Prem B. Parajuli

Source specific fecal bacteria modeling using soil and water assessment tool model

Fecal bacteria can contaminate water and result in illness or death. It is often difficult to accurately determine sources of fecal bacteria contamination, but bacteria source tracking can help identify non-point sources of fecal bacteria such as livestock, humans and wildlife. The Soil and Water Assessment Tool (SWAT) microbial sub-model 2005 was used to evaluate source-specific fecal bacteria using three years (2004-2006) of observed modified deterministic probability of bacteria source tracking data, as well as measure hydrologic and water quality data. This study modeled source-specific bacteria using a model previously calibrated for flow, sediment and total fecal coliform bacteria (FCB) concentration. The SWAT model was calibrated at the Rock Creek sub-watershed, validated at the Deer Creek sub-watershed, and verified at the Auburn sub-watershed and then at the entire Upper Wakarusa watershed for predicting daily flow, sediment, nutrients, total fecal bacteria, and source-specific fecal bacteria. Watershed characteristics for livestock, humans, and wildlife fecal bacterial sources were first modeled together then with three separate sources and combinations of source-specific FCB concentration: livestock and human, livestock and wildlife and human and wildlife. Model results indicated both coefficient of determination (R(2)) and Nash-Sutcliffe Efficiency Index (E) parameters ranging from 0.52 to 0.84 for daily flow and 0.50-0.87 for sediment (good to very good agreement); 0.14-0.85 for total phosphorus (poor to very good agreement); -3.55 to 0.79 for total nitrogen (unsatisfactory to very good agreement) and -2.2 to 0.52 for total fecal bacteria (unsatisfactory to good agreement). Model results generally determined decreased agreement for each single source of bacteria (R(2) and E range from -5.03 to 0.39), potentially due to bacteria source tracking (BST) uncertainty and spatial variability. This study contributes to new knowledge in bacteria modeling and will help further understanding of uncertainty that exists in source-specific bacteria modeling.

Characterization of shallow groundwater quality in the Lower St. Johns River Basin: a case study

Characterization of groundwater quality allows the evaluation of groundwater pollution and provides information for better management of groundwater resources. This study characterized the shallow groundwater quality and its spatial and seasonal variations in the Lower St. Johns River Basin, Florida, USA, under agricultural, forest, wastewater, and residential land uses using field measurements and two-dimensional kriging analysis. Comparison of the concentrations of groundwater quality constituents against the US EPA’s water quality criteria showed that the maximum nitrate/nitrite (NOx) and arsenic (As) concentrations exceeded the EPA’s drinking water standard limits, while the maximum Cl, SO42 −, and Mn concentrations exceeded the EPA’s national secondary drinking water regulations. In general, high kriging estimated groundwater NH4+ concentrations were found around the agricultural areas, while high kriging estimated groundwater NOx concentrations were observed in the residential areas with a high density of septic tank distribution. Our study further revealed that more areas were found with high estimated NOx concentrations in summer than in spring. This occurred partially because of more NOx leaching into the shallow groundwater due to the wetter summer and partially because of faster nitrification rate due to the higher temperature in summer. Large extent and high kriging estimated total phosphorus concentrations were found in the residential areas. Overall, the groundwater Na and Mg concentration distributions were relatively more even in summer than in spring. Higher kriging estimated groundwater As concentrations were found around the agricultural areas, which exceeded the EPA’s drinking water standard limit. Very small variations in groundwater dissolved organic carbon concentrations were observed between spring and summer. This study demonstrated that the concentrations of groundwater quality constituents varied from location to location, and impacts of land uses on groundwater quality variation were profound.

The biological control of Pomacea canaliculata population by rice-duck mutualism in paddy fields

Abstract Duck has been used as a non-chemical control method against Pomacea canaliculata Lamarck, but little is known about its principles that underlie the control of snail populations. An indoor experiment was initially used to observe the predation potential of ducks, followed by replicated field trials. In the indoor studies, ducks effectively preyed on juvenile snails, but had a weak predatory effect on large snails and egg clusters. In the field, application of a rice-duck mutualism system significantly reduced the numbers of snails (especially number of immature individuals), number of snail egg clusters and snail damage to rice plants. The controlling effect was longer and more stable than the chemical application, resulting in a better yield than with the pentachlorophenol sodium and tea seed powder treatment. Our experimental results also suggested that the snail age structure in the rice-duck mutualism plots was shifted towards older snails by ducks preying, indicating a trend towards population decline, and ducks caused snails to oviposit on sites not ideal for hatchling establishment. Throughout the studies, it is suggested that a rice-duck mutualism system could be used for controlling P. canaliculata in organic rice production.

