Papers by Yakov Pachepsky
Frontiers in water, Nov 1, 2021
<p>Escherichia coli is the most commonly assessed indicator of fecal contam... more <p>Escherichia coli is the most commonly assessed indicator of fecal contamination. The presence of elevated levels of E. coli is used to evaluate the microbial water quality in recreational and irrigation water sources.  E. coli concentrations are spatially and temporally variable. Monitoring of the variability inherent in water measurements can help create and implement effective monitoring designs and solutions. The objective of this work is to determine if there exist spatial patterns that are stable in time over years of observations. Two irrigation ponds in Maryland USA were monitored for three years during the growing seasons (June to August). Water samples and in situ measurements were collected in the same 47 locations biweekly for three years. The presence of stable spatial patterns was researched for relative differences between the logarithm of concentrations in specific locations and the average logarithm across the pond for each of observation times. The mean of these relative differences (MRD) over the observation period formed consistent spatial patterns. We found stable patterns of locations across the pond and found higher MRD values near the banks than the pond interiors.  MRDs computed for separate years were more variable and had amplitudes different from the overall average MRD over the three years, although the similarities between patterns across years was apparent. </p>
Water Research, 2021
Both algae and bacteria are essential inhabitants of surface waters. Their presence is of ecologi... more Both algae and bacteria are essential inhabitants of surface waters. Their presence is of ecological significance and sometimes of public health concern triggering various control actions. Interactions of microalgae, macroalgae, submerged aquatic vegetation, and bacteria appear to be important phenomena necessitating a deeper understanding by those involved in research and management of microbial water quality. Given the long-standing reliance on Escherichia coli as an indicator of the potential presence of pathogens in natural waters, understanding its biology in aquatic systems is necessary. The major effects of algae and aquatic vegetation on E. coli growth and survival, including changes in the nutrient supply, modification of water properties and constituents, impact on sunlight radiation penetration, survival as related to substrate attachment, algal mediation of secondary habitats, and survival inhibition due to the release of toxic substances and antibiotics, are discussed in this review. An examination of horizontal gene transfer and antibiotic resistance potential, strain-specific interactions, effects on the microbial, microalgae, and grazer community structure, and hydrodynamic controls is given. Outlooks due to existing and expected consequences of climate change and advances in observation technologies via high-resolution satellite imaging, unmanned aerial vehicles (drones), and mathematical modeling are additionally covered. The multiplicity of interactions among bacteria, algae, and aquatic vegetation as well as multifaceted impacts of these interactions, create a wide spectrum of research opportunities and technology developments.
Microbial water quality monitoring is an essential component of food safety. E. coli bacterium is... more Microbial water quality monitoring is an essential component of food safety. E. coli bacterium is the major indicator organism used in assessing microbial water quality but dense sampling of water to assess spatial variability is impractical. The objective of this work was to test the hypothesis that sUAS imaging can provide information about the differences in E. coli habitats across two Maryland irrigation ponds and guide water sampling. We used modified GoPro cameras and a MicaSense RedEdge camera in flights shortly before sampling. Ponds P1 (0.37ha) and P2 (0.48ha) were sampled from a boat in the same locations, biweekly, during the 2018 growing season. Average concentrations of E. coli were 0.60±0.04 and 1.04±0.04 (mean ± st. error, log CFU/100 mL) in P1 and P2, respectively. The random forest (RF) machine learning algorithm was applied to relate ground sampling data with co-located image sections. The sensitivity of results to parameters of the RF algorithm was assessed with m...
Journal of environmental quality, 2018
Microbial contamination in beach water poses a public health threat due to waterborne diseases. T... more Microbial contamination in beach water poses a public health threat due to waterborne diseases. To reduce the risk of exposure to fecal contamination, informing beachgoers in advance about the microbial water quality is important. Currently, determining the level of fecal contamination takes 24 h. The objective of this study is to predict the current level of fecal contamination (enterococcus [ENT] and ) using readily available environmental variables. Artificial neural network (ANN) and support vector regression (SVR) models were constructed using data from the Haeundae and Gwangalli Beaches in Busan City. The input variables included the tidal level, air and water temperature, solar radiation, wind direction and velocity, precipitation, discharge from the wastewater treatment plant, and suspended solid concentration in beach water. The dependence of fecal contamination on the input variables was statistically evaluated; precipitation, discharge from the wastewater treatment plant,...
