ranges, i.e. sand, silt, and clay undoubtedly appears to be convenient for data presentation and textural class definition. However, it is not warranted that current sand, silt, and clay size ranges can provide the best representation of soil texture when these three size ranges are used for pedotransfer purposes. The objective of this work was to test the hypothesis that the cumulative particle size distribution and soil bulk density can be estimated more accurately if the boundaries of the sand, silt, and clay size ranges will be shifted. We used the entropy-based representation of particle size distributions to convert the three class particle size representation into particle size distributions and to define ranges of soil textural heterogeneity. Experimental data on seven size fraction contents and bulk density for 6300 predominantly coarse-texture soil samples were extracted from the USKSAT database. The predicted cumulative particle size distribution was not significantly different from the measured at 95% probability level in 25% of soils when the traditional sand, silt, and clay percentages were used for prediction, and in 85% of soils when very coarse, coarse, medium sand (fraction 1), fine and very fine sand (fraction 2) and clay and silt (fraction 3) were used. Similarly, the prediction of mean bulk density for the soils with different textural entropy resulted in the coefficient of determination of 0.001 when the traditional sand, silt, and clay percentages were used for prediction and in the coefficient of determination greater than 0.95 when very coarse, coarse, medium sand (fraction 1), fine and very fine sand (fraction 2) and clay and silt (fraction 3) were used. Overall, the textural size range selection may be more efficient in PTF develop
Model Abstraction to Assess Uncertainty in Flow and Transport Modeling
AGU Fall Meeting Abstracts, Dec 1, 2004
ABSTRACT
Simulation of E. coli release from streambed to water column during base flow periods
EGU General Assembly Conference Abstracts, Apr 1, 2017
Escherichia coli Release from Streambed to Water Column during Baseflow Periods: A Modeling Study
Journal of Environmental Quality, 2017
Streambed sediments can harbor large populations that are released into the water column during h... more Streambed sediments can harbor large populations that are released into the water column during high-flow events. Few studies have been conducted on the rates of transfer from streambed sediment to water column in low-flow conditions in natural streams. The aim of this work was to apply the watershed-scale model SWAT (Soil and Water Assessment Tool) to a natural stream to evaluate the need to account for the release from streambed sediments during baseflow periods and to compare the results of simulating such a release by assuming predominantly passive transport, driven by groundwater influx, against simulations assuming predominantly active transport of random or chemotaxis-driven bacteria movement. concentrations in water during baseflow periods were substantially underestimated when release from the streambed was attributed only to streambed sediment resuspension. When considered in addition to the release due to sediment resuspension at high flows, the active and passive release assumptions provided 42 and 4% improvement, respectively, in the RMSE of logarithms of concentrations. Estimated fluxes to water column during the baseflow periods from June to November ranged from 3.3 × 10 colony-forming units (CFU) m d in the game land area to 1.4 × 10 CFU m d in the mixed pasture and cropland. Results demonstrate that release of from streambed sediments during baseflow periods is substantial and that water column concentrations are dependent on not only land management practices but also on in-stream processes.
Geoderma, Oct 1, 2006
The accuracy-based performance measures may not suffice to discriminate among soil water flow mod... more The accuracy-based performance measures may not suffice to discriminate among soil water flow models. The objective of this work was to attempt using information theory measures to discriminate between different models for the same site. The Richards equation-based model HYDRUS-1D and a water budget-type model MWBUS were used to simulate one-year long observations of soil water contents and infiltration fluxes at various depths in a 1-m deep loamy Eutric Regosol in Bekkevoort, Belgium. We used the (a) metric entropy and (b) the mean information gain as information content measures, and (c) the effective measure complexity and (d) the fluctuation complexity as complexity measures. To compute the information content and complexity measures, time series of fluxes were encoded with the binary alphabet; fluxes greater (less) than the median value were encoded with one (zero). Fifty Monte Carlo simulation runs were performed with both models using hydraulic properties measured along a trench. The two models had the similar accuracy of water flux simulations. Precipitation input data demonstrated a moderate complexity and relatively high information content. Model outputs showed distinct differences in their relationships between complexity and information content. Overall, more complex simulated soil flux time series were obtained with the HYDRUS-1D model that was perceived to be conceptually more complex than the WMBUS model. An increase in the complexity of water flux time series occurred in parallel with the decrease in the information content. Using both complexity and information content measures allowed us to discriminate between the soil water models that gave the same accuracy of soil water flux estimates.
Journal of Environmental Quality, Nov 1, 2005
Attachment of bacteria to soil is an important component of bacteof the bacteria attachment to so... more Attachment of bacteria to soil is an important component of bacteof the bacteria attachment to soil. High clay content rial fate and transport. Escherichia coli are commonly used as indicain soil solid phase was reported to promote bacterial tors of fecal contamination in the environment. Despite the fact that E. coli are derived exclusively from feces or manure, effect of the adsorption to soil (Hagedorn et al., 1978; Bengtsson, presence of manure colloids on bacteria attachment to agricultural 1989). Jackson et al. (1994) studied the effect of sodium soils was never directly studied. The objective of this work was to dodecylbenzene sulfonate (DDBS) on Pseudomonas evaluate the magnitude of the effect of manure on E. coli attachment pseudoalcaligenes attachment to silty clay soil. Sodium to soil. Escherichia coli attachment to soil was studied in batch experidodecylbenzene sulfonate enhanced the negative charge ments with samples of loam and sandy clay loam topsoil that were associated with the surfactant bacterial complex, retaken in Pennsylvania and Maryland. Escherichia coli cells were sulting in decreased bacterial attachment to soil. Maradded to the water-manure suspensions containing 0, 20, and 40 g shall et al. (1971) studied reversible and irreversible L Ϫ1 of filtered liquid bovine manure, which subsequently were equilisorption of Achromobacter R8 onto glass surfaces in brated with air-dry sieved soil in different soil to suspension ratios. The the presence MgSO 4 and NaCl solutions of different Langmuir isotherm equation was fitted to data. Manure dramatically affected E. coli attachment to soil. Attachment isotherms were closer concentrations. The number of reversibly sorbed bacteto linear without manure and were strongly nonlinear in the presence ria increased with increasing electrolyte charge and conof manure. The maximum E. coli attachment occurred in the absence centration. of manure. Increasing manure content generally resulted in de-Organic compounds in soil solutions were shown to creased attachment.
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