Economic Analysis Using SWAT-Simulated Potential Switchgrass and Miscanthus Yields in the Yazoo River Basin

This study was carried out in the Yazoo River basin (YRB) in northwestern Mississippi to assess the potential crop yield of switchgrass (Panicum virgatum L.) and miscanthus (Miscanthus × giganteus) using the Soil and Water Assessment Tool (SWAT) model. Model-simulated long-term streamflow, and soybean and corn yields for the watershed were compared with available observed data. The results showed good agreement between simulated and observed values. The average yield predicted by the calibrated SWAT model was 11 Mg ha-1 (from 8 to 13 Mg ha-1) for switchgrass and 34 Mg ha-1 (from 25 to 45 Mg ha-1) for miscanthus. Both switchgrass and miscanthus yields were determined higher in the central part of the YRB than in other areas. The economic analysis estimated the average farm-gate breakeven prices of switchgrass and miscanthus at

Economic Evaluation of Syngas Production: Model Development and Analysis

111 Mg-1 and

Evaluating Spatial and Temporal Variability of Fecal Coliform Bacteria Loads at the Pelahatchie Watershed in Mississippi

39 Mg-1, respectively. The breakeven prices of both switchgrass and miscanthus were estimated lower in the central regions of the YRB than in the other areas of the watershed due to higher crop yields. Conversely, the breakeven prices of both crops were higher in the northern regions of the watershed due to lower crop yields. This study demonstrated that SWAT-simulated bioenergy crop yields at the watershed scale can be used effectively in watershed-scale economic analysis to determine the farm-gate breakeven price, which may provide useful information to producers and watershed managers who are charged with significant land use decisions.

Relationships between water table and model simulated ET

The objective of this study was to develop and apply an economic model to predict the unit cost of syngas production from a micro-scale bio-gasification facility. The economic model was programmed in C++ and developed using a parametric-cost approach, which included processes to calculate the total capital costs and the total operating costs of a bio-gasification facility. The model used data measured from the bio-gasification facility at Mississippi State University. The modeling results showed a unit cost and energy cost of syngas production of

A STELLA model to estimate soil CO 2 emissions from a short-rotation woody crop

1.258 Nm-3 and

Assessing Climate Variability Impact on Thermotolerant Coliform Bacteria in Surface Water

0.217 MJ-1, respectively, for a 60 Nm3 h-1 bio-gasifier capacity. The operating cost was determined to be a large proportion of the total production cost, in which equipment purchase cost and labor cost were a major part of the total capital cost and the total operating cost, respectively. When the production capacity increased from 60 to 2,400 Nm-3 h-1 with a higher operating mode, the total annual production cost increased while the syngas unit cost decreased. Sensitivity analysis of the model results indicated that equipment purchase cost ranked highest, followed by employee pay rate, feedstock price, loan life, interest rate, electricity price, and waste treatment price. The unit cost of syngas production increased with the increase of all parameters with the exception of loan life. The loan life and annual interest rate showed a non-linear relationship, while the other parameters showed a linear relationship with percent changes in the unit cost of syngas production. The economic model and analysis techniques developed in this study were found to be useful and can be applied in other similar conditions as needed.

Identify temporal trend of air temperature and its impact on forest stream flow in Lower Mississippi River Alluvial Valley using wavelet analysis

ABSTRACT Bacterial contaminations of surface waters are an increasing concern for scientists and public health agencies because pathogenic bacteria can cause adverse effects on human health. This research was performed to investigate spatial and seasonal variability of fecal coliform bacteria (FCB) concentrations in the Pelahatchie watershed (527 km2) in Mississippi, USA. Livestock manure, poultry litter, and effluent from failing septic systems were identified as major sources of FCB in the Pelahatchie watershed. The Soil and Water Assessment Tool (SWAT)/microbial sub-model was applied, and model-simulated FCB concentrations were compared with the monthly measured FCB concentrations (years 2001–2008) at the outlet of the watershed. New methodologies were introduced to incorporate bacteria loads into the bacteria model. Results showed coefficients of determination (R 2) of 0.71 to 0.75, and Nash-Sutcliffe efficiency index (NSE) of 0.67 to 0.75 during the bacteria models calibration and validation periods, respectively. Seasonal analysis of the model-simulated results determined the highest bacteria concentrations in January, whereas the lowest concentrations were simulated in June. Furthermore, the FCB contributions to the watershed outlet from the sources of contamination varied with time of year. This study will help watershed managers to implement best management practices for improvement of water quality.