Journal of Environmental Management, 2017
Limited information exists on the unhindered release of bioactive phosphorus (P) from a manure la... more Limited information exists on the unhindered release of bioactive phosphorus (P) from a manure layer to model the partitioning and transport of component P forms before they reach an underlying soil. Rain simulations were conducted to quantify effects of intensity (30, 60, and 90 mm h À1) on P release from an application of 60 Mg ha À1 of dairy manure. Runoff contained water-extractable-(WEP), exchangeable and enzyme-labile bioactive P (TBIOP), in contrast to the operationally defined "dissolved-reactive P" form. The released P concentrations and flow-weighed mass loads were described by the log-normal probability density function. At a reference condition of 30 mm h À1 and maintaining the surface at a 5% incline, runoff was minimal, and WEP accounted for 20.9% of leached total P (TP) concentrations, with an additional 25e30% as exchangeable and enzyme-labile bioactive P over the 1-h simulation. On a 20% incline, increased intensity accelerated occurrence of concentration max and shifted the skewed P concentration distribution more to the left. Differences in trends of WEP, TBIOP, or net enzyme-labile P (PHP o) cumulative mass released per unit mass of manure between intensities were attributable to the higher frequency of raindrops striking the manure layer, thus increasing detachment and load of colloidal PHP o of the water phases. Thus, detailed knowledge of manure physical characteristics, bioactive P distribution in relation to rain intensity, and attainment of steady-state of water fluxes were critical factors in improved prediction of partitioning and movement of manure-borne P under rainfall.
Journal of Environmental Quality, 2016
Understanding pathogenic and indicator bacteria survival in soils is essential for assessing the ... more Understanding pathogenic and indicator bacteria survival in soils is essential for assessing the potential of microbial contamination of water and produce. The objective of this work was to evaluate the effects of soil properties, animal source, experimental conditions, and the application method on temperature dependencies of manure-borne generic , O157:H7, and fecal coliforms survival in soils. A literature search yielded 151 survival datasets from 70 publications. Either one-stage or two-stage kinetics was observed in the survival datasets. We used duration and rate of the logarithm of concentration change as parameters of the first stage in the two-stage kinetics data. The second stage of the two-stage kinetics and the one-stage kinetics were simulated with the model to find the dependence of the inactivation rate on temperature. Classification and regression trees and linear regressions were applied to parameterize the kinetics. Presence or absence of two-stage kinetics was controlled by temperature, soil texture, soil water content, and for fine-textured soils by setting experiments in the field or in the laboratory. The duration of the first stage was predominantly affected by soil water content and temperature. In the model dependencies of inactivation rates on temperature, parameter estimates were significantly affected by the laboratory versus field conditions and by the application method, whereas inactivation rates at 20°C were significantly affected by all survival and management factors. Results of this work can provide estimates of coliform survival parameters for models of microbial water quality.
Journal of Environmental Quality, 2015
Microbial pathogens present a leading cause of impairment to rivers, bays, and estuaries in the U... more Microbial pathogens present a leading cause of impairment to rivers, bays, and estuaries in the United States, and agriculture is often viewed as the major contributor to such contamination. Microbial indicators and pathogens are released from landapplied animal manure during precipitation and irrigation events and are carried in overland and subsurface flow that can reach and contaminate surface waters and ground water used for human recreation and food production. Simulating the release and removal of manure-borne pathogens and indicator microorganisms is an essential component of microbial fate and transport modeling regarding food safety and water quality. Although microbial release controls the quantities of available pathogens and indicators that move toward human exposure, a literature review on this topic is lacking. This critical review on microbial release and subsequent removal from manure and animal waste application areas includes sections on microbial release processes and release-affecting factors, such as differences in the release of microbial species or groups; bacterial attachment in turbid suspensions; animal source; animal waste composition; waste aging; manure application method; manure treatment effect; rainfall intensity, duration, and energy; rainfall recurrence; dissolved salts and temperature; vegetation and soil; and spatial and temporal scale. Differences in microbial release from liquid and solid manures are illustrated, and the influential processes are discussed. Models used for simulating release and removal and current knowledge gaps are presented, and avenues for future research are suggested.
Journal of Hydrology, 2010
Environmental models typically require a complete time series of meteorological inputs, thus reco... more Environmental models typically require a complete time series of meteorological inputs, thus reconstructing missing data is a key issue in the functionality of such physical models. The objective of this work was to develop a new technique to reconstruct missing daily precipitation data in the central part of Chesapeake Bay Watershed using a two-step reconstruction method (RT + ANN) that employed artificial neural networks (ANN) with inputs only from stations that were found to be influential in bootstrap applications of regression trees (RT). The predictive performance of RT + ANN was also compared with those of stand-alone RT and ANN methods. In addition to statistical comparisons of the reconstructed precipitation time series, these resulting data in the Soil and Water Assessment Tool (SWAT) watershed model were used to perform an error propagation analysis in streamflow simulations. The RT provided a transparent visual representation of the similarity between the stations in their daily precipitation time series. Seven years of data from 39 weather stations showed that both RT and ANN provided the reconstruction accuracy comparable to (or better than) published earlier results of precipitation reconstruction. The RT + ANN method significantly improved accuracy and was more robust when compared to RT or ANN methods. This method also provided more accurate and robust SWAT streamflow predictions with reconstructed precipitation.
