Raghupathy Karthikeyan

Potential for Plant-Based Remediation of Pesticide-Contaminated Soil and Water using Nontarget Plants such as Trees, Shrubs, and Grasses

Appropriate environmental management of pesticides includes their proper application, use of filter strips and riparian buffers to contain pesticides in runoff from fields, prompt cleanup of spills, and treatment processes for wastewater associated with manufacturing and equipment usage. Plants have beneficial effects in the management of pesticide-contaminated soil and water, including direct metabolism of many pesticides, stimulation of microbial activity in the root zone, extraction of contaminated water, and reduction of infiltrating contaminated water. In this work, we review the literature on nontarget plants that can grow in pesticide-contaminated soil and water, and the fate of pesticides in filter strips, riparian buffers, and vegetated remediation environments. Past research indicates that there are significant differences in the tolerance of plants to pesticides present in soil and water, and that some plants are more effective than others in the remediation of pesticide-contaminated soil and water. Thus, there is value in the identification of tolerant plants and favorable plant-based remediation technologies for management of pesticides and contaminated sites.

Spatially Explicit Load Enrichment Calculation Tool to Identify Potential E. coli Sources in Watersheds

In 2006, bacterial pathogens were the leading cause of water quality concerns in the U.S. With more than 300 water bodies in the state of Texas failing to meet water quality standards because of bacteria, managing bacteria pollution commanded the attention of regulatory agencies, researchers, and stakeholders across Texas. In order to assess, monitor, and manage water quality, it was necessary to characterize the sources of pathogens within the watershed. The objective of this study was to develop a spatially explicit method to estimate potential E. coli loads in Plum Creek watershed in east central Texas. Locations of contributing non-point and point sources in the watershed were defined using Geographic Information Systems (GIS). By distributing livestock, wildlife, wastewater treatment plants, septic systems, and pet sources, the bacterial load in the watershed was spatially characterized. Contributions from each source were quantified by applying source specific bacterial production rates, and ranking of each contributing source was assessed for the entire watershed. Cluster and discriminant analyses were used to identify similar regions within the watershed for selecting appropriate best management practices. Based on the statistical analysis and the spatially explicit method, four clusters of subwatersheds were found and characterized. The analysis provided a basis for development of spatially explicit identification of best management practices (BMPs) to be applied within the Watershed Protection Plan (WPP).

Characterization of tetracycline-resistant bacteria in an urbanizing subtropical watershed

The objective of this study was to determine whether varying levels of urbanization influence the dominant bacterial species of mildly resistant (0·03 mmol l−1 tetracycline) and highly resistant (0·06 mmol l−1 tetracycline) bacteria in sediment and water. Also, the level of urbanization was further evaluated to determine whether the diversity of tetracycline resistance genes present in the isolates and the capability of transferring their resistance were influenced.

Effects of ultraviolet light disinfection on tetracycline-resistant bacteria in wastewater effluents.

The ubiquitous use of antibiotics has led to an increasing number of antibiotic-resistant bacterial strains, including strains that are multidrug-resistant, pathogenic, or both. There is also evidence to suggest that antibiotic resistance genes (ARGs) spread to the environment, humans, and animals through wastewater effluents. The overall objective of this study was to investigate the effect of ultraviolet (UV) light disinfection on antibiotic-resistant bacteria. Wastewater effluent samples from a wastewater treatment plant (WWTP) in Texas were evaluated for differences in tetracycline-resistant bacteria before and after UV treatment. The effects of photoreactivation or dark repair on the reactivation of bacteria present in WWTP effluent after UV disinfection were also examined. Culture-based methods were used to characterize viable heterotrophic, tetracycline-resistant heterotrophic, Escherichia coli, and tetracycline-resistant E. coli bacteria present before and after UV treatment. UV disinfection was found to be as effective at reducing concentrations of resistant heterotrophs and E. coli, as it was at reducing total bacterial concentrations. The lowest survival ratio following UV disinfection was observed in tetracycline-resistant E. coli showing particular susceptibility to UV treatment. Photoreactivation and dark repair rates were found to be comparable to each other for all bacterial populations.

Glacier mass balance simulation using SWAT distributed snow algorithm

ABSTRACT Application of a temperature-index melt model incorporated into the Soil and Water Assessment Tool (SWAT) is presented to simulate mass balance (MB) and equilibrium line altitude (ELA) of three glaciers. The snow accumulation/melt parameters were adjusted to glacierized and free glacier areas, respectively. The SWAT snow algorithm enabled us to consider spatial variation of snow parameters by elevation bands across the sub-basins, while in the previous studies using SWAT, the related parameters were constant for an entire basin. The results show slight improvement in runoff simulation and significant improvement in simulated MB when considering ELA in model calibration. The results showed that SWAT can be applied to simulate MB, vertical MB distribution and annual ELA, with light calibration efforts for data-scarce catchments. The accuracy of the results depends on the modelled area of ablation zone from which most of the meltwater is released.

