Ali M. Sadeghi

MODELING BACTERIA FATE AND TRANSPORT IN WATERSHEDS TO SUPPORT TMDLS

Fecal contamination of surface waters is a critical water-quality issue, leading to human illnesses and deaths. Total Maximum Daily Loads (TMDLs), which set pollutant limits, are being developed to address fecal bacteria impairments. Watershed models are widely used to support TMDLs, although their use for simulating in-stream fecal bacteria concentrations is somewhat rudimentary. This article provides an overview of fecal microorganism fate and transport within watersheds, describes current watershed models used to simulate microbial transport, and presents case studies demonstrating model use. Bacterial modeling capabilities and limitations for setting TMDL limits are described for two widely used watershed models (HSPF and SWAT) and for the load-duration method. Both HSPF and SWAT permit the user to discretize a watershed spatially and bacteria loads temporally. However, the options and flexibilities are limited. The models are also limited in their ability to describe bacterial life cycles and in their ability to adequately simulate bacteria concentrations during extreme climatic conditions. The load-duration method for developing TMDLs provides a good representation of overall water quality and needed water quality improvement, but intra-watershed contributions must be determined through supplemental sampling or through subsequent modeling that relates land use and hydrologic response to bacterial concentrations. Identified research needs include improved bacteria source characterization procedures, data to support such procedures, and modeling advances including better representation of bacteria life cycles, inclusion of more appropriate fate and transport processes, improved simulation of catastrophic conditions, and creation of a decision support tool to aid users in selecting an appropriate model or method for TMDL development.

Applications of the SWAT Model Special Section: Overview and Insights

The Soil and Water Assessment Tool (SWAT) model has emerged as one of the most widely used water quality watershed- and river basin-scale models worldwide, applied extensively for a broad range of hydrologic and/or environmental problems. The international use of SWAT can be attributed to its flexibility in addressing water resource problems, extensive networking via dozens of training workshops and the several international conferences that have been held during the past decade, comprehensive online documentation and supporting software, and an open source code that can be adapted by model users for specific application needs. The catalyst for this special collection of papers was the 2011 International SWAT Conference & Workshops held in Toledo, Spain, which featured over 160 scientific presentations representing SWAT applications in 37 countries. This special collection presents 22 specific SWAT-related studies, most of which were presented at the 2011 SWAT Conference; it represents SWAT applications on five different continents, with the majority of studies being conducted in Europe and North America. The papers cover a variety of topics, including hydrologic testing at a wide range of watershed scales, transport of pollutants in northern European lowland watersheds, data input and routing method effects on sediment transport, development and testing of potential new model algorithms, and description and testing of supporting software. In this introduction to the special section, we provide a synthesis of these studies within four main categories: (i) hydrologic foundations, (ii) sediment transport and routing analyses, (iii) nutrient and pesticide transport, and (iv) scenario analyses. We conclude with a brief summary of key SWAT research and development needs.

A SWAT/Microbial Sub-Model for Predicting Pathogen Loadings in Surface and Groundwater at Watershed and Basin Scales

Despite the many potential sources of release of pathogenic organisms into the environment, agronomic practices that utilize animal manures contaminated with pathogenic or parasitic organisms appear to be the major contributors to watershed or basin contaminations. High rates of land-applied raw manure increase the risks of surface or ground water contamination, both from excess nutrients and pathogenic organisms. Unfortunately, current technologies are not adequate for handling large-scale treatment processes (e.g., composting, digestion, etc.) for stabilizing human pathogens in animal manures before application to agricultural lands. Therefore, there is a need for modeling capabilities to assess risks associated with individual and cumulative impacts of various pollutants and pollutant sources on watershed and basin impairment. The aim of this project is to extend Soil and Water Assessment Tool (SWAT) capability by incorporating a microbial sub-model for use at watershed or basin levels. The model formulations have been structured to be comprehensive, flexible, and at a minimum contain: 1) functional relationships for both the die-off and re-growth rates that are dynamic and, at best, cover a range of representative values from less persistent to more persistent pathogenic bacterial species; and 2) optional processes that can easily be adaptable to simulate both the release and transport of pathogenic organisms from various sources that have distinctly different biological and physical characteristics. Model performance has been tested for pasture and crop fields at one location. Preliminary results appear to portray the general patterns of the fate and transport of bacteria, for the three field sites examined.