International Journal of Environment and Pollution, 2011
... coli O157:H12 die-off in submerged sediment, and (b) that E. coli O157:H12was able ... Mechan... more ... coli O157:H12 die-off in submerged sediment, and (b) that E. coli O157:H12was able ... Mechanisms of adaptation of E. coli to the freshwater sediment environments need to be established ... Banning, N., Toze, S. and Mee, B. (2003) 'Persistence of biofilm-associated Escherichia coli ...
International Journal of Remote Sensing, 2009
This paper presents an overview of the state of the National Oceanic and Atmospheric Administrati... more This paper presents an overview of the state of the National Oceanic and Atmospheric Administration (NOAA) satellite ozone programme including assessments of the current Solar Backscatter Ultraviolet (SBUV/2) and the future Ozone Mapping and Profiler Suite (OMPS) instruments and products. It provides evaluation of the quality of the NOAA Polar-orbiting Operational Satellites (POES) SBUV/2 measurements and the Version 8 algorithm
Simulations of soil water flow are often carried out with parameters estimated using pedotransfer... more Simulations of soil water flow are often carried out with parameters estimated using pedotransfer functions (PTFs), which are empirical relationships between the soil hydraulic properties and more easily obtainable basic soil properties available, for example, from soil surveys. The use of pedotransfer functions is necessary when the simulations have to be done for large-scale projects, or for pilot studies. Results of PTF applications are always uncertain, because the accuracy of pedotransfer functions outside of its development dataset is unknown. The use of several PTFs (multimodel ensemble prediction techniques) has been shown to be an efficient approach for estimating hydraulic properties within an uncertainty context. The computer program PTF calculator (CalcPTF) has been developed to estimate parameters of the Brooks and Corey and van Genuchten water retention equation to support the multimodeling approach. Seven PTFs estimate the Brooks and Corey parameters, four PTFs estimate the van Genuchten parameters, and five models fit the van Genuchten equation to pairs (capillary pressure, water content) estimated with PTFs. The PTF calculator also estimates the net capillary drive parameter of the three-parameter Parlange infiltration equation. The code is written in FORTRAN and is invoked from an Excel worksheet. Examples of input and output files are given. Disclaimer Although the code has been tested by its developers, no warranty, expressed or implied, is made as to the accuracy and functioning of the program modifications and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the developers in connection therewith.
Applied Microbiology
Irrigation waters may facilitate the spread of antibiotic-resistant bacteria or genes to humans a... more Irrigation waters may facilitate the spread of antibiotic-resistant bacteria or genes to humans and animals. Monitoring of resistance in irrigated waters has become common; however, many studies do not incorporate a spatial component into sampling designs. The objective of this work was to assess spatiotemporal variations in tetracycline-resistant E. coli in an irrigation pond. Water samples were collected at 10 locations and two different water depths, and in situ and laboratory water quality measurements were performed. The percentage of E. coli resistant to the low (4 μg mL−1) and high (16 μg mL−1) tetracycline doses varied by date and location but were observed to be as high as 12.7% and 6.3% of the total population throughout the study, respectively. While significant differences were not observed between resistance levels measured at different depths, on one date resistant E. coli were only detected in samples collected at depth. Nitrate, fluorescent dissolved organic matter, ...
Journal of Food Protection
Proceedings of the Korea Water Resources Association Conference, 2017
Water, Air, & Soil Pollution, 2021
Small to medium irrigation ponds provide substantial quantities of water for irrigation in the Mi... more Small to medium irrigation ponds provide substantial quantities of water for irrigation in the Mid-Atlantic region of the U.S. The concentrations of the fecal indicator organism Escherichia coli (E. coli) are used to evaluate the microbial water quality of irrigation sources. Little is known about the spatiotemporal variability of E. coli concentrations in pond water and the possible effects on monitoring and management of the microbial quality of irrigation water from these ponds. The objective of this work was to test the hypotheses that (a) spatial patterns of E. coli concentrations exist that are preserved both intra- and interannually, and (b) persistent spatial patterns in water quality parameters exist and correlate with persistent patterns of E. coli concentrations. Sampling was conducted fortnightly during the summer months in 2016 to 2018 and consisted of taking water quality measurements at 23 and 34 locations in ponds P1 and P2, respectively. Interannual variability of E. coli was observed in both ponds as was substantial spatial variability of E. coli concentrations within each year. The mean relative difference (MRD) analysis was used to identify temporally stable patterns of E. coli concentrations within the ponds. These patterns found for individual years showed significant positive correlations with each other and with the overall pattern derived from the 3-year dataset. Correlation coefficients of patterns varied from 0.487 to 0.842 in P1 and from 0.467 to 0.789 in P2 (p < 0.05). MRD patterns of water quality parameters and of E. coli concentrations were also significantly correlated. Within the 3-year dataset, the highest positive correlations were observed for chlorophyll-a and turbidity while the dissolved oxygen concentrations demonstrated the greatest negative correlations. Results of the present study emphasize the advisability and feasibility of finding temporally stable spatial patterns in microbial water quality within irrigation ponds.
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Papers by Yakov Pachepsky