Spatial and temporal variability of temperature, precipitation, and streamflow in upper Sang-kan basin, China

Temporal streamflow variability in an inland hydrologic station and temporal trends and frequency changes at three weather stations in a semiarid river basin located in Loess Plateau, China, were detected by using linear regression, Mann–Kendall analysis, and wavelet transform methods. Double cumulative curve and ordered clustering were used to identify the hydrological periods of upper Sang-kan (USK) basin between 1957 and 2012. The results indicate that (1) precipitation in the USK basin over the study period did not show any trend, while the temperature showed a significant increase; (2) streamflow flowing out of the USK basin indicated a significant decrease; (3) two distinct hydrological periods – the ‘natural period’ from 1957 to 1984 and the ‘human impact period’ from 1985 to 2012 – were present; and (4) the contributions of climate change and human activities to reduce the streamflow were 36.9% and 63.1% respectively. The results indicate that human activities may be contributing to a decrease in streamflow in the USK basin. Copyright

Effectiveness of ultrasound, UV-C, and photocatalysis on inactivation kinetics of Aeromonas hydrophila

In this study, bactericidal effects of 24 kHz ultrasound, ultraviolet (UV-C) irradiation, and titanium dioxide (TiO2) photocatalyst were studied on inactivation of Aeromonas hydrophila, an emerging pathogen listed on the US Environmental Protection Agencys (US EPA) candidate contaminant list. Metabolic activity (using the AlamarBlue dye) assays were performed to assess the residual activity of the microbial cells after the disinfection treatments along with culture-based methods. A faster inactivation rate of 1.52 log min−1 and inactivation of 7.62 log10 was observed within 5 min of ultrasound exposure. Ultrasound treated cells repaired by 1.4 log10 in contrast to 5.3 log10 repair for UV-C treated cells. Ultrasound treatment significantly lowered the reactivation of Aeromonas hydrophila in comparison to UV-C- and UV-C-induced photocatalysis. Ultrasound appeared to be an effective means of inactivating Aeromonas hydrophila and could be used as a potential disinfection method for water and wastewater reuse.

Biological manganese oxidation by Pseudomonas putida in trickling filters.

ABSTRACT Biological oxidation has been researched as a viable alternative for treating waters with high manganese (Mn) concentrations, typically found in mine drainage or in some geological formations. In this study, laboratory-scale trickling filters were constructed to compare the Mn removal efficiency between filters inoculated with the Mn oxidizing bacteria, Pseudomonas putida, and filters without inoculation. Manganese oxidation and removal was found to be significantly greater in trickling filters with Pseudomonas putida after startup times of only 48 h. Mn oxidation in Pseudomonas putida inoculated trickling filters was up to 75% greater than non-inoculated filters. One-dimensional advective-dispersive models were formulated to describe the transport of Mn in trickling filter porous media. Based on the experimental transport parameters obtained, the model predicted that a filter depth of only 16 cm is needed to reduce influent concentration of 10 mg L−1 to 0.05 mg L−1.

Role of free-ranging mammals in the deposition of Escherichia coli into a Texas floodplain

Abstract Context. The role of wildlife in faecal pollution of water bodies (deposition of Escherichia coli (E. coli)) is not well understood. Current water-quality and land-use planning research largely relies on unreliable wildlife data (e.g. poor sourcing of abundance estimates, population density estimates applied to multiple fundamentally different areas, suspect or insufficiently described data collection techniques) Aims. Our goal for the present research was to investigate deposition of E. coli into a floodplain by free-ranging mammals. Objectives of the research were to determine the density of important free-ranging meso- and large mammals in the study area, determine faecal E. coli loads for each species, and evaluate spatial data on species-specific faecal deposition. Methods. We conducted our research in south-eastern Texas, USA, on two cattle ranches bisected by Cedar Creek (44-km long). Cedar Creek has elevated E. coli concentrations. We conducted mark–recapture and mark–resight population density estimates (2008/09) for meso- and large mammals in the study areas. We collected faecal samples from all captured wildlife. We also conducted transects through the study area to determine faecal-deposition patterns. Key results. We found that raccoons (Procyon lotor), wild pigs (Sus scrofa), Virginia opossums (Didelphis virginiana) and white-tailed deer (Odocoileus virginianus) all had substantial faecal E. coli loads and population densities, thus implying an important role in E. coli deposition into the study floodplain. All species were widely distributed through the floodplain. Conclusions. Free-ranging mammals contribute E. coli to floodplains and potentially affect water quality. We determined that four species commonly found in floodplains throughout North America all contributed E. coli to the study floodplain, thus implying mammal E. coli contributions in many locations and this is potentially important for E. coli management. Implications. Improved locally specific mammal population estimates and estimates of locally derived E. coli concentration will improve floodplain and water-quality models that often depend on data of various quality. Additionally, our analyses demonstrated the need for continued research into the role of wildlife in E. coli deposition.

Concentration as a Function of Stream Order and Watershed Size

This research examines the relationship of concentrations to stream order and watershed size and considers the implications on water quality standards. To assess geospatial effects, data were obtained from 743 monitoring stations in the Central Great Plains, Cross Timbers, and South Central Plains ecoregions of Texas and Oklahoma. Median and geometric mean concentrations were analyzed for correlation with stream order and watershed size at each site. Comparison of the three ecoregions revealed concentrations were highest in the westernmost Central Great Plains and lowest in the easternmost South Central Plains. Similarly, the strength of s correlation with stream order and watershed area decreased with ecoregion moving west to east. Thus, incorporating ecoregion approaches when defining stream water quality standards is supported. Analysis showed no significant relationship of stream order or watershed size to concentrations in least-impacted watersheds (i.e., watersheds with minimal wastewater discharge and urbanization). Conversely, analysis of data from all sites showed a weak negative relationship between concentration and stream order and watershed size, with concentration generally decreasing with increasing stream order and watershed size. However, variability in smaller watersheds and lower-order streams supports continued use of site-specific studies to determine appropriate standards. Three-parameter exponential models provided an approach to estimate concentrations using Shreve stream order and watershed area and identify outlier streams potentially affected by anthropogenic activities where further investigation or remediation may be warranted.