Water quality and conservation practice effects in the Choptank River watershed

The Choptank River is an estuary, tributary of the Chesapeake Bay, and an ecosystem in decline due partly to excessive nutrient and sediment loads from agriculture. The Conservation Effects Assessment Project for the Choptank River watershed was established to evaluate the effectiveness of conservation practices on water quality within this watershed. Several measurement frameworks are being used to assess conservation practices. Nutrients (nitrogen and phosphorus) and herbicides (atrazine and metolachlor) are monitored within 15 small, agricultural subwatersheds and periodically in the lower portions of the river estuary. Initial results indicate that land use within these subwatersheds is a major determinant of nutrient concentration in streams. In addition, the 18O isotope signature of nitrate was used to provide a landscape assessment of denitrification processes in the presence of the variable land use. Herbicide concentrations were not correlated to land use, suggesting that herbicide delivery to the streams is influenced by other factors and/or processes. Remote sensing technologies have been used to scale point measurements of best management practice effectiveness from field to subwatershed and watershed scales. Optical satellite (SPOT-5) data and ground-level measurements have been shown to be effective for monitoring nutrient uptake by winter cover crops in fields with a wide range of management practices. Synthetic Aperture Radar (RADARSAT-1) data have been shown to detect and to characterize accurately the hydrology (hydroperiod) of forested wetlands at landscape and watershed scales. These multiple approaches are providing actual data for assessment of conservation practices and to help producers, natural resource managers, and policy makers maintain agricultural production while protecting this unique estuary.

Efficient multi-objective calibration of a computationally intensive hydrologic model with parallel computing software in Python

With enhanced data availability, distributed watershed models for large areas with high spatial and temporal resolution are increasingly used to understand water budgets and examine effects of human activities and climate change/variability on water resources. Developing parallel computing software to improve calibration efficiency has received growing attention of the watershed modeling community as it is very time demanding to run iteratively complex models for calibration. In this research, we introduce a Python-based parallel computing package, PP-SWAT, for efficient calibration of the Soil and Water Assessment Tool (SWAT) model. This software employs Python, MPI for Python (mpi4py) and OpenMPI to parallelize A Multi-method Genetically Adaptive Multi-objective Optimization Algorithm (AMALGAM), allowing for simultaneously addressing multiple objectives in calibrating SWAT. Test results on a Linux computer cluster showed that PP-SWAT can achieve a speedup of 45-109 depending on model complexity. Increasing the processor count beyond a certain threshold does not necessarily improve efficiency, because intensified resource competition may result in an I/O bottleneck. The efficiency achieved by PP-SWAT also makes it practical to implement multiple parameter adjustment schemes operating at different scales in affordable time, which helps provide SWAT users with a wider range of options of parameter sets to choose from for model(s) selection. PP-SWAT was not designed to address errors associated with other sources (e.g. model structure) and cautious supervision of its power should be exercised in order to attain physically meaningful calibration results. Integrating Python, mpi4py, OpenMPI to efficiently perform parallel calibration of SWAT using AMALGAM.Enhancing calibration by applying multipliers and addends at higher resolutions than is typically done for SWAT.Discussion of implications of model structure setup for SWAT calibration.

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.

Using NEXRAD and rain gauge precipitation data for hydrologic calibration of SWAT in a Northeastern watershed.

The value of watershed-scale, hydrologic and water quality models to ecosystem management is increasingly evident as more programs adopt these tools to evaluate the effectiveness of different management scenarios and their impact on the environment. Quality of precipitation data is critical for appropriate application of watershed models. In small watersheds, where no dense rain gauge network is available, modelers are faced with a dilemma to choose between different data sets. In this study, we used the German Branch (GB) watershed (~50 km2), which is included in the USDA Conservation Effects Assessment Project (CEAP), to examine the implications of using surface rain gauge and next-generation radar (NEXRAD) precipitation data sets on the performance of the Soil and Water Assessment Tool (SWAT). The GB watershed is located in the Coastal Plain of Maryland on the eastern shore of Chesapeake Bay. Stream flow estimation results using surface rain gauge data seem to indicate the importance of using rain gauges within the same direction as the storm pattern with respect to the watershed. In the absence of a spatially representative network of rain gauges within the watershed, NEXRAD data produced good estimates of stream flow at the outlet of the watershed. Three NEXRAD datasets, including (1) non-corrected (NC), (2) bias-corrected (BC), and (3) inverse distance weighted (IDW) corrected NEXRAD data, were produced. Nash-Sutcliffe efficiency coefficients for daily stream flow simulation using these three NEXRAD data ranged from 0.46 to 0.58 during calibration and from 0.68 to 0.76 during validation. Overall, correcting NEXRAD with rain gauge data is promising to produce better hydrologic modeling results. Given the multiple precipitation datasets and corresponding simulations, we explored the combination of the multiple simulations using Bayesian model averaging. The results show that this Bayesian scheme can produce better deterministic prediction than any single simulation and can provide reasonable uncertainty estimation. The optimal water balance obtained in this study is an essential precursor to acquiring realistic estimates of sediment and nutrient loads in future GB modeling efforts. The results presented in this study are expected to provide insights into selecting precipitation data for watershed modeling in small Coastal Plain catchments.

BACTERIA MODELING WITH SWAT FOR ASSESSMENT AND REMEDIATION STUDIES: A REVIEW

A module to simulate bacteria fate and transport in watersheds was first tested in SWAT 2000 and fully integrated into the SWAT2005 code. Since then, few investigators have utilized SWAT to model bacteria fate and transport in spite of bacteria being a major cause of streams impairment in the U.S. In this article, bacteria equations are briefly presented. Modeling applications, which range from 16 to 3,870 km2, from Missouri, Kansas, and Georgia in the U.S. and from Brittany in France, are reviewed, highlighting the modeling successes and the challenges. In all cases, land use included agricultural and forested land with a mix of point and nonpoint sources. Nonpoint sources included indirect (manure deposited on land) and direct contributions from cattle or wildlife to the streams. In some cases, urban and residential contributions were included. Strategies to represent the different sources, calibration methods, and goodness of fit were compared. Changes to the models code that were necessary to handle contributions from urban areas were reviewed. Overall, SWAT reasonably simulated the range and frequencies of bacteria concentrations. In all cases, direct bacteria inputs into streams appeared to have a major impact on the model results. This review also indicates that the model processes that simulate the release and transport of bacteria in surface runoff may need to be revisited. This improvement could enable SWAT to be more reliable for predicting bacteria concentrations and evaluating the impact of different management scenarios on bacteria contributions to surface water resources.

Runoff transport of faecal coliforms and phosphorus released from manure in grass buffer conditions

Aims:  To test the hypothesis that faecal coliform (FC) and phosphorus (P) are transported similarly in surface runoff through the vegetative filter strip after being released from land‐applied manure.

Long-term effect of thj.age and rainfall on herbicide leaching to shallow groundwater

The interaction of conventional tillage (CT) and no-tillage (NT) crop production practices with rainfall on the movement of three herbicides into shallow groundwater was evaluated over 4 yr. Groundwater was sampled from unconfined (< 1.5m deep) and confined (<3 m and 4.5 to 11 m deep) monitoring wells in 1989–1992 and analyzed for atrazine, alachlor, and cyanazine . Pesticide concentrations were cyclical: residues were highest soon after application, declined during the growing season, then increased during winter recharge. Alachlor and cyanazine were at nondetectable levels within 3 mo after application. Atrazine residues, present in confined groundwater all year, ranged in concentration between 0.03 to 1.9 and 0.16 to 3.7 ug L−1 for the CT and NT plots, respectively. Herbicide residues were higher in unconfined (< 1.5 m deep) than confined (< 3 m deep) groundwater. Atrazine was sporadically detected in groundwater to 4.6 m, but not deeper. Lateral transport in confined groundwater to untreated areas was evident. The rapid movement of herbicides to groundwater with the first major rain after application suggest that preferential transport may be common. Results of this study also indicate that timing, amount and intensity of rainfall relative to pesticide application may be the primary factors governing pesticide leaching.