Impact of flow conditions on coliform dynamics in an urban lake in the Brazilian semiarid

ABSTRACT

The seasonal and interannual variations of total coliforms (TC) and Escherichia coli (EC) were investigated in an urban tropical lake. Precipitation and flow rate were the controlling parameters influencing coliform dynamics. Correlations were obtained to describe the lake inlet conditions of flow rate, TC and EC. While TC increased with flow rate, EC slightly decreased. This unexpected behaviour for EC was attributed to the counterbalancing impact of coliform loading and surface runoff dilution. Correlations were computed to obtain first-order decay rates of TC and EC as functions of the Reynolds number, assuming the plug-flow model. A general mechanistic-empirical model was proposed to simulate coliform dynamics. The results indicated that seasonal coliform variations are more pronounced than interannual variations. Considering both the plug-flow and complete-mix models, it was shown that eliminating dry weather load reduces TC and EC but still leads to exceedances of the mandatory standards during the rainy season.

KEYWORDS:

• Total coliforms
• Escherichia coli
• seasonal and interannual trends
• coliform decay
• hydraulics
• water quality modelling

Acknowledgements

The authors acknowledge the scholarships from the Brazilian National Research Council – CNPq and thank the two anonymous reviewers whose comments helped significantly strengthen the manuscript.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work undertaken for this investigation was supported through the Coordination for the Improvement of Higher Education Personnel – CAPES [Research Grant PROEX 20/2016] and by the Ceará State Research Foundation – FUNCAP [Research Grant PNE-0112-00042.01.00/16].