Modeling Bacteria Fate and Transport in Watersheds to Support TMDLS

Abstract

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.

Comparing calibrated parameter sets of the SWAT model for the Scandinavian and Iberian peninsulas

“…Different strategies have been proposed in the literature to model karst areas (Baffaut and Benson 2009), but all of these are strongly connected with knowledge of the local systems. Many studies have addressed the karst issue in terms of SWAT modelling (Spruill et al 2000, Coffey et al 2004, Afinowicz et al 2005, Benham et al 2006, Fig. 11 Variation of calibrated parameters in each step between the Scandinavian Peninsula and the Iberian Peninsula.…”

Impact of Climate Change on Flood Frequency and Intensity in the Kabul River Basin

“…The Harmonized World Soil Database (available from http://webarchive. iiasa.ac.at/Research/LUC/External-World-soil-database) and European Space Agency's land cover data for 2009 [11] (available from http://due.esrin.esa.int/page_globcover.php) were employed.…”

A Review of Water Quality Responses to Air Temperature and Precipitation Changes 2: Nutrients, Algal Blooms, Sediment, Pathogens

“…Simulations of pollutant fate and transport can be subject to error (Novotny and Stefan 2007), and inadequacies have been reported in many studies (Tu 2009;Crossman et al 2013;Jha et al 2015;Johnson et al 2015). Areas of concern include sediment resuspension processes (Jamieson et al 2004;Droppo et al 2009;Coffey et al 2010a, b), subsurface transport, and capabilities to simulate pollutant responses during extreme flow events (Benham et al 2006;Beckers et al 2009). In addition, modeling cyanobacterial blooms is currently difficult due to the many causal factors that can initiate events (Lopez et al 2008;Ho and Michalak 2015;Brooks et al 2